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Determination of sediment volumes, accumulation rates and turbidite emplacement frequencies on the Madeira Abyssal Plain (NE Atlantic): a correlation between seismic and borehole data

Determination of sediment volumes, accumulation rates and turbidite emplacement frequencies on the Madeira Abyssal Plain (NE Atlantic): a correlation between seismic and borehole data
Determination of sediment volumes, accumulation rates and turbidite emplacement frequencies on the Madeira Abyssal Plain (NE Atlantic): a correlation between seismic and borehole data
The sedimentary infill history of the Madeira Abyssal Plain (MAP) is established from correlation of ODP Leg 157 drillsites (Sites 950–952) with an almost regular grid of ?7000 km of intermediate-resolution seismic reflection profiles covering the central part of the abyssal plain. The most conspicuous seismic reflectors bounding the seismostratigraphic units have been identified and mapped. Correlation between seismic and borehole data using synthetic seismograms allows the lithological attribution and dating of the reflectors and seismostratigraphic units. Lateral mapping and correlation of seismic units also allows both the volumes and rates of accumulation of sediments within each seismostratigraphic unit and equivalent time periods of deposition to be determined. These calculations have been corrected for the effect of compaction, calculated at around 40% at the base of the drillholes. Three main turbidite types have been identified at the drillsites and their emplacement frequency has been calculated for each site and time period. Our results show that Cretaceous oceanic crust was draped with red pelagic clays, and the fracture-zone valleys were completely infilled and levelled in a geologically rather short time, probably during the latest Oligocene and Early Miocene, by organic-rich turbidites derived from the NW African continental margin. At 16 Ma, the topography was levelled enough to allow large turbidity current flows to cover the entire plain. During the Middle and Late Miocene (16–5.9 Ma), organic-rich turbidites were emplaced on the abyssal plain at a low rate of accumulation (?12 m/my). In the uppermost Miocene–Early Pliocene (5.9–3.6 Ma), turbidite emplacement increased markedly in both frequency and accumulation rate (e.g., ?26 m/my for organic-rich turbidites). During this time, period emplacement of volcanic-rich turbidites also increased in volume and frequency, a trend that continued into the Pliocene. Increased volcanic-rich turbidite emplacement correlates well with increased volcanic activity on the Canary Islands, and increased organic-rich turbidite emplacement may correlate with periods of erosion on the NW African continental margin. These erosional periods may be related to global cooling and falling sea level, intensification of bottom-water currents, and enhanced upwelling on the margin.
Madeira Abyssal Plain, sedimentary infill, seismic stratigraphy, synthetic seismogram, turbidite, continental margin
0025-3227
225-250
Alibés, B.
80494289-9640-4951-a824-a5f1184e417e
Rothwell, R.G.
fe473057-bf44-46d1-8add-88060037beb5
Canals, M.
bebbc764-f420-47bd-8963-1f5ee6706251
Weaver, P.P.E.
1ab10035-6132-46aa-8a5c-6fb23a1b8ab4
Alonso, B.
0ed9c0bb-85d7-4237-addf-3e546ad43a86
Alibés, B.
80494289-9640-4951-a824-a5f1184e417e
Rothwell, R.G.
fe473057-bf44-46d1-8add-88060037beb5
Canals, M.
bebbc764-f420-47bd-8963-1f5ee6706251
Weaver, P.P.E.
1ab10035-6132-46aa-8a5c-6fb23a1b8ab4
Alonso, B.
0ed9c0bb-85d7-4237-addf-3e546ad43a86

Alibés, B., Rothwell, R.G., Canals, M., Weaver, P.P.E. and Alonso, B. (1999) Determination of sediment volumes, accumulation rates and turbidite emplacement frequencies on the Madeira Abyssal Plain (NE Atlantic): a correlation between seismic and borehole data. Marine Geology, 160 (3-4), 225-250. (doi:10.1016/S0025-3227(99)00026-2).

Record type: Article

Abstract

The sedimentary infill history of the Madeira Abyssal Plain (MAP) is established from correlation of ODP Leg 157 drillsites (Sites 950–952) with an almost regular grid of ?7000 km of intermediate-resolution seismic reflection profiles covering the central part of the abyssal plain. The most conspicuous seismic reflectors bounding the seismostratigraphic units have been identified and mapped. Correlation between seismic and borehole data using synthetic seismograms allows the lithological attribution and dating of the reflectors and seismostratigraphic units. Lateral mapping and correlation of seismic units also allows both the volumes and rates of accumulation of sediments within each seismostratigraphic unit and equivalent time periods of deposition to be determined. These calculations have been corrected for the effect of compaction, calculated at around 40% at the base of the drillholes. Three main turbidite types have been identified at the drillsites and their emplacement frequency has been calculated for each site and time period. Our results show that Cretaceous oceanic crust was draped with red pelagic clays, and the fracture-zone valleys were completely infilled and levelled in a geologically rather short time, probably during the latest Oligocene and Early Miocene, by organic-rich turbidites derived from the NW African continental margin. At 16 Ma, the topography was levelled enough to allow large turbidity current flows to cover the entire plain. During the Middle and Late Miocene (16–5.9 Ma), organic-rich turbidites were emplaced on the abyssal plain at a low rate of accumulation (?12 m/my). In the uppermost Miocene–Early Pliocene (5.9–3.6 Ma), turbidite emplacement increased markedly in both frequency and accumulation rate (e.g., ?26 m/my for organic-rich turbidites). During this time, period emplacement of volcanic-rich turbidites also increased in volume and frequency, a trend that continued into the Pliocene. Increased volcanic-rich turbidite emplacement correlates well with increased volcanic activity on the Canary Islands, and increased organic-rich turbidite emplacement may correlate with periods of erosion on the NW African continental margin. These erosional periods may be related to global cooling and falling sea level, intensification of bottom-water currents, and enhanced upwelling on the margin.

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Published date: 1 September 1999
Keywords: Madeira Abyssal Plain, sedimentary infill, seismic stratigraphy, synthetic seismogram, turbidite, continental margin
Organisations: Marine Geoscience

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Local EPrints ID: 355628
URI: http://eprints.soton.ac.uk/id/eprint/355628
ISSN: 0025-3227
PURE UUID: 296c11d5-09c2-40ac-bbca-d4c374fbc11e

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Date deposited: 09 Aug 2013 09:13
Last modified: 16 Jul 2019 21:26

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Contributors

Author: B. Alibés
Author: R.G. Rothwell
Author: M. Canals
Author: P.P.E. Weaver
Author: B. Alonso

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