New insights into lithology and hydrogeology of the northern Newark Rift Basin

Abstract

AbstractThe marginal facies of the Triassic rift basins in the eastern United States are poorly documented, particularly on the hinge or hanging wall margins. This study presents a lithological description and multiscale petrophysical analysis of basement rocks, overlying marginal facies of the early synrift strata, and the basal contact of the Palisade Sill that were drilled and cored in the northeastern part of the Newark Basin, near its terminus. The expression of the Stockton Formation differs from that in the central basin in having thinner layers, with uncertain temporal relationship to the type area. The bottom 50 m is lithologically distinct with brick‐red to dark‐purple mudstones and sandstones, abundant gypsum‐filled fractures, and a thin zone with anomalously high uranium concentration, not associated with organic‐rich mudstones as other occurrences in the basin. The crystalline basement is apparently Fordham gneiss, overlain by a thin sandstone layer and a dark‐purple hydrophilic mudstone. Despite the abundance of coarse‐grained strata and multiple sets of tectonic fractures, hydraulically transmissive zones are sparse, and do not uniquely correlate to fracture and/or matrix characteristics. Enhanced transmissivity may exist along intrusion boundaries due to enhanced thermal fracturing, but more hydraulic data are needed to verify it. Comparison of petrophysical data in two boreholes ∼210 m apart shows no direct correlation of individual lithological units and their hydraulic properties, although the overall formation characteristics are similar. The results highlight challenges for outcrop correlation at the marginal edges of the rift basins and estimating reservoir properties of these heterogeneous formations.