Browsing by Subject "Till"

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    Analysis of Antarctic glacigenic sediment provenance through geochemical and petrologic applications
    (Elsevier, 2017-05) Licht, Kathy J.; Hemming, Sidney R.; Department of Earth Sciences, School of Science
    The number of provenance studies of glacigenic sediments in Antarctica has increased dramatically over the past decade, providing an enhanced understanding of ice sheet history and dynamics, along with the broader geologic history. Such data have been used to assess glacial erosion patterns at the catchment scale, flow path reconstructions over a wide range of scales, and ice sheet fluctuations indicated by iceberg rafted debris in circumantarctic glacial marine sediments. It is notable that even though most of the bedrock of the continent is ice covered and inaccessible, provenance data can provide such valuable information about Antarctic ice and can even be used to infer buried rock types along with their geo- and thermochronologic history. Glacigenic sediments provide a broader array of provenance analysis opportunities than any other sediment type because of their wide range of grain sizes, and in this paper we review methods and examples from all size fractions that have been applied to the Antarctic glacigenic sedimentary record. Interpretations of these records must take careful consideration of the choice of analytical methods, uneven patterns of erosion, and spatial variability in sediment transport and rock types, which all may lead to a preferential identification of different elements of sources in the provenance analyses. Because of this, we advocate a multi-proxy approach and highlight studies that demonstrate the value of selecting complementary provenance methods.
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    Provenance Study of Reedy Glacier and West Antarctic Ice Stream Tills
    (2008-10-10T18:03:25Z) Kramer, Katie L.; Licht, Kathy J.; Swope, R. Jeffery; Barth, Andrew, 1958-
    In January 2007, 26 samples of till from 6 different moraines along the Reedy Glacier, East Antarctica were collected with the goal of differentiating between these samples and till collected from the base of the Whillans, Kamb, and Bindschadler Ice Streams of West Antarctica. The ability to differentiate between East and West Antarctic ice will allow us to constrain ice flow into the central Ross Sea during the Last Glacial Maximum (LGM), which has implications for more accurate reconstructions of the Ross Ice Sheet and its behavior. Moraines sampled from the head of Reedy Glacier give insight to the geology beneath the EAIS, and may be representative of what the glacier is eroding from its bed. Samples along the trunk of the glacier capture representative rock types eroded along the length of Reedy Glacier. At each moraine 3 replicate sub-sites were selected for collection to represent the diversity of material within each moraine. Comparisons are based on the composition of pebbles, particle size distributions, and sand petrography. Analysis of the pebble fraction shows that each sub-site contains similar rock types, however, the concentration of each rock type varies as much as 25-35%. Similar variation is also seen within the sub-site sand fraction. Both the pebble and sand fraction reflect the mapped bedrock geology. The dominant pebble types are coarse-grained felsic and intermediate igneous rocks, as well as quartzite. Similarly felsic igneous grains, quartzite, quartz, and feldspar characterize the sand fraction. Particle size analysis shows that v Reedy Glacier till averages 85% sand. The subglacial West Antarctic samples contain approximately 30% sand, and equal amounts of silt and clay, approximately 35% each. An observation of the sand fraction from beneath the West Antarctic Ice Streams shows composition similar to tills from Reedy Glacier. However, tills from the base of the West Antarctic Ice Streams contain up to 75% polymict grains, and in contrast, these grains are absent in the tills from Reedy Glacier. These sand-sized polymict grains dominate material from the base of Whillans and Bindschadler Ice Streams, whereas material from the base of Kamb Ice Stream contains grains of felsic igneous, quartz, feldspar, and few to no polymict grains. In addition to the polymict grains, the sand fraction in the ice stream cores contains trace fragments of sedimentary, and volcanic rocks, both of which are absent from the Reedy Glacier sand fraction. However, polymict grains are believed to represent a process occurring beneath the ice sheet, rather than indicate provenance. It is difficult to differentiate between the two tills, as both contain high concentrations of felsic-intermediate igneous lithics, quartz, and feldspar. The central Ross Sea contains sediment similar in rock type and mineralogy as seen within sediments from both Reedy Glacier, and the base of the ice streams of West Antarctica.
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    RECONSTRUCTING PAST ANTARCTIC ICE FLOW PATHS IN THE ROSS EMBAYMENT, ANTARCTICA USING SAND PETROGRAPHY, PARTICLE SIZE AND DETRITAL ZIRCON PROVENANCE
    (2010-05-03T19:50:00Z) Schilling, Andrea J.; Licht, Kathy J.; Swope, R. Jeffery; Pachut, Joseph F., 1950-
    Tills for this study were analyzed from sites in East Antarctica (EA), West Antarctica (WA) and along a transect in the Ross Sea. Particle size, sand petrography, and detrital zircons were used to provide new information on the subglacial geology of Antarctica, as well as assisting in the reconstruction of Last Glacial Maximum (LGM) ice flow paths. Statistical analyses using the Kolmogorov-Smirnov (K-S test) reveal that EA and WA zircon age distributions are distinct at a P-value <0.05. This makes it possible to trace the unique signatures from EA and WA into the Ross Sea.