101-3 Applying CT (Computed Tomography) to Characterize Middle Jurassic Thrombolites, Cody, Wyoming

Session: Paleontology, Biogeography/Biostratigraphy & Phylogenetic/Morphological Patterns

Presenting Author:

Authors:

Abstract:

The Sundance Sea of the Middle Jurassic in Cody, Wyoming, offers a glimpse into organosedimentary deposits known as thrombolites, to which this study applies CT to characterize surficial and tomographical traits, detailing the paleoenvironment. Past studies applied isotopic, lithological, and thin-section analysis to detail the formation of these thrombolites, which inhabited a region of maximum transgression. Identifying thrombolites, and by extension, all microbialites hinge on grain, cement, and density distribution within the deposit. The previous studies classified these microbialites as thrombolites based on the clotting of grains and the presence of unlaminated micritic cement.

In collaboration with the University of Texas' Austin UTCT lab, this study applied both CT and µCT to corroborate the previous thrombolytic identification, in addition to determining new characteristics such as grain distribution, density gradients, and surficial texture via 2D and 3D reconstruction. This study found that the thrombolites exhibited two distinct regions: an internal structure characterized by a primarily homogeneous density, and an outer crust with a semi-laminated zone, possibly featuring ooid and peloid accretion. It is postulated that the outer crust may either be the original texture (internal regions modified by diagenesis), or that a change in environmental conditions or benthic algal constituents occurred towards the end of the thrombolite’s active phase. CT and µCT revealed that while this method is effective in characterizing thrombolites, it is best applied in conjunction with additional methods to provide a holistic understanding of these thrombolites.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9771

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.