Clay mineral distribution in surface sediments of the South Atlantic: sources, transport, and relation to oceanography (original) (raw)
Related papers
Significance of clay mineral assemblages in the Antarctic Ocean
Marine Geology, 1992
Typical examples from different morphological and geological settings in the Antarctic Ocean are reviewed in order to discuss the value of clay mineral assemblages for reconstructing the glacial history of Antarctica, the paleoceanographic history of the Antarctic Ocean and the sedimentary processes at the Antarctic continental margin. The significance of clay minerals for paleoenvironmental reconstructions strongly varies with both the position of the sites under investigation and the age of the sediments. In late Mesozoic to Paleogene sediments clay mineral assemblages are sensitive tools for reconstructing climatic conditions. For example, the shift from smectite-dominated assemblages to illite-and chlorite-dominated assemblages in the earliest Oligocene clearly documents the transition from chemical weathering conditions under a warm and humid climate to physical weathering under cooler conditions. Submarine elevations such as Maud Rise and Kerguelen Plateau give the best record for direct paleoclimatic and paleoceanographic studies. At the proximal sites of the continental slope and shelf, as well as in the deep sea, the paleoclimatic information normally is masked by a variety of processes resulting in sediment redistribution. At those sites, in contrast, the clay mineral assemblages bear a wealth of information on different sedimentary processes. After the establishment of a continental East Antarctic ice sheet, physical weathering prevailed. Variations in the clay mineral records predominantly reflect the influence of different sediment sources resulting from different glacial, hydrographic or gravitational transport processes. Because these sedimentation processes are generally linked to climatic variations, the clay mineral assemblages in most of the Neogene and Quaternary sediments provide indirect paleoclimatic information. The processes are best documented in the clay mineral composition in those areas where changes in source regions with distinct petrographic differences are expected and where distances from the source region are low.
Clay Minerals and Oceanic Evolution
Clays and Clay Minerals, 1967
A REVIEW Of mineralogical aI~.d geochemical studies on Recent sediments indicates that the clay fraction of marine sediments is not in isotopic or chemical equilibrium with the oceanic reservoir and will not reflect the chemical environment of deposition. Consideration of the sedimentary geochemistry of the alkali metals suggests that frautionation of these elements, which may be one of the major features of the chemical evolution of ocean water, occurs in the terrestrial weathering environment during the formation of clay minerals and in the subsurface environment during clay mineral diagenesis. It is proposed that during the initial stages of oceanic development the NarK ratio of ocean water was adjusted to a value of forty to fifty by the extensive diagenesis of the existing natural water. With an increase in oceanic volume and a major change in the hydrologic cycling of natural waters the chemical evolution of alkali metals in ocean water has now become primarily controlled by mixing with continental drainage water.
International Journal of Earth Sciences, 2014
ice growth, nearby cratonic east antarctica shield provided biotite-rich sediments to the depositional site. On the other hand, the presence of smectite, only in the clay size fraction, suggests the effective role of sorting probably due to the deposition from distal source in ice retreat condition. During times of ice retreat, smectite-rich sediment derived from Ross Orogen is transported to the core site through surface or bottom water currents. Poor crystallinity of illite due to degradation further corroborates the ice retreat condition. The ice sheet proximal sediments of U1359 show that in the eastern part of Wilkes land, the 'warming' was initiated during late Miocene.
Clay Minerals, 1993
A B S T RA CT: The distribution of clay minerals from the N and S Atlantic Cretaceous deep-sea sediments is related to rifting, sea-floor spreading, sea-level variations and paleoceanography. Four main clay mineral suites were identified: two are inherited and indicative of ocean geodynamics, whereas the others result from transformation and authigenesis and are diagnostic of Cretaceous oceanic depositional environments. Illite and chlorite, together with interstratified illite-smectite and smectite occur above the sea-floor basalts and illustrate the contribution of volcanoclastic materials of basaltic origin to the sediments. Kaolinite, with variable amounts of illite, chlorite, smectite and interstratified minerals, indicates detrital inputs from continents near the platform margins. Kaolinite decreases upward in the series due to open marine environments and basin deepening. It may increase in volume during specific time intervals corresponding to periods of falling sea-level during which overall facies regression and erosion of the surrounding platforms occurred. Smectite is the most abundant clay mineral in the Cretaceous deep-sea sediments. Smectite-rich deposits correlate with periods of relatively low sedimentation rates. As paleoweathering profiles and basal deposits at the bottom of Cretaceous transgressive formations are mostly kaolinitic, smectite cannot have been inherited from the continents. Smectite is therefore believed to have formed in the ocean by transformation and recrystallization of detrital materials during early diagenesis. Because of the slow rate of silicate reactions, transformation of clay minerals requires a long residence time of the particles at the water/sediment interface; this explains the relationships between the observed increases in smectite with long-term sea-level rises that tend to starve the basinal settings of sedimentation. Palygorskite, along with dolomite, is relatively common in the N and S Atlantic Cretaceous sediments. It is not detrital because correlative shelf deposits are devoid of palygorskite. Palygorskite is diagnostic of Mg-rich environments and is indicative of the warm and hypersaline bottom waters of the Cretaceous Atlantic ocean.
Marine Geology, 2002
The clay-mineral composition of marine isotope stages 1–3 sediments at the Ocean Drilling program (ODP) Site 1055 on the Carolina Slope consists mainly of illite, kaolinite, chlorite and smectite. Clay-mineral variability is marked by a distinct increase in the relative amounts of kaolinite and smectite during the Holocene and by high illite and to a lesser extent chlorite relative amounts during marine isotopic stages 2 and 3. This grouping of clay minerals as two different assemblages during different isotopic stages suggest their different source affinities. The increase in the ‘kaolinite+smectite’ assemblage in the Holocene is accompanied by a significant increase in the sedimentation rate. The change in the sedimentation regime after the Last Glacial Maximum is interpreted to be related to resuspension and advection of clays and silts by increased deep water activity over the Bermuda Rise, followed by their transport to Site 1055 on the Carolina Slope by shallow elements of the North Atlantic Deep Water. High amplitude variations with high illite amounts characterize marine isotope stage 3 and appear to be related to Heinrich events.
The South Atlantic in the Late Quaternary, 2003
Terrigenous sediment parameters in modem sea-bottom samples and sediment cores of the South Atlantic are used to infer variations in detrital sources and modes of terrigenous sediment supply in response to environmental changes through the late Quaternary climate cycles. Massaccumulation rates of terrigenous sediment and fluxes of ice-rafted detritus are discussed in terms of temporal variations in detrital sediment input from land to sea. Grain-size parameters ofterrigenous mud document the intensity of bottom-water circulation, whereas clay-mineral assemblages constrain the sources and marine transport routes of suspended fine-grained particulates, controlled by the modes of sediment input and patterns of ocean circulation. The results suggest low-frequency East Antarctic ice dynamics with dominant lOO-kyr cycles and high rates of Antarctic Bottom Water formation and iceberg discharge during interglacial times. In contrast, the more subpolar ice masses of the Antarctic Peninsula also respond to short-term climate variability with maximum iceberg discharges during glacial terminations related to the rapid disintegration of advanced ice masses. In the northern Scotia Sea, increased sediment supply from southern South America points to extended ice masses in Patagonia during glacial times. In the southeastern South Atlantic, changes in regional ocean circulation are linked to global thermohaline ocean circulation and are in phase with northern-hemispheric processes of ice build-up and associated formation of North Atlantic Deep Water, which decreased during glacial times and permitted a wider extension of southern-source water masses in the study area.
Initial Reports of the Deep Sea Drilling Project, 1984
In the South Atlantic, at Sites 519 to 523, the dissolution of calcareous oozes ended in the formation of red clays rich in iron and manganese. The early authigenesis of manganese oxides and clays is described in Miocene marly calcareous oozes. The mineralogical and geochemical influences of basaltic basement weathering are shown by the occurrence of palagonite, authigenic clays, and oxides in the basal sediments. The development of red clay facies can be inhibited by local topographic and paleoceanographic changes, as at Site 520.
Clay mineral signature of the NW Atlantic Boundary Undercurrent
Marine Geology, 1996
Surface sediments were sampled along 2 transects, across the Iceland and Irminger basins and in the Labrador Sea. Clay mineral assemblages (deduced from X-ray analyses of the carbonate-free < 2 pm fraction) are largely dominated by smectites (about 60%) in the Iceland and Irminger basins. In the Labrador Sea, smectites are present along the Greenland Slope, but absent or rare in sediments from the Labrador Slope. They may, however, represent up to 50% of the clay fraction at depths between 2800 and 3400 m along both margins of the Labrador Sea, i.e., along the axis of the Western Boundary Undercurrent (WBUC). A detrital supply from the adjacent continents is unlikely. The WBUC is thought to be responsible for erosion and transport of fine particles from the smectite-rich Irminger and Iceland Basins, then for their redeposition in the Labrador Sea. These results suggest that clay minerals can be used as paleocurrent indicators in the Northwest Atlantic.