HEAVY MINERAL ANALYSIS OF PECAN ISLAND, LOUISIANA CHENIER PLAIN

This study reports the preliminary results of a heavy mineral analysis of samples from Pecan Island and associated ridges on the Louisiana Chenier Plain. The goal of the study is to provide additional insight on the sources of the sand comprising the ridges. Chenier plains are multi-membered, progradational ridge-interridge mudflat sequences (Augustinus, 1989). Chenier plains develop when there is a large amount of mud supplied by a river and can be transported to a coastal location.

This study includes analysis of Pecan Island and the truncation of the attached cheniers including Cypress Point, Front Ridge, and Kochs Ridge. Cheniers east of the Mermatau River, which are truncated by Grand Chenier, were also analyzed. The Pecan Island trend is one of the most persistent chenier ridges. There have been several hypotheses proposed and tested on the development of Louisiana chenier plains. The various suggested sources of the sand grains include: the Mississippi River, especially the Teche sub-delta; the Mermatau and Calcasieu Rivers; and the reworking of older mudflat and chenier ridges.

Several liters of sand were collected from a depth of 0.5 to 2.0 meters at locations near the crest of the ridges, along the natural levees of the Mermatau, and from the Trinity Shoal area of Vermilion Bay. The samples were separated using sieves (very fine sand to coarse silt) and sodium polytungstate (heavy mineral separation). Qualitative analyses by energy dispersive X-ray analysis with grain mount on the SEM (Scanning Electron Microscope) garnet, tourmaline, ilmenite, sphene, titanium, apatite, biotite, and zircon were discovered. There were also various Ca-content pyroxenes and amphiboles. In the samples, minerals containing cerium and barium were found, which were unable to be identified at the present.

Determinations of sediment supply are defined once the heavy minerals are clustered according to texture, grain size, and chemical compositions. This should contribute to an improved understanding of chenier plain formation during the late Holocene.

This research is funded by GAEMP which is supported by NSF-OEDG award GEO-0303138.