Size differences of the post-anoxia, biotic recovery brachiopod, Dyoros sp., in Hughes Creek Shale (Carboniferous), Richardson County, Nebraska.

Abstract

Two localities of the Carboniferous Hughes Creek Shale in southeastern Nebraska contain both fossiliferous limestones and shales, as well as black shales interpreted as being deposited under anoxic conditions in ancient oceans. Fossils within strata above the anoxic layers represent life that had recovered from a local killing event. Examining the killing/recovery patterns on expanded, regional scales is made difficult due to the relative lack of good exposures between outcrops. Previous miscorrelations have occurred for the Hughes Creek Shale in two established collecting localities separated by only a few kilometers. Specimens of the brachiopod fossil, Dyoros sp., abundant at both localities were compared using the size frequency distributions of their length measurements. Null hypotheses of the equality of the medians and equality of the overall distributions were not able to be rejected, adding support to the current accepted interpretation of correlation for the two localities, allowing for future use of both for examining killing/recovery of life on expanded geographic scale.