A lithologic analysis of the Galveston beach sand with special emphasis on heavy minerals
Adams, Henry Clay
Rogers, John J. W.
Master of Arts
In this thesis, mineralogical and textural analyses of the sand-silt beach ,deposits of Galveston. Island, Texas, are presented, with special emphasis on. heavy minerals. It is the intent of the author; 1) to describe the min.eralogical composition. of each of the heavy min.eral suites, an.d to test the significan.ce of variations foun.d among 4 of the more dominant heavy minerals (zircon, tourmaline, hornblende, and garnet); 2) to describe the size-distributions of the zircon and tourmaline present in. each heavy mineral suite; and 3) to postulate means or con.ditions by which any mineralogical or size-distribution. variations may be explained. The present study is concerned with the sand beach which circumscribes Galveston. Isla-nd. The island is composed of recent sandy and silty sediment and occupies a position at the mouth of Galveston. Bay some 50 miles south of Houston. Inasmuch as Galveston Island is essentially an over-sized off-shore bar, which, for the most part, separates the Gulf of Mexico from Galveston Bay, the beaches that rim the island consist of two contrasting sedimentary environments. A frontal beach environment occurs on. the Gulf side of the island, whereas a back-bay environ.ment exists on the bay side. The present thesis is largely concerned with the determination. of any consistent differen.ces, mineralogical or textural, which might exist between. the beach sands formed under these differing conditions. Galveston. Island extends in a NE - SW direction and is approximately 30 miles long. Samples were taken on both sides of the islan.d at roughly 5-mile intervals. This sam.plin.g procedure made possible the grouping of samples in pairs, one from the front-beach and on.e from the back-beach, and. provided opportunity for a continuous check of variations as the laboratory work progressed. The sampling procedure and. sample grouping is explained. more thoroughly in the next section. This thesis is the third in a series concerned with the petrologic and lithologic properties of Gulf Coast sediments, the two previous being written by Powell (1957) and Dawson (1958).