Heavy-Mineral Zones of Louisiana and Texas Gulf Coast Sediments

Abstract

The method of sample preparation and the procedure for examination of the heavy minerals under the petrographic microscope are briefly outlined. The heavy-mineral assemblages characterizing five mineral zones in the subsurface Cenozoic formations of the Louisiana Gulf Coast are described and the variation in mineral assemblage which occurs with depth is illustrated by heavy-mineral well logs. Heavy-mineral assemblages from outcropping Cenozoic formations in Texas and Louisiana are described and graphically illustrated. Comparisons between the mineral assemblages in the formations at the outcrop and in the subsurface are made and interpreted. It is concluded that several distributive provinces of differing mineralogical composition contemporaneously contributed sediments to the coastal region. The data suggest that a substantial portion of the Cenozoic sediments in the subsurface of southern Louisiana was brought there not directly from the interior but from the east or west, or both directions, presumably by longshore currents. It is demonstrated that mineral-zone boundaries may transect formations and paleontologic horizons. For example, the base of the Kyanite zone is shown to transgress from Eocene strata in the interior into Miocene post-Discorbis zone sediments near the coast.