Diagenesis of the Newark Rift Basin, Eastern North America

Late Triassic nonmarine strata in the Newark Rift Basin, eastern North Amer ica, accumulated in a subsiding half-graben prior to opening of the Atlanti c Ocean. These strata consist, in ascending order, of the Stockton, Lockato ng, and Passaic formations. Although different in specific lithology, these formations all exhibit diagenetic fabrics dominated by authigenic albite a nd analcime. These same minerals have a similar presence in Late Triassic ( Newark Supergroup) strata of other rift-related basins to the north, sugges ting that related authigenesis is Plot simply a result of local diagenetic factors. The basal deposit, the Stockton Formation, is composed of fluvial sandstone s and overbank mudstones, with nodular pedogenic calcite (calcrete). During burial, original micrite was first recrystallized into sparry calcite and then later subjected to partial replacement by authigenic albite, which is also present as overgrowths and void fillings in overbank mudstones. The Lo ckatong Formation contains organic-rich shales, carbonates, and evaporative mudstones deposited under cyclic conditions in laterally extensive lacustr ine environments. Analcime comprises up to 40% of these strata by volume, o ccurring within the matrix, as a replacement of original carbonates and eva porites, and as fillings in macrovoids, The overlying Passaic Formation is made up of massive red mudstones, evaporites, and local calcareous lacustri ne sequences. Evaporites are replaced by coarse-grained anhydrite together with some authigenic albite. A central question concerns the source for the Na, Si, and Al required for albite and analcime authigenesis. It is suggested that, in addition to alte ration of primary siliciclastic material, sodium in particular was supplied in two ways: (1) from high concentrations in original evaporative brines a nd groundwaters (Lockatong and Passaic formations); and (2) from dissolutio n of associated sodium-bearing evaporites (Lockatong and Passaic Formation) during diagenesis. It is proposed here that basin-sourced, Na-enriched bri nes circulated through the section over time. As albite is more stable at e levated temperatures relative to analcime, it developed in the lowermost st rata of the basin (Stockton Formation). Analcime is more prevalent in the o verlying Lockatong Formation.