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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.

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