2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 140-40
Presentation Time: 6:45 PM

GYPSUM, PYRITE, AND IRON OXIDES IN THE RIPLEY FORMATION, OKTIBBEHA COUNTY, MISSISSIPPI


KILLIAN, Courtney, Geology, Mississippi State University, 21 Ace Ave Apt 106B, Starkville, MS 39759, BRIDGES, Susan, Episcopal Collegiate School, 1701 Cantrell Road, Little Rock, AR 72205, KIRKLAND, Brenda L., Department of Geosciences, Mississippi State University, P.O. Box 5448, Mississippi State, MS 39762, MEEKS, Christina, Geosciences, Mississippi State University, 113 Prairie Ct, Madison, AL 35758, OLSSON, Ola, San Diego Unified School District, 2720 Gregory Street, San Diego, CA 92104, PIERCE, Patrick, Geosciences, Mississippi State University, 405 Mallory Lane, Starkville, MS 39759, TAVERNIER, Lyle, NASA, Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109 and WEREMEICHIK, Jeremy M., Department of Geosciences, Mississippi State University, 108 Hilbun Hall, PO box 5448, Mississippi State, MS 39762-5448

The intent of this study was to determine if microbes within the Ripley Formation in Oktibbeha County, Mississippi play a role in the formation of 2-3 cm thick layers of gypsum crystals, calcite, pyrite, and iron oxide. Students collected samples in the field and prepared them for petrographic and confocal imaging, as well as scanning electron microscopy (SEM) and XRD analysis. The outcrop studied was approximately 50 x 16 m exposing roughly 6.5 m of silty chalk. Gypsum crystals found near the base of the Ripley Formation at the surface of the outcrop appear to have formed in situ based on delicate crystal orientation. Pyrite nodules are abundant at the base of the outcrop as well as large (10-20 cm) Exogyra cancellata. XRD analysis revealed that pyrite nodules contain gypsum and quartz. Using SEM, gypsum crystals appeared to form underneath Cretaceous coccolith fragments. Pronounced dissolution of gypsum and pyrite crystal remnants is common, sometimes occurring along sharp interfaces directly opposite abundant amorphous organic matter. SEM images indicate an abundance of microorganisms. Fungal hyphae (>10 µm wide), filamentous bacteria (<5 µm wide), and dehydrated biofilm were found along with possible coccoid bacteria. XRD data show the presence of pyrite and gypsum, which suggest microbial influences on their formation. This research is applicable to studies of sulfate reducing bacteria, descriptive research on Mars, environmental hazards, mine waste, coal scrubbing, and acidic soils.

Session No. 140

T238. Sedimentary Geology: The Now and the Next Generations of Scientists (Posters)
Monday, 20 October 2014: 9:00 AM-6:30 PM
Exhibition Hall C (Vancouver Convention Centre-West)
Geological Society of America Abstracts with Programs. Vol. 46, No. 6, p.356
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