Nd and Pb isotope signatures of the clay-size fraction of sediment core MD99-2227

Nd and Pb isotopes were measured on the fine fraction of one sediment core drilled off southern Greenland. This work aims to reconstruct the evolution of deep circulation patterns in the North Atlantic during the Holocene on the basis of sediment supply variations. For the last 12 kyr, three sources have contributed to the sediment mixture: the North American Shield, the Pan-African and Variscan crusts, and the Mid-Atlantic Ridge. Clay isotope signatures indicate two mixtures of sediment sources. The first mixture (12.2-6.5 ka) is composed of material derived from the North American shield and from a "young" crustal source. From 6.5 ka onward the mixture is characterized by a young crustal component and by a volcanic component characteristic of the Mid-Atlantic Ridge. Since the significant decrease in proximal deglacial supplies, the evolution of the relative contributions of the sediment sources suggests major changes in the relative contributions of the deep water masses carried by the Western Boundary Undercurrent over the past 8.4 kyr. The progressive intensification of the Western Boundary Undercurrent was initially associated mainly with the transport of the Northeast Atlantic Deep Water mass until 6.5 ka and with the Denmark Strait Overflow Water thereafter. The establishment of the modern circulation at 3 ka suggests a reduced influence of the Denmark Strait Overflow Water, synchronous with the full appearance of the Labrador Seawater mass. Our isotopic data set emphasizes several changes in the relative contribution of the two major components of North Atlantic Deep Water throughout the Holocene.

Mineralogy of the clay fraction from Cenozoic Strata at DSDP Leg 94

Leg 94 Sites are located in a large geographic area of the northeastern Atlantic. Clay mineral analyses of the sediments recovered on Leg 94 (Eocene to the present), together with results obtained from previous DSDP legs (47B, 48, 80, 81, 82), provide greater insight into the paleoenvironmental evolution of the northeastern Atlantic. The characteristics of Eocene clay sediments are regional, reflecting, in the absence of strong bottom currents, the influence of neighboring petrographic environments: basic volcanic rocks (Sites 403-406, 552, and 608) and acid volcanic rocks (Sites 508 to 510). During the Oligocene, atmospheric circulation patterns left their mineralogical signatures in the southern part of the area investigated (Sites 558 and 608), whereas during the Miocene the intrusion of northern water masses led to the gradual homogenization of the clay sedimentation throughout the North Atlantic. In the late Pliocene, input from glacial sources became widespread.

Clay minerals and their assemblages at DSDP Leg 63 Holes

This paper discusses the distribution of clay minerals and identification of their assemblages in relation to sedimentary facies encountered during DSDP Leg 63 drilling off southern California and Baja California. We also consider how these assemblages are determined by source areas and changes in general paleogeographic environments during different periods of sedimentation.

Radiocarbon ages and clay minerals in sediment cores obtained during a 2009 Jan Mayen cruise to the Norwegian Sea

The origin of two acoustic sediment units has been studied based on lithological facies, chronology and benthic stable isotope values as well as on foraminifera and clay mineral assemblages in six marine sediment cores from Kveithola, a small trough west of Spitsbergenbanken on the western Barents Sea margin. We have identified four time slices with characteristic sedimentary environments. Before c. 14.2 cal. ka, rhythmically laminated muds indicate extensive sea ice cover in the area. From c. 13.9 to 14.2 cal. ka, muds rich in ice-rafted debris were deposited during the disintegration of grounded ice on Spitsbergenbanken. From c. 10.3 to 13.1 cal. ka, sediments with heterogeneous lithologies suggest a shifting influence of suspension settling and iceberg rafting, probably derived from a decaying Barents Sea Ice Sheet in the inner-fjord and land areas to the north of Kveithola. Holocene deposition was episodic and characterized by the deposition of calcareous sands and shell debris, indicative of strong bottom currents. We speculate that a marked erosional boundary at c. 8.2 cal. ka may have been caused by the Storegga tsunami. Whilst deposition was sparse during the Holocene, Kveithola acted as a sediment trap during the preceding deglaciation. Investigation of the deglacial sediments provides unprecedented details on the dynamics and timing of glacial retreat from Spitsbergenbanken.