Fossil plant remains in DSDP Leg 80 holes

The lower part of the syn-rift Barremian-?Hauterivian section at Site 549 contains a large amount of acid-resistant land-derived organic matter that, as elsewhere in the Cretaceous sediments of the IPOD Leg 80 sites, is thermally immature. This plant debris was derived from a vegetation made up of many species of pteridophytes and gymnosperms. The palynofacies indicate that the sediments were deposited in shallow marginal and nonmarine environments and that the climate was probably warm temperate and fairly moist at the time. Source potential for gas is suggested at some horizons. Most of the younger Lower Cretaceous sediments at this and the other sites were deposited in more open marine conditions. Although they generally contain less organic matter, land plant remains continue to comprise a major part of the palynofacies. The Upper Cretaceous sediments were mainly deposited in well oxygenated conditions and are organically lean. However, stratigraphically restricted dark-colored shales at Sites 549 to 551 contain relatively large quantities of amorphous detritus of at least partly marine origin. These characteristics are suggestive of deposition during periods of restricted circulation and also of source potential for oil and gas if maturation levels had been higher.

Clay and silica minerals of ODP Site 123-765

Sediments recovered from Site 765 can be divided into seven mineral associations, based on differences in clay mineralogy. These clay mineral associations correlate with the lithologic units and reflect the rift-to-drift history of the passive Australian margin. In general, the Lower to mid-Cretaceous sediments represent altered volcanic material and detrital aluminosilicates that were deposited during the early formation of the Argo Basin. The predominant clay mineral is randomly interstratified illite/smectite (I/S) that contains less than 10% illite layers. The transformation of smectite to illite is suggested by an increase in the percentage of illite layers in the basal sediments (from <10% to 40%) that corresponds to the silica transformation of opal-CT to quartz. This mixed-layered illite/smectite has an average composition of (K0.14 Na0.29 C0.07)(Al0.88 Mg0.43 Fe0.61 Ti0.06)(Si3.88 Al0.12)(O)10(OH)2. The highly smectitic composition of the I/S and its association with bentonite layers and zeolite minerals suggest that much of the I/S was derived from the alteration of volcanic material. The condensed middle to Upper Cretaceous sediments consist of palygorskite and detrital I/S that contains 30% to 60% illite layers. The condensed Paleogene sediments contain no palygorskite and are dominated by detrital clay minerals or by highly smectitic I/S associated with bentonite layers and zeolite minerals. The overlying, rapidly deposited Neogene clayey calcareous turbidites consist of three distinct clay mineral associations. Middle Miocene sediments contain palygorskite, kaolinite, and a tentatively identified mixed-layered illite/smectite/chlorite (I/S/C) or saponite. Upper Miocene sediments contain abundant sepiolite and kaolinite and lesser amounts of detrital I/S. Detrital I/S and kaolinite dominate the clay mineralogy of Pliocene and Pleistocene sediments. The fibrous, magnesium-rich clay minerals sepiolite and palygorskite appear to be authigenic and occur intimately associated with authigenic dolomite. The magnesium required to form these Mg-rich minerals was supplied by diffusion from the overlying seawater, and silica was supplied by the dissolution of associated biogenic silica.

TEST

Der Müller und die fünf Räuber, Überfall²³

(Table 1) B content, d11B, d18O, degree of alteration, and lithology of basalts from ODP Hole 504B

Boron contents and boron isotopic compositions were determined for the uppermost 1.3 km section of typical 6.2 Ma oceanic crust from DSDP/ODP Hole 504B, Costa Rica Rift, Galapagos Spreading Center. Both the boron content and the d11B value in the oceanic crust are controlled by two types of alteration: 1. (1) low-temperature alteration (0 to 60°C; Zones I and II) and 2. (2) high-temperature hydrothermal alteration (200 to 400°C; Zones III and IV). Basalts subjected to the low-temperature alteration are characterized by their relatively high boron contents (0.69 to 19.3 ppm) and high d11B values (+2.2 to +10.6?), indicating uptake of boron into secondary phases in equilibrium with seawater or evolved seawater. Hydrothermally altered basalts contain less abundant boron (0.17 to 0.52 ppm) and relatively constant d11B values (?0.1 to +1.0?). Although basalts from the upper part of these hydrothermal zones (<1300 mbsf) show equilibrated boron content and d11B value with aqueous fluid, effective leaching of boron from basalt is predominant in the lower part (>1300 mbsf). Original boron content and d11B value of the Hole 504B MORB were 0.35 ppm and +0.2?, respectively. The present data provide fundamental information in understanding of the distribution of boron and boron isotopes in the oceanic crust.