Swath Mapping on the Continental Shelf and Slope: The Eel River Basin, Northern California

First Paragraph The STRATAFORM program sponsored by the Office of Naval Research (Nittrouer and Kravitz, 1996, this issue) seeks to understand how sedimentary processes lead to the formation of the stratigraphic sequences on continental margins. A central challenge facing this effort is to understand the transport of sediments in shore-parallel as well as shore-perpendicular directions• Multidimensionality is necessary to describe, for example, the accumulation of sediments from river inputs, the distribution of gullies and canyons on the slope, the meandering of channels, and the structure of slumps and slides

Recovery Act: 'Carbonsheds' as a Framework for Optimizing United States Carbon Capture and Storage (CCS) Pipeline Transport on a Regional to National Scale

Carbonsheds are regions in which the estimated cost of transporting CO{sub 2} from any (plant) location in the region to the storage site it encompasses is cheaper than piping the CO{sub 2} to a storage site outside the region. We use carbonsheds to analyze the cost of transport and storage of CO{sub 2} in deploying CCS on land and offshore of the continental U.S. We find that onshore the average cost of transport and storage within carbonsheds is roughly $10/t when sources cooperate to reduce transport costs, with the costs increasing as storage options are depleted over time. Offshore transport and storage costs by comparison are found to be roughly twice as expensive but t may still be attractive because of easier access to property rights for sub-seafloor storage as well as a simpler regulatory system, and possibly lower MMV requirements, at least in the deep-ocean where pressures and temperatures would keep the CO{sub 2} negatively buoyant. Agent-based modeling of CCS deployment within carbonsheds under various policy scenarios suggests that the most cost-effective strategy at this point in time is to focus detailed geology characterization of storage potential on only the largest onshore reservoirs where the potential for mitigating emissions is greatest and the cost of storage appears that it will be among the cheapest

Geochemical results from wireline logs in the Celebes Sea, Sites 767 and 770 of Leg 124

Journal ArticleGeochemical well logs were obtained at ODP Sites 767 and 770 in the Celebes Sea. The log data obtained at sea have been corrected for borehole size changes, the effects of drilling fluids, and logging-speed variations. The processed logs are then used to calculate the amounts of the three major radioactive elements (Th, U, and K) and the dry weight percentages of oxides every 0.1524 m throughout the logged intervals. Numerous oxide core measurements were made for Site 767 and for the basement section of Site 770. Core and log measurements of CaO, A12O3, FeO*, K2O, and TiO2 agree well. At both sites, however, the log-derived SiO2 is higher than that measured on cores. The discrepancy is due to the fact that MgO or Na2O could not be calculated from the logs, causing each of the elements measured by the geochemical tool to be slightly high, an effect that is most apparent in SiO2 because it makes up the greatest portion of the rock-forming elements

Gravity gradiometry resurfaces

Twelve years ago, reading a passage from the submarine novel The Hunt for Red October by Tom Clancy was as dose as any exploration geophysicist got to gravity gradiometry. This early technique in Gulf Coast exploration, which faded from use with the development of modern gravity instrumentation in the 1930s, had been relegated to brief historical sections of introductory texts. In the 1970s, driven by both navigation and missile launching requirements, the U.S. Navy spent hundreds of millions of dollars developing a system to measure gravity gradients; this system was somewhat more complex than the fictional one Clancy installed on the Red October. The end of the Cold War triggered the introduction of classified military technology to exploration geophysics and other fields. Three years ago the U.S. Navy began to explore civilian applications for submarine gravity gradient technology. This article describes gravity gradients, the developing uses of gravity gradiometry in exploration, and future possibilities for the technique

Transient erosion in the Valencia Trough turbidite systems, NW Mediterranean Basin

12 pages, 9 figuresSubmarine canyons can efficiently drain sediments from continental margins just as river systems do in subaerial catchments. Like in river systems, submarine canyons are often arranged as complex drainage networks that evolve from patterns of erosion and deposition. In the present paper we use a morphometric analysis of submarine canyon-channel long-profiles to study the recent sedimentary history of the Valencia Trough turbidite system (VTTS) in the NW Mediterranean Sea. The VTTS is unique in that it drains sediment from margins with contrasting morphologies through a single “trunk” conduit, the Valencia Channel. The Valencia Channel has been active since the late Miocene, evolving in response to Plio-Quaternary episodes of erosion and deposition. The integrated analysis of long-profiles obtained from high-resolution bathymetric data across the entire turbidite system shows evidence for transient canyon incision in the form of knickpoints and hanging tributaries. Multiple factors appear to have triggered these periods of incision. These include a large debris flow at 11,500 yr BP that disrupted the upper reaches of the VTTS and glacio-eustatic lowstands that forced shifting of sediment input to the VTTS. Based on these inferences, long-term time-averaged incision rates for the Valencia Channel have been estimated. The evidence we present strongly suggests that Foix Canyon has played a key role in the drainage dynamics of the VTTS in the past. This study builds conceptually on a recent modeling study that provides a morphodynamic explanation for the long-term evolution of submarine canyon thalweg profiles. The procedure and results from this work are of potential application to other submarine sediment drainage systems, past and present, including those containing mid-ocean type valleys like the Valencia ChannelThis research was supported by the HERMIONE project, EC contract 226354-HERMIONE, funded by the European Commission's Seventh Framework Programme, and the HERMES Project, EC contract GOCE-CT-2005-511234, funded by the European Commission's Sixth Framework Programme under the priority “Sustainable Development, Global Change and Ecosystems”. It has also benefited from inputs by the PROMETEO (CTM2007-66316-C02-01/MAR), EDINSED3D (CTM2007-64880/MAR), and the GRACCIE CONSOLIDER (CSD2007-00067) projects, funded by the Spanish RTD Programme. GRC Geociències Marines is supported by Generalitat de Catalunya “Grups de Recerca Consolidats” grant 2009 SGR 1305Peer reviewe

Transient erosion in the Valencia Trough turbidite systems, NW Mediterranean Basin

Submarine canyons can efficiently drain sediments from continental margins just as river systems do in subaerial catchments. Like in river systems, submarine canyons are often arranged as complex drainage networks that evolve from patterns of erosion and deposition. In the present paper we use a morphometric analysis of submarine canyon-channel long-profiles to study the recent sedimentary history of the Valencia Trough turbidite system (VTTS) in the NW Mediterranean Sea. The VTTS is unique in that it drains sediment from margins with contrasting morphologies through a single "trunk" conduit, the Valencia Channel. The Valencia Channel has been active since the late Miocene, evolving in response to Plio-Quaternary episodes of erosion and deposition. The integrated analysis of long-profiles obtained from high-resolution bathymetric data across the entire turbidite system shows evidence for transient canyon incision in the form of knickpoints and hanging tributaries. Multiple factors appear to have triggered these periods of incision. These include a large debris flow at 11,500 yr BP that disrupted the upper reaches of the VTTS and glacio-eustatic lowstands that forced shifting of sediment input to the VTTS. Based on these inferences, long-term time-averaged incision rates for the Valencia Channel have been estimated. The evidence we present strongly suggests that Foix Canyon has played a key role in the drainage dynamics of the VTTS in the past. This study builds conceptually on a recent modeling study that provides a morphodynamic explanation for the long-term evolution of submarine canyon thalweg profiles. The procedure and results from this work are of potential application to other submarine sediment drainage systems, past and present, including those containing mid-ocean type valleys like the Valencia Channel

Geochemical Logging in the Cajon Pass Drill Hole and Its Application to a New, Oxide, Igneous Rock Classification Scheme

A new elemental oxide classification scheme for crystalline rocks is developed and applied to geochemical well logs from the Cajon Pass drill hole. This classification scheme takes advantage of measurements of elements taken by a geochemical logging tool string. It uses K_2O versus SiO_2/Al_2O_3 to distinguish between granites, granodiorites, tonalites, syenites, monzonites, diorites, and gabbros. Oxide measurements from cores are used to calibrate the elemental abundances determined from the well logs. From these logs, a detailed lithologic column of the core is generated. The lithologic column derived from the well log classification scheme is compared with a lithologic column constructed from core samples and well cuttings. In the upper 1295 m of the well, agreement between the two columns is good. Discrepancies occur from 1295 to 2073 m and are believed to be caused by the occurrence of rock types not distinguished by the classification scheme and/or the occurrence of secondary minerals. Despite these discrepancies, the well log-based classification scheme helps to distinguish changes in rock type and shows potential as an aid to the construction of lithologic columns in boreholes of crystalline rocks

Longitudinal flow evolution and turbulence structure of dynamically similar, sustained, saline density and turbidity currents

Experimental results are presented concerning flow evolution and turbulence structure of sustained saline and turbidity flows generated on 0°, 3°, 6°, and 9° sloping ramps that terminate abruptly onto a horizontal floor. Two-component velocity and current density were measured with an ultrasonic Doppler velocity profiler and siphon sampler on the slope, just beyond the slope break and downstream on the horizontal floor. Three main factors influence longitudinal flow evolution and turbulence structure: sediment transport and sedimentation, slope angle, and the presence of a slope break. These controls interact differently depending on flow type. Sediment transport is accompanied by an inertial fluid reaction that enhances Reynolds stresses in turbidity flows. Thus turbidity flows mix more vigorously than equivalent saline density flows. For saline flows, turbulent kinetic energy is dependent on slope, and rapid deceleration occurs on the horizontal floor. For turbidity flows, normalized turbulent kinetic energy increases downstream, and mean streamwise deceleration is reduced compared with saline flows. The slope break causes mean bed-normal velocity of turbidity flows to become negative and have a gentler gradient compared with other locations. A reduction of peak Reynolds normal stress in the bed-normal direction is accompanied by an increase in turbulent accelerations across the rest of the flow thickness. Thus the presence of particles acts to increase Reynolds normal stresses independently of gradients of mean velocity, and sediment transport increases across the break in slope. The experiments illustrate that saline density currents may not be good dynamic analogues for natural turbidity currents

Survival of a submarine canyon during long-term outbuilding of a continental margin

Net-depositional submarine canyons are common in continental slope strata, but how they survive and prograde on constructional margins is poorly understood. In this study we present field evidence for the coevolution of a submarine canyon and the adjacent continental slope. Using a three-dimensional seismic data cube that images the Ebro margin (northwest Mediterranean), we identify a preserved canyon on a middle Pleistocene paleosurface and relate it directly to its expression on the present-day seafloor. A subparallel stacking pattern of seismic reflectors, similar to that seen between prograding clinoforms in intercanyon areas, is observed between the modern and paleocanyon thalwegs. The concavity of the modern long profile differs from the convex-concave long profile on the middle Pleistocene surface, suggesting a long-term change in canyon sedimentation. We interpret this change as a shift to a canyon dominated by turbidity currents from one strongly influenced by the pattern of sedimentation that built the open-slope canyon interfluves. We find support for our interpretation in previous studies of the Ebro margin