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

Morphology of the Faial Island shelf (Azores): the interplay between volcanic, erosional, depositional, tectonic and mass-wasting processes

[1] The extents of volcanic island shelves result from surf erosion, which enlarges them, and volcanic progradation, which reduces them. However, mass‐wasting, tectonics and sediment deposition also contribute to their morphology. In order to assess the relative significance of these various processes, we have mapped in detail Faial Island's shelf in the Azores archipelago based on interpretation of geophysical and geological data. The nearshore substrates of the island, down to 30–50 m depth, are rocky and covered by volcaniclastic boulder deposits formed by surf action on now‐submerged lava flows. Below those depths, sandy and gravel volcaniclastic beds dominate, building clinoforms up to the shelf edge. In some sectors of the coast, prograding lava has narrowed the shelf, but, in contrast to nearby Pico Island, we find fewer submarine‐emplaced lavas on the shelf. In this island, we interpret the distance between the coastline and the shelf edge as almost entirely a result of a straightforward competition between surf erosion and lava progradation, in which erosion dominates. Therefore shelf width can be used as a proxy for coastline age as well as for wave energy exposure. The stratigraphy of shelf deposits in boomer seismic data is examined in detail to assess the roles of different sediment sources, accommodation space and wave exposure in creating these deposits. We also show evidence of mass‐wasting at the shelf edge and discuss the possible origins of slope instability. Finally, we discuss the contributing role of tectonics for the development of the shelf.publishe

Effects of Environmental Temperature Change on the Efficiency of Coal- and Natural Gas-Fired Power Plants

Modeling studies predict that droughts and hotter water and air temperatures caused by climate warming will reduce the efficiency (η) of thermoelectric plants by 0.12–0.45% for each 1 °C of warming. We evaluate these predictions using historical performance data for 39 open- and closed-loop coal and natural gas plants from across the U.S., which operated under daily and seasonal temperature fluctuations multiples greater than future average warming projections. Seven to 14 years of hourly water (<i>T</i>_w), dry-bulb air (<i>T</i>_a), and wet-bulb air (<i>T</i>_wb) temperature recordings collected near each plant are regressed against efficiency to attain estimates of Δη per 1 °C increase. We find reductions in η with increased <i>T</i>_w (for open-loop plants) up to 1 order of magnitude less than previous estimates. We also find that changes in η associated with changes in <i>T</i>_a (open-loop plants) or <i>T</i>_wb (closed-loop plants) are not only smaller than previous estimates but also variable; i.e., η rises with <i>T</i>_a or <i>T</i>_wb for some plants and falls for others. Our findings suggest that thermoelectric plants, particularly closed-loop plants, should be more resilient to climate warming than previously expected

A Classification of Clay-Rich Subaqueous Density Flow Structures

This study presents a classification for subaqueous clay-laden sediment gravity flows. A series of laboratory flume experiments were performed using 9%, 15%, and 21% sediment mixture concentrations composed of sand, silt, clay, and tap water, on varying bed slopes of 6 degrees, 8 degrees, and 9.5 degrees, and with discharge rates of 10 and 15m(3)/hr. In addition to the characteristics of the boundary and plug layers, which have been previously used for the classification of open-channel clay-laden flows, the newly presented classification also incorporates the treatment of the free shear layer. The flow states within the boundary and free shear layers were established using calculation of the inner variable, self-similarity considerations, and the magnitude of the apparent viscosity. Based on the experimental observations four flow types were recognized: (1) a clay-rich plug flow with a laminar free shear layer, a plug layer, and a laminar boundary layer, (2) a top transitional plug flow containing a turbulent free shear layer, a plug layer, and a laminar boundary layer, (3) a transitional turbidity current with a turbulent free shear layer, no plug layer, and a laminar boundary layer, and (4) a fully turbulent turbidity current. A connection between the emplaced deposits and the relevant flow types is drawn and it is shown that a Froude number, two Reynolds numbers, and a dimensionless yield stress parameter are sufficient to associate an experimental flow type with a natural large-scale density flow. Plain Language Summary Deposits of submarine density flows can be important hydrocarbon reservoirs. Quality of these reservoirs is primarily controlled by grain size and clay concentration of the sediment mixture at the time of deposition. These parameters are dictated by the structures of the sediment carrying flow at the time of deposition. This study proposes a classification for muddy subaqueous density flows based on the flow structures. According to this classification a clay-rich flow may fall within one of four distinct flow types: (1) a cohesive plug flow with laminar free shear and boundary layers and a plug, (2) a top transitional plug flow containing a turbulent free shear layer, a plug layer, and a laminar boundary layer, (3) a transitional turbidity current with a turbulent free shear layer and a laminar boundary layer, and (4) a turbulent turbidity current. A connection between the emplaced deposit and the relevant flow type is drawn through the results obtained from flume experiments. It is proposed that a Froude number, a boundary layer Reynolds numbers, a free shear layer Reynolds number, and a dimensionless yield stress parameter are sufficient to connect a flow type with a natural large-scale density flow

Simulating migrated and inverted seismic data by filtering a geologic model

The simulation of migrated and inverted data is hampered by the high computational cost of generating 3D synthetic data, followed by processes of migration and inversion. For example, simulating the migrated seismic signature of subtle stratigraphic traps demands the expensive exercise of 3D forward modeling, followed by 3D migration of the synthetic seismograms. This computational cost can be overcome using a strategy for simulating migrated and inverted data by filtering a geologic model with 3D spatial-resolution and angle filters, respectively. A key property of the approach is this: The geologic model that describes a target zone is decoupled from the macrovelocity model used to compute the filters. The process enables a target-orientedapproach, by which a geologically detailed earth model describing a reservoir is adjusted without having to recalculate the filters. Because a spatial-resolution filter combines the results of the modeling and migration operators, the simulated images can be compared directly to a real migration image. We decompose the spatial-resolution filter into two parts and show that applying one of those parts produces output directly comparable to 1D inverted real data. Two-dimensional synthetic examples that include seismic uncertainties demonstrate the usefulness of the approach. Results from a real data example show that horizontal smearing, which is not simulated by the 1D convolution model result, is essential to understand the seismic expression of the deformation related to sulfate dissolution and karst collapse.GeotechnologyCivil Engineering and Geoscience