About This Item
Share This Item
The Upper Triassic Lockatong Formation is composed of cycles of fine-grained sediments interpreted as lacustrine deposits. These sedimentary
cycles were deposited in the Newark basin formed during rifting events associated with formation of the present-day Atlantic Ocean. Sedimentary cycles consist of laminated black shale, thin-bedded mudstones with sinuous polygonal mudcracks, brecciated mudstones containing angular fragments of thin-bedded mudstone "float" in a red muddy matrix, massive mudstones with abundant millimeter-scale mud aggregates and analcime or dolomite void fillings. Black shale and thin-bedded mudstones indicate a shallowing perennial-lake environment. Other textures found in these cycles have been attributed to subaqueous dewatering mechanisms. Our study suggests that these textures are the result of subaerial exposure and soil-producing processes in an arid environment.
In modern playa deposits, brecciation results from superimposition of mudcracks and mudcrack fillings; massive muds result from repeated wetting and drying, vesicle development, and clay illuviation. Coatings, around grains and void walls, by aligned clays (cutans) and iron oxides are seen in both modern muds and ancient massive mudstones. These microfeatures increase upward in the ancient cycles in the same manner as recent desert soils.
Desert "soils" overlying lake deposits in the Mojave indicate a transition from pluvial Pleistocene modern arid conditions in which sedimentation is slow and sporadic. Similar periods of long, continued aridity may be inferred for the Lockatong, and other similar formations, in Triassic basins along the east coast of North America.
End_of_Article - Last_Page 272------------