Trace and rare elements and factors at DSDP Hole 71-511

The distribution of paragenetic assemblages of trace and rare elements, as revealed by factor analysis (R-mode, Q-mode), the ratios of elements to Zr and the interpretation of these data in the context of the known mineralogy, lithology, and geology of the region, provide the bases for the outline of the geochemical history of sedimentation in the study area that forms the subject of this chapter. Two stages may be discerned. 1. Late-Middle Jurassic-Early Cretaceous (160-106? Ma). The sediments that accumulated in relatively shallow water (shelf) were predominantly clay, with dispersed sapropelic organic matter, plant fragments, pyrite, admixtures of acid-medium volcanic glass, and epigenetic crystals of gypsum. The bottom water layers of the basin are notably stagnant. The sediments are characterized by higher amounts of V, Zn, Cu, Cr, Rb, and Be associated with organic matter. Lower Cretaceous sediments, separated from those of the Upper Jurassic by a hiatus, accumulated in a deepened and enlarging basin. These Lower Cretaceous deposits are chemically similar to those of the Upper Jurassic, but contain diagenetic concentrations of Zn, Ni, and La. 2. Early-middle Albian (Unit 5)-middle Maestrichtian (1067-66.6Ma). The prevailing regime was that of an open ocean basin that tended to expand and deepen. During the second half of the early-middle Albian, the biogenic components Ba, Sr, and CaCO3 accumulated. By the end of this interval, Ti/Zr values had increased. In conjunction data on mineral composition, they testify to an outburst of basaltoid volcanism related to tectonic activity before an erosional hiatus (late Albian-Cenomanian). At the end of the Cenomanian-Turonian, residual deposits of predominantly clay sediments with relatively high amounts of Ti and Zr and associated rare alkalis (Li, Rb) accumulated. Clay sediments deposited during the Coniacian-Santonian were characterized by higher concentrations of Ti, Zr, Li, and Rb, by diagenetic carbonate phases of Ni, Zn, and La, and by sulphides and Fe-oxides with an admixture of Ni and Co. The latter half of the interval saw the deposition of fine basaltoid volcanoclastic material, diagenetically altered by zeolitization and carbonatization and enriched with Se, Pb, Ti, Sr, Ba, Y, and Yb. Sediments with a similar chemistry accumulated in the Campanian-middle Maestrichtian. Strong current activity preceding a global hiatus at the Mesozoic/Cenozoic boundary is reflected in both lower sedimentation rates and the presence of higher residual concentrations of Ti, Zr, Ba, Sr, and other elements studied in this chapter.

Natural oxides, elements and remanent magnetization intensities and directions at DSDP Hole 93-603B

Dark green spherules occur in the lower part of a turbidite in Section 603B-22-3, at the 70 cm level. In all probability these spherules originally consisted of massive glass, but now appear to have become completely altered into smectite. The presence of numerous microscopic fissures in the spherules probably mediated in the alteration process. Judging by the presence of similar spherules at the Cretaceous/Tertiary (K/T) boundary in DSDP Hole 390B, the green spherules are thought to represent diagenetically altered impact ejecta from one large or several smaller extraterrestrial objects at the end of the Cretaceous. The presence of anomalously high concentrations of Ni, Co, and As higher up in the turbidite are in agreement with an expected enrichment of these elements in the K/T boundary clay. However, precise Ir analyses are necessary in order to confirm this.

Mineral composition, major element oxides and trace element concentration of sediments from ODP Leg 180 sites

Middle Miocene to Holocene fine-grained argillaceous sediments (clays, claystones/muds, and mudstones), which volumetrically dominated the sediment recovery in the Woodlark Basin during Leg 180, were chemically analyzed for major elements, trace elements, and some rare earth elements by X-ray fluorescence. Selected samples also underwent X-ray diffraction (XRD) analysis for mineral determination. The results shed light on sediment provenance when combined with shipboard sediment descriptions, smear slide study, and XRD. The oldest sediments recovered (Site 1108) of middle-late Miocene age include volcanogenic muds with distinctive high MgO and K2O, indicative of a relatively basic calc-alkaline source related to an inferred Miocene forearc succession. The forearc basement, composed of diabase and basalt, was locally exposed (Site 1109) and eroded in the late Miocene (<5.4-9.93 Ma), giving rise to fluvial conglomerates (Sites 1109, 1115, and 1118). Chemically distinctive fine-grained claystones and siltstones (with relatively high Ti, low K) are compatible with derivation from tropically weathered basic igneous rocks, correlated with the Paleogene Papuan ophiolite. Overlying latest Miocene-Pleistocene fine-grained sediments throughout the Woodlark Basin were partly derived from calc-alkaline volcanic sources. However, relatively high abundances of Al2O3 and related element oxides (K2O and Na2O) and trace elements (e.g., Rb and Y) reflect an additional terrigenous input throughout the basin, correlated with pelitic metamorphic rocks exposed on Papua New Guinea and adjacent areas. In addition, sporadic high abundances of Cr and Ni, some other trace metals, and related minerals (talc, crysotile, and chlorite) reflect input from an ophiolitic terrain dominated by ultramafic rocks, correlated with the Paleogene Papuan ophiolite. The source areas possibly included serpentinized ultramafic ophiolitic rocks exposed in the Papua New Guinea interior highlands. Chemical evidence further indicates that fine-grained terrigenous sediment reached the Woodlark Basin throughout its entire late Miocene-Holocene history. Distinctive high-K volcanogenic muds rich in tephra and volcanic ash layers that appear at <2.3 Ma (Sites 1109 and 1115) are indicative of high-K calc-alkaline volcanic centers, possibly located in the Dawson Strait, Moresby Strait, or Dobu Seamount area. Chemical diagenesis of fine-grained sediments within the Woodlark Basin is reflected in clay neomorphism and localized formation of minerals including dolomite, ankerite, and zeolite but has had little effect on the bulk chemical composition of most samples.

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.

Geochemistry of ocean floor and forearc serpentinites

We provide new insights into the geochemistry of serpentinites from mid-ocean ridges (Mid-Atlantic Ridge and Hess Deep), passive margins (Iberia Abyssal Plain and Newfoundland) and fore-arcs (Mariana and Guatemala) based on bulk-rock and in situ mineral major and trace element compositional data collected on drill cores from the Deep Sea Drilling Project and Ocean Drilling Program. These data are important for constraining the serpentinite-hosted trace element inventory of subduction zones. Bulk serpentinites show up to several orders of magnitude enrichments in Cl, B, Sr, U, Sb, Pb, Rb, Cs and Li relative to elements of similar compatibility during mantle melting, which correspond to the highest primitive mantle-normalized B/Nb, B/Th, U/Th, Sb/Ce, Sr/Nd and Li/Y among subducted lithologies of the oceanic lithosphere (serpentinites, sediments and altered igneous oceanic crust). Among the elements showing relative enrichment, Cl and B are by far the most abundant with bulk concentrations mostly above 1000 µg/g and 30 µg/g, respectively. All other trace elements showing relative enrichments are generally present in low concentrations (µg/g level), except Sr in carbonate-bearing serpentinites (thousands of µg/g). In situ data indicate that concentrations of Cl, B, Sr, U, Sb, Rb and Cs are, and that of Li can be, increased by serpentinization. These elements are largely hosted in serpentine (lizardite and chrysotile, but not antigorite). Aragonite precipitation leads to significant enrichments in Sr, U and B, whereas calcite is important only as an Sr host. Commonly observed brucite is trace element-poor. The overall enrichment patterns are comparable among serpentinites from mid-ocean ridges, passive margins and fore-arcs, whereas the extents of enrichments are often specific to the geodynamic setting. Variability in relative trace element enrichments within a specific setting (and locality) can be several orders of magnitude. Mid-ocean ridge serpentinites often show pronounced bulk-rock U enrichment in addition to ubiquitous Cl, B and Sr enrichment. They also exhibit positive Eu anomalies on chondrite-normalized rare earth element plots. Passive margin serpentinites tend to have higher overall incompatible trace element contents than mid-ocean ridge and fore-arc serpentinites and show the highest B enrichment among all the studied serpentinites. Fore-arc serpentinites are characterized by low overall trace element contents and show the lowest Cl, but the highest Rb, Cs and Sr enrichments. Based on our data, subducted dehydrating serpentinites are likely to release fluids with high B/Nb, B/Th, U/Th, Sb/Ce and Sr/Nd, rendering them one of the potential sources of some of the characteristic trace element fingerprints of arc magmas (e.g. high B/Nb, high Sr/Nd, high Sb/Ce). However, although serpentinites are a substantial part of global subduction zone chemical cycling, owing to their low overall trace element contents (except for B and Cl) their geochemical imprint on arc magma sources (apart from addition of H2O, B and Cl) can be masked considerably by the trace element signal from subducted crustal components.

Alkenone composition, UK'37 index, and carbon, sulphur, nitrogen and element oxides of ODP Site 186-1151

Ocean Drilling Program (ODP) Site 1151 (Sacks, Suyehiro, Acton, et al., 2000, doi:10.2973/odp.proc.ir.186.2000) is located in an area where the surface water mass is influenced by both the Kuroshio and Oyashio Currents. The site also receives a relatively high flux of detrital materials from riverine input from Honsyu Island and eolian input from Central and East Asia. We analyzed alkenones and alkenoates in the sediments to reconstruct alkenone unsaturation index (Uk'37)-based sea-surface temperature (SST), total organic carbon, and total nitrogen to estimate the terrigenous contribution by the C/N ratio during the last glacial-interglacial cycle. The major elements were also analyzed to examine the variation in terrigenous composition.