KENT, DENNIS V., W. K. WITTE, and P. E. OLSEN, Lamont-Doherty Geological Observatory of Columbia University, Palisades, NY

ABSTRACT: Late Triassic to Earliest Jurassic Geomagnetic Polarity Sequence from the Newark Continental Rift Basin

The Newark Continental Rift Basin contains a very thick section of lacustrine and fluviatile sediments that spans at least 25 million years of the Late Triassic (Carnian) to earliest Jurassic (Hettangian). The section is apparently complete and records lake level (climatic) variations interpreted as Milankovitch cycles that provide a basis for detailed stratigraphic correlation as well as chronostratigraphic control with an internal resolution of better than 20,000 years. Outcrop is sporadic but the gently tilted section has recently been continuously cored under an NSF-funded project in cooperation with Amoco Production Company SHADS group. Nearly 20,000 feet of 2.5 inch diameter rock core was recovered from offset six drill sites, with an overall core recovery of 99.9%. Evidence of he full range of climate cyclicity predicted by celestial mechanics, including cycles with periodicities of 20,000, 100,000, 400,000, and 2,000,000 years, is already evident in the variations of physical and biotic properties of the cores. A magnetostratigraphy consisting of 35 normal and reversed polarity intervals, ranging from less than 30 feet to over 1000 feet in stratigraphic thickness and with an average duration of about 750,000 years, has been delineated based on complete demagnetization analysis of samples taken at nominal nine foot intervals. The lateral continuity and internal consistency of magnetozones and lithologic cycles within stratigraphically overlapping portions of cores more than 40 km apart provide evidence that these properties were acquired close to the time of d position. The Newark Continental Rift Basin cores should thus yield a complete reference sequence of Late Triassic to earliest Jurassic geomagnetic reversal history with a temporal resolution, based on Milankovitch cyclicity, that is comparable to Cenozoic polarity time-scales.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.