CARBONATE DEPOSITIONAL EVENTS IN EARLY MESOZOIC NEWARK RIFT BASIN LAKES: LITHO- AND CHEMOSTRATIGRAPHIC EVIDENCE FOR MILLENIAL-SCALE CLIMATE EVENTS?

The Newark Basin Coring Project (NBCP) cores (Kent and Olsen, 1992; Olsen and other, 1996) provide an opportunity to analyze high frequency litho- and chemostratigraphic changes within a well established, orbitally forced cyclostratigraphy. Here, we examine distinctive CaCO3 zones commonly found within the black clay/mudstone lithofacies (perennial lake) of seven precession cycles from the Nursery member of the Lockatong formation and the Warford member of the Passaic formation. Best preserved in the perennial lake facies, these carbonate zones persist into shallower lake facies despite desiccation and bioturbation processes. Spatial and temporal validity of the carbonate zones can be established given a 30% core overlap and the lateral distance between the seven NBCP cores necessary to achieve complete stratigraphic recovery. Distinctive carbonate zone patterns within well correlated precession cycles (e.g. Perkasie and Nursery members) can be traced across the Newark basin for at least 40 km. suggesting basin-wide depositional events. Inorganic chemostratigraphy (Ca/Al, Mn/Al, Ba/Al, Al/K and other trace elemental ratios) suggests that these zones are the result of rapid and strong lake turnover producing algal blooms. Though the carbonate zones have several lithologic textures, some of which are undoubtedly diagenetic, all begin and end abruptly. Our preliminary analysis of carbonate temporal distributions is based on the number of carbonate zones per precession cycle(12 ± 2) and the long-term sedimentation rate (ca. 165 m/my) from the magnetostratigraphy of Kent and Olsen suggests a millennial scale, quasi-periodic cyclicity. If our preliminary chemical and temporal data withstand more rigorous statistical analysis (in progress), the NBCP cores may preserve sub-precession-scale climate change indicators for middle-late Triassic time akin to those more commonly found in late Pleistocene and Holocene climate records.