engleski

Tethys-wide occurrence of Lower Aptian Lithocodium-Bacinella facies: Shoalwater expression of basinal OAE1a black shales

Lithocodium aggregatum and Bacinella irregularis are now extinct microencrusters of unknown taxonomic origin that thrived in (sub)tropical platform environments. During parts of the Early Aptian, these organisms experienced bloom periods and temporarily replaced rudist-coral assemblages as the dominant framework builders. Within the limitations of geological time resolution, this “out-of-balance” shoalwater facies seems to be coeval with the OAE1a-related black shale deposition in oceanic basins but the triggering environmental factors that caused this mass occurrence remain insufficiently understood. Having previously established the OAE1a synchronous nature of Lithocodium-Bacinella facies across the Arabian Platform in Oman, recent work focuses on OAE1a time-equivalent exposures in Croatia, France and Portugal. Time correlation is based on high-resolution carbon-isotope stratigraphy supported by Sr-isotope stratigraphy focussing on selected rudist shell material. It is not the mere presence of Lithocodium-Bacinella as such that is of interest here. Lithocodium-Bacinella co-existed with many other neritic organisms throughout much of the Mesozoic, but the transient mass occurrence of these microencrusters and the coeval demise of the dominant mid-Cretaceous frameworkbuilders (rudists and corals). Obviously, the transient dominance of Lithocodium-Bacinella facies is but one of the known responses of neritic platform systems to factors that also caused OAE1a. From other Tethyan localities, platform drowning or the presence of bituminous limestones have been reported. An improved comprehension of the effects of C-cycle perturbation on neritic palaeo-ecosystems is instrumental in understanding anoxic events to their full extent.

Aptian; anoxia; Tethys; platform; basin; correlation.

To reference a Goldschmidt2009 abstract in an article, please note that they were published in a special edition of GCA (Geochimica et Cosmochimica Acta), Volume 73, Issue 13 Supplement 1 (June 2009).