Once lacustrine deposition began, lakes fluctuated with orbital cycles; however, maximum lake depth (MLD) began shallow, rapidly deepened, and then slowly and exponentially shallowed toward the Triassic-Jurassic boundary.

These observations suggest a model based on the filling of trough,the simplest of which is a graben where the volumetric sedimentation rate (V) is constant and extension is uniform. First, S equals subsidence until hydrographic closure. Afterward, S=BV/L[(B^2)(D^2)]+{[2BVt(A-D)/L]^(-1/2)} (t=time after closure and A, D, B, and L are the final widths, depth, and length of the graben). The observed changes in MLD conform to predictions of this filling model. Half-graben are more complex, but similar patterns result. Major deviations reflect tectonic events.

One dramatic deviation occurred at the Triassic-Jurassic boundary, where S and MLD greatly increased. This coincided with massive tholeeitic magmatism, probably reflecting increased extension rates and marked basin asymmetry.

This model explains why Newark hydrocarbon targets are in strata of either the early Late Triassic or Early Jurassic, because those intervals were deposited by the deepest lakes.

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