Multibeam Converter - a tool to create Ocean Data View import files from multibeam files

The software Multibeam Converter is a tool to convert files or folders of files (ascii/tab-separated data files with or without metaheader), downloaded from PANGAEA via the search engine or the data warehouse to the ODV import format, e.g. for visualization or further processing. MultibeamConverter is distributed as freeware for the operating systems Microsoft Windows, Apple OS X and Linux.

Pan2Applic - a tool to convert and compile PANGAEA output files

The software Pan2Applic is a tool to convert files or folders of files (ascii/tab-separated data files with or without metaheader), downloaded from PANGAEA via the search engine or the data warehouse to formats as used by applications, e.g. for visualization or further processing. It may also be used to convert files or zip-archives as downloaded from CD-ROM data collections, published in the WDC-MARE Reports series. Pan2Applic is distributed as freeware for the operating systems Microsoft Windows, Apple OS X and Linux.

Magnetic properties of Cenozoic MORB and Cretaceous MORB from DSDP and ODP holes

The fact that the natural remanent magnetization (NRM) intensity of mid-oceanic-ridge basalt (MORB) samples shows systematic variations as a function of age has long been recognized: maximum as well as average intensities are generally high for very young samples, falling off rather rapidly to less than half the recent values in samples between 10 and 30 Ma, whereupon they slowly rise in the early Tertiary and Cretaceous to values that approach those of the very young samples. NRM intensities measured in this study follow the same trends as those observed in previous publications. In this study, we take a statistical approach and examine whether this pattern can be explained by variations in one or more of all previously proposed mechanisms: chemical composition of the magnetic minerals, abundance of these magnetization carriers, vectorial superposition of parallel or antiparallel components of magnetization, magnetic grain or domain size patterns, low-temperature oxidation to titanomaghemite, or geomagnetic field behavior. We find that the samples do not show any compositional, petrological, rock-magnetic, or paleomagnetic patterns that can explain the trends. Geomagnetic field intensity is the only effect that cannot be directly tested on the same samples, but it shows a similar pattern as our measured NRM intensities. We therefore conclude that the geomagnetic field strength was, on-average, significantly greater during the Cretaceous than during the Oligocene and Miocene.

Composition of phyllosilicates from hydrothermally altered basalts of DSDP Hole 83-504B, Costa Rica Rift, Pacific Ocean

Phyllosilicates occurring as replacements of olivine, clinopyroxene and interstitial materials and as veins or fracture-fillings in hydrothermally altered basalts from DSDP Hole 504B, Leg 83 have been studied using transmission and analytical electron microscopy. The parageneses of phyllosilicates generally change systematically with depth and with the degree of alteration, which in turn is related to permeability of basalts. Saponite and some mixed-layer chlorite/smectite are the dominant phyllosilicates at the top of the transition zone. Chlorite, corrensite, and mixed-layer chlorite/corrensite occur mainly in the lower transition zone and upper levels of the sheeted dike zone. Chlorite, talc, and mixed-layer talc/chlorite are the major phyllosilicates in the sheeted dike zone, although replacement of talc or olivine by saponite is observed. The phyllosilicates consist of parallel or subparallel discrete packets of coherent layers with packet thicknesses generally ranging from < 100 A to a few hundred A. The packets of saponite layers are much smaller or less well defined than those of chlorite, corrensite and talc, indicating poorer crystallinity of saponite. By contrast, chlorite and talc from the lower transition zone and the sheeted dike zone occur in packets up to thousands of A thick. The Si/(Si + A1) ratio of these trioctahedral phyllosilicates increases and Fe/(Fe + Mg) decreases in the order chlorite, corrensite, saponite, and talc. These relations reflect optimal solid solution consistent with minimum misfit of articulated octahedral and tetrahedral sheets. Variations in composition of hydrothermal fluids and precursor minerals, especially in Si/(Si+A1) and Fe/(Fe+Mg) ratios, are thus important factors in controlling the parageneses of phyllosilicates. The phyllosilicates are generally well crystallized discrete phases, rather than mixed-layered phases, where they have been affected by relatively high fluid/rock ratios as in high-permeability basalts, in veins, or areas adjacent to veins. Intense alteration in basalts with high permeability (indicating high fluid/rock ratios) is characterized by pervasive albitization and zeolitization. Minimal alteration in the basalts without significant albitization and zeolitization is characterized by the occurrence of saponite ± mixed-layer chlorite/smectite in the low-temperature alteration zone, and mixed-layer chlorite/corrensite or mixed-layer talc/chlorite in the high-temperature alteration zone. Textural non-equilibrium for phyllosilicates is represented by mixed layering and poorly defined packets of partially incoherent layers. The approach to textural equilibrium was controlled largely by the availability of fluid or permeability.

Chemical and isotope composition of poor fluid from gas-hydrate samples of ODP Site 146-892

Although the presence of extensive gas hydrate on the Cascadia margin, offshore from the western U.S. and Canada, has been inferred from marine seismic records and pore water chemistry, solid gas hydrate has only been found at one location. At Ocean Drilling Program (ODP) Site 892, offshore from central Oregon, gas hydrate was recovered close to the sediment-water interface at 2-19 m below the seafloor (mbsf) at 670 m water depth. The gas hydrate occurs as elongated platy crystals or crystal aggregates, mostly disseminated irregularly, with higher concentrations occurring in discrete zones, thin layers, and/or veinlets parallel or oblique to the bedding. A 2- to 3-cm thick massive gas hydrate layer, parallel to bedding, was recovered at ~17 mbsf. Gas from a sample of this layer was composed of both CH4 and H2S. This sample is the first mixed-gas hydrate of CH4-H2S documented in ODP; it also contains ethane and minor amounts of CO2. Measured temperatures of the recovered core ranged from 2 to -1.8°C and are 6 to 8 degrees lower than in-situ temperatures. These temperature anomalies were caused by the partial dissociation of the CH4-H2S hydrate during recovery without a pressure core sampler. During this dissociation, toxic levels of H2S (delta34S, +27.4?) were released. The delta13C values of the CH4 in the gas hydrate, -64.5 to -67.5? (PDB), together with deltaD values of -197 to -199? (SMOW) indicate a primarily microbial source for the CH4. The delta18O value of the hydrate H2O is +2.9? (SMOW), comparable with the experimental fractionation factor for sea-ice. The unusual composition (CH4-H2S) and depth distribution (2-19 mbsf) of this gas hydrate indicate mixing between a methane-rich fluid with a pore fluid enriched in sulfide; at this site the former is advecting along an inclined fault into the active sulfate reduction zone. The facts that the CH4-H2S hydrate is primarily confined to the present day active sulfate reduction zone (2-19 mbsf), and that from here down to the BSR depth (19-68 mbsf) the gas hydrate inferred to exist is a >=99% CH4 hydrate, suggest that the mixing of CH4 and H2S is a geologically young process. Because the existence of a mixed CH4-H2S hydrate is indicative of moderate to intense advection of a methane-rich fluid into a near surface active sulfate reduction zone, tectonically active (faulted) margins with organic-rich sediments and moderate to high sedimentation rates are the most likely regions of occurrence. The extension of such a mixed hydrate below the sulfate reduction zone should reflect the time-span of methane advection into the sulfate reduction zone.

Characterization of the defined MDC types and compilation of MDC initiation times (excel-file 19 kB)

Mud accumulates on continental shelves under a variety of environmental conditions and results in a diverse formation of mud depocenters (MDCs). Their three-dimensional architectures have been in the focus of several recent studies. Due to some terminological confusion concerning MDCs, the present study sets out to define eight individual MDC types in terms of surface sediment distribution and internal geometry. Under conditions of substantial sediment supply, prodeltas (distal zones off river deltas; triangular sheets), subaqueous deltas (disconnected from deltas by strong normal-to-shore currents; wedge-like clinoforms), and mud patches (scattered distribution) and mud blankets (widespread covers) are formed. Forced by hydrodynamic conditions, mud belts in the strict sense (detached from source; elongated bodies), and shallow-water contourite drifts (detached from source; growing normal to prevailing current direction; triangular clinoforms) develop. Controlled by local morphology, mud entrapments (in depressions, behind morphological steps) and mud wedges (triangular clinoforms growing in flow direction) are deposited. Shelf mud deposition took place (1) during early outer-shelf drowning (~14 ka), (2) after inner-shelf inundation to maximum flooding (9.5-6.5 ka), and (3) in sub-recent times (<2 ka). Subsequent expansion may be (1) concentric, in cases where the depocenter formed near the fluvial source, (2) uni-directional, extending along advective current transport paths, and (3) progradational, forming clinoforms that grow either parallel or normal to the bottom current direction. Classical mud belts may be initiated around defined nuclei, the remote sites of which are determined by seafloor morphology rather than the location of the source. From a stratigraphic perspective, mud depocenters coincide with sea-level highstand-related, shelf-wide condensed sections. They often show a conformable succession from transgressive to highstand systems tract stages.