Friday, March 29, 2024 1:45 pm, Mendenhall Laboratory Room 291 or online using the Zoom link
Dr. Rachel Laker
NSF EAR Postdoctoral Fellow
University of Cincinnati
Email: lakerrl@ucmail.uc.edu
Host: Jill Leonard-Pingel
Title: How much time is recorded in a fossil assemblage?
Time averaging, the co-occurrence of fossils from different moments in time, is pervasive in the fossil record. Time averaging can increase species richness allowing for efficient sampling of a community, but temporal coarsening can also underestimate community response to change over time, so quantifying time averaging of an assemblage is necessary to understand what biases a fossil assemblage may contain. While a core aspect of any fossil assemblage, quantifying time averaging can be difficult without absolute dating. Here, I use sequence stratigraphy to estimate exposure duration, burial rate, and burial environment in several siliciclastic settings to (1) understand taphonomic processes on timescales that exceed actualistic experiments, and (2) identify the taphonomic signature of time averaging in fossil assemblages. Traditional thin-section analysis of marine vertebrate (cetacean) bone reveals that both bone microtaphonomic damage and authigenic minerals infilling bone provide complimentary records of early diagenetic histories (i.e., recording bone burial environment). Importantly, these records persist in the face of later diagenetic and modern processes that continue to alter the fossil. I further find that fossils from highly time-averaged settings (due to sediment starvation or erosion) display poorer preservational condition than fossils buried during comparatively rapid sedimentation. The occurrence of mixed environmental signaling at the maximum flooding surface, suggesting evidence of a higher-order cryptic sequence boundary, prompts more questions: at what rates do taphonomic features develop, and how sensitive are they to different environments? To answer these questions, I turn to natural experiments (bones accumulating on modern landscapes) to quantify taphonomic change across the last several thousand years. By evaluating changes in taphonomic condition of bones across a latitudinal gradient, I am exploring how temperature influences the rate and mechanisms of taphonomic change, which not only provides new foundational insight into taphonomic processes relevant to the fossil record, but develops assessments of historical records available for conservation paleobiological applications.