Facies (2005) 50:647–664DOI 10.1007/s10347-004-0041-6

O R I G I N A L A R T I C L E

Immo Sch�lke · Adrian Popp

Microfacies development, sea-level change, and conodont stratigraphyof Famennian mid- to deep platform deposits of the BeringhauserTunnel section (Rheinisches Schiefergebirge, Germany)

Received: 19 August 2004 / Accepted: 10 November 2004 / Published online: 18 February 2005� Springer-Verlag 2005

Abstract High resolutional microfacies data from theBeringhauser Tunnel section in the northern part of theRheinisches Schiefergebirge allow the reconstruction of arelative sea-level curve. Distinctive sedimentological sig-nals in this cephalopod limestone section indicate the po-sitions of sea-level lowstands that correlate well with pre-existing sea-level curves. Only slight differences in somelowstand positions have been observed by means of con-odont biostratigraphy. The basal Famennian portion of thesuccession at the Beringhauser Tunnel section exposesmicrobial sedimentary structures reported from the Rhei-nisches Schiefergebirge for the first time that are indicativeof initial mud-mound formation or mud-mound flanks.Further mud-mound growth with the development of asynsedimentary relief was stopped, probably due todrowning.

Keywords Conodont stratigraphy · Microfacies ·Rheinisches Schiefergebirge · Late Devonian ·Sea-level curve

Introduction

The Beringhauser Tunnel section in the RheinischesSchiefergebirge was proposed by the German Subcom-mission on Devonian Stratigraphy (SDS) as a referencesection for subdivision of the Famennian into substages,especially for the future Lower-Middle Famennianboundary (Sch�lke et al. 2003). On the substage level thefinal boundary definition of the international SDS will notinclude the designation of a global stratotype section andpoint (GSSP), but is planned to be accompanied by thenomination of three to four sections from different sedi-

mentary settings as reference sections. The BeringhauserTunnel section has been accepted during the businessmeeting of the SDS 2002 in Toulouse as a potential ref-erence section representing a pelagic cephalopod limestonesetting typical of Upper Devonian outer shelf deposits.

Paralleling the biostratigraphic studies of the well-pre-served conodont fauna from this section, the lithology andmicrofacies development of the sedimentary successionhas been investigated from the uppermost part of theFrasnian (linguiformis-Zone) to the upper middle Famen-nian (Upper postera-Zone) (Popp 2002). We found a suc-cession of strata that to some extent differed from othersknown from the Rheinisches Schiefergebirge (e.g., Schin-dler 1990; Becker 1993a; Schindler et al. 1998), fromcomparable settings in the Montagne Noire (e.g., Feist1990; Schindler 1990; Klapper et al. 1993; Morzadec et al.2000), or from the Holy Cross Mountains in Poland (e.g.,Szulczewski 1995). At least in the lower Famennian part ofthe section the microfacies analysis revealed winnowingphenomena and scoured surfaces in some beds that canindicate a deposition above storm wave base and are un-usual in typical cephalopod limestone settings, althoughwinnowing activity is also known to be triggered by bot-tom current activity. Since the conodont faunal successionequals that of settings clearly without any indication oflevel bottom wave or current turbulence and consequentlyallows high resolution biostratigraphic dating, we launcheda fine-scale microfacies analysis in order to correlate theregional sea-level development with conodont biostratig-raphy.

Distinctive signals of sea-level fluctuations can onlyrarely be correlated to the widely used Famennian con-odont biozonation (“Late Devonian standard conodontzonation”; Ziegler and Sandberg 1990), because it isbased on pelagic conodont successions. Zonations fromshallow water deposits (e.g., Sandberg and Dreesen 1984)are not equally elaborated due to the rare occurrence andcomparatively slow evolution of the conodont taxa. Onthe other hand, sequence- or cyclostratigraphic ap-proaches mainly focus on shallow water siliciclastic andcarbonate settings that are sensitive to sea-level changes

I. Sch�lke ()) · A. PoppInstitut f�r Geologie und Pal�ontologie,Universit�t Hannover,Callinstraße 30, 30167, Hannovere-mail: schuelke@geowi.uni-hannover.deTel.: +49-0511-762-3883Fax: +49-0511-762-2172

of even small amplitudes, but generally lack good bios-tratigraphic control. Such studies produce valuable andhigh-resolution stratigraphic schemes that stand incon-gruously aside the deeper marine biozonations (e.g., Chenet al. 2001; Smith and Jacobi 2001). In this study wewould like to add some information to the regional sea-level development and compare it to other sea-levelcurves reconstructed for the Upper Devonian. Individualdifferences and similarities of the compared sea-levelcurves may indicate the regional control or the eustaticcharacter of sea-level signals.

The correlation of both approaches is essential forstratigraphic purposes, because sea-level fluctuations canbe used for correlation, for example, for marine to non-marine facies transition. The faunal diversity of LateDevonian conodonts also follows a species area functionin the Famennian with major faunal turnovers caused bylarge-scale (worldwide ?) sea-level falls (Sch�lke 2003,Sch�lke et al. in press).

A variety of discrete extinction events during the LateDevonian biotic crisis are evidently influenced by sea-level fluctuations. The well-known Late Devonian anoxicevents (Kellwasser event, annulata event) are developedduring (caused by ?) a widespread sea-level fall (Kell-wasser ev.) or sea-level rise (annulata ev.; Walliser 1995and numerous others).

The sea-level curves interpreted for the Late Devoniandiffer in their degree of resolution (Smith and Jacobi

2001). The ones provided by Johnson et al. (1985) or Sa-voy and Mountjoy (1995) appear to be quite generalizedwhen compared with detailed curves as shown by VanTassell (1994) for the late Frasnian and Smith and Jacobi(2001) for the early Famennian. The varying quality andresolution of these curves has to be attributed to the dif-ferent quality of data or the individual scope of the in-vestigations. In addition, the sea-level curves of the aboveregional studies (Smith and Jacobi 2001; Van Tassel 1994)are also supposed to reflect syndepositional fault activitythat modulates the eustatic signal (Smith and Jacobi 2001)and expose only rudimentary similarities in some seg-ments.

In the studied section herein we are able to recognizesome comparatively sharp sea-level signals by the mi-crofacies analysis of the sediments and a high-resolutionconodont record. This adds further data to the recon-struction of a future regional sea-level curve, which is yetbased on comparatively scarce high-resolution sedimen-tological data.

Setting, methods, and material

Geographical position and geological setting

The Beringhauser Tunnel section is situated about 7 kmsouthwest of the town of Marsberg in the northern part of

Fig. 1 a Geographic position ofthe Beringhauser Tunnel sectionin the northern part of theRheinisches Schiefergebirge.b Combined geological andgeographical map of the studyarea (modified after Clausen etal. 1991)

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the Rheinisches Schiefergebirge, the Sauerland, in Ger-many (Fig. 1a). The nominal village (Beringhausen) ispositioned about 3.5 km to the northeast. The strata of thereferred section crop out on a steep mountainous ridgethat is crossed by the Beringhauser railroad tunnel on thenortheastern slope of an unnamed mountain rising abovethe valley of the rivulet Hoppecke. The Gauss-Kr�ger-coordinates (topographic mapsheet: TK25 4518 Madfeld)are r 34789781 h 5696950 for the base of the measuredsection (Fig. 1b). The section is positioned on the south-ern flank of the Messinghauser Sattel (MessinghausenAnticline) between the so-called Ostsauerl�nder Haupt-sattel and the Briloner Sattel (B�r 1968; Clausen et al.1991) (Fig. 1b).

The middle to upper Upper Devonian deposits areunderlain by Givetian to basal Upper Devonian reefal anddebris limestones (Stritzke 1989, 1991; Clausen et al.1991). The mid-Frasnian to upper Famennian successionis about 35 m thick and consists of mainly well-bedded tosubordinately nodular cephalopod limestones. The stratacrop out in a variety of natural exposures starting from theupper Frasnian (Lower rhenana-Zone), connected byshort artificial trenches that have been dug during twofield campaigns in 1999 and 2000. The investigated Fa-mennian part of the succession is exposed in two partialsections (Fig. 2) that are separated by a small thrust faultwith a displacement of only a few decimetres. The indi-vidual beds can be easily correlated across the fault.Following another tectonic contact, the Upper Devonianstrata (Upper postera-Zone) are capped by Lower Car-boniferous slaty deposits, the so-called Alaunschiefer(Clausen et al. 1989, 1991).

Methods and material

Oriented rock samples for microfacies analysis weretaken bed by bed. Whenever possible, these samplescovered the complete thickness of the beds except for afew horizons composed of nodular marls. The samplethickness coverage varied between 5–20 cm. The sampleswere cut and prepared as polished slabs. A complete peelfrom each slab was taken using the standard techniquedescribed by Davies and Till (1968). Slabs and peels wereused to designate parts of the samples for thin sectionsthat covered both representative and macroscopically in-teresting parts of the slabs with special regard on beddingsurfaces. In total, 267 thin sections were studied, 80 ofwhich are formatted 7�5 cm and the others 4.8�2.8 cm.The thin sections were used for microfacies analysisfollowing the carbonate classification by Dunham (1962)and Embry and Klovan (1972). In addition, fossil contenthas been analyzed on a semiquantitative scale during fieldwork and microfacies studies. The results of the faunisticand the microfacies analysis were used to define micro-facies types that allow the reconstruction of the deposi-tional setting.

For conodont biostratigraphic analysis bulk samples ofeach bed were taken that yielded between a few (3–4)hundred and more than 10,000 conodont elements per kg

host rock. These samples have been processed using astandard technique. The figured and additional material ofthis study is reposited under the catalogue-no. IGP 2003 I1-267 in the collection of the “Institut f�r Geologie undPal�ontologie”, University of Hannover, Germany.

Results of microfacies analysis

Matrix, sedimentary textures, and fossil content and as-sociations can be similarly developed in the well-beddedand the nodular limestones. We were able to separate thefollowing five microfacies types, each with a considerablelithological variability (Figs. 3–5)

Fig. 2 Sketch map showing the spatial distribution and lithologiesof beds in the artificial trenches at the Beringhauser Tunnel section.Tree trunks are added for orientation in the field. Lower part of thesection (Fig. 5a, b) on northwestern side; upper part of section(Fig. 5c) on southeastern side (modified after Popp 2002)

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Microfacies type (MF) 1: Tentaculite-ostracodwackestone (Fig. 3a–d)

The limestones of MF 1 are dark grey with intercalatedblack horizons. They are restricted to the lowermost partof the measured section (beds 1–4c) and represent anequivalent of the upper Kellwasser horizon of the up-permost Frasnian. The beds appear massive and exposeonly weak even to wavy bedding planes.

They are internally laminated on cm scale and show ahighly variable microfacies. Generally, they have a mi-crosparitic to sparitic recrystallized matrix with rare in-tercalated micritic horizons. Beds 4b and 4c are coarselyrecrystallized, which is a sedimentary feature frequentlydeveloped in the uppermost parts of Kellwasser horizons,e.g., Steinbruch Schmidt (Schindler 1990) and Sessackertrench VI (Schindler et al. 1998). The fossil content iscommonly high with homoctenids as the dominatingfaunal component (20–50%) followed by abundant os-tracodes. Additional faunal elements are brachiopods,cephalopods (goniatites and rare nautiloids), as well asrare bivalves and trilobites. Brachiopods and cephalopodsare enriched in a few 3–4 cm-thick horizons (e.g., base ofbed 3).

The sediments are mostly wackestones with a com-paratively high component content varying around 25%.In some horizons packing of components requires aclassification as pack- or grainstones when greater fossilremains (e.g., goniatites, brachiopods, trilobites) arepresent. The skeletal remains frequently show micriticenvelopes and are leached internally to varying degree.

The beds contain extensive penetration by sheetcracks(several dm lateral extent), stromatactis (a few cm), and insome parts, especially the upper surface of bed 3, irreg-ular fenestrae (a few mm in diameter). The stromatactisstructures show a smooth lower surface that is sometimesformed be finely laminated mudstones and digitatingroofs (Fig. 3b). They are commonly filled by isopachousfibrous calcite cement crusts and with geopetal, some-times laminated micritic mud- to wackestone sediments.The rocks of MF 1 are dolomitized to a varying degree byeuhedral replacement dolomite. The dolomite crystalsoccur scattered or partly patchy, and can be enriched inthe finely laminated internal sediments of stromatactis.The rocks contain dispersed framboidal pyrite crystalsand rare pyrite moulds of small bivalves.

Depositional environment

The interpretation of the Kellwasser sediments (= MF 1)based on microfacies alone would be insufficient. Ac-cording to Chen et al. (2001), who described similar de-posits from southern China, the sediments are interpretedas middle to deep subtidal facies near, but below thestorm-wave base due to the dominance of pelagic or-ganisms (cephalopods, ostracodes, homoctenids). Therare occurrence of benthic organisms—enrichment ofbrachiopods and trilobites in a few horizons—can be at-

tributed to the state of bottom oxigenation that is sup-posed to be rather poor during the Kellwasser crisis (e.g.,Schindler 1990; Buggisch 1991; Walliser 1995). Thisinterpretation is sustained by the presence of dispersedframboidal pyrite that usually crystallizes in the upperportion of the sediment column under anaerobic todysaerobic conditions in the bottom water whereas theformation of pyrite moulds would point to anoxic con-ditions that are restricted to the sediment column (Can-field and Raiswell 1991). However, the observed phe-nomena do not indicate a prolonged presence of anoxicbottom water. Short phases with dysaerobic or possiblybetter oxygenated bottom water allowed benthic lifewhile the dominating anoxic conditions (e.g., Schindler1990) hindered seafloor colonization. Flush appearancesof pelagic organisms during the formation of the Kell-wasser sediments have frequently been observed and at-tributed to eutrophication of marine realm (e.g., Schindler1990: homoctenids, ostracodes; Sch�lke 1999: polyg-nathid conodonts). In contrast, Wendt and Belka (1991)described current-oriented nautiloid layers that indicatesubstrate contact of (storm) wave turbulence in Morcoc-can pelagic platform deposits. Although on outcrop-scaleno imbrication or current-orientation of skeletal remainshas been observed, a tempestitic origin of the enrichmentlayers of brachiopods and trilobites is also possible.

Several examples of sheetlike stromatactis (sheet-cracks) have been reported from Devonian subtidal de-posits (e.g., Playford and Lowry 1966; Tucker 1973,1974; Wendt and Belka 1991; Schindler et al. 1998). Thepresence of irregular fenestrate carbonates (e.g., Playfordand Cockbain 1976) and micritic envelopes around skel-etal remains also indicates intense microbial activity andprobably formation of microbial mats that bound thesediment surfaces (Pratt 1982). The almost complete lackof benthic organisms in the stromatactoid-rich parts of thedeposits seems to confine microbial surface activity topoorly oxygenated conditions. However, the microbial-influenced deposits of this MF type do not indicate mud-mound formation, because on outcrop-scale (up to 3 mlateral extent) there is no evidence for a moundlike pa-leorelief. Mud-mounds did not form in this case, perhapsbecause the necessary environmental conditions for ac-cretion did not persist for sufficient time (Pratt 1982).

Microfacies type 2 (MF 2):brachiopod-ostracode-microbialwacke- to grainstone (Fig. 3e)

MF type 2 is developed in the lower part of the sectionabove the Frasnian-Famennian boundary. It is best rep-resented by beds 6a–7b. On macroscopic scale thesesediments are dark grey, thick and poorly bedded lime-stones that have wavy bedding planes.

This microfacies type is mainly characterized by amicritic to only rarely microsparitic matrix. The compo-nents consist of skeletal remains and up to cm-sized ir-regular to poorly rounded clasts that internally show an

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Fig. 3 Details of carbonate microfacies, Beringhauser Tunnel. aMF 1 tentaculite-ostracod wackestone, sparitically recrystallizedwith “ghosted” skeletal remains; white arrow indicates palma-tolepid conodont (scale of bar: 1 mm, bed 4a, part of Kellwasserhorizon, uppermost Frasnian, sample no. IGP 2003 I-BK4aPr16). bLarge stromatactis structure with layered geopetal filling; filling isrecystallized with euhedral replacement dolomite; black arrow in-dicates corroded surface of bladed calcite cement (scale of bar:1 mm, bed 4c, part of Kellwasser horizon, uppermost Frasnian,sample no. IGP 2003 I-BK4cF-F). c Large stromatactis structurewith geopetal filling; contact of filling with cement developed asstylolite; black arrow indicates Homoctenus sp. (tentaculite) (scale

of bar: 1 mm, bed 1, part of Kellwasser horizon, uppermost Fras-nian, sample no. IGP 2003 I-BK1Pr1). d Frasnian-Famennianboundary (white arrow) developed as a scoured surface, lower partuppermost Frasnian (MF 1) overlain by Famennian (MF 3a) (scaleof bar: 1 mm, bed 4c, sample no. IGP 2003 I-BK4cF-F). e polishedslab of bed 7b (MF 2) showing large stromatactis structures andreworked mudstone clasts (scale of bar: 1 cm, basal Famennian,Middle triangularis-Zone, sample no. IGP 2003 I-BK7bPr029).f MF 2 preserved as filling in gutter cast overlying MF3a;black arrow indicates mudstone clast (scale of bar: 1 mm, bed 28,early Famennian, Lower crepida-Zone, sample no. IGP 2003I-BK28Pr053)

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ostracode-wackestone lithology. In bed 5a these usuallyirregular-shaped clasts are the dominant component of thesediment. Some of these “clasts” are reworked nautiloidor articulated brachiopod shells that have a sedimentfilling.

The fossil content is generally high and varies betweenabout 10% and 35%. Most abundant ostracode shells arefollowed in order of frequency by brachiopods, echino-derms, nautiloid cephalopods, rare bivalves and trilobites,and single occurrences of goniatites and the tabulate coralCladochonus sp. (D. Weyer, Berlin, personal communi-cation). The abundance and diversity of the brachiopodfauna is unusually high for the lowermost Famennian incephalopod limestone settings from the RheinischesSchiefergebirge (genera: Praewaagenoconcha, Rhipi-dorhynchus, Aulacella, Tenticospirifer, Coeloter-orhynchus, Brachythyris, Cyrtiopsis, Schizophoria, andAmbocoelia, det. G. Trost, D�sseldorf, personal commu-nication).

Generally, the sediments are wackestones whereas inpockets in a variety of irregular scoured surfaces withinthe beds fossil components are enriched and the rocks aredeveloped as grainstone that grades upward into wacke-stone.

The limestones are intensely penetrated by cm sizedstromatactis—frequently below clasts—that grade intosheetcracks with a lateral extent on outcrop-scale, andirregular fenestrae. These fabrics form a transitionalreticulate to laminoid framework (Fig. 3e; comp frame-work III in Pratt 1982: Fig. 16). In some parts of the bedsbelonging to this microfacies type the strata seem vaguelylaminated.

Within grainstone parts of this microfacies fossilskeletons frequently preserve geopetal sedimentary fillsand sparitic shelter pores (bed 6a–7b). Some of the geo-petal infills are rotated so that the surfaces of the sedi-mentary fills are set at diverse angles towards the beddingplanes. This indicates a complex multiphase burial, earlycementation, and reworking. Orthoconic nautiloids arecurrent-oriented and rarely show cone-in-cone interpen-etration. Dolomitization by coarse usually dispersed eu-hedral replacement dolomite crystals is less intense thanin MF 1. Small pyrite crystals are also scattered in thematrix.

Depositional environment

MF 2 represents similar deposits that have been describedfrom mud-mound flanks or bases (e.g., T�neb�hn 1991;Wallace 1987; Reitner and Neuweiler 1995). Sedimentsurfaces have been stabilized by microbial mats whichresulted in the formation of sheetcracks, stromatactis, andfenestrae (similar to MF 1). MF 2 is separated from MF 1by the presence of clear winnowing and reworking phe-nomena (grainstones, scoured surfaces, clasts) that canindicate bottom contact of wave turbulence and a positionabove storm wave base. However, even oceanic currents(e.g., contour currents, currents at interfaces of water

masses) or gravity driven downslope mass transport mayresult in reworking and scouring of deposits. Reworkingand winnowing phenomena from comparable lithologieshave been described by Wallace (1987). He interpretedthem to develop by near-surface internal erosion and re-sedimentation in a precursor cavity system. The waveenergy required for such a process within the substrate iscomparably high, possibly above fair weather wave base.On the other hand, mud-mound and comparable depositsare not depth specific (Brachert et al. 1992), and theabove processes can be interpreted as storm-induced and,consequently, to be more time-averaged. We favor a de-positional setting above the storm wave base and belowfair weather wave base for this microfacies type. Bottomcurrent activity and re-suspension of deposits is a featurethat can be concluded from a variety of phenomena ob-served in the complete studied section (see discussionbelow). The scouring phenomena typical to this MF typeare restricted to certain parts of the section at whichscouring seems to be a continuous process and was in-tense enough for the reworking of microbially stabilizedsurfaces. The present fauna (brachiopods, corals, trilobiteswith large eyes) also points to shallower conditions, butwithout a sharp restriction of water depth.

Microfacies type 3a: sparsely fossiliferous mudstone

The sediments represented by MF type 3a vary in theirmacroscopic appearance from evenly bedded, wavy-platybedded to nodular, which is apparently due to primarydilution by terrigenous clay content and the degree ofpressure solution such sediments underwent during burialdiagenesis. In polished slabs the deposits show a “mottledtexture” that resulted from diffuse burrowing activity.

The bioclastic content of the rocks—independent frommacroscopic appearance—varies around 1–2%. It isdominated by entomozoan ostracode and echinoderm re-mains as well as rare occurrences of thin bivalve shells,nautiloids, and ammonoids. The poorly preserved fossilremains are scattered in the micritic matrix and consist ofmostly thin and unrecognizable shell fragments. Rarely,the deposits contain euhedral replacement dolomite andpyrite crystals.

Depositional environment

The interpretation of sparsely fossiliferous mudstones inthe literature appears to be rather controversial (see Brettand Allison 1998 for extensive discussion). In our casethe key phenomena for interpretation are the presence of adiffuse burrowing activity throughout the MF type, thedominance of pelagic taxa (entomozoan ostracodes, ce-phalopods) or post mortem floated skeletal remains(echinoderms), and the generally fragmented preservationof shells. We interpret this MF type to represent the en-vironment with the greatest water depth, well below stormwave base. The sediment water interface and at least the

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uppermost portions of the sediment column were oxy-genated or at least dysoxic, which is indicated by thebioturbation. The fragmented shell preservation can beattributed to a variety of destruction mechanisms includ-ing water currents, scavenging, or bioturbation (e.g.,Hallam 1987; Brett and Allison 1998). There is no evi-dence for bottom level water turbulence or currents,whereas the deposits are intensely bioturbated. The minorpresence of benthic faunal elements (thin-shelled bi-valves) and the biodeformational structures point to a softbottom habitat that had an instable substrate (soupground,e.g., Etter 1995; Wetzel and Uchmann 1998) due toburrowing or comparatively high sedimentation rates thatlead to a loose and possibly flocculent sediment on the seafloor (Brett and Allison 1998).

Microfacies type 3b: ostracode mud-to wackestone (Fig. 4a)

MF type 3b generally grades into type 3a, but is distin-guished by the presence of shell-rich layers or patches.The macroscopic appearance is similar to that of MF 3a.The strata are also partly bioturbated. The matrix of thesediments is mainly micritic and can be partly recrystal-lized as microsparite that shows a patchy distribution.

The component content is usually lower than 10%.Skeletal hard parts are enriched in somewhat diffuse topartly distinct layers or lenses where the content can reachabout 25%. Especially, those layers show diffuse bur-rowing activity (mottled texture) whereas other parts ofthe beds are not or only weakly bioturbated. The latterparts rarely show distinct burrows with sparitic seams ofindistinguishable origin.

Skeletal remains are dominated by ostracode shells(entomozoan and “thuringian” ecotype forms sensu Blu-menstengel 1965). In nodular limestones of this MF typethe ostracodes are usually followed in frequency by cri-noid remains and thin bivalve filaments. Limestones witheven bedding planes frequently contain more brachiopod,cephalopod (nautiloids and goniatites), trilobite, andlarger bivalve shells than crinoid remains. Gastropods aregenerally rare, but can be present in shell-rich layers.Rugose corals (e.g., Kozlowskinia cf. phyllis, det. D.Weyer, Berlin) and fish remains are rare. In some shell-rich layers articulated ostracodes with closed shells andnautiloids preserve geopetal fillings. The sediment sur-face of these geopetal fillings are displaced compared tothe bedding planes. Most of the ostracode, brachiopod,bivalve, and trilobite shells are disarticulated or evenfragmented whereas nautiloid, ammonoid, and gastropodremains are in most cases completely preserved. Shellsusually have no preferred orientation, although someshell-rich layers show partly convex-up or convex-downorientation or even a cup-and-saucer stacking.

The deposits are extensively penetrated by stylolitesand solution seams—dependent on carbonate content.They are dolomitized to a varying degree by euhedralreplacement dolomite. Frequently, dolomite crystals are

enriched in solution seams. Disseminated small pyritecrystals are also present in various amounts. They can beenriched around burrows that also show sparitic seams.Generally, pyrite content is higher in sparsely fossilifer-ous than in shell-rich layers.

Depositional environment

Shell accumulations separated by very sparsely fossilif-erous mudstone intervals (1–2%) can be produced byvarious sedimentary and taphonomic processes, e.g., in-stantaneous accumulations due to geologic events andenvironmental or biostratigraphic condensation (Brett andAllison 1998). We interpret these strata to represent pa-rautochthonous aggregations produced by episodic seafloor disturbances by storms (Aigner 1985). Possibly, theymight reflect low-density turbidites or tempestites due totheir high degree of shell fragmentation (e.g., Piper andStow 1991). Cup-and-saucer stacking of shells can formdue to even weak bottom level turbulence (Brett andAllison 1998) and may also indicate scouring processesthat winnowed away the mud and concentrated the shellydebris (e.g., “swell lags” model, Specht and Brenner1979). On the other hand, any type of primary sedimen-tological or taphonomic feature (e.g., lamination, normalgrading, azimuthal orientation of fossils) may have beendestroyed by intense bioturbation, especially of the shell-rich layers, although distinct bioturbation structures lacksave the diffuse “mottled texture” that can be tracedthroughout the section. Bioturbation can also be respon-sible for shell fragmentation. Speyer and Brett (1991) andParsons et al. (1988) have proposed a different interpre-tation where the shell beds reflect complex backgroundconditions and the sparsely fossiliferous layers representmuddy distal turbidites or storm-generated currents. Theabove scenarios—or a combination of all—are possible(e.g., Kidwell 1991) and point to a discontinuous sedi-mentation at least partly influenced by bottom currentsthat is typical to deep platform or ramp sediments de-posited below storm wave base.

Microfacies type 3c: cephalopod/crinoid-ostracodwackestone (to packstone) (Figs. 3f and Fig. 4b, c, f)

MF type 3c grades into MF 3b, but is distinguished by theconsiderably higher content of large cephalopod and es-pecially crinoid remains in the shell-rich layers. Onmacroscopic scale limestones of MF type 3c exhibitsimilar lithological features as MF 3a, b with a partly wellto wavy-platy bedded and partly nodular outer appear-ance.

The matrix of MF 3c is mainly micritic with mi-crosparitic parts and rare coarsely sparitic patches. Thefossil content varies between ca. 10% to above 30% inshell-rich layers. It is commonly dominated by ostracoderemains (entomozoans and small numbers of “thuringian”ecotype forms). A characteristic feature of MF type 3c is

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Fig. 4 Details of carbonate microfacies, Beringhauser Tunnel;scale of bar: 1 mm. a MF 3b dense ostracod-bivalve filamentwackestone layer with abundant articulated ostracodes (bed 8, earlyFamennian, Upper triangularis-Zone, sample no. IGP 2003 I-BK8Pr033). b MF 3c wackestone with current-oriented orthoconiccephalopod shells with geopetal fillings (bed 28, early Famennian,Lower crepida-Zone, sample no. IGP 2003 I-BK28Pr053). c MF 3ccrinoid wackestone, extensively dolomitized (bed 96, basal part,

middle Famennian, Upper marginifera-Zone, sample no. IGP 2003I-BK95/96Pr125). d Euhedral replacement dolomite in matrix ofbed 96 (sample no. IGP 2003 I-BK95/96Pr125). e MF 3c mudstoneclast with goniatite shell (white arrow) in dolomitized wackestone(top of bed 95, Upper marginifera-Zone, sample no. IGP 2003 I-95/96Pr125). f MF 3c crinoid and trilobite-rich wackestone, note en-tomozoan ostracode shells (bed 85, middle Famennian, rhom-boidea-Zone, sample no. IGP 2003 I-BK85Pr108)

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the abundant occurrence of disarticulated and frequentlyfragmented crinoid ossicles that are partly enriched inshell layers. Some of these ossicles have surficial bio-erosion phenomena as small borings possibly of microbialorigin. Additionally, such layers contain complete or largefragments of ammonoids, gastropods, trilobites, andfragments of thick-shelled bivalves with micritic en-velopes. Solitary rugose corals also rarely occur. Skeletalfragments display no preferred orientation in most of theshell-rich layers, but sometimes convex-up and -downorientation and cup-and-saucer stacking are observed.Mostly, bed coherence of the shell layers is lost due tointense, but diffuse burrowing activity (mottled texture).Geopetal fillings of articulated ostracode shells, am-monoids, and gastropods are present. The surfaces of theinternal sediments within the shells are mostly set atvarying angles towards the bedding planes.

The deposits expose wide solution seams and stylolitesand contain disseminated euhedral replacement dolomiteand rare pyrite crystals.

Depositional environment

This microfacies is developed in only a few beds in themiddle and upper part of the studied section. It grades intothe shell-rich layers of MF 3b, but can be separated by avariety of features. The most striking difference is theapparent mixing of skeletal remains from different de-positional environments that display different taphonomiccharacters. The abundant crinoid ossicles and the frag-ments of thick-shelled bivalves are allochthonous remainsthat show taphonomic features (borings, micritic en-velopes) of a habitat with extensive microbial activity.Such features lack in the autochthonous or pa-rautochthonous fossils from the background deposits thatpredominate this section. The above remains yield evi-dence for discontinuities in the sedimentation process thatinclude transport of shell fragments from a nearby shal-lower habitat into the pelagic deposits, possibly by tur-bidites or tempestites. Such deposits have been termed“environmentally time-averaged” (Kidwell 1991) and aresupposed to reflect discontinuities that can be related toimportant flooding surfaces (Brett and Allison 1998).When compared with other segments of the section, amajor condensation and time-averaging typical of lagconcentrations seems not probable, because these layersare developed in parts of the succession that exposecomparatively thick deposits within a single conodontzone (rhomboidea- and Lower trachytera-Zone).

Sedimentological features of biotic event horizons

Kellwasser event (Frasnian-Famennian boundary)

The Frasnian-Famennian boundary horizon and its sur-face is of special interest, because research on the Kell-wasser event is in need for sedimentological data that help

to decipher the event processes. In some sections (e.g.,Schindler 1990; Schindler and K�nigshof 1997: Coumiacsection, Southern France; Sch�lke 1999: Causses etVeyran section, Southern France) the Frasnian-Famenni-an transition (uppermost part of linguiformis-Zone tolower to middle part of the Lower triangularis-Zone) isdeveloped as a hiatus represented by limonitic crusts.Some boundary sections in Morocco and in southernFrance expose a thick anoxia-related Kellwasser faciesextending deep into the Famennian with no obvious facieschanges above the biotic event horizon (e.g., Wendt andBelka 1991: Morocco). Well-studied examples without atypical dark Kellwasser facies are known from NorthAmerica (e.g., Morrow 2000) or from Australia (e.g.,Playford 1980). The latter sections show major facieschanges across the Frasnian-Famennian boundary, butprovide no direct evidence for the event processes re-leased by bottom level anoxia.

The uppermost Frasnian deposits of the BeringhauserTunnel section represent the typical thin upper Kellwasserhorizon as it is commonly developed in the RheinischesSchiefergebirge. The sedimentary rocks are MF 1 withsome additional features. The limestones of bed 4b andthe lower part of 4c are recrystallized to a spariticwackestone with commonly leached skeletal remains. It ispenetrated by large stromatactis (>2 cm thickness) orsheetcrack structures with geopetal fillings, some ofwhich are completely recrystallized with euhedral tosubhedral replacement dolomite. The internal deposits inthe stromatactis voids are laminated mudstone bearingrare skeletal remains with intercalated isopachous crustsof stubby calcite crystals that indicate a complex openingand filling process or, possibly, microbial activity. Similarphenomena have been described by Wendt and Belka(1991) with the additional information that the isopachouscalcite cements expose an isotopic signature of meteoriccements. In contrast, the sheetcracks from MoroccanFrasnian-Famennian boundary sections probably indicatean emersion phase at which cements crystallized (Wendtand Belka 1991).

The isopachous calcite crusts sometimes exposeslightly corroded surfaces (Fig. 3b) which can be a resultof a variety of processes including synsedimentary solu-tion or diagenetic overprint due to dolomitization orpressure solution. Some of the stromatactis structurescorrespond to the stromatactis type B of Flajs et al. (1996)lacking geopetal fillings and having their centers crys-tallized with equant calcite spar.

The Frasnian-Famennian boundary itself is developedas a scoured surface (Fig. 3d) that shows rare encrustingforaminifers (Tolypammina-group) and an irregular relief.Occasionally, the overlying lowermost Famennian de-posits cut into stromatactis structures of bed 4c with in-ternal sediments. In such cases the significant differencebetween the basal Famennian deposits and the void fill-ings can be observed. The basalmost Famennian sedi-ments (upper part of bed 4c) are brownish-grey micritic tomicrosparitic and sparsely fossiliferous mudstones (1–2%component content) where conodonts and bivalve shell

655

fragments are the most abundant skeletal remains. Thebivalve shells show isopachous crusts of short-bladedcalcite crystals. A few small, sparitic, and irregularlyshaped clasts from the underlying uppermost Frasnian arecontained in the basal Famennian deposits. The differenceof the void sediments and the lowermost Famennian de-posits indicate a multiphase deposition, reworking, andsolution process. The whole succession is enriched indisseminated small framboidal pyrite crystals.

The conodont succession adds further data to thesedimentological record. The boundary horizon showsmixed conodont faunas in the uppermost Frasnian de-posits (lower part of bed 4c) as well as in the lowermostFamennian bed (upper part of bed 4c). The first onescontained predominantly Frasnian conodonts and thelatter predominantly Famennian conodonts. We presumethat Famennian conodonts from the uppermost Frasniansediments are buried in the geopetal fillings of stromat-actis whereas the few and poorly preserved Frasnianconodonts in the lowermost Famennian deposits werereworked from eroded Frasnian deposits. Such a burial ofFamennian conodonts requires a surface-near cavity sys-tem that is open to bottom level water at least during thebasalmost Famennian.

However, the conodont fauna from the lowermostFamennian (upper part of bed 4c) only comprises dwarfedspecimens of Palmatolepis triangularis which is typicalfor the lowermost part of the Lower triangularis-Zone(e.g., Sch�lke 1998, 1999; Schindler et al. 1998).

The complex sedimentation processes of the Frasnian-Famennian boundary interval at the Beringhauser Tunnelsection may have been triggered by anoxia. The presenceof disseminated (framboidal) pyrite has been interpretedto be released by anoxia both in the sediment column andin the bottom water (Canfield and Raiswell 1991). Undersuch conditions the biochemistry of organic degradationhas significant effects on ambient waters and the zone ofsulfate reduction may have raised into the bottom waters,although other indicators lack in the section. In the zonesof sulfate reduction and methanogenesis carbonate alka-linity and ammonia concentrations increase with depth(Gieskes et al. 1982) and can induce carbonate recrys-tallization, solution, or early diagenetic precipitation ofauthigenic dolomite (Wright 1997). A further hint onearly diagenetic recrystallization of the uppermost Fras-nian bed (4c lower part) are the reworked sparitic clasts inthe following bed 4c (upper part). Before the depositionof this layer recrystallisation and reworking took placeand the scoured surface was inhabited by rare foramsunder oxic or at least dysoxic conditions.

The uppermost part of the Kellwasser horizon fre-quently yields conodont faunas that have a slightly ele-vated icriodid content interpreted to indicate a sea-levelfall starting in the uppermost Frasnian (e.g., Sandberg etal. 1988; Sch�lke 1998). In the Sessacker trench sectionVI the icriodid abundance is as high as 50% faunal pro-portion, but it is developed in Frasnian (!) deposits fol-lowing the Kellwasser horizon (Sch�lke 1998). In theBeringhauser Tunnel section a similar increase in icriodid

abundance cannot be observed. It shows values below 5%throughout the Kellwasser deposits and an increase onlyin the lower Famennian sediments. The evidence of a sea-level fall during late Kellwasser event time is furtherstrengthened by the Nd-isotope studies of Dopieralska(2003). On the other hand, an emersion of the Kellwasserdeposits and subaerial scouring, as has been shown beWendt and Belka (1991) from Moroccan sections, is notprobable here.

The Nehden event

The Nehden event (House et al. 1985) is a comparativelyshort-termed event with a global biotic signal regardingconodonts (Sch�lke 1999, 2003; Sch�lke et al. in press)and goniatites (e.g., House et al. 1985; Becker and House1997). In some sections from the Montagne Noire and theRheinisches Schiefergebirge it can be exactly identifiedby an Icriodus-peak (up to 65% generic abundance), aconodont genus that is presumed to reflect shallow waterconditions (Sandberg and Dreesen 1984), possibly due toits feeding mode (Sch�lke 2001). The Nehden event ispositioned in the upper part of the Lower crepida-Zone/lower part of Middle crepida-Zone and interpreted to betriggered by a short sea-level fall (Sch�lke 2003). Thestratigraphic position of this event is inexact which can beattributed to the poor quality of Palmatolepis termini asan index fossil. For example, the position of Icrioduspeaks within two adjacent and highly similar sections inthe Montagne Noire (Causses and Veyran and AbandonedQuarry Coumiac) differs between the above zonal dates,but Palmatolepis termini is only rarely present in theCoumiac section with specimens that are interpreted asvery early forms of this species. In other sections theNehden event is developed as moderate increase followedby a sharp decrease of icriodid abundance (e.g., La Serretrench C, Montagne Noire; Sch�lke 1999). This is also thecase in the Beringhauser Tunnel section where Icriodusshows a slight increase (up to 18%) towards the upper partof the Lower crepida-Zone and then a fall towards lessthan 1% generic abundance (bed 27: 18.2%, bed 28:0.2%, sample only from upper part of bed).

The sedimentological signal is comparatively sharp,represented by a gutter cast in the middle of bed 28 whichis cut into deposits belonging to MF 3b (Fig. 3f). It isfilled with a partly well-winnowed grainstone with re-worked clasts, current-oriented nautiloids, and stromat-actis (MF 2) that grades into packstone towards the top ofbed 28.

Taking the icriodid abundance and the sedimentolog-ical record into account, the deposits of the upper part ofbed 28 represent a sea-level rise. In the sea-level curve ofJohnson et al. (1985) and younger adaptations of thiscurve a sharp regression-transgression couplet is posi-tioned in the middle part of the Middle crepida-Zone. Thesea-level curve provided by Dopieralska (2003) shows nodistinct sea-level fall during this interval. The poor qualityof Palmatolepis termini as an index fossil may have

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caused the difference in stratigraphic interpretations, andtherefore after careful investigation of conodont faunas ofvarious sections we think the position of this event/transgression-regression couplet should be placed in theupper part of the Lower crepida-Zone in terms of zonalstratigraphy.

The Condroz event(s) (mid-Famennian events I, II)

The Condroz event has been named after the BelgianCondroz “shelf” facies and coincides with the disap-pearance of formerly widespread Cheiloceras shales(Dreesen 1982). This regressive event has been identifiedthroughout the world (e.g., Hollard 1960; Szulczewski1986; Becker and House 1997). The biotic signal of thisevent is bipartite to rather “smeared” (Becker and House1997) with a successive faunal turnover during a two-“pulsed“ regression that started in the Upper crepida-Zone (“Lower Condroz pulse” after Becker and House1997). This sea-level fall is well documented by thestudies of Dopieralska (2003) that show a regression witha significant amplitude. The “Upper Condroz (regressive)pulse” is positioned in the Upper rhomboidea-Zone. Thesea-level curve of Johnson et al. (1985) shows a sharpsea-level fall in the Uppermost crepida-Zone which af-terwards continued slowly with the maximum lowstand inthe basal Lower marginifera-Zone.

In the Beringhauser Tunnel section the sedimentolog-ical signals for the Condroz regression are not as clear asfor the Nehden regression. The lower Condroz regressionpulse after Becker and House (1997) can be marked by athin, bioturbated shell-rich layer of cephalopod wacke-stone to packstone (bed 46, MF 3c) with enriched goni-atites, gastropods, trilobites, and fragments of thick-shelled bivalves. The faunal content changes from ostra-codes and thin-shelled bivalves dominant towards bra-chiopod, trilobite, and goniatite dominated deposits fol-lowing bed 46. Otherwise, the microfacies exposes noother significant differences apart from a more frequentpresence of wackestone layers in the predominatingmudstones.

The final lowstand or upper Condroz regressive pulsein the Upper rhomboidea-Zone after Becker and House(1997) is similarly recorded by the succession of beds 63–65/83–85 of the two parts of the section. In these beds MF3c is typically developed where some parts of the shell-rich layers are packstone lithology. This possibly indi-cates a mixing of different facies and provenance offossils where a few thick-shelled bivalve remains exhibitmicritic rims in the respective horizons that otherwiselack the autochthonous to parautochthonous filamentousbivalves and other skeletal remains. The depositionalsetting of the Beringhauser Tunnel section probably re-mained below storm wave base during this stratigraphicinterval.

The annulata event

The annulata event has been named after the mass ap-pearances of clymeniids, especially Platyclymenia annu-lata, in a worldwide recognizable horizon in the upperpart of the Upper trachytera-Zone of the Famennianconodont biozonation (Walliser 1995). It is frequentlydeveloped as a double black shale layer according to(Becker 1992, 1993b) in the Variscan realm.

In the Beringhauser Tunnel section the annulata ho-rizon (bed 119) is positioned in the middle of the Uppertrachytera-Zone. In the field it has been identified as adark gray to green marl to shale layer only 3–6 cm thickwith limestone nodules grading laterally into a dark graynodular limestone. In thin section two brownish-blackshale layers a few millimetre in thickness each are in-tercalated in the greyish-green marls and shales. Theunderlying bed 118 that is developed as a wackestonewith packstone layers (MF 3c), and the overlying bed 120,a darkgrey nodular limestone classified as mudstone,contain both an enrichment of the nominal clymeniids.

This horizon coincides with a widely recognizable sea-level rise but of comparably small amplitude when re-garding the sea-level curve of Johnson et al. (1985). Theunderlying bed 118 in the studied section is partly de-veloped as a packstone which we interpret to representlowstand conditions in the overall deep platform faciesbelow storm wave base. It contains abundant gastropodand cephalopod shells with geopetal fillings, limestoneclasts, and thick-shelled bivalve fragments that belong toGlyptohallicardia sp. (det. M. Amler, Marburg). Theannulata horizon itself is consequently presumed to re-present transgressive or early highstand conditions (comp.Walliser 1995; Becker and House 1997) Fig. 6.

Reconstruction of relative sea-level curve (Fig. 6)

For the reconstruction of the local sea-level developmentthe sedimentological features of the deposits of theBeringhauser Tunnel section have to be considered con-cerning information on the relative position of the sea-level. As stated in the descriptions and environmentalinterpretations of the microfacies types, we found severalsedimentological features that indicate a deposition abovethe storm wave base. Such features are repeated win-nowing and reworking of sediments that can be indicatedby the presence of “prefossilized” material, for example,rotated geopetal structures or shell infillings that do notmatch surrounding matrix sediment (Seilacher 1973). Therepeated burial and reworking over longer time periodspoints to a continuous (storm) wave-related bottom levelwater turbulence (F�rsich 1978; Brett and Allison 1998).The deposits represented by MF type 2 are consequentlyinterpreted to be deposited above storm wave base. MF 2is twice present in the basal Famennian part (Lower toMiddle triangularis-Zone and upper part of Lower crep-ida-Zone) of the section (Fig. 5a–c). The remaining partsof the succession provide only sparse or ambiguous evi-

657

Fig. 5 Microfacies interpretation, local sea-level curve and im-portant conodont ranges of the Beringhauser Tunnel section. Li-thology is figured according to the nomenclature of Dunham (1962)

and Embry and Klovan (1972). a, b Shows the succession of thenorthwestern part of the outcrop, c shows the southeastern part.Signatures are provided in a. SWB Storm wave base

658

Fig. 5 (continued)

659

Fig. 5 (continued)

660

dence for sea-level changes, because they were depositedbelow storm-wave base. Although sometimes, especiallyin the shell-rich layers, geopetal structures and alsoskeletal remains with micritic rims that are presumed tostem from a different environmental setting are occa-sionally present, they can be interpreted to be transportedby distal tempestites or turbidites and not by bottomcontact of wave turbulence. A possible indicator for sea-level changes in the depositional setting of the Bering-hauser Tunnel section can be the abundance of shell-richlayers, especially the presence of packstone layers (beds46, 83, 85), and the frequency of faunal elements (trilo-bites, brachiopods) that are usually attributed to shallowerenvironmental conditions (for semiquantitative analysiscomp. Popp 2002). On the other hand, one of the mostprominent transgressions in the Famennian (base of theLower marginifera-Zone, e.g., Johnson and Sandberg1989; Sandberg et al. 1989) has not induced any obvioussedimentological signal in the Beringhauser Tunnel sec-tion (Sch�lke et al. 2003). Only the conodont recordpoints to minor stratigraphic condensation at this level,because several palmatolepid conodonts that have theirfirst appearance dates starting from the uppermost part ofthe rhomboidea-Zone to the lower part of the Lowermarginifera-Zone firstly occur together in bed 88(Fig. 5c; comp. Sch�lke et al. 2003).

In contrast, we interpret the segments of the sectionthat are dominated by sparsely fossiliferous mudstonesand rarely show shell-rich layers to represent deeper waterconditions. Although there are a variety of interpretationsof intercalations of shell-rich beds in a sparsely fossilif-erous mudstone facies (for discussion comp. Brett andAllison 1998), the succession of the Beringhauser Tunnelsection shows an increase in shell layer frequency duringregressive phases, e.g., the rhomboidea-Zone, accordingto the sea-level curve of Johnson et al. (1985) and others.On the other hand, a decrease in shell layer frequency canbe observed during highstand phases (e.g., Upper trian-gularis-Zone to Lower crepida-Zone; Middle crepida-

Zone; Uppermost crepida-Zone; Fig. 5a, c). The strikingcoincidence allows the preliminary reconstruction of alocal sea-level curve also for stratigraphic intervals atwhich more distinctive sedimentological signals lack(Figs. 5 and Fig. 6).

The sea-level curve can be compared with the fewother sea-level curves that have been reconstructed for theLate Devonian (Johnson et al. 1985; Johnson and Sand-berg 1989; Savoy and Mountjoy 1995; Smith and Jacobi2001; Dopieralska 2003).

The general trend of the sea-level curve proposedherein indicates a successive deepening after a lowstandin the basal Famennian until Upper crepida-Zone fol-lowed by a moderate shallowing up to the Upper postera-Zone. This general trend reflects that of the sea-levelcurve provided by Johnson and Sandberg (1989) to a veryhigh degree. In contrast, the sea-level curve of Savoy andMountjoy (1995) promotes a continued rising sea-leveluntil the end of the Devonian. The regional sea-levelcurve as reconstructed by Smith and Jacobi (2001) for theearly Famennian reveals only rudimentary similarities asthe sharp sea-level fall directly above the Frasnian/Fa-mennian boundary followed by an equally sharp rise inthe Upper triangularis-Zone. The following general re-gressive development contradicts our observations and ispresumably triggered by syndepositional fault activityrather than eustasy. These differences are discussed bySmith and Jacobi (2001) in detail. The sea-level curveprovided by Dopieralska (2003) exposes a short-term sea-level fall during the upper Kellwasser horizon and a fol-lowing sharp sea-level rise starting in the uppermost partsof the Kellwasser event (Uppermost Frasnian) until thebasal Famennian Lower triangularis-Zone which wecannot clearly identify in our sedimentological analysis.The scouring and reworking are of course products of asea-level fall, but the following sea-level rise is not doc-umented. In the lower Famennian segment the sea-levelcurve of Dopieralska (2003) shows a similar successive

Fig. 6 Comparison betweendifferent Late Devonian sea-level curves. Sea-level curveaccording to Johnson andSandberg (1989) has been ad-justed in the Upper crepida-Zone segment that is nowadayssubdivided into Upper and Up-permost crepida-Zones. Con-odont zones are figured equallyspaced, although they are wellknown to represent highly dif-ferent time intervals and cannotbe used as a time increment

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deepening with short-term sea-level falls as proposed byJohnson and Sandberg (1989).

Beyond the general accordance of the Johnson et al.(1985), Johnson and Sandberg (1989), or Dopieralska(2003) sea-level curve trend, the lower order transgres-sive/regressive development fits remarkably well with ourobservations and interpretions. Only minor differences insome positions of lowstands are present that possiblyoriginate from refined conodont resolution or differentinterpretation of conodont stratigraphy for our section(Fig. 6). For example, the lowstand in the uppermost partof the Lower crepida-Zone which corresponds to theNehden event shows only minor differences with theJohnson and Sandberg (1989) or Dopieralska (2003)curves. The postulated two-pulsed regression marking theCondroz event is also documented in the BeringhauserTunnel section. The first regression in the Upper crepida-Zone is well exposed in the study of Dopieralska (2003)whereas in the publication of Johnson and Sandberg(1989) the position cannot clearly be correlated, becausethe separation of the former Upper into Upper and Up-permost crepida-Zones followed after the publication ofthat curve. The upper Condroz regressive pulse is alsoexposed in our section. In the Beringhauser Tunnel sec-tion we found lowstand deposits with packstone layers(bed 83, 85) and a subsequent minor stratigraphic con-densation representing the widespread Lower marginiferasea-level rise (Johnson and Sandberg 1989). The lowstandin the Upper marginifera-Zone that is present in the sea-level curves of Savoy and Mountjoy (1995) and Johnsonand Sandberg (1989) is represented by the extensivelydolomitized upper part of bed 95 and bed 96 with itswackestone to partly grainstone lithology.

The last remarkable sea-level fluctuation in the LateDevonian covered by the Beringhauser Tunnel successionis connected with the annulata-horizon (bed 119). Belowthe annulata layer the frequency of shell-rich layers in-creases (bed 115–117). Directly underlying this horizonbed 118 exposes wackestone lithology with grainstonelayers which we interpret representing lowstand deposits.This is sustained by a remarkable decrease in the pal-matolepid abundance towards the top of bed 118 (Sch�lkeet al. 2003).

Conclusions

The uppermost Frasnian and Famennian part of theBeringhauser Tunnel section exposes a variety of veryinteresting sedimentological features, and for the firsttime, we were able to describe a carbonate lithology in theRheinisches Schiefergebirge which is usually aligned tomud-mounds as a flank or basal facies with sedimento-logical features resulting from intense microbial activity.Mud-mound formation with a typical relief towards thesurrounding seafloor has not been observed. The Kell-wasser horizon of this section, especially the event sur-face, provide new data for the interpretation of the eventprocesses. Possibly, the deposits were early lithified by

microbial activity and subsequently recrystallized beforeor parallel to reworking and scouring due to changing pH/eh conditions released by bottom anoxia. We reconstructa local sea-level curve that has a high degree of accor-dance to the pre-existing curves, especially that of John-son and Sandberg (1989). Conodont biostratigraphy al-lows the high resolutional correlation of these curveswhich resulted in slight differences of lowstand ages(upper part of Lower crepida-Zone (Nehden event); upperpart of rhomboidea-Zone), but a general coincidence.However, all reconstructions have been carried out usingsettings from the same Laurussia shelf system.

Acknowledgements We would like to thank Willi Ziegler (†) forvaluable and helpful comments on conodont stratigraphy. We arealso indebted to Michael Amler (Marburg, bivalves), Dieter Korn(Berlin, cephalopods), Raimund Feist (Montpellier, trilobites), andGerd Trost (D�sseldorf, brachipods) for their help in the determi-nation of the macrofossils. Heartfelt thanks are extended to R.Thomas Becker (M�nster), Eberhard Schindler (Frankfurt), andMatthias Piecha (Krefeld) for their cooperation in the Late Devo-nian working group of the German Subcommission on DevonianStratigraphy. We would like to thank Z. Belka (T�bingen) forvaluable comments. J. Over (Geneseo) improved the English of themanuscript. W. Buggisch (Erlangen) and R. Henrich (Bremen)kindly reviewed the manuscript and provided helpful comments

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