ABSTRACT: Distribution of Evaporites and Authigenic Minerals in the Newark Supergroup (Triassic-Jurassic), Newark Basin, New Jersey

EL TABAKH, MOHAMED, Graduate School C.U.N.Y., New York, NY, B. CHARLOTTE SCHREIBER, Queens College C.U.N.Y., Flushing, NY, and PAUL E. OLSEN, Lamont-Doherty Geological Observatory, Palisades, NY

The presence of a number of evaporitic minerals displaying diverse crystal morphology (primary, displacive, and replacive) and of numerous authigenic minerals within mudstones of the Newark Supergroup (Triassic-Jurassic age) indicates a complex sedimentological and diagenetic history. From studies of cores obtained by the Newark Basin Continental Drilling Project, we find that significant volumes of evaporites, now present as anhydrite and authigenic minerals such as dolomite, low-temperature albite, analcime, and calcite, are well preserved in a unique vertical distribution following the sedimentary cycles and subcycles of the Stockton, Lockatong, and Passaic formations. This distribution is a reflection of the synsedimentary evolution of basinal groundwater.

Petrographic, SEM, and XRD analyses show a complicated diagenetic history of the authigenic minerals that began forming as several different evaporative minerals growing displacively (syndepositionally) within the soft muds and the clays of lakes, playas, and mud flats. Later stage alteration has also played a major role in the development of these deposits, and a complex diagenetic sequence has affected these rocks including void-filling cementation, gypsum fi anhydrite transformation, recrystallization, and replacement by various silicates. The overprint of even later stage diagenetic fluid movements including deep circulating groundwaters and hydrothermal fluids left evidence of a complicated diagenetic history shown by the presence of zeolites, coarse void-filling dolomites, zoned fracture fillings (many containing dead oil), and sporadic late-stage mineralization. Rehydration and dissolution due to exhumation completes

the sequence of alteration, further overprinting the original sediments and resulting in a palimpsest-like picture.

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