PRESERVED ORGANIC MOLECULES IN THE OPECHE SHALE

The mid-Permian Opeche Shale is a subsurface unit underlying eastern Montana, northwestern South Dakota, and western North Dakota, part of the extensive system of Permian red beds found in the mid-continent of the United States. Previously, a detailed sedimentology study revealed features indicative of deposition in an ancient saline pan system, including thick bedded and chaotic halites, while fluid inclusion geochemical data suggested that this nonmarine system could have been extremely acidic. In the modern, such acidic evaporative environments have been found to contain a consortium of extremophiles, including halophilic Archaea and Bacteria. The pigments made by these halophilic microorganisms have been shown to be very amenable to Raman spectroscopic analyses both in lab tests of isolated molecules as well as in modern and near-modern environments. Using a hand-held DeltaNu Rockhound portable Raman spectrometer, we analyzed halite samples cored through the Opeche Shale. As halite is not Raman active, the only bands present are those from material within the core. In addition to some ferric compounds, we detected the presence of preserved organic molecules consistent with diagenetically-altered pigment molecules. The detection and identification of preserved biological macromolecules within these cores suggests a complementary line of evidence to the conclusions of earlier mineralogical and sedimentological studies that these rocks represented an evaporative environment, and highlight the utility of Raman Spectroscopy in characterizing the biota preserved in ancient rocks.