SEM microfabric analysis of glacial varves, Geneseo, N. Y

Conference · Mon Mar 01 04:00:00 EST 1993 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5588266

Pietraszek, S R ^[1]

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1. Potsdam Coll., State Univ. of New York, Potsdam, NY (United States). Geology Dept.

A detailed study of the microfabric of Pleistocene varved silty-clay from Geneseo Valley (Geneseo, N.Y.) indicates rapid deposition of sediment in a flocculated state into a glacial lake. Ten varve couplets of a 10 cm thick sample were studied using the Scanning Electron Microscope to determine their microfabric. Each varve ranges from 0.5 cm to 2.0 cm and represents an annual ( ) deposit. Varves consists of a lower light colored, coarse zone of silt and clay, and an upper darker colored, organic fine clayey zone. Graded bedding is observed in each couplet, and random clay particle orientation is dominant throughout a varve, with the exception of the top 0.5 mm of the fine layer. The upper and lower contacts are sharp. Fabric features are instrumental in reconstructing a depositional environment. Microfabric results of the glacial unit indicate that an initial heavy concentration of clay and silt was introduced into the basin in a single pulse during spring runoff. The majority of silt settled together with clay in a flocculated or aggregated state, forming the lower coarse zone of random orientation. As the silt concentration diminished, the clay continued to flocculate and settled as a fine clay aggregate. It is proposed that the settling took place during the spring and summer months. Finally, during the winter months, the sediment surface of the varve was disturbed by nemotode burrows, which reoriented the clay flakes into a zone of preferred fabric. Microfabric analysis of these glacial varves, thus suggests that sediment was rapidly deposited in a flocculated state.

• OSTI ID: 5588266
• Report Number(s): CONF-9303211--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 25:2
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
CENOZOIC ERA
DEPOSITION
DEVELOPED COUNTRIES
ELECTRON MICROSCOPY
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC HISTORY
GEOLOGY
GLACIERS
LAKES
MICROSCOPY
MICROSTRUCTURE
MORAINES
NEW YORK
NORTH AMERICA
PETROLOGY
PLEISTOCENE EPOCH
QUATERNARY PERIOD
SCANNING ELECTRON MICROSCOPY
SEASONAL VARIATIONS
SEDIMENTS
STRATIFICATION
STRATIGRAPHY
SURFACE WATERS
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