STARVED RIPPLES AS FAUNAL TRAPS. COLLECTION OF NOVEL DEPOSITS IN THE SUNDANCE FORMATION OF NATRONA COUNTY, WYOMING

Starved ripple deposition can act as a trap preserving small fossils on the lee side of the ripple structures. In starved ripples the sand or larger sediment is eroded from the stoss side of the ripple structure and then it is deposited on the lee side. Starved ripples may be preserved if it is then blanketed by finer grain mud. The starved ripple deposits in the Sundance Formation have been found to contain both vertebrate and invertebrate debris. Shark teeth and fish teeth have been found with regularity. The deposition matrix is made up of disarticulated crinoid pieces consisting of stem and feeding arms. Isolated teeth are found within the finer matrix on top of the crinoid assemblage mass. The heavy teeth may have collected within the trough of the ripples along with heavy sediments either reworked from the underlying mass or washed in by wave and current action causing objects to drop out of suspension. There is a small amount of grain size change in the sediment surrounding the debris. However, the fine-grained fill matrix does not contain the normal amounts of pelecypod shell debris and belemnite guards of less than 2mm. This debris is relatively common in the sandy-shale of the Sundance Formation. The teeth are from both hybodont sharks, either Hybodus or Asteracanthus and unidentified fish. Isolated fish bones and arthropod material have also been found. This material was previously known only from scattered and limited remains the Stockade Beaver Member of the Lower Sundance Formation and gastric contents of marine reptiles from the Redwater Shale of the Upper Sundance Formation. The tiny delicate fossils found in an unexpected collection point such as these deposits can give more detailed view of this paleoenvironment.