Trace Element Geochemical History of Late Mesozoic Sedimentation in the Southwest Atlantic, Falkland Plateau, Site 511

Abstract

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. . 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. (1067-66.6Ma). The prevailing regime was that of an open ocean basin that tended to expand and deepen. Early-middle Albian (Unit 5)-middle MaestrichtianDuring the second half of the early-middle Albian, the biogenic components Ba, Sr, and CaCO 3 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.

Extreme polar warmth during the Cretaceous greenhouse? Paradox of the late Turonian δ18O record at Deep Sea Drilling Project Site 511

“…Sediments in core 47‐1 and upper 47‐2 are carbonaceous and tended to yield no foraminifera or too few individuals for stable isotope measurements. Below 47‐2, 33 cm, the planktonic foraminiferal and calcareous nannofossil assemblages include cosmopolitan species that are associated with normal, open marine depositional settings, an environmental interpretation supported by the sedimentary trace element geochemistry [ Varentsov , 1983].…”

South Atlantic organic-rich sediments: facies, processes and environments of deposition

“…Inorganic geochemical analyses of the organicrich sediments at Site 511 (Varentsov 1983) reveal concentrations of trace metals (Zn, Cu, Cr, Rb and Ba) associated with the late Jurassic section, and relatively lower concentrations of V, Zn, Cu and Cr in the early Cretaceous black shales. In this latter section, diagenetic concentrations of Zn, Ni, La and perhaps Mo are associated with the carbonate phase.…”