Paper No. 19-2
Presentation Time: 1:30 PM-5:30 PM
ORIGIN OF SAND AT CLAY PIT POND STATE PARK, STATEN ISLAND, NY, AN SEM STUDY
Clay Pit Pond State Park is located in the southern portion of Staten Island, New York. Within the park are limited surficial outcrops of brightly colored layers of brown to yellow sand, gravel, and multicolored clay outcrops of the Cretaceous Raritan and Magothy Formations. On Staten Island, these formations are disconformably overlain by layers of poorly to well-sorted Pleistocene gray to brown sand and gravel and red cross-bedded outwash sand from the Harbor Hill Terminal moraine. An SEM study was conducted of quartz sand grains from recently exposed deposits to determine their origin and depositional environment, as this area of Kreischerville was extensively quarried from 1858-1873 for its fine clay deposits. Sand samples were washed, dried in a kiln, and split into two portions. One sand portion was coated with gold and one was not in order to determine the best visible grain SEM morphology using the criteria of Whalley & Krinsley (1974) and Culver, Bull & others (1983). Using an FEI Quanta 250 SEM, quartz grains were examined for their overall surface morphology including roundness, angularity, conchoidal fractures, striations, v-shaped pits, chemical weathering solution pits. Glacially transported angular to sub rounded quartz grains typically have ridges, curved and straight grooves, striations, and show little or no chemical weathering effects as they are geologically young. Well rounded to sub rounded Cretaceous quartz grains have dish-shaped concavities that may indicate pressure solution from overlying layers from long-term burial as part of the Raritan-Magothy formation. In addition V-shaped pits within sub-rounded Cretaceous quartz sand is more indicative of their prolonged presence in a buried chemical weathering environment. Quartz grains examined in several samples ranged from round to sub rounded with rare angular to faceted grains and there is a lack of conchoidal fracturing and suggest their transport within a glacier or as part of moraine material. Based upon these preliminary criteria, we conclude that these outcrops consist of mixed deposits from both the Harbor Hill Moraine and the Cretaceous Raritan-Formation perhaps from past mining activities.