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Abstract. In 1966, drilling at Camp Century, Greenland, recovered 3.44 meters of sub-glacial material from beneath 1350 meters of ice. Although prior analysis of this material showed that the core includes glacial sediment, ice, and sediment deposited during an interglacial, the sub-glacial material had never been thoroughly studied. To better characterize this material, we analyzed 26 of the 30 core samples remaining in the archive. We performed a multi-scale analysis including X-ray diffraction, micro-computed tomography, and scanning electron microscopy to delineate stratigraphic units and assign facies based on inferred depositional processes. At the macro-scale, quantitative X-ray diffraction revealed that quartz and feldspar dominated the sediment and that there was insignificant variation in relative mineral abundance between samples. Meso-scale evaluation of the frozen material using micro-computed tomography scans showed clear variations in the stratigraphy of the core characterized by the presence of bedding, grading, and sorting. Micro-scale grain size and shape analysis, conducted using scanning electron microscopy, showed an abundance of fine-grained materials in the lower part of the core and no correspondence between grain shape parameters and sedimentary structures. These multiscale data define 5 distinct stratigraphic units within the core based on sedimentary process; K-means clustering analysis supports this proposed unit delineation. Our observations suggest that ice retreat uncovered the Camp Century region exposing basal till, covered with a remnant of basal ice or firn (Units 1 and 2). Continued ice-free conditions led to till disruption by liquid water causing a slump deposit (Unit 3) and the development of a small fluvial system of increasing energy up core (Units 4–5). Analysis of the Camp Century sub-glacial material indicates a diverse stratigraphy preserved below the ice that recorded episodes of glaciated and deglaciated conditions in northwestern Greenland. Our physical, geochemical, and mineralogic analyses reveal a history of deposition, weathering, and sediment transport preserved under the ice and show the promise of sub-glacial materials to increase our knowledge of past ice sheet behavior over time.
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Holocene Depositional History Inferred From Single‐Grain Luminescence Ages in Southern California, North America
Abstract Significant sediment flux and deposition in a sedimentary system are influenced by climate changes, tectonics, lithology, and the sedimentary system's internal dynamics. Identifying the timing of depositional periods from stratigraphic records is a first step to critically evaluate the controls of sediment flux and deposition. Here, we show that ages of single‐grain K‐feldspar luminescence subpopulations may provide information on the timing of previous major depositional periods. We analyzed 754 K‐feldspar single‐grains from 17 samples from the surface to ∼9 m‐depth in a trench located downstream of the Mission Creek catchment. Single‐grain luminescence subpopulation ages significantly overlap at least eight times since ∼12.0 ka indicating a common depositional history. These depositional periods correspond reasonably well with the Holocene intervals of wetter than average climate conditions based on hydroclimatic proxies from nearby locations. Our findings imply a first‐order climatic control on sediment depositional history in southern California on a millennial timescale.
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- Award ID(s):
- 1728145
- PAR ID:
- 10359943
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 48
- Issue:
- 15
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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