ABSTRACT: Twenty Thousand Feet of Core from the Newark Continental Rift Basin Record 24 M.Y. of Milankovitch Cycle Control of Organic Shale Distribution

OLSEN, PAUL E., and DENNIS V. KENT, Lamont-Doherty Geological Observatory of Columbia University, Palisades, NY

During the winter and spring of 1990-1991, ten wells at six sites were continuously cored in the Newark continental rift basin of early Mesozoic age under an NSF-funded cooperative agreement with Amoco Production Company. The 19,610 ft of Late Triassic to Early Jurassic age core documents the evolution of the rift and shows a continuous pattern of cyclic deposition.

Moving window evolutive spectral analysis shows that 24 m.y. of the sequence show a linked hierarchical pattern of lacustrine cycles which average about 19,000, 23,000, 24,000, 90,000, 120,000, 400,000, 1,600,000-2,000,000, and 4,000,000-6,000,000 years. The first seven of these periods are explicitly predicted by the Milankovitch or Orbital theory of climate change. The cycles are developed as variations in organic content and organic type in mudstones of various fabrics indicating deposition in lakes fluctuating dramatically in depth.

The distribution of potential source rocks follows the Milankovitch pattern slavishly with significant accumulations of organic-rich shale occurring during peak deep-lake episodes. Monsoonal precipitation was the control on lake depth in the near equatorial Newark rift, and similar patterns and similar deterministic behavior is predicted for source rocks of other tropical continental rift systems.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)