DEPOSITIONAL ENVIRONMENTS OF THE MISSISSIPPIAN (CHESTERIAN) LOYALHANNA MEMBER OF THE MAUCH CHUNK FORMATION AT THE KEYSTONE QUARRY IN SOUTHWESTERN PENNSYLVANIA

The Mississippian (Chesterian) Loyalhanna Member of the Mauch Chunk Formation in Pennsylvania, and the equivalent Loyalhanna Limestone Member of the Greenbrier Formation in western Maryland, have been interpreted by various workers as either marine or eolian deposits. At the Keystone Quarry in southwestern Pennsylvania (near the town of Springs), the Loyalhanna Member is a 15 meter thick carbonate-cemented quartzose sandstone that overlies the Mississippian Burgoon Sandstone and is overlain by the Mississippian Deer Valley Limestone Member of the Mauch Chunk Formation. At this quarry, the Loyalhanna Member consists of the following four facies: (1) a medium- to fine-grained sandstone with mm-scale discontinuous laminations interspersed with cm-scale layers and lenses of coarse- to medium-grained sandstone; (2) a coarse- to fine-grained sandstone with alternating packages of mm-scale low-angle laminations (some of which coarsen upwards) and cm-scale high-angle cross-strata that downlap onto the low-angle laminations; (3) a 30-50 cm thick poorly sorted coarse- to fine-grained sandstone with zones of carbonate-coated grains, nodules with carbonate cement, and some more continuous carbonate horizons containing a few matrix-supported grains of quartz sand; (4) a basal coarse-grained sandstone with granules that fines upward to a medium- to fine-grained sandstone. Beds of this facies are characterized by a basal scour surface overlain by continuous to discontinuous laminations, cross-strata, and (or) structureless zones. These four facies are interpreted, respectively, as the deposits of sabkhas, eolian dunes, pedogenic calcretes, and fluvial (wadi) channels. At the Keystone Quarry, the overall facies succession from base to top of the Loyalhanna Member is as follows: eolian dune, sabkha, eolian dune, pedogenic calcrete, sabkha, eolian dune, and fluvial (wadi) channels. These facies suggest that the climate was arid or semi-arid during deposition of the Loyalhanna Member.