Late Pleistocene sediment accumulation in the lower slope off the Rio Grande terrace, southern Brazilian Continental Margin

2020 ◽  
Author(s):  
Renato Pereira Lopes ◽  
Carla Bonetti ◽  
Gilberto Silveira dos Santos ◽  
Maria Alejandra Gomez Pivel ◽  
Sandro Monticelli Petró ◽  
...  
Keyword(s):  
Late Pleistocene ◽  
Continental Margin ◽  
Sediment Accumulation ◽  
Rio Grande ◽  
Pleistocene Sediment ◽  
Lower Slope

scholarly journals Gas Seeps at the Edge of the Gas Hydrate Stability Zone on Brazil’s Continental Margin

Geosciences ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 193 ◽  
Author(s):  
Marcelo Ketzer ◽  
Daniel Praeg ◽  
Maria A.G. Pivel ◽  
Adolpho H. Augustin ◽  
Luiz F. Rodrigues ◽  
...  
Keyword(s):  
Gravitational Collapse ◽  
Continental Margin ◽  
Gas Hydrate ◽  
Deep Sea ◽  
Rio Grande ◽  
Cold Seep ◽  
Stability Zone ◽  
The Stability ◽  
Sea Fan ◽  
Hydrate Stability

Gas hydrate provinces occur in two sedimentary basins along Brazil’s continental margin: (1) The Rio Grande Cone in the southeast, and (2) the Amazon deep-sea fan in the equatorial region. The occurrence of gas hydrates in these depocenters was first detected geophysically and has recently been proven by seafloor sampling of gas vents, detected as water column acoustic anomalies rising from seafloor depressions (pockmarks) and/or mounds, many associated with seafloor faults formed by the gravitational collapse of both depocenters. The gas vents include typical features of cold seep systems, including shallow sulphate reduction depths (<4 m), authigenic carbonate pavements, and chemosynthetic ecosystems. In both areas, gas sampled in hydrate and in sediments is dominantly formed by biogenic methane. Calculation of the methane hydrate stability zone for water temperatures in the two areas shows that gas vents occur along its feather edge (water depths between 510 and 760 m in the Rio Grande Cone and between 500 and 670 m in the Amazon deep-sea fan), but also in deeper waters within the stability zone. Gas venting along the feather edge of the stability zone could reflect gas hydrate dissociation and release to the oceans, as inferred on other continental margins, or upward fluid flow through the stability zone facilitated by tectonic structures recording the gravitational collapse of both depocenters. The potential quantity of venting gas on the Brazilian margin under different scenarios of natural or anthropogenic change requires further investigation. The studied areas provide natural laboratories where these critical processes can be analyzed and quantified.

scholarly journals Pleistocene sediment offloading and the global sulfur cycle

2015 ◽  
Vol 12 (10) ◽  
pp. 3043-3060 ◽  
Author(s):  
S. Markovic ◽  
A. Paytan ◽  
U. G. Wortmann
Keyword(s):  
Sea Level ◽  
Considerable Increase ◽  
Sediment Accumulation ◽  
Sulfur Cycle ◽  
Sea Level Fluctuations ◽  
Sediment Budgets ◽  
Shelf Sediment ◽  
Continental Shelves ◽  
Shelf Sediments ◽  
Pleistocene Sediment

Abstract. Quaternary sea level fluctuations have greatly affected the sediment budgets of the continental shelves. Previous studies suggested that this caused a considerable increase in the net loss of shelf sediments. Since sediment accumulation and erosion are closely tied to the formation and re-oxidation of pyrite, we use a high-resolution record of sulfur isotope ratios (34S / 32S) of marine sulfate to evaluate the implications of the so-called "shelf sediment offloading" on the global sulfur cycle. Modeling of our δ34S record suggests that erosion during sea level lowstands was only partly compensated by increased sedimentation during times of rising sea level and sea level highstands. Furthermore, our data suggests that shelf systems reached a new equilibrium state about 700 ka, which considerably slowed or terminated shelf sediment offloading.

scholarly journals Late Pleistocene-Holocene sedimentary fluxes of organic carbon and biogenic silica in the northwestern Ross Sea, Antarctica

1998 ◽  
Vol 27 ◽  
pp. 697-703 ◽  
Author(s):  
M. Frignani ◽  
F. Giglio ◽  
L. Langone ◽  
M. Ravaioli ◽  
A. Mangini
Keyword(s):  
Late Pleistocene ◽  
Biogenic Silica ◽  
Ross Sea ◽  
Sediment Accumulation ◽  
Stratigraphic Correlation ◽  
Radiocarbon Dates ◽  
Marine Sedimentation ◽  
Core Logging ◽  
Bulk Organic Matter ◽  
Biogenic Components

Eight sediment gravity cores, collected from the joides and Drygalski basins, were analysed in order to understand late Pleistocene-Holocene biogenic flux changes in the Ross Sea, driven by paleoenvironmental changes. Core lithologies and magnetic-susceptibility depth profiles were used for core logging and stratigraphic correlation. Nineteen AMS radiocarbon dates of bulk organic matter were used to set chronological constraints and calculate sediment accumulation rates. These rates, which vary from 1.4-38 cm ka−1. were used to obtain the burial fluxes of biogenic components. The highest fluxes occur in the deepest parts of the basins (TOC, 0.05-0.2 g cm−2ka−1; biogenic silica, 1.5-5 g cm−1ka−1), where as topographic highs show the lowest values (TOC, 0.01-0.1 g cm−2ka−1; biogenic silica, 0.1-1.4 g cm−2ka−1). Dramatic changes in both physical properties and fluxes record the establishment of open marine-sedimentation conditions which occurred first in the joides basin and then, with a delay of ca. 6000 years, in the Drygalski basin. Both TOC and biogenic-silica fluxes increase through the Holocene, though slightly differently. The high fluxes of both10Be and biogenic Ba suggest that sediment accumulation at basin sites is strongly influenced by lateral transport.

scholarly journals O Gênero Stylatractus Haeckel, 1887 (Radiolaria) em Sedimentos do Pleistoceno Superior - Holoceno da Margem Continental do Rio Grande do Sul

2001 ◽  
Vol 28 (2) ◽  
pp. 263
Author(s):  
SIMONE BAECKER FAUTH ◽  
VALESCA BRASIL LEMOS
Keyword(s):  
Detailed Analysis ◽  
Continental Margin ◽  
Species Distribution ◽  
Rio Grande ◽  
Growth Patterns ◽  
Rio Grande Do Sul ◽  
Upper Pleistocene ◽  
Holocene Sediments ◽  
First Occurrence

The genus Stylatractus Haeckel, 1887 (Radiolaria, Actinommidae) is abundant in upper Pleistocene – Holocene sediments form the Rio Grande do Sul continental margin. Some species of this genus are important Cenozoic biostratigraphic tools. A detailed analysis of the species distribution in Core T18 (GEOMAR VII), as well as an estimate of the chronology of these sediments was done. A revision of Stylatractus is proposed, based on the growth patterns of the Actinommidae skeletons. Three species of Stylatratus were identified in the studied material: Stylatractus neptunus Haeckel, emend., Stylatractus pluto Haeckel n. comb. and Stylatractus nerinus n.sp. The occurrence of Stylatractus nerinus n.sp. suggests that these sediments were deposited in the upper Pleistocene. The Pleistocene-Holocene transition is established by the first occurrence of Stylatractus pluto Haeckel n. comb. The results obtained from Core T18 can be extended to other cores from the Rio Grande do Sul continental margin where the genus was reported.

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