OSTRACODES AS A TOOL FOR UNDERSTANDING PALEOENVIRONMENTAL CHANGE IN PERMO-CARBONIFEROUS STRATA

Ostracode faunas from the Maritimes basin of Newfoundland and Nova Scotia, the Black Warrior basin of Alabama and Mississippi, and the Robledo Mountains of New Mexico have been used to develop and test a paleoenvironmental tool, which is based upon plotting ostracode faunas in ternary space. The tool has broad applicability to any Permian and Carboniferous, freshwater through shallow marine (shoreline to shelf edge), ostracode fauna and in the absence of other data may be predictive in nature. The tool operates at a sufficiently high taxonomic level so as to negate many of the taxonomic issues that often plague the effective use of late Paleozoic ostracodes. The tool is of particular importance in the study areas because transgressive/regressive cyclicity led to the deposition of sequences which contain fine-grained clastic sediments that may appear lithologically similar, or mixed carbonate-clastic assemblages many of which were deposited close to shoreline. By way of example: Shale sequences found in each of the study areas, which in outcrop may appear lithologically indistinguishable, can be shown to contain radically differing ostracode faunas in short vertical sequences. Such changes are indicative of variable paleoenvironmental conditions that are not discernable from the lithologies alone. Since the ternary diagram relies upon gross morphological characteristics it can be used by a non-specialist to interpret faunas from both subsurface and outcrop settings.