Depositional Environment and Fossil Biota of a Thin Clastic Unit of the Kiowa Formation, Lower Cretaceous (Albian), McPherson County, Kansas

A thin unit (no more than 10 cm [4 in] thick) consisting of a conglomerate overlying a sandstone was discovered in shales of the Late Cretaceous Kiowa Formation (Albian) in a shale pit in McPherson County, Kansas. The two parts of this unit, called the classic unit, have a sharp contact. Both the conglomerate and sandstone are the result of storm activity. The sandstone appears to have been deposited by a relaxation flow, caused by a coastal setup, which was the result of storm-generated winds pushing surface waters towards shore. When the storm was over the winds died down, releasing the coastal setup and causing a storm surge that picked up lithic clasts and fossils from near a river mouth or estuary. The clasts consist of siderite and rhodochrosite nodules, which were forming beneath the sediment/water interface in reducing conditions caused by bacterial action. The clastic unit is in the Inoceramus comancheanus zone of the Kiowa Formation, which is a facies equivalent of the lower part of the Longford Member of the Kiowa. The Longford was derived from environments ranging from fluvial to near-shore, representing the edges of the transgressing Kiowa Sea. It is possible that the clastic unit was derived from similar deposits. Fossil vertebrates include many shark and ray taxa indicating a near-shore, brackish or fresh-water habitat, as well as turtles, plesiosaurs, crocodiles, and some unidentifiable reptile remains. Invertebrate fossils include lingulid brachiopods, which were a very common element of the fossil fauna from the clastic unit, pyritized shrimp, gastropods, an ammonite from the surrounding shales, and a few bivalve molds from the shales immediately above the clastic unit