Geological Sciences

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    The Wrong Way Glacier in the Sixmile Creek Valley, Tompkins County, NY
    Karig, Daniel E. (2024-02-07)
    The Sixmile Creek Valley, between Van Natta’s and the 30’ dams, have some post-Valley Heads features that are difficult to explain. Two ridges that nearly cross the valley and are convex downstream look very much like moraines deposited by a glacier that was flowing downstream, but this is seemingly impossible because ice flow during the last glaciation moved southward and up the Sixmile Creek Valley. A second enigmatic feature is exposures of sand and gravel that form isolated patches along the edge of the valley. These features were either ignored or misinterpreted in earlier publications but following the recognition of northward subglacial drainage after the Valley Heads period they were reconsidered, re-investigated, and reinterpreted. The interpretation presented here identifies the sand and gravel patches as remnants of deposits in subglacial R channels. This phase evolved into a tunnel valley in which the interglacial gorge was largely re-excavated, and which now forms the walls of the valley in most of the study area. The ridges formed after this excavation because they lie on the bedrock floor of the gorge and are identified as moraines because of their shape, their parallel flanks and the composition of till within them. Field relationships show that the northward subglacial drainage began shortly after the Brooktondale readvance, during the early part of the Mackinaw Phase. The duration of this phase was much less than 1000yrs long, indicating that all these events must have all occurred within the span of a few hundred years. The moraines require that ice in the Sixmile valley had separated from that in the Cayuga trough but ideas as to how and why this occurred are extremely speculative. Nevertheless, this lack of understanding does not negate the conclusion that the ridges are moraines formed from ice moving down the Sixmile Creek Valley.
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    Guide to the Sedimentology of Quaternary Sediments within and adjacent western Fall Creek Valley, Tompkins County, New York
    Jordan, Teresa (2023-03-10)
    Late Quaternary glaciation of south-central New York State generated accumulations of sediment in Tompkins County which are still unconsolidated, now mostly hidden beneath forests, fields, and towns. Elevations of the contact between unconsolidated sediment and Devonian bedrock imply that the ancestral position of Fall Creek valley west of 76.43° longitude, prior to Quaternary glaciation, trended west-southwest across what is now the plain between modern Fall Creek and Cascadilla Creek valleys. The fill of ancestral Fall Creek Valley records a complex mosaic of sediments accumulated under time-variable and spatially variable conditions. At five locations along the north wall of Fall Creek valley west of 76.433°W longitude and at two boreholes south of Fall Creek Valley, details of the texture, fabric, and bed architectures underpin interpretations of environmental conditions during deposition. This manuscript is a field guide to those sediments, which range in thickness from 25 m (80 ft) to 60 m (200 ft) overlying Devonian rock, and are either contemporaneous with the last widespread glacial cover of this area, the Valley Heads readvance, or predate the Valley Heads readvance. Through the 2.5 km (8200 ft) long sector of modern Fall Creek Valley reported here, a till that is attributed to the Valley Heads ice readvance occupies the upper valley wall. At the westernmost valley-wall section, about 30 m of sediment include a basal till and an uppermost Valley Heads till, between which sand deposits dominate with several meters of interbedded gray muds. The sands and muds were deposited from water with high degrees of suspended sediment load, potentially in a set of small proglacial lakes or pools at the front of a retreating glacier. At the Varna High Bank, three units record distinct environmental conditions. Below the 20-m-thick Valley Heads till, a 15-m-thick unit of sands and gravels was deposited by stream flow, with an upper interval made of a laterally continuous gravel distinguished by foreset beds to 10-m-height that record the merger of a stream into a deep pool or lake. Below a contact that is interpreted as a comparatively long-lived depositional lacuna, the basal 5-m-thick brown gravel also likely formed by stream flow. At the easternmost valley-wall section analyzed, three major units of differing depositional conditions again crop out. Valley Heads till caps the section, below which occur well stratified silty sands and well sorted gravels, in turn overlying a basal clay with floating cobble clasts that lacks internal organization. In the middle unit, the sands were deposited rapidly from flowing water with a high load of suspended sediment, and the gravel is interpreted to be glacial outwash. The basal clay and cobble unit probably reflects a sequence of two environmental conditions, first lacustrine deposition and then overriding by a glacier. At these three Fall Creek locations, the lower two units differ from those at their lateral neighbors, which is interpreted to mark a high degree of lateral variation of post-depositional preservation. The two boreholes, roughly 1.2 km and 1.3 km south of the westernmost valley wall exposures, penetrate unconsolidated sediment over Devonian bedrock that is similar in thickness (24 m) to more than twice as thick (60 m) as the Fall Creek valley Quaternary sediments. In both, a surficial till that is inferred to be Valley Heads is underlain by a 5-m-thick unit of very well laminated silty clay interpreted to be lacustrine. In both boreholes the next underlying unit is a matrix-rich till that persists to bedrock in one and to at least 30 m subsurface in the other. The nature of the remaining nearly 30-m-thick unit in the borehole where bedrock is deeper is poorly documented, including both gravels and sands, some subrounded to rounded, suggesting that the stack of sediments records important shifts of depositional conditions.
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    Karig, Daniel E. (2022-07-21)
    Fall Creek is the largest tributary to Cayuga Lake but it earlier had a much larger drainage, which included that of the Tioughnioga River above Cortland. This beheading must have occurred before the Erie Interstade. Several earlier synopses of the Fall Creek history called for a proglacial Freeville-Dryden Lake trapped behind ice in the Cayuga trough, draining either south of Dryden or into Cascadilla Valley. Recent LiDar imagery and field work have produced a very different post Valley Heads (VH) history. There is no evidence for Lake Freeville-Dryden but a large proglacial lake Freeville that drained into the VH ice front in South Cortland did exist between the peak of the VH readvance and a subsequent Brooktondale readvance, which marked the end of the VH period. This minor readvance was a glacial surge that resulted in eskers, a field of crevasse squeeze moraine and pitted outwash in the area around Freeville. The Fall Creek drainage after the Brooktondale readvance was subglacial into the Cayuga trough, but rapid ice retreat during that time led to the uncovering of the stream channel to the lake and its incision into the Quaternary infill, leading to the formation of the Holocene Fall Creek Gorge. The pre -VH history of Fall Creek is little known, but the earliest recognized element is a broad flat-floored bedrock valley that is probably pre-Wisconsin in age. A bedrock channel is incised into the floor of this valley at least as far upstream as Varna and is probably of Sangamon age. The oldest Quaternary sediment in the upstream high banks along the Holocene gorge is a lacustrine clay that has been mobilized into till, possibly during the middle Wisconsin. The clay is overlain by fluvial sand with an OSL age of about 28 ka, and thus pre LGM (Nissouri Stade). In these upstream high banks the sand is sharply overlain by glacial outwash, itself mobilized to till, most probably during the LGM ice advance. Another till, clearly of VH age, lies with either a sharp or gradational contact over the outwash/till. Downstream exposures along Fall Creek show very different Quaternary stratigraphies, with sediment sections between the Nissouri and VH tills, which contributes an argument for the limited extent of the Erie Interstade ice front retreat. The more downstream of the exposures reveal a fluvial to lacustrine section with low to moderate energy environments of deposition. Two OSL ages of a fine sand at this exposure gave ages of 20 and 22ka. The other, more upstream exposure is of an ice proximal varved lacustrine section, paleomagnetic declination measurements on which suggest an age of somewhat less than 18 ka. The ages and environments of deposition of these two exposures indicate that the Erie Interstade was oscillatory, a conclusion also reached in the Cayuga Inlet Valley. The varved section was likely deposited in the same lake as the coarse clastic foresets at the Varna high bank, not far upstream. The VH readvance covered the entire Fall Creek drainage. In addition to a surficial till there appeared to be a till-filled channel, expressed at high bank 1 that conveyed subglacial and englacial water to the ice front.
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    Karig, Daniel E. (2015-07-30)
    Discussion of the Quaternary geology of the Sixmile watershed is logically separated into two sections: the Sixmile-Willseyville Trough and the upper Sixmile drainage, both of which can be further divided into sub-units based on geological characteristics. The Sixmile Trough section displays evidence for 4 glacial advances based on morphologic and/or lithologic criteria. The oldest advance is associated with the broad U-shaped upper valley slope section and is possibly pre-Illinoian. The probable Illinoian age of an inner glacial trough is derived from the assumed Sangamon age of a very large interglacial gorge incised into the floor of that trough. The inner glacial trough is overlain by an array of mid- Wisconsin (Cherrytree stade) deposits that document a glacial advance that reached into the Sixmile Trough. An interstadial gorge was cut into the base of the Sangamon gorge, probably following the mid Wisconsin glaciation but before the Late Wisconsin glaciation, which overrode the entire area and overprinted most of the earlier glacial features.
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    Karig, Daniel E. (2004-05-20)
    The Tompkins County Hillview Landfill was located on the site of an older landfill that had no containment and partially overlay permeable glacial deposits. After its use by the County it was capped and monitored in accordance with NYS Department of Conservation regulations, but there still remained the possibility that leachate could escape downward into local aquifers and from these into major aquifers underlying Cayuga Inlet Valley. Following closure, a number of test and monitoring wells were drilled around the periphery of the landfill, most of which showed little or no leachate migrating from the site. A review of well data by the Hillview Landview Citizens’ Committee determined, however, that the DGC-2 well cluster, at the northeastern corner of the landfill, did show significantly elevated levels of volatile organic compounds and dissolved metals. Together with a presumed northward groundwater flow gradient, based on water elevations in existing wells, this information suggested the possibility of a contaminant plume escaping from the landfill.