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Gross M.,Universalmuseum Joanneum | Piller W.E.,University of Graz | Ramos M.I.,Coordenacao de Ciencias da Terra e Ecologia | Douglas da Silva Paz Jackson J.,Federal University of Mato Grosso
Journal of South American Earth Sciences | Year: 2011

In Miocene times a vast wetland existed in Western Amazonia. Whereas the general development of this amazing ecosystem is well established, many questions remain open on sedimentary environments, stratigraphical correlations as well as its palaeogeographical configuration. Several outcrops located in a barely studied region around Eirunepé (SW Amazonas state, Brazil) were investigated to obtain basic sedimentological data. The observed deposits belong to the upper part of the Solimões Formation and are biostratigraphically dated to the Late Miocene. Vertically as well as laterally highly variable fine-grained clastic successions were recorded. Based on the lithofacies assemblages, these sediments represent fluvial deposits, possibly of an anastomosing river system. Sand bodies formed within active channels and dominant overbank fines are described (levees, crevasse splays/channels/deltas, abandoned channels, backswamps, floodplain paleosols). Lacustrine environments are restricted to local floodplain ponds/lakes. The mollusc and ostracod content as well as very light δ18O and δ13C values, measured on ostracod valves, refer to exclusively freshwater conditions. Based on palaeontological and geological results the existence of a long-lived lake (" Lake Pebas" ) or any influx of marine waters can be excluded for that region during the Late Miocene. © 2011 Elsevier Ltd.


Gross M.,Universalmuseum Joanneum | Ramos M.I.,Coordenacao de Ciencias da Terra e Ecologia | Caporaletti M.,University of Graz | Piller W.E.,University of Graz
Journal of South American Earth Sciences | Year: 2013

Western Amazonia's landscape and biota were shaped by an enormous wetland during the Miocene epoch. Among the most discussed topics of this ecosystem range the question on the transitory influx of marine waters. Inter alia the occurrence of typically brackish water associated ostracods is repeatedly consulted to infer elevated salinities or even marine ingressions. The taxonomical investigation of ostracod faunas derived from the upper part of the Solimões Formation (Eirunepé; W-Brazil) documents a moderately diverse assemblage (19 species). A wealth of freshwater ostracods (mainly Cytheridella, Penthesilenula) was found co-occurring with taxa (chiefly Cyprideis) usually related to marginal marine settings today. The observed faunal compositions as well as constantly very light δ18O- and δ13C-values obtained by measuring both, the freshwater and brackish water ostracod group, refer to entirely freshwater conditions. These results corroborate with previous sedimentological and palaeontological observations, which proposed a fluvial depositional system for this part of western Amazonia during the Late Miocene. We demonstrate that some endemic, " brackish" water ostracods (i.e., Cyprideis) have been effectively adapted to freshwater conditions. Thus, their occurrence is no univocal evidence for the influence of brackish or marine waters in western Amazonia during the Miocene. © 2012 Elsevier Ltd.


Gohlich U.B.,Geologisch palaontologische Abteilung | Gross M.,Universalmuseum Joanneum
Palaeobiodiversity and Palaeoenvironments | Year: 2014

Among the rich late Middle Miocene vertebrate fauna from Gratkorn [MN(7+)8] in Styria, Austria, birds are among the rarest of vertebrate fossils. Only isolated elements - 13 bones and two claws - have been recorded, most of which are fragmentary, thereby hampering systematic determinations. However, four different taxa have been identified as representing at least three different species of galliforms (Miogallus altus, cf. Palaeocryptonyx edwardsi, cf. Palaeocryptonyx sp.) and the mousebird Necrornis cf. palustris. All of these taxa have been known to be present before from Middle Miocene deposits in Europe, but there existence has been proven for the first time in Austria. © 2014 Senckenberg Gesellschaft für Naturforschung and Springer-Verlag Berlin Heidelberg.


Reuter M.,University of Graz | Piller W.E.,University of Graz | Erhart C.,Universalmuseum Joanneum
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2012

Siliciclastic influx is a major control for neritic carbonates. Herein, we present a shallow-marine mixed silici-volcaniclastic carbonate system from the Middle Miocene coralline algal-dominated Leitha Limestone in the Styrian Basin (Austria). The analyses of facies and stratal geometries reveal a succession of four depositional units and six facies types (reef facies, inter-reef facies, coralline algal debris facies, rhodolith-Porites facies, quartz sand-Planostegina facies, coral carpet facies). Depositional unit 1 comprises patch reefs (reef facies) and surrounding carbonate sands (inter-reef facies), which show a characteristic lateral succession of biotic associations (reef corals-rhodoliths-nodular celleporiform bryozoans-Planostegina). A similar modern analogue occurs in the Red Sea at the transition from patch reefs to seagrass meadows. In contrast, the coralline algal debris facies of depositional unit 2 represents a high-energetic submarine dune environment. A deepening-shallowing trend is suggested by the gradual shift from the muddy rhodolith-Porites facies to the detritic quartz sand-Planostegina facies in depositional unit 3, while the vertical transition of coral carpet facies to rhodolith-Porites facies in depositional unit 4 suggests again a deepening.Despite an isolated inner basin setting on the Middle Styrian High the coralline algal- and coral-dominated benthic carbonate communities in all depositional units and facies were strongly influenced by terrigenous sedimentation. Coarser siliciclastic sedimentation was linked to low-stands of relative sea level while fine clay fraction was deposited at any time due to the submarine alteration and reworking of volcanic ashes. Despite a high sedimentation stress the variety of coral communities (patch reefs, coral carpets, non-framework coral communities) and coral diversity is unique for the entire Central Paratethys. Leptoseris and two not identified coral species, one with thin-platy plocoid, the other with phaceloid branching growth form, are new coral records for the Central Paratethys. This is of particular importance for paleobiogeographic reconstructions since the Styrian Basin was located close to the northern margin of the global coral reef belt. It is assumed that the relatively high total coral diversity reflects dynamic habitat and population structures in an unstable coral ecosystem at the edge of coral reef distribution which was highly vulnerable to tectonically controlled changes affecting nature and distribution of clastic sediments. In general, increasing siltation stress reduced coral diversity, coral cover and colony sizes and led to the replacement of massive by platy growth forms and of suprastratal by constratal growth fabrics. © 2012 Elsevier B.V.


Kern A.K.,Natural History Museum Vienna | Harzhauser M.,Natural History Museum Vienna | Soliman A.,University of Graz | Soliman A.,Tanta University | And 2 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2012

High resolution pollen and dinoflagellate analyses were performed on a continuous 98-cm-long core from Tortonian deposits of Lake Pannon in the Styrian Basin in Austria. The sample distance of 1-cm corresponds to a resolution of roughly one decade, allowing insights into environmental and climatic changes over a millennium of Late Miocene time. Shifts in lake level, surface water productivity on a decadal- to centennial-scale can be explained by variations of rainfall during the Tortonian climatic optimum. Related to negative fine scale shifts of mean annual precipitation, shoreline vegetation belts reacted in an immediate replacement of Poaceae by Cyperaceae as dominant grasses in the marshes fringing the lake. In contrast to such near-synchronous ecosystem-responses to precipitation, a delayed lake level rise of 4-6. decades is evident in the hydrological budget of Lake Pannon. This transgression, caused by a precipitation increase up to > 1200 mm/yr, resulted in a complete dieback of marshes. Simultaneously, "open-water" dinoflagellates, such as Impagidinium, took over in the brackish lagoon and fresh water dinoflagellates disappeared. As soon as the rainfall switched back to moderate levels of ~. 1100-1200. mm/yr, the rise of the lake level slowed down, the marsh plants could keep up again and the former vegetation belts became re-established.Thus, mean annual precipitation, more than temperature, was the main driving force for high-frequency fluctuations in the Tortonian wetlands and surface water conditions of Lake Pannon. Such high resolution studies focusing on Tortonian decadal to centennial climate change will be crucial to test climate models which try to compare the Tortonian models with predictions for future climate change. © 2011 Elsevier B.V.

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