1995 Articles

Late Triassic-earliest Jurassic geomagnetic polarity reference sequence from cyclic continental sediments of the Newark rift basin

Kent, Dennis V.; Olsen, Paul E.; Witte, William K.

The global nature of geomagnetic polarity reversals has made magnetostratigraphy an essential tool for precise correlation between widely distributed sections of rocks of different lithological and biotic facies. The best documented history of geomagnetic polarity reversals is for the Jurassic to Recent and is based on the analysis of numerous marine magnetic anomaly profiles from the global ocean (e.g., Cande and Kent, 1992; Gradstein et al., 1994). The relative spacing of polarity intervals established from the anomaly patterns is calibrated in time by correlation to magnetostratigraphic sections with biostratigraphy, radiometric dates, and cyclostratigraphy. Because of the absence of seafloor and hence marine magnetic anomalies, a precise geomagnetic polarity reference scale for pre-Jurassic time has been more difficult to develop. There has already been significant progress made for the Late Triassic by assembling relatively condensed or discontinuous marine (e.g., Gallet et al., 1992; 1993) and continental (e.g.. Molina-Garza et at., 1991) sedimentary sections, but thick, continuous magnetostratigraphic sections with good chronostratigraphic control are needed to construct a high resolution reference scale.