Geo log i cal Quar terly, 2012, 56 (4): 845–852 DOI: http://dx.doi.org/10.7306/gq.1063
Early Eocene age of a sand stone from the Buntmergel For ma tion (Gresten Klippen Zone, Lower Aus tria)
M. Adam GASIŃSKI, Volker HOECK, Andrzej ŚLĄCZKA and Corina IONESCU
Gasiński M.A., Hoeck V., Ślączka A. and Ionescu C. (2012) – Early Eocene age of a sand stone from the Buntmergel For ma tion (Gresten Klippen Zone, Lower Aus tria). Geol. Quart., 56 (4): 845–852, doi: 10.7306/gq.1063
The Gresten Klippen Zone is an in di vid ual geo log i cal unit, mainly out crop ping at the north ern rim of the North ern Cal car e ous Alps. It is best ex posed be tween the Enns Val ley in the west and the Vi enna For est in the east. It con tains a rock se quence rang ing from Early Ju ras - sic to Early Cre ta ceous, in clud ing sand stones, var i ous lime stones, brec cias and radiolarites. The late Early Cretaceous–Paleogene is rep - re sented by the Buntmergel For ma tion. A sand stone block from the lat ter yields well-pre served plank tonic foraminiferids which al low an as sign ment to the Early Eocene (E-7 Zone). The low den sity cur rents which de pos ited the par al lel lam i nated sand stones orig i nated in the lower shelf-mid dle slope.
M. Adam Gasiński and Andrzej Ślączka, In sti tute of Geo log i cal Sci ences, Jagiellonian Uni ver sity, Oleandry 2a, 30-063 Kraków, Po - land, e-mails: adam.gasinski@uj.edu.pl, andrzej.slaczka@uj.edu.pl; Volker Hoeck, De part ment of Ge og ra phy and Ge ol ogy, Paris Lodron Uni ver sity, Salzburg, Aus tria and De part ment of Ge ol ogy, Babeş-Bolyai Uni ver sity, Cluj-Napoca, Ro ma nia, e-mail:
volker.hoeck@sbg.ac.at; Corina Ionescu, De part ment of Ge ol ogy, Babeş-Bolyai Uni ver sity, Cluj-Napoca, Ro ma nia, e-mail:
corina.ionescu@ubbcluj.ro (re ceived: July 11, 2012; ac cepted: Oc to ber 9, 2012; first pub lished on line: De cem ber 10, 2012).
Key words: Gresten Klippen Zone, Eocene, plank tonic foraminiferids, Lower Aus tria.
INTRODUCTION
The Gresten Klippen Zone (GKZ), de spite be ing known as an in di vid ual geo log i cal unit since the mid of 20th cen tury (Prey, 1952, 1953), is still not com pletely un der stood from biostratigraphic and tec tonic points of view. It is part of the Helvetic Zone (in clud ing the Ultrahelvetic Zone), which ex - tends in the East ern Alps along the north ern rim of the North ern Cal car e ous Alps, from Vorarlberg in the west to Lower Aus tria and the Vi enna For est in the east (Prey, 1980). In this pa per we pro vide new in sight into the biostratigraphy of the Paleogene part of the Buntmergel For ma tion (Piller et al., 2004) which be - longs to the GKZ in Lower Aus tria (Fig. 1). The fos sil find ings pre sented here come from a sin gle block only, con tain ing very well-pre served foraminiferids. On go ing re search in the Paleogene sec tion fo cuses on the over all strati graphic scheme of the whole se quence.
GEOLOGICAL SETTING
The most com plete strati graphic se quences in the Helvetic and Ultrahelvetic zones, re spec tively, are found east of Salz - burg, in a 75 km west-east strik ing area, ter mi nated in the west by the Pechgraben close to the Enns Val ley, and in the east by the Traisen Val ley (Figs. 1 and 2). This par tic u lar area is known as the “Gresten Klippen Zone”. Fur ther to the east, it is called the “Hauptklippen Zone”. It con sists of a pre dom i nantly Ju ras - sic se quence form ing the “Klippen” and an en ve lope se quence – the Buntmergel For ma tion – that ranges from the late Early Cre ta ceous (Albian) to the Eocene (Fig. 2). The klippen are formed by in di vid ual blocks rang ing in size from a few metres to sev eral hun dreds of metres (Aberer, 1951; Prey, 1953;
Schnabel, 1970; Ślączka et al., 2009).
One of the most im por tant se quences in the GKZ is the Gresten For ma tion of early to mid-Ju ras sic age that forms the stratigraphically deep est level and has no known base ment.
Fig. 1. Sim pli fied geo log i cal map of the Gresten Klippen Zone east of Enns
The map is based on the tec tonic over view map of Lower Aus tria by Schnabel (1992) and Schnabel et al. (2002). The in sert in the up - per left shows the po si tion of the map within Aus tria. The black rect an gle marks the study area (shown in de tail in Fig. 2)
Fig. 2. Sim pli fied geo log i cal map of the area of the Gresten Klippen Zone be tween Pechgraben and Waidhofen a.d. Ybbs, based on Schnabel et al. (2002)
The ar row points to the where the sand stone block was found
Faupl (1975) dis tin guished three ma jor lithofacies: (a) a basal flu - vial fa cies suc ces sion, (b) a se quence as so ci ated with coals and (c) a ma rine suc ces sion. They grade into a se quence of pre dom i nantly grey marls and shales interlayered with sand stones, marly lime - stones and some coarse clastic de pos its (Posidonia marls of Bajocian–Callovian age; Trauth, 1950; Wessely, 2006). These sed i ments pass into cherty lime stones and radiolarites of Mid dle Ju ras sic and ear li est Oxfordian age (Lampelsberg For ma tion).
The Late Ju ras sic and the lower part of the Early Cre ta ceous are rep re sented by si li ceous lime stones (Scheibbsbach For ma tion), red nod u lar Arzberg lime stones, dark grey Arthof lime stones, Aptychus lime stones (Lower Blassenstein For ma tion) and the spot ted marls and marly lime stones of the Up per Blassenstein For ma tion that lasted un til the Barremian–Aptian. Within the Tithonian–Barremian de pos its, lenses of con glom er ates known as the Konradsheim lime stones (Faupl, 1975; Widder, 1988;
Wessely, 2006) oc cur. Re cently, a se quence of Barremian–Aptian con glom er ate was de scribed as the Konradsheim For ma tion (Höck et al., 2003, 2005; Ślączka et al., 2009).
The con tact re la tion of the Buntmergel For ma tion with the Late Jurassic–Early Cre ta ceous car bon ate se quence is un clear.
Rarely, depositional con tacts have been de scribed (Prey, 1980) but in gen eral the con tact is tec toni cally over printed (Schnabel, 1970; Widder, 1988; Wessely, 2006; Ślączka et al., 2009). The Buntmergel For ma tion is rep re sented by red to green, rarely grey marls and marly shales with sub or di nate thin-bed ded quartzitic sand stones with glauconite.
Dur ing the Early Paleogene, num mu lit ic lime stones, graded sand stones and con glom er ates (e.g., Konradsheim con - glom er ates) were deposited. Within these clastic de pos its of Paleogene age, Faupl (1978) dis tin guished four dif fer ent fa cies types: (1) coarse-grained lime stone brec cia and con glom er ates with abun dant siliciclastic ma te rial (“Bernreith fa cies”), (2) calcirudite and calcarenite (“Texing fa cies”), (3) quartz arenite and con glom er ate (“Schaitten fa cies”) and (4) a turbidite fa - cies. The marls be tween the coarse clastic ho ri zons are grey,
green, and in places blu ish in col our; the typ i cal Up per Cre ta - ceous red marls are miss ing. Thin lay ers of glauconitic sand - stone are com mon (Widder, 1988). There are sed i men tary brec cias of Paleocene age sim i lar to the first fa cies type de - scribed by Faupl and Schnabel (1987) from the Scheibbs area.
The lithic frag ments in the coarse-grained clastic lay ers in clude metagranites, gneiss es, var i ous types of micaschists, green - schists, and in ter me di ate to acidic vol ca nic rocks. They are sim i lar to those found in the Ju ras sic clastic se quences and in di - cate a sim i lar hin ter land for the Ju ras sic and Paleogene sed i - ments. Blocks of sed i men tary rocks such as chert, Calpionella lime stone, Trocholina lime stone and Litothamnium lime stone with Orbitoides and Num mu lites are also pres ent.
RESULTS AND DISCUSSION
LITHOLOGY OF THE SAMPLE
The fossiliferous rock piece (Sam ple S9) was found in the Maigraben in Grossau – an area of the Gresten For ma tion that out crops at N47°57’20’’ and E14°39’07’’ – as a loose decimetre-sized block of sand stone (see ar row in Fig. 2).
The Gresten For ma tion in Grossau is fairly well-known since the sec ond half of the 19th cen tury due to the in tensive coal min ing (e.g., Lipold et al., 1865). Aberer (1951) de scribed a se quence of grey sandy, oc ca sion ally also marly shale, interbedded with sand stones.
In the Maigraben pro file, the Gresten For ma tion, dip ping in gen eral to wards the south, is di rectly en vel oped by the Buntmergel For ma tion. The rel a tively high amount of red marls and the lack of clastic beds in the scarce ex po sures ar gue for a Cre ta ceous sec tion of the Buntmergel For ma tion (Aberer, 1951).
The sand stone block found in Maigraben is thin bed ded, with light brown and me dium grey laminae up to sev eral mm in thick ness (Fig. 3A). The light brown lay ers are rel a tively rich in
Early Eocene age of a sandstone from the Buntmergel Formation (Gresten Klippen Zone, Lower Austria) 847
Fig. 3. The sand stone from the Buntmergel For ma tion
A – mac ro scopic im age, show ing the al ter na tion of fine lay ers of al most pure quartz (me dium grey) and quartz + car bon ate (light brown);
B – crossed polars, light mi cro pho to graph, show ing fine-grained quartz ce mented by cal cite; the area marked by X rep re sents the light brown lay ers rich in calcitic ce ment, vis i ble in A
car bon ate whereas the me dium grey lay ers con sist of pre dom i - nantly quartz grains with only a small amount of car bon ate. Mi - cro scop i cally, it re veals a well-sorted sand stone with an gu lar to subangular grains rang ing from 20 to 100 mm in size (Fig. 3B).
Min er al og i cally, the sand stone con sists of quartz, rare feld - spars (mainly plagioclase) and some mus co vite and bi o tite.
Glauconite is ubiq ui tous. The calcitic ce ment is inhomogeneously dis trib uted within the rock, with a vis i ble con cen tra tion in elon gated lenses form ing thin laminae. These laminae con tain very well-pre served, whole foraminiferal tests.
Al though this sand stone was found in the area of the Gresten
For ma tion out crops, it dis tinctly dif fers from the sand stones known from the Gresten For ma tion (Faupl, 1975) by fine laminae, a good sort ing, a smaller grain size and the abun dance of glauconite. Our sam ple fits best to the sand stones from the
“turbidite fa cies” of the Buntmergel For ma tion stratigra - phically as signed to late Early Eocene (Faupl, 1978).
MICROPALEONTOLOGY
The foraminiferids ana lysed were rec og nized from the thin sec tion made from the block de scribed above (sam ple S9).
Fig. 4. Plank tonic foraminiferids
A – Acarinina sp.; B – Subbotina yeguaensis (Weinzierl and Applin); C – Subbotina sp.; D, E – Acarinina pseudotopilensis Subbotina; F, G – Subbotina yeguaensis (Weinzierl & Applin); H, I – Acarinina cf. bulbrooki (Bolli); J–L – Acarinina bulbrooki (Bolli). A–G – dif fer ently ori ented
sec tions; H–I – cross-sec tions; J–L – ax ial sec tions
They show well-pre served tests. The foraminiferids are well–preserved for sev eral rea sons: (a) the con tain ing rocks are only slightly al tered and (b) they were trans ported and emplaced by den sity cur rents.
The in dex plank tonic spe cies iden ti fied are: Subbotina yeguaensis (Weinzierl and Applin), Acarinina pseudotopilensis Subbotina, Parasubbotina inaequispira (Subbotina), Acarinina bulbrooki (Bolli) and Acarinina esnehensis (Nakkady). All spe cies iden ti fied are shown in Fig - ures 4A–L and 5A–L. Un dam aged frag ile tests are par tic u larly vis i ble in Fig ure 5G. Some spec i mens have or na mented test
walls (Figs. 4G, J–L and 5A, J) and vis i ble po si tions of the ap - er ture (Figs. 4F, K, L and 5A, B).
BIOSTRATIGRAPHICAL POSITION OF THE FORAMINIFERAL ASSEMBLAGE
The rich and well-pre served char ac ter is tic plank tonic in dex spe cies al low as sign ment to a high-res o lu tion biozone level. Fig - ure 6 shows the po si tion of the fos sil as sem blage within the stan - dard biostratigraphic chart of Pearson et al. (2006). The age of the sam ple stud ied can be es ti mated as late Early Eocene, i.e. E-7 Zone (Berggren and Pearson, 2005), which cor re sponds to zone
Early Eocene age of a sandstone from the Buntmergel Formation (Gresten Klippen Zone, Lower Austria) 849
Fig. 5. Plank tonic foraminiferids
A, B – Parasubbotina inaequispira (Subbotina); C, D – Acarinina esnehensis (Nakkady); E, F – Subbotina yeguaensis (Weinzierl and Applin), G – Globigerina sp. – ju ve nile forms; H – Globanomalina sp.; I – Acarinina sp.; J, K – Acarinina esnehensis (Nakkady); L – Acarinina sp. – frag ment
P9 sensu Berggren et al. (1995) and to the lower part of AE 4 Zone sensu Huber and Quillievere (2005). The morphotypes of the plank tonic taxa, in par tic u lar the pres ence of keeled forms, in di - cate an ex ter nal shelf-mid dle slope depositional (i.e. a bathy-pe - lagic) en vi ron ment (Gasiński, 1997).
Due to the spar sity of avail able ma te rial, de ter mi na tion of the depositional en vi ron ment for the sand stone is dif fi cult.
How ever, the fine lami na tions, the vis i ble lack of gra da tion and in par tic u lar the well-pre served, un dam aged frag ile tests of rel - a tively deep-wa ter plank tonic foraminiferids ar gue for sed i - men ta tion by low den sity cur rents and fall out with out trac tion (Read ing, 1996). The laminae show milli metre-sized folds (Fig. 3A), sug gest ing lo cal syn-sed i men tary slid ing. Nev er the - less, this sand stone can be gen er ally in cluded among the
“deep-wa ter turbidite fa cies” (Read ing, 1996).
CONCLUSIONS
Well-pre served deep sea plank tonic foraminiferids oc cur in a loose sand stone block in the Grossau area (Maigraben) in Lower Aus tria. The fol low ing foraminiferids were found:
Acarinina sp., Acarinina pseudotopilensis Subbotina, Acarini - na bulbrooki (Bolli), Parasubbotina inaequspira (Subbotina), Acarinina esnehensis (Nakkady), Subbotina sp., Subbotina yeguaensis (Weinzierl and Applin), Globigerina sp. and Globa nomalina sp. The per fectly pre served palaeontological fea tures of the foraminiferids al low their pre cise biostratigraphic as sign ment to the E-7 Zone of Pearson et al.
(2006). There fore, the block of sand stone can be as signed to the up per, Early Eocene part of the Buntmergel For ma tion of the Gresten Klippen Zone. The clastic ma te rial of the sand stone in - ves ti gated was pri mar ily de pos ited on a slope of the ba sin and later on re de pos ited by low den sity cur rents to deeper parts of the ba sin. As a re sult of our stud ies, new data con cern ing the clastic de pos its from the Eocene part of the Buntmergel For ma - tion have been ob tained.
Ac knowl edge ments. We thank Prof. Dr. B. Olszewska and Prof. Dr. T. Peryt (Pol ish Geo log i cal In sti tute – Na tional Re - search In sti tute), and an anon y mous re viewer for crit i cal re - marks which im proved the manu script. Dr. P. Wójcik-Tabol and W. Obcowski (In sti tute of Geo log i cal Sci ences, Jagiellonian Uni ver sity) kindly helped with the il lus tra tions.
Mrs. M. Mereu (Babeş-Bolyai Uni ver sity) is thanked for com - puter-as sisted draw ings.
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Early Eocene age of a sandstone from the Buntmergel Formation (Gresten Klippen Zone, Lower Austria) 851
