T172 Quantifying Geomorphic Processes and Rates of Landscape Evolution (Posters)

Tuesday, 6 November 2018
9:00 AM - 6:30 PM
Halls J-K

SYSTEMATICALLY INHERITED COSMOGENIC 10BE IN LATE HOLOCENE AGE MORAINE BOULDERS IN THE BHAGIRATHI VALLEY, GARHWAL

Paper number: T172-7
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

Excess inventory of (10Be) cosmogenic nuclides often precludes us to accurately (exposure) date recent geological materials, especially for materials/landforms which are younger than 2 ka. Here, we showed the inherited 10Be concentration in ten historically dated moraine boulders in one of the largest and erosive glaciers of the Garhwal Himalaya, northern India. We choose 30.2 km-long Gangotri glacier in the Bhagirathi valley to investigate systematically inherited 10Be concentration during glacier transportation and inclusion by random rockfall events from the valley walls. In conjunction with a detailed geomorphic mapping and cosmogenic 10Be dating, we presented that even for an erosive, high-velocity glacier (20–44 m/a) with a large ablation area (93 km2 or 64%), a minimum of 0.09–0.60 104 atoms/g (i.e., 0.05-0.12 ka) of systematic excess 10Be concentration is expected, with some outliers could be as old as >4 ka (i.e., >14.15 104 atoms/g). We also applied a numerical rockfall model to simulate inherited 10Be concentration in boulders/blocks due to random events and compared with our field data. Our results indicate that boulder/block rotation during transportation and/or deposition likely offset some of the excess inventory of (10Be) cosmogenic nuclides on the sampled surface, particularly for large dynamic glaciers. Several key geomorphic process uncertainties are, therefore, proposed for future inheritance analysis that will likely target young geological materials/landforms. In addition, we also 10Be dated nine new moraine boulders from the main Gangotri and the tributary Meru glaciers to improve the Late Holocene local glacial chronostratigraphies in the catchment. Morphostratigraphically, from oldest to youngest, the Late Holocene moraines are dated to ~0.8±0.3 and ~0.3±0.1 ka, respectively. We used our inheritance estimates to correct for the possible overestimation of young moraine ages and proposed a robust Holocene local glacial chronology in the valley.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-320045

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