T181 Growing a Skeleton: Methodological and Theoretical Approaches to Unraveling the Stories Preserved in Skeletal Materials I

Thursday, 29 October 2020
10:00 AM - 12:00 PM
Meeting Rooms

RUDIST BIVALVES AS ENVIRONMENTAL ARCHIVES

Paper number: T181-2
Program: Technical Sessions
Time: 10:15 AM – 10:30 AM

Authors

Abstract

Bivalve shells biomineralization is influenced by various biological (physiological) and surrounded environmental processes, expressed by different growth rates, incremental banding, and life-strategies, which are ultimately reflected by their shell morphology and chemical composition. This renders them valuable for sclerochronological and geochemical approaches to reconstruct paleoenvironmental conditions and several paleophysiological aspects of these organisms. Rudist bivalves became increasingly dominant in the Tethys Ocean during the Late Jurassic and flourished throughout the Cretaceous. Well-preserved rudist (Macgillavryia sp., Vaccinites sp., Torreites sanchezi) and oyster (Oscillopha figari) specimens were collected in life-position from the Campanian Samhan Formation in central Oman. Measurements of growth increments as well as geochemical analyses (δ13C and δ18O) were employed to constrain growth rates and longevity. Petrographic thinsection images under translucent and fluorescence light were used to visualize and accurately count the fine internal increments. Shell mineralogy and composition were inspected via Micro-Raman Spectrometry and EDX. The linearly correlated δ13C and δ18O values was assigned previously to photosymbiotic dinoflagellates in T. sanchezi, and we use this relationship to verify eventual photosymbiosis in all four species. Combined with individual growth performance we discuss the role of symbionts for enhanced calcification. The rudists have external annual growth banding with finer internal increments, but with different numbers in each species. Internal lines in Macgillavryia sp. are characterized by two sequential bundles of finer lines and comparatively thicker ones. The inner fine banded dark-light layers in Vaccinites sp. and Torreites sanchezi were counted, resulting in >400 fine internal increments of extremely regular growth. These are likely daily bands, which would imply a rapid growth of ~5.8 cm/year in the presence of symbionts. Isotopic patterns lacked seasonality but showed ~7 day cycles. Reconstructed temperatures from δ18O range from 35 to 40°C.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-352219

© Copyright 2020 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.