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ABSTRACT: Anatomy of a Nearshore Mixed Siliciclastic-Carbonate Deposit, the Miami Limestone of Southeastern Broward County, Florida

MISSIMER, THOMAS M., ROBERT G. MALIVA, CHARLES W. WALKER, and ELIZABETH OWOSINA , CDMMissimer International, Inc., Fort Myers, Florida

Mixing of terrestrial siliciclastic sediments from the southern Appalachians and the tropical carbonate environments of the Caribbean occurred within the Miami Limestone of southern Broward County, Florida, to produce some unusual and perhaps unique rock types. Sediment compositions range from over 90% quartz with some minor occurrences of feldspars and other silicates to nearly 100% carbonates, containing a diverse number of locally-produced skeletal and non-skeletal carbonate grains. Transport of the siliciclastic component was via longshore movement from the north with most of the erosion-prone grains removed, but feldspar and hornblende grains occur in the sediments. Feldspar grains are rare or non-existent in the recent beach sands of southern Florida.

The bulk of the sediments were deposited in relatively high-energy beach and nearshore environments. A distinct correlation was found between depositional environments suggested by the skeletal carbonate grains and the grain size statistical analyses of the siliciclastic component. There was also a correlation between the occurrence of some marine cements and the sediment characteristics. The diagenetic history of the sediments included: early marine cementation, precipitation of blocky and poikilotopic calcite cements and concurrent aragonite neomorphism, and late dissolution of aragonite fossils. Although the studied cores encompass the current coastal mixing zone between freshwater and seawater, no evidence was found for dolomitization or other mixing zone diagenetic phenomena.


AAPG Search and Discovery Article #90908©2000 GCAGS, Houston, Texas