Stratigraphy, paleoclimatic implications, and permeability distribution of fine-grained lacustrine deltas along the eastern margin of late Pleistocene Lake Bonneville

Fine-grained lacustrine deltas deposited along the eastern margin of Late Pleistocene Lake Bonneville have received little attention, especially in comparison to the classic coarse-grained Gilbert deltas. However, these fine-grained deltas are important groundwater recharge areas and represent ideal subsurface analogues. Therefore, three of these deltas have been reinterpreted in light of new stratigraphic and sedimentary concepts.; Analysis of facies architecture indicates the Weber and Spanish Fork deltas are wave-influenced, situated along openly exposed portions of the shoreline. The Bear River delta, nestled in a relatively isolated northeast arm of the lake, was influenced by both wave and fluvial processes. The sequence stratigraphy of all three deltas implies that limnostasy (lake level change), tectonics, and sediment yield were similar for all three deltas. However, basin physiography differs most significantly and is the most influential forcing parameter.; The established Bonneville hydrograph provides excellent time constraints to examine sediment yield rates. A late Pleistocene sediment yield rate of 705 {dollar}rm msp3/kmsp2{dollar}/yr is estimated for the Weber River drainage using the geomorphic expression of the Weber River delta as a sediment volume and the drainage area. A sediment yield/precipitation regression equation developed for similar basins in New Zealand provides a first order approximation for paleoprecipitation of 1.9 m/yr when applied to the late Pleistocene eastern margin of Lake Bonneville. This paleoprecipitation value is up to 33% higher than modern values. Previous climate models and this 33% paleoprecipitation increase suggest a maximum decrease in basin floor paleotemperatures of approximately 13{dollar}spcirc{dollar}C.; In applications of modelling groundwater recharge and surface contamination problems of the Wasatch front, permeability is an important parameter for characterizing these Bonneville shoreline deposits. The permeability distributions of Weber River delta facies were examined at a small scale (individual lithofacies) as well as a large scale (composite section of grouped lithofacies). Permeabilities of over 400 undisturbed sediment cores within fine-grained facies ranged from approximately 0.04 to 26 darcys. Horizontal/vertical anisotropy ratios were generally less than 2:1. The permeability distributions of individual lithofacies in the delta appear to be normal. The permeability distribution of a composite section through the delta is approximately lognormal. This suggests that the traditional assumption of lognormality is based on grouped permeability samples or based on hydraulic conductivity/permeability tests over intervals that span several lithofacies. This information, in conjunction with the established stratigraphic framework, can serve as a guide to future stochastic modelling and groundwater simulations.