New Mexico Geological Society Annual Spring Meeting — Abstracts

The middle Proterozoic Lanoria Formation is exposed in the Franklin Mountains of El Paso, Texas. It is at least 750 m thick and consists of metamorphosed sandstone, siltstone and mudstone. These strata were deposited in a variety of marginal marine paleoenvironments in a foreland basin of the Grenville orogeny. The age of the unit is constrained to the Stenian period using geochronology of detrital zircons, cross-cutting granites, and the overlying Thunderbird Formation. The fourth, unofficial member of the Lanoria Formation at NMMNH (New Mexico Museum of Natural History) locality 10809 contains abundant traces of microbial activity and mat-related structures. These can be described as follows: wrinkle structures (aff. Rugalichnus), multidirectional ripple marks, several types of syneresis cracks (elongate, spindle, and polygonal, and sinusoidal, aff. Manchuriophycus), mat roll-ups (and possible “cigar rolls”), gas domes, discoidal microbial colonies and associated merged gas domes, elongate microbial surface trails with levees, lobate radial projections (or tool marks), and impressions of filamentous extracellular polymeric substances. As part of an ongoing study of the microbial mat-related structures in the Lanoria Fm., we present new microscopic data. Microstructures found in thin section include floating grains, grain plucking, sinoidal structures, leveled laminating structures, shrinkage cracks, filamentous structures, laminated mica grain concentrations, and interstitial calcite. When combined with the macro-structures listed above, these microstructures confirm the existence of ancient microbial mats and their effects during sedimentation and lithification.