

@mastersthesis {6678,
	title = {Landscape evolution of the {Needles} fault zone, {Utah}, investigated through chronotstratigraphic and terrain analyses},
	year = {2014},
	note = {1584411},
	school = {Utah State University},
	type = {phdM.{S}.},
	address = {Ann Arbor},
	abstract = {Landscape evolution of the needles fault zone, Utah investigated through chronostratigraphic and terrain analyses by Faye L. Geiger, Master of Science Utah State University, 2014 Major Professor: Dr. Joel L. Pederson Department: Geology Arcing eastward from the deeply incised Cataract Canyon of the Colorado River in southeastern Utah is a series of alternating horst and graben within the Needles fault zone. Despite this deforming system{\textquoteright}s importance to structural geologists and genetic linkage to the history of the Colorado River, it has been little studied from a geomorphic perspective. This work relates results from detailed chronostratigraphic analysis of graben-fill to known climate fluctuations of the late Quaternary and also addresses patterns identified in topographic analysis that reveal where and when Colorado River incision and salt movement-related subsidence have influenced this unusual terrain. Unusual features called swallow holes expose the top 6-14 m of sediment accumulated in graben bottoms. Facies exposed are mostly granuley sands, sand, and silt beds deposited on avulsing alluvial fans and via settiling in ponded water. OSL and radiocarbon ages indicate that most of this material accumulated at a rapid pace of up to 3 m/kyr from 9 to 5 ka during the middle Holocene, with relatively minor latest Pleistocene and late Holocene strata preserved. This pulse of mid-Holocene sedimentation is only broadly synchronous across the basins studied, suggesting that local sediment supply, autogenic fan processes, and/or halokinetic or groundwater-driven accommodation space changes may be the dominant controls on apparent sedimentation rate at the scale of these exposures. Topographic analysis of seven watersheds within the Needles fault array resulted in spatial correlation between hypsometric integral, normalized steepness, and previously reported modern deformation. Stream longitudinal profile analysis reveals that streams transecting the Needles fault array share three distinct reaches, delimited by knickpoints. The lowermost reaches are within 7 km of the Colorado River, have deeply incised gorges and high kqsn; knickpoints are maintained by resistant carbonate beds of the Lower Cutler and Honaker Trail formation. The middle reaches traverse the salt-deformed horst and graben terrain and have low steepness and numerous small knickpoints where they cross normal faults. Their upper knickpoints separate them from the mostly-undeformed upper reaches, which were used to model paleo-profiles. Paleo-profiles projected to baselevel and scaled to assumed Colorado River incision rates constrain the initiation of the pulse of baselevel fall and tributary incision to 1.9{\textendash}1.3 Ma. Tributary profile deformation due to salt movement is constrained to 700{\textendash}200 ka based on scaling to InSAR measured subsidence and estimation of the depth at which deformation began. These independent temporal estimates for the Needles fault array are consistent with those from previously published modeling results. (172 pages) PUBLIC ABSTRACT Landscape evolution of the needles fault zone, Utah investigated through chronostratigraphic and terrain analyses Arcing eastward from the deep gorge of Cataract Canyon on the Colorado River is a series of aligned valleys (graben) and ridges (horst). This unusual landscape has formed as subsurface salt deforms toward the river and dissolves away, causing the overlying rocks to fault, slide, and subside. Geologists have long been interested in this actively evolving area they call the Needles fault zone, because understanding its mechanics and origin may shed light on how faults work in general and similar, yet inaccessible places like offshore rift zones or even the surface of the Moon. Despite this interest, the timing and long-term patterns of deformation here and are poorly constrained. This study uses analysis of digital landscape models to better delineate these patterns and provide better age constraints on the development of the Needles fault zone. We find that the Colorado River incision that led to deformation here began as recently as 1 million years ago, and that faulting due to subsurface salt movement initiated between 700 and 200 thousand years ago. The first part of this study takes advantage of how the development of graben valleys has changed the path of many of the streams in the study area, resulting in numerous captured streams terminating into a type of sinkhole, called a swallow hole, that develops above opening faults. These fissures are so named because, by ongoing opening, they are "swallowing" material that is flushed into them by local drainages. By recording and numerically dating the exposed upper 6-14 m of basin-fill strata, we determined that sediment was deposited to an alluvial fan and to ponded water. We also compared calculated sediment yields over time to paleoclimate records for the region to test extant hypotheses about how drylands respond to changing climate of the same scale as modern climate change. Against expectations, our results suggest that the greatest sediment yield and storage in these upper basins occurred during the relatively warm and dry time from 9 to 5 thousand years ago, when overland flow to transport sediment was weak. This implies that we are actually measuring sediment storage, as the faults that form swallow holes were relatively less active, allowing sediment to accumulate, rather than be flushed out of the basins. Faye L. Geiger},
	keywords = {0372:Geology, 0484:Geomorphology, Chronostratigraphy, Earth sciences, Geology, Geomorphology, Long profile, Needles fault zone, OSL, Salt tectonics},
	url = {http://search.proquest.com/docview/1659797666?accountid=14270},
	author = {Geiger, Faye L.}
}
