19 Micro- to Macroscopic Evidence of Life and its Implications for the Evolution and Interpretation of the Biosphere in Earth Systems (Posters)

Tuesday, 14 March 2017
9:00 AM - 5:30 PM
Grand Ballroom CDE

ABERRANT BIVALVES AND TENACIOUS CORALS OF THE EARLY JURASSIC, MOROCCO: SURVIVORS OF EXTINCTION AND OCEANIC ANOXIA

Paper number: 19-2
Program: Theme Sessions
Time: 9:00 AM – 5:30 PM

Authors

Abstract

Reef ecosystems are particularly sensitive to environmental changes, and examination of reef turnover in deep time provides context for evaluating the long-term trajectory of modern ecosystems. Therefore, comprehensive inclusion of diverse paleo-reef ecologies is key, especially those that persist in distinct post-extinction environments (i.e. survivors). The Early Jurassic is characterized by pronounced environmental disruptions; in the late Pliensbachian and early Toarcian there is the emplacement of the Karoo-Ferrar large igneous province, rapidly increased atmospheric CO2 concentrations, global warming, sea-level rise, and associated perturbations to global geochemical cycles. In the oceans, the early Toarcian is marked by 1) the deposition of organic-rich black shales (Toarcian Oceanic Anoxic event [T-OAE]), which record pulses of oceanic anoxia, 2) possible ocean acidification, 3) a multi-phased mass extinction at the Pliensbachian-Toarcian boundary/T-OAE, and 4) a significant metazoan reef crisis. During the Early Jurassic, a group of large, reef-building bivalves (Lithiotids) proliferated. Unlike other regions at this time, in Morocco, Lithiotids are frequently associated with corals and these communities persist across the Pliensbachian-Toarcian boundary.

For this study, detailed lithostratigraphic data were collected for two sections of late Pliensbachian and early Toarcian strata in the Western High Atlas that record extensive Lithiotid buildups and biostromal growth along a mixed carbonate-siliciclastic ramp. All five Lithiotid genera are documented here and display diverse growth forms and colony architectures. Notably, the occurrence of Lithiotids (and co-occurrence with corals) is rarely observed within the early Toarcian, and this study documents Lithiotid-coral associations bracketing the Pliensbachian/Toarcian boundary. The Moroccan sites studied here provide spectacular, expanded stratigraphy for the study of the proliferation and collapse of unique Lithiotid-coral reef ecosystems not possible elsewhere in the world. Continued examination of this interval has the potential to expand our understanding of the ecology of aberrant reef-forming bivalves and the reef dynamics of intervals of characterized by environmental perturbations.

Geological Society of America Abstracts with Programs. Vol. 49, No. 1

doi: 10.1130/abs/2017SC-289242

© Copyright 2017 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.