Sedimentary development of the Louisiana continental shelf related to sea level cycles: Part II—seismic response

1988 ◽  
Vol 8 (2) ◽  
pp. 109-119 ◽  
Author(s):  
James M. Coleman ◽  
Harry H. Roberts
Keyword(s):  
Continental Shelf ◽  
Seismic Response ◽  
Sea Level ◽  
Louisiana Continental Shelf

Basalt from Louisiana continental shelf

1984 ◽  
Vol 4 (2) ◽  
pp. 69-76 ◽  
Author(s):  
Richard Rezak ◽  
Thomas T. Tieh
Keyword(s):  
Continental Shelf ◽  
Louisiana Continental Shelf

scholarly journals A model of the methane cycle, permafrost, and hydrology of the Siberian continental margin

2015 ◽  
Vol 12 (10) ◽  
pp. 2953-2974 ◽  
Author(s):  
D. Archer
Keyword(s):  
Continental Shelf ◽  
Sea Level ◽  
Methane Hydrate ◽  
Fossil Fuel ◽  
Methane Flux ◽  
Pore Fluid ◽  
Permafrost Zone ◽  
Sediment Surface ◽  
Sediment Column ◽  
Atmospheric Flux

Abstract. A two-dimensional model of a sediment column, with Darcy fluid flow, biological and thermal methane production, and permafrost and methane hydrate formation, is subjected to glacial–interglacial cycles in sea level, alternately exposing the continental shelf to the cold atmosphere during glacial times and immersing it in the ocean in interglacial times. The glacial cycles are followed by a "long-tail" 100 kyr warming due to fossil fuel combustion. The salinity of the sediment column in the interior of the shelf can be decreased by hydrological forcing to depths well below sea level when the sediment is exposed to the atmosphere. There is no analogous advective seawater-injecting mechanism upon resubmergence, only slower diffusive mechanisms. This hydrological ratchet is consistent with the existence of freshwater beneath the sea floor on continental shelves around the world, left over from the last glacial period. The salt content of the sediment column affects the relative proportions of the solid and fluid H2O-containing phases, but in the permafrost zone the salinity in the pore fluid brine is a function of temperature only, controlled by equilibrium with ice. Ice can tolerate a higher salinity in the pore fluid than methane hydrate can at low pressure and temperature, excluding methane hydrate from thermodynamic stability in the permafrost zone. The implication is that any methane hydrate existing today will be insulated from anthropogenic climate change by hundreds of meters of sediment, resulting in a response time of thousands of years. The strongest impact of the glacial–interglacial cycles on the atmospheric methane flux is due to bubbles dissolving in the ocean when sea level is high. When sea level is low and the sediment surface is exposed to the atmosphere, the atmospheric flux is sensitive to whether permafrost inhibits bubble migration in the model. If it does, the atmospheric flux is highest during the glaciating, sea level regression (soil-freezing) part of the cycle rather than during deglacial transgression (warming and thawing). The atmospheric flux response to a warming climate is small, relative to the rest of the methane sources to the atmosphere in the global budget, because of the ongoing flooding of the continental shelf. The increased methane flux due to ocean warming could be completely counteracted by a sea level rise of tens of meters on millennial timescales due to the loss of ice sheets, decreasing the efficiency of bubble transit through the water column. The model results give no indication of a mechanism by which methane emissions from the Siberian continental shelf could have a significant impact on the near-term evolution of Earth's climate, but on millennial timescales the release of carbon from hydrate and permafrost could contribute significantly to the fossil fuel carbon burden in the atmosphere–ocean–terrestrial carbon cycle.

scholarly journals Flowing into the unknown: inferred paleodrainages for studying the ichthyofauna of Brazilian coastal rivers

2018 ◽  
Vol 16 (3) ◽  
Author(s):  
Andréa T. Thomaz ◽  
L. Lacey Knowles
Keyword(s):  
Information System ◽  
Continental Shelf ◽  
Sea Level ◽  
Brazilian Coast ◽  
Strongly Correlated ◽  
Bathymetric Data ◽  
Biological Studies ◽  
Coastal Rivers ◽  
Coastal Basins ◽  
Geologic Data

ABSTRACT The eastern coastal basins of Brazil are a series of small and isolated rivers that drain directly into the Atlantic Ocean. During the Pleistocene, sea-level retreat caused by glaciations exposed the continental shelf, resulting in enlarged paleodrainages that connected rivers that are isolated today. Using Geographic Information System (GIS), we infer the distribution of these paleodrainages, and their properties for the east Brazilian coast. Specifically, using elevation/bathymetric data for the largest sea-level retreats during the Pleistocene, the paleodrainages, their area and the number of contemporary basins connected by each palaeodrainage, was inferred. For the 145 inferred paleodrainages, total paleodrainage area is strongly correlated with the contemporary area encompassed by each paleodrainage, as well as with the number of contemporary basins encompassed by a paleodrainage. Differences in the continental shelf exposure along the coast affected the degree of past connectivity among contemporary rivers. With our results freely available, we discuss how paleodrainages have tremendous utility in biological studies, especially in regions with limited geologic data. With respect to the diverse ichthyofauna of the Brazilian coast, and its high endemism, we highlight how the inferred paleodrainages provide a backdrop to test hypotheses about the effect of past riverine connectivity on diversity patterns.

scholarly journals Arrecifes de arenisca en el Golfo de Salamanca, plataforma continental del Caribe colombiano

2019 ◽  
Vol 48 (1) ◽  
Author(s):  
Sven Zea ◽  
Gladys Bernal ◽  
Gloria López ◽  
Marion Weber ◽  
Rocío Del Pilar García-Urueña
Keyword(s):  
Continental Shelf ◽  
Sea Level ◽  
Petrographic Analysis ◽  
Saline Environments ◽  
Fine Grained ◽  
Lagoon System

In tropical seas there are submerged hard bottoms that harbor corals but that are not coralline in origin. This is the case for the “Banco de las Ánimas” sector in the continental shelf of the Gulf of Salamanca, Colombian Caribbean. In its upper portion (14–16 m in depth), there are low mounds of sandstone blocks and slabs, conforming reefs, colonized by coralline biota and sparse corals. To confirm their lithology an initial petrographic analysis was carried out, which showed the rocks are made up of fine-grained sands, mature in texture, cemented by dolomite. It is proposed that these reefs were formed in a beach–dune–lagoon system during an ancient sea level, similar to the recent coastal bar of Salamanca. In these high-evaporation, supratidal saline environments, they could have been formed as beach rocks or as eolianites, by aragonite cementation, modified later into dolomite. Whether the foundation of the deeper coral formations of the bankis also sandstone or in fact coralline, remains to be determined.

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