EL TABAKH, MOHAMED E., Queens College (C.U.N.Y.), Department of Geology, Flushing, NY; B. C. SCHREIBER, Queens College (C.U.N.Y.) and Lamont-Doherty Geological Observatory, Pallisades, NY; and G. D. KARNEV, Lamont-Doherty Geological Observatory, Pallisades, NY

ABSTRACT: Diagenesis of the Upper Triassic Newark Rift-basin Sediments: Implications for Intrabasinal Fluid Flow and Hydrothermal Events

The sediments of the Upper Triassic Newark rift-basin of eastern North America are characterized by the presence of many different types of authigenic minerals. Diagenetic features and minerals observed within the coarse clastics of the basal sedimentary section include: calcite cementation, quartz, laumontite, and analcime overgrowths, feldspar dissolution with generation of secondary porosity, and late hematite cements. Black to grey shales and mudstones associated with lacustrine cycles in the middle of the section contain overmature organic matter, and pseudomorphs of aragonite and evaporitic minerals now composed of coarse calcite, and dolomite, with fine-grained analcime and low-temperature albite. Evaporitic sediments are replaced by fine to coarse-grained anhydrite, calcite, d lomite, analcime, and albite. Fluid inclusion studies of the coarse grained anhydrite within evaporite pseudomorphs indicate that the minimum temperatures of crystallization was 160-260 degrees C. Analcime to albite replacement identified in transects across the basin, also implies comparable alteration temperatures. The distribution of fission-track ages within the Newark basin vicinity define a regionally consistant pattern: apatite and zircon grains, both within the basin and the basement, have been completely reset to 150 Ma and 180 Ma, respectively, i. e., these ages are younger than the age of the host sediment/basement rocks. In contrast, fission-track ages from rocks along the basin border fault have either failed to be reset or are only partially reset. This shift in reset tempe atures from >230 degrees C to 120 degrees C across a 5-10 km wide zone of gently dipping sediments cannot be due solely to the heat-advecting effects of differential erosion and burial conditions. From these studies we conclude that the sediments within the Newark basin have experienced high-temperature, hydrothermal, fluid-flow events during and immediately after rifting.

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