Mass Physical Properties of High Latitude Sediments

This short contribution deals with the behaviour and modification of heavy mineral assemblages in a 500 m-thick turbidite succession deposited in the rift valley of the 3300 m deep Escanaba Trough of the Juan de Fuca Plate. To our knowledge, there have been no previous studies on the effects of hydrothermal fluid circulation on heavy minerals in such an active geochemical environment. The sediments were transported mainly from glacial lakes of the Columbia drainage basin by cataclysmic floods during the last 60 ka. Climatic and sediment transport conditions imply minor weathering of the source rocks, with little sorting and mechanical abrasion of heavy minerals during transit. Our results indicate that the heavy minerals experienced severe chemical etching and dissolution by circulating hydrothermal pore fluids that caused, at various depths, the complete loss of particular species, especially the chemically highly unstable ortho-and clinopyroxenes. These specific geochemical conditions also generated new minerals, mainly titanite, iron-rich magnesite, barite, and pyrite. However, at present there is insufficient data to fully constrain the kinetics of dissolution of the various minerals as a function of pH, temperature, composition of pore fluids, and sediment-permeability. The length of time during which the sediments were affected by pore fluid movements is constrained by the very young (Late Pleistocene, $60 ka) age of the sediments.

Initial Reports of the Deep Sea Drilling Project, 1982

Routine geotechnical property measurements, tabulated in the Appendix at the end of this chapter, include (1) bulk density (Mg/m 3), (2) porosity (%), (3) water content (% total weight), (4) undrained shear strength (kPa), and (5) compressional sound velocity (km/s). Shipboard measurements and computations were performed utilizing procedures, equipment, correction factors, and standards outlined by Boyce (1975, 1977). Evaluations, recurring problems, and sources of errors for many of these techniques are summarized by Bennett and Keller (1973) and Demars and Nacci (1977), hence only modifications to these procedures and specific problems pervasive to Leg 66 analyses will be discussed. Good core recovery at most sites allowed regular sampling from least disturbed core sections. Core disturbance resulting from normal drilling and handling operations appeared limited, but some cored intervals of gassy sediments were very disturbed and displayed expansion features and erratic values of geotechnical properties. Technical problems prevented logging, except through the drill pipe, thus precluding any correlations with in situ physical properties. All index properties reported are uncorrected for salt content. Bulk density and porosity were determined shipboard by continuous gamma ray attenuation of unsplit cores and by two-minute gamma ray and gravimetric analyses of rock chunk samples. Shorebased measurements were performed utilizing an air comparison pycnometer. Initial Reports volumes are replete with discussions of GRAPE (gamma ray attenuation and porosity evaluator) data. Although these data are presented graphically in the site chapters and in the geotechnical property summary tables at the conclusion of this chapter to follow previous DSDP format, all interpretations of porosity and bulk density data are based on gravimetric and air comparison pycnometer data. Grain and fluid densities of 2.70 Mg/m 3 and 1.025

In the Eocene turbidite systems of the south-central Pyrenees, high-resolution correlations within the apparently monotonous successions of thin beds of the major channeloverbank deposits have been facilitated by the occurrence of decimetre-thick, yellowish beds of micritic limestones and marlstones, which thus serve as marker beds. These yellow beds (YB) occur after deposition of a sandy stage of growth at turbidite system scale but can be only recognized in the overbank deposits of major turbidite channel complexes. The YB, which occur in the mud deposits that belong to early sedimentation of lowstand deltas, are interpreted as condensed sections where zones of burrowed and abundant planktonic and benthic microfossil assemblages were sustained by oxygen and nutrients transferred by warmer and fresher submarine currents that passed through the canyon. Whole-rock and fine-fraction XRD analysis indicate that most YB contain detrital clay and consistently high concentrations of Fe, Mn and P, which are ascribed to condensation-driven, redox elemental redistribution. The YB are also richer in dolomite and calcite than the adjacent claystones, what is attributed to colonization by cryptobacteria algae. Dolomite varies in shape, zoning pattern and chemistry. The early zones are nearly pure dolomite, whereas the later zone is ferroan. The low d 18 O VPDB values (À10.4% to À6.2%) of Fe-dolomite, which broadly correlate with d 18 O VPDB values (À8.1% to À5.6%) of calcite suggest formation at elevated temperatures related to burial diagenesis. Likewise, dolomite has a more radiogenic 87 Sr/ 86 Sr signature (0.707926 and 0.707876) than ambient sea water, suggesting partial derivation of Sr from detrital aluminosilicates. These laterally-extensive dolomitic YB can act as potential impermeable barriers for fluid flow in major channel-overbank complexes.

1978

1977

sponsored by the Unlted States Government. Nenher the United States nor the Umted States Department of Energy, nor any of their employees, nor any of thelr contractors, subconlractors, 01 thezr employees. makes any warranty, express or implied, or assumes any legal liability or responribthty for the accuracy, completeness or usefulness of any informatton, apparatus, product or p r o w s disclosed, or represents that 11s would ,lot EARTH SCIENCES DIVISION LAWRENCE BERKELEY LABORATORY UNIVERSITY OF CALIFORNIA D e t e r m i n a t i o n o f t h e p r o p e r t i e s o f s o i l s and s o f t r o c k s by i n s i t u measurements. J.K. MITCHELL and W.C.B. VILLET High p r e c i s i o n mass spectrometry. M.C. MICHEL Radon i n subsurface waters as an earthquake p r e d i c t o r , C e n t r a l C a l i f o r n i a s t u d i e s. A.R.

Geological Society, London, Special Publications, 1984

To introduce this collection of papers presented at an international research workshop in Halifax, Canada (1982), we highlight briefly three aspects of deep-water fine-grained sediments that are alluded to throughout the volume but never discussed specifically. These are: (a) an historical outline of the research that has made both possible and necessary the workshop and the volume; (b) a review of the methodology currently used in the study of fine-grained sediments; and (c) an assessment of the state of terminology as applied to this class of rocks.

2002

1990

Chemical analyses for calcium carbonate, organic carbon, and major constituents (Al, Ti, Ca, Mg, K, Fe) of bulk sediments collected in Hole 671B have been carried out. Organic carbon contents in Pleistocene through middle Miocene sediments above the zone of decollement are very low (<0.1%); below the decollement considerably higher concentrations of organic carbon occur (up to 1 %). Changes in Ti/Al and Fe/Al ratios are minor, but K/Al and Mg/Al ratios show clear trends with the age of the sediments. Preliminary comparisons of these ratios with mineralogic information on clays indicate good correspondence with clay abundances. Calculations of the mass flux of magnesium from the overlying ocean into the pore fluids suggest that addition of magnesium to the sediments is difficult to detect, especially in the absence of a background reference concentration.

Doklady Earth Sciences, 2008