ABSTRACT

Sarasota and Little Sarasota Bays are shallow, coastal bays located landward of a Holocene barrier/inlet complex on the west-central, microtidal Gulf coast of Florida. Sediments presently accumulating in the bay consist of 1) fine to very fine quartz sand contributed from the Gulf shoreline during storm-generated washover, through tidal inlets, and from reworking of older deposits; 2) fine sand to pebble-sized quartz and phosphatic sediment contributed by Tertiary and Pleistocene deposits; 3) biogenic carbonate debris which is produced within the bays and/or derived from the Gulf of Mexico; 4) clay minerals derived from weathering of Tertiary and Pleistocene carbonates and clays; and 5) particulate organic debris. Interpretations from 51 vibracores from throughout the bays have enable delineation of four major depositional sedimentary facies resulting from specific environmental conditions: protected bay, open bay, tidal delta/washover, and storms. Bedrock in the area ranges from 0 to about -8 m MSL and is largely responsible for the areal configuration of the bay and the location of the barrier islands.

The Holocene stratigraphy of both bays has been greatly influenced by the passage of major hurricanes which carried large volumes of sand and shell gravel into the bays. At least four of these storms are documented in these cores. Three storm units from Sarasota Bay have been radiocarbon dated at 2,270, 1,320 and 240 years before present (YBP). Historically-documented severe hurricanes influenced this coast in 1848 and 1921. Hurricanes interrupted the normal, low energy, slow deposition in the bays and caused inlets to open and close.

Three storm-generated sedimentary facies are identified: 1) a graded storm facies which is composed of conspicuously fining upward units ranging from sandy shell-gravel to slightly shelly quartz sand, 2) a homogenous storm facies consisting of homogenous and relatively thin shelly-sand and gravel units, and 3) a fluvial storm facies which is muddy and generally free of shells representing terrigenous influx from runoff.