Isotopic composition (O, C, Sr, and Nd) and trace element ratios (Sr/Ca, Mg/Ca) of Miocene marine and brackish ostracods from North Alpine Foreland deposits (Germany and Austria) as indicators for palaeoclimate

Janz, Horst; Vennemann, Torsten

doi:10.1016/j.palaeo.2005.06.012

Cited by 51 publications

(37 citation statements)

References 29 publications

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“…Furthermore, palynological data from the Molasse bordering the Eastern Alps do not indicate a change in palaeoclimate (Bruch, 1998). There, palaeoclimate followed gobal trends (at least since 20 Ma, Janz & Vennemann, 2005) and appears not to have been influenced by Alpine orogeny. Thus, it is unclear at the moment whether the shift towards drier and more continental conditions as inferred for the Swiss Molasse was a local phenomen that only affected the central part of the Alps.…”

Section: The Development Of Palaeoclimatementioning

confidence: 74%

Possible environmental effects on the evolution of the Alps-Molasse Basin system

2007

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Environmental effects on the evolution of the Alps-Molasse 383 ABSTRACT We propose three partly unrelated stages in the geodynamic evolution of the Alps and the sedimentary response of the Molasse Basin. The first stage comprises the time interval between ca. 35 and 20 Ma and is characterized by a high ratio between rates of crustal accretion and surface erosion. The response of the Molasse Basin was a change from the stage of basin underfill (UMM) to overfill (USM). Because the response time of erosional processes to crustal accretion and surface uplift lasts several millions of years, the orogen first experienced a net growth until the end of the Oligocene. As a result, the Molasse basin subsided at high rates causing the topographic axis to shift to the proximal basin border and alluvial fans to establish at the thrust front. During the Aquitanian, however, ongoing erosion and downcutting in the hinterland caused sediment discharge to the basin to increase and the ratio between the rates of crustal accretion and surface erosion to decrease. The result was a progradation of the dispersal systems, and a shift of the topographic axis towards the distal basin border. The second stage started at ca. 20 Ma at a time when palaeoclimate became more continental, and when the crystalline core became exposed in the orogen. The effect was a decrease in the erosional efficiency of the Swiss Alps and hence a reduction of sediment discharge to the Molasse Basin. We propose that this decrease in sediment flux caused the Burdigalian transgression of the OMM. We also speculate that this reduction of surface erosion initiated the modification of Alpine deformation from vertically-to mainly horizontally directed extrusion (deformation of the Southern Alps, and the Jura Mountains some Ma later). The third stage in the geodynamic development was initiated at the Miocene/Pliocene boundary. At that time, palaeoclimate possibly became wetter, which, in turn, caused surface erosion to increase relative to crustal accretion. This change caused the Alps to enter a destructive stage and the locus of active deformation to shift towards to the orogenic core. It also resulted in a net unloading of the orogen and thus in a flexural rebound of the foreland plate.We conclude that the present chronological resolution is sufficient to propose possible feedback mechanisms between environmental effects and lithospheric processes. Further progress will result from a down-scaling in research. Specifically, we anticipate that climate-driven changes in sediment flux altered the channel geometries of USM and OSM deposits, the pattern of sediment transport and thus the stacking arrangement of architectural elements. This issue has not been sufficiently explored and awaits further detailed quantitative studies.

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Section: The Development Of Palaeoclimatementioning

confidence: 74%

Possible environmental effects on the evolution of the Alps-Molasse Basin system

2007

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“…For the Late Sarmatian and Pannonian (12 to 8.5 Ma) in the Molasse Basin, the occurrence of Cyprideis spp. and candonid species indicate brackish conditions (Janz & Vennemann 2005).…”

Section: Discussionmentioning

confidence: 99%

Early Miocene ostracods from the Sadovi section (Mt Požeška gora, Croatia)

Hajek–Tadesse¹,

Belak²,

Sremac³

et al. 2009

Geologica Carpathica

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Abstract:The study of the Early Miocene (Late Ottnangian/Early Karpatian) ostracod fauna from the Sadovi section (Mt Požeška gora, Croatia) led to several results concerning Neogene paleobiogeography and paleoecology. Brackish deposits of Late Ottnangian and Early Karpatian age have been recognized for the first time in the North Croatian Basin. These deposits indicate the first marine ingression into the Early Miocene lake in this area. Twenty-nine ostracod species were determined, including the new taxa Fabaeformiscandona slavonica nov. sp. and Herpetocypris sadovii nov. sp.

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“…Oxygen isotopic compositions of ostracods have been reliably used to determine oxygen isotope composition of water in continental as well as marine environments (e.g., Holmes and Chivas, 2002;von Grafenstein, 2002;Janz and Vennemann, 2005) and, given the knowledge of a vital offset, this use is justified.…”

Section: Oxygen Isotope Fractionationmentioning

confidence: 99%

“…Many studies have used the stable isotope composition of ostracod fossils to reconstruct palaeoenvironmental conditions (e.g., von Grafenstein et al, 1999a;Ricketts et al, 2001;Schwalb, 2003;Belis and Ariztegui, 2004;Janz and Vennemann, 2005;Anadó n et al, 2006;Tü tken et al, 2006). The use of ostracod valves as a geochemical archive is based on the assumption that the organism crystallised its carapace in equilibrium with water.…”

Section: Introductionmentioning

confidence: 99%

Controls on ostracod valve geochemistry: Part 2. Carbon and oxygen isotope compositions

Decrouy

Vennemann

Ariztegui

2011

Geochimica et Cosmochimica Acta

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The stable carbon and oxygen isotope compositions of fossil ostracods are powerful tools to estimate past environmental and climatic conditions. The basis for such interpretations is that the calcite of the valves reflects the isotopic composition of water and its temperature of formation. However, calcite of ostracods is known not to form in isotopic equilibrium with water and different species may have different offsets from inorganic precipitates of calcite formed under the same conditions. To estimate the fractionation during ostracod valve calcification, the oxygen and carbon isotope compositions of 15 species living in Lake Geneva were related to their autoecology and the environmental parameters measured during their growth. The results indicate that: (1) Oxygen isotope fractionation is similar for all species of Candoninae with an enrichment in 18 O of more than 3& relative to equilibrium values for inorganic calcite. Oxygen isotope fractionation for Cytheroidea is less discriminative relative to the heavy oxygen, with enrichments in 18 O for these species of 1.7 to 2.3&. Oxygen isotope fractionations for Cyprididae are in-between those of Candoninae and Cytheroidea. The difference in oxygen isotope fractionation between ostracods and inorganic calcite has been interpreted as resulting from a vital effect. (2) Comparison with previous work suggests that oxygen isotope fractionation may depend on the total and relative ion content of water. (3) Carbon isotope compositions of ostracod valves are generally in equilibrium with DIC. The specimens' d 13 C values are mainly controlled by seasonal variations in d 13 C DIC of bottom water or variation thereof in sediment pore water. (4) Incomplete valve calcification has an effect on carbon and oxygen isotope compositions of ostracod valves. Preferential incorporation of CO 3 2À at the beginning of valve calcification may explain this effect. (5) Results presented here as well as results from synthetic carbonate growth indicate that different growth rates or low pH within the calcification site cannot be the cause of oxygen isotope 'vital effects' in ostracods. Two mechanisms that might enrich the 18 O of ostracod valves are deprotonation of HCO 3 À that may also contribute to valve calcification, and effects comparable to salt effects with high concentrations of Ca and/or Mg within the calcification site that may also cause a higher temperature dependency of oxygen isotope fractionation.

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Isotopic composition (O, C, Sr, and Nd) and trace element ratios (Sr/Ca, Mg/Ca) of Miocene marine and brackish ostracods from North Alpine Foreland deposits (Germany and Austria) as indicators for palaeoclimate

Cited by 51 publications

References 29 publications

Possible environmental effects on the evolution of the Alps-Molasse Basin system

Possible environmental effects on the evolution of the Alps-Molasse Basin system

Early Miocene ostracods from the Sadovi section (Mt Požeška gora, Croatia)

Controls on ostracod valve geochemistry: Part 2. Carbon and oxygen isotope compositions

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