Abstract The Newark Basin Coring Project (NBCP) has recovered over 6730 m of continuous core from 7 coring sites. Cores spanning the 4800 m of Lockatong and Passaic formations are characterized by cyclic lacustrine mudstone and shale, which reflect rise and fall of lake level in response to climatic fluctuations at intervals of 20,000 years and larger patterns of 100,000- and 400,000-year intervals. Sedimentary structures in the mudstones include: 1. Organic-rich laminites with thin, flat, continuous lamination; thick lamination with diffuse or irregular boundaries; silty or sandy laminae; or crystal-rich lamination. 2. Mudcracked, thin-bedded mudstone with lenticular sandstone layers; graded sandstone layers; mudstone layers with sharp contacts; muddy siltstone curls; or crystal-rich layers. 3. Massive mudstones with angular breccia fabric; vesicular fabric; rounded breccia fabric; root-disrupted fabric; or crystal-rich fabrics. These structures define five types of cycles: 1. Cycles dominated by thick, organic-rich laminites deposited in deep lakes and rounded breccias, reflecting deflated, salt-encrusted mudflats. 2. Cycles similar to the previous, but with more thin-bedded mudstone and massive mudstone with upward-fining crystal sequences reflecting saline mudflats. 3. Cycles with mudcracked thin beds grading to brecciated mudstone, then vesicular fabric reflecting shallow lakes drying up to dry playa mudflats. 4. Cycles similar to the previous, but with more organic-rich laminites or thin beds and root-disrupted mudstone at top, indicating wetter conditions and vegetation growth before lake transgressions. 5. Cycles dominated by root-disrupted mudstone and thin, organic-poor laminites or thin beds reflecting thick soils superimposed on shallow lake deposits. The abundance of each cycle type changes through the stratigraphic section, reflecting the change from arid conditions in a narrow basin upward to semi-arid to subhumid conditions in a broad basin. The use of climatic patterns and tectonic setting can provide important information toward modeling source and reservoir rocks in rift basin lacustrine deposits.

Abstract The Lockatong Formation lacustrine sequences are the most extensive Upper Triassic deep-lake deposits exposed in eastern North America. Sedimentation took place within tropical lakes in a developing rift basin. These lacustrine deposits and their sedimentary structures exhibit a generally upward-shallowing sedimentary pattern and follow an internal repetitive pattern of cyclicity. The sequences suggest that lake depth responded to continuing changes in climatic conditions, although the basinal bounding faults were also active during sedimentation and may have had some general control. The identified lithologies formed in these lakes are black and gray shales, carbonate-rich mudstones, siltstones, and evaporite-bearing mudstones. The authigenic minerals present are analcime, dolomite, and calcite. Petrographic and electron microprobe investigations suggest that (1) analcime formed both as a direct chemical precipitate from lake and groundwaters and as an early diagenetic mineral, due to the early alteration of original clay minerals by the increasingly concentrated alkaline waters; (2) the lacustrine calcites are primary and/or early diagenetic; and (3) dolomite also was formed penecontemporaneously during evaporative concentration of shallow groundwaters. These observations are supported by carbon and oxygen isotopic ratios of the carbonates taken from major sections of the Lockatong Formation, and show that variations in the stable isotope ratios closely match the lithological alternations of the Lockatong Formation. The sedimentary succession shows an overall upward trend of increased evaporation, upsection increase in evaporite development, and, with this, a concomitant enrichment in δ 18 O. The δ 13 C isotope ratio, on the other hand, remains quite constant throughout the section, having a value appropriate to lacustrine deposition.