Seismic Facies and Late Quaternary Growth of Amazon Submarine Fan

Flood, Roger D.; Manley, P. L.; Kowsmann, Renato Oscar; Appi, Ciro Jorge; Pirmez, Carlos

doi:10.1007/978-1-4684-8276-8_23

Cited by 108 publications

(150 citation statements)

References 14 publications

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“…The sediments recovered comprise sand beds with mudclast intervals and are separated by muddier units. On seismic reflection profiles this facies forms characteristic flat, high-amplitude, lobe-like packets (HARPs) that have been recognized at the base of all the channel-levee systems in the middle fan and extend partly to the lower fan (Flood et al, 1991). HARPs are thought to be formed after avulsion of a previously active channel-levee system by rapid aggradation of sheet-flow sand.…”

Section: Late Pleistocene Channel 5 Systemmentioning

confidence: 99%

Clay mineral distribution and significance in Quaternary sediments of the Amazon Fan

Debrabant¹,

López²,

Chamley³

1997

Proceedings of the Ocean Drilling Program, 155 Scientific Results

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The clay mineral assemblages of samples from the Amazon Fan were investigated in middle Pleistocene to Holocene sediments from 16 Ocean Drilling Program Leg 155 sites and were placed in lithologic successions to study continental evolution and transport conditions. The sediments sampled along a transect parallel to the main channel reflect moderate differential settling processes, whereas those studied along a transect roughly parallel to the coast clearly suggest winnowing effects related to the North Brazil Current. High-resolution analyses of Holocene deposits reflect the dominant influence of downstream soil erosion relative to supply from the Andean range and the progressive increase of soil-derived relative to rock-derived outputs. The middle Pleistocene to uppermost Pleistocene and Holocene successions are marked by a constantly warm climatic background and by noticeable modifications in the rock-derived (illite, chlorite) and soil-derived (smectite, kaolinite) products. These products successively reflect sea-level changes, tectonic rejuvenation in the Andean range, regressive erosion, and rainfall increase.

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Section: Late Pleistocene Channel 5 Systemmentioning

confidence: 99%

Clay mineral distribution and significance in Quaternary sediments of the Amazon Fan

Debrabant¹,

López²,

Chamley³

1997

Proceedings of the Ocean Drilling Program, 155 Scientific Results

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“…This cyclic pattern was recognized within the upper and middle Amazon Fan and led to the identification of four stacked channel-levee complexes. The youngest, the Upper Levee Complex (ULC, isotope Stages 2−4), overlies both the Middle Levee Complex (MLC, isotope Stage 6) and the Lower Levee Complex (LLC, isotope Stage 8) while the Bottom Levee Complex (BLC) appears stratigraphically below all three (Flood et al, 1991; (Fig. 2).…”

Section: Introductionmentioning

confidence: 99%

“…Within the middle fan, lobe-like, high-amplitude refection packets (HARPs) underlie the newly formed channel-levee systems and are related to the avulsion. These HARP units extend downfan from the point of bifurcation to form part of the lower fan (Flood et al, 1991). Thus, several seismic architectural units (e.g., channel-levee systems, mass-transport deposits, HARs, and HARPs) have been previously mapped throughout the Amazon Fan (Damuth et al, 1988;Manley and Flood, 1988;Flood et al, 1991;Pirmez, 1994;Pirmez and Flood, 1995).…”

Section: Introductionmentioning

confidence: 99%

“…These HARP units extend downfan from the point of bifurcation to form part of the lower fan (Flood et al, 1991). Thus, several seismic architectural units (e.g., channel-levee systems, mass-transport deposits, HARs, and HARPs) have been previously mapped throughout the Amazon Fan (Damuth et al, 1988;Manley and Flood, 1988;Flood et al, 1991;Pirmez, 1994;Pirmez and Flood, 1995). During ODP Leg 155, holes at 17 sites were drilled through these acoustically defined units, and approximately 4 km of Pleistocene-age sediment was recovered (Figs.…”

Section: Introductionmentioning

confidence: 99%

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Grain-size characterization of Amazon Fan deposits and comparison to seismic facies units

Manley¹,

Pirmez²,

Busch³

et al. 1997

Proceedings of the Ocean Drilling Program, 155 Scientific Results

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Prior to Ocean Drilling Program Leg 155, the architecture of the Amazon Fan, as well as those of other modern submarine fans, had been investigated primarily by seismic reflection profiles. The acoustic facies and stratal patterns observed on these profiles provided a wealth of information that allowed deciphering fan growth patterns and the geometry of fan deposits. However, lithofacies could only be inferred from the seismic reflection data. Here we analyze grain-size data from 13 sites drilled during Leg 155, and place the results in the context of the stratigraphic units interpreted from seismic reflection data. Clay, silt, and fine sand are the dominant grain sizes of all cores retrieved from the Amazon Fan. In this mud-rich fan, sand is concentrated within the channel thalweg, at the base of channel-levee systems within the middle fan, and forms a significant fraction of the lower fan deposits drilled. All channel-levee deposits drilled are characterized by a fining-upward trend and by an overall coarsening in the downfan direction. Downfan coarsening of the levee deposits probably results from very efficient sorting associated with the channelized flow of turbidity currents together with the overall decrease in channel relief downfan. Finingupward cycles within a channel-levee system are observed in the middle fan where multiple phases of levee development are stacked upon each other. Each growth phase is marked by an abrupt coarsening that marks a channel bifurcation occurring downslope, followed by a fining-upward sequence of levee aggradation. Channel bifurcation results in the reworking of older channel deposits, and the formation of laterally widespread units. High-amplitude reflections (HARs) beneath the channel axis and high-amplitude reflection packet (HARPs) units are composed of two distinct grain-size populations. HARs and HARPs are the coarsest units that form the fan, with sizes up to 0 ø. Both units display an overall coarsening downfan. These characteristics are likely the result of multistep transport of sand downfan. Thick acoustically transparent units on seismic profiles are correlated to large mass-transport deposits, displaying grain-size characteristics similar to levee deposits with an overall finingupward and downfan-coarsening trend.

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“…Detailed mapping of the Amazon Fan with seismic-reflection profiles, long-range side-scan sonar (GLORIA), and SeaBeam bathymetry have shown the development of the extensive MTDs of more than 50,000 km 3 (Damuth et al, 1983;Damuth and Flood, 1985;Flood and Damuth, 1987;Manley and Flood, 1988;Damuth et al, 1988;Flood et al, 1991) (Figs. 1, 2).…”

Section: Introductionmentioning

confidence: 99%

Computed tomography scan analysis of Site 941 cores, western mass-transport deposit, Amazon Fan

Soh¹

1997

Proceedings of the Ocean Drilling Program, 155 Scientific Results

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X-ray computed tomography (CT) and pore-water chemistry analyses were performed using whole round-core samples from the regionally extensive Western Mass-Transport Deposit (WMTD), Site 941 of Ocean Drilling Program (ODP) Leg 155, on the Amazon Fan. Here, the CT value has a good correlation with the bulk density and water content of the sediment. The CT image shows a plume-shaped, fluidized structure with gas bubbles in the mud sediment, Sample 155-941B-6H-4, 0−20 cm, at 47 meters below seafloor, at the top of a 2-m-thick soupy and gassy sediment interval. Significant increase in the water content was recognized in the fluidized sediment when compared to those of the surrounding unfluidized sediments. The content coincided with the fresh-water dilution estimated from the anomalous pore-water chemistry. The fluidization was thus caused by the dissociation of gas hydrate. The quantitative CT value analysis allows us to estimate that the percentage of gas hydrate content reaches ~10 vol% of the fluidized sediment (17.5 vol% of the pore space). This content seems to be equivalent to the highest contents of the gas hydrate above bottom-simulating reflectors (BSRs) reported from other hydrate regions. BSRs underlie parts of the continental slope updip from the WMTD. The 2-m-thick soupy and gassy sediment is inferred to be derived from a part of "missing" sediment interpreted from seismic-reflection profiles of the source area of the WMTD that is bounded by scarps up to 200 m high. Furthermore, the disassociation of gas hydrate should be the most important trigger mechanism for causing the regionally extensive slope failure that produced the WMTD.

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Seismic Facies and Late Quaternary Growth of Amazon Submarine Fan

Cited by 108 publications

References 14 publications

Clay mineral distribution and significance in Quaternary sediments of the Amazon Fan

Clay mineral distribution and significance in Quaternary sediments of the Amazon Fan

Grain-size characterization of Amazon Fan deposits and comparison to seismic facies units

Computed tomography scan analysis of Site 941 cores, western mass-transport deposit, Amazon Fan

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