Abstract/Details

Lateral variability of facies and cycles in the Furongian (late Cambrian) carbonate platform: an example from the Big Horse Member of the Orr Formation in western Utah, U.S.A.


2011 2011

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Abstract (summary)

Carbonate depositional cycles and sequences have been proposed to be formed by glacioeustatic sea-level changes. This mechanism would be questionable during times of high atmospheric CO2 and negligible continental ice sheets such as the supergreenhouse time in the Furongian (Late Cambrian), during which limited glacioeustatic sea-level changes would be expected. A detailed sedimentological study of the Furongian Orr Formation in western Utah is aimed at testing the hypothesis that, under supergreenhouse climate conditions, most meter-scale carbonate cycles may have been formed through autocyclic processes and thus they should be laterally variable. The research was conducted in a small area (< 1.2 km2</super>) where excellent exposure permits lateral tracing of key surfaces and facies.

The Big Horse Member of the Orr Formation in the study area mainly consists of shale, siltstone, cryptic microbialites, thrombolites, wackestone, and cross-laminated oolitic grainstone/packstone that were deposited from deep subtidal to supratidal environments. Meter-scale cycles are expressed by shallowing-upward trends with subtidal shale/siltstone at the base and supratidal microbialites with desiccation cracks, dissolution cavities, and karstic breccias at the top. Among the seven closely-spaced sections with traceable marker beds, the cycle numbers vary and the thickness of individual cycles change from 2 m to 36 m. Individual cycles are found to change within a few hundreds of meters to non-cyclic interval or, in some cases, several cycles merge into a single cycle within 200–1100-meter distance. However, two stratigraphic discontinuities marked by intensive subaerial exposure were traceable among sections. These features suggest that meter-scale cycles of the Big Horse Member were mainly formed by autocyclic process through interactions among tidal island aggradation, local carbonate production rates, and tectonic/thermal subsidence. Forced regression during times of high carbonate production formed the laterally persistent discontinuities, but their duration may have varied, with significant lag time recorded in some sections.

Indexing (details)


Subject
Geology;
Geochemistry
Classification
0372: Geology
0996: Geochemistry
Identifier / keyword
Earth sciences; Big horse member; Carbonate; Cycle; Greenhouse; Late cambrian; Western utah
Title
Lateral variability of facies and cycles in the Furongian (late Cambrian) carbonate platform: an example from the Big Horse Member of the Orr Formation in western Utah, U.S.A.
Author
Widiarti, Ratna
Number of pages
66
Publication year
2011
Degree date
2011
School code
0506
Source
MAI 49/06M, Masters Abstracts International
Place of publication
Ann Arbor
Country of publication
United States
ISBN
9781124735993
Advisor
Jiang, Ganqing
Committee member
Campbell, Felicia F.; Hanson, Andrew D.; Rowland, Stephen M.
University/institution
University of Nevada, Las Vegas
Department
Geoscience
University location
United States -- Nevada
Degree
M.S.
Source type
Dissertations & Theses
Language
English
Document type
Dissertation/Thesis
Dissertation/thesis number
1495551
ProQuest document ID
879337451
Copyright
Database copyright ProQuest LLC; ProQuest does not claim copyright in the individual underlying works.
Document URL
http://search.proquest.com/docview/879337451
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