Radiolarians as Paleoenvironmental Indices for Exploration

Richard E. Casey, Carl O. Nelson, Amy L. Weinheimer

Aside from the classical uses of determining age and general environment (tropical, etc), radiolarians have been developed into extremely powerful tools as paleoenvironmental indices for exploration. Recently, phaeodarian radiolarians have been used as indices of thermal maturation and as indices of basin and bottom-water oxygen content. Polycystine radiolarians are currently used as paleodepth indices and are especially useful for determining the paleoshelf break. Reconstructions of the provenance of water masses, their directions of circulation, and the dynamics of these circulations have been made using polycystine radiolarians as indicators. These organisms have also been used for determining the presence and magnitude of paleo-upwelling and therefore as measurements of paleoproductivity. Recent uses of polycystine radiolarians as paleotemperature indicators suggest that short-term (seasonal and annual) variations may be detected from some rocks (Monterey siliceous facies) and that the frequency of these short-term variations may determine the major Neogene limatic regimes. These short-term paleotemperature variations may also be useful for enhancing the resolution of current radiolarian biostratigraphies. Recently developed radiolarian extraction techniques will allow the extension of these paleoenvironmental interpretations into the older and altered Monterey rocks that have previously escaped firm paleoenvironmental interpretations (as well as firm biostratigraphic dating, which should also be cured by these radiolarian extraction techniques).

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.