Consolidation Characteristics and Permeability of Mississippi Fan Sediments

Self Cite

Sediments cored from the Barbados Ridge accretionary complex at ODP Sites 671, 672, and 676 are progressively underconsolidated with depth. Very low measured intergranular permeabilities contribute substantially to the probable excess pore-water pressures that account for the underconsolidated behavior. The estimated pore pressures immediately overlying the incipient decollement at the reference site are nearly equal to the overburden stress. Data show that the pore fluids within the fine-grained sediments of the complex are absorbing the tectonic shock of underthrusting as they are accreted, effectively leading to "lubricated subduction" of the underthrust Oligocene and older sediments. Lateral compression and dewatering by fracture permeability is taking place in the accreted section despite apparent underconsolidation, resulting in limited pore-volume reduction and sediment strengthening from east to west on the ridge.

Section: Methodsmentioning

confidence: 99%

Sediment Consolidation and Permeability at the Barbados Forearc

Taylor¹,

Leonard²

1990

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“…Consolidation Characteristics Inferred From Sediment Shear Strength Bryant et al (1986) stated that the most direct and definitive way of determining the degree of consolidation for normally and underconsolidated sediment conditions is to measure the in-situ pore water pressures. However, in-situ pore water pressure measurements have been conducted only in very rare cases (see Dunlap et al, 1978Dunlap et al, ,1979Schultheiss and McPhail, 1986).…”

Section: Resultsmentioning

confidence: 99%

“…The preconsolidation pressure, p c , is the greatest load to which the sediment has ever been subjected. The preconsolidation pressure was determined from the rebound characteristics and the reload curve, as described by Bryant et al (1986), and Bryant and Bennett (1988). The ratio between the preconsolidation pressure (p c ) and the present overburden pressure ip o ) is called the overconsolidation ratio (OCR).…”

Section: Materials Methods and Definitionsmentioning

confidence: 99%

See 1 more Smart Citation

Consolidation Characteristics and Permeabilities of Sediments from the Japan Sea (Sites and 799)

Höller¹

1992

The results of laboratory consolidation tests and undrained shear strength determinations of sediments from the Oki Ridge and the Kita Yamato Trough show that the sediments are overconsolidated to normally consolidated to a depth of about 20 m below the seafloor. Below that depth, the sediments are highly underconsolidated, implying high excess pore-water pressures. The most probable mechanism for the generation of the excess pore-water pressure is gas in sediments.

“…This increase does not appear to occur in either Hole 886B or 886C. Bryant et al (1986) used an empirical relationship between the undrained shear strength (S u ) and effective overburden pressure (Pj) (Skempton, 1970) to infer the state of consolidation in the sediment column. Application of this technique to the data from Holes 885A, 886B, and 886C produced the profiles of SJP 0 ' vs. depth for Holes 885A, 886B, and 886C, presented in Figure 20.…”

Section: Index Properties and Vane Shear Strengthmentioning

confidence: 99%

Site 885/886

Rea¹,

Basov²,

Janecek³

et al. 1993

Total core recovered (m): 9.7Core recovery (%): 100Rea, D.K., Basov, LA., Janecek, T.R., A., et al., Proc. ODP, Init. Repts., 145: College Station, TX (Ocean Drilling Program)." Shipboard Scientific Party is as given in list of participants preceding the contents. Oldest sediment cored:Depth ( Principal results: The site survey for Leg 145 proposed Site NW-4A (Sites 885/886, Fig. 1) began at 0200 hr (local time) on 3 September 1992, only 36 hr after the Golden Dragon had judged all Worms fit for passage across the International Date Line. A beacon was dropped at 0337 hr; the survey was finished and the ship positioned on Site 885 by 0730 hr. The first attempt at an APC core came up water only. The drillers attempted to "feel" bottom with the drill string and were uncertain, so decided to shift the ship~s position 400 m east before trying again. At the new offset location. Hole 885 A was spudded at 0000 hr on 4 September. Core 145-885 A-6H crossed into pelagic clays from the siliceous ooze above, but the barrel on Core 145-885A-7H did not stroke out, and the core returned with basalt chips in the core-catcher sample. Asingle XCB core (145-885A-8X), was recovered after drilling 6 m and encountering unstable hole conditions. A rubble of basalt and yellow-brown, baked, bricklike rock was recovered from the core-catcher sample. Assuming we had encountered a sill, we offset the ship 2.2 km east to a sediment pond encountered during the site survey, dropped a new beacon, and began Site 886 at 1800 hr on 4 September. Core 145-886A-1H missed the mud line and was full, so we pulled up 7 m and tried again; Core 145-886B-1H recovered the mud line and 1.8 m of siliceous clay. Eight cores were recovered at Hole 886B, reaching basalt at a depth of 68.5 mbsf. The final core (145-886B-9X) came up with only a few rock chips, so we pulled up the drill pipe, offset and spudded Hole 886C at 0630 hr on 5 September. Our intent was to collect a set of cores to overlap with those from Hole 886B. The last core (145-886C-8H) was on deck by 1445 hr, and the JOIDES Resolution was under way at 0030 hr on 6 September to the last site of Leg 145, at the Patton-Murray Seamounts in the Gulf of Alaska.Drilling at Sites 885 and 886 encountered 66 m of sediment overlying basalt. The sediment can be divided into three units: clay with diatoms, diatom ooze, and clay. Unit I (0-17.3 mbsf) is an upper Pliocene to Pleistocene clay containing diatoms and spicules. Unit is an upper Miocene to upper Pliocene diatom ooze with clay. Several large manganese nodules, both brown and black in color, occur at mid-depth in this unit, roughly 40 mbsf. Unit III (50.3-71.9 mbsf in Hole 886C) is clay. This unit is the deep chocolate color of the classic North Pacific Ocean '•red" clays. Lithologic Unit IV, 52.1-58.8 in Hole 886A and 68.5-68.9 in Hole 886B, is basalt that has been baked to a yellow brown color and was recovered only as pieces of rubble.No nannofossils and few foraminifers occur in the section. Diatoms and radiolarians are abundant above 50 mbsf, wh...