LOWER-MIDDLE PALEOZOIC STRATIGRAPHY AND SEDIMENTATION, MUD SPRINGS MOUNTAINS, SIERRA COUNTY, NEW MEXICO

In the Mud Springs Mountains, Sierra County, NM, the lower-middle Paleozoic succession is 377 m thick and divided into: Upper Cambrian-Lower Ordovician Bliss Fm, 54 m; Lower Ordovician El Paso Group--Hitt Canyon Fm (140 m) and McKelligon Limestone (36 m); Upper Ordovician Montoya Fm--Cable Canyon Sandstone (6 m), Upham (19 m), Aleman (46 m) and Cutter (39 m) mbrs; and Devonian Percha Fm (38 m). The Bliss Fm rests on Precambrian basement and is dark-colored sandstone, siltstone, shale and rare, thin, fossiliferous carbonate beds. Sandstone sedimentary structures are horizontal and ripple lamination, trough crossbedding and rare herringbone crossbedding, indicating deposition in a tidally-influenced, shallow marine setting. The lower part of the Hitt Canyon Fm is brownish, dolomitic siltstone-sandstone with ripple lamination, rare crossbedding and common bioturbatation, and limestone with crinoidal debris. The upper part is gray, bioturbated limestone, intercalated crinoidal limestone and massive, stromatolitic limestone. The Hitt Canyon Fm is of shallow marine origin, with siliciclastic influx in the lower part. The McKelligon Limestone is bedded and massive, partly cherty limestone, commonly bioturbated (subtidal). The Cable Canyon Mb is massive and crossbedded sandstone, probably of shallow marine origin (shoreface). It has an erosional contact on the underlying Hitt Canyon Fm. The overlying Upham Mb starts with sandy dolomite, grading into thick-bedded and cherty dolomite (deepening upward). The Aleman Mb is mostly cherty dolomite. The Cutter Mb starts with a thin carbonate conglomerate, overlain by laminated, bioturbated dolomite with rare chert. A massive chert horizon (1.5m) is present in the lower part. The Devonian strata should be termed Percha Fm. The lower part (“Oñate”) is marly shale with intercalated thin, marly limestone beds in the lower part. In the middle small coral colonies and very fossiliferous (brachiopods, crinoids, solitary corals, bryozoans) limestone nodules and shale occur. In the upper part thin limestone beds are intercalated. The upper part of the Percha Fm (“Sly Gap”) is marly shale with small, locally abundant limestone nodules and intercalated nodular limestone containing brachiopods. These marine strata are unconformably overlain by the Pennsylvanian Red House Fm.