Late Cambrian microbial build-ups, Llano Area, Central Texas: A three-phase morphological evolution
Hopson, Heath H.
Droxler, André W.
Droxler, Dylan A.
Harris, Paul M.
KAUST DepartmentAli I. Al-Naimi Petroleum Engineering Research Center (ANPERC)
Physical Science and Engineering (PSE) Division
Online Publication Date2019-12-02
Print Publication Date2020-02
Embargo End Date2020-10-21
Permanent link to this recordhttp://hdl.handle.net/10754/660985
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AbstractAlthough Late Cambrian microbial build-ups were recognized in the Point Peak Member of the Wilberns Formation in Central Texas (USA) nearly 70 years ago, only a few studies focused specifically on the build-ups themselves. This study focuses on the interpretation of the regional (15 measured sections described in literature representing an area of 8000 km2) and local (field and drone photogrammetry studies in a 25 km2 area from within south Mason County) microbial build-up occurrence, describes their growth phases and details their interactions with the surrounding inter-build-up sediments. The study establishes the occurrence of microbial build-ups in the lower and upper Point Peak members (the Point Peak Member is informally broken up into the lower Point Peak and the upper Point Peak members separated by Plectotrophia zone). The lower Point Peak Member consists of three <1 m thick microbial bioherms and biostrome units, in addition to heterolithic and skeletal/ooid grainstone and packstone beds. One, up to 14 m thick, microbial unit associated with inter-build-up skeletal and ooid grainstone and packstone beds, intercalated with mixed siliciclastic–carbonate silt beds, characterizes the upper Point Peak member. The microbial unit in the upper Point Peak member displays a three-phase growth evolution, from an initial colonization phase on flat based, rip-up clast lenses, to a second aggradation and lateral expansion phase, into a third well-defined capping phase. The ultimate demise of the microbial build-ups is interpreted to have been triggered by an increase of water turbidity caused by a sudden influx of fine siliciclastics. The lower Point Peak member represents inner ramp shallow subtidal and intertidal facies and the upper Point Peak member corresponds to mid-outer ramp subtidal facies. Understanding the morphological architecture and depositional context of these features is of importance for identifying signatures of early life on Earth.
CitationKhanna, P., Hopson, H. H., Droxler, A. W., Droxler, D. A., Lehrmann, D., Kubik, B., … (Mitch) Harris, P. M. (2019). Late Cambrian microbial build-ups, Llano Area, Central Texas: A three-phase morphological evolution. Sedimentology. doi:10.1111/sed.12679
SponsorsThis research was a part of the Rice/Trinity Industry Microbial Consortium (funded by Shell, Statoil, Chevron and ConocoPhillips). Part of this research was possible because of newly accessible outcrops on private lands. We are grateful to the owners Mr and Mrs Don and Rosie Shepard and caretakers Mr and Mrs Mark and Priscilla Krauss of Eagle Ridge Ranch, and Mr and Mrs Gene and Patsy Zesch, Mr Scott Zesch for allowing us to conduct research on their ranches. We would also like to thank the reviewers, whose critical comments has helped us drastically improve this manuscript as well as Dr Jeff Dravis for his comments and suggestions throughout the research project.