Stephen T. Hasiotis1, James G. Honey2, Timothy M. Demko3
(1) Indiana State University, Terre Haute, IN
(2) University of Colorado Museum, Boulder, CO
(3) ExxonMobil Upstream Research Company, Houston, TX
ABSTRACT: Integrating Ichnology, Paleopedology, and Sedimentology to Resolve Sequence Stratigraphic Surfaces in Continental Rocks: Examples from Outcrop and Core
Burrowed intervals and other paleosols, along with sandstone and mudrock successions, can be used to identify alluvial stacking patterns and significant stratigraphic surfaces in rocks deposited in fully continental basins or in rocks updip and conterminous with marine deposystems. The resultant stacking patterns and significant surfaces are analogous to parasequences, parasequence sets, and sequence boundaries in marine and marginal marine settings. Pedogenesis occurs in nearly every continental environment at different rates depending on the rate and frequency of depositional events, distance from sediment source, parent material, the composition of biotic communities--represented in the geologic record by plant, invertebrate, and vertebrate ichnofossils, the groundwater profile and its fluctuations, the landscape topography, and the climatic setting. Data from ichnofossils, paleosols, and sedimentology can be used to delineate genetically related successions of continental strata.
Based on Mesozoic and Cenozoic outcrop and core examples, a continental sequence stratigraphic scheme can be based on 1) alluvial units, 2) alluvial unit sets, and 3) alluvial sequences that reflect changes in continental landscapes through time due to interactions between climate, tectonics, and sediment supply. Alluvial units composed of increasingly immature paleosols with less bioturbation that are associated with isolated channel sandstone bodies reflect higher sedimentation rates, base level, and accomodation space. Alluvial units composed of increasingly mature paleosols with greater degrees of bioturbation that are associated with progressively interconnected sandbodies reflect lower sedimentation rates, base level, and accomodation space. Alluvial units bounded by surfaces marked by well-developed paleosols with or without intense bioturbation and their contemporaneous channels delineate sequence boundaries and define an alluvial sequence. Several alluvial sequences can spatially and temporally exhibit stratal patterns of overall high aggradation, low aggradation, or degradation depending on the interplay between climate, tectonics, and sediment supply across a basin.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado