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A dolomitized shelfedge hardground in the northern Gulf of Mexico

Sedimentary Geology

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Abstract

An elongated calcareous hardground occurs on the shelfedge northeast of the Mississippi Trough. High-resolution seismic reflection profiles show that the hardground is in 90-110 m of water, is 70-250 m wide, at least 2.3 km long, and of low relief (5-10 m). The hardground is composed of dolostone and coquinoid limestone, and exhibits a dead biofacies of nodular and encrusting calcium carbonate-secreting organisms that are significantly different from those forms living in the adjacent unconsolidated sediments. Cementation of the hardground substrate by primary dolomite was initiated during early diagenesis close to the sea floor and progressed by concretionary growth under an interstitial environment partially open to marine molecular fluxes. The bicarbonate necessary to form the dolomite came from an admixture of isotopically light thermogenic and sedimentary organic carbon sources and an isotopically heavier marine source. Exposed surfaces of the dolostone, which have been heavily bioeroded, are covered by an oxidized, goethite-rich, reddish-brown rind. The coquina is primarily composed of whole and fragmented mollusk shells and was deposited in a higher-energy environment than the precursor sediments of the dolostone. The hardground was preserved during the Holocene transgression because of its lithified nature and the top has been intermittently swept free of finer detritus by current action. ?? 1990.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
A dolomitized shelfedge hardground in the northern Gulf of Mexico
Series title:
Sedimentary Geology
Volume
66
Issue:
1-2
Year Published:
1990
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Sedimentary Geology
First page:
29
Last page:
44
Number of Pages:
16