Stable isotope ratios of interstitial fluids from ODP Leg 110 sites

Delta18O values of pore waters from the northern Barbados accretionary prism range from -0.3 to -3.6? and reflect pervasive reaction of volcanic ash to form smectite within the sedimentary sequence and continued low temperature alteration of basalt in the underlying ocean crust with the overprint of diffusive exchange between water in the sediment pores and the open ocean. Delta D values of pore waters in sediments sampled seaward of the deformation front drop from +5? at the sediment surface to -6? at the deepest levels sampled. These changes may also be related to alteration processes but remain largely enigmatic. Sediment deformation caused by impingement of the Caribbean plate on the Atlantic plate has instigated migration of chemically and isotopically distinct fluid along faults and coarse-grained sedimentary beds; delta18O values of pore waters are also locally affected by thrust stacking which increases diffusive pathlengths and possibly modifies diagenetic reaction rates in Pleistocene sediments. Migrating fluids are distinguished by anomalous delta18O values that are as much as 1? higher than those of surrounding fluids. Uncertainties in hydrogen isotope fractionation resulting from processes occurring under these conditions hinder identification of the hydrogen isotope composition of expelled fluid. Stable isotope analyses of pore waters help constrain the fluid migration history of the accretionary prism by limiting the source of fluids, the paths along which fluid flows, and the timing of faulting and subsequent fluid flow.

Sm-Nd isotope and Mn/Ca ratios for cleaned Neogloboquadrina pachyderma from ODP Hole 105-647A (Table 1)

The neodymium (Nd) isotope composition of ancient seawater is a potentially useful tracer of changes in continental inputs and ocean circulation on timescales of a few ka. Here we present the first Nd isotope record for seawater using sedimentary foraminifera cleaned using standard oxidative-reductive techniques. The data, along with Mn/Ca ratios, suggest that cleaned foraminifera provide a reliable record of Nd in seawater and hold out the prospect of using Nd in foraminifera to examine changes in seawater that accompany glacial-interglacial climatic cycles. The principal potential problem to be overcome with the use of forams as records of trace elements in ancient seawater is their diagenetic Fe-Mn coatings. These contain large amounts of Nd and other trace elements but can be cleaned off using highly reducing reagents. Mn(Ca ratios for the majority of the cleaned sedimentary foraminifera analysed here lie within the range (10-100 µmol/mol) that has yielded success in studies of transition elements in forams. Mass-balance modelling suggests that for residual Mn/Ca ratios <100 µmol/mol, Nd added to the foram in the coating will never shift the measured Nd isotope composition significantly away from the seawater value acquired by the foram test in the water column. Additionally, Nd concentrations measured in cleaned sedimentary foraminifera are comparable with those for a modern sample that has never encountered diagenetic fluids. Finally, core-top planktonic foraminifera for two sites have Nd isotope compositions that are identical to local surface seawater. The data we present here for Labrador Sea forams over the past 2.5 m.y. are interpreted in terms of changes in the seawater isotopic composition. The data show a pronounced shift from epsilon-Nd values of ~-12 to ~-19 in the period 2.5-1.5 Ma. This change is interpreted to result from the initiation of Northern Hemisphere glaciation and the increased derivation of Labrador Sea Nd via ice-rafting from Archaean terranes in central Canada. In combination with stable isotope and foraminiferal relative species abundance data, the new Nd data are consistent with the surface hydrography of the Labrador Sea being dominated by a fluctuating balance between cold, polar waters containing unradiogenic Nd and warm, subtropical waters containing more radiogenic Nd. The major change in Labrador Sea Nd that is observed in the past 2.5 Ma can, on its own, account for the change in the Nd isotope composition of North Atlantic Deep Water over the same time period.

Petrophysical measurement of ODP Leg 122 and 123 samples (Tables 1, 2)

The capillary-pressure characteristics of 22 samples of lithified post-Paleozoic Indian-Ocean carbonates were compared to published data from older carbonate rocks (lower Paleozoic Hunton Group of Texas and Oklahoma). The Indian-Ocean samples are considerably more porous than are the Paleozoic samples, yet all of the Indian-Ocean samples fit readily into a descriptive petrofacies scheme previously established for the Hunton Group. The Indian-Ocean samples may be assigned to four petrophysical facies (petrofacies) based on the shapes of their capillary-pressure curves, their pore-throat-size distributions, their estimated recovery efficiency values (for nonwetting fluids), and the visual characteristics of their pore systems, as observed with a scanning-electron microscope. Petrofacies assignments for the Indian-Ocean samples are as follows. Petrofacies I includes six samples collected from the coarse basal portions of event deposits (primarily turbidites). These samples have large throats, leptokurtic throat-size distributions, low- to moderate recovery efficiency values, concave cumulative-intrusion capillary-pressure curves, and high porosity values. Petrofacies II includes two sedimentologically dissimilar samples that have medium-size throats, platykurtic throat-size distributions, moderate- to-high recovery efficiency values, gently sloping cumulative-intrusion capillary-pressure curves, and high porosity values. Petrofacies III includes two polymictic sandstones and a skeletal packstone that have small throats, polymodal throat-size distributions, moderate recovery efficiency values, gently sloping cumulative-intrusion capillary-pressure curves, and high porosity values. Petrofacies IV includes 11 samples, mostly recrystallized neritic carbonates, that have small throats, leptokurtic throat-size distributions, high recovery efficiency values, convex cumulative-intrusion capillary-pressure curves, and low porosity values. Comparison of petrofacies assignment to core-, thin-section-, and smear-slide data, and to inferred depositional setting, suggests that pore systems in most samples from Holes 765C and 766A result from primary depositional features, whereas pore systems in samples from Hole 761C and one sample from Hole 765C have been strongly influenced by diagenetic processes. For Hole 761C, prediction of petrophysical parameters should be most successful if based on diagenetic facies patterns. By contrast, the distribution of favorable reservoir facies and of permeability barriers in less highly altered rocks collected from Holes 765C and 766A is related to depositional patterns. Recovery efficiency is inversely related to both porosity and median throat size for the present data set. This relationship is similar to that observed for carbonates of the lower Paleozoic Hunton Group and the Ordovician Ellenburger dolomite, but opposite of that observed for some other ancient carbonates. The coarse deposits of the massive basal units of turbidites are petrophysically distinct and form a coherent petrophysical group (Petrofacies I) with substantial reservoir potential. Two samples assigned to Petrofacies I have extremely large throats (median throat size at least 4 ?m, and at least six times that of any other sample) and therefore high permeability values. These two samples come from thin, coarse turbidites that lack or have poorly developed fine divisions and are interpreted to have been deposited on channeled suprafan lobes in a proximal mid-fan setting. The restriction of extremely high permeability values to a single depositional facies suggests that careful facies mapping of deep-sea fans in a deliberate search for such coarse turbidites could dramatically enhance the success of exploration for aquifers or hydrocarbon reservoirs. Such reservoirs should have substantial vertical heterogeneity. They should have high lateral permeability values but low vertical permeability values, and reservoir sections should include numerous thin units having widely differing petrophysical characteristics.

Description of manganese nodules and crust collected from the Hakuho Maru Cruise KH-71-1, January-March, 1971, East Mariana, Caroline and Philippine Basins

The cores, dredges and submarine camera observations described in this report were taken on the KH-71-1 Expedition in January-March, 1971 by the Ocean Research Institute, University of Tokyo from the Hakuho Maru. A total of 24 cores, dredges and camera station sites have been recovered.

(Table 1) Chemical composition of palygorskite and host sediments from Core VITYAZ4599-GC

Palygorskite streak veinlets were studied in the lower part of a sediment core collected at Station VITYAZ4599 in the central (Mid-Indian) basin of the Indian Ocean. It is suggested that this palygorskite is of hydrothermal origin and was formed in pre-Pliocene time.