BARAN, Janet ('00) (Advisor: Bruce Selleck)
Late Pleistocene (~13,500 ybp) kame terrace gravel near Norwich, New York was deposited by meltwater streams issuing from glacial ice that formed semi-continuous valley floor tongues during the wasting of the Wisconsin ice sheet. Coarse, well-sorted layers of gravel and sand deposited in contact with stagnant ice form irregular to flat-topped terraces with steep, angle-of- repose slopes into the valley floor. Quarry excavations exhibit slump-related deformation structures such as rotated bedding and soft-sediment folding and faulting. The gravel contains abundant clasts of local middle and upper Devonian sandstone and limestone clasts of the lower and middle Devonian derivation.
Calcite-cemented zones occur commonly in terrace gravel on the western margin of the Chenango Valley near Norwich, New York. Rinds of multilayer calcite cement up to 2 cm in thickness occur within grain-supported gravel overlaying matrix-rich gravel. These rinds are comprised of coarsely-crystalline, blocky to prismatic calcite and contain numerous internal truncation surfaces that mark discrete episodes of precipitation followed by partial dissolution. These cements are interpreted as phreatic in origin, forming when the pores are fluid-filled. Pendant, microstalactitic cement interpreted as vadose in origin occurs in association with the thick rind cements. Vadose cements also occur higher in the exposure as thin rims coating the undersides of pebbles near the base of modern soil weathering zone.
The coarse gravel midway in the airport exposure contains clasts of calcite-cemented gravel. These clasts resemble the in situ cemented gravel within the exposure, but were clearly transported and rounded after cementation. These clasts may document a pre-Wisconsin phase of cementation or the cements may have formed within the glacial meltwater depositional system.
Radiocarbon dating of two samples of thick rind cement produced ages of 4510 These ages represent the average age of precipitation of that multilayer cement, and document that most calcite precipitation occurred after deglaciation. The relatively young radiocarbon age also suggests that the bulk of carbon in cement carbonate was derived from post-Pleistocene organic carbon of soil zone origin, or directly from atmospheric carbon dioxide. Only small amounts of "dead" carbon from dissolution of limestone can be present in these cements. Stable isotopes of carbon (range -7.2 to -9.9 per mil PDB) and oxygen (range -6.6 to -8.6 per mil PDB) in the thick rind cements are consistent with precipitation of calcite form local groundwater( O~per mil SMOW), with carbonate derived form soil zone carbon dioxide with some admixture of atmospheric CO .
