Paleoenvironmental Significance of Cenozoic Clay Deposits from the Norwegian Sea: ODP Leg 104

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.

Section: Introductionmentioning

confidence: 99%

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

Saito¹

1998

“…For the reasons outlined, no attempt was made to show quantitative changes in mineralogy. A semiquantitative measure of mineral proportion was, however, made by adopting the procedures of Froget et al (1989). The reflections from the major clay minerals were normalized, using the intensity (square of the amplitude) of the quartz (101) reflection at 3.34 Å as an internal reference.…”

Section: Results Of X-ray Diffractometrymentioning

confidence: 99%

“…It is recommended that further studies be made on the clay mineralogy on land, employing the semiquantitative analysis of sizefractionated, oriented mounts normalized to internal standards (e.g., following the method of Froget et al, 1989).…”

Section: Clay Mineralsmentioning

confidence: 99%

Sites 889 and 890

Westbrook¹,

Carson²,

Musgrave³

1994

Time on hole: 2 days, 16 hr, 48 min Position: 48°41.958'N, 126°52.098'W Bottom felt (rig floor; m; drill-pipe measurement): 1322.0 Distance between rig floor and sea level (m): 10.8 Water depth (drill-pipe measurement from sea level; m): 1311.2 Total depth (rig floor; m): 1667.8 Penetration (m): 345.8 Number of cores (including cores with no recovery): 44 Total length of cored section (m): 325.8 Total core recovered (m): 223.14 Core recovery (%): 68 Oldest sediment cored: Depth (mbsf): 346.0 Nature: glauconitic clayey silt Earliest age: late Pliocene Time on hole: 1 day, 1 hr, 36 min Position: 48°41.850'N, 126°52.392'W Bottom felt (rig floor; m; drill-pipe measurement): 1327.0 Distance between rig floor and sea level (m): 10.8 Water depth (drill-pipe measurement from sea level; m): 1316.2 Total depth (rig floor; m): 1713.5 Penetration (m): 386.5 Number of cores (including cores with no recovery): 21 Total length of cored section (m): 189.5 Total core recovered (m): 48.15 Core recovery (%): 25

“…Smectite was also found to be the major constituent of Eocene to Miocene/Pliocene sediments recovered near the Vøring Plateau at ODP Site 643 ( Fig. 1; Froget et al, 1989).…”

Section: Introductionmentioning

confidence: 94%

Grain-size distribution and significance of clay and clay-sized minerals in Eocene to Holocene sediments from Sites 918 and 919 in the Irminger Basin

Heiden¹,

Holmes²

1998

Lower Eocene to Holocene sediments recovered from Ocean Drilling Program Sites 918 and 919 were studied to determine the grain-size distribution (sand to clay sizes) and mineralogy of the <2 µm size fraction. The minerals are believed to be of detrital origin. The clay minerals consist of chlorite, smectite, illite, kaolinite, and a mixed-layer illite/smectite. Several nonclay minerals were identified as well, including quartz, plagioclase, alkali-feldspar, amphibole, pyroxene, zeolite, and calcite. Relative abundances of the clay minerals were semiquantified using an oriented internal standard. Smectite abundances were found to increase with depth, while illite and chlorite abundances decrease with depth. The Eocene sediments of Site 918 are characterized by a predominance of smectite with some kaolinite and very small amounts of chlorite and illite. This mineral assemblage is indicative of warm climatic conditions at the time of deposition. Oligocene sediments show an increase in chlorite and illite, suggesting that a sediment dam may have existed on the continental shelf, trapping these sediments and preventing their transport into the Irminger Basin, prior to this time. A warming trend in the early to middle Miocene is indicated by increased amounts of kaolinite. Variations in the relative amounts of chlorite and illite at this time may be the result of short-term eustatic sea level changes. Near the end of the Miocene, a cooling trend is indicated by increasing amounts of chlorite and illite relative to smectite abundance. This follows deposition of glauconitic hardgrounds at the top of a chalk unit with coarse sediment deposited above them, often with erosion of the underlying hardground. This interval is believed to coincide with the spillover of Arctic seawater into the Irminger Basin. The hardgrounds indicate hiatuses of short duration (thousands to tens of thousands of years) followed by high density turbidity currents or renewed chalk deposition. Non-clay minerals in the <2 µm size fraction become common in upper Miocene to Holocene sediments of Sites 918 and 919, as glacial rock-flour that signals the onset of Greenland glaciation. Using R-mode factor analysis, the clay assemblages of Pliocene-Pleistocene age sediments were found to be significantly different from older sediments, with a dramatic transition at 457 mbsf, recording the beginning of significant Greenland glaciation.