WESTERN UNITED STATES NONMARINE OSTRACODS DURING THE EOCENE–OLIGOCENE TRANSITION: THE EARLY OLIGOCENE FAUNAS OF SOUTHWESTERN MONTANA

Vol. 2, 2019. - 118518
Oral
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Resumo

The coarse to fine-grained siliciclastic and carbonate sediments of the Renova Formation are characteristic of Paleogene sedimentary sequences from southwestern Montana. These were deposited in a broad basin dominated by mid- to high altitude streams and small lake paleoenvironments; the sediment infill later broke during the Miocene–Pliocene into the remnants currently observed in several places, including the Upper Ruby River and the Medicine Lodge valleys, as wells as Horse Prairie. A new ostracod fauna was identified and described from these areas in the present work and its faunal relationships were examined in the context of paleoenvironmental shifts of faunas of the Paleogene within the Mountain West region of the United States. The analysis of early Cenozoic ostracod assemblages from southwestern Montana is important to our understanding of changes in ostracod paleoecology and paleozoogeography of this region during the Eocene-Oligocene transition (EOT), and helps to explain biotic response to climatic change. Early Oligocene strata of the region present six genera of the suborder Cypridocopina: _Amplocypris_ ?, _Candona_ (including the species _Candona rangliensis_ ? and _Candona_ sp. aff. _Candona ohioensis_), _Cypricercus_ ?, _Cyprois_ , _Eucypris_ and _Paracypridopsis_?. These ostracods likely inhabited mostly stable small lakes, characterized by arboreal surroundings reminiscent of forests in highland regions that were buffered against the drastic climatic deterioration observed during EOT. Further south, changes in climate, enhanced by volcanic events with their apexes during the same time interval, negatively affected the establishment of long-lasting, highly diverse ostracod faunas in lowland areas. Early Oligocene southwestern Montana may have represented a refugium for Eocene ostracod genera that became extinct or Lazarus taxa during that time, but would explode in diversity during the Miocene.

Programação
11:00 até 12:00 em 24/10/2019
Auditório Charles D…
Instituições
  • 1 University of Connecticut, Center for Integrative Geosciences, Mansfield, Estados Unidos.
  • 2 University of Connecticut, Center for Integrative Geosciences, Mansfield, Estados Unidos.
  • 3 University of Illinois at Chicago, Department of Earth and Environmental Sciences, Chicago, Estados Unidos.
  • 4 Department of Geological Sciences and Ohio Center for Ecology and Evolutionary Studies, Clippinger Laboratories, Ohio University, Athens, Estados Unidos.
Eixo Temático
  • Cenários: Paleoecologia e Paleoambientes