Taphonomy and Paleoecology of Lower Cretaceous oyster mass occurrences from west-central Argentina and evolutionary paleoecology of gregariousness in oysters

TOSCANO, A.G., LAZO, D.G. AND LUCI, L.

PALAIOS

SEPM-SOC SEDIMENTARY GEOLOGY

Lugar: Lawrence; Año: 2018 vol. 33 p. 237 - 255

0883-1351

Oyster mass accumulations (OMAs) first occurred in the Lower Jurassic and were fairly common throughout the rest of the Mesozoic, Cenozoic and even in present times. In this paper, a Lower Cretaceous (lower Hauterivian) study case from the Neuquén Basin (west-central Argentina) is analyzed in terms of taphonomy and paleoecology in order to characterize its origin, reconstruct the oyster-dominated paleocommunities and its paleoenvironmental implications. In addition, an evolutionary paleoecological analysis is presented to place the studied Lower Cretaceous OMAs in the context of global paleobiogeographic distribution of carbonate bioherms during the Jurassic-Cretaceous time interval. A laterally extensive oyster-bearing sedimentary interval with high oyster abundance was analyzed at three localities situated along a 75 km N-S transect. Two different types of OMAs were differentiated regarding their genesis, biogenic and mixed sedimentologic-biogenic. The development of these different types of OMAs could indicate different paleoenvironmental settings regarding water energy and sedimentation rate. This Lower Cretaceous study case is framed in a general context of a global shift of OMAs from a Tethyan restricted distribution during the Middle and Late Jurassic to a mainly eastern Pacific distribution in the Cretaceous. This change in global distribution may result from different types of ecological, environmental and/or tectonic fluctuations that forced OMAs to occupy different environmental settings.