Abstract

Several outcrop belts of Wellington conchostracan-bearing beds were discovered in Harvey and Sedgwick counties, Kansas. Data of the present study indicate that these belts are restricted, relatively narrow, and discontinuous. In turn, this reflects the distribution and characteristics of the Leonardian ponds represented. These were small (in some cases puddle size), areally nonpersistent, and very shallow. A conchostracan-bearing horizon, the C 1 horizon, was found to be traceable throughout the 2-county area. At a critical exposure, (Annelly 1A), it was found to be 11+ or - ft. above the Annelly gypsum. At this same exposure, but nowhere else in the 2-county area, 2 younger clam-shrimp horizons were found. Once the interval above the Annelly of the C 1 horizon was established, it was possible to locate clam-shrimp beds at predicted localities. The biota associated with fossil clam-shrimp include: vertebrate remains (lizard scales, plates, teeth), arthropods (insects, ostracods, xiphosurans), mollusks (pelecypods, gastropods), plant remains (seeds, leaves, carbonized and silicified wood, charophytes, spores). New forms are figured and described. Variable salinity in, and differential evaporation of, contemporaneous Leonardian ponds can account for the observed sporadic occurrence of hopper crystals and cubic salt casts in clam-shrimp beds. A method for deriving maximum clam-shrimp occupancy (in years) in different contemporaneous Leonardian ponds is outlined. Three different types of events are postulated to account for the observed distribution of the fresh-water and/or brackish-water mollusks: speciation in small pond situations, connections of discontinuous ponds by temporary drainage, and marine invasion.

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