Ultimate Demise of Large Upper Cambrian Microbial Reefs (Mason County, Central Texas)

Singh, Pulkit; Droxler, André W.; Hopson, Heath Hilton; Khanna, Pankaj; Lehrmann, Dan; Droxler, Dylan A.; Rodelli, Daniel; Jovane, Luigi; Harris, Paul M.; Dravis, Jeffrey J.

doi:10.1130/abs/2016am-283255

Cited by 1 publication

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“…The shallowing event increased the siliciclastic influx as the shoreline advanced shelfward, subsequently leading to a decrease in carbonate content due to the negative effects of turbidity on the carbonate factory. Evidence of increased levels of siliciclastic influx, occurring at the end of Phase 1 is reported from James River (two samples of the silty unit onlapping Phase 1 reported 36% and 60% CaCO 3 ; Singh et al ., ; Hopson, ). Typically, these silts onlap the sides of Phase 1 build‐ups without interfingering, and never cover the full Phase 1 microbial reefs.…”

Section: Discussionmentioning

confidence: 97%

“…The ultimate demise of the upper Point Peak microbial reef complex is marked by a large influx of fine‐grained siliciclastics. The initial fine‐grained deposits onlapping the sides of the Phase 3 rinds contain as much as 84% siliciclastics (Singh et al ., ; Hopson, ), explained by closer proximity to the shoreline and a reduction in accommodation. This increase in turbidity in the water column would have limited light penetration and ended microbial growth.…”

Section: Discussionmentioning

confidence: 99%

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Late Cambrian microbial build‐ups, Llano Area, Central Texas: A three‐phase morphological evolution

et al. 2019

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Although 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 km 2) and local (field and drone photogrammetry studies in a 25 km 2 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.

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Section: Discussionmentioning

confidence: 97%

Section: Discussionmentioning

confidence: 99%