Downloaded from geology.gsapubs.org on January 7, 2014 Long-term ecosystem stability in an Early Miocene estuary Martin Zuschin1*, Mathias Harzhauser2, Babette Hengst1, Oleg Mandic2, and Reinhard Roetzel3 1University of Vienna, Department of Palaeontology, Althanstrasse 14, A-1090 Vienna, Austria 2Natural History Museum Vienna, Department of Geology and Palaeontology, Burgring 7, A-1010 Vienna, Austria 3Geological Survey of Austria, Neulinggasse 38, A-1030 Vienna, Austria ABSTRACT southern estuarine part, probably connected to The question of ecosystem stability is central to ecology and paleoecology and is of particu- a huge, south-north–trending river system in the lar importance for estuaries, which are environmentally highly variable, considered as geo- adjoining Vienna Basin, and a northern marine logically short lived, and among the most degraded modern ecosystems of our planet. Under- part (Harzhauser et al., 2002; Latal et al., 2006). standing their ecological dynamics over geological time scales requires paleontological data in A connection to the large epicontinental Parate- a sequence stratigraphic framework, which allows evaluation of paleocommunity dynamics thys Sea was most probably established along in an environmental context. A 445-m-thick estuarine succession in a satellite basin of the the northeastern margin of the Korneuburg Ba- Vienna Basin (Austria) shows continuous sedimentation over 700 k.y. and can be divided into sin (Fig. 1) (Harzhauser and Wessely, 2003). The two transgressive systems tracts and a highstand systems tract. In contrast to expectations, foraminifera in parts of the basin were adapted no major physical disturbances of the ecosystem involving abrupt changes in diversity and to brackish-water conditions and indicate a very biofacies composition occurred at fl ooding surfaces and at the sequence boundary. Accom- shallow water environment through basin his- modation space remained remarkably constant over the depositional history of the basin, tory, with maximum water depth not exceeding and all changes between depositional environments were therefore more or less gradational. 30 m (Rögl, 1998). The fi sh fauna (e.g., Gobi- Biotic change along the studied succession can be described as a gradual faunal replacement idae, Sparidae, Dasyatidae, Myliobatidae) in the in response to habitat tracking, a process also reported for some normal marine shelf environ- southern Korneuburg Basin indicate littoral and ments. Benthic assemblages in the estuarine succession were strongly dominated by a few taxa shallow sublittoral conditions in a subtropical to and developed along two indirect gradients, water depth and hydrodynamic energy. These tropical environment with freshwater infl uence gradients show subtle long-term trends, corresponding to the sequence stratigraphic architec- (Reichenbacher, 1998). ture. Tectonics affected the sequence architecture in this particular marginal marine setting: it controlled accommodation space and sedimentary input, and provided stable boundary STRATIGRAPHY conditions over hundreds of thousands of years. Our study demonstrates for the fi rst time The section near the village of Stetten in the that estuaries, which are under great environmental pressure today, are resilient to natural Korneuburg Basin can be divided into Stetten environmental perturbations and can persist over geological time scales. West (total thickness of 445 m) and Stetten East (total thickness of 165 m) (Fig. 1; Fig. DR1 in INTRODUCTION and belong to the most degraded modern eco- the GSA Data Repository1). Thin coaly depos- The fossil record is rich in examples of eco- systems of our planet (Lotze et al., 2006). Be- its, washed-in land-, and freshwater snails in- system stability exceeding millions of years, cause of their highly variable physicochemical dicate marginal marine conditions. Sand pack- mostly in Paleozoic and Mesozoic marine characteristics, estuaries also count as naturally ages with trough cross-bedded sets are mostly level bottom communities, interrupted by brief stressed areas: their biotas have the ability to interpreted as tidal sand waves of the shoreface. episodes of strong turnover (DiMichele et al., adapt to various stressors and the ecosystem can Pelitic sediments mostly show even lamination 2004). Ecosystem stability at the scale of tens compensate for changes in the environment, a to wavy bedding or thinly alternating sandy and to hundreds of thousands of years is a typical feature termed homeostasis (Elliott and Quinti- muddy layers, indicative of tidal fl at deposits feature of Pleistocene coral reefs (Pandolfi and no, 2007). The study of turnover and communi- (Reineck and Singh, 1975; Boyd et al., 2006). Jackson, 2006), but has only rarely been report- ty stability in such a fl uctuating ecosystem over The succession is dominated by upward-fi ning ed from Phanerozoic soft bottom assemblages hundreds of thousands of years is therefore of parasequences, which are typical for a tidal fl at (Holterhoff, 1996). High-resolution studies of major ecological and paleoecological interest. to subtidal environment on a muddy, tide-domi- this kind require a stratigraphic framework to nated shoreline (Van Wagoner et al., 1990). The evaluate paleocommunity dynamics in their en- STUDY AREA astronomical tuning of the gamma ray record vironmental context (Holland and Patzkowsky, The Korneuburg Basin, a satellite basin of the fi xed the deposition to the time interval from 2004; Scarponi and Kowalewski, 2004). Here Vienna Basin, is located in Lower Austria and is 17.0 to 16.3 Ma, yielding a total duration of we report for the fi rst time on ecosystem stabil- 20 km long and 7 km wide (Fig. 1). It was formed 700 k.y. (our data). ity over 700 k.y. in a Miocene estuarine succes- by Burdigalian pull-apart movements within the sion (Fig. 1). Alpine-Carpathian thrust belt. The basin sedi- SAMPLE PREPARATION Estuaries are semienclosed coastal water ments mostly belong to the Miocene Korneuburg We took a total of 118 bulk samples, weigh- bodies with salinities that differ from the open Formation, which was dated into nannoplankton ing ~1 kg each, from 96 shell beds. The sedi- sea. They exhibit distinct biota (Whitfi eld and zone NN4, paleomagnetic chron C5C, and mam- ment material >1 mm mesh size was quanti- Elliott, 2011), are environmentally highly vari- mal zone MN5 (Harzhauser and Wessely, 2003). tatively picked under a binocular microscope able (Elliott and Quintino, 2007), are considered Faunal composition and stable isotopes show for all biogenic components. For sponges, ev- as geologically rather short lived (Wolff, 1983), that the Korneuburg Basin was divided into a ery bioeroded biogenic hard part with distinct *E-mail: [email protected]. 1GSA Data Repository item 2014002, Table DR1 (abundance and species richness of higher taxa), Table DR2 (environmental and stratigraphic affi liation of samples in biofacies), Figure DR1 (section Stetten East), Figures DR2–DR4 (results of two-way cluster analysis and ordination [nMDS]), and Appendix DR1 (actualistic comparison of abundant taxa), is available online at www.geosociety.org/pubs/ft2014.htm, or on request from [email protected] or Documents Secretary, GSA, P.O. Box 9140, Boulder, CO 80301, USA. GEOLOGY, January 2014; v. 42; no. 1; p. 7–10; Data Repository item 2014002 | doi:10.1130/G34761.1 | Published online 6 December 2013 GEOLOGY© 2013 Geological | January Society 2014 of America.| www.gsapubs.org Gold Open Access: This paper is published under the terms of the CC-BY license. 7 Downloaded from geology.gsapubs.org on January 7, 2014 STETTEN WEST Sequence Rarefied Natural radioactivity Lithology stratigraphy Biofacies DC 1 DC 2 species richness (gamma log) 123 12 4 6 8 10 16° 20' Lithology 440 )2 m depth energy Sand TS shallow high low high Silt-Clay T( Vienna Interbedding Kleinebers- 48° 30' 2 dorf N Sand-Silt Lignite c t AUSTRIAAUSTRIA WE Flysch basement a S 400 r t -400 m Sequence Stratigraphy s m -100 m Roseldorf Zone e parasequences t retrogradational s parasequence sets y 360 s aschberg Unit Swell aggradational to W progradational e rg Basin parasequence sets v 0 m u i i s s Schliefberg fault e e KorneubKorneuburg Basin r Stetten Bisamberg fault 320 g 123 12 4 6 8 10 -600 m 286-324 m s Stetten Profile gap n a a 123 12 4 6 8 10 ienna Basin r 0 m V Korneuburg 48° 280 Flysch Unit 20' T Rhenodanubian 5 km 240 270 Samples Biofacies Intertidal 240 Agapilia biofacies Granulolabium- 210 Agapilia biofacies high energy Subtidal 180 Nassarius-Turritella- 200 Corbula biofacies 150 Nassarius-Paphia- Loripes biofacies DCA 2 DCA 120 ec ssa ne 90 rr ucco 160 m 60 of land snails of land H i g h s t a n d y e m r c (HST) 30 ) low energy 1 0 T 0 40 80 120 160 200 240 280 320 S T( 1 1 T( deep DCA 1 shallow 120 t t c c Taxa Cliona designating taxa 400 a of intertidal biofacies t r Porites Megabalanus designating taxa 320 Paphia of subtidal biofacies e m s Donax Peronaea Balanus Cerithium Lasaeina Ocenebra 240 Timoclea AcanthocardiaCrassostrea Sandbergeria 80 t Perna Terebralia Loripes Sparidae Hydrobia s Granulolabium s y 160 Polinices Perrona Circomphalus Pyrene Nassarius Cubitostrea Turritella Cingula DCA 2 DCA 80 Nucula C.arcellum e Striarca Pelecyora Anadara Agapilia v Natica Antalis C.praeplicata s i 0 Cyllenina Acteon 40 s s Lesueurigobius Clavatula -80 e Bittium r Corbula Turboella g s s g -160 Parvicardium n a r r a n -160 -80 0 80 160 240 320 400 480 DCA 1 0 T 123 12 4 6 8 10 50 30 10 cps Figure 1. Korneuburg Basin, Austria, with studied transect and results of detrended correspondence analysis (DCA). Upper left: Sediment thickness and major structural units in region of basin (after Wessely, 1998). Arrows indicate freshwater infl ow in south and connection with open sea in north. Center left: Ordination plot of DCA of samples, showing four biofacies.