Witte Hi Pt S P Geology

Deposits laid down by rivers flowing out from

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Unformatted text preview: awangunk Formation (fig. 5) show that the ancient rivers flowed in a northwesterly direction. This demonstrates that a mountain range to the east was the source of the Shawangunk sediments. Later, and after deep burial by younger materials, a silica-rich fluid cemented the sand and gravel, forming the rock that makes up the Shawangunk Formation. This tough cement also makes the rock very resistant to weathering and erosion. 6 The Bloomsburg Red Beds are of Late Silurian age and conformably overlie the Shawangunk Formation. The Red Beds are about 1400 feet thick, consisting of repetitively layered sediments 3 to 9 feet thick. Each sequence of layers typically has three parts. The lower part consists of gray to red, cross-bedded sandstone containing pebbles. It gradually changes into the middle part consisting of very thinly layered, finer-grained sandstone or siltstone that locally contains trace fossils. Cross-bedding in the sandstone layers shows that water currents flowed back and forth, suggesting that the Bloomsburg sediments were deposited under tidal conditions along the coast of a large inland sea. The upper part consists of red shale containing mud cracks, root traces, and evidence of soil formation. These features show that the sediment was exposed during short periods when sea level was lowered and the shoreline retreated seaward. The cycles of sedimentation show that sea level rose and fell many times during deposition of the Bloomsburg Red Beds. Regionally, fossil shells and marine animal burrows in the formation also show a change in depositional environment proceeding from continental, to nearshore, to offshore oceanic environments. Younger, carbonate rock, which lies outside the park, conformably overlies the Bloomsburg Red Beds, indicating a change to clear, warm shallow seas. Structure of the Rocks Compressional or pushing forces caused by the collision of continental plates hundreds of millions of years ago formed folds, faults, joints, and cleavage in the rocks that underlie the park. Folds...
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This document was uploaded on 03/21/2014 for the course GEOL 3265 at Kean.

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