Depositional sequences and correlation of middle(?) to late Miocene carbonate complexes, Las Negras...

Sedimentology (1991) 38,871-898

Depositional sequences and correlation of middle(?) to late Miocene carbonate complexes, Las Negras and Nijar areas, southeastern Spain

E V A N K . F R A N S E E N ' a n d C A R O L M A N K I E W I C Z '

University of Wisconsin, Department of Geology and Geophysics. 1215 W Dayton St., Madison, W153706, USA

ABSTRACT

During Serravallian through Messinian time, marine carbonates flanked topographic highs that rimmed Neogene basins in the Western Mediterranean. Middle to upper Miocene carbonate strata in the Las Negras and Nijar areas (southeastern Spain) are 5&150 m thick and display 5&200 m of shelf-to-basin relief over 1-2 km. Detailed studies in those areas document the effects of relative sea-level change on sedimentation, biotic composition, and reef development. We identify three previously unrecognized, regionally correlatable depositional sequences (DS1, DS2, DS3) that occur between the underlying basement and the overlying Terminal Carbonate Complex. The lower depositional sequences (DSl, DS2) are mostly normal marine shelf (ramp) carbonates deposited on the flanks of basement highs. The basal part of DS2 locally contains some megabreccia reef blocks composed of Tarbellasfraea and Porites. These blocks are the first evidence of reef growth in the area and represent a previously unrecognized period of reef development prior to the fringing reef development. The reef blocks probably formed as upslope patch reefs that were eroded and transported to distal slope locations. The upper sequence (DS3) is characterized by clinoform strata of a Porites-dominated fringing reef complex that prograded basinward in a downstepping style with successively younger reefs forming in a topographically lower and more basinward position as a result of a net sea-level drop.

Regional correlation of Miocene shallow-marine strata between basins in Spain and elsewhere in the western Mediterranean is complicated because basins were semi-isolated from adjacent basins making physical correlation impossible. In addition, age-definitive biostratigraphic markers are poorly preserved in most of the Miocene shallow-water strata; basinal sediments that are more easily dated by microfossils do not typically interfinger with the shallow-marine strata in outcrop. Even where datable microfossils are found, resolution of dating is poor.

Our studies in the Las Negras and Nijar areas illustrate the usefulness of integrating sedimentological, geometric and biotic data with locally derived relative sea-level (accommodation space) curves for correlation. The relative sea-level curves for each area show remarkable similarities in shape and magnitude of sea-level changes. These curves indicate several relative sea-level fluctuations during Miocene carbonate deposition prior to the major sea-level drop at the end of DS3 deposition that culminated in the exposure of the basin margin deposits and the deposition of evaporites in basinal areas during the Messinian.

The depositional sequences in the Las Negras and Nijar areas may correlate with depositional sequences of similar age throughout the southern Cab0 de Gata area, in Mallorca some 600 km to the northeast, and possibly in other Mediterranean locations. The widespread occurrence and possible correlation of the depositional sequences suggest regional processes such as eustacy or tectonism for their formation.

The integration of sedimentological, palaeontological and sequence stratigraphic studies, and the construction of relative sea-level (accommodation space) curves may help in the interpretation of depositional histories of shallow-marine carbonate complexes and correlation of these strata between isolated areas. Other dating methods, in addition to microfossil dating, may allow for better age determination of the sequences and aid in identifying the importance of eustacy and tectonism in sequence development.

Present addresses : 'Kansas Geological Survey, University of Kansas, 1930 Constant Avenue, Campus West, Lawrence, KS 66047, USA; *Beloit College, Departments of Geology and Biology, 700 College St., Beloit, WI 53511, USA.

871

872 E. K . F‘ranseen and C. Mankiewicz

INTRODUCTION

During the middle to late Miocene, reef complexes developed around margins of Neogene Mediterranean basins. The reef complexes and associated strata developed during both normal marine periods (Serra- vallian-Tortonian) and during the so-called late Miocene (Messinian) ‘salinity crisis’ (Hsii, 1973), when a thick sequence of evaporites was deposited in the Mediterranean basin. Since the discovery of these evaporites, controversy has been generated concern- ing the depth and morphology of the Mediterranean basin($ during evaporite accumulation, the mecha- nisms responsible for evaporite deposition (e.g. Dietz & Woodhouse, 1989; Friedman, 1989; Schmalz, 1989; Schreiber & Helman, 1989), and to the lateral traceability and correlatability of the evaporites with the basin margin carbonate deposits (e.g. Esteban, 1979; Rouchy, 1982; Dabrio et al., 1985; Martin & Braga, 1990).

A general stratigraphic interpretation for relating Miocene and Pliocene basin margin deposits to basinal evaporites is shown in Fig. 1. This interpretation, based in large part on studies from southeastern Spain by earlier workers, is thought to be applicable to most of the western Mediterranean basin margin areas. Ongoing studies of the western Mediterranean Mio- cene strata (e.g. Esteban, 1988; Saint-Martin & Rouchy, 1990) are adding detail to the general model. According to the model in Fig. 1, the older reefs (Type A of Esteban, 1979) are typically found topographically higher than younger reefs (Type B of Esteban, 1979). The older reefs record normal marine conditions and contain as many as 15 species of frame-building

BASIN / SUBSURFACE + * I OUTCROP

I TERMINAL CARBONATE COMPLEX

ENOUS SEDIMENT

/ UPPER EVAPORITE

LOWER EVAPORITE

Fig. 1. General stratigraphic model of Miocene strata in the Mediterranean as interpreted by early workers based mainly on field studies in southeastern Spain. Note that the left- hand part of the diagram represents what is observed in outcrop and the right-hand part of the diagram is interpreted from subsurface data. After Esteban (1979).

coral (predominantly Tarbellastraea and Porites). Fringing reefs and atolls typify younger reefs. These younger reefs record more restricted marine conditions and contain only one frame-building coral species (Porites). This change is interpreted by Esteban (1979) to indicate increasingly stressed environments associated with the onset of the Messinian ‘salinity crisis’. The youngest reefs are extensively eroded and truncated along a surface showing evidence of subaerial exposure. This surface has regional significance and probably correlates with initial evaporite deposits in the basin during a major sea-level drop. The eroded fringing reef complexes on the basin margins are overlain by cyclical shallow-water, restricted-marine carbonates (oolites, stromatolites, locally some Porites thickets) termed the Terminal Carbonate Complex (TCC) by Esteban (1979). This facies was deposited during transgression of the sea onto the basin margins and is interpreted to interfinger with the uppermost evaporite deposits in the basin (Esteban & Giner, 1980).

The Miocene reef complexes and associated strata of southeastern Spain and the Balearic Islands are probably the largest, best developed and best exposed in the western Mediterranean (Esteban, 1981). The Spanish reef complexes, which are about 50-150 m thick and commonly preserve 50-200 m of relief over a distance of only 1-2 km, cover topographic highs of various substrates in an archipelago setting (Fig. 2). Substrates include Mesozoic and Palaeozoic meta- morphic and sedimentary rocks, older reefs, and Neogene volcanic rocks. The excellent exposures result from regional uplift during the Pliocene and later (Rehault et al., 1985), from a drop in sea-level of approximately 50-100 m since the Miocene (Haq et al., 1987), and from the aridity of the region. The Miocene strata display little structural deformation and have had only shallow burial (probably less than 350m) since deposition (Armstrong et al., 1980; Goldstein et al., 1990). The extensive outcrops reveal that the present-day topography is similar to that of the Miocene; today’s hills (many less than 250 m high) and valleys were coincident with islands and basins that formed an archipelago in the Miocene (Esteban, 1979). The stratigraphy of the Miocene strata reveals several different scales of cyclicity that indicate a complex history of sea-level change. In addition to the excellent exposures that make the Miocene strata of southeastern Spain attractive for sedimentological and stratigraphic studies, these rocks serve as surface

Middle-late Miocene carbonate complexes, SE Spain 873

-----_

STUDY AREA

0 10 u

Scale in kilometres

C a b de Gsta

Miocene Reef Complexes Betic Basement

Neooene Volcanic Rocks

0 Neogene Basins Areas of Reconnaissance

Fig. 2. Location and general geological map showing distribution of middle to upper Miocene reefs in southeastern Spain, study areas of Las Negras and Nijar, and areas of reconnaissance study (El Plomo, Mesa RoldAn, Sorbas area, Mallorca). Modified from Dabrio er al. (1985).

analogues to extensive subsurface Oligo-Miocene strata that are well-known petroleum reservoirs in the Mediterranean and Indo-Pacific regions.

Despite the quality of exposure, regional correlation of Miocene shallow-marine strata between basins in Spain and elsewhere in the western Mediterranean is complicated. In previous studies, carbonate complexes in southeastern Spain have been correlated on the basisof presumed ages and on similarities with respect to coral diversity (Esteban, 1979). However, different ages have been assigned by different workers (e.g. Esteban, 1979; Megias, 1985; Santisteban & Dawans, 1985; Mankiewicz, 1987; Franseen et al., 1988; Franseen, 1989).

Some of the reasons for the problems with correlation are :

(1) basins were semi-isolated, making physical correlation impossible. These separate basins, with

differing morphologies, possibly experienced somewhat different uplift and subsidence histories and could have had restricted circulation at different times;

(2) age-definitive biostratigraphic markers are poorly preserved in many parts of the middle to late Miocene ;

(3) basinal sediments that are more easily dated by microfossils do not typically interfinger with reef sediments on outcrop;

(4) even in areas where datable microfossils are found, biostratigraphic resolution is usually not sufficient to determine whether the deposit is Serravallian, Tortonian, or Messinian in age.

Our research on the Las Negras and Nijar Miocene carbonates is some of the first to integrate sedimentological and palaeontological data and sequence- stratigraphic concepts (recognition of stratal geome-

874 E. K . Franseen and C. Mankiewicz

tries, stratigraphic breaks or sequence boundaries, and facies changes) to interpret the depositional histories of several carbonate complexes. Our study suggests that by integrating these different disciplines and constructing local relative sea-level (or accommodation space) curves for each area, the carbonate complexes in the areas of Las Negras and Nijar can be correlated. Our sequence stratigraphic framework may apply to the surrounding southeastern Spain carbonate complexes, those on Mallorca (about ‘600 km northeast of Las Negras and Nijar) and possibly throughout the western Mediterranean (e.g. Morocco, Sicily). The recognition of similar depositional sequences, which appear to have similar ages based on limited microfossil data, suggests that the techniques we applied in our study will be useful for more detailed and reliable correlations and for better understanding the depositional history of Miocene carbonate complexes throughout the Mediterranean region.

Regional geology and palaeogeography

The topography of southeastern Spain has many similarities with the middle to late Miocene palaeogeography. The present-day Betic Mountains and volcanic highs (Fig. 2) were islands in the Miocene (Esteban, 1979). These structuresresulted from Alpine orogenic compression that started in Eocene time and prevailed until the middle Miocene (Serravallian) (Rehault et al., 1985) and from Neogene volcanism associated with compression of the African and Iberian plates. Volcanism in the Cab0 de Gata area was active from about 17 to 6 M a (L6pez-Ruiz & Rodriguez-Badiola, 1980). Since the Pliocene, com- pressional tectonics have dominated, inducing strike- slip movements along faults (de Larouzitre et al., 1988) and resulting in general regional uplift in the eastern Betic area (Montenat & Ott d’Estevou, 1977).

Figure 2 shows the study area and areas of reconnaissance. The major tectonic element that was active in the study area throughout the Tortonian- Messinian and Pliocene (Montenat et al., 1987) is the sinistral strike-slip Carboneras Fault.

Foraminifera1 distributions indicate that the Medi- terranean Sea and Indian Ocean connection was severed in early Miocene time, at c. 20 Ma (Bizon, 1985). During the Miocene, the Mediterranean was connected to the Atlantic by the ‘Betic Strait’ in Spain and the ‘Rif Strait’ in Africa (Fernex et al., 1967). Later, beginning in the Messinian-earliest Pliocene, the Gibraltar area became the lone connection

between the Mediterranean Sea and Atlantic Ocean (Hsii et al., 1976). The Atlantic-Mediterranean connection was apparently closed (periodically?) for part of the Messinian, creating the ‘salinity crisis’ that resulted in depositionof a thick sequence of evaporites in basinal areas and extensive erosion of the middle to late Miocene strata on the basin margins. Opening of the connection at Gibraltar allowed the basins and margins to flood, resulting in deposition of uppermost Miocene (Terminal Carbonate Complex equivalent) and Pliocene strata in those areas.

Previous studies and stratigraphic terminology

Estebanetal. (1978) andEsteban (1979)firstdescribed major features of the upper Miocene reefs of Spain and elsewhere in the western Mediterranean. The emphasis was on stratigraphic, sedimentological and paleoecological studies and on relating reef features to the increasingly stressed environments associated with the Messinian ‘salinity crisis’. Other studies focused on various sedimentological, palaeontological or paleoecological aspects of southeastern Spain Miocene carbonates (Permanyer & Esteban, 1973 ; Dabrio, 1974,1975; Montenat, 1975,1977; Alvarez et al., 1977; Dronkert & Pagnier, 1977; Esteban & Giner, 1977; Pagnier, 1977; Addicott et al., 1978; Esteban, 1979, 1988; Santisteban & Taberner, 1980; Poore & Stone, 1981; Veeken, 1983; Megias, 1985; Dabrio et al., 1985; Miiller & Hsii, 1987; Braga & Martin, 1988; Martin et al., 1989; Braga et al., 1990; Martin & Braga, 1990; Serrano, 1990).

The Nijar and Las Negras area carbonates were reported on by Dabrio & Martin (1978), Esteban & Giner (1980), Esteban & Pray (1981), and Santisteban & Dawans (1985). Dabrio et al. (1981) focused on the palaeoecology and sedimentology of the carbonate strata exposed near Nijar and presented a general model for late Miocene reef sedimentation in the western Mediterranean.

Formal and informal stratigraphic terminology has been proposed for Miocene strata of southeastern Spain by Dutch, Spanish and American geologists. The Dutch geologists (Ruegg, 1964; Volk & Rondeel, 1964; and, most notably, Volk, 1967; all reported in Dabrio et al., 1981) !%st proposed a stratigraphic framework for Neogene basins based on work in the Sorbas and Vera basins. Volk’s work has been refined by Dronkert & Pagnier (1977) in the Sorbas Basin, by Dabrio & Martin (1978) in the Almeria area, by Dabrio et al. (1981) in the Nijar Basin and by Veeken (1983) in the Pulpi Basin. These revisions have


resulted in the 'composite' stratigraphic framework (Fig. 3) adopted by most geologists working in southeastern Spain.

The Turre Formation comprises three members : the Azagador Member (fossiliferous sediments of an open-marine platform) and Cantera Member (reef complex) may be shallow-water equivalents of the deep-water Abad Member (basinal marls and probable turbiditic deposits). Dabrio & Martin (1978) and Dabrio et al. (1981) provide more detailed lithological descriptions and palaeoenvironmental interpretations. The early workers in southeastern Spain recognized only one depositional sequence (Turre Formation) between the basement and overlying TCC (e.g. Esteban, 1979; Dabrio et al., 1981). They divided this depositional sequence into two continuous informal units termed the Marginal Terrigenous Complex (mixed carbonates and siliciclastics) and the Reef Complex (distal, proximal and talus foreslopes and reef core).

We recognize three discrete andgenetically separate depositional sequences (all belonging to the Turre Formation) between the basement rocks and overlying Terminal Carbonate Complex. We informally desig- nate them from the base to the top as depositional sequence (DS) 1, 2 and 3 (Figs 3 & 4). We interpret our DS1 to be equivalent to much of the Marginal Terrigenous Complex, DS2 to be equivalent to the lower part of the Reef Complex, and DS3 to be equivalent to the upper part of the Reef Complex.

IFI I ?E I

The uppermost carbonate strata (TCC) exposed near Las Negras and Nijar probably belong to the overlying Caiios Formation. The Caiios Formation can be divided into the time-equivalent Yesares Member (basinal facies), the Sorbas Member (coastal and lagoon facies) and the Zorreras Member (conti- nental and fluvial facies). Martin & Braga (1990) show that the Yesares Member overlies the Reef Complex in the Sorbas Basin. Dabrio & Martin (1978) state that the TCC strata in Cab0 de Gata most closely resemble material described for the Sorbas Member.

The depositional sequences (DS1, DS2, DS3) in the Las Negras and Nijar areas can be distinguished by their bedding geometries and depositional facies. Sequence boundaries separate depositional sequences and are characterized by facies shifts across the surfaces and locally by sharp truncation surfaces overlain by megabreccias. We number these sequence boundaries (SB) 1, 2, 3, 4. SB1 is oldest and SB4 is youngest (Figs 3 & 4). We recognize nine facies in the Las Negras and Nijar areas (Fig. 5): volcaniclastic/ carbonate conglomerate (VCC), red algal-rich packstone/grainstone (RAPG), fine-grained wackestone/ packstone (FGWP), coarse-grained packstone/grainstone (CGPG), megabreccia 1 (MBl), megabreccia 2 (MB2), volcaniclastic sandstone/conglomerate (VSC), reef core/talus (RCT), and Halimeda-rich facies (HR). Not all of these facies occur in the Nijar area. The absence of some facies and the slight differences in character of the same facies in the Nijar and Las

LAS NEGRAS AREA

(f)

Fig. 3. Various interpretations of stratigraphy in the Nijar and Las Negras areas. The 'composite' stratigraphic framework shown in (a) and (b) is so named because it results from the work of Volk (1967), Dronkert & Pagnier (1977), Dabrio & Martin (1978), Dabrio et al. (1981), and Veeken (1983). (a) Composite showing named stratigraphic units; (b) composite showing possible facies relationships suggested by Dabrio et al. (1981); (c) Addicott etal. (1978); (d) Megias (1985); (e) and (f) from our work. Abbreviations in (e) and (f) are as follows: DSI =depositional sequence 1, DS2=depositional sequence 2, DS3 =depositional sequence 3, and TCC= Terminal Carbonate Complex; Serr. = Serravallian, and Mess. = Messinian.


Fig. 4. Photographs of Miocene exposures at Las Negras and Nijar. (a) North side of La Molata at Las Negras. V = volcanic rocks, DS1 =depositional sequence 1 , DS2 =depositional sequence 2, DS3 =depositional sequence 3, TCC = Terminal Carbonate Complex. (b) West side, Nijar. DSl =depositional sequence 1, DS2=depositional sequence 2, DS3 =depositional sequence 3.

Negras areas probably reflect (i) dissimilar basement rocks in the two areas, and (ii) different positions within the depositional basin.

Although defined somewhat differently in our paper, many of the features in our facies were recognized by previous workers. Some deposits similar to our VCC and VSC facies were described as part of the Marginal

Terrigenous Complex in Esteban (1979) and in Dabrio et al. (1981). RAPG facies are similar to platform deposits described in Dabrio & Martin (1978), some of the Marginal Terrigenous Complex described in Dabrio et al. (1981), the bryozoan-rich wedge described in Esteban & Giner (1980) and rhodalgal units described by Rouchy et al. (1986). FGWP, CGPG


LAS NEGRAS AREA LAS NEGRAS AREA

Fig. 5. Facies abundances and vertical trends within the three depositional sequences in Las Negras and Nijar. See Appendix 1 for descriptions of facies. TCC =Terminal Carbonate Complex, VCC = volcaniclastic-carbonate conglomerate, RAPG =red algal-rich packstone/grainstone, FG WP = fine-grained wackestone/packstone (y = yellow, o = orange, w = white), MBI = megabreccia 1 , CGPG = coarse-grained packstone/grainstone, MB2 = megabreccia 2, VSC = volcaniclastic sandstone/ conglomerate, RCT = reef core/talus, HR = Huhedu-rich; r =rare, c =common, a = abundant.

and HR facies are similar to some facies described in the Reef Talus Slope of Dabrio & Martin (1978), and as part of the distal to proximal Fore-Reef Slope facies of Esteban & Giner (1980) and Dabrio et al. (1981). Features similar to our RCT were described in the Reef Wall Framework facies of Dabrio & Martin (1978), Esteban (1979) and Esteban & Giner (1980), and in the Reef-Core Framework facies of Dabrio et al. (1981). MBl and MB2 were not singled out as separate facies in previous works. Similar reef blocks were described as part of the Reef Talus Slope facies in Esteban (1979) and Dabrio & Martin (1978), and as talus slope deposits in the Fore-Reef Slope facies of Esteban & Giner (1980) and Dabrioet al. (1981).

Other studies have somewhat different stratigraphic frameworks from those just described above (Fig. 3). Addicott et al. (1978) described and named informal units from the Almeria area.

Megias (1985) and Dabrio et al. (1985) have proposed that the evaporites of the Yesares Member were deposited prior to the reefs of the Cantera Member or the Sorbas Member on the margins of the basins. This theory differs from the ‘composite’ stratigraphic interpretation that places the Yesares Member as the latest Messinian. These workers also place the Tortonian-Messinian and Messinian-Pli- ocene boundaries differently than the ‘composite’ stratigraphic framework (Fig. 3).


We cannot disprove the stratigraphic interpretation of Megias (1985) and Dabrio et al. (1985). However, on the basis of detailed field studies, laboratory work, and application of sequence stratigraphic concepts, we favour the ‘composite’ interpretation of the stratigraphy. We differ, however, regarding ages of formations; some nannofossil dates (“6, Berggren et al., 1985) from the Las Negras area suggest that most of the carbonate strata in our study area are Tortonian (some lowermost strata may even be Serravallian) and not Messinian as suggested by the ‘composite’ stratigraphic interpretation (Fig. 3).

DEPOSITIONAL SEQUENCES AND CORRELATION OF LAS NEGRAS AND

NfJAR STRATA

Introduction

The general characteristics of the depositional sequences in the Las Negras and Nijar areas are illustrated in Fig. 6. These general characteristics are

PROXIMAL

summarized first in this section and followed by more detailed descriptions of depositional sequence characteristics and criteria used to interpret relative sea level for each of the Las Negras and Nijar study areas. Facies abundances with respect to depositional sequences are shown in Fig. 5. Facies characteristics are summarized in Appendix 1. Because of space limitations and the scope of this paper, it is not possible to describe and illustrate all the specific locations, facies details, and stratigraphic features used for our interpretations. These details can be found in Mankiewicz (1987, 1991) and in Franseen (1989, 1991). In this section, certain stratigraphic and sedimentological relationships will be discussed in terms of ‘distal’ or ‘proximal’ positions. These terms are used in general to describe the location of sedimentary deposits in proximity to the underlying topographically highest basement area (volcanic cone in the Las Negras area). The combination of field studies, recognition of facies patterns, depositional sequences, sequence boundaries and relative sea-level curves constructed for each area allows us to correlate

DISTAL

- - - - - -

100 rn

DS3

DS2

DS1

Approx Scale

Fig. 6. Composite, idealized cross-section constructed from field studies of Las Negras and Nijar complexes. Diagram shows characteristics (numbered 1-14) of the three depositional sequences that are identifiable in the field. Differences in position within the basin, local tectonics, and source area affect which features will occur in any area. (1) Irregular basement surface overlain by DSI strata; (2) onlapping of DSl strata onto basement; (3) relatively shallow-dipping, fine-grained wackestones and packstones of DS1; (4) wedge of relatively steep-dipping DS1 strata that can display downlap (4a) and toplap (4b); (5 ) large allochthonous reef blocks of basal DS2; (6) onlapping wackestones, packstones, and grainstones of DS2. Sequence generally fines upward; (7) channelling of packstones and grainstones that can be arranged in fining-upward sedimentary packages; (8) sharp (locally erosional) surface with possible palaeosol formation; (9) cross-bedded lens of DS3; (10) allochthonous blocks of basal DS3; (1 1) clinoform strata of DS3 that commonly contain beds of fragments of Hulimedu; (12) downstepping arrangement of clinoform strata from oldest (12a) to youngest (12c). Porites reefs occur at tops of clinoforms. Locally, preserved reefs may show some aggradation in oldest portions; (1 3) erosive surface that evidences subaerial exposure; (14) deposition of Terminal Carbonate Complex (TCC).

Middleelate Miocene carbonate complexes, SE Spain 879

between the Las Negras and Nijar areas. The relative sea-level curves are constructed from field, petro- graphic and palaeontological data. Criteria include estimates of accommodation space based on direct physical measurements of stratal and surface geometries, identification of subaerial exposure features, and facies interpretations of relatively deep-water versus shallow-water deposits. No corrections for compaction are made in constructing the curves because of the lack of stylolites, pressure-solution features, or other evidence of significant compaction.

General depositional sequence characteristics

SB1 occurs as an irregular, locally erosional and terraced surface on older Neogene volcanic rocks in the Las Negras area and Mesozoic-Palaeozoic rocks and older Neogene sedimentary rocks in the Nijar area. Evidence of subaerial exposure was not recognized in the field. SB1 is locally overlain by conglomerates, sandstones, marls or coarse-grained carbonates.

DS1 strata in both study areas comprise shallow- dipping and onlapping beds that contain similar facies and fauna. The lower DS1 strata consist of conglomerates, f6ssiliferous turbidites, and other carbonate rocks that contain abundant coarse-grained bivalve fragments (locally whole pectens), bryozoans, red algal fragments, benthic foraminifera (some planktonic foraminifera), solitary corals, echinoderms and inter- stratified terrigenous grains. In the Nijar area, the strata are described as having a lobate fan morphology (Dabrio er al., 1981); in Las Negras they are either tabular beds or are mound- to wedge-shaped deposits (Franseen, 1989).

Lower DS1 strata grade upward to fine-grained wackestones and packstones in both areas. These fine- grained strata are characteristically light in colour, have shallow primary dips and are extensively bioturbated. Macro- and microfossils are rare but include mollusc fragments and planktonic foraminifera (locally filled with glauconite in Nijar). Variable amounts of sand-sized terrigenous grains and non- carbonate mud occur.

In both areas, uppermost DS1 in proximal positions locally consists of prograding wedge deposits of coarse- grained packstones/grainstones and/or red algal-rich packstones/grainstones containing an abundance of shallow-marine macrofossils. Primary dips in these beds approach 20" and the beds locally downlap onto the underlying fine-grained wackestones/packstones.

SB2 in Las Negras occurs at a stratigraphic horizon

marked by a megabreccia (MB 1) composed of predominantly allochthonous reef blocks, or, in a proximal position, is the upper surface of the top wedge (locally overlain by MBl). In Nijar, SB2 is a sharp surface in proximal and intermediate locations and becomes a conformable surface in distal locations. No evidence of subaerial exposure was identified in either field area. SB2 is most easily recognized by the onlapping geometry of the overlying DS2 strata onto the sequence boundary. The shallow-dipping, onlapping geometry of strata appears to be the most characteristic feature of DS2 strata in both study areas. MB1 is characteristic of basal DS2 deposits in Las Negras and represents the first evidence of reef growth in the area. The eroded blocks probably formed as patch reefs in upslope positions. Although the section studied at Nijar does not contain MB1 deposits, lower DS2 strata contain channels filled with deposits that contain rhodoliths, terrigenous grains, and centimetre- to metre-sized clasts of underlying lithology. These features are similar to those found along with MB1 deposits in Las Negras. In addition, both study areas contain oysters and Ophiomorpha tubes that appear to be more common to DS2 strata if compared with the overlying and underlying depositional sequences. Other reef sections in the Nijar area contain exposures of allochthonous reef blocks in possible DS2-equivalent strata which may indicate some early reef development prior to the DS2 fringing reefs (T. Douthit, personal communication, 1990).

Upper DS2 strata consist of fine-grained wackestones/packstones and locally coarse-grained packstones/grainstones at Las Negras and fining- and thinning-upward grainstone/packstone units at Nijar. An additional observation is the greater generic diversity of calcareous algae and relative abundance of large benthic foraminifera in DS2 strata compared with overlying and underlying strata (Nijar area; Mankiewicz, 1987).

DS3 strata are characterized in both areas by clinoform strata of the Porites-dominated fringing reef complexes that prograded basinward in a distinctive downstepping style with each successively younger reef forming in a topographically lower and more basinward position. This downstepping style of progradation is attributed to continued reef development during net sea-level fall (e.g. Esteban et al., 1978; Dabrio et al., 1981).

SB3 is a sharp and traceable surface in both the Las Negras and Nijar areas. In the Las Negras area SB3 is overlain by a megabreccia (MB2) composed of Porites-dominated reef blocks and fragments in


intermediate and distal locations and/or is eroded and channellized and overlain by coarse-grained carbonates (some deposits are cross-bedded and contain coated grains) or volcaniclastic sandstones and conglomerates. Locally, some possible caliche occurs on top of MB2 in an intermediate location. In the Nijar area, SB3 is an erosion surface that is sporadically overlain by coarse-grained, mixed-fossil hash ; a possible soil zone occurs along the surface in a proximal location in Nijar.

Overlying DS3 strata in Las Negras and Nijar consist of distal to proximal (dipping <1&30" basinward) foreslope deposits predominantly composed of fine-grained wackestones/packstones and coarse-grained packstones/grainstones. The upper parts of the reef complex are dominated by Porites talus blocks and local in-situ Porites reef core. A distinctive feature in DS3 is the occurrence of Halimeda concentrated in only the youngest strata. Five Halimeda-rich beds can be identified and traced in Nijar and two can be traced in Las Negras.

SB4 and the TCC rocks that unconformably overlie DS3 strata can be traced in both the Las Negras and the Nijar areas. SB4 in Las Negras is a sharp, erosional surface that locally shows evidence of subaerial exposure. Although SB4 is not well exposed in the section studied at Nijar, it is identified in other Nijar sections and Dabrioet al. (198 1) propose that subaerial exposure produced the unconformity. The Terminal Carbonate Complex is easily recognized and correlated by its flatter bedded nature as compared to DS3 strata and due to its distinctive restricted marine carbonate lithologies.

Las Negras area

Depositional sequence 1 (DSl)

DS1 varies from 0 to 60m thick in a basinward direction. It is bounded below by volcanic rocks. This sequence boundary (SB 1) is a non-conformity characterized by a low-angle (< 10-15"), basin-sloping surface (locally eroded and terraced) that is overlain by a volcanic/carbonate conglomerate (VCC). SB 1 has an exposed relief of 100-130 m over a distance of 1 km. Locally, the volcanic rocks are fractured and filled with DS1 carbonates. Volcanic topographic highs occur throughout the area, only some of which have a carbonate cover.

DS1 consists mostly of shallow-dipping (< 12") strata that onlap the underlying volcanic basement. Red algal-rich packstones/grainstones, coarse-grained

packstones/grainstones and fine-grained wackestones/packstones are the most abundant facies in DS1. From bottom to top, DSl strata occur in the following general vertical lithofacies succession:

volcanic/carbonate conglomerate (VCC) : this facies occurs locally overlying the volcanic basement in proximal to basinal positions; red algal-rich packstones/grainstones (RAPG) or coarse-grained packstones/grainstones (CGPG); burrowed fine-grained wackestones/packstones (FGWP), locally with interbedded, normally graded coarse-grained packstones/grainstones (CGPG).

There is a general increase basinward in fine- grained wackestones/packstones and a shelfward increase in red algal-rich packstones/grainstones and coarse-grained packstones/grainstones. Varying amounts of terrigenous material occur in discrete layersor admixed with thecarbonate beds. In proximal areas, red algal-rich packstones/grainstones and coarse-grained packstones/grainstones occur as wedge deposits or lenticular-shaped beds interpreted as broad (tens of metres wide), low-relief (up to several metres deep) channel-fill deposits or prograding clinoforms (forming at the distal portion of a ramp or at the edge of a fan-delta slope?).

Interpretation and relative sea-level curve. The volcanic rocks in the Las Negras area are interpreted to have been deposited in a submarine environment (J . Martin, personal communication, 1986). The locally eroded and terraced upper contact of some of the volcanic substrata is suggestive of erosion and planation by wave action in relatively shallow water as a result of lowered sea level (Fig. 7). Although no evidence of exposure along the upper volcanic sub- strate contact was identified, such evidence could have been removed by reworking during the subsequent transgression. The volcanic/carbonate conglomerate that immediately overlies the volcanic contact contains some well-rounded clasts that indicate reworking in a shallow-water (possibly beach) environment. The dominant matrix-supported texture of volcanic/carbonate conglomerate clasts in carbonate matrix (containing shallow-water fauna and planktonic foraminifera) suggests transport of material from shallow- water areas by debris flows, turbidity currents and other bottom-hugging currents to their preserved, presumably deeper water positions. These lowest deposits are interpreted as lowstand and perhaps transgressive deposits on Fig. 8.

Middle-late Miocene carbonate complexes, SE Spain 88 1

INTERPRETED RELATIVE SEA LEVEL N~JAR AREA

60 0 - Metres

'r 1-?

INTERPRETED RELATIVE SEA LEVEL LAS NEGRAS AREA

80 0

Fig. 7. Proposed correlation of Las Negras and Nijar depositional sequences and interpreted relative sea-level curves. Some of the differences in stratigraphy and possibly shape of the curves, and magnitude of some of the sea-level changes between Las Negras and Nijar are attributed to a more basinward section preserved at Nijar as compared to Las Negras.

PROXIMAL

DS3

DS2

DSl

DISTAL

DS3

VOLCANIC BASEMENT

DS2

DS1

PROXIMAL Approx. scale in metres

DISTAL

- ----

Fig. 8. Cross-sections of the Las Negras (a) and Nijar (b) areas and interpretation of strata in relation to relative sea level. H = highstand, T = transgression, L = lowstand. Stippled pattern in (a) represents volcaniclastic units (VSC facies) discussed in text.

882 E. K . Eranseen and C. Mankiewicz

A subsequent rise in relative sea level (Fig. 7) is indicated by : (1) distal beds onlapping the basement: bedding

geometries indicate onlapping relief of at least 20- 40 m;

(2) basal coarse-grained carbonates grade upward into fine-grained carbonates with planktonic foraminifera in both distal and proximal positions.

These deposits are interpreted as transgressive deposits (Fig. 8) on a gently sloping open-marine carbonate shelf (ramp). Alternating coarse- and fine-grained carbonates (some with normal grading, current ripple- lamination, flame structures) may indicate deposition from storms, turbidity currents or higher frequency sea-level fluctuations (sawtooth shaped curve in Fig. 7) during the net sea-level rise.

Locally, in a proximal position, uppermost DS1 strata are composed of two progradational wedges (Fig. 8) that taper basinward (the upper wedge pinches out further basinward than the lower wedge). These wedges consist of coarse-grained carbonate (RAPG, CGPG) with some admixed volcaniclastic grains. These wedges, 5-10 m thick and 100-250 m in length, may be interpreted as distal ramp deposits or the distal portions of fan-delta lobes; the upper surface on the wedges shows proximal-distal relief of about 10- 20 m. This facies relationship indicates progradation as a result of a reduction in accommodation space during the interpreted late highstand of sea level (Figs7 & 8). The upper surface of the top wedge represents SB2.

Depositional sequence 2 (DS2)

The middle sequence (DS2) in the Las Negras area is the first to contain evidence of reef development during carbonate deposition. DS2 total thickness (ranging from 1 to 30 m) is greatest in medial positions and decreases in both proximal and distal directions.

SB2 occurs at a stratigraphic horizon marked by the base of MBI and locally, in proximal positions, the sharp upper contact of the top DS1 wedge (Fig. 6). This top wedge is locally overlain by MB I . No erosion or subaerial exposure evidence was identified along the top wedge upper surface. SB2 is scoured and eroded in some other more distal locations. In some distal locations, where no MBl blocks occur, SB2 is difficult to recognize in the field and must be approximated between separate outcrops of MB1 blocks. MB1 consists predominantly of boulder-sized allochthonous reef-fzcies blocks. The blocks are mostly matrix supported (fine-grained carbonate) and

only locally clast supported. Some strata underlying and encasing MB1 blocks show evidence of soft- sediment deformation. Although in most places MB1 is not a continuous, traceable layer, mapping in the Las Negras area suggests separate MB1 outcrops occur at a correlatable horizon. Based on correlation of MBI, at least 160 m of vertical relief occurs along SB2 over a distance of 1.5-2.0 km.

Most DS2 beds have shallow ( < 12") primary dips and the beds locally onlap underlying strata. Some basal beds drape underlying strata (mostly MB 1 blocks). Other beds are lenticular in shape and interpreted as channel-fill deposits. Fine-grained carbonates (FGWP) are volumetrically the most abundant facies in DS2. From base to top, DS2 strata generally occur in the following vertical lithofacies succession :

MBl occurs locally at the base and consists of reef blocks composed of Tarbellastraea and Porites framework (similar to Type A reefs described by Esteban, 1979). Steeply-dipping (< 25") beds may develop on the sides of blocks. Locally, volcaniclastic sandstones and conglomerates occur with the MBI unit; burrowed fine-grained carbonates (FGWP), locally draping MBl blocks; locally interbedded with normally graded coarse-grained carbonates (CGPG); coarse-grained carbonates (CGPG) locally (channels, cross-bedding, current-ripple lamination, silt/clay drapes, rip-up clasts, and scoured bases filled with shell lag deposits may be present). Where coarse-grained beds are not present, fine- grained carbonates form the uppermost DS2 strata.

Interpretation and relative sea-level curve. DS2 strata are interpreted to have been deposited on a gently sloping open-marine carbonate shelf (ramp) with broad undulations or swales, and channels with the axes generally orientated basinwards. The abundance of fine-grained carbonates and the shallow dips of beds suggest deposition in a relatively deep-water environment. MB1 blocks at the base of DS2 are interpreted to have originally been upslope surf-zone patch reefs that were eroded and transported to a more distal position. The extensive erosion and regional occurrence of the MB1 blocks at a stratigraphic horizon suggests a relative drop in sea level (Fig. 7). The MB1 depositsare interpretedas lowstand deposits (Fig. 8). A relatively shallower water interpretation is supported by channelling, cross-bedding,


rhodolith (coralline algae nodule) morphology, relative abundance of Ophiomorpha burrows and volcaniclastic sandstones and conglomerates in basal DS2 deposits. The local occurrence of volcaniclastic sandstones and conglomerates in the distal slope positions suggests coastal terrigenous material was able to migrate further basinward (bypassing the shelf margin) possibly as a result of lowered sea level. The amount of relative sea-level drop is unknown (no evidence of exposure is identified along SB2). It appears a minimum fall of 10 m to several tens of metres could have resulted in the erosion and transport of originally submerged patch reefs and created conditions for local development of relatively shallower water deposits on the sides of the transported blocks.

An interpreted rapid increase in accommodation space due to rising sea level (Fig. 7) after MB1 deposition is based upon the abrupt return to burrow- mottled fine-grained carbonate deposits that locally drape MB1 blocks. These upper DS2 strata are interpreted as highstand deposits (Fig. 8); no distinct transgressive facies were recognized, which may indicate a relatively rapid rise in sea level. The similarity of upper DS2 deposits with upper DS1 fine- grained carbonates suggests a similar depositional environment of pelagic/hemipelagic accumulations in open-marine water in distal slope (ramp) locations. Although, in general, upper DS2 strata are composed of shallow-dipping beds, the lack of field evidence, such as onlapping geometries of the upper DS2 strata, makes estimating sea-level rise difficult. However, the similarity of DS2 fine-grained carbonates to those of upper DS1 strata suggests a rise of several tens of metres with a consequent return to the type of sedimentation which prevailed prior to MB1 erosion and deposition. Features in several interbedded coarse-grained carbonate beds (sole marks, normal grading) suggest deposition by turbidity currents, possibly as a result of storms or higher frequency sea- level oscillations (sawtooth shaped curve in Fig. 7) during the net sea-level rise. The local occurrence of coarser grained carbonates, some of which are cross- bedded and current-ripple laminated, in the uppermost portion of some DS2 strata may represent a shallowing-upward trend, possibly indicating a stillstand or a relative lowering of sea level during latest DS2 time.


DS3 is the youngest and volumetrically the most abundant of the three depositional sequences in Las

Negras with preserved thicknesses of 20-70 m. The uppermost DS3 strata have been eroded and are unconformably overlain by the TCC. DS3 deposits are characterized and easily recognized by clinoform strata that prograded basinward, downlapping over DS2 with successively younger reefs developed in a lower topographic position.

SB3 is a sharp contact (locally erosional on a scale of metres) overlain either by a megabreccia (MB2) in distal and intermediate locations, or by coarse-grained packstones and grainstones or volcaniclastic conglomerates/sandstones in proximal locations (Fig. 8). SB3 is a distinct, mappable horizon throughout the Las Negras area and its exposed trace indicates a relief of 120-1 70 m over a distance of 1.5-2.0 km. No evidence of exposure was identified along the SB3 trace in the field. However, some possible subaerial exposure features (caliche, rootlet moulds) were locally identified on top of MB2 in an intermediate position.

DS3 consists predominantly of low-angle (< 12") to high-angle (< 30") prograding and downlapping reef complex strata. Some lowermost DS3 strata in distal positions are flat bedded and apparently onlap the lower DS3 sequence boundary or MB2 (Fig. 6). In the most proximal locations, the prograding clinoforms are overlain by flat-bedded and massive reef core strata. Lenticular-shaped beds (channel-fill deposits) and wedge-shaped foreslopes (thinning and pinching out downslope) are common in the prograding clinoforms. DS3 strata show the following generalized vertical lithofacies succession from base to top :

(1) megabreccia (MB2) or coarse-grained packstone/ grainstone (CGPG), both with abundant Porites. MB2 occurs in medial and distal locations and coarse-grained carbonates (with some coated grains) occur in proximal positions;

(2) volcanic sandstone/conglomerate (VSC) layers and wedges (10cm to 12m thick), locally with alternating beds of coarse-grained (CGPG) and fine-grained carbonates (FGWP);

(3) coarse-grained packstones/grainstones (CGPG) locally interbedded with fine-grained wackestones/packstones (FG WP) ;

(4) Halimeda-rich facies (HR). Two traceable layers occur in youngest DS3 strata in reef-core to distal- slope settings;

(5) reef talus (RCT). Mostly slumped Porites framework reef blocks (rotated geopetals) on high-angle foreslopes;

(6) reef core (RCT). Massive to layered Porites framestone, locally occurring in proximal areas.


Several repetitive volcaniclastic sandstone-cofi- glomerate/carbonate units occur upward and basinward. Generally, the grain size decreases basinward. Within each clinoform package there is a gradation from framestones in a proximal position to grainstones and packstones in an intermediate position to finer grained packstones and wackestones in a distal position.

Interpretation and relative sea-level curve. Following the deposition of DS2 strata, a reduction of accommodation space occurred as a result of a sea-level fall (Fig, 7). This interpretation is based on: (i) the shallowing-upward trend at the end of DS2 deposition, (ii) the sediments that overlie the sharp, locally eroded and channelled SB3, and (iii) the possible subaerial exposure features on top of MB2. Basal DS3 strata consisting of megabreccia (MB2), coarse-grained carbonates, and volcaniclastic sandstones and conglomerates are interpreted as shallower marine deposits as compared to most upper DS2 strata. The basal strata in proximal to distal areas are interpreted as being deposited during a sea-level lowstand or during the initial stages of transgression (Fig. 8). The MB2 deposit occurs only in distal slope locations and apparently is confined to a large, broad basinward sloping ‘trough’ (100-150 m wide; metres to 10 m (?) deep) that forms the DS3 sequence boundary (Fran- seen, 1989). Locally, in distal areas, basal DS3 strata consist of fine-grained carbonates that appear to onlap the sequence boundary and, locally, MB2. The proximal trace of the sequence boundary suggests a generally flat (terraced?) area that is locally scoured and channelled (several metres to 10m wide; 0.5- 1.0 m deep). This proximal location may have been a shallow-water (< 10 m?) area that was bypassed by MB2 deposits but collected shallow-water grainstones. Some of the basal DS3 coarse-grained carbonates in proximal areas are cross-bedded and contain coated carbonate grains that indicate relatively shallow water. Locally, in a proximal position, the DS3 sequence boundary is overlain by a volcaniclastic wedge interpreted as a fan delta lobe that prograded basinward as a result of lowered sea level.

The amount of sea-level drop is unknown for basal DS3 strata as no definitive exposure evidence was identified along SB3. The locally eroded and terraced morphology of the DS3 sequence boundary may indicate planation by wave action in relatively shallow water. In addition, the occurrence of eroded MB2 reef blocks in distal locations and cross-bedded coarse- grained carbonates containing some coated grains in

proximal locations suggest a drop of 10 m to several tens of metres (similar to the drop interpreted for erosion of MB1 reef blocks). A drop of this magnitude would lower storm and normal(?) wave base suffi- ciently for channelling, erosion of reefs and other shallow-water marine deposits and allow for basinward transport of volcaniclastic conglomerates/sandstones. If the top of MB2 was indeed subaerially exposed in an intermediate position just after deposition, this would indicate a minimum sea-level drop of 55 m.

A subsequent increase in accommodation space as a result of a sea-level rise (Fig. 7) is indicated from :

(1) a shelfward or proximal shift of shallow-water carbonate deposits. The earliest traceable surf- zone reefs have a relief of 40m and suggest a relative sea-level rise of similar magnitude because basal DS3 strata are interpreted to have been deposited in <10m water depth. Some of the shallow-water basal DS3 strata are overlain by fine-grained distal foreslope strata containing deeper marine fauna (e.g. planktonic foraminifera);

(2) some basal DS3 strata in distal locations appear locally to onlap MB2 strata, possibly indicating deposition during transgression after an initial fall (Fig. 8).

The upper DS3 reef strata are fringing reefs characterized by a low-diversity fauna and interpreted to be representative of Type B reefs of Esteban (1979). These reefs apparently aggraded somewhat (approximately 5 m can be recognized in the field; an accurate estimate is difficult to determine due to erosion of much of the upper DS3 strata) and prograded basinward during the late stages of the sea-level highstand (stillstand?) (Fig. 8).

Upper DS3 strata continued to prograde basinward in pulses (sawtooth shapes on curve in Fig. 7) during a net sea-level drop as evidenced by the characteristic downstepping style of the latest reefs. The punctuated drop in sea level is interpreted from the occurrence of the alternating volcaniclastic/carbonate strata and from the Halimeda beds (Franseen, 1990). The volcaniclastic strata are interpreted as being deposited during each successively lower sea level and the carbonates deposited during intervening relative rises. Each successively younger volcaniclastic wedge occurs at least 10-20 m further basinward, suggesting similar magnitude sea-level changes, but with each successive drop in sea level lower than the previous. The Halimeda beds may be event strata (Mankiewicz, 1987, 1988)


that were deposited during episodic sea-level fluctuations similar to those interpreted for the volcaniclastic/ carbonate cycles during the net sea-level drop. Alternatively, the volcaniclastic/carbonate cycles could result from basinward progradation of shifting fan-delta lobes or from storm events, with larger storms resulting in the successively further basinward volcaniclastic accumulations ; the Halimeda beds could also represent transport and deposition from storm events. However, the occurrence of similar deposits in other areas of southeastern Spain (e.g. Sorbas, Nijar) suggests regional processes such as higher frequency glacio-eustatic fluctuations or tectonism associated with the isolation of the Mediterranean from the world oceans during the net sea-level drop.

DS3 time closed with probable subaerial exposure of all outcropping DS3 strata indicating a minimum relative sea-level drop of 180-200 m.

Terminal Carbonate Complex (TCC)

Flat-bedded TCC strata (youngest Miocene), a complex association of cross-bedded, coated-grain carbonate deposits, stromatolite boundstones, and other restricted marine facies (Porites is locally present) unconformably overlie the depositional sequences in the Las Negras area (Fig. 6). SB4 locally contains evidence of subaerial exposure (soil, caliche, root moulds) and underlying DS3 strata were eroded prior to TCC deposition. SB4 has 90 m of demonstrable relief from proximal to basinal positions in Las Negras and probably far more.

Interpretation and relative sea-level curve. The locally terraced geometry of SB4 and the deposition of flat- bedded, onlapping TCC strata in these terraced areas suggest planation as a result of wave action and deposition during transgression of the sea back onto basin-margin areas. The subaerial exposure of an estimated 180-200 m of DS3 strata indicates a sea- level rise of at least that amount necessary to deposit TCC strata in the topographically highest positions.

Nijar area

Characteristics of the depositional sequences and distribution of facies in Nijar are similar to those in Las Negras (Figs 5 & 6). In Nijar, however, the fine- grained wackestones and packstones (FGWP) can be divided into several subfacies that are distinguishable on the basis of colour. FGWPy has a yellow-orange colour and is finer grained than the typically coarser grained orange FGWPo subfacies; both of these

subfacies contain a high percentage (c. 10-35%) of terrigenous mud that probably contribute to the colour difference. The grey-green to white fine-grained wackestones and packstones of FGWPw have little (typically < 5-10%) terrigenous mud. The three FGWP subfacies are restricted in distribution with relation to the depositional sequences: FGWPy and FGWPo occur only in DS1 and FGWPw occurs in DS2 and DS3. The distribution may reflect a punctuated change from siliciclastic-mud-rich to siliciclastic-mud-poor deposits.

Depositional sequence I (DSI)

Only the upper 25 m of DS1 was studied in detail. Dabrio et al. (1981) studied the entire sequence over a wide area and referred to it as the Marginal Terrigen- ous Complex. The entire sequence ranges in thickness from 0 to 100 m. To the north and northeast of the study area (proximal localities), SB1 occurs as an irregular surface on Mesozoic and Palaeozoic basement rocks and older Neogene sediments, and is locally overlain by conglomerates, sandstones, or marls.

DS1 mainly consists of beds that dip basinward at < 10". The lower part of DS1, which was studied only in reconnaissance, includes yellow+xange fine- grained wackestones and packstones. In addition, metre-thick, commonly graded beds of coarser grained deposits containing large (7-10 cm) whole and fragmented pectenid bivalves and oysters are common throughout the lower part; the coarse beds diminish in abundance stratigraphically upward. Dabrio et al. (198 1) attributed the coarse-grained beds to turbidite deposition. An alternative explanation is that they represent storm deposits or higher frequency sea-level fluctuations (Fig. 7).

The upper part of DS1, which was studied in more detail, consists of terrigenous-clastic-rich, burrow- mottled wackestones and packstones. Terrigenous components comprise clays, quartz, and rock fragments derived from the basement. Yellow-coloured fine-grained wackestones to packstones (FGWPy subfacies) that contain planktonic foraminifera dominate the upper part of DS1.

In proximal positions, the upper part of DS1 coarsens upward and beds display steeper dips (14- 20"). These relatively steeply dipping beds downlap onto the finer grained, more shallow-dipping underlying strata (FGWPy subfacies) and are arranged into a sedimentary package that is wedge shaped in cross- section. The wedge represents a prograding clinoform


composed of beds in a parallel oblique configuration (Mitchum et al., 1977); the foreset beds of the more distal parts of the wedge display toplap. Packstones (FGWPo subfacies) dominate in the wedge-shaped packages; they are coarser grained, skeletal rich, and terrigenous-clastic poor relative to the underlying wackestones and packstones of FGWPy. Shallow-, normal-marine biota constitute the skeletal components of the wedges and include mollusc, echinoid, bryozoan, and coralline algae fragments, and benthic foraminifera. The number of whole (relative to fragmented) elements increases upward, possibly indicating a change from more offshore to onshore components.

Interpretation and relative sea-level curve. Dabrio et al. (1981) suggested that DS1 strata (their Marginal Terrigenous Complex) represented fan-delta to slope to basin environments. Because the lower strata were not studied in detail, we cannot add to or modify this interpretation with confidence. The 100-m-thick sequence, however, evidences the large amount of accommodation space available for normal-shelf, turbidite, and/or storm sedimentation.

The FGWPy subfacies dominates the upper part of DS1. The abundance of extensively burrowed fine- grained carbonate rocks and marls, relatively shallow- dipping beds, and, locally, glauconite-filled planktonic foraminifera suggest a low-energy marine environment, probably in a distal shelf (ramp) setting.

In proximal locations, the uppermost part of DS1 consists of a wedge-shaped deposit (1-35 m thick) that tapers basinward. The wedge displays about 50 m of depositional relief over a distance of about 250 m. The coarser grain size, abundance of shallow-marine macrofossils, and steeper dips of beds suggest a shallower marine origin for the wedge-shaped deposits relative to the underlying FGWPy subfacies.

The geometry, occurrence of toplap, coarse grain size, and abundant skeletal constituents of the wedge- shaped deposit indicate progradation of the clinoform strata during uppermost DS1 deposition and suggest a decrease in accommodation space due to a relative fall or stillstand in sea level (Figs 7 & 8). The upper surface of the wedge represents SB2. No evidence of erosion or subaerial exposure was noted at this boundary.


DS2 ranges in thickness from 0 to 23 m. Thickness is greatest in intermediate locations and thins both proximally and distally.

SB2 dips at about 15" in proximal positions and flattens to c. < 10" basinward. At least 60 m of vertical relief occurs along SB2 over a distance of 700 m. In proximal positions grey grainstones to packstones (dipping at < 10" basinward) onlap the upper surface of the DS1 wedge-shaped deposit; the surface of onlap markedly defines SB2. In intermediate positions, the boundary is recognizable due to a change in lithologies and weathering characteristics across the sequence boundary: non-resistant, yellow, fine-grained wackestones below SB2 and resistant, coarse-grained, red- algal-rich grainstones above. In distal locations, DS2 strata are seemingly conformable with DS1 strata. Nonetheless, SB2 can be distinguished by a colour change in the fine-grained wackestones to packstones that are yellow-orange in DSl and white to light grey- green in DS2. Unlike DS2 strata in Las Negras, however, there is no evidence of reef formation in correlative strata in the studied Nijar section.

DS2 is characterized by several fining-upward successions or sedimentary packages. Packages attain a maximum thickness of c. 2-7 m; thickest packages occur in the lower parts of DS2. Each package thins in the proximal direction where it onlaps DS1 strata or other DS2 strata; each also thins in the distal direction. Grainstones and packstones (CGPG) typify the lower part of the package and fine sand to mud packstones (FGWPw subfacies) characterize the upper part. Bedding varies from the base to the top of the package from channellized or cross-bedded to parallel laminated to burrow mottled (Fig. 6). Coarse grain size, channelling, cross-bedding, abundant traces of Ophiomorpha, and morphology of coralline algae nodules (rhodoliths) indicate shallow-marine or at least energetic conditions. The diminution in grain size within each package suggests fluctuating conditions from relatively high to low energy.

DS2 strata display the following generalized vertical succession from base to top :

(1) coarse-grained packstones/grainstones (CGPG) that are characterized by planar lamination and rare oscillation-ripple lamination. Channelling and cross-bedding is common. Most allochems are skeletal and include red algal and mollusc fragments and large benthic foraminifera; simple- branched Ophiomorpha dominate the trace fossils;

(2) fine-grained packstones/wackestones (FGWPw subfacies) that are interbedded with CGPG facies and cap each fining-upward package. FGWPw contains small benthic foraminifera and small


skeletal fragments and is burrow mottled. This fine-grained subfacies becomes more common stratigraphically upward at the expense of CGPG.

In general, grain size decreases basinward within DS2. Thus, CGPG dominates in more proximal locations whereas FGWPw characterizes more distal areas.

Interpretation and relative sea-level curve. A net reduction in accommodation space due to relative sea-level fall is inferred prior to DS2 deposition (Fig. 7). No evidence of subaerial exposure was found, but there is a marked change in facies across SB2 : terrigenous- mud-rich deposits of DSl are abruptly replaced by more skeletal-rich deposits of DS2. In addition, basinward of the wedge-shaped strata of DSl, coarse- grained, cross-bedded, and channellized deposits immediately overlie fine-grained distal deposits of DS1. An estimated relative sea-level fall of at least 50 m occurred prior to DS2 deposition as determined by the difference between the topographically highest occurrence of the DS1 wedge and the topographically lowest occurrence of onlapping DS2 strata.

A subsequent increase in accommodation space due to relative sea-level rise (Fig. 7) is indicated by the onlapping geometry of the DS2 beds onto the underlying DS1 wedge. The onlapping beds represent transgressive deposits that are volumetrically most important in DS2 strata in Nijar (Fig. 8). The stacked and irregular arrangement of the fining-upward packages suggests that sea-level rise was episodic (sawtooth shaped curve in Fig. 7). Channelling, cross- bedding, and deposition of coarser grained sediments occurred during minor lowstands whereas volumetrically less important, bioturbated, finer grained sediments accumulated during relative highstands. The thinning of packages upward indicates that higher energy deposition diminished in importance over time. The most parsimonious explanation is that relative water depth increased over DS2 time. The finer grained packstones and wackestones define a highstand deposit (Fig. 8).

A reduction in accommodation space due to a relative sea-level fall (Fig. 7) characterizes latest DS2 time as suggested by:

(1) coarsening of grain size in uppermost DS2 strata; (2) a probable palaeosol that indicates subaerial

exposure. The top of the palaeosol best defines SB3.


Even more so than at Las Negras, the original thickness of DS3 at Nijar is not known due to extensive erosion of the uppermost parts; preserved thickness ranges from 0 to 40 m. Prograding clinoform geometries characterize DS3 strata in Nijar; each successive clinoform package is basinward of, but topographically lower than, the preceding one. This downstepping arrangement was first noted by Esteban et al. (1 978).

SB3 is a distinct, traceable surface in proximal positions and exhibits a relief of 55 m over a down- dip distance of about 400 m. It is locally erosional and overlain by coarse-grained fossil hash; proximal locations evidence subaerial exposure and a cross- bedded unit 0.5 m thick which is interpreted as a lowstand deposit (Fig. 8). In distal locations, SB3 is not easily discernible. Here, wackestones and packstones of both facies are seemingly conformable and cannot be differentiated by colour. If these fine- grained beds show a marked increase in dip in the proximal direction, however, and if they interfinger with more proximal deposits of DS3, they can be considered as DS3 deposits (as discussed below).

DS3 consists of high-angle (< 30") to relatively low- angle (< 12") prograding and downlapping strata that reflect deposition in normal-marine water of near-surf zone to distal foreslope environments, respectively. The change in dip can occur over short horizontal distances (<50-100 m); no other depositional sequence shows such variation in dip along a single bed. Skeletal grainstones and packstones dominate the sequence that contains ubiquitous but minor amounts of terrigenous-clastic grains.

DS3 is the first sequence to evidence reef development in the section studied here. Porites reefs occur at the tops of clinoforms.

DS3 displays the following generalized vertical lithofacies succession from base to top :

(1) fine-grained wackestones/packstones (FGWPw) that contain small benthic and planktonic foraminifera;

(2) coarse-grained grainstones/packstones (CGPG) that contain numerous skeletal fragments of molluscs, serpulid worms, and coralline algae. Rarely, thickets of coralline algae occur that might better be termed bafflestones. CGPG locally alternates or interfingers with FGWPw;

(3) Halimeda-rich strata (HR) up to 7 m thick occur in youngest DS3 strata in reef talus to distal foreslope settings. They are interbedded with

888 E. K . Franseen and C . Mankiewicz

CGPG facies. Five distinct Halimeda-rich beds occur in Nijar suggesting temporal changes in environmental conditions that favour prolifera- tion of Halimeda (Mankiewicz, 1988);

(4) Porites reef talus (RCT) occurs on high-angle foreslopes as slumped reef blocks that are up to 3 m in diameter;

(5 ) reef core (RCT) constructed by stick-shaped Porites occurs in proximal areas at the tops of clinoforms.

In general, grain size decreases basinward. In addition, stratigraphically upward within each clinoform package, grainstones and packstones replace finer packstones and wackestones that are in turn replaced by framestones.

Interpretation and relative sea-level curve. A reduction of accommodation space due to relative sea-level fall (Fig. 7) is indicated by several features evident along SB3. These include:

(1) evidence of erosion along SB3 ; (2) the occurrence of fossil hash that locally overlies

the sequence boundary; (3) a zone of subaerial exposure (palaeosol develop-

ment) at the sequence boundary in the proximal position;

(4) cross-bedded lens basinward of the area of subaerial exposure.

The difference between the elevation of the most proximal occurrence of upper DS2 strata and that at which the cross-bedded unit occurs yields a minimum estimate of sea-level fall of 35 m.

A subsequent increase in accommodation space due to relative rise of sea level (Fig. 7) is indicated by the abrupt change from subaerial exposure or shallow- water sediments at or below the sequence boundary to finer grained carbonates that contain deeper marine fauna (e.g. planktonic foraminifera) above SB3.

Sea level is interpreted to have dropped in pulses during upper DS3 time (sawtooth-shaped curve in Fig. 7) with the onset of reef progradation in the characteristic downstepping style. Relationships between successive clinoforms within DS3 support the hypothesis proposed by Esteban et al. (1978) and Dabrio et al. (1981) that the reef prograded basinward and downward due to a reduction in accommodation space. Repetitive successions within each clinoform suggests episodic and pulsing, rather than continuous, sea-level fall (Mankiewicz, 1987, 1988). All reef complexes at Nijar fringe topographic highs and are

characterized by low diversity; they are interpreted as representative of Type B reefs of Esteban (1979) (Fig. 1).

Extensive subaerial exposure marked the end of DS3 deposition and indicates a fall in relative sea level of perhaps at least 120 m (Fig. 7). Because the TCC does not crop out in the study area, an estimate of subsequent sea-level rise cannot be ascertained. On the basis of the relationship of the TCC with DS3 strata within 2-3 km of the study area, the sea-level rise probably at least matched the magnitude of the previous fall of 120 m.

Terminal Carbonate Complex (TCC)

The TCC does not crop out in the immediate study area but does occur 2-3 km to the east (Dabrio et al., 1981). This unit contains a variety of lithologies including stromatolite boundstones and oolitic and gastropod grainstones. The TCC unconformably overlies packstones and Porites framestones that are correlative with DS3 strata exposed in the study area. Dabrio et al. (1981) proposed that subaerial erosion produced the unconformity ; marine processes subse- quently modified the erosion surface. They did not estimate the magnitude of relative sea-level rise responsible for deposition of the TCC.

REGIONAL CORRELATIONS

Reconnaissance study of surrounding areas in southeastern Spain and Mallorca (Fig. 2) revealed stratigraphic, sedimentological and age similarities with the Las Negras and Nijar sequences, as well as similar local relative sea-level curves, that we believe allow correlations over a wide area (Figs 9 & 10).

Two of the areas (El Plomo and Mesa Roldkn- Agua Amarga) are within the Cab0 de Gata volcanic .complex and contain depositional sequences that are essentially identical to those of Las Negras. Other areas outside the Cab0 de Gata volcanic complex contain features that are similar to both the Las Negras and Nijar areas and that we believe validate our correlations.

Mesa RoldPn-Agua Amarga area

The eroded volcanic basement in the Mesa Roldin- Agua Amarga area is overlain by a volcanic/carbonate conglomerate and bryozoan-rich wedges with abundant red algae, bivalves, solitary corals and other

,

Middle-late Miocene carbonate complexes, SE Spain

M ALLORC A NiJAR LAS NEGRAS AREA

889

LAS NEGRAS AREA EL PLOMO MESA ROLDAN

VOLCANIC BASEMENT

_ _ - - Conglomerate

-*. Reel Blocks 0 20 - metres

Fig. 9. Proposed correlation of the Las Negras and Nijar depositional sequences to those at El Plomo (Franseen, 1989), Mallorca (section after Sim6 & Rambn, 1986; Pomar, 1991) and Mesa Roldin (modified from Esteban & Giner, 1980).

skeletal fragments (Esteban & Giner, 1980); these basal strata are identical to DS1 basal strata at Las Negras (Fig. 9). These coarser grained carbonates are succeeded upward by finer grained carbonates. Allo- chthonous reef blocks (composed of Tarbellastraea and Porites framework) are probable equivalents of the MB1 unit of basal DS2 strata at Las Negras. A sharp surface overlying the blocks in the Mesa RoldBn-Agua Amarga area is interpreted to be equivalent to SB3 in Las Negras. The overlying strata at Mesa RoldLn are high-angle, prograding clinoforms of Porites (and Halimeda) reef complex strata inter-

preted as being equivalent to the upper DS3 strata at Las Negras. Uppermost reef complex strata at Mesa RoldLn are truncated by a subaerial erosion surface and overlain by TCC strata as at Las Negras.

El Plomo

The El Plomo area contains a basal volcanic/carbonate conglomerate (Muertos conglomerate of Addicott et al., 1978) that unconformably overlies the eroded volcanic basement; this conglomerate probably correlates with the basal DS1 conglomerate at Las


INTERPRETED INTERPRETED RELATIVE SEA LEVEL EL PLOMO RELATIVE SEA LEVEL MALLORCA

INTERPRETED

80 0

RELATIVE SEA LEVEL MESA R O L D ~ - -- 7 - d?

TCC_ 9 s-

DS3 c DS2 CJ7 VOLCANIC BASEMENT

DS1

-- .- Fig. 10. Interpreted relative sea-level curves for the reconnaissance study areas of El Plomo, Mallorca, and Mesa Roldan. Note the similarity in shape and magnitude of sea-level changes for the relative sea-level curves from each of the areas to those of Nijar and Las Negras in Fig. 7. These relative sea-level curves, in combination with other evidence described in the text, aid in correlation between the areas.

Negras. Allochthonous reef blocks composed of Tarbellastraea and Porites framework (the informal Plomo formation of Addicott et al., 1978) overlie fine- grained carbonates and are interpreted to correlate with the MBl unit of basal DS2 strata at Las Negras. A sharp surface above the allochthonous blocks separates fine-grained carbonates from overlying Porites-rich coarse-grained carbonates. This surface at El Plomo is interpreted to be equivalent to SB3 at Las Negras (Fig. 9). Strata overlying this surface at El Plomo consist of coarse-grained carbonate rocks and prograding Porites reef complex strata that probably correlate with upper DS3 strata at Las Negras. El Plomo sediments yielded no age-diagnostic microfossils. The ages (Tortonian and possibly older) determined by Addicott et al. (1978) for most El Plomo strata compare favourably with our interpreted ages for Las Negras and Nijar carbonate strata.

MaUorca

We studied Miocene successions on Mallorca only in reconnaissance in an early stage of our detailed studies

at Las Negras and Nijar. However, the Miocene sedimentary sequence on Mallorca has been well studied by many workers (Pomar, 1976, 1979, 1988, 1991; Esteban, 1979; Pomar et al., 1983; Rodriguez- Perea, 1984; Alvaro et al., 1984; Sim6 & Rambn, 1986; Oswald et al., 1990). Pomar (1991) described and interpreted the reef section in Mallorca in great detail. Our aim here is only to point out similarities in the larger-scale packaging of carbonate rocks and to suggest possible correlations to the Las Negras and Nijar sequences. Figures 9 and 10 show our interpretations of the relative sea-level curve for Mailorca and correlation of Las Negras and Mailorca depositional sequences.

On Mallorca, the Mesozoic and Palaeozoic basement is eroded and overlain by mixed terrigenous/ carbonate conglomerate. Limestones and mark that overlie the conglomerate onlap underlying strata and the basement. These strata (Heterostegina calcisiltites) contain red algae, benthic foraminifera (Heteroste- gina), bryozoans, bivalves, echinoids, and interlayered terrigenous horizons. These geometries, lithologies and skeletal material are similar to basal strata at Las

Middle-late Miocene carbonate complexes, SE Spain 89 1

Negras and 'Nijar and suggest correlation to DS1 strata at Las Negras (Heterostegina is only found in basal DS1 strata at Las Negras). Strataoverlying these basal carbonates on Mallorca are bioturbated calcisiltites (with red algal fragments and oysters), similar to upper DS1 strata at Las Negras and Nijar. The oldest Mallorcan reefs (platform facies) consist of both Tarbellastraea and Porites framestone, similar to, and probably correlative with, MBl facies of basal DS2 strata at Las Negras. Pomar (1991) states that Tarbellastraea occurs only in older reef cycles and its disappearance as a major reef builder is sharp and occurs at a mappable discontinuity surface that crosses different reef facies (this may be equivalent to SB3). The occurrence of preserved in-place reefs in Mallorca versus exclusively transported reef blocks of the MBl facies at Las Negras could reflect a more proximal section preserved on Mallorca than the section that is preserved at Las Negras. This first reef horizon on Mallorca is overlain by a second Porites-dominated reef complex (with Halimeda) that is characterized by basinward prograding (downstepping) clinoforms similar to, and probably equivalent to, upper DS3 strata at Las Negras and Nijar. As in our study areas, the upper reef complex strata (DS3) in Mallorca are truncated by a subaerial erosion surface and overlain by the flat-bedded TCC (Pomar, 1991). The late Serravallian-early Tortonian age for the lowest carbonate unit, late Tortonian-early Messinian age for reef complex strata, and Messinian age for the TCC determined by Pomar (1991) and Simb & Ram6n (1986) for strata in Mallorca favourably match the ages we have interpreted for carbonate depositional sequences at Las Negras and Nijar.

DISCUSSION

We can only speculate on some other areas around the Mediterranean Basin from limited reconnaissance, literature review and discussions with other Miocene workers that may suggest correlation of some or all of these sections with the sequences at Las Negras and Nijar. Additional studies will prove or disprove the possibility of regional time-equivalent sequence development.

In Spain (apart from the areas discussed previously), the Sorbas Basin contains excellent exposures of Miocene carbonate strata that were deposited on basement similar to the Nijar setting. Reconnaissance near the town of Cariatiz reveals extensive prograding reef complex strata predominantly composed of

Porites (and Halimeda). This reef complex is probably equivalent to the DS3 strata at Las Negras and Nijar. Locally these strata downlap underlying fine-grained carbonates and marls, likely equivalent to DS2 strata at Las Negras and Nijar. Exposures of the lower portion of the section in areas around Cariatiz contain some blocks of reef facies (Tarbellastraea and Porites) that may correlate to MB1 in Las Negras (J. Martin, personal communication, 1990). Other areas described by Dabrio & Martin (1978), and more recently by Martin & Braga (1990) near Lucainena de las Torres in the Sorbas Basin, contain carbonates with stratal geometries, lithofacies and stratigraphic breaks similar to those described at Las Negras and Nijar. Dabrio & Polo (1986) and Braga & Martin (1988) describe reefs/carbonates from the Almanzora River Valley, some of which display characteristics (sequences, facies, bounding surfaces) similar to those at Las Negras and Nijar. Fortuna, Purchena and Santa Pola are areas in southeastern Spain with prominent carbonate development and characteristics that suggest correlation with the Las Negras and Nijar sequences (Mankiewicz, 1987). The island of Menorca contains carbonate sequences similar to those at Las Negras (Pomar et al., 1983; A. Simb, personal communication, 1988; Pomar, 1991). Saint-Martin & Rouchy (1990) described sections in Morocco and Grasso & Pedley (1988) described sections in northern Sicily that are similar to the sections at Las Negras and Nijar. These latter areas are just two examples of the possibility of widespread, correlatable carbonate sequence development throughout areas surrounding the Mediterranean Basin.

The recognition of regionally occurring depositional sequences and sequence boundaries of similar ages that are probably strongly correlatable suggests a regional process for controlling facies architecture and geometries of the depositional sequences. Vail (1987) stated that the combination of eustacy and tectonic subsidence produces the relative changes in sea level (accommodation space) that are responsible for the depositional sequences. He believed that tectonic subsidence creates accommodation space for deposition and that eustatic sea-level change is the major control over stratal patterns and lithofacies distribution.

In their study of the carbonate section in northern Sicily, Grasso & Pedley (1988) suggested that the lateral persistence of beds and, in particular, the erosion surfaces argued for some form of eustatic control, in spite of synsedimentary tectonism during carbonate deposition. They suggested a study of the


Miocene from elsewhere in the Mediterranean where tectonism was relatively minor to test the possible effects of eustatic fluctuations on carbonate deposition. We believe our study area in southeastern Spain represents such a location.

The overall similarity of the relative sea-level (accommodation space) curve shapes and magnitudes (Fig. 10) and the similarity of interpreted ages for the depositional sequences in the different areas suggest regional processes such as eustacy or tectonism for their formation. Our field data (supported by the work of A. Arribas, personal communication, 1987) suggest no major local tectonic events during carbonate deposition in the Las Negras and Nijar areas despite the occurrence of a major tectonic feature (Carboneras Fault) that separates the two areas. Esteban & Giner (1980) showed that marine planation surfaces (pre- Miocene carbonates and pre-TCC) occur at essentially the same heights throughout the study area. Although the apparent regional correlations suggest eustatic fluctuations, further testing is necessary to rule out tectonism. One such test would be to compare the sequences from southeastern Spain with Miocene carbonate sequences exposed in northern Morocco, The Morocco exposures are probably in an area that would have experienced some tectonic influence on sedimentation during the closing of the Mediterranean and Atlantic connection. If sequences similar to those in southeastern Spain, and with similar ages, occur in Morocco, this would further support global or local Mediterranean eustacy as the dominant controlling factor for sequence development.

The relative sea-level curves constructed for Las Negras and Nijar (as well as the other reconnaissance areas) suggest that there were several fluctuations during Miocene carbonate deposition prior to the major sea-level drop in the Messinian that culminated in erosion of basin-margin deposits and evaporite deposition in the basin. With the previous drops, sea level essentially returned to its previous high point. The smaller scale interpreted fluctuations in the curves (sawtooth shapes) may similarly be due to regional processes or due to allogenic processes such as storms, earthquakes, shifting of local depositional systems (e.g. fan-delta lobes), or normal shedding of material in a slope environment via tractive currents, turbidity currents and mass movements. The occurrence of these smaller scale cycles of strata in similar positions within the major depositional sequences may suggest regional processes such as eustatic fluctuations or tectonism. However, more detailed study of these smaller scale packages is needed to determine their

sedimentological origin and to test the possibility of regional processes creating small-scale cyclicity.

If our interpreted ages are correct, then our three depositional sequences between the basement rocks and the overlying TCC were deposited over a period of approximately 4 Myr (c. 10.5-6.3 Ma using the timechartofHaqetal., 1987). Ifthecurvesconstructed for each area reflect regional processes, then the largest scale fluctuations are probably 3rd order (1- 10 Myr) or 4th order (10-100 kyr) cycles and the higher frequency fluctuations are 5th order (< 10 kyr) cycles. Clearly, a better understanding of the depositional sequence ages is necessary to determine their correlatability and the regionality of the relative fluctuations. In the absence of biostratigraphic control and good biostratigraphic resolution, other methods for better dating (such as 87Sr/86Sr analysis and magnetostratigraphy) and correlation are necessary.

Only a few studies have focused on the diagenesis of the reefs and associated facies (e.g. Esteban, 1979; Armstrong et al., 1980; Esteban & Calvet, 1983; Dawans & Lapre, 1985; Dawans, 1988). Some recent work (e.g. Goldstein et al., 1990; Oswald et al., 1990, 1991) illustrates the potential for diagenetic studies to aid in correlation and determining sea-level history. Detailed diagenetic studies in combination with sequence stratigraphic studies will aid in better characterization and understanding of potential petroleum targets in subsurface Oligo-Miocene strata in the Mediterranean and Indo-Pacific regions.

CONCLUSIONS

(1) The 50-1 50-m-thick Las Negras and Nijar carbonate complexes can be divided into three previously unrecognized depositional sequences (DS1, DS2 and DS3) based on recognition of stratal geometries, stratigraphic breaks (sequence boundaries) and facies changes. These sequences (mostly Tortonian, possibly some Serravallian) are bounded below by earlier Neogene volcanic (Las Negras) and Palaeozoic and Mesozoic and older Neogene basement (Nijar) and above by the Terminal Carbonate Complex (Messinian).

(2) Correlation of depositional sequences between the Las Negras and Nijar areas by classic techniques such as fossil dating is difficult because of the lack of datable fossils in the shallow-water strata in those areas. However, correlation between the two areas is facilitated by integrating sedimentological, sequence stratigraphic and biotic data


(3)

with locally derived relative sea-level (or accommodation space) curves for each area. The lower two sequences (DS1, DS2) were deposited as mostly normal-marine carbonate deposits on the slopes (ramps) of basement highs. DS2 locally contains megabreccia blocks (MB 1) of reef (Tarbellastraea and Porites) facies. These blocks have not been previously recognized as representing a period of reef growth separate from the fringing reefs in DS3. Most MB1 blocks probably developed as patch reefs that were eroded from an original position upslope of their preserved positions. MBl blocks are interpreted as Type A reefs (or intermediate between Type A and Type B) of Esteban (1979). The upper sequence (DS3) is the only one to show major fringing-reef development. This upper sequence is characterized by clinoforms of Porites-dominated fringing reefs interpreted as Type B of Esteban (1979). The reefs prograded basinward in a distinctive downstepping style with each successively younger reef forming in a topographically lower and more basinward position. This is interpreted to be a result of a net sea-level drop that culminated in exposure of the basin-margin deposits and evaporite deposition in basinal areas. The relative sea-level curves for the Las Negras and Nijar areas suggest several sea-level fluctuations during Miocene carbonate deposition prior to the major sea-level drop at the end of DS3 deposition.

(4) The depositional sequences of the Las Negras and Nijar areas may correlate with similar depositional sequences throughout the southern Cab0 de Gata area and in Mallorca, some 600 km to the northeast, and possibly to other Mediterranean areas. Construction of interpreted relative sea- level curves for these areas results in curves similar to those for Las Negras and Nijar which helps support our correlations.

(5 ) Although allogenic processes cannot be ruled out entirely for development of the major depositional sequences, the regional occurrence of similar, probably correlatable, depositional sequences throughout the Mediterranean area (e.g. Mallorca, Sicily) support a regional process (tectonism or eustacy) for creating the depositional sequence geometries.

(6) Depositional histories and correlation of shallow- water Miocene strata in separate basins may be aided by integrating sedimentological, sequence stratigraphic and palaeontological data and by

constructing relative sea-level (accommodation space) curves for the separate basins. If the locally derived relative sea-level curves can eventually be correlated with global eustatic sea-level curves by integrating dating methods such as microfossil dating, 87Sr/86Sr analysis, magnetostratigraphy and diagenetic studies, then this provides a useful tool for determining the importance of regional versus local, and tectonic versus eustatic processes responsible for depositional sequence geometries and may aid in regional correlation and age determination of strata.

ACKNOWLEDGMENTS

We thank L. C. Pray for introducing us to the Miocene carbonate rocks in southeastern Spain and for super- vising the two PhD studies that formed the foundation of this paper. Financial support for field-work was provided by : AAPG Grants-In-Aid ; Sigma Xi Scienti- fic Research Society Grants-In-Aid of Research; University of Wisconsin Ibero-American Studies Field Research Grants Program; Geological Society of America Research Grants; Department of Geology and Geophysics, University of Wisconsin-Madison; Department of Geology, Beloit College; Marathon Oil Co., Denver and Erico Petroleum Information Ltd, London. C. Mendelson, T. E. Fekete and J. Kalinec provided valuable field assistance. We thank Renate Hensiek for drafting and Lea Ann Davidson for word processing. The manuscript was greatly improved through reviews by M. Esteban, J. M. Martin and Sedimentology reviewers, C. Dabrio and A. Simo.

REFERENCES ADDICOTT, W.O., SNAVELY, P.D., JR, BUKRY, D. & POORE,

R.Z. (1978) Neogene stratigraphy and paleontology of southern Almeria Province, Spain: an overview. Bull. US geol. Suro., 1454,49 pp.

ALVAREZ, G . , BUSQUETS, P., PERMANYER, A. & VILAPLANA, M. (1977) Growth dynamic and stratigraphy of the Sant Pau d’Ordal miocene patch-reef (province of Barcelona, Catalonia). 2nd Int Symp on Corals and Fossil Coral Reefs, Mem. B.R.G.M., 89,367-377.

ALVARO, M., BARNOLAS, A,, DEL OLMO, P., RAMIREZ, DEL Pozo, J. & SIM~, A. (1984) El Ne6geno de Mallorca: Caracterizacibn sedimentol6gica y bioestratigrifica. Bol. geof. Min., 95,3-25.

ARMSTRONG, A.K., SNAVELY, P.D., JR & ADDICOTT, W.O. (1980) Porosity evolution of upper Miocene reefs, Almeria Province, southern Spain. Bull. Am. Ass. petrol. Geol., 64,

BERGGREN, W.A., KENT, D.V., FLY”, J.J. & VAN COUVER- ING, J.A. (1985) Cenozoic geochronology. Bull. geol. Soc. Am., 96,1407-1418.

188-208.


BIZON, G. (1985) Mediterranean foraminifera1 changes as related to paleoceanography and paleoclimatology. In : Geological Evolution of the Mediterranean Basin (Ed. by D.J. Stanley & F.C. Wezel), pp. 453470. Springer-Verlag, New York, 589 pp.

BRAGA, J.C. & MART~N, J.M. (1988) Neogene coralline-algal growth-forms and their palaeoenvironments in the Alman- zora river valley (Almeria, S.E. Spain). Palaeogeogr. Pulaeoclim. Palueoecol., 67,285-303.

BRAGA, J.C., MARTIN, J.M. & ALCALA, B. (1990) Coral reefs in coarse-terrigenous sedimentary environments (upper Tortonian, Granada basin, southern Spain). Sediment. Geol., 66, 135-150.

DABRIO, C.J. (1974) Los niveles arrecifales del Neogeno de Purchena (SE Cordilleras BBticas). Cuad. Geol., 5,7948.

DABRIO, C.J. (1975) La sedimentacih arrecifal Ne6gena en la region deI Rio Almanzora. Est. Geol., 31,285-296.

DABRIO, C.J., ESTEBAN, M. &MARTIN, J.M. (1981)Thecoral reef of Nijar, Messinian (uppermost Miocene), Almeria Province, SE Spain. J. sedim. Petrol., 51,521-539.

DABRIO, C.J. & MARTIN, J.M. (1978) Las arrecifes Messi- niense de Almeria (SE de Espafia). Cuad. Geol., 8-9, 85- 100.

DABRIO, C.J., MART~N, J.M. & M E G ~ , A.G. (1985) The tectosedimentary evolution of Mio-Pliocene reefs in the province of Almeria (SE Spain). In: Excursion Guidebook (Ed. by M.D. Milh & J. Rosell), pp. 271-305. International Association of Sedimentologists 6th European Regional Meeting, 600 pp.

DABRIO, C.J. & POLO, M.D. (1986) Modelos arrecifales neogenos de la depresion del rio Almanzora (Alrneria). Geogaceta, 1, 31-33.

DAWANS, J.M. (1988) Microbial biodiagenesis and its role in the formation of carbonate rocks: evidence from dolomite spherulites. In : Int. Ass. Sedimentologists 9th Eur. Regional Meeting Abstracts, p. 48 (abstract).

DAWANS, J.M. & LAPRE, J.F. (1985) Discrimination of dolomite diagenesis in Miocene reefs of southeastern Spain. Int. Ass. Sedimentologists 6th Eur. Regional Meeting Abstracts, (abstract).

DIETZ, R.A. & WOODHOUSE, M. (1989) Mediterranean sub- bottom giant Messinian salt as a precipitite. Geol. SOC. Am., Abstracts with Programs, p. 363 (abstract).

DRONKERT, H. & PAGNIER, H. (1977) Introduction to Mio- Pliocene of the Sorbas Basin. Messinian Seminar 3, Field Trip 2, pp. 1-21.

ESTEBAN, M. (1979) Significance of the upper Miocene coral reefs of the western Mediterranean. Palaeogeogr. Palaeo- climatol. Palaeoecol., 29, 169-188.

ESTEBAN, M. (1981) Miocene carbonate models. Internal Report., Erico Company, Inc., London, 46 pp.

ESTEBAN, M. (1988) Miocene reefsinwestern Mediterranean. Bull. Am. Ass. petrol. Geol., 72, 182 (abstract).

ESTEBAN, M. & CALVET, F. (1983) Cementation of upper Miocene reefs in western Mediterranean. Bull. Am. Ass. petrol. Geol., 67,457 (abstract).

J., PoMAR,L., SALAS, R. &PERMANYER,A. (1978)Aberrant features of the Messinian coral reefs, Spain. Acra geol. H i p . , 13,20-22.

ESTEBAN, M. & G~NER, J. (1977) Field-guide to Santa Pola reef. 3rd Messinian Seminar, pp. 23-30. IUGS IGCP.

ESTEBAN, M. & GINER, J. (1980) Messinian coral reefs and

ESTEBAN, M., CALVET, F., DABRIO, c . , BAR6N, A,, GiNER,

erosion surfaces in Cab0 de Gata (Almeria, SE Spain). Actageol. Hisp., 15,97-104.

ESTEBAN, M. & PRAY, L.C. (1981) A guidebook to the Tertiary reef carbonate and associated facies, southeastern Spain and the Balearic Platform. Internal Report., Erico Company, Inc., London, 74 pp.

FERNEX, F., MAGNB, J. & MONGIN, D. (1967) The palaeogeography of the eastern Betic ranges of southern Spain during the Caenozoic. In : Aspects of Tethyan Biogeography (Ed. by C.G. Adams & D.V. Ager), Syst. Ass. Publ., 7,

FRANSEEN, E.K. (1989) Depositionalsequences and correlation of middle to upper Miocene carbonate complexes, Lus Negras Area, southeastern Spain. PhD thesis, University of Wisconsin-Madison, 374 pp.

FRANSEEN, E.K. (1990) Middle to upper Miocene mixed carbonate and volcaniclastic slope deposits, Las Negras and Rodalquilar area, southeastern Spain. Abstracts of Posters, 13th Int. Sedimentological Congr., Nottingham, pp. 80-81 (abstract).

FRANSEEN, E.K. (1991) The middle to late Miocene reef complex in the Las Negras area, Almeria Province, southeastern Spain. In : Miocene Reefs: A Global Compari- son (Ed. by C. Jordan, M. Colgan, & M. Esteban). Springer-Verlag, Berlin (in press).

FRANSEEN, E.K., MANKIEWICZ, C. & PRAY, L.C. (1988) Depositional sequences and correlation of middle to upper Miocene reef complexes, Nijar and Las Negras areas, southeastern Spain. Bull. Am. Ass. petrol. Geol., 72, 1 8 6 187 (abstract).

FRIEDMAN, G.M. (1989) Messinian (Miocene) evaporites of the Mediterranean basin: a new approach to an old bandwagon. Geol. Soc. Am. Abstracts with Programs, pp. 364 (abstract).

GOLDSTEIN, R.H., FRANSEEN, E.K. & MILLS, M.S. (1990) Diagenesis associated with subaerial exposure of Miocene strata, southeastern Spain : implications for sea-level change and preservation of low-temperature fluid inclu- sions in calcite cement. Geochim. Cosmochim. Acta, 54,

GRASSO, M. & PEDLEY, H.M. (1988) The sedimentology and development of Terravecchia Formation carbonates (upper Miocene) of North Central Sicily: possible eustatic influence on facies development. Sediment. Geol., 57, 131- 149.

HAQ, B.U., HARDENBOL, J. & VAIL, P.R. (1987) Chronology of fluctuating sea levels since the Triassic. Science, 235, 11561166.

Hsb, K.J. (1973) The dessicated deep-basin model for the Messinian events. In: Messinian Events in the Mediterra- nean (Ed. by C . W. Drooger), pp. 60-67. Geodynamiques Scientific Report No. 7, North-Holland Publishing Co., Amsterdam, 272 pp.

Hsb, K.J., MONTADERT, L., BERNOULLI, D., CITA, M.B., ERICKSON, A., GARRISON, R.E., KIDD, R.B., MBLIERBS, F., M~LLER, C. & WRIGHT, R. (1976) History of the Mediterranean salinity crisis. Nature, 267,399403.

DE LAROUZI~RE, F.D., BOLZE, J., BORDET, P., HERNANDEZ, J., MONTENAT, C. & O n DESTEVOU, P. (1988) The Betic segment of a lithospheric Trans-Alboran shear zone during upper Miocene. Tectonophysics, 152,41-52.

LbEZ-RUIZ, J. & RODRIGUEZ-BADIOLA, E. (1980) La region volcbnica Neogena del sureste de Espafia. Est. Geol., 36,

239-246.

699-704.

5-63.


MANKIEWICZ, C. (1987) Sedimentology and calcareous algal pa feoecology of Miocene reef complexes near For tuna (Murcia Province) and NQar (Almeria Province), Southeastern Spain. PhD thesis, University of Wisconsin-Madison, 341 pp.

MANKIEWICZ, C. (1988) Occurrence and paleoecologic significance of Halimeda in late Miocene reefs, southeastern Spain. Coral Reefs, 6,271-279.

MANKIEWICZ, C. (1991) The middle to upper Miocene reef complex of Nijar, Almeria Province, southeastern Spain. In: Miocene Reefs: A Global Comparison (Ed. by C. Jordan, M. Colgan, & M. Esteban). Springer-Verlag, Berlin (in press).

MARTiN, J.M. & BRAGA, J.C. (1990) Arrecifes Messinienses de Almeria : tipologias de crecimiento, posicion estrati- grhfica y relacibn con las evaporitas. Geogaceta, 7,66-68.

MARTIN, J.M., BRAGA, J.C. & RIVAS, P. (1989) Coral successions in upper Tortonian reefs in SE Spain. Lethaia,

M E G ~ , A.G. (1985) Tectosedimentary relationships between Mio-Pliocene reefs and evaporites in Almeria and Sorbas Basins, SE Iberian Peninsula. In : Int. Ass. Sedimentologists 6th Ann. Meeting, pp. 292-295.

MITCHUM, R.M., JR, VAIL, P.R. & THOMPSON, S., 111 (1977) Part 11: The depositional sequence as a basic unit for stratigraphic analysis. In : Seismic Stratigraphy-Applica- tions to Hydrocarbon Exploration (Ed. by C.E. Payton), Mem. Am. Ass. petrol. Geol., 26,53-62.

MONTENAT, C. (1975) Le Neogene des Cordilleres Betiques, essay de synthese stratigraphique et paleogeographique. Internal Report, Paris, C.N.R.S., 187 pp.

MONTENAT, C. (1977) Les basins Nkogenes du levant d’Alicante et de Murcia (Cordilleres Betiques orientales- Espangne); stratigraphie, palkogkographie et kvolution dynamique. Doc. Lab. Gkol. Fac. Sci., Lyon, 69, 345 pp.

MONTENAT, C. & On, DESTEVOU, P. (1977) Presence du Pliocene marin dans le bassin de Sorbas (Espagne meridionale) : Conskquences palkogkographiques et tecto- niques. C.r. Soc. giol. France, 4,209-2 1 1.

MONTENAT, C., OTT, D*ESTEVOU, P. & MASSE, P. (1987) Tectonic-sedimentary characters of the Betic Neogene basins evolving in a crustal transcurrent shear zone (SE Spain). Bull. Centres Rech. Expior.-Prod., Elf-Aquitaine, 11, 1-22.

MOLLER, D.W. & HsO, K.J. (1987) Event stratigraphy and paleoceanography in the Fortuna Basin (southeast Spain) : a scenario for the Messinian salinity crisis. Paleoceanog- raphy, 2,679-696.

OSWALD, E.J., FRANSEEN, E.K. & MEYERS, W.J. (1991) Similarities in the dolomitization of upper Miocene reef complexes in Mallorca and the Las Negras area, Spain: possibleevidence for a Mediterranean dolomitizing event during the Messinian. Bull. Am. Ass. petrol. Geol., 75, 649 (abstract).

OSWALD, E.J., MEYERS, W.J. & POMAR, L. (1990) Dolomiti- zation of an upper Miocene reef complex, Mallorca, Spain : evidence for a Messinian dolomitizing Mediterranean sea. Bull. Am. Ass. petrol. Geol., 74,735 (abstract).

PAGNIER, H. (1977) Excursion to Messinian reef deposits in the part of Sorbas Basin: an Introduction. Messinian Seminar 3 Field Trip, pp. 44-53.

PERMANYER, A. & ESTEBAN, M. (1973) El arrecife Miocene de Sant Pau d’Ordal (provincia de Barcelona). Rev. Int. Inv. Geol:, Dept. Prov., Barcelona, 28,45-72.

POMAR, L. (1976) Tectonica de gravedad en 10s depbsitos

22,271-286.

Mesozoicos, Palebgenos y Nebgenos de Mallorca (Espaiia). Bol. Soc. Hist. Nut. Baleares, 21, 159-175.

POMAR, L. (1979) La evolucibn tectonosedimentaria de las Baleares: analisis critico. Acta gedl. Hisp., XIV, 293-310.

POMAR, L. (1988) Upper Miocene reef complex of Mallorca, Balearic Islands, Spain. Bull. Am. Ass. petrol. Geol., 72, 237 (abstract).

POMAR, L. (1991) Reef geometries, erosion surfacesand high- frequency sea-level changes, upper Miocene reef complex, Mallorca, Spain. Sedimentology, 38,243-270.

POMAR, L., OBRADOR, A., FORNOS, J. & RODRIGUEZ-PEREA, A. (Eds.) (1983) El Terciario de las Baleares (Mallorca, Menorca). Guia de las Excursiones del X Congreso Nacional de Sedimentologia. Inst. Est. Balearics and Universidad de Palma de Mallorca, 256 pp.

POORE, R.Z. & STONE, S.M. (1981) Biostratigraphy and paleoecology of the upper Miocene (Messinian) and lower Pliocene(?), Cerro de Almendral section, Almeria Basin, southern Spain. Pro$ Pap. geol. Surv., 774-F, FI-F11.

REHAULT, J.-P., BOILLOT, G. & MAUFFRET, A. (1985) The western Mediterranean basin. In : Geologic Evolution of the Mediterranean Basin (Ed. by D.J. Stanley & F.C. Wezel), pp. 101-130. Springer-Verlag, New York, 589 pp.

RODR~GUEZ-PBREA, A. (1984) El Mioceno de la Serra Nord de Mallorca, estratigrafia, sedimentologia e implicaciones es- tructurales. PhD thesis, Universidad de Barcelona y Palma de Mallorca, 532 pp.

ROUCHY, J.-M. (1982) La crise tvaporitique messinienne de Mtditerranke : nouvelles propositions pour une interpretation genetique. Bull. Mus. natn. Hist. nut., Paris, 4‘ ser.,

ROUCHY, J.-M., SAINT-MARTIN, J.P., MAURIN, A. &BERNET- ROLLANDE, M.C. (1986) Evolution et antagonisme des communautks bioconstructrices animales et vkgetales i la fin du Miocene en MCditerrante occidentale : biologie et skdimentologie. Bull, Centres Rech. Explor. Prod. Erf- Aquitaine, 10,333-348.

RUEGG, G . J.H. (1964) Geologische onderzoe-kingen in het Bekken van Sorbas, SE Spanje. PhD thesis, Geological Institute University of Amsterdam, 64 pp.

SAINT-MARTIN, J.P. & ROUCHY, J.-M. (1990) Les plates- formes carbonattes messiniennes en Mkditerrante occidentale : leur importance pour la reconstitution des variations du niveau marin au Miocene terminal. Bull. SOC. gkol. France, 8,83-94.

SANTISTEBAN, C. & DAWANS, J.M. (1985) Essay on the correlation between reefs and evaporites of the upper Miocene of Southeast Spain. Int. Ass. Sedimentologists 6th Ann. Meeting, pp. 415419 (abstract).

SANTISTEBAN, C. & TABERNER, C. (1980) The siliciclastic environments as a dynamic control in the establishment and evolution of reefs : sedimentary models. Int. Ass. Sedimentologists 1st Eur. Meeting, pp. 208-21 1 (abstract).

SCHMALZ, R.F. (1989) Curiouser and curiouser. In: Geol. Soc. Am., Abstracts with Programs, p. 363 (abstract).

SCHREIBER, B.C. & HELMAN, M.L. (1989) What are the problems in forming deepwater Messinian evaporites? Geol. Soc. Am., Abstracts with Programs, p. 363 (abstract).

SERRANO, F. (1990) Presencia de Serravalliense marino en la cuenca de Nijar (Cordillera Bttica, Espaiia). Geogaceta, 7, 95-97.

S I M ~ , A. & h M 6 N , X. (1986) AnLlisis sedimentologico y descripcibn de las secuencias deposicionales del Neogeno postorogtnico de Mallorca. Bol. geol. Min., 97,445472.

4,107-136.


VAIL, P.R. (1987) Part 1 : Seismic stratigraphy interpretation VOLK, H.R. (1967) Zur Geologie und Stratigraphie des procedure. In: Atlas of Seismic Stratigraphy (Ed. by A.W. Neogenbechen von Vera, Siidost-Spanien. PhD thesis, Bally), Am. Ass. petrol. Geol., Studies in Geology, 27, 1-10, Amsterdam University, Amsterdam, 160 pp.

VEEKEN, P.C.H. (1983) Stratigraphy of the Neogene- VOLK, H.R. & RONDEEL, H.E. (1964) Zur Gliedering des Quaternary Pulpi Basin, Provinces Murcia and Almeria Jungtertaars in Bechen von Vera, Siidost-Spanien. Geol. (SE Spain). Geologie Mijnb., 62,255-265. Mijnnb., 43,310-315.

(Manuscript received 26 June 1990; revision received I5 March 1991)

APPENDIX: FACIES CHARACTERISTICS Table A l . Halimeda-rich beds (HR).

Las Negras ~

Nijar

Bedding (dips) Skeletal & non-skeletal

massive; very thinly to thickly bedded (0-30") Halimeda; coralline algae (fragments,

components rhodoliths, crusts) serpulids, bivalves, Porites, bryozoans, gastropods, volcaniclastics

Dominant grain sizes Porosity (visual estimates) 5-50% Cements

Other

coarse sand to pebble

dolomite, fibrous to bladed isopachous calcite,

occurs in reef core to distal foreslope positions equant calcite, poikilitic calcite

very thinly to thickly bedded (10-25") Halimeda, coralline algae (fragments,

rhodoliths, crusts, thickets) molluscs, serpulids, Porites, bryozoans, echinoids, peloids

mud to pebble trace to 40% dolomite, isopachous calcite, equant calcite,

occurs in reef core to distal foreslope pendant calcite

positions ~ ~~ ~

Table A2. Reef core or talus (RCT).

Las Negras Nijar

Bedding (dips) Skeletal & non-skeletal

massive; locally tabular (0-30") Poritesdominant framework, locally

branching red algae, foraminifera, bryozoans, bivalves, gastropods, echinoderms, peloids, coated grains, intraclasts, volcaniclastics

components serpulids; encrusting, fragmented and

Dominant grain sizes Porosity (visual estimates) < 5-25%

Cements

mud to boulder

equant or spherulitic/polyhedral dolomite ; micritic and fibrous to bladed calcite; coarse (poikilitic) calcite

coral framework is minor compared to matrix, local vadose fabrics

Other

massive; locally tabular (0-30") Poritesdominant framework ; locally

serpulids; encrusting fragmented and branching red algae, foraminifera, bryozoans, bivalves, gastropods, echinoderms, peloids, coated grains, intraclasts, siliciclastics (4% by weight)

mud to boulder trace to 25%

equant dolomite; micritic and fibrous to bladed calcite; coarse boikilitic) calcite

coral framework is minor compared to matrix, local vadose fabrics

Table A3. Volcaniclastic/carbonate conglomerate (VCC) and volcanic sandstone/conglomerate (VSC) only present in Las Negras area.

vcc vsc Bedding (dips) massive Skeletal & non-skeletal volcanic clasts, coralline algae (fragments),

components bryozoans, bivalves, solitary corals, gastropods, serpulids, benthic and planktonic foraminifera, echinoderms

Dominant grain sizes Porosity (visual estimates) 5 4 5 % Cements equant dolomite, equant calcite Other mostly matrix-support texture

micrite to boulder

thinly to thickly bedded (0-30") volcanic clasts, coral, serpulids, coralline

algae (fragments), bivalves, gastropods, bryozoans, peloids

micrite to cobble 10-35% rare: locally equant dolomite common as channel-fill deposits or wedge-

shaued deDosits

Middle-late Miocene carbonate complexes, SE Spain a97

Table A4. Megabreccia 1 (MB1) and megabreccia 2 (MB2) only present in Las Negras area.

MB 1 MB2

Bedding (dips)

Skeletal & non-skeletal

massive, isolated blocks; encased in strata dipping < 10"

TurbeZZustruea, Porites, coralline algae (crusts, components fragments), bryozoans, peloids, planktonic

and benthic foraminifera, serpulids, bivalves, echinoderms, gastropods

Dominant grain sizes

Porosity (visual estimates) 0-25%? mud to boulder

Cements

Other

fibrous to bladed isopachous calcite; equant calcite cement; bladed-equant dolomite

clast matrix is more abundant than coral framework

layers 1-3 m thick; some isolated blocks

Porites, coralline algae (crusts, fragments), encased in strata (O-lOo)

serpulids, bryozoans, foraminifera, gastropods, bivalves, echinoderms, peloids, intraclasts, composite grains, volcaniclastics

coarse sand to boulder 5 4 0 % fibrous to bladed isopachous calcite; equant

matrix in clasts is more abundant than coral calcite, equant dolomite

framework

Table A5. Red algal-rich packstones/grainstones (RAPG) only present in Las Negras area.

RAPG

Bedding (dips)

Skeletal & non-skeletal components

massive, thinly to thickly bedded (< 10") coralline algae (fragments, rhodoliths), bryozoans, bivalves,

gastropods, benthic and planktonic foraminifera, solitary corals, echinoderms, serpulids, peloids, intraclasts, volcaniclastics

Dominant grain sizes Porosity (visual estimate) 5-3574 Cements equant dolomite, equant calcite Other

silt to granule

common as channel-fill deposits or wedge-shaped deposits

Table A6. Coarse-grained packstones/grainstones (CGPG).

Las Negras Niiar

Bedding (dips)

Skeletal & non-skeletal components

Dominant grain sizes Porosity (visual estimates) Cements

Other

well bedded, thinly to very thickly bedded local cross-bedding and cross-lamination (< 10- 30")

bivalves, coralline algae (fragments, rhodoliths, crusts, branching), echinoderms, bryozoans, gastropods, serpulids, Porites fragments, foraminifera, ostracods, peloids, coated grains, volcaniclastics, intraclasts

medium sand to pebble 540% equant dolomite, fibrous to bladed, isopachous

normally graded units locally; common as calcite, equant calcite

channel-fill deposits

in DS3 : well bedded, very thinly to thickly bedded; parallel lamination common (12- 25"). In DS2: massive to cross-bedded (< 100)

molluscs, serpulids, bryozoans, echinoids. In DS3 : coralline algae (fragments, rhodoliths, crusts, branching thickets), some encrusting Porites, minor siliciclastics (7% by weight). In DS2: coralline algae (fragments, rhodoliths), benthic foraminifera, brachiopods, siliciclastics (average of 16% by weight)

mud to pebble trace to 40%

dolomite, isopachous calcite, void-filling

in DS3 : prograding wedge geometry calcite, poikilotopic calcite, pendant calcite

common; rhythmic pattern of biotic constituents and sedimentary structures. In DS2 : lenticular-shaped, fining-upward packages are characteristic; channels and cross-bedding common in the lower part of packages ; Ophiomorphu burrows common

m

\o

m

Tabl

e A7. F

ine-

grai

ned

wac

kest

ones

/pac

ksto

nes.

(FC

WP)

(F

GW

PY)

(FG

WPo

) (F

GW

Pw)

Las

Neg

ras

Nija

r N

ijar

Nija

r

Bed

ding

(dip

s)

mas

sive

; loc

ally

thin

ly to

thic

kly

bedd

ed,

loca

lly la

min

ated

and

cros

s-la

min

ated

plan

kton

ic fo

ram

inif

era,

cor

allin

e al

gae

(110

0)

Skel

etal

& n

on-

skel

etal

(f

ragm

ents

), bi

valv

es, e

chin

oder

ms,

co

mpo

nent

s ga

stro

pods

, pel

oids

, vol

cani

clas

tics

Dom

inan

t gra

in

Poro

sity

(vis

ual

540%

mud

to fi

ne sa

nd; l

ocal

ly p

ebbl

e si

zes

estim

ates

)

Cem

ents

Oth

er

rare

equ

ant d

olom

ite, e

quan

t cal

cite

exte

nsiv

e bi

otur

batio

n ch

arac

teri

stic

loca

lly

mas

sive

(<

10")

m

ediu

m to

thic

kly

bedd

ed

(1 0-

20")

plan

kton

ic f

oram

inif

era

(loca

lly

mol

lusc

s, co

ralli

ne a

lgae

gl

auco

nite

-fill

ed),

mol

lusc

s, si

licic

last

ics

(fra

gmen

ts, r

hodo

liths

), (3

1% by

wei

ght)

echi

noid

s, b

enth

ic

fora

min

ifer

a, b

ryoz

oans

, se

rpul

ids,

sili

cicl

astic

s (1

3% by

wei

ght)

mud

to fi

ne sa

nd

mud

to p

ebbl

e

trac

e to

5%

tr

ace

to 4

0%

dolo

mite

exte

nsiv

e bi

otur

batio

n

dolo

mite

, poi

kilo

topi

c ca

lcite

, pen

dant

cal

cite

wed

ge-s

hape

d, p

rogr

adin

g cl

inof

orm

thin

to m

ediu

m b

edde

d,

mas

sive

, loc

ally

b

la

min

ated

(<

12')

3

"rl

i2 be

nthi

c fo

ram

inif

era,

2

cora

lline

alg

ae fr

agm

ents

, 2

silic

icla

stic

s (12

% by

w

eigh

t)

plan

kton

ic a

nd sm

all

3: n & ? 5

mud

to fi

ne sa

nd

3

?? L'

F tr

ace

to 5%

isop

acho

us c

alci

te, d

olom

ite

2'

burr

owin

g ch

arac

teri

stic

Depositional sequences and correlation of middle(?) to late Miocene carbonate complexes, Las Negras...

Documents

Transcript of Depositional sequences and correlation of middle(?) to late Miocene carbonate complexes, Las Negras...