(Table 3) Textural and bulk mineralogy of Pliocene and Pleistocene sediments from ODP Hole 161-976B

The Pliocene and Pleistocene deposits recovered at Site 976 from the northwestern Alboran Sea at the Málaga base-of-slope include five main sedimentary facies: hemipelagic, turbidite, homogeneous gravity-flow, contourite, and debris-flow facies. The thickness and vertical distribution of these facies into lithostratigraphic Units I, II, and III show that the turbidites and hemipelagic facies are the dominant associations. The Pliocene and Pleistocene depositional history has been divided into three sedimentary stages: Stage I of early Pliocene age, in which hemipelagic and low-energy turbidites were the dominant processes; Stage II of early Pleistocene/late Pliocene age, in which the dominant processes were the turbidity currents interrupted by short episodes of other gravity flows (debris-flows and homogeneous gravity-flow facies) and bottom currents; and Stage III of Pleistocene age, in which both hemipelagic and low-energy gravity-flow processes occurred. The sedimentation during these three stages was controlled mainly by sea-level changes and also by the sediment supply that caused rapid terrigenous sedimentation variations from a proximal source represented by the Fuengirola Canyon.

Petrology and geochemistry of sideromelane glass shards from Pleistocene as layers north and south of Gran Canaria

Major elements, S, F, Cl concentrations and relative proportions of S6+ to total S were analyzed with electron microprobe in sideromelane glass shards from Pleistocene volcaniclastic sediments drilled during ODP Leg 157. Glasses are moderately to strongly evolved and represent a spectrum from alkali basalt, basanite and nephelinite through hawaiite, mugearite and tephrite to phonolitic tephrite. Measured S6+/SumS (0.03±0.98) and calculated Fe2+/Fe3+ (2.5±5.8) ratios in the melt yield preeruptive redox conditions ranging from NNO-1.4 to NNO+2.1. The morphology of the glass shards, variations of S and Cl concentrations (0.010±0.127 wt% S, 0.018±0.129 wt% Cl), calculated preeruptive temperatures (1030±1200 °C) and oxygen fugacities suggest that glasses deposited even within the same ash layers have diverse origin and may have resulted from both submarine and subaerial eruptions. Most vesicle-free glasses are characterized by high concentrations of S and represent undegassed or slightly degassed submarine lavas, whereas vesiculated glasses with low concentrations of S and Cl are strongly degassed and can be ascribed to the eruptions in shallow water or on land. Sideromelane glass shards at Sites 953 are thought to have resulted from submarine eruptions northeast of Gran Canaria, glasses at Site 954 represent mostly volcaniclastic material of shallow water submarine and subaerial eruptions on Gran Canaria and Tenerife, and glasses deposited at Site 956 resulted from submarine or explosive eruptions on Tenerife.

Stable oxygen and carbon isotope ratios of Globigerinoides obliquus of quantitative range chart of the ostracodes in the Pliocene-Pleistocene interval of ODP Hole 107-654A

Deep-water benthic ostracodes from the Pliocene-Pleistocene interval of ODP Leg 107, Hole 654A (Tyrrhenian Sea) were studied. From a total of 106 samples, 40 species considered autochthonous were identified. Detailed investigations have established the biostratigraphic distribution of the most frequent ostracode taxa. The extinction levels of Agrenocythere pliocenica (a psychrospheric ostracode) in Hole 654A and in some Italian land sections lead to the conclusion that the removal of psychrospheric conditions took place in the Mediterranean Sea during or after the time interval corresponding to the Small Gephyrocapsa Zone (upper part of early Pleistocene), and not at the beginning of the Quaternary, as previously stated. Based on a reduced matrix of quantitative data of 63 samples and 20 variables of ostracodes, four varimax assemblages were extracted by a Q-mode factor analysis. Six factors and eight varimax assemblages were recognized from the Q-mode factor analysis of the quantitative data of 162 samples and 47 variables of the benthic foraminifers. The stratigraphic distributions of the varimax assemblages of the two faunistic groups were plotted against the calcareous plankton biostratigraphic scheme and compared in order to trace the relationship between the benthic foraminifers and ostracodes varimax assemblages. General results show that the two populations, belonging to quite different taxa, display almost coeval changes along the Pliocene-Pleistocene sequence of Hole 654A, essentially induced by paleoenvironmental modifications. Mainly on the base of the benthic foraminifer assemblages (which are quantitatively better represented than the ostracode assemblages), it is possible to identify such modifications as variations in sedimentation depth and in bottom oxygen content.

Tropical Atlantic SST during the mid-Pleistocene transition (MPT) of ODP Hole 175-1077B

We compare a new mid-Pleistocene sea surface temperature (SST) record from the eastern tropical Atlantic to changes in continental ice volume, orbital insolation, Atlantic deepwater ventilation, and Southern Ocean front positions to resolve forcing mechanisms of tropical Atlantic SST during the mid-Pleistocene transition (MPT). At the onset of the MPT, a strong tropical cooling occurred. The change from a obliquity- to a eccentricity-dominated cyclicity in the tropical SST took place at about 650 kyr BP. In orbital cycles, tropical SST changes significantly preceded continental ice-volume changes but were in phase with movements of Southern Ocean fronts. After the onset of large-amplitude 100-kyr variations, additional late glacial warming in the eastern tropical Atlantic was caused by enhanced return flow of warm waters from the western Atlantic driven by strong trade winds. Pronounced 80-kyr variations in tropical SST occurred during the MPT, in phase with and likely directly forced by transitional continental ice-volume variations. During the MPT, a prominent anomalous long-term tropical warming occurred, likely generated by extremely northward displaced Southern Ocean fronts. While the overall pattern of global climate variability during the MPT was determined by changes in mean state and frequency of continental ice volume variations, tropical Atlantic SST variations were primarily driven by early changes in Subantarctic sea-ice extent and coupled Southern Ocean frontal positions.