Paleomagnetic characterization and age of several ODP Leg 198 sites, Shatsky Rise

Shatsky Rise, a medium-sized large igneous province in the west Central Pacific Ocean, has three main topographic highs that preserve a thick sedimentary record from Cretaceous through Cenozoic. During Ocean Drilling Program (ODP) Leg 198 to Shatsky Rise, a total of ~768 m of late Miocene-Holocene sediments was recovered from six sites. Sites 1207 and 1208 were drilled on the Northern and Central Highs, respectively, and yielded expanded late Miocene-Holocene sequences. Sites 1209, 1210, 1211, and 1212 were drilled on the Southern High and yielded shorter sequences of similar age. Clearly interpretable magnetic stratigraphies were obtained from all sites using the shipboard pass-through magnetometer. These results were augmented using discrete sample cubes (7 cm**3) collected shipboard and measured postcruise. Miocene age sediments are separated by a hiatus from Oligocene, Eocene, and Cretaceous age sediments beneath. An astrochronological age model was developed for the six sites based on cycles observed in reflectance data, measured shipboard. This age model is in good agreement with published astrochronological polarity chron ages in the 1 to 6 Ma interval.

Geochemistry of phosphate and glauconites of ODP Leg 128 samples

Glauconites and phosphates have been detected in almost all investigated samples at Sites 798 (uppermost Miocene or lower Pliocene to Pleistocene) and 799 (early middle Miocene to Pleistocene). Autochthonous occurrences appear in very minor quantities (generally below 0.2%) throughout the drilled sequences, whereas allochthonous accumulations are limited to the lower Pliocene or uppermost Miocene sequence at Site 798 (glauconites) and to the upper and middle Miocene sequence at Site 799 (upper and middle Miocene: glauconites; middle Miocene: phosphates). X-ray fluorescence, microprobe, and bulk chemical analyses indicate high variabilities in cations and anions and generally low oxide totals. This is probably related to the substitution of phosphate and fluoride aniors by hydroxide and carbonate anions in phosphates and to the depletion of iron, aluminum, and potassium cations and the enrichment in hydroxide and crystal water in glauconites. Gradients in pore-water contents of dissolved phosphate and fluoride at Sites 798 and 799 suggest a depth of phosphate precipitation between 30 and 50 mbsf, with fluoride as the limiting element for phosphate precipitation at Site 798. Phosphate and fluoride appear to be balanced at Site 799. Crude extrapolations indicate that the Japan-Sea sediments may have taken up approximately 7.2*10**10 g P total/yr during the Neogene and Pleistocene. This amount corresponds to approximately 0.3% of the estimated present-day global transfer of phosphorus into the sediments and suggests that the Japan Sea constitutes an average sink for this element. The two main carriers of phosphorus into the present Japan Sea are the Tshushima and the Liman currents, importing approximately 6.6*10**10 g P and 5.7*10**10 g P per year, respectively. Bulk chemical analyses suggest that at least 36% of P total in the sediments is organically bound phosphorus. This rather high value, which corresponds to the measured Japan-Sea deep-water P organic/P total ratios, probably reflects rapid transport of organic phosphorus into the depth of the Japan Sea.

Eolian grain-size record of early Paleogene sediments from DSDP Hole 22-215 and ODP Leg 208 sites

To date, the only Southern Hemisphere eolian grain-size record constructed for the early Paleogene comes from Deep Sea Drilling Project Site 215. Ten early Paleogene sediment samples from Site 215 were collected and processed to show that the existing eolian grain-size record at this site can be reproduced. Five samples each from Ocean Drilling Program Sites 1263 and 1267 were similarly examined to test the possibility of generating new Southern Hemisphere eolian grain-size records for the early Paleogene. Our results indicate that an eolian grain-size signal can be constructed at Walvis Ridge, although the record will be complicated by hemipelagic terrigenous inputs. Further, we assert that a record generated at a site located on the deep flanks of Walvis Ridge is particularly susceptible to hemipelagic influence.

Late Eocene-early Oligocene radiolarian events and abundances in ODP Leg 199 sediments

During Ocean Drilling Program Leg 199, eight sites (Sites 1215-1222) were cored in the Central Pacific. Late Eocene-early Oligocene thick radiolarian-rich biogenic sediments were collected from Holes 1218A, 1219A, and 1220A. This is the first attempt to calibrate the ages of Paleogene radiolarian events using magnetostratigraphy in this region. A total of 107 species and species groups, which are valuable for stratigraphic correlation, are listed with numeric data and figures. Among these three holes, a total of 77 radiolarian events were recognized and their ages were calibrated by correlation with paleomagnetic events recorded in Hole 1220A.

Composition of ODP Leg 126 sandstones

Early diagenesis in Leg 126 forearc and backarc sands/sandstones is characterized by the dissolution of intermediate to mafic brown glass, the alteration of colorless rhyolitic glass to clay minerals, precipitation of thin clay-mineral rim cements, and minor precipitation of clinoptilolite cements. Later, more intense diagenesis is restricted to Oligocene forearc basin sediments at Sites 787,792, and 793. In these sections, the effects of early diagenesis have been intensified and overprinted by later diagenetic effects including (1) large-scale dissolution of feldspar and pyroxene crystals, (2) further dissolution of vitric components, (3) precipitation of minor carbonate cements, and (4) pervasive, multiple-staged zeolite cementation. Zeolite minerals present include analcite, mordenite, natrolite, heulandite, wairakite, chabazite, erionite, herschelite, and phillipsite. The latest diagenetic events appear to be the minor dissolution of zeolite cements and the precipitation of minor carbonate and potassium feldspar(?) cements. Observed porosity types include primary interparticles; primary intraparticles in vesicular glass and foraminifers; primary interparticles reduced by compaction and cementation; secondary intraparticles produced by dissolution of feldspar, nonopaque heavy minerals, volcanic glass, and foraminifer tests; and secondary interparticles produced by the dissolution of zeolite cements. Within forearc Oligocene sections at Sites 787 and 792, diagenetic effects appear to decrease with depth in the Oligocene section; however, at Site 793 the majority of samples are intensely altered.

Neogene calcareous nannofossils in ODP Leg 116 holes

The three sites (717, 718, and 719) drilled on the distal Bengal Fan during ODP Leg 116 cored turbidite sediments almost exclusively. Calcareous nannofossils were recovered sporadically and, although all of them probably have been redeposited, it is possible to date the sediments at all three sites with reasonable confidence. Site 717 penetrated the uppermost middle Miocene Catinaster coalitus highest occurrence datum and represents the most nearly continuous succession of turbidites. Site 718 penetrated the lower Miocene, well below the Helicosphaera ampliaperta highest occurrence datum, but this site contains a major late Pliocene to mid-Pleistocene hiatus. Site 719, the shallowest hole, penetrated only into the upper Miocene. Identification of several critical lowest occurrence datums allows using the poorly constrained but more numerous highest occurrence datums for comparison with the model succession (zonal markers) and thereby to derive a reasonably accurate time framework for the sediments.

Major and trace element geochemistry of ODP Leg 178 holes

Geochemical analyses have been performed on sediment samples collected during Ocean Drilling Program Leg 178 from the continental rise and outer continental shelf of the Antarctic Peninsula. A suite of 21 trace elements was measured by neutron activation analysis in 39 sediment samples, and major element oxides were determined in 67 samples by electron microprobe analyses of fused glass beads. These geochemical data, combined with the X-ray diffraction and X-ray fluorescence data from shipboard analyses, provide a reasonable estimate of the mineral and chemical composition of sediments deposited along the western margin of the Antarctic Peninsula.