Chemical and mineral compositions of cherty and siliceous-clayey rocks from accretionary complexes in Sikhote Alin

The paper reports results of a study of clastic heavy mineral assemblages and geochemical features of some assemblages in several Permian-Mesozoic cherty and siliceous-clayey sequences of the Sikhote Alin Region. They are composed of pelagic and hemipelagic sediments of the Panthalassa (Paleopacific) Ocean. Four typical mineral assemblages and their environments are established. In one of the ocean segments, where the sedimentary cover formed during Late Paleozoic - Early Cretaceous, the Permian pelagic domain was characterized by the amphibole-pyroxene assemblage with heavy minerals derived from ophiolites. The Triassic-Jurassic stage was marked by development of the clinopyroxene assemblage with heavy minerals derived from intraplate alkaline volcanic complexes. Middle-Late Jurassic hemipelagic sediments host the zircon-clinopyroxene assemblage with greater role of continental environments and presence of volcanic products of the convergence zone. Another segment of the ocean accumulated red cherts and siliceous-clayey sediments during Jurassic - Early Cretaceous under influence of island-arc volcanism.

Magnetic properties of ODP Site 191-1179 sediments

As reported by Shipboard Scientific Party (2001b, doi:10.2973/odp.proc.ir.191.104.2001) in the Site 1179 chapter of the Initial Reports volume, Leg 191 Site 1179 is located on abyssal seafloor northwest of Shatsky Rise, ~1650 km east of Japan. This part of the Pacific plate was formed during the Early Cretaceous, as shown by northeast-trending M-series magnetic lineations that become younger toward the northwest (Larson and Chase, 1972, doi:10.1130/0016-7606(1972)83[3627:LMEOTW]2.0.CO;2; Sager et al., 1988, doi:10.1029/JB093iB10p11753; Nakanishi et al., 1989, doi:10.1029/1999JB900002). The site is situated on magnetic Anomaly M8 (Nakanishi et al., 1999, doi:10.1029/1999JB900002), corresponding to an age of ~129 Ma and the Hauterivian stage of the Early Cretaceous (Gradstein et al., 1994, doi:10.1029/94JB01889; 1995). The sediments recovered at Site 1179 are split into four lithostratigraphic units based on composition and color (Shipboard Scientific Party, 2001b, doi:10.2973/odp.proc.ir.191.104.2001). Unit I (0-221.52 meters below seafloor [mbsf]) is a dominantly olive-gray clay- and radiolarian-bearing diatom ooze. Unit II (221.52-246.0 mbsf) is a yellowish brown to light brown clay-rich and diatom-bearing radiolarian ooze. Unit III (246.0-283.53 mbsf) is composed of brown pelagic clay. Unit IV (283.53-377.15 mbsf) is composed of chert and some porcellanite; any softer sediments present were washed out of the core barrel by the fluid circulating during the coring process.

(Table 1) Mass-accumulation rates for the non-authigenic, inorganic, crystalline, eolian component of sediments recovered at DSDP Hole 62-463

Elevated regions in the central parts of ocean basins are excellent for study of accumulation of eolian material. The mass-accumulation rates of this sediment component appear to reflect changes in the influx of volcanic materials through the Early Cretaceous to Recent history of Deep Sea Drilling Project Site 463, on the Mid-Pacific Mountains. Four distinct episodes of eolian accumulation occurred during the Cretaceous: two periods of moderate accumulation, averaging about 0.2 to 0.3 g/cm**2/10**3 yr, 67 to 70.5 m.y. ago and 91 to 108 m.y. ago; a period of low accumulation, approximately 0.03 g/cm**2/10**3 yr, 70.5 to 90 m.y. ago; and a period of high accumulation, about 0.9 g/cm**2/10**3 yr, 109 to 117 m.y. ago (bottom of the hole). Much of the Cenozoic section is missing from Site 463. Upper Miocene to Recent sediments record an upward increase in accumulation rates, from less than 0.01 to about 0.044 g/cm**2/10**3 yr. The late Pliocene-Pleistocene peak may reflect the change to glacial-wind regimes, as well as an increase in volcanic source materials.

Massic magnetic susceptibility and CaCO3 content at the P. ohmi and T. hugii zones from the Rio Argos X.Ag-1 section, southeastern Spain

An orbital floating time scale of the Hauterivian-Barremian transition (Early Cretaceous) is proposed using high-resolution magnetic susceptibility measurements. Orbital tuning was performed on the Río Argos section (southeast Spain), the candidate for a Global boundary Stratotype Section and Point (GSSP) for the Hauterivian-Barremian transition. Spectral analyses of MS variations, coupled with the frequency ratio method, allow the recognition of precession, obliquity and eccentricity frequency bands. Orbitally-tuned magnetic susceptibility provides minimum durations for ammonite biozones. The durations of well-constrained ammonite zones are assessed at 0.78 myr for Pseudothurmannia ohmi (Late Hauterivian) and 0.57 myr for Taveraidiscus hugii (Early Barremian). These results are consistent with previous estimates from the other reference section (Angles, southeast France) and tend to show that the Río Argos section displays a complete succession for this time interval. They differ significantly from those proposed in the Geologic Time Scale 2008 and may help to improve the next compilation. The Faraoni Oceanic Anoxic Event, a key Early Cretaceous oceanographic perturbation occurring at the P. ohmi/P. catulloi subzone boundary has a duration estimated at 0.10-0.15 myr, which is similar to previous assessments.

(Figure 2) Foraminifera in lower to middle Albian sediments of DSDP Hole 80-549

The Early Cretaceous series of Site 549 have been analyzed from both an ecological and a chronostratigraphical viewpoint. Lithology and microfaunal assemblages allow the division of these deposits into two parts. The lower part extends from the lower Barremian to the basal upper Barremian and possibly down into the upper Hauterivian. Three foraminiferal associations suggest an orderly evolution from a low-energy, littoral environment, in which continental influences dominated, to progressively more open marine conditions. A dolosparite bed (which has not yet been dated) separates these synrift deposits from lower to basal middle Albian postrift sediments that developed in a pelagic bathyal environment on the middle to nearby lower continental slope.

Composition of bottom sediments from the Clarion Fracture Zone

New data on lithology and stratigraphy of Cenozoic sediments from the Clarion Transform Fault Zone (Pacific Ocean) have been obtained on the base of polygon studies. It has been established that on different blocks (uplifted and subsided) of the Clarion tectonic structure deposits of different age (Eocene to Quaternary) occur. Unconsolidated sediments have been deposited under pelagic conditions since Eocene (probably, since Early Cretaceous) until now. Their mineral composition and content of different ore components are given.

Basalt analyses from different DSDP Holes in the Mozambique Basin and Ridge and from the Southwest Indian Ridge

Basalts from DSDP Sites 248, 249, 250 and 251 in the southwestern Indian Ocean formed in a complex tectonic region affected by the separation of Africa and South America. The different ages and variable geochemical features of these DSDP basalts probably reflect this tectonic complexity. For example, Site 251 on the flanks of the Southwest Indian Ridge is represented by normal MORB which probably originated at the Southwest Indian Ridge. Site 250 in the Mozambique Basin includes an older incompatible- element enriched unit which may represent basalt associated with the Prince Edward Fracture Zone; the upper unit is normal MORB. Basalts at Site 248 also in the Mozambique Basin are geochemically very unlike MORB and have strong continental affinities; they are also comparable in age to some of the continental Karroo basalts. They appear to be related to a subcontinental mantle source or to contamination by continental basement associated with the tectonic elevation of the Mozambique Ridge. Basalts from Site 249 on the Mozambique Ridge are relatively weathered but appear to be normal MORB. Their age, location, and composition are consistent with their origin at an early Cretaceous rift which has been postulated to have separated the Falkland Plateau from the Mozambique Ridge.

(Table 2) Terrigenous, authigenic and biogenic composition of sediments at DSDP Hole 93-603B

Pelagic sedimentation during the Early Cretaceous at Site 603 produced alternations of laminated marly limestone and bioturbated limestone-a facies typical of the "Blake-Bahama Formation" of the western Atlantic. This limestone is a nannofossil micrite, rich in calcified radiolarians, with variable amounts of organic matter, pyritized radiolarian tests, fish debris, and micaceous silt. The laminated marly limestone layers are enriched in organic matter when compared with the intervals of bioturbated limestone. The organic carbon is predominantly terrestrial plant debris; where the organic-carbon content is in excess of 1%, there is also a significant marine-derived component. Laminations can result either from bands of alternately enriched and depleted opaque material and clay, or from bands of elongate lenses (microflasers) of micrite, which could be plastically deformed pellets or diagenetic features. The alternating intervals of laminated and bioturbated structures may have resulted from combined changes in surface productivity, in the influx of terrigenous organic matter, and in the intensity of bottom circulation, which led to episodic oxygen depletion in the bottom water and sediments. Variations in the relative proportions of laminated clay-rich and bioturbated lime-rich limestone and in the development of cycles between these structures make it possible to subdivide the Lower Cretaceous pelagic facies into several subunits which appear to be regional in extent. Bioturbated limestone is dominant in the Berriasian, laminated marly limestone in the Valanginian and Barremian-lower Aptian, and well-developed alternations between these end members in the Hauterivian. The Hauterivian to lower Aptian sediments contain abundant terrigenous clastic turbidites associated with a submarine fan complex. These changes in the general characteristics of the pelagic sediment component of the Blake-Bahama Formation at Site 603 are synchronous with those in the Blake-Bahama Basin (Sites 534 and 391) to the south. Carbonate sedimentation ended in the early Aptian, probably because of a regional shoaling of the carbonate compensation depth.

(Appendix) Total organic carbon, pyrolysis characteristics, and organic matter types at DSDP Holes 77-535 and 77-540

Lower to middle Cretaceous sediments in the eastern Gulf of Mexico are richer in organic matter and have a more marine organic facies than their counterparts in the nearby western North Atlantic, suggesting that the Gulf was the more productive of the two areas. As in the western North Atlantic, the rate of supply of terrestrial organic matter was high when the rate of supply of noncarbonate clastic materials was high (at times of low sea level) and diminished as sea level rose. The rate of supply of marine organic matter was lower in the Early Cretaceous than in the Cenomanian, perhaps in response to the global rise in sea level over this period. Where they are thermally mature, the organic matterrich units drilled at Sites 535 and 540 should be excellent sources for liquid hydrocarbons. The Pleistocene sediments of the eastern Gulf are dominated by terrestrial organic matter representing Mississippi River effluent.