--> Sedimentology of Pleistocene Lake Bonneville Delta Deposits, Northern Utah: Applications to Hydrogeologic Facies, by M. A. Chan, D. R. Lemons, and M. R. Milligan; #90986 (1994).

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Abstract: Sedimentology of Pleistocene Lake Bonneville Delta Deposits, Northern Utah: Applications to Hydrogeologic Facies

Marjorie A. Chan, David R. Lemons, Mark R. Milligan

There are few sedimentologic studies of Lake Bonneville deposits since G.K. Gilbert's landmark work in 1885 and 1890. Surface contamination is a major problem along the heavily populated Wasatch Front corridor, where significant portions of the valley areas are underlain by Lake Bonneville and older basin-fill sediments. Recharge to the valley groundwater system occurs through deltaic and shoreline deposits at the eastern margin of Lake Bonneville, where groundwater is especially vulnerable to contamination. Studies of stratigraphic heterogeneities and facies architecture in the Lake Bonneville deltaic deposits can provide good analogues for interpreting hydrogeologic facies in the basinal aquifers.

Deltaic facies are grouped into conglomeratic, sandy, and mixed systems. Horizontal, coarse-grained, transgressive delta sediments were deposited during the lake-level rise to the Bonneville stage. Coarse-grained Gilbert deltas formed at the mouths of steep canyons during the regressive Provo lake stage. Classic foresets have extremely high permeabilities, but are local to a few drainage areas. Several fine-grained sandy deltas (derived from Cretaceous sandstones and other reworked sources) provide the best analogues for basin-fill aquifers. Hydraulic conductivity was evaluated with both remolded and undisturbed sand samples. Increasing mud content corresponds to a decrease in permeability. Transgressive lacustrine and distal deltaic deposits are typically fine-grained, and comprise p rmeability barriers. Depositional facies and fabrics within each deltaic system exert a strong control on fluid flow. A better understanding of the facies architecture provides sound geologic input for aquifer characterization (e.g., permeabilities and position of reservoir boundaries), and for groundwater modeling.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994