13 Advances in Sedimentology, Stratigraphy, and Geochemistry of Carbonates and Mixed Carbonate Clastic Systems

Tuesday, 14 March 2017
8:00 AM - 12:00 PM
Grand Ballroom B

ENVIRONMENTAL AND SEQUENCE STRATIGRAPHIC CONTROL ON MICROBIALITE MORPHOLOGY AND MICROFACIES IN A MARINE MIXED CARBONATE SILICICLASTIC SYSTEM, UPPER CAMBRIAN POINT PEAK FM., LLANO RIVER AND MILL CREEK, MASON COUNTY, CENTRAL TEXAS

Paper number: 13-5
Program: Theme Sessions
Time: 9:05 AM – 9:25 AM

Authors

Abstract

The Upper Cambrian microbiallites exposed near Mason serve as an excellent analogues for hydrocarbon rich microbial reservoirs offshore Brazil.

Alternating siliciclastic and carbonate facies and high-frequency oscillations in gamma ray depict high-frequency cyclic fluctuations in sea level and two additional lower-frequency oscillations that define depositional sequences. Siliciclastics were delivered into shoreline and shallow-marine environments during regression. Increasing carbonate proportions represent transgression. Detrital sand is reworked with skeletal and intraclastic carbonate in high-energy tidal channels and storm deposits. Glauconitic siltstone accumulated in lower energy intertidal and shallow subtidal environments. Flaser bedded heterolithic facies with reversing ripple forms, tidal bundles and desiccation cracks is interpreted to represent the intertidal zone on tidal flats. Biostromes composed of amalgamated low thrombolitic microbial mounds are associated with the heterolitihc facies and thus are interpreted to be intertidal.

Higher relief isolated “bread loaf mounds” in the lower Point Peak and larger microbial buildups and “reef complexes” in the upper Point Peak are associated with carbonate skeletal and oolitic grainstone and burrowed glauconitic siltstones interpreted to represent somewhat deeper subtidal environments and greater accommodation during transgressive phase of depositional sequences. However, the close association of intertidal facies indicates that relatively shallow conditions prevailed on the vast ramp even during transgression.

Both the biostromes and the breadloaf mounds are composed of a thrombolitic and micro-digitate columns and calcimicrobial framework. Siliciclastics and glauconite are incorporated in the microbialite biostromes and breadloaf mounds but not within the larger buildups and indicating that the microbialites thrive even in the presence of siliciclastics, but that with sufficient relief siliciclastics may be transported on the seafloor adjacent to but not overlapping the top of actively growing mounds. Thick buildups and “reef complexes” of the upper Point Peak are associated with the thickest skeletal and oolitic grainstone and maximum transgressive phase in the sequence stratigraphy.

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

doi: 10.1130/abs/2017SC-288844

© 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.