Evolution of a coquina barrier in Shark Bay, Australia by GPR imaging: Architecture of a Holocene reservoir analog

The Holocene hypersaline carbonate system in Shark Bay, Australia is represented by microbial deposits (stromatolites and thrombolites) and a supratidal coquina beach ridge system which overlies the Pleistocene Bibra Formation and is prograding seaward, since 4500years ago, over supratidal–intertida...

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Bibliographic Details
Published in:Sedimentary geology 2012-12, Vol.281, p.59-74
Main Authors: Jahnert, Ricardo, de Paula, Osni, Collins, Lindsay, Strobach, Elmar, Pevzner, Roman
Format: Article
Language:English
Subjects:
Architecture
Bivalve beach ridge
Bivalvia
Construction
Coquina ridge
Deposition
GPR
Holocene deposits
Holocene reservoir
Marine
Microorganisms
Reservoirs
Ridges
Sea level
Shark Bay
Sharks
Storms
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Summary:The Holocene hypersaline carbonate system in Shark Bay, Australia is represented by microbial deposits (stromatolites and thrombolites) and a supratidal coquina beach ridge system which overlies the Pleistocene Bibra Formation and is prograding seaward, since 4500years ago, over supratidal–intertidal microbial deposits as a consequence of Late Holocene sea level fall, and the high volume of bivalve shells available. The extent, internal architecture and ridge constructional types of coquina deposits in this World Heritage area have not been previously investigated in detail by cores tied with geophysical images. Here we document external and internal architecture of the Holocene coquina system in southeast Hamelin Pool showing three depositional units which comprise the ridge system construction: (1) tabular layers complex, (2) convex-up ridges and (3) washover deposits. Bivalve skeletons represent almost the total amount of bioclasts with symmetrical semi-circular formats and valve sizes 5–9mm. Based on Ground Penetrating Radar (GPR) images the number of prograding layers present in each transect line varies from 252 to 433, which when compared with the measured 14C ages, shows lateral growth of the system at average rates from 10years per layer on proximal older sequences to 30years per layer in the younger and thicker packages which display more gentle inclination and sub-horizontal arrangement. Divergent orientation of tabular layers relates to changes in energy of currents and waves and involves time gaps and erosion. After earliest crest construction the system experienced a decrease in sea level (3600–3000 14C years BP) that left behind a sequence of parallel tabular layers with dip angles (>10° to
ISSN:0037-0738
1879-0968
DOI:10.1016/j.sedgeo.2012.08.009