Heavy-mineral reconnaissance off the coast of the Apalachicola river delta, northwest Florida: A summary and new interpretations

Two-hundred-and-fifty sediment samples were collected for heavy-mineral and textural analysis along the northwest Florida coastline from approximately 24 km offshore of Apalachee Bay to the same distance offshore of Pensacola Bay. The heavy-mineral suite characterizing sediments within this region consists of opaque minerals, kyanite, staurolite, tourmaline, zircon and rutile. Minor constituents of this suite include epidote, sphene, amphibole, sillimanite, garnet and leucoxene. The average heavy-mineral concentration within these sediments is approximately 0.12 wt.%. Specifically, the 2 to 3??? grain-size interval contains an average of 0.51 wt.%, whereas the 3 to 4??? interval contains an average of 4.39 wt.% heavy minerals. Note that the 3 to 4??? interval typically represents only 4% of the sample volume. There is a general westward increase in heavy-mineral concentrations throughout the study area. Superimposed on this regional trend, areas of maximum heavy-mineral concentration occur within sediments offshore of St. George and Santa Rosa islands. The primary source of sediments in the region is the crystalline rocks of the southern Appalachians. Granulometric analyses of these sediments reveal a westward increase in values of sample mean grain size, and decrease in standard deviation, and percent fines. It is postulated from these data, in addition to the interpretation of sample grain-size distributions, skewness, and kurtosis, that these inner continental shelf sediments are primarily fluvial in origin. These sediments have been transported to the shelf by the Apalachicola and surrounding major rivers during Pleistocene low sea-level stands. Data also indicate evidence of reworking by coastal or marine offshore wave processes. ?? 1989.