DETERMINATION OF PROVENANCE OF CAT ISLAND SEDIMENT BY HEAVY MINERAL ANALYSIS

Cat Island, located offshore of Gulfport MS, is the westernmost barrier island in the Gulf Islands National Seashore. The unusual "T" shape of Cat Island is commonly interpreted as the result of westward longshore currents reworking the original shore-parallel island following the abandonment of the St. Bernard delta of the Mississippi River. The goal of this project is to use heavy mineral analysis to identify the provenance of Cat Island sediment and to improve understanding of the coastal processes responsible for the curious shape of the island.

Upper-shoreface sand samples were collected from 18 sites around the island. Carbonate grains were removed from the samples by washing in 10% acetic acid, and the samples were split into < 60 mesh and > 60 mesh size fractions. Heavy minerals were concentrated by differential settling in a 2.85 g/cc sodium polytungstate solution, and 300 translucent grains were identified in each sample.

The kyanite and staurolite content of samples from the shore-parallel part of the island ranges from 45% to 53% and averages 50%, with more kyanite and staurolite present to the east. Samples contained averages of 15% apatite, 13% zircon, and 20% other translucent minerals. The kyanite and staurolite content of samples from the crosscutting "T" ranges from 42% to 69% and averages 53%, with higher kyanite content at the northern and southern tips and higher staurolite content near the center of the eastern side. Samples contained averages of 11% apatite, 17% zircon, and 15% other translucent minerals. Garnet was absent from or in trace abundance in all the samples. The heavy mineral suite on Cat Island is similar to that found in sediments and on other barrier islands in the northern Gulf of Mexico.

Abundant garnet, epidote, and zircon and smaller amounts of tourmaline, kyanite, and staurolite characterize the heavy mineral suite of Mississippi River sediment. The heavy mineral suite that forms Cat Island implies that the most probable provenance of the sediment is the crystalline metamorphic region of the southern Appalachians.