New Mexico Geological Society Annual Spring Meeting — Abstracts

The Castner Formation of El Paso, Texas is the oldest Precambrian rock unit (Stenian, ~1260Ma) exposed in the Franklin Mountains of West Texas. This unit is now marble, but was initially a carbonate/clastic sedimentary succession and has been metamorphosed to hornblende-hornfels facies. Originally named by Harbour (1960) as the “Castner Limestone,” it contains exquisitely preserved bedding structures, including soft sediment deformation, imbricated edgewise conglomerates, and two types of stromatolites. Microbial Induced Sedimentary Structures (MISS) were first recognized in the Castner Formation by Pittenger (1994), who reported cryptalgal laminites. We describe several other MISS not associated with the previously described stromatolites. These MISS include gas domes, syneresis cracks, and possible discoidal microbial communities. In addition, we also offer an alternative hypothesis for the formation of edgewise conglomerates, namely that they may have formed due to microbial binding of individual beds, which has been reported elsewhere (i.e., Van Kranendonk et al., 2003).

References:

1. Harbour, R.L., 1960. Precambrian rocks at North Franklin Mountain, Texas. AAPG Bulletin, 44(11), pp.1785-1792.
2. Pittenger, M.A., Marsaglia, K.M. and Bickford, M.E., 1994. Depositional history of the middle Proterozoic Castner Marble and basal Mundy Breccia, Franklin Mountains, West Texas. Journal of Sedimentary Research, 64(3b), pp.282-297.
3. Van Kranendonk, M.J., Webb, G.E. and Kamber, B.S., 2003. Geological and trace element evidence for a marine sedimentary environment of deposition and biogenicity of 3.45 Ga stromatolitic carbonates in the Pilbara Craton, and support for a reducing Archaean ocean. Geobiology, 1(2), pp.91-108.