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R.D. Powell

Publications and source records attributed to R.D. Powell.

14 recordsLinked to original sources
USGS2017

The marine record of the Russell Fiord outburst flood, Alaska, U.S.A

The advance of Hubbard Glacier, near Yakutat, Alaska, U.S.A., in spring 1986 blocked the entrance to Russell Fiord with an ice-and-sediment dam, behind which a lake formed. The water level in Russell Lake rose to 25.5 m a.s.l. The dam catastrophically failed in October 1986, releasing 5.4 km 3 of water into Disenchantment Bay. High-resolution seismic-reflection profiles show a 7.5 km long channel system cut into and buried by glacimarine sediment, represented by continuous, parallel reflections. The chaotic seismic facies filling the channel is interpreted to be debris flow deposits. A gravity core from channel-overbank deposits contained sandy diamicton with mud clasts. Above the channel a 1-2 m thick sediment drape extends across the bay. Laminated mud, fining-upward sand beds and diamicton were recovered from this unit. The sediment-drape deposits were produced by suspension settling from turbid plumes and non-channelized turbidity currents generated by the outburst flood.

Alaska↗
USGS2007

Late Cenozoic Climate History of the Ross Embayment from the AND-1B Drill Hole: Culmination of Three Decades of Antarctic Margin Drilling

Because of the paucity of exposed rock, the direct physical record of Antarctic Cenozoic glacial history has become known only recently and then largely from offshore shelf basins through seismic surveys and drilling. The number of holes on the continental shelf has been small and largely confined to three areas (McMurdo Sound, Prydz Bay, and Antarctic Peninsula), but even in McMurdo Sound, where Oligocene and early Miocene strata are well cored, the late Cenozoic is poorly known and dated. The latest Antarctic geological drilling program, ANDRILL, successfully cored a 1285-m-long record of climate history spanning the last 13 m.y. from subsea-floor sediment beneath the McMurdo Ice Shelf (MIS), using drilling systems specially developed for operating through ice shelves. The cores provide the most complete Antarctic record to date of ice-sheet and climate fluctuations for this period of Earth’s history. The >60 cycles of advance and retreat of the grounded ice margin preserved in the AND-1B record the evolution of the Antarctic ice sheet since a profound global cooling step in deep-sea oxygen isotope records ~14 m.y.a. A feature of particular interest is a ~90-m-thick interval of diatomite deposited during the warm Pliocene and representing an extended period (~200,000 years) of locally open water, high phytoplankton productivity, and retreat of the glaciers on land.

Open-File Report↗
USGS2003

Antarctic Climate Evolution (ACE) Research Initiative

The Antarctic Climate Evolution (ACE) project is a new international research initiative to study the climate and glacial history of Antarctica by linking climate and ice sheet modeling studies with geophysical surveys and geological studies on and around the Antarctic continent (Fig. 1). The rationale for the ACE programme, outlined herein, was developed and refined, before, during and after the Antarctic Earth Science Symposium in Erice, Italy, in September 2001 (Cooper et al., 2002, Florindo et al., 2003).

Terra Antarctica↗
USGS1999

Growth of a post-Little Ice Age submarine fan, Glacier Bay, Alaska

A small Holocene fan is forming where Queen Inlet, a hanging valley, enters West Arm fjord, Glacier Bay, Alaska. Queen fan formed in the last 80 years following retreat of the Little Ice Age glacier that filled Glacier Bay about 200 yr BP. It was built mainly by a turbidite system originating from Carroll Glacier delta, as the delta formed in the early 1900s at the head of Queen Inlet. The Late Holocene Queen fan is comparable to large Pleistocene fans that formed in the Gulf of Alaska and differs from trough-mouth fans formed by cooler climate glacier systems.

Geo-Marine Letters↗
USGS1997

Evaluation of conditions along the grounding line of temperate marine glaciers: An example from Muir Inlet, Glacier Bay, Alaska

In the marine environment, stability of the glacier terminus and the location of subglacial streams are the dominant controls on the distribution of grounding-line deposits within morainal banks. A morainal bank complex in Muir Inlet, Glacier Bay, SE Alaska, is used to develop a model of terminus stability and location of subglacial streams along the grounding line of temperate marine glaciers. This model can be used to interpret former grounding-line conditions in other glacimarine settings from the facies architecture within morainal bank deposits. The Muir Inlet morainal bank complex was deposited between 1860 A.D. and 1899 A.D., and historical observations provide a record of terminus positions, glacial retreat rates and sedimentary sources. These data are used to reconstruct the depositional environment and to develop a correlation between sedimentary facies and conditions along the grounding line. Four seismic facies identified on the high-resolution seismic-reflection profiles are used to interpret sedimentary facies within the morainal bank complex. Terminus stability is interpreted from the distribution of sedimentary facies within three distinct submarine geomorphic features, a grounding-line fan; stratified ridges, and a field of push ridges. The grounding-line fan was deposited along a stable terminus and is represented on seismic-reflection profiles by two distinct seismic facies, a proximal and a distal fan facies. The proximal fan facies was deposited at the efflux of subglacial streams and indicates the location of former glacifluvial discharges into the sea. Stratified ridges formed as a result of the influence of a quasi-stable terminus on the distribution of sedimentary facies along the grounding line. A field of push ridges formed along the grounding line of an unstable terminus that completely reworked the grounding-line deposits through glacitectonic deformation. Between 1860 A.D. and 1899 A.D. (39 years), 8.96 x 108 m3 of sediment were deposited within the Muir Inlet morainal bank complex at an average annual sediment accumulation rate of 2.3 x 107 m3/a. This rate represents the annual sediment production capacity of the glacier when the Muir Inlet drainage basin is filled with glacial ice.

Marine Geology↗
USGS1997

Lithofacies and seismic-reflection interpretation of temperate glacimarine sedimentation in Tarr Inlet, Glacier Bay, Alaska

High-resolution seismic-reflection profiles of sediment fill within Tart Inlet of Glacier Bay, Alaska, show seismic facies changes with increasing distance from the glacial termini. Five types of seismic facies are recognized from analysis of Huntec and minisparker records, and seven lithofacies are determined from detailed sedimentologic study of gravity-, vibro- and box-cores, and bottom grab samples. Lithofacies and seismic facies associations, and fjord-floor morphology allow us to divide the fjord into three sedimentary environments: ice-proximal, iceberg-zone and ice-distal. The ice-proximal environment, characterized by a morainal-bank depositional system, can be subdivided into bank-back, bank-core and bank-front subenvironments, each of which is characterized by a different depositional subsystem. A bank-back subsystem shows chaotic seismic facies with a mounded surface, which we infer consists mainly of unsorted diamicton and poorly sorted coarse-grained sediments. A bank-core depositional subsystem is a mixture of diamicton, rubble, gravel, sand and mud. Seismic-reflection records of this subsystem are characterized by chaotic seismic facies with abundant hyperbolic diffractions and a hummocky surface. A bank-front depositional subsystem consists of mainly stratified and massive sand, and is characterized by internal hummocky facies on seismic-reflection records with significant surface relief and sediment gravity flow channels. The depositional system formed in the iceberg-zone environment consists of rhythmically laminated mud interbedded with thin beds of weakly stratified diamicton and stratified or massive sand and silt. On seismic-reflection profiles, this depositional system is characterized by discontinuously stratified facies with multiple channels on the surface in the proximal zone and a single channel on the largely flat sediment surface in the distal zone. The depositional system formed in the ice-distal environment consists of interbedded homogeneous or laminated mud and massive or stratified sand and coarse silt. This depositional system shows continuously stratified seismic facies with smooth and flat surfaces on minisparker records, and continuously stratified seismic facies which are interlayered with thin weakly stratified facies on Huntec records.

Marine Geology↗
USGS1989

Glacimarine sedimentary processes, facies and morphology of the south-southeast Alaska shelf and fjords

High precipitation from Gulf of Alaska air masses can locally reach up to 800 cm a −1 . This precipitation on tectonically active mountains creates cool-temperate glaciation with extremely active erosion and continuously renewed resources. High basal debris loads up to 1.5 m thick of pure debris and rapid glacial flow, which can be more than 3000 m a −1 , combine to produce large volumes of siliciclastic glacimarine sediment at some of the highest sediment accumulation rates on record. At tidewater fronts of valley glaciers, sediment accumulation rates can be over 13 m a −1 and deltas commonly grow at about 10 6 m 3 a −1 . Major processes influencing glacimarine sedimentation are glacial transport and glacier-contact deposition, meltwater (subaerial and submarine) and runoff transport and deposition, iceberg rafting and gouging, sea-ice transport, wave action and storm reworking, tidal transport and deposition, alongshelf transport, sliding and slumping and gravity flows, eolian transport, and biogenic production and reworking. Processes are similar in both shelf and fjord settings; however, different intensities of some processes create different facies associations and geometries. The tectonoclimatic regime also controls morphology because bedrock structure is modified by glacial action. Major glacimarine depositional systems are all siliciclastic. They are subglacial, marginal-morainal bank and submarine outwash, and proglacial/paraglacial-fluvial/deltaic, beach, tidal flat/estuary, glacial fjord, marine outwash fjord and continental shelf. Future research should include study of long cores with extensive dating and more seismic surveys to evaluate areal and temporal extent of glacial facies and glaciation; time-series oceanographic data, sidescan sonar surveys and submersible dives to evaluate modern processes; biogenic diversity and production to evaluate paleoecological, paleobiogeographic and biofacies analysis; and detailed comparisons of exposed older rock of the Yakataga Formation to evaluate how glacial style has evolved over 6.3 Ma.

Marine Geology↗
USGS1989

Turbidity-current channels in Queen Inlet, Glacier Bay, Alaska

Queen Inlet is unique among Glacier Bay fjords because it alone has a branching channel system incised in the Holocene sediment fill of the fjord floor. Bathymetry and seismic-reflection profiles show that four channels begin on, or at the base of, the delta front of this marine-outwash fjord. By midpoint of the fjord, these channels have merged into one main channel that extends the length of the fjord. The main channel cuts deeply into the scarp that separates this hanging tributary from the West Arm of Glacier Bay. The Queen Inlet channel ends on the main fjord floor as several small distributaries that form part of a lobate-fan deposit. Sand from the channel and lobate fan, in contrast to fjord-floor mud, plus steep truncated channel walls indicate that turbidity currents created this apparently active channel system. Queen Inlet and other known channel-containing fjords are marine-outwash fjords; the tidewater glacial fjords do not have steep delta fronts on which slides are generated and may not have a sufficient reservoir of potentially unstable coarse sediment to generate channel-cutting turbidity currents. Presence or absence of channels, as revealed in the ancient rock record, may be one criterion for interpreting types of fjords.

Alaska↗
USGS1984

Interlaminated ice-proximal glacimarine sediments in Muir Inlet, Alaska

Muir Inlet in Glacier Bay, Alaska, is a glacial fjord receiving a tremendous volume of sediment annually. The rate of sediment accumulation is greatest proximal to Muir Glacier (about 9 m yr −1 ) and decreases away from the glacier. The primary sediment sources are meltwater streams discharging at subglacial and ice-marginal positions to form overflows, interflows, and underflows (continuous turbidity currents). Overflows and interflows interact with diurnal tidal currents and their volume and sediment concentration varies diurnally and annually with meltwater discharge. These effects produce cyclic deposits of a thin fine-grained sand or silt lamina that grades normally to a thicker poorly to very poorly sorted mud lamina. This lamina couplet is termed a cyclopel . Underflows are suggested to occur in this glacimarine environment because of conditions unique to subglacial fluvial systems. Underflow deposits occur only in proximal positions (<0.5 km from glacier face), and are coarse-grained, reverse to normal graded, and exhibit an increase in sorting and sand content up-layer. Ice-rafted debris (identified as particles >177 μ m) is ubiquitous, though low (<5% by weight), and occurs as isolated particles, frozen pellets, or as lenses that in cores may have a lamina appearance. Proximally, ice-rafted debris is difficult to identify because proximal sediment is often as coarse-grained. Deposited sediment may be reworked by tidal currents, and sediment gravity flows. Depositional processes operating in Muir Inlet produce interlaminated sand/silt/clay that characterizes sediment proximal to a glacier and fines seaward to mud. Sediment is classified into one of three sediment types: (1) Type I sediment is very fine grained (mean 8.65--7.17 ~), low in sand (0.1--11.2%), and very poorly to poorly sorted. It is the dominant sediment type in Muir Inlet, and is transported by plumes and deposited by suspension settling. (2) Type II sediment is fine- to coarse-grained (mean 6.70--3.12 ~), low to high in sand (5.1---86.6%), and very poorly to moderately sorted. It represents reworked sediment, proximal plume deposits, or coarse-grained laminae of cyclopels. (3) Type III sediment is coarse-grained (mean 3.89--2.38 ~), high in sand (58.0--100.0%), and poorly to well sorted. It is deposited by sediment gravity flows or underflows.

Alaska↗
USGS1980

Debris-flow deposits of Early Miocene age, Deadman Stream, Marlborough, New Zealand.

Detailed analysis is presented of a conformable succession of conglomerates and sandstones lying between massive marine mudstones. The coarse sediments reflect deposition by a spectrum of subaqueous debris-flow mechanisms during an early pulse of tectonism that ultimately resulted in Plio-Pleistocene eversion of the Kaikoura Mountains. Sparse pebbly mudstones and rare sandy conglomerates show disoriented clasts and reflect high-viscosity flows and slurry- creep flow mechanisms. Other deposits have little mud matrix, hence appear to reflect low-viscosity flow processes. Common sorted sandstones and some conglomeratic sandstones show diffuse parallel lamination. Other conglomeratic sandstones show trough cross-bedding which we attribute to entrained bedload movement during intersurge episodes of debris flow. - from Authors

Sedimentary Geology↗