Sedimentology and Provenance of Cat Island, Offshore Mississippi

F. L. Lynch, A. T. Pitalo, L. B. Barnhart, J. L. Clark, J. G. Harris, and D. W. Schmitz
Department of Geosciences, Mississippi State University, Mississippi

Cat Island, located offshore of Gulfport Mississippi 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.

High-energy upper- and middle-shoreface, surface and subsurface sands are composed of quartz and 0-5% potassium feldspar and plagioclase feldspar regardless of sample depth or location on the main shore-parallel island body or on the longshore reworked “T”. The translucent heavy mineral suite from these sands averages 50% kyanite and staurolite, and lesser amounts of apatite, zircon, and other minerals. Garnet is absent or in trace amount 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 from Cat Island implies that the most probable provenance of the sediment is the crystalline metamorphic region of the southern Appalachians.

Clay minerals from high-energy environments are rare, but where present are composed of subequal amounts (~10-20% each) of kaolinite, chlorite, mixed-layer illite/smectite and ~50% illite. Offshore muds recovered from beneath the reworked long shore sands consist of lesser amounts of kaolinite and chlorite (~10% each), and subequal amounts of illite/smectite and illite (~40% each).

AAPG Search and Discovery Article #90032©2004 GCAGS 54th Annual Convention, San Antonio, Texas, October 10-12, 2004