biostratigraphy and palaeoenvironment of the … · biostratigraphy and palaeoenvironment of the...

BIOSTRATIGRAPHY AND PALAEOENVIRONMENT OF THE LOWER GOSAU SUBGROUPOF EISENBACH BROOK IN SALZKAMMERGUT ( UPPER AUSTRIA)

Lenka Hradecká , Harald Lobitzer , Franz Ottner , Felix Schlagintweit , Marcela Svobodová , István Szente* Lilian Švábenická & Irene Zorn1 2 3 4 5 1 6

1

3

4

5

6

Czech Geological Survey, Klárov 3, CZ-118 21 Praha 1, Czech Republic. ;

Lindaustrasse 3, A-4820 Bad Ischl, Austria.

Universität für Bodenkultur, Institut für Angewandte Geologie, Peter Jordan Strasse 70, A-1190 Wien, Austria.

Lerchenauerstrasse 167, D-80935 München, Deutschland.

Institute of Geology, v.v.i., Academy of Sciences of the Czech Republic, Rozvojová 269, CZ-165 00 Praha 6, Czech Republic.

Geologische Bundesanstalt, Neulinggasse 38, A-1030 Wien, Austria.

hradecka@cgu.cz svab@cgu.cz

harald.lobitzer@aon.at

franz.ottner@boku.ac.at

EF.Schlagintweit@t-online.de

msvobodova@gli.cas.cz

irene.zorn@geologie.ac.at

*Museum of Natural History, Faculty of Science, Eötvös University, Pázmány P. sétány 1/c, H-1117 Budapest, Hungary. szente@ludens.elte.hu

2

Bilateral cooperation betweenGeologische Bundesanstalt Vienna

andCzech Geological Survey Prague

BIVALVIA

Sample EB 1: fossil collecting point (mainlygastropods) in „black shales“ below a bridgecrossing the Eisenbach stream on the border ofmapsheet 66 and 67.Sample EB 2: fossiliferous „black shales“ withgastropods and bivalves with thick fossil-richlayers of bituminous limestone (?tempestites);downstream from sample point EB 1, alreadyon mapsheet 66.Sample EB 8: grey marls in the higher part ofthe Eisenbach creek, about 895 m above sealevel.Samples EB 9A, B: see paper by Schlagintweitet al. (2003). A thin section of sample EB 9Ashows mudstone with a finely dispersed pyritecontent; no microfossils.

Sample EB 9B can be classified as green algaewackestone with Halimeda paucimedullaris

Schlagintweit & Ebli, Neomeris circularis Badve& Nayak, Dissocladella? pyriformis

Schlagintweit and most abundant thedasycladale Thrysoporella eisenbachensis

Schlagintweit.Sample EB 10: light grey, fossil-rich marls withbivalves, gastropods, corals. Upstream fromsample point EB 8 on mapsheet 67.Samples EB 11A, B: as locality EB 10, however,hard marly limestones. Thin sections showbioturbate wackestone with fine clastic debris.Benthic foraminifera include Vidalina hispanica

Schlumberger and other miliolids. In additionsome echinoid spines, ostracodes, debris of thegreen alga Halimeda and isolated fertileampullae of Neomeris circularis Badve &Nayak.

Samples EB 15A, B: 30 cm thick black marlylimestone layer with mollusks and „blackshales“, mapsheet 66. Thin sections show afloatstone with extremely reduced content ofmicrofossils.

Sample EB 21: soft grey marls with somebivalves from a 30-40 m long marl exposurewith subordinate sandstone intercalations.Mapsheet 66, about 250 m upstream from theforest road branch to Eisenbachstube.

Sample EB 25: lilac red sequence of hardsandstones and subordinate marly sandstones,about 70 m upstream from the first bridgecrossing the Eisenbach brook after the tunnel.Mapsheet 66.

?Albian

to

Turonian Lower Middle

nannofossil zones (Burnett 1998) UC7 UC10

EB10 EB1 EB 8 EB 8A EB 8B EB 8C EB 8D EB21 EB26

abundance of nannofossils VL L L VL L VL L L M

nannofossil preservation VP VP VP VP VP VP VP VP VP

Braarudosphaera bigelowii * R R R R

Calculites ovalis R R

Eiffellithus eximius R R R R

Eiffellithus turriseiffelii-eximius R R R

R

Lucianorhabdus maleformis F R

Lucianorhabdus quadrifidus R R F R R R

R

R F R R F R

? ?

R R R R

Quadrum intermedium (7 elements)* R R

R

R R

R

Cribrosphaerella ehrenbergii R R R R R

f F R R F R R

R R R F F R

Helicolithus trabeculatus R R

Microrhabdulus belgicus R

Prediscosphaera columnata R F R R R F R

Prediscosphaera ponticula R

Prediscosphaera spinosa R R

R R ? R

R R R R

R

Zeugrhabdotus bicrescenticus R R R

Braarudosphaera regularis ? ? ?

R R R

R R R R R R

Cyclagelosphaera margerelii R R

R

Lithraphidites carniolensis R R R F R

f f

R R

R R R

R R R R R R R R

R R

F F F F F F F C F

R R R R R R

Zeugrhabdotus diplogrammus R F R R R R R

Zeugrhabdotus embergerii R R R R R

R

Cen. r

Braarudosphaera africana r r

r

Isocrystallithus compactus r ? r

?

Nannoconus cf. vocontientis r r

r r r r

r

r

Micrantholithus hoschulzii r f r r r r r r

r r

Nannoconus globulus minor r

r

r r r r

r r

r r

rWatznaueria manivitae

Zeugrhabdotus noeliae

Micrantholithus obtusus

Nannoconus kamptneri

Nannoconus steinmanii

Cruciellipsis cuvillieri

Discorhabdus striatus

Conusphaera mexicana

Lithraphidites acutus

Nannoconus truittii

Cretarhabdus conicus

Retacapsa crenulata

Corollithion kennedyi

Cretarhabdus striatus

Nannoconus elongatus

Tegumentum stradneri

Watznaueria barnesae

Watznaueria britannica

Lithraphidites bollii

T u r o n i a n Coniacian

sample No.

Rhagodiscus plebeius*

Quadrum gartneri

Micula staurophora**

Middle

UC8b

Eisenbach-Traunsee

Eprolithus octopetalus

Amphizygus brooksii

Broinsonia signata

Prediscosphaera cretacea

Jura

ssic

and

Cre

taceous

long-r

angin

gspecie

sA

pt.

-Cen.

specie

sth

ey

may

form

Turo

nia

nor

Conia

cia

nnannoflora

lassem

bla

ges

rew

ork

ed

nannofo

ssils

FO

Cenom

ania

n-T

uro

nia

n-C

onia

cia

nlo

wer

Low

er

Cre

taceous

Tithon.

FO

Aptian-A

lbia

n

Rhagodiscus splendens

Quadrum gartneri-gothicum

Helenea chiastia

Retacapsa angustiforata

Manivitella pemmatoidea

Eprolithus floralis

Eiffellithus turriseiffelii

Radiolithus orbiculatus

Rhagodiscus angustus

Chiastozygus litterarius

CALCAREOUS NANNOPLANKTON

Sediments provided very rare calcareousnannofossils (1-2-5 specimens in maximum perone field of view of the microscope; calciumcarbonate material of anorganic origin is themajor component). Specimens are poorlypreserved and mostly in fragments.Nannofossil assemblages are characterized byfollowing phenomena (see distribution tab.):Presence of species they first appear in theTuronian, such as Eprolithus octopetalus,

Quadrum gartneri, Eiffellithus eximius,Lucianorhabdus maleformis, and L. quadrifidus.

Presence of long-ranging species known in theinterval from Jurassic or Lower Cretaceous upto Campanian-Maastrichtian.

Reworked species the first occurrence of whichis known in the Aptian or Albian and theydisappear during the Upper Cretaceous.Reworked nannofossils fixed on the ?Aptian-Albian-Cenomanian interval exclusively.Reworked nannofossils fixed on theCenomanian stage exclusively (Corollithion

kennedyi – sample EB 8C).Reworked Jurassic and lower LowerCretaceous species.Deposits of sample EB 2 and EB 25 providedmostly calcium carbonate detritus of anorganic

FORAMINIFERA

C O N C L U S I O N S

Distribution of calcareous nannofossil taxaAbundance of nannofossil taxa: F = few (>5 specimens per20 fields of view), R = rare (<5 specimens per 20 fields ofview); ? = questionable taxon, f = fragments, r = reworked.Estimates of the abundance of nannofossils in samples: M= medium (>5 specimens per 1 field of view), L = low (1-5specimens per 1 field of view), VL = very low (<1 specimenper 1 field of view). Preservation of nannofossils: VP =very poor (etching and especially mechanical damage isintensive making identification of some specimensdifficult).FO = first occurrence, * = taxon the first occurrence ofwhich is known from Cenomanian.

Sample EB 8 provided following taxa:Brachycythere sp., Cytherella parallela Reuss,1844, Cytherella sp., Dolocytheridea aff. crassa

Damotte, 1971, Dordoniella turonensis Damotte,1962, Dordoniella aff. strangulata Apostolescu,1955, Schuleridea neglecta (Reuss, 1854),Schuleridea sp. and several otherindeterminable faunal elements.Sample EB 21 yielded only two ostracod species,namely Cytherella aff. dordoniensis Damotte,1971 and Cytherella sp.

Ostracoda from the locality EB 8:

Fig.1a-b: Reuss, 1844, 1a:carapace from the left, 1b: dorsal view, coll.Nr.2003/5/3, x 125, Fig. 2: sp., coll. Nr.2003/5/5 , x 85, Fig. 3: aff.Damotte, 1971, coll. Nr. 2003/5/7, x 85, Fig. 4:

aff. Damotte, 1971,coll. Nr. 2003/5/9, x 110, Fig. 5:

Danotte, 1962, coll. Nr. 2003/5/10, x100, Fig.6: aff. Apostolescu,1955, coll. Nr. 2003/5/11, x 100, Fig. 7:aff. Apostolescu, 1955, coll. Nr. 2003/5/12,x100, Fig.8: (Reuss, 1854), male,coll. Nr. 2003/5/14, x85, Fig. 9:coll. Nr. 2003/5/1, x 100.

Cytherella parallela

CytherellaDolocytheridea crassa

Dolocytheridea crassaDordoniella

turonensisDordoniella strangulata

Dordoniellastrangulata

Schuleridea neglectaBrachycythere sp.

OSTRACODA

The beds of locality EB 8 are largelyrepresented by in situ, but loose blocks andhave yielded a bivalve fauna consisting of 9taxa. The bivalve shells are usually more or lesschalkified. Almost 200 specimens wereidentified in the field in order to characterisethe assemblage quantitatively. Only small-sizedsolitary corals and internal moulds ofgastropods were encountered as associatedmacro-faunal elements.

Thrysoporella eisenbachaensis n. sp. from Lower Gosau Group of EisenbachDASYCLADALES

From the Middle Turonian of the lower Gosau Group of Eisenbach a new dasycladale is described as n. sp. The new taxonoccurs within a marly limestone bed intercalated within a series of marls. The microfacies represents a lagoonalwackestone where the new species occurs together with pelecypod remains, ostracodes,

S c h l a g i n t w e i t & E b l i a n d m i l i o l i d s , e . g . S c h l u m b e r g e r .The new species is distinguished from other representatives of above all by its high number of primary branches.

V i d a l i n a h i s p a n i c a

Thrysoporella eisenbachensis

Neomeris circularisD i s s o c l a d e l l a ? p y r i f o r m i s

Thrysoporella

Badve & Nayak,y ,

Turonian-

Coniacian? Middle-Upper

Turonian? Turonian Santonian

?

? ? M.schnee-

gansi Z.? ? ? ?

Eisenbach am Traunsee

EB 1 EB 2 EB 8 EB 10 EB21 EB 25 EB 26Ammobaculites sp. r rHaplophragmoides cf. latidorsatum rBigenerina sp. rGaudryina rugosa fMarssonella oxycona f rGaudryina trochus fGaudryina laevigata

Trochammina sp. rDorothia filiformis ? fPseudotextularia sp. ?

Quinqueloculina angusta r r f rSpirillina cretacea f f fTriloculina sp. ? r rLenticulina sp. r rVaginulina trilobata rGavelinella sp. rMarginotruncana schneegansi rHedbergella planispira rHedbergella simplex rHedbergella delrioensis

Heterohelix globulosa rGlobigerinelloides ultramicra ? rPraeglobotruncana sp. rGlobotruncana stuartiformis ? rMarginotruncana angusticarinata ? rOstracoda c c c c cGastropoda c c c c c rf = frequent c = common r = rare

In the assemblages from the light grey marls(EB 8 in part, EB 10, EB 21, EB 25),agglutinated species as Gaudryina, Marssonella

and Dorothia are dominating. Calcareousbenthos and plankton occur rarely and theirtests are usually recrystallized. Theforaminiferal assemblage of the red colouredsediments of sample EB 25 is very poor ofspecies, only a few badly preserved,recrystallized tests of foraminifers were found.Samples from „black shales“ contain mostlyMiliolidae as Spirillina cretacea andQuinqueloculina angusta.

Distribution of foraminiferaf = frequent c = common r = rare

MINERALOGY

T a b l e 1 : S e m i q u a n t i t a t i v e b u l k m i n e r a l c o m p o s i t i o n ( i nm a s s - % )

Sample Quartz Layer silic. Feldspar Calcite Dolomite Pyrite5799 EB1 18 31 2 39 7 3

5800 EB2 20 32 1 36 5 6

5386 EB8 14 38 0 39 6 3

5801 EB10 15 32 1 42 7 3

5802 EB21 16 28 1 48 4 3

Table 2: Semiquantitative clay mineral composition in theclay fraction (<2µm) in mass-%

Sample Smectite VermiculiteMixedLayer

Kaolinite Illite ChloriteUnweath.

vs.weathered

5799 EB1 8 0 4 4 66 18 84:16

5800 EB2 7 0 2 11 64 16 80:20

5386 EB8 tr. 0 tr. 5 76 19 95:05

5801 EB10 11 0 3 3 72 11 83:17

5802 EB21 12 0 6 9 57 16 73:27

tr.: traces

Bulk mineralsThe mineralogical composition of the blackshale samples EB 1 and EB 2 shows a quartzcontent of 18 to 20 mass-% whereas the marlscontain less quartz in the range of 14 to 16 mass%. The feldspar content is generally very low 0-2 mass %). Layer silicates (mica, chlorite etc.)are a dominant (28-38 mass %) mineral groupin all samples. Carbonate minerals arerepresented mainly by calcite in a range from36 to 48 mass %, dolomite can only be found inrather low amounts. The marls EB 10 and EB21 consist of 49-52 mass % carbonate minerals.The content of pyrite is in all samples around 3mass % except in the black shale EB2 whichcontains 6 mass % of this mineral.

The clay mineralogical composition of the<2µm-fraction is dominated by illite whichoccurs in a range from 57-76 mass %.Furthermore, moderate amounts of chlorite canbe found. Kaolinite is present only in smallamounts except in the black shale EB 2, thekaolinite content in this sample reaches a valueof 11 mass %.The swellable clay mineral smectite is present inthe black shales in amounts of 7-8 mass % andin the marls as well. The content in EB 10 andEB 21 is 11-12 mass %, only traces of thismineral could be found in EB 8. Vermiculitesare completely absent. Small amounts of amixed layer mineral illite/smectite regularlyordered could be found in all samples. Illite andchlorite represent more or less the unweatheredclay minerals in the samples, whereas smectite,the mixed layer mineral and kaolinite representthe weathered clay minerals. From this point ofview the sample EB 8 is the less weatheredsample (95 mass % unweathered clay minerals),and EB 21 is the most weathered sample with 73mass % unweathered and 27 mass % weatheredclay minerals.

The Eisenbach locality is situated on the easternside of Lake Traunsee, approximately oppositethe Traunkirchen peninsula. The outcropsoccur along the Eisenbach brook, which rises onthe foothills of Mt. Hochstein on mapsheet 67Grünau im Almtal and flows to the southwestinto the Karbach stream, entering the area ofmapsheet 66 Gmunden. Silty fossiliferous greymarls, including „black shales“, with subordiatesandstone and marly limestone intercalationsdominate the sequence. Sediments formineralogical and microfossil analyses weresampled in, respectively on the slopes of theEisenbach brook. However, the study of thebivalve fauna and of the foraminifers werefocused so far only on the grey marls of localityNo. EB 8.

BIOSTRATIGRAPHY

Nannofossil species Prediscosphaera columnata

of which one specimen was found in theextremely poor assemblage of sample EB 10allows to state stratigraphic range of sedimentsfrom the Albian up to Turonian (sensu Burnett1998). Presence of Quadrum gartneri supportsthe lower part of Lower Turonian, zone UC7(sample EB 1). Nannofossil species Eiffellithus

eximius and Lucianorhabdus quadrifidus giveevidence for zone UC8b that is correlated withthe Middle Turonian (samples EB 8, EB 8A-D,EB 21).

The determination of stratigraphic age ofstudied samples on the basis of foraminifers isvery difficult because stratigraphicallyimportant planktonic species are absent.Onlythe presence of Marginotruncana schneegansi insample EB 8 makes it possible to include thissample to planktonic zone Marginotruncanaschneegansi sensu Robaszynski & Caron (1995).

The occurrence of ostracod species Dordoniella

turonensis Damotte, 1962 supports the Turonianage of sample EB 8.

Biostratigraphically important is theangiosperm pollen Trudopollis (sample EB 8),which firstly appear in Middle Turonian(Góczán et al. 1967, Méon et al. 2004).Moreover, the palynofacies is characterized bythe prevalence and diversity of Complexiopollis

pollen. Such a level of angiospermous pollendiversification/composition accords with thatfound in other microfloras of the MiddleTuronian age.

Most of the grey silty marls show a typical biotaof shallow marine, partly maybe muddy water,environment. However, a minor part of thesequence - in particular part of the „blackshale“ intercalations - could also representbrackish water influenced, probably prodeltaenvironment deposits. Many of the marlylimestone intercalations represent bioclasticpackstones to rudstones consisting of denselypacked shells (mainly of gastropods) and can beinterpreted as tempestites (storm deposits)leading to the shell enrichment within distinctcoquina beds.

The bivalve fauna is clearly dominated byinfaunal shallow-burrowing forms and consistsof relatively few taxa if compared to otherbenthic assemblages of the Lower GosauSubgroup (see e. g. Szente 2003). Theabundance of P. (P.) hillana, suggest abnormalbottom conditions.

Genus Protocardia Beyrich, 1845 is a commonelement in brackish-water bivalve assemblages(Fürsich 1994), however, it has also beenrecorded from black shales deposited in dysoxicconditions (e. g. Wignall 1990). Both salinityand dissolved oxygene content can be excluded,on the basis of the presence of stenohalineorganisms as well as of the macroscopicallybioturbated nature of the sediments, as thegoverning factor causing the mass occurrence ofthe Protocardia.

Poor nannofossils and especially the rareoccurrence of species they formed component ofthe Turonian assemblages may indicate apioneer character of nannoflora during marinetransgression. Moreover, presence of genusLucianorhabdus and fragments ofBraarudosphera bigelowii reflects shallow-watersedimentation.Abundance of benthonic foraminiferal speciesQuinqueloculina angusta and Spirillina cretacea

especially in the „black shale“ samples EB 1 andEB 2 points to an environment with about 10 mdepth of water with low oxygen content and alsowith low salinity (? brackish water).

The assemblage of ostracods withBrachycythere, Cytherella, Dolocytheridea,Dordoniella and Schuleridea indicates a shallowmarine environment.

Marine influence is documented by the presenceof dinoflagellate cysts and faunal chitinousforaminiferal linings. Dinocysts consistpredominantly of shallow water types.

PALAEOENVIRONMENTAL INTERPRETATION

Palynomorph ratio in Eisenbach (EB 8)

foraminif.

dinocyst

spores

gymnosp.

angiosp.

PALYNOMORPHS

The spore-pollen flora is diverse and has aslightly predominant angiosperm component.Mostly triporate angiosperm pollen grains ofNormapolles group - Complexiopollis, i.e.,Complexiopollis cf. christae, C. vulgaris, C. cf.praeatumescens and Complexiopollis spp.prevail.

Detailed micropalaeontological analysis ofsample EB 8 disclosed a relatively wellpreserved but not rich assemblage of spores,pollen grains, organic-walled microplankton,and microforaminifers. The palynomorph ratio(Text-fig. 2) consists of 23% of pteridophytespores, 25% of gymnosperm pollen, 26% ofangiosperm pollen, 16% of non-calcareousmarine microplankton (dinoflagellate cysts),and 10% of planispiral type of innermicroforaminiferal linings.

The lower land plants (pteridophyte spores) areparticularly well represented by abundant largestriate spores with long appendices – Plicatella

tricuspidata (Schizaeaceae) and other triletespores.The gymnosperms are represented by abundantinaperturate Taxodiaceaepollenites hiatus,Cycadopites sp., and Corollina torosa.Palynofacies includes rich yellow- to red-brown-striped tracheidal phytoclasts.Palynomorph assemblage of „black shale“sample EB 1 consists of abundant gymnospermpollen of Taxodiaceaepollenites hiatus,Cycadopites sp. and Corollina torosa. Triporateangiosperm pollen from the Normapolles group- Complexiopollis spp. and large tricolporatepollen - are common. Marine elements are rare,mostly microforaminiferal linings, some brokendinocysts, i.e., Spinidinium sp. and acritarchsMicrhystridium sp. occasionally occur.Miospores contain reworked Permian disaccatepollen of Lueckisporites sp.

Text-fig. 2Text-fig. 2

The grey marls and also the„black shale-type“intercalations are consideredas sediments of the MiddleTuronian marinetransgression of theEisenbach Lower GosauSubgroup. Because a largerpart of the marls ischaracterized by a highamount of small coalifiedplant particles, mostprobably a near shore,

maybe in part a delta-influenced, nutrient-richmuddy water depositionalenvironment existed.Sediments of the abovementioned lithostratigraphicunits of the Lower GosauSubgroup are interpreted asshallow-water depositsprobably of a transgressionalcharacter.

CONCLUSION

Braarudosphaera sp. Lucianorhabdus sp. Eiffellithus eximius

The character of foraminiferal assemblage issimilar to that one of Weißenbachalm localitynear Bad Aussee (samples WB 1, 1A, Hradeckáet al. 1999) but the Eisenbach assemblage ismuch more poorer (see distribution table).