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South-Central Section - 48th Annual Meeting (17–18 March 2014)

Paper No. 5
Presentation Time: 10:40 AM

CONTINUOUS VOLCANISM THROUGHOUT THE DEPOSITION OF THE EAGLE FORD FORMATION IN SOUTH TEXAS


DARMAOEN, Shariva, Earth and Environmental Science, University of Texas at Arlington, 500 Yates Street, 107 Geoscience Building, Arlington, TX 76019, BASU, Asish, Earth and Environmental Science, University of Texas at Arlington, 500 Yates St, 107 Geoscience Building, Arlington, TX 76019 and TINNIN, Beau, Pioneer Natural Resources, 5205 N' Oconnor Blvd, Suite 200, Irving, TX 75039, sdarmaoen@gmail.com

Upper Cretaceous (including the Cenomanian-Turonian transition) volcanism is ubiquitous in the mixed carbonate and siliciclastic Eagle Ford Formation. A comprehensive dataset was collected from seven subsurface wells covering a distance of ~58 miles along a NE-SW strike within three contiguous counties in south Texas, Live Oak, Karnes and DeWitt. This study area parallels remnant Cretaceous shelf margins (Sligo and Edwards/Stuart City).

High precision geochemical analytical measurements for 14 rare earth elements (REE) and 10 major elements for a total of 272 Eagle Ford black shale samples were made. Immobile rare earth elements and select major elements are sensitive to sediment source and can be used as provenance indicators. The REEs are plotted normalized to chondrite and post-Archean Australian Shale (PAAS)-average upper continental crustal (UCC) composition. Chondrite normalized REE patterns show light REE enrichment and prominent negative Ce anomalies in all samples. The majority (85%) of the samples show a small negative Eu anomaly while the rest of the samples show no Eu anomaly. PAAS- normalized REE patterns illustrate that all samples are strikingly different from average upper continental crust, showing a light REE depletion, less of a negative Eu anomaly and a heavy REE depletion, all with respect to PAAS.

The geochemical data indicate two potential sources for the Eagle Ford sediments: volcanoclastic and detrital siliciclastic sources. Sediments of volcanoclastic sources reflect an intermediate to mafic igneous character in three of the seven wells, plotting as basalt and basaltic-trachy andesite in a Total Alkali-Silica diagram. Four wells reflect siliciclastic sediment influx from terrigenous sources diluting the signature of volcanism. Our geochemical data reveal that local paleo-environmental conditions were affected by influences from distal outside sources implying persistent volcanism throughout the deposition of the Eagle Ford Formation.

Session No. 12

S3. Late Cretaceous Tectonics, Magmatism, and Sedimentation of the South-Central Region
Tuesday, 18 March 2014: 8:00 AM-12:00 PM
Bella Vista Room (The Chancellor Hotel)
Geological Society of America Abstracts with Programs. Vol. 46, No. 1, p.35
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