T229 Mineralogy, Geochemistry, Petrology, and Volcanology Student Session

Wednesday, 25 September 2024
8:00 AM - 12:00 PM
207D

ORGANIC MATTER DEPOSITION AND PALEOENVIRONMENTAL CONDITIONS DURING THE TURONIAN-CONIACIAN ON THE COAHUILA BLOCK (NE MEXICO)

Paper number: T229-5
Program: Technical Sessions
Time: 8:50 AM – 9:05 AM

Authors

Abstract

Organic-rich limestone and mudstone were accumulated on the Coahuila Block (northeast Mexico) during the Turonian-Coniacian. They are represented by the Indidura Formation, which is equivalent to the Eagle Ford Formation deposited in the Sabinas Basin and South Texas. In this study, the paleoenvironmental conditions and hydrocarbon source rock potential of the Indidura Formation are investigated based on the sedimentological, petrographic, and geochemical analysis of the Las Brujas Section (80 m thick, Cuatro Ciénegas-Coahuila). The lower and middle parts of the section (0–42 m) consist of an alternation of black to dark-gray laminated mudstone and limestone (wackestone/packstone), poorly to moderately bioturbated (Bioturbation Index-BI: 1–3), with oxidized horizons, and pyrite occurring as disseminations and thin horizons. Furthermore, they contain abundant calcispheres and planktonic foraminifera, and exhibit high concentrations of TOC (up to 1.76%), detrital elements (Al, Ti, Zr), redox-sensitive (U, V, Mo), and productivity-sensitive (Ni, Cu, Zn) trace elements. The Tmax values from Rock-Eval indicate that the preserved organic matter is immature to the early mature (oil generation window, Tmax: 416 to 447 °C). The middle-upper part of the section (42–70 m) is characterized by an intercalation of laminated mudstone with bioturbated limestone (packstone, BI: 3–5) poor in organic matter (TOC < 0.17%) and low trace elements concentrations. A dramatic facies change occurs at the top of the section (70–80 m), represented by thick sandy-limestone with abundant inoceramids, common ammonites, and planktonic foraminifera. The results suggest that the accumulation of organic-rich sediments was favored by an increased detrital input accompanied with nutrients that led to eutrophication and anoxic/dysoxic bottom waters. The δ13Corg values range from -27.03 to -23.46 ‰. The resulting curve shows positive excursions that likely reflect the occurrence of Turonian–Coniacian episodes of accelerated global change, mainly the Late Turonian-Coniacian Event (LTCE). This event is characterized by a positive excursion of ~3‰ at the top of the section.

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-402553

© Copyright 2024 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.