2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 135-11
Presentation Time: 9:00 AM-6:30 PM


ANDESKIE, Anna Sofia1, EICHENLAUB, Lynnette A.2 and BENISON, Kathleen C.1, (1)Department of Geology and Geography, West Virginia University, Morgantown, WV 26506-6300, (2)Department of Geology and Geography, West Virginia University, 98 Beechurst Ave, Morgantown, WV 26506, asandeskie@mix.wvu.edu

The goal of this project is to determine if the Triassic red mudstones and evaporites of Northern Ireland formed in acid saline environments. We described for the first time the 591 m-thick Triassic Mercia Mudstone Group, as found in the Carnduff 2 core from County Antrim, Northern Ireland. This group includes the Glenstaghey, Knocksoghey, Pore More, and Collin Glen formations. The Mercia Mudstone Group is composed of halite-cemented red mudstone and bedded and displacive evaporites. The bedded evaporites include bedded halite and gypsum. Both bedded and displacive evaporites were rich in red mud. Soil slickenslides, blocky peds, circumgranular cracks, suspected root features, and reduction spots were observed in some red mudstones. Other red mudstones were massive. Other features observed include small-scale ripple cross-bedding, mud drapes over bedded halite and gypsum crystals, mudcracks, rip-up clasts, halite-filled dissolution pipes, hematite concretions, and late-stage sylvite veins.

These rocks were deposited in a terrestrial setting characterized by saline pans and paleosols. The main processes in saline pans are flooding, evapoconcentration, and desiccation. Flooding in the Mercia Mudstone Group is indicated by climbing ripple cross-bedding, mud drapes, and halite-filled dissolution pipes. Evapoconcentration is suggested by bedded halite and gypsum. Desiccation is indicated by mudcracks and rip-up clasts. Red mudstones with soil slickenslides, blocky peds, circumgranular cracks, and suspected root features are suggestive of paleosols. The massive red mudstone could have been eolian, flood deposited, or precipitated directly from lake water.

Our preliminary results suggest that the Mercia Mudstone Group formed in acid, saline environments. The presence of halite, gypsum, iron oxides, kaolinite, and the lack of carbonates are characteristic of modern and ancient acid lakes and adjacent environments. Halite is ubiquitous regardless of the facies, showing that surface waters and groundwaters were saline. Scarce fossils of low diversity in the Mercia Mudstone Group suggest extreme environments. Our ongoing studies of petrography, mineralogy, and fluid inclusions will focus on the confirmation of depositional environment, acidity, and salinity of the Triassic of northeastern Pangea.