Miocene “Kingshill Seaway” —a Dynamic Carbonate Basin and Shelf Model, St. Croix, U.S. Virgin Islands1
H. G. Multer, S. H. Frost, L. C. Gerhard, 1977. "Miocene “Kingshill Seaway” —a Dynamic Carbonate Basin and Shelf Model, St. Croix, U.S. Virgin Islands", Reefs and Related Carbonates—Ecology and Sedimentology, Stanley H. Frost, Malcolm P. Weiss, John B. Saunders
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Deposition of pelagic chalk, turbidites, debris flows, and calcareous sandstone of the Kingshill Marl resulted from a variety of sedimentary processes active in an open basin and adjacent shelf in central St. Croix, U.S. Virgin Islands. Foraminiferal, coral, and nannoplankton index-fossil evidence indicates an age for the Kingshill ranging from middle early Miocene to middle Miocene.
The dominant lithology of the Kingshill is a bedded sequence of alternating (1) porous, pale orange, pelagic, biogenic chalk and (2) sandy to conglomeratic, light brown, terrigenous and ben-thic, skeletal marl. The latter unit represents periodic turbidite and debris flows (containing 0.5 m terrigenous bed-rock blocks and shallow-water coral boulders) that moved from shelf environments into adjacent deep basins. A third, less common, rock type is a basin-margin facies consisting of biosparites containing a wide variety of marine invertebrates and algal skeletal constituents.
Shallowing of the southern part of the Kingshill Seaway is indicated by the appearance of foraminiferal (Amphistegina) biosparites which appear to be truncated by younger Tertiary carbonate rocks.
Core analysis of carbonate sediments being deposited in the basin margin and adjacent open basin off St. Croix reveals lithologic characteristics similar to those of Miocene rocks. The origin of today’s sediment is believed to involve processes which were also responsible for Kingshill deposition (pelagic fallout, turbidity and debris flows).
The Kingshill Marl has retained much of its original porosity because the framework of plank-tonic foraminiferal tests has not collapsed. Subsequent carbonate loss by solution leaching far exceeded redeposition of calcite cement, leaving a relatively porous marl.
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Reefs and Related Carbonates—Ecology and Sedimentology
Studies in Geology 4: Reefs and Related Carbonates–Ecology and Sedimentology