(Appendix) Chemical composition of bottom sediments at DSDP Leg 72 Holes

The distributions of calcium carbonate, of amorphous silica, and of 21 chemical compounds and elements in sediments of Holes 515A, 515B, 516, 516F, 517, and 518 are highly nonuniform; they change depending on the sediment types, grain size, and mineral composition. The main source of the lithogenous elements (K, Li, Rb, Fe, Ti, Zr, Ni, Cr, Sn) is terrigenous matter of South America. These elements correlate well or at least satisfactorily with each other and with the sum of clay minerals. CaCO3, amorphous SiO2 and organic C form a second group, the main source of which is biota of the ocean. Zn, Cu, Ba, Mo, (V, Na) are a third group, which is supplied by both terrigenous and biogenic matter. Judging by the distribution of chemical elements and components in sediments of Site 515, this area of the Brazil Basin is characterized by the rather constant conditions of pelagic terrigenous sedimentation from upper Eocene till Holocene. Small changes in chemical composition of sediments throughout the section are linked mainly to the evolution of subaerial source provinces, changes in hydrodynamic regime, and fluctuations of the ocean level. The chemical composition of sediments from the Rio Grande Rise sites suggests the existence of three main stages of sedimentation in this area. The first stage is the initial period of sediment accumulation on basalts at the beginning of the Late Cretaceous. Then followed sedimentary conditions notable for their sharp changes in chemical composition and type. Beginning in the middle Eocene and persisting into the Holocene, stable conditions of sedimentation characterize a third stage, represented by the formation of approximately 700 m of nannofossil oozes of rather monotonous chemical composition.

Calcareous nannofossils from ODP Leg 105 holes

Neogene calcareous nannofossils were examined from 10 holes at three sites cored during ODP Leg 105. Sediment recovered in Baffin Bay at Site 645 is virtually barren of calcareous nannofossils, with the exception of a sparse lower Miocene assemblage. Sites 646 and 647 in the Labrador Sea contain upper Miocene to Holocene sediments having numerous barren intervals. Upper Pleistocene fossil coccolithophorid floras in the Labrador Sea indicate alternations of cold subpolar with transitional (subpolar/subtropical) assemblages. Extreme variations in the abundance of Coccolithus pelagicus were observed at Sites 646 and 647. These variations are correlated with stable isotopic data to interpret oceanographic responses to warming and cooling trends. The climatic history indicated by the changes of these assemblages closely approximates the past climatic fluctuations recorded in other North Atlantic cores. One new taxon, Discoaster bergenii, is described.

Diagenetic development of deep-sea carbonate sediments from DSDP Holes 30-228, 30-289 and 33-316

Laboratory measurements of ultrasonic velocity (VP, VS) and attenuation (QP**-1, QS**-1) in deep-sea carbonate sequences at DSDP Sites 288, 289 and 316 in the equatorial Pacific were made in conjunction with studies of sediment density, porosity and pore geometry in order to investigate the role of diagenesis in the development of physical properties. Bulk porosity decrease appears to be related more significantly to depth of burial than to age of strata. Both depth of burial and age, however, are important factors controlling the modal pore diameter. In deep-burial diagenesis the modification of pore geometry is influenced by the presence of silica during diagenesis. In carbonate sequences at the three DSDP sites studied, shear wave attenuation anisotropy (QSHH**-1/QSHV**-1) correlates with the shear wave velocity anisotropy. Pore orientation, resulting from overburden pressure and other deep-burial diagenetic processes, is an important factor controlling the increase of VP anisotropy with age and depth of burial. On the basis of observed minor changes in anisotropy values with increasing pressure for some samples, other contributions to VP anisotropy such as grain orientation and bedding lamination cannot be ruled out.

Depths and ages of seismic sequence boundaries in ODP Leg 166 holes

High-resolution, multichannel seismic data collected across the Great Bahama Bank margin and the adjacent Straits of Florida indicate that the deposition of Neogene-Quaternary strata in this transect are controlled by two sedimentation mechanisms: (1) west-dipping layers of the platform margin, which are a product of sea-level-controlled, platform-derived downslope sedimentation; and (2) east- or north-dipping drift deposits in the basinal areas, which are deposited by ocean currents. These two sediment systems are active simultaneously and interfinger at the toe-of-slope. The prograding system consists of sigmoidal clinoforms that advanced the margin some 25 km into the Straits of Florida. The foresets of the clinoforms are approximately 600 m high with variable slope angles that steepen significantly in the Pleistocene section. The seismic facies of the prograding clinoforms on the slope is characterized by dominant, partly chaotic, cut-and-fill geometries caused by submarine canyons that are oriented downslope. In the basin axis, seismic geometries and facies document deposition from and by currents. Most impressive is an 800-m-thick drift deposit at the confluence of the Santaren Channel and the Straits of Florida. This "Santaren Drift" is slightly asymmetric, thinning to the north. The drift displays a highly coherent seismic facies characterized by a continuous succession of reflections, indicating very regular sedimentation. Leg 166 of the Ocean Drilling Program (ODP) drilled a transect of five deep holes between 2 and 30 km from the modern platform margin and retrieved the sediments from both the slope and basin systems. The Neogene slope sediments consist of peri-platform oozes intercalated with turbidites, whereas the basinal drift deposits consist of more homogeneous, fine-grained carbonates that were deposited without major hiatuses by the Florida Current starting at approximately 12.4 Ma. Sea-level fluctuations, which controlled the carbonate production on Great Bahama Bank by repeated exposure of the platform top, controlled lithologic alternations and hiatuses in sedimentation across the transect. Both sedimentary systems are contained in 17 seismic sequences that were identified in the Neogene-Quaternary section. Seismic sequence boundaries were identified based on geometric unconformities beneath the Great Bahama Bank. All the sequence boundaries could be traced across the entire transect into the Straits of Florida. Biostratigraphic age determinations of seismic reflections indicate that the seismic reflections of sequence boundaries have chronostratigraphic significance across both depositional environments.

Compressional and shear wave velocities and elastic constants at DSDP Leg 59 Holes

Prior to the Deep Sea Drilling Project the composition of the oceanic crust could only be inferred from seismic-refraction and gravity data and the recovery of a wide variety of dredged rocks. Through the success of the Deep Sea Drilling Project, it is now clear that the top of oceanic Layer 2 usually consists of basalt. Several laboratory studies (e.g., Fox et al., 1972; Christensen and Shaw, 1970; Hyndman and Drury, 1976) have demonstrated that the seismic velocities of oceanic basalt are similar to velocities reported from refraction studies of Layer 2 and that the variability in Layer 2 velocities has many causes, the most important being fracturing and sea-floor alteration produced by the interaction of basalt and sea water (Christensen and Salisbury, 1973). To date, most reported measurements of velocities in oceanic basalts are from samples obtained from the main ocean basins. With the exception of an earlier study of velocities and related elastic properties of a suite of rocks from DSDP Sites 292, 293, 294, and 296 located in the Philippine Sea (Christensen et al., 1975; Fountain et al., 1975), elastic properties have not been determined for oceanic rocks from marginal basins. In this chapter compressional- and shear-wave velocities and elastic constants are reported at elevated confining pressures for basalt and volcanic breccias from Holes 447A, 448, and 448A.