LATE PENNSYLVANIAN (MISSOURIAN, VIRGILIAN) AMMONOIDS FROM SOUTHEASTERN
NEBRASKA
   Roger K. Pabian , Conservation and Survey Division, IANR, University of
   Nebraska, Lincoln, NE 68588-0517; Darwin R. Boardman, Royal H. Mapes,
   Department of Geology, Ohio University, Athens, OH 45701

   Recent collecting activity has shown that ammonoids are much more common
in Nebraska than had been previously thought.  Pabian (1970) indicated four
genera to be known in Nebraska's Pennsylvanian-Permian section, but current
collections indicate at least 13 genera representing the families
Pseudohaloritidael; Thalassaceratidae, Gonioloboceratidae, Dimorphoceratidae,
Glaphyritidae, and Schistoceratidae are present.
   Ammonoid distribution appears to be facies controlled, and most specimens
have been recovered from the transgressive or offshore facies of the
cyclothem.  Mature ammonoids occur with more diverse faunas, including
coelenterates, bryozoans, brachiopods, clams, snails, arthropods, echinoderms
and fishes in the upper parts of the transgressive limestones.  Mature
ammonoid imprints odcur in the black shale facies of several Missourian
units.
   Ammonoids appear to be most abundant in Wabaunsee sediments where they
occur in the non-black facies of the offshore shales.  The amonoids are
pyritized (often altered to limonite) and occur as pre-nepionic to juvenile
growth stages preserved as internal molds.  Associated faunas inelude
bivalves, snails, brachiopods, trilobites, fish and plant remains.
   Several species, including Neodimorphoceras sp. cf.  N. texanum and
 Neoaganides sp. cf.  N. grahamense may prove to be of considerable value
in correlating late Pennsylvanian units between Nebraska, Kansas, Oklahoma,
and Texas.