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Geology topics

Deborah R. Hutchinson

Publications and source records attributed to Deborah R. Hutchinson.

At least 19 recordsLinked to original sources
USGS2015

Seismic velocities within the sedimentary succession of the Canada Basin and southern Alpha-Mendeleev Ridge, Arctic Ocean: evidence for accelerated porosity reduction?

The Canada Basin and the southern Alpha-Mendeleev ridge complex underlie a significant proportion of the Arctic Ocean, but the geology of this undrilled and mostly ice-covered frontier is poorly known. New information is encoded in seismic wide-angle reflections and refractions recorded with expendable sonobuoys between 2007 and 2011. Velocity–depth samples within the sedimentary succession are extracted from published analyses for 142 of these records obtained at irregularly spaced stations across an area of 1.9E + 06 km 2 . The samples are modelled at regional, subregional and station-specific scales using an exponential function of inverse velocity versus depth with regionally representative parameters determined through numerical regression. With this approach, smooth, non-oscillatory velocity–depth profiles can be generated for any desired location in the study area, even where the measurement density is low. Practical application is demonstrated with a map of sedimentary thickness, derived from seismic reflection horizons interpreted in the time domain and depth converted using the velocity–depth profiles for each seismic trace. A thickness of 12–13 km is present beneath both the upper Mackenzie fan and the middle slope off of Alaska, but the sedimentary prism thins more gradually outboard of the latter region. Mapping of the observed-to-predicted velocities reveals coherent geospatial trends associated with five subregions: the Mackenzie fan; the continental slopes beyond the Mackenzie fan; the abyssal plain; the southwestern Canada Basin; and, the Alpha-Mendeleev magnetic domain. Comparison of the subregional velocity–depth models with published borehole data, and interpretation of the station-specific best-fitting model parameters, suggests that sandstone is not a predominant lithology in any of the five subregions. However, the bulk sand-to-shale ratio likely increases towards the Mackenzie fan, and the model for this subregion compares favourably with borehole data for Miocene turbidites in the eastern Gulf of Mexico. The station-specific results also indicate that Quaternary sediments coarsen towards the Beaufort-Mackenzie and Banks Island margins in a manner that is consistent with the variable history of Laurentide Ice Sheet advance documented for these margins. Lithological factors do not fully account for the elevated velocity–depth trends that are associated with the southwestern Canada Basin and the Alpha-Mendeleev magnetic domain. Accelerated porosity reduction due to elevated palaeo-heat flow is inferred for these regions, which may be related to the underlying crustal types or possibly volcanic intrusion of the sedimentary succession. Beyond exploring the variation of an important physical property in the Arctic Ocean basin, this study provides comparative reference for global studies of seismic velocity, burial history, sedimentary compaction, seismic inversion and overpressure prediction, particularly in mudrock-dominated successions.

Geophysical Journal International↗
USGS2012

Imaging the midcontinent rift beneath Lake Superior using large aperture seismic data

We present a detailed velocity model across the 1.1 billion year old Midcontinent Rift System (MRS) in central Lake Superior. The model was derived primarily from onshore-offshore large-aperture seismic and gravity data. High velocities obtained within a highly reflective half-graben that was imaged on coincident seismic reflection data demonstrate the dominantly mafic composition of the graben fill and constrain its total thickness to be at least 30km. Strong wide-angle reflections are observed from the lower crust and Moho, indicating that the crust is thickest (55–60km) beneath the axis of the graben. The total crustal thickness decreases rapidly to about 40 km beneath the south shore of the lake and decreases more gradually to the north. Above the Moho is a high-velocity lower crust interpreted to result from syn-rift basaltic intrusion into and/or underplating beneath the Archean lower crust. The lower crust is thickest beneath the axis of the main rift half-graben. A second region of thick lower crust is found approximately 100km north of the axis of the rift beneath a smaller half graben that is interpreted to reflect an earlier stage of rifting. The crustal model presented here resembles recent models of some passive continental margins and is in marked contrast to many models of both active and extinct Phanerozoic continental rift zones. It demonstrates that the Moho is a dynamic feature, since the pre-rift Moho is probably within or above the high-velocity lower crust, whereas the post-rift Moho is defined as the base of this layer. In the absence of major tectonic activity, however, the Moho is very stable, since the large, abrupt variations in crustal thickness beneath the MRS have been preserved for at least a billion years.

Lake Superior↗
USGS2012

Canada Basin revealed

More than 15,000 line-km of new regional seismic reflection and refraction data in the western Arctic Ocean provide insights into the tectonic and sedimentologic history of Canada Basin, permitting development of new geologic understanding in one of Earth's last frontiers. These new data support a rotational opening model for southern Canada Basin. There is a central basement ridge possibly representing an extinct spreading center with oceanic crustal velocities and blocky basement morphology characteristic of spreading centre crust surrounding this ridge. Basement elevation is lower in the south, mostly due to sediment loading subsidence. The sedimentary succession is thickest in the southern Beaufort Sea region, reaching more than 15 km, and generally thins to the north and west. In the north, grabens and half-grabens are indicative of extension. Alpha-Mendeleev Ridge is a large igneous province in northern Amerasia Basin, presumably emplaced synchronously with basin formation. It overprints most of northern Canada Basin structure. The seafloor and sedimentary succession of Canada Basin is remarkably flat-lying in its central region, with little bathymetric change over most of its extent. Reflections that correlate over 100s of kms comprise most of the succession and on-lap bathymetric and basement highs. They are interpreted as representing deposits from unconfined turbidity current flows. Sediment distribution patterns reflect changing source directions during the basin’s history. Initially, probably late Cretaceous to Paleocene synrift sediments sourced from the Alaska and Mackenzie-Beaufort margins. This unit shows a progressive series of onlap unconformities with a younging trend towards Alpha and Northwind ridges, likely a response to contemporaneous subsidence. Sediment source direction appeared to shift to the Canadian Arctic Archipelago margin for the Eocene and Oligocene, likely due to uplift of Arctic islands during the Eurekan Orogeny. The final stage of sedimentation appears to be from the Mackenzie-Beaufort region for the Miocene and Pliocene when drainage patterns shifted in the Yukon and Alaska to the Mackenzie valley. Upturned reflections at onlap positions may indicate syn-depositional subsidence. There is little evidence, at least at a regional seismic data scale, of contemporaneous or post-depositional sediment reworking, suggesting little large-scale geostrophic or thermohaline-driven bottom current activity.

Conference Paper↗
USGS2012

Variations in the reflectivity of the moho transition zone beneath the Midcontinent Rift System of North America: results from true amplitude analysis of GLIMPCE data

True amplitude processing of The Great Lakes International Multidisciplinary Program on Crustal Evolution seismic reflection data from the Midcontinent Rift System of North America shows large differences in the reflectivity of the Moho transition zone beneath the axial rift, beneath the rift flanks, and outside of the rift. The Moho reflection from the axial rift has a discontinuous, diffractive character marginally stronger (several decibels) than an otherwise transparent lower crust and upper mantle. Beneath the axial rift, Moho is interpreted to be a synrift igneous feature. Beneath the rift flanks, the reflectivity of the Moho transition is generally well developed with two identifiable boundaries, although in places it is weakly reflective to nonreflective, similar to Moho outside the rift. The two boundaries are interpreted as the base of essentially intact, although stretched, prerift Archean crust (upper boundary) and new synrift Moho 1-2 s (6-7 km) deeper (lower boundary). Beneath the rift flanks, the layered reflection Moho transition results from the preexisting crustal composition and fabric modified by synrift igneous processes and extensional tectonic/metamorphic processes. The geologic evidence for extensive basaltic magmatism in the rift is the basis for interpreting the Moho signature as a Keweenawan structure that has been preserved for 1.1 b.y. Extension and magmatism appear to enhance reflectivity in the lower crust and Moho transition zone only where stretching factors are moderate (rift flanks) and not where they are extreme (axial rift). This leads to the prediction that the reflectivity across analogous volcanic passive continental margins should be greatest beneath the moderately stretched continental shelves and should decrease towards the ocean-continent boundary.

Journal of Geophysical Research B: Solid Earth↗
USGS2012

Limitations of quantitative analysis of deep crustal seismic reflection data: Examples from GLIMPCE

Amplitude preservation in seismic reflection data can be obtained by a relative true amplitude (RTA) processing technique in which the relative strength of reflection amplitudes is preserved vertically as well as horizontally, after compensating for amplitude distortion by near-surface effects and propagation effects. Quantitative analysis of relative true amplitudes of the Great Lakes International Multidisciplinary Program on Crustal Evolution seismic data is hampered by large uncertainties in estimates of the water bottom reflection coefficient and the vertical amplitude correction and by inadequate noise suppression. Processing techniques such as deconvolution, F-K filtering, and migration significantly change the overall shape of amplitude curves and hence calculation of reflection coefficients and average reflectance. Thus lithological interpretation of deep crustal seismic data based on the absolute value of estimated reflection strength alone is meaningless. The relative strength of individual events, however, is preserved on curves generated at different stages in the processing. We suggest that qualitative comparisons of relative strength, if used carefully, provide a meaningful measure of variations in reflectivity. Simple theoretical models indicate that peg-leg multiples rather than water bottom multiples are the most severe source of noise contamination. These multiples are extremely difficult to remove when the water bottom reflection coefficient is large (>0.6), a condition that exists beneath parts of Lake Superior and most of Lake Huron.

Great Lakes↗
USGS2011

Submarine landslides in Arctic sedimentation: Canada Basin

Canada Basin of the Arctic Ocean is the least studied ocean basin in the World. Marine seismic field programs were conducted over the past 6 years using Canadian and American icebreakers. These expeditions acquired more than 14,000 line-km of multibeam bathymetric and multi-channel seismic reflection data over abyssal plain, continental rise and slope regions of Canada Basin; areas where little or no seismic reflection data existed previously. Canada Basin is a turbidite-filled basin with flat-lying reflections correlateable over 100s of km. For the upper half of the sedimentary succession, evidence of sedimentary processes other than turbidity current deposition is rare. The Canadian Archipelago and Beaufort Sea margins host stacked mass transport deposits from which many of these turbidites appear to derive. The stratigraphic succession of the MacKenzie River fan is dominated by mass transport deposits; one such complex is in excess of 132,000 km2 in area and underlies much of the southern abyssal plain. The modern seafloor is also scarred with escarpments and mass failure deposits; evidence that submarine landsliding is an ongoing process. In its latest phase of development, Canada Basin is geomorphologically confined with stable oceanographic structure, resulting in restricted depositional/reworking processes. The sedimentary record, therefore, underscores the significance of mass-transport processes in providing sediments to oceanic abyssal plains as few other basins are able to do.

Alaska↗
USGS2011

Elevated gas hydrate saturation within silt and silty clay sediments in the Shenhu area, South China Sea

Gas hydrate saturations were estimated using five different methods in silt and silty clay foraminiferous sediments from drill hole SH2 in the South China Sea. Gas hydrate saturations derived from observed pore water chloride values in core samples range from 10 to 45% of the pore space at 190–221 m below seafloor (mbsf). Gas hydrate saturations estimated from resistivity (R t ) using wireline logging results are similar and range from 10 to 40.5% in the pore space. Gas hydrate saturations were also estimated by P wave velocity obtained during wireline logging by using a simplified three-phase equation (STPE) and effective medium theory (EMT) models. Gas hydrate saturations obtained from the STPE velocity model (41.0% maximum) are slightly higher than those calculated with the EMT velocity model (38.5% maximum). Methane analysis from a 69 cm long depressurized core from the hydrate-bearing sediment zone indicates that gas hydrate saturation is about 27.08% of the pore space at 197.5 mbsf. Results from the five methods show similar values and nearly identical trends in gas hydrate saturations above the base of the gas hydrate stability zone at depths of 190 to 221 mbsf. Gas hydrate occurs within units of clayey slit and silt containing abundant calcareous nannofossils and foraminifer, which increase the porosities of the fine-grained sediments and provide space for enhanced gas hydrate formation. In addition, gas chimneys, faults, and fractures identified from three-dimensional (3-D) and high-resolution two-dimensional (2-D) seismic data provide pathways for fluids migrating into the gas hydrate stability zone which transport methane for the formation of gas hydrate. Sedimentation and local canyon migration may contribute to higher gas hydrate saturations near the base of the stability zone.

Journal of Geophysical Research B: Solid Earth↗
USGS2008

Scientific objectives of the Gulf of Mexico gas hydrate JIP leg II drilling

The Gulf of Mexico Methane Hydrate Joint Industry Project (JIP) has been performing research on marine gas hydrates since 2001 and is sponsored by both the JIP members and the U.S. Department of Energy. In 2005, the JIP drilled the Atwater Valley and Keathley Canyon exploration blocks in the Gulf of Mexico to acquire downhole logs and recover cores in silt- and clay-dominated sediments interpreted to contain gas hydrate based on analysis of existing 3-D seismic data prior to drilling. The new 2007-2009 phase of logging and coring, which is described in this paper, will concentrate on gas hydrate-bearing sands in the Alaminos Canyon, Green Canyon, and Walker Ridge protraction areas. Locations were selected to target higher permeability, coarser-grained lithologies (e.g., sands) that have the potential for hosting high saturations of gas hydrate and to assist the U.S. Minerals Management Service with its assessment of gas hydrate resources in the Gulf of Mexico. This paper discusses the scientific objectives for drilling during the upcoming campaign and presents the results from analyzing existing seismic and well log data as part of the site selection process. Alaminos Canyon 818 has the most complete data set of the selected blocks, with both seismic data and comprehensive downhole log data consistent with the occurrence of gas hydrate-bearing sands. Preliminary analyses suggest that the Frio sandstone just above the base of the gas hydrate stability zone may have up to 80% of the available sediment pore space occupied by gas hydrate. The proposed sites in the Green Canyon and Walker Ridge areas are also interpreted to have gas hydrate-bearing sands near the base of the gas hydrate stability zone, but the choice of specific drill sites is not yet complete. The Green Canyon site coincides with a 4-way closure within a Pleistocene sand unit in an area of strong gas flux just south of the Sigsbee Escarpment. The Walker Ridge site is characterized by a sand-prone sedimentary section that rises stratigraphically across the base of the gas hydrate stability zone and that has seismic indicators of gas hydrate.

Conference Paper↗
USGS2008

Physical property studies in the USGS GHASTLI Laboratory

One of the many challenges in studying methane hydrate is that it is unstable at typical surface pressure and temperature conditions. To enable methane hydrates and hydrate-bearing sediments to be formed, analyzed, and experimented with, the National Energy Technology Laboratory (NETL), and the U.S. Geological Survey (USGS) in Woods Hole, MA collaborated in the development of the Gas Hydrate And Sediment Test Laboratory Instrument (GHASTLI). Over the past decade, the USGS has been operating GHASTLI and collaborating in the development of new sample handling tools and procedures, in an effort to improve our ability to analyze methane hydrate in the lab. These tools will enable hydrate researchers to more confidently link field studies (for example geophysics or drilling) with theoretical and predictive studies, leading to a better understanding of the geological conditions and processes that control the growth and concentration of natural gas hydrates, how hydrates affect the properties of the host sediments, and how the hydrate-sediment system changes when hydrate dissociates and releases the previously bound gas. To date, GHASTLI has been used to measure natural samples from ODP Leg 164 (Blake Ridge off the U.S. southeast Atlantic margin), Leg 204 (Hydrate Ridge off the Pacific Northwest margin) and the Mallik well (Mackenzie Delta in northwestern Canada). Additional samples in the queue for analysis are from the Chevron Joint Industry Project Experiment in the Gulf of Mexico and most recently, from IODP Leg 311 off Vancouver Island. Several foreign nations have asked whether GHASTLI will be available to analyze samples that might be recovered during national drilling programs. The ability to perform lab testing of hydrates within sediments is one of the unique capabilities of GHASTLI that separates it from other simulators at NETL and elsewhere.

Fire in the Ice: NETL Methane Hydrate Newsletter↗
USGS2007

Law of the sea, the continental shelf, and marine research

The question of the amount of seabed to which a coastal nation is entitled is addressed in the United Nations Convention on the Law of the Sea (UNCLOS). This treaty, ratified by 153 nations and in force since 1994, specifies national obligations, rights, and jurisdiction in the oceans, and it allows nations a continental shelf out to at least 200 nautical miles or to a maritime boundary. Article 76 (A76) of the convention enables coastal nations to establish their continental shelves beyond 200 nautical miles and therefore to control, among other things, access for scientific research and the use of seabed resources that would otherwise be considered to lie beyond national jurisdiction. To date, seven submissions for extended continental shelves (ECS) have been filed under UNCLOS (Table 1). These submissions have begun to define the ambiguities in A76. How these ambiguities are resolved into final ECS boundaries will probably set important precedents guiding the future delimitation of the ECS by the United States, which has not ratified the convention, and other coastal nations. This report uses examples from the first three submissions—by the Russian Federation, Brazil, and Australia—to identify outstanding issues encountered in applying A76 to ECS delimitation.

Eos, Transactions, American Geophysical Union↗
USGS2007

USGS goals for the coming decade

The U.S. Geological Survey (USGS) proposes six strategic directions for managing ecosystems along with modernization of observation networks of land, water, and biological resources.

Science↗
USGS2006

GIS of selected geophysical and core data in the northern Gulf of Mexico continental slope collected by the U.S. Geological Survey

Since 1982 the U. S. Geological Survey (USGS) has collected a large amount of surficial and shallow subsurface geologic information in the deep-water parts of the US EEZ in the northern Gulf of Mexico. These data include digital sidescan sonar imagery, digital seismic-reflection data, and descriptions and analyses of piston and gravity cores. The data were collected during several different projects that addressed surficial and shallow subsurface geologic processes. Some of these datasets have already been published, but the growing interest in the occurrence and distribution of gas hydrates in the Gulf of Mexico warrants integrating these existing USGS datasets and associated interpretations into a Geographic Information System (GIS) to provide regional background information for ongoing and future gas hydrate research. This GIS is organized into five different components that contain (1) information needed to develop an assessment of gas hydrates, (2) background information for the Gulf of Mexico, (3) cores collected by the USGS, (4) seismic surveys conducted by the USGS, and (5) sidescan sonar surveys conducted by the USGS. A brief summary of the goals and findings of the USGS field programs in the Gulf of Mexico is given in the Geologic Findings section, and then the contents of each of the five data categories are described in greater detail in the GIS Data Catalog section.

Gulf of Mexico↗
USGS2006

USGS analysis of the Australian UNCLOS submission

In November 2004, the Government of Australia made a submission to the Commission on the Limits of the Continental Shelf (CLCS) for 10 extended continental shelf (ECS) regions, utilizing Article-76 of the United Nations Convention on the Law of the Sea (UNCLOS). With information provided in the Australian Executive Summary, the USGS examined the 10 regions of the submission from geological, morphological, and resource perspectives. By their own request, the Australians asked that CLCS take no action on the Australian-Antarctic Territory. The major limitation in this analysis is that no bathymetric soundings or detailed hydrographic profiles were provided in the Australian Executive Summary that might show why the Foot of the Slope (FOS) was chosen or where the 2,500-m contour is located. This represents a major limitation because more than half of the 4,205 boundary points utilize the bathymetric formula line and more than one-third of them utilize the bathymetric constraint line. CLCS decisions on the components of this submission may set a precedent for how ECSs are treated in future submissions. Some of the key decisions will cover (a) how a 'natural prolongation' of a continental margin is determined, particularly if a bathymetric saddle that appears to determine the prolongation is in deep water and is well outside of the 200-nm limit (Exmouth Plateau), (b) defining to what extent that plateaus, rises, caps, banks and spurs that are formed of oceanic crust and from oceanic processes can be considered to be 'natural prolongations' (Kerguelen Plateau), (c) to what degree UNCLOS recognizes reefs and uninhabited micro-islands (specifically, rocks and/or sand shoals) as islands that can have an EEZ (Middleton and Elizabeth Reefs north of Lord Howe Island), and (d) how the Foot of the Slope (FOS) is chosen (Great Australian Bight). The submission contains situations that are relevant to potential future U.S. submissions and are potentially analogous to certain features of the US margins. The Australian margin has significant geological and morphological variety, similar to the US margin and gives a good idea of the complexity of issues related to the U.S. margin. Decisions about basins and ridges in the Lord Howe Rise and Three Kings Ridge regions will likely bear on the status of ridges in the Arctic, such as Lomonosov Ridge. The Naturaliste Plateau and the South Tasman Rise appear to have parallels with the Chukchi Plateau in the Arctic and the Blake Plateau off the southeastern U.S. The ECS on Macquarie Island/Ridge may determine how boundaries along ridges such as the Mariannas are treated.

Open-File Report↗
USGS2006

Gas hydrate potential of the mid Atlantic outer continental shelf

For the last two years, the Minerals Management Service (MMS) has been studying the resource potential of gas hydrates in federal offshore lands of the Outer Continental Shelf (OCS) off the Atlantic, Gulf of Mexico, Pacific, and Alaska in collaboration with the U.S. Geological Survey (USGS), the Department of Energy (DOE), the National Oceanic and Atmospheric Administration (NOAA), the Naval Research Lab (NRL) and academia. Utilizing its extensive seismic, well, and geochemical databases, the MMS will be reporting the in-place resource numbers within the next few months. Though the methodology of the study was not prospect oriented, discrete prospects have been recognized.

Fire in the Ice: NETL Methane Hydrate Newsletter↗