Abstract

Mixing of terrestrial siliciclastic sediments from the southern Appalachians and the tropical carbonate sediments of the Caribbean occurs within the nearshore Plio-Pleistocene sediments of southern Broward County, Florida, to produce some unusual and perhaps unique rock types. Eight primary rock types were recognized that are associated with specific depositional environments. Sediment compositions ranged from over 90% quartz with some minor occurrences of feldspars and other silicates to nearly 100% carbonates containing a diverse suite of skeletal and non-skeletal carbonate grains. Transport of the siliciclastic component was via longshore movement from the north with most of the erosion-resistant grains removed, but feldspar and hornblende grains occur in the sediments. No feldspar grains have been reported in the recent beach sands of southern Florida. Skeletal carbonate components were locally added from adjacent environments or transported via marine processes.

The bulk of the sediments were deposited in relatively high-energy beach and nearshore environments. A distinct correlation was found between depositional environments predicted 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.