Demko, Timothy1, Stephen Hasiotis2
(1) University of Minnesota Duluth, Duluth, MN
(2) The University of Kansas, Lawrence, KS
ABSTRACT: Stratal Architecture and Paleoclimate in Continental Depositional Systems: The Record of Landscape Evolution in the Upper Triassic Chinle and Upper Jurassic Morrison Formations, Colorado Plateau, USA
The Upper Triassic Chinle and Upper Jurassic Morrison Formations of the Colorado Plateau region expose, at a regional scale, a detailed record of continental landscape evolution and allow the testing and application of sequence stratigraphic concepts in strata that were deposited far up depositional dip from the influence of relative sea level. In the Colorado Plateau region, both formations are comprised of fluvial, lacustrine, and eolian strata deposited under monsoonal to seasonal paleoclimatic conditions, and overlie formations that were deposited in near shore or coastal plain settings. The stratigraphic framework of both formations is characterized by several regional unconformities. The base of the lower Chinle Formation is marked by an erosional unconformity at the bottom of a paleovalley system. The complicated fill of the valley is characterized by several periods of aggradation and degradation, creating smaller, inset, paleovalleys. The upper Chinle is dominantly aggradational, but also has evidence of lower amplitude base level changes. The Morrison Formation, which also has a basal unconformity, can be separated into two aggradational stratal packages by a regional unconformity in the middle of the formation. The unconformities within these formations are surfaces that were created during regional periods of erosion, low or no deposition, and extensive interfluve pedogenesis. The nature of these sequence-bounding unconformities, and sedimentary paleoclimatic indicators (paleosols, clay mineralogy, trace fossils, etc.) within the intervening aggradational packages provide important clues as to the control of sediment supply and fluvial discharge on the sequence stratigraphic framework of these and other ancient continental deposits.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.