Major and trace element geochemistry of sediments from East Greenland Continental Rise: an implication for sediment provenance and source area weathering

Abstract

The bulk geochemistry of the nonbiogenic fraction of 70 samples from Ocean Drilling Program Site 918 in the Irminger Basin was determined by X-ray fluorescence. These data enabled the reconstruction of several aspects of Cenozoic paleoenvironmental evolution. By means of chemical stratigraphic analysis of the bulk sediments, seven major geochemical stages were identified and correlated with the significant lithologic units. The chemical compositions of the geochemical stages were basically controlled by differences in source area (volcanic/plutonic) and the degree of source area weathering. Important elements for characterizing source rock lithology are iron and sodium, whereas those for intensity of weathering are sodium, calcium, and potassium. The sodium-ferric iron ratio and potassium-calcium ratio provide useful indexes for the degree of the plutonic input and source area weathering, respectively.Major chemical shifts occur at 550 meters below seafloor, which coincides with the beginning of ice-rafted debris (IRD) deposition in the upper Miocene. Mobile elements from weathering, such as calcium, manganese, and sodium, decrease downsection while immobile potassium increases. IRD is clearly distinguished from turbidites by its high content of the mobile elements. The chemical difference is explained by the difference between mechanical erosion by ice sheets and chemical weathering on land. Mechanical erosion by ice sheets does not involve source area chemical weathering and selective transportation by rivers. Turbidite materials were derived, however, from chemically weathered plutonic, metamorphic, and basaltic rocks on Greenland. Potassium in turbidites was recycled from basement rocks and paleosols, while sodium was removed during weathering and transportation.The major Cenozoic paleoenvironmental changes in the East Greenland Margin are reconstructed from sediment compositions and geochemistry. Eocene sediments are derived from a weathered basaltic region. The upper Oligocene to lowermost Miocene is characterized by a weathered continental input. Fresh volcanic input began during the early Miocene. The supply of continental materials became dominant again during the middle Miocene, which coincides with the development of modern North Atlantic Deep Water. Unweathered IRD has been supplied since the late Miocene, which coincides with the first occurrence of dropstones.

The late Miocene to Pleistocene ice‐rafting history of southeast Greenland

“…This is in agreement with the deepest dropstone observed at site 918 (Shipboard Scienti c Party 1994a), and with a distinct geochemical shift resulting from the initial deposition of mechanically weathered material (e.g. sediment enriched in mobile elements), presumably via iceberg rainout (Saito 1998). Our data support Larsen et al's (1994) hypothesis that glaciation began in SE Greenland in the late Miocene.…”

Lithium isotopic composition of marine sediments

“…Three major types of sediments are encountered in ODP hole 918 in the Irminger Basin: ice rafted debris, turbidites and volcaniclastic sediments [ Larsen et al , 1994]. On the basis of the major and trace element chemistry of the sediments, sources of these sediments are interpreted to be fresh and variably weathered plutonic and volcanic rocks [ Saito , 1998].…”

Reconstruction of Holocene oceanographic conditions in the Northeastern Baffin Bay

“…High counts of this element therefore indicate minimal contribution of terrestrial-sourced material to the bulk sediment (Calvert and Pedersen, 1993;Rothwell and Croudace, 2015). K and Rb are both typical for environments with terrestrial influence (Saito, 1998;Steenfelt, 2001;Steenfelt at al., 1998). The Ca/Ti and Ca/Sr ratios can be used as indicators of the marine biogenic origin of Ca (Bahr et al, 2005;Richter et al, 2005).…”