47231-AC8
Shapes, Scales and Spacing of Channel-belt Sand Bodies in Ancient and Experimental Avulsion-dominated Alluvial Basins
This project is designed to examine the occurrence, distribution and origins of “avulsion clusters,” apparent groupings of channel body sandstones developed in some alluvial basins. These features appear to differ from incised valley fills that form in response to changes in relative sea-level, in that the latter can be traced downstream to attendant shorelines, are regionally synchronous and correlated, increase in size downstream, are confined to erosional containers (valleys), and have punctuated deposits reflecting bypass and weathering along paleo-interfluves. In contrast avulsion clusters appear to be a less restricted grouping of several channel deposits that are not characterized by placement within valley walls, and can not be regionally correlated.
The study has been attacked in five parts. First and foremost, we have been undertaking a field study of a well exposed cross section of fluvial deposits that appear to be clustered. The exposure is of the Ferris Formation (Late Cretaceous), exposed in the Hanna Basin of south-central Wyoming. The area, roughly 2 x 2 km, provides an opportunity to collect geospatial data that can be analyzed by statistical approaches in order to characterize the degree of organization in size and spacing of sand bodies. In addition statistical characterization of other distributions, such as paleoflow directions, channel paleoflow depths, grain sizes and number of stories is being done. This work is being undertaken by Elizabeth Hajek as part of her Ph.D. degree requirements. She is planning to finish the study during the summer of 2009, coincident with the end of the grant.
The second part of the study concerns a field comparison between the size and distribution of the avulsion clusters in the Ferris Formation with deposits of the Lance Formation, deposited at the same time, in the Bighorn Basin of northern Wyoming. That study described downstream changes in channel body size and organization based on two study areas located more or less along flow direction of each other. This enabled us to look for changes associated with position down the paleobasin. The study was undertaken by Jennifer McHarge who completed her M.S. degree last April. The major results were that while there were no significant changes in architecture down basin in the southern Bighorn Basin, there is a correlation of what is seen in the Lance Formation in this study area with what is observed in the Ferris Formation. The key difference between the areas is scale of the river systems. That is, while all aspects of channel sand bodies in the Lance Formation are c. 5 times larger than those seen in the Ferris Formation, all of these differences disappear when the channel bodies are scaled by preserved channel flow depths, which are also about 5 times deeper than flow depth of channels preserved in the Ferris Formation.
The third part of this study has not yet begun, but involves collecting spatial statistics on channel sand bodies created during large-scale experiments in the XES facility (aka Jurassic Tank) housed at the St. Anthony Falls Laboratory at the University of Minnesota. That data is slated be collected by Elizabeth Hajek under the direction of Dr. Chris Paola during the 2008-2009 academic year. These data will be compared to the results from the Hanna Basin field area.
The fourth part of this study involves using statistical descriptions of vertical (one dimensional) spacing of sand bodies as seen in well log data, to characterize the degree of organization (clustering). This study, spearheaded by Dr. Snehalata Huzurbazar, will use some of the many wells available through the Lance Formation in the Wind River Basin, central Wyoming. The goal is to attempt to characterize spacing characteristics of major sand bodies in vertical sections and then describe if and how these characteristics change as a function of location within the basin. Such a result should be very useful in generating a development strategy for these types of hydrocarbon reservoirs.
Finally a project has begun, as part of a class effort, to study the regional pattern of basin subsidence during Late Cretaceous time across the north-central Rocky Mountains. The goal of this study is to try to work out a relative chronology for Laramide uplift in this part of the world. In addition, well data should provide enough 3-D control on basin subsidence geometries that we can better define the evolution effective elastic plate thickness and bending moment associated with the onset of the Laramide Orogeny.
