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GEOLOGICA CARPATHICA, FEBRUARY 2006, 57, 1, 29—39
www.geologicacarpathica.sk
Heavy mineral provenance and paleocurrent data of the
Upper Cretaceous Gosau succession of the Apuseni
Mountains (Romania)
VOLKER SCHULLER and WOLFGANG FRISCH
University of Tübingen, Institute for Geosciences, Sigwartstrasse 10, D-72076 Tübingen, Germany; volker.schuller@uni-tuebingen.de;
frisch@uni-tuebingen.de
(Manuscript received January 26, 2005; accepted in revised form June 16, 2005)
Abstract: Heavy mineral assemblages from profiles of Upper Cretaceous Gosau sediments of the Apuseni Mts (Roma-
nia) help to reveal source areas and to get clues about geodynamic processes leading to erosion of distinct rocks in the
surrounding geological units. The samples from the Lower Gosau Subgroup reflect no distinct heavy mineral predomi-
nance: metamorphic and magmatic sources are largely balanced. The Upper Gosau Subgroup is characterized by an
increase in minerals derived from metamorphic rocks. Increasing amounts of apatite reflect the onset of the banatite
magmatism during Campanian time. Cr-spinel was found in most of the profiles and in different stratigraphic horizons,
reflecting erosion of obducted oceanic crust situated south and southeast of the Gosau basin (in present-day coordinates).
Paleocurrents indicate that sedimentary supply was provided from both sides of the elongated forearc basin. On the basis
of paleocurrent indicators and heavy mineral spectra we propose a scenario with erosion of a forearc ridge on the one side
of the basin and a crystalline basement on the other. The increase in metamorphic heavy minerals indicates enhanced
erosion in the uplifting crystalline hinterland (mainly composed of the Bihor Autochthonous Unit) during sedimentation
of the Upper Gosau Subgroup.
Key words: Eastern Alps, Apuseni Mts, Gosau succession, paleocurrent directions, heavy minerals.
Introduction
The Upper Cretaceous Gosau successions of the Apuseni
Mts have been described by several geologists, generally
on the basis of classical sedimentological and paleontologi-
cal data (e.g. Lupu 1970; Pitulea & Lupu 1978; Lupu &
Lupu 1983; Lupu & Zacher 1996). The common characters
of similar Upper Cretaceous deposits in the Alpine Orogen
are the stratigraphic range (Turonian to end of Cretaceous
or Early Tertiary), sedimentological and facies analogies,
and a similar geodynamic frame in which this basin
evolved. The Gosau successions of the Eastern Alps were in
the focus of a number of geological investigations (Toll-
mann 1976 and references therein; Woletz 1967; Faupl &
Wagreich 1992; Wagreich 1995). These deposits give a
clue to understanding the geodynamic processes during an
important evolutionary period of the Alpine Orogen. Upper
Cretaceous sediments with similar features as the Gosau oc-
currences of the Eastern Alps are also known from the West-
ern Carpathians (Slovakia; Wagreich & Marschalko 1995;
Faupl et al. 1997) and the Transdanubian Range (Hungary;
Siegl-Farkas & Wagreich 1997), where this succession is
known under regional denominations. In the Apuseni Mts
the term Gosau has commonly been adopted by regional
geologists (Lupu 1985; Lupu et al. 1993; Lupu & Zacher
1996). For this reason the name Gosau is used in the present
paper for description of the Upper Cretaceous Gosau-type
successions of the Apuseni Mts.
Generally, the Gosau succession is subdivided on the
basis of its sedimentary facies into the Lower Gosau Sub-
group (terrestrial to shallow marine deposits) and the Up-
per Gosau Subgroup (deep marine, turbiditic environ-
ment). As proposed by Wagreich (1995), subduction
erosion led to sudden subsidence and the creation of ac-
commodation space for the deep-water Upper Gosau Sub-
group. Studies of the assemblages of heavy minerals of the
Gosau successions of the Eastern Alps (Woletz 1967; Fau-
pl & Wagreich 1992) indicate the erosion of an accretion-
ary wedge with ophiolites during the period of the Lower
Gosau Subgroup, which supplied Cr-spinel. The predomi-
nance of metamorphic heavy minerals in the Upper Gosau
Subgroup indicates exhumation and uplift of the Aus-
troalpine crystalline complex in the hinterland.
Similarities of the Gosau successions in the Apuseni
Mts and the Eastern Alps are evident with respect to their
heavy mineral spectra and source areas. This indicates that
similar geotectonic processes prevailed during the Late
Cretaceous in both regions. The aim of this paper is to get
a clue about the source areas and transport directions of
the clastic sediments within the geodynamic framework of
this time and to compare the Gosau successions of the
Eastern Alps with those of the Apuseni Mts.
Geological overview
In a position between the Tertiary Pannonian and Tran-
sylvanian Basins (Fig. 1), the Apuseni Mts formed during
the Cretaceous and Early Tertiary orogenies due to the col-
lision of the two microplates Tisia and Dacia (Sănduelscu
30 SCHULLER and FRISCH
1984; Csontos et al. 1992; Csontos 1995; Tari et al. 1995;Linzer et al. 1998). The amalgamated block experienced a
70—90° clockwise rotation in the Miocene (Pătra�cu et al.1994; Panaiotu et al. 1997) followed by eastward drift, whichwas caused by retreating subduction (Royden 1993) in theCarpathian Flysch Ocean (Ceăhlau ocean; Zweigel 1997).
The Apuseni Mts are tectonically divided into the BihorAutochthonous Unit (with low- to medium-grade meta-morphic rocks of the greenschist and garnet-staurolitezone, Variscan granitic intrusive rocks and a Permo-Meso-zoic sedimentary cover sequence), the Mesozoic tectoniccomplex and Tertiary tectonic complex. The Mesozoic
Fig. 1. Structural map of the Apuseni Mts (after Ianovici et al. 1976; Balintoni 1997). The names of the main Gosau occurrences are
shown in the rectangular frames. The Gosau sediments of the South Apuseni Mts belong to the Tertiary tectonic complex, those of the
North Apuseni Mts belong to the Mesozoic tectonic complex and to the Bihor Autochthonous Unit.
31HEAVY MINERAL PROVENANCE PALEOCURRENT DATA OF THE APUSENI MOUNTAINS (ROMANIA)
tectonic complex comprises the nappes of the “AustrianTransylvanides” and the Apusenides. The “Austrian Tran-sylvanides” consist of a metamorphic basement, Jurassicophiolites, deep-marine sediments and Upper Jurassic toLower Cretaceous platform carbonates deformed duringthe late Early Cretaceous orogeny. The metamorphic rocksof the basement deformed under conditions of the green-schist facies. However, in one outcrop metamorphic rocksin eclogite facies have been described by Szadetzki(1930; Fig. 1). The Apusenides are built up by the Bihariaand Codru nappe units with low- to medium-grade meta-morphic rocks and remnants of nonmetamorphic Permo-Mesozoic sediments. The Tertiary tectonic complex(“Laramian Transylvanides” after Balintoni 1997) com-prises the rocks of the “Austrian Transylvanides” andLower to Upper Cretaceous, mainly siliciclastic sedimentsincluding the studied Gosau successions. The AustrianTransylvanides were thus incorporated in the Early Tertia-ry orogeny and tectonically overprinted during this event.
Besides a Variscan granite of the Bihor AutochthonousUnit (Muntele Mare granite), the Late Cretaceous to EarlyTertiary calc-alkaline magmatism (“banatites”) and theNeogene, mostly calc-alkaline magmatism form magmaticsuites in the Apuseni Mts.
Lithostratigraphy and facies of the Gosau sediments ofthe Apuseni Mts (Fig. 2) are similar to the well studied Go-sau successions of the Eastern Alps (Tollmann 1976 andreferences therein; Lupu 1970; Pitulea & Lupu 1987;Lupu & Zacher 1996). A subdivision into a Lower and Up-per Gosau Subgroup has been adopted since in Romanianliterature these deposits are commonly described as Gosausediments. However, in Romanian literature only the shal-low marine succession was described as Gosau sediments,whereas the deep marine succession was separated. In thispaper, the classification into a Lower and Upper Subgrouplike in the Eastern Alps is made. The shallow marine Low-er Gosau Subgroup and the deep marine Upper Gosau Sub-group are known from the Southern and Eastern ApuseniMts. The turbiditic Upper Gosau Subgroup, however, islargely missing in the northern Apuseni Mts, where onlyshallow marine sedimentation until latest Campanian timeis recorded. Moreover, the Gosau sediments of the ApuseniMts were deposited from latest Turonian to latest Maas-trichtian time. Sedimentation terminated around the Cre-taceous/Tertiary boundary (Lupu & Zacher 1996; Schuller& Frisch 2003). In contrast, the sequences in the EasternAlps continue until Eocene times in places.
Sampling and analytical methods
67 samples of coarse- to medium-grained sandstoneshave been collected from outcrops along profiles of themain Gosau occurrences. They were processed by usingstandard laboratory techniques (Boenigk 1983). Determi-nation and counting was performed on the fraction of100—200 µm in immersion fluid with refractiony indicesof nf=1.6 and nf=1.7. A minimum of 100 monomineralswas determined for each sample, except for few samples, in
Fig. 2. Schematic profile of the Upper Cretacous Gosau succession of
the Apuseni Mts. The Lower Gosau Subgroup comprises terrestrial and
shallow marine sediments, locally with thick limestones. The turbidites
of the Upper Gosau Subgroup show a fining-upward trend. A horizon
with debris flows and olistoliths can be traced through all occurrences.
The banatite magmatism is responsible for subvolcanic intrusions
(dikes, sills) and tuff layers. Note: the thicknesses of each subgroup
vary locally; the maximum thickness of the Upper Gosau Subgroup is
unknown, due to postsedimentary basin inversion and erosion.
which only an insufficient number of grains could be sep-arated (Table 1). Only monominerals are used for statisti-cal processing, graphical presentation and interpretation.Furthermore, minerals with either very low portions or lowprovenance information (e.g. dolomite, glauconite) are notincluded in the graphical presentation.
In order to fix changes in the mineral spectra in the se-quences with high precision, we tried to cover the complete
32 SCHULLER and FRISCH
Table 1: Percentages of non-opaque heavy minerals (without layer silicates and lithic fragments).
33HEAVY MINERAL PROVENANCE PALEOCURRENT DATA OF THE APUSENI MOUNTAINS (ROMANIA)
stratigraphic succession within each Gosau occurrence.Minerals with similar stability and provenance informationhave been grouped for clearness. Staurolite, epidote andzoisite form such a group of relatively stable minerals de-rived from low- to medium-grade metamorphic rocks.Zircon and tourmaline have been grouped because oftheir extreme weathering resistivity and transport stabili-ty. Although rutile shows the same characteristics, it ispresented separately, because its origin is primarily relatedto high-pressure metamorphic rocks. A later redepositionfrom sediments, however, cannot be excluded for thishigh-resistivity mineral group.
Results
The analysed samples record broad heavy mineral spec-tra. The dominating minerals are garnet, straurolite, tourma-line, zircon, apatite and rutile (in this order). Cr-spinel,chloritoid, glaucophane or allanite are generally rare but ofhigh interest with respect to their provenance information.
The majority of the mineral assemblages record high per-centages of minerals derived from metamorphic rocks (gar-net, staurolite, rutile). In the Upper Gosau Subgroup of theDrocea, Vidra, Gilău, Hă�date and Ro�ia occurrences(Figs. 3, 5; for localization of the occurrences see Fig. 1),garnet and minerals of the staurolite-epidote-zoisite-groupreplace zircon and tourmaline as the predominating miner-als. This reflects a change from a mainly magmatic to amainly metamorphic source. This change is also accompa-nied by the appearance of rutile. The Sălciua-Ocoli�, Gilău,Hă�date and Ro�ia occurrences record increased rutile per-centages in the Upper Gosau Subgroup, which can be ex-plained by the erosion of high-pressure metamorphic rocksof the Transylvanides, since high-pressure rocks are onlyknown from small eclogite outcrops in the Austrian Tran-sylvanides (Fig. 1; Szadetzki 1930).
The Permo-Mesozoic sedimentary cover is also a possiblesource for rutile. Together with tourmaline and zircon, rutileforms a group of very stable minerals which is often inter-preted as erosion of sedimentary successions.
Within the zircon—tourmaline group, tourmaline domi-nates. The source of tourmaline is proposed to be eitherthe medium-grade metamorphic complexes of the BihorAutochthonous and the Codru Unit, but more likely theVariscan granites and pegmatites (Muntele Mare granite).We relate the increased amounts of zircon in samples ofthe Upper Gosau Subgroup (e.g. M60, Ro�ia) to the bana-tite magmatism, which started around the Campanian/Maas-trichtian boundary.
Because apatite can be supplied from both magmatic andmetamorphic rocks, this mineral is present in almost everysample, irrespective of its stratigraphic position. In the lower
Fig. 3. Heavy mineral assemblages of the main Gosau occurrences.
Y-axis shows the sample numbers in stratigraphic order for each
occurrence (youngest on top). Minerals with low frequency or
isolated appearance are displayed as symbols. The grey line be-
tween the sample numbers marks the boundary between the Lower
and Upper Gosau Subgroup.
�
34 SCHULLER and FRISCH
part of the sequence the apatite is interpreted to be mainlyderived from the Muntele Mare granite but also from themetamorphic rocks of the Codru and Biharia Nappes. Inthe Upper Gosau Subgroup an important portion of the ap-atite probably derives from the coeval banatite magma-tism. The banatite magmatism is probably also indicatedby the appearance of cassiterite and sphalerite in samplesM65 and 41 (Vidra occurrence). The high allanite contentin sample 163 of the Vlădeasa occurrence also reflects thecoeval banatite magmatism. This sample has been takenfrom the matrix of a conglomerate layer of the volcano-sedimentary series of the Vlădeasa succession.
Although present in low amounts only, Cr-spinel provesa contribution from the ophiolites of the Austrian Transyl-vanides (Fig. 1), at present exposed in the region to thesouth of the Gosau occurrences. This shows that the ophi-olites were already exposed in Late Coniacian times (sam-ple M65, Ro�ia: Figs. 3 and 5). Cr-spinel has even beenidentified in the Gosau occurrences situated in the north-ern parts of the Apuseni Mts (Ro�ia, Vlădeasa). Consider-ing the postsedimentary compressional tectonics andbasin inversion, this reflects a transport distance of clearlymore than 100 km within the Gosau basin.
Glaucophane was found in two samples and in lowamounts only. Nevertheless, as a high-pressure/low-tem-perature metamorphic mineral, it witnesses the exposure ofa subducted complex, which is completely eroded today.Cr-spinel and glaucophane indicate that ophiolites and asubduction complex were exposed to the south (inpresent-day coordinates) of the Gosau basin. The rutilecould also be derived from subduction complexes.
Chloritoid has been detected in low amounts in somesamples from different stratigraphic horizons. The diffuse
Fig. 4. Qualitative overview of the identified heavy minerals and their assumed provenance. Light grey fields indicate inferred and mi-
nor contributions, dark fields main contributions of the respective rock.
distribution shows erosion of low grade metamorphicrocks throughout sedimentation of the Gosau succession.
Pyroxene, amphibole and anatase have been found invery low amounts in a few samples. Because of the lowamount and the broad source rock spectra the provenanceinformation cannot be constrained. These minerals areshown for completeness only (Fig. 3).
Interpretation
Most of the heavy minerals from the Gosau sedimentsof the Apuseni Mts can be assigned to various rock units(Fig. 4). Nevertheless an isolation is possible. Low- tomedium-grade metamorphic minerals (primarily garnet,staurolite, chloritoid, amphibole) were mainly suppliedfrom the Bihor Autochthonous Unit and the crystallinerocks of the Biharia and Codru Units. The source for thehigh pressure minerals (rutile and glaucophane) wereprobably the Transylvanides, since the scarce high-pres-sure metamorphic rocks are only known from these rockunits. Zircon, tourmaline and apatite were mainly sup-plied from the banatite magmatism and the Variscangranites (Muntele Mare granite). Only the Cr-spinel indi-cates an unambiguous source lithology: the ophiolites ofthe Austrian Transylvanides.
Besides the supply of tourmaline and zircon from mag-matic rocks, and rutile from high-pressure metamorphicrocks, these three minerals could also have been derivedfrom the Permo-Mesozoic cover rocks of the Apuseni Mts.
For the interpretation of the heavy mineral assemblag-es and their variations, a compilation for all studied oc-currences was made, which considers the stratigraphicposition of the samples within the profile as well as the
35HEAVY MINERAL PROVENANCE PALEOCURRENT DATA OF THE APUSENI MOUNTAINS (ROMANIA)
Fig. 5. Main heavy mineral groups of the Gosau occurrences and stratigraphic position of sample points. The grey line marks the bound-
ary between the Lower and Upper Gosau Subgroup. Only minerals with provenance interest are shown, which explains the gaps to 100 %.
36 SCHULLER and FRISCH
facies change from the Lower to the Upper Gosau Subgroup(Fig. 5). Onset of sedimentation and the intra-Gosauan fa-cies change, however, did not occur synchronously.
Although some occurrences record high percentagesof metamorphic minerals in both the Lower and the Up-per Gosau Subgroup (e.g. Sălciua-Ocoli�, Borod), thereis a clear trend towards an increasing importance ofmetamorphic minerals towards higher stratigraphic lev-els. In the Drocea and Vidra profile the change of theheavy mineral suites from Lower to Upper Gosau Sub-group is evident. The Borod and Vlădeasa occurrencesdo not record Upper Gosau sediments. They are sur-rounded by the metamorphic rocks of the Bihor Au-tochthonous Unit, which explains their high percentageof metamorphic minerals. Metamorphic minerals alsodominate in the entire succession of the Sălciua-Ocoli�occurrence. This is probably due to supply from the Bi-haria Unit to the north.
The relative increase in the garnet/staurolite/epidote/zoisite-group in higher stratigraphic levels may also rep-resent a shift of sources from older sediments to meta-morphic basement rocks. The sediments were largelyeroded during the early stage of the basin fill.
As already mentioned, the Cr-spinel must have beensupplied from the ophiolitic ultrabasic rocks of the Tran-sylvanides to the south. This conforms to the occurrenceof radiolarite pebbles in debris flows and olistoliths (Bu-cur et al. 2004). The radiolarites are also only known fromthe Transylvanides.
Paleocurrent measurements
The determination of paleocurrent directions is basedon pebble imbrications, oblique lamination and erosionmarks on the base of Bouma Ta layers in the turbidites ofthe Upper Gosau Subgroup. Some of the sole marks do notindicate the transport direction, for example, groove castsor badly preserved flute casts. The paleocurrent directionsare shown in present-day coordinates, that block rotations
like the approx. 90° rotation in the Miocene have notbeen rotated back (Fig. 6). The paleocurrent data recordtransport form different directions for both the Lower andthe Upper Gosau Subgroup.
The dominant flow directions are both from N to NWand S to SE. This indicates that the elongated Gosau basin
Fig. 6. Directions of paleocurrents of the Gosau sediments of the Apuseni Mts (in present-day coordinates). Bipolar arrows indicate un-
known transport direction. Each arrow represents an average of a dataset with several measurements. The simplified sketch illustrates
the average basin orientation (in present-day coordinates) with range of the main transport directions.
37HEAVY MINERAL PROVENANCE PALEOCURRENT DATA OF THE APUSENI MOUNTAINS (ROMANIA)
received detrital material from both flanks during sedi-mentation of both the Lower and the Upper Gosau Sub-group. NE-orientated flow in the Câmpeni occurrenceshows local deviation into a direction, which was proba-bly parallel to the basin axis.
Comparison with the Gosau sediments in the
Eastern Alps
The heavy mineral assemblages of the Gosau sedi-ments of the Apuseni Mts record a similar dynamic evo-lution as those of the Eastern Alps. Cr-spinel as acharacteristic mineral in the Lower Gosau Subgroup ofthe Eastern Alps (Woletz 1967; Gruber et al. 1991; Fau-pl & Wagreich 1992) gives evidence for the erosion ofophiolites from an accretionary wedge to the north ofthe Gosau basin. This accretionary wedge formed bysubduction of the South Penninic Ocean along thenorthern margin of the Austroalpine mega-unit. In theUpper Gosau Subgroup, garnet as a metamorphic miner-al predominates, indicating uplift and exhumation ofthe Austroalpine crystalline basement in the south (Faupl& Wagreich 1992; Wagreich & Faupl 1994).
Fig. 7. Interpretative sketch illustrating the subduction of the Pennin-
ic and Transylvanian Ocean during the Gosau sedimentation period.
a – Geodynamic position of the Gosau depositional area during
Late Cretaceous times. b – Situation of the Apuseni Mts in present-
day coordinates. c – Profile (see line in a) for Late Cretaceous time.
Although the Cr-spinel is not dominating in the heavymineral suites of the Apuseni Mts, it indicates erosion ofan obducted ophiolitic complex, probably in the forearcregion (Fig. 7). Erosion of a forearc region is supported bythe appearance of glaucophane as a characteristic mineralforming in subduction zones. The glaucophane indicatesthat an offscraped subduction complex was part of the ac-cretionary wedge. Glaucophane-bearing rocks are actuallynot exposed in the Apuseni Mts, they have completelybeen eroded. The obducted ophiolites in contrast, are stilllargely exposed in the southern Apuseni Mts (Fig. 1). Inthe Eastern Alps remnants of the South Penninic oceaniccrust are known from occurrences in the Tauern Window,where they have been metamorphosed in Tertiary times,and from minor exposures along the southern margin ofthe Rhenodanubian flysch zone.
Predominance of garnet and other metamorphic miner-als in the Upper Gosau succession of the Apuseni Mts is inline with the heavy mineral data from the Eastern Alps. Inboth areas it shows exhumation of a metamorphic hinter-land (Fig. 7). In the Apuseni Mts this hinterland was occu-pied by the Bihor Autochthonous Unit over large areas.
Conclusion
Heavy mineral assemblages and paleocurrent measure-ments from the Apuseni Mts give evidence that erosionand sedimentary transport was both from N to NW andfrom S to SE (in present-day coordinates) during the entireperiod of the Gosau sedimentation. In our interpretation,which is in line with the geodynamic situation in the East-ern Alps, the basin was positioned in the forearc regionabove the Transylvanian subduction zone (Penninic sub-duction zone in the Eastern Alps) and was supplied fromthe accretionary wedge on the one side, and from the crys-talline Bihor hinterland (Austroalpine for the EasternAlps) on the other (Fig. 7).
The presented data and interpretation give new insightsconcerning the Late Cretaceous geodynamic evolution ofthe Alpine-Carpathian orogen. Similarities to the AlpineGosau sequences indicate a coherent geodynamic evolu-tion during the Late Cretaceous, with a basin located onthe northern margin of the Adriatic microplate (includingthe Austroalpine unit) and the southward subducting Pen-ninic Ocean. The change in the heavy mineral spectra indirection to more metamorphic detritus roughly coincideswith the abrupt and asynchronous basin subsidence at thestart of the Upper Gosau succession. We interpret this interms of accelerated incision of the contributing rivers inthe source area into the crystalline basement.
Acknowledgments: This work is part of a project financed bythe DFG (Deutsche Forschungsgemeinschaft). Special thanksare addressed to our collaborating colleagues from theBabe�-Bolyai University/Cluj-Napoca (Romania), especiallyDr. N. Har, Prof. Dr. I. Bucur and E. Săsaran. Particular thanksare directed to Prof. I. Bucur and Dr. R. Aubrecht for review-ing this article as well as helpful suggestions and comments.
38 SCHULLER and FRISCH
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