Thickness and duration of biostratigraphic zones, assemblages, ages and sedimentation rates at DSDP Sites 76-534 and 44-391

In this Initial Report of the Deep Sea Drilling Project, detailed studies of Sites 533 (gas hydrates) on the Blake Outer Ridge and 534 (oldest ocean history) in the Blake-Bahama Basin have provided answers to many geological and geophysical questions posed over the decade that deep drilling has been undertaken in this part of the western North Atlantic. The history of drilling and a historical review of key scientific accomplishments have been presented in the Introduction (Gradstein and Sheridan, this volume). In this final chapter we review highlights of new geological, geophysical and paleoceanographic interpretations presented in this volume, and offer a critical review of this information. We conclude with a listing of some outstanding problems and recommendations for future research, including data collection.

Geochemical analyses at DSDP Holes 72-515B and 72-516F

The petroleum-generating potential of five samples from Hole 515B, Vema Channel, and of 23 samples from Hole 516F, Rio Grande Rise, was analyzed. Organic carbon and pyrolysis data indicated that source rocks of good quality are not present. Microscopic examination showed predominance of woody organic matter, which is more favorable for the generation of gas in a mature stage; all samples, however, are still thermally immature.

Concentrations of major-element oxides and minor and trace elements at DSDP Legs 87, 57, 56 and 31

Sediments from Sites 582 (11 samples), 583 (19 samples), 584 (31 samples), 294 (1 sample), 296 (9 samples), 297 (3 samples), 436 (11 samples), and 439 (3 samples) were analyzed by X-ray fluorescence and/or instrumental neutron activation analysis. Ten major elements and 24 minor and trace elements (including 7 rare earth elements) were determined with these methods. Geochemistry varies systematically with both the site location and sediment age. Such variations are explained in terms of changes in sedimentation processes caused by plate motion and changes in ocean currents.

Datum events and their estimated magnetochronology at DSDP Site 72-516

Calcareous plankton biostratigraphy (foraminifers and nannoplankton) and magnetostratigraphy of the upper Oligocene to Pleistocene have been studied in hydraulic piston Cores 516-1 to 516-44, 516A-5 to 516A-11, and 516F-1 to 516F-11, Rio Grande Rise (water depth 1313 m). Some 80 biostratigraphic datum events have been correlated to the magnetic polarity stratigraphy over an interval representing the Matuyama to Chron 5, and Chrons 16 to 23. Coring disturbance and biostratigraphic evidence of a condensed section preclude unambiguous identification of polarity or biostratigraphic events over an approximately 30-m interval in the middle and upper Miocene. Sedimentation rates varied considerably during the Neogene, but an abnormally thick upper Oligocene and lower Miocene section allows a high degree of magnetobiochronologic resolution. A new planktonic foraminiferal zonation for the Miocene completes the midlatitude Neogene zonation of the South Atlantic. Important magnetobiostratigraphic correlations at Site 516 and their estimated magnetochronology include: (1) Oligocene/ Miocene boundary = first appearance datum (FAD) Globorotalia kugleri = last appearance datum (LAD) Reticulofenestra bisecta = mid-Anomaly 6C (Chron 23) = 23.7 Ma; (2) Aquitanian/Burdigalian boundary = LAD G. kugleri = between base Anomaly 6A and top of unnumbered anomaly between 6A and 6B (Chron 21) = 21.8 Ma; (3) Zone N6/N7 boundary = LAD Catapsydrax dissimilis (= FAD G. pseudomiozea and G. zealandica) = Chron 16/17 boundary = 17.6 Ma; (4) early/middle Miocene (= Burdigalian/Langhian) boundary = FAD Praeorbulina sicana = midpart of Anomaly 5C (Chron 16) = 16.6 Ma or FAD P. glomerosa = just above Anomaly 5C (inferred) = 16.3 Ma; (5) Zone N8/N9 boundary = FAD Orbulina suturalis above Anomaly 5C (later part Chron 16, inferred); (6) Miocene/ Pliocene boundary = LAD Globoquadrina dehiscens LAD Globorotalia lenguaensis = basal Gilbert Chron = 5.3 Ma.

Elemental abundance and water content at DSDP Leg 86 Holes

X-ray fluorescence analyses of 1143 samples from Site 576 (32°21.4'N, 164°16.5'E) and 539 samples from Site 578 (33°55.6'N, 151°37.7'E) for the elements Na, Mg, Al, Si, P, K, Ca, Ti, Mn, Fe, Ba, and S show consistent trends from Si-rich surficial deposits to dark brown clays rich in Mn, Fe, P, and Ti in early Cenozoic sections. These data sets form the basis for a detailed paleogeochemical stratigraphy of North Pacific "red" clays.

Platinum group elements and geochemistry of altered oceanic crust of ODP Hole 140-504B

Primary chemical heterogeneity in the sheeted dike complex in Deep Sea Drilling Project Hole 504B makes these rocks unsuitable for conventional mass balance calculations in determining element mobility associated with hydrothermal alteration. Due to the original heterogeneity and variable degrees of fractionation in the dikes, an appropriate reference sample on which calculations can be based is difficult to find. Therefore, the use of incompatible element ratios is developed to evaluate geochemical changes during alteration(s). For example, on a Zr/Yb-La/Yb plot, scatter along a straight line suggests tapping of a variably depleted mantle source and deviation from the line suggests element mobility (gain or loss). Using this method, our data indicates that the hydrothermal evolution of the sheeted dike complex was accompanied by significant loss of Cu, Zn, and Ti and some loss of La. The sheeted dike complex has low platinum group element (PGE) concentrations and steep PGE patterns, typical of mid-ocean ridge basalts (MORBs) on the global scale. We propose that the unusual PGE patterns of MORBs cannot be entirely generated by a partial melting and sulfide segregation model; instead, these patterns in part must have been inherited from their mantle source. The Au data show no evidence for mobilization during hydrothermal alteration of the dikes.

Displaced diatom, discoasters and benthic foraminifers at DSDP Hole 72-515A

Late Pliocene to Recent sediments from the southern Brazil Basin (DSDP Hole 515A, hydraulic piston core) were analyzed for evidence of episodic flow of Antarctic Bottom Water (AABW) through the Vema Channel. Carbonate-enriched layers punctuate the post-Pliocene section, otherwise composed predominantly of terrigenous silt and clay. Carbonate enrichment is thought to result from rapid deposition of fine-grained calcareous turbidites, originating in canyons incised on the northern margin of the Rio Grande Rise. The composition of benthic foraminiferal assemblages and the presence of stratigraphically displaced discoasters is consistent with a turbidite origin. Based on the presence of displaced Antarctic diatoms, AABW flow through the Vema Channel apparently has had a major influence on this site for only four periods during the last 2.7 Ma (about 45 to 250; 375 to 430; 700 to 780; 1320 to 1345 thousand yr. ago).

Grain-size distribution, carbon and calcium carbonate at DSDP Leg 63 Holes

Sand-silt-clay distribution was determined at Scripps on samples collected at the time the cores were split and described. The sediment classification used here is that of Shepard (1954); sand, silt, and clay boundaries are determined on the basis of the Wentworth (1922) scale. Thus the sand, silt, and clay fractions are composed of particles whose diameters range from 2000 to 62.5 µm, 62.5 to 3.91 µm, and less than 3.91 µm, respectively. This classification is applied regardless of sediment type and origin.

Sediment paleomagnetism at DSDP Leg 78 Holes

The results of paleomagnetic studies of samples from DSDP Leg 78A are reported. For Site 541, the interval from 60 to 200 m sub-bottom was correlated with the Matuyama through Gilbert polarity epochs. For Site 543, the interval from 150 to 190 m sub-bottom was correlated with marine magnetic Anomalies 5C through 5E. Down-dip directions of tilted beds inferred from declination values for Sites 541 and 542 suggest a pattern of monoclinal folding. Results from basalt samples are comparable to those from other DSDP sites in relatively old basalts.

Quaternary radiolarians and plamktonic foraminifera from the mouth of the Gulf of California

I recovered well-preserved radiolarian assemblages from the Quaternary sediments drilled at all four sites at the mouth of the Gulf of California during Leg 65. The sites, with positions and water depths averaged for all hole locations per site, are Site 482 - 22°47.4'N, 107°59.6'W; water depth, 3022 meters. Site 483 - 22°53.0'N, 108°44.8' W; water depth, 3070 meters. Site 484 - 23°11.2'N, 108°23.6'W; water depth, 2887 meters. Site 485 - 22°44.9'N, 107°54.2'W; water depth, 2981 meters. The nearly 200 taxa I identified are listed alphabetically in the systematic reference list. The only reliable radiolarian biostratigraphic datum determined for the Quaternary sedimentary section is the highest occurrence of Axoprunum angelinum (Hays) at Sites 483, 484, and 485.

Relationship between definitive datum levels and magnetic polarity and revised geomagnetic polarity time-scale at DSDP Hole 72-516F

This paper contains magnetobiostratigraphic correlation charts for each of the four sites occupied during DSDP Leg 72. Microfossil zonal boundaries and magnetic polarity determinations for Sites 515 through 518 are summarized in Figures 1 through 4, respectively. Our discussion focuses on the correlations derived for the Paleogene and late Cretaceous (Coniacian-Maestrichtian) of Site 516, because of the value of this site as a stratigraphic reference section for the South Atlantic.

Minerals and geochemistry of DSDP Hole 81-552A

The acid insoluble coarse fractions of the glacial-interglacial sequence of Hole 552A in the NE Atlantic are made up of varying amounts of terrigenous detritus, biogenic silica, and pyroclastic material, principally volcanic glass. Volcanic ash content varies significantly over the entire interval, and the three North Atlantic ash horizons of Ruddiman and Glover (1972) can be recognized satisfactorily. The terrigenous detritus is of mixed metamorphic-basaltic type and probably originated on the Greenland landmass

Quantity, provenance, and thermal maturity of organic matter at DSDP Holes 95-612 and 95-613

Using methods of analysis from organic geochemistry and organic petrography, we investigated six Pliocene to Maestrichtian samples from DSDP Site 612 and five Pliocene to Eocene samples from DSDP Site 613 for the quantity, type, and thermal maturity of organic matter. At both sites, organic carbon content is low in the Eocene samples (0.10 to 0.20%) and relatively high in the Pliocene/Miocene samples (0.87 to 1.15%). The Maestrichtian samples from Site 612 contain about 0.6% organic carbon. The organic matter is predominantly terrigenous, as indicated by low hydrogen index values from Rock-Eval pyrolysis and the dominance of long-chain wax alkanes in the extractable hydrocarbons. The organic matter is at a low level of thermal maturity; measured vitrinite reflectance values were between 0.27 and 0.44%.