High-resolution chemostratigraphy of Quaternary distal turbidites: a case study of new methods for the analysis and correlation of barren sequences

Abstract

The late Quaternary distal turbidites of the NE Atlantic Madeira Abyssal Plain (MAP), represent one of the most intensely studied sequences in the modern deep ocean. More than 160 sediment cores have been recovered from the 68 x 10 3 km 2 of the plain, and existing litho-and biostratigraphies, when integrated with oxygen stable-isotope data for other areas of the NE Atlantic, provide a tight spatial and temporal framework. We have used the MAP as a test-bed to assess the applications of inorganic geochemistry as a sedimentological and stratigraphic tool. Data for 22 major and trace elements were obtained in over 500 samples taken from representative cores. Chemostratigraphic sequences are highly uniform across the plain, and several turbidites have unique geochemical signatures, providing a means of establishing bed-by-bed correlations over distances of > 500km. Cluster and principal component analysis confirm the statistical validity of empirically derived correlations and groupings. Vertical and lateral geochemical trends within beds document the sedimentological evolution of flows, and may be used to establish palaeotransport pathways. Four compositional groups are interpreted as representing derivations from different source areas: (1) the margins of the NW Africa off Morocco; (2) off Western Sahara; (3) the Canary Islands; (4) the Cruiser-Great Meteor East seamount chains. The study amply demonstrates the viability of chemostratigraphy for the correlation and analysis of sedimentary sequences, providing a stratigraphic resolution and reliability which matches or exceeds that obtainable by other techniques.

Use of Calibrated ITRAX XRF Data in Determining Turbidite Geochemistry and Provenance in Agadir Basin, Northwest African Passive Margin

“…A number of terrigenous (USGS MAG-1 and SCo-1) and volcanic (USGS BHVO-2 and BIR-1; JGS JB-1a, JB-2, JB-3 and JGB-1) geochemical reference materials (GRMs) were used to assess analytical accuracy and precision (Appendix 2). The ranges of concentrations used in the production of artificial standards were constrained by element concentrations from previous studies of Madeira Abyssal Plain turbidites (de Lange et al 1987;Pearce and Jarvis 1995).…”

“…However, these studies used a limited number of samples from turbidite mudcaps for analysis by ICP-AES (de Lange et al 1987;Pearce and Jarvis 1995). The ITRAX μXRF core scanner allows direct and non-destructive measurement of sediment chemistry in-situ.…”

“…Previous studies analysed bulk samples from each turbidite mudcap using inductively coupled plasma optical emission spectroscopy (ICP-OES) (de Lange et al 1987;Pearce and Jarvis 1995;Jarvis et al 1998). However, such methodologies requiring acid digests of numerous sub-samples are time-consuming, destructive and expensive.…”

Oxidation fronts in Madeira Abyssal Plain turbidites: persistence of early diagenetic trace-element enrichments during burial, Site 950

“…This is a consequence of the available electron acceptors for organic-matter oxidation being consumed consecutively in order of decreasing thermodynamic advan-,,,,,,, ,,,,,,, ,,,,,,, ,,,,,,, ,,,,,,, ,,,,,,, ,,,,,,, ,,,,,,, ,,,,,,, ,,,,,,, ,,,,,,, ,,,,,,, ,,,,,,, Pearce and Jarvis (1995). Gray arrows = organic-rich, black = volcanic, and white = calcareous turbidites.…”

“…Carbonate debrisflows characterize the interval 306−333 mbsf (Unit II), whereas pelagic red clays, thin turbidites, and ash layers dominate below 333 mbsf (Units II, IV). From experience with more recent MAP sediments , 1989Pearce and Jarvis, 1995), shipboard classification identified three major types of turbidite in Unit I: gray volcanic-rich beds, sourced largely from volcanic islands within the basin (Fig. 1); green organic-rich examples, originating from the northwest African margin; and white calcareous turbidites, derived from seamounts located to the west of the plain.…”