BALSAM, WILLIAM L.
Department of Geology, University of Texas at Arlington, Box 19049, Arlington, TX 76019

Abstract: Surface Sediment Distribution in the Gulf of Mexico Inferred from Visible Light Reflectance Spectra

Diffuse reflectance spectra were utilized to determine modern sediment composition, distribution, and sedimentary processes throughout the Gulf of Mexico. One hundred eighty six core top and grab samples were analyzed from 250-850 nm, from the near-ultraviolet (250-400 nm, NUV), through the visible (400-700 nm, VIS), and into the near infrared (700-850, NIR). The reflectance spectra were analyzed by taking the first derivative of the percent reflectance data at 10 nm intervals, assembling these first derivative data into a matrix, and then factor analyzing the first derivative matrix to produce factors that grouped covarying first derivative wavlengths. Factors were interpreted by comparing factor pattern curves to first derivative Curves for suspected sediment components and minerals. To assist factor interpretation, calcium carbonate-content analysis and smearslide sediment classification were performed on each sample. The most easily interpreted factors were produced by analyzing only the VIS and extracting seven factors which explained -98% of the cumulative variance. These factors are interpreted as 1) calcareous sediments, 2) glauconite, 3) kaolinite(?), 4) organic matter, 5) phosphorite(?), 6) hematite, and 7) goethite. The most interesting observation concerns the distribution of hematite, which appears to be transported from the rivers of south Texas (e.g. Rio Grande), across the shelf then eastward downslope along the base of the Sigsbee Escarpment. This eastward transport seems to be only explainable by bottom-current transport in currents flowing along the base of the Sigsbee Escarpment.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas