USING GEOGRAPHIC INFORMATION SYSTEMS (GIS) TO SYNTHESIZE THE BIOSTRATIGRAPHY OF CRETACEOUS AND PALEOGENE FRESHWATER MOLLUSKS IN EASTERN MONTANA, USA

The existing paleontological locality and specimen databases at the University of North Dakota comprise data from several thousand freshwater mollusk localities, including detailed geographic, stratigraphic, and taxonomic information for a wealth of sites in eastern Montana. These data have been utilized in the past to answer specific stratigraphic and ecological questions, but no general model has previously been produced. Here we use GIS to synthesize existing freshwater mollusk locality and taxonomic data to make it easier to understand for analyses, with the aim of answering several specific species-based questions.

Using a queryable GIS database of localities with stratigraphic data and specimen taxonomic information, biostratigraphic intervals can be characterized at a submeter- or lithosome-unit-scale across the study area according to distance from major stratigraphic contacts and the K/Pg boundary. These intervals form the basis of the model and can be correlated with other rock marker contacts and time unit boundaries.

Plotting relatively densely distributed, stratigraphically controlled mollusk localities over the study area can result in a more detailed geologic map than previously published, improving the planning process for future prospecting of new localities in specific geologic units and assessing the validity of existing maps.

Summarizing the density of localities, where species of interest are found at narrowly defined intervals, is the first step in being able to statistically determine the change in abundance of these species through a specified stratigraphic interval. Inclusion of the relative abundance of specimens of taxa collected at each locality improves these analyses.

Illustrating the distribution of localities graphically in GIS as a series of stratigraphic slices makes the identification of outlying specimen identifications straightforward. Identified specimens that are far outside the known stratigraphic or geographic range of a particular taxon, if properly assigned, can lead to future work in that area.

GIS allows the construction of a graphical interface to view such data in order to make them more understandable at a glance and to spark curiosity, even for researchers who are relatively unfamiliar with freshwater mollusks in this area or in general.