Short-term spectral analysis of ODP Hole 114-704B

Short-term spectral analysis was carried out on geochemical logging data from ODP Site 704. The FFT was used to compute the amplitude spectra of short-term overlapping segments to produce depth-period-amplitude spectrograms of the logging data. The spectrograms provided a means of evaluating the significance of the observed periodic components. The periodic components that were consistently present and prominent across a given record interval were considered to be significant. Changes in the spectrogram characteristics seem to reflect changes in either lithology, sedimentation rates, or hiatuses and may therefore provide useful information to aid in stratigraphic and paleoenvironmental studies. The dominant periodicity during the late Pleistocene and Brunhes Chron (0.97 to 0.47 Ma) was determined to be > 100,000 yr whereas the upper Matuyama Chron was dominated by the 41,000-yr periodicity. These periodicities suggest that the sedimentation patterns within the upper Matuyama Chron (0.98-1.78 Ma) were influenced by the Milankovitch obliquity cycle and those within the latest Matuyama-Brunhes Chron (<0.98 Ma) by the eccentricity cycle. The Brunhes/Matuyama boundary therefore represents a major discontinuity. Periodicities observed within the lower Matuyama and the upper Gauss Chron did not correlate with any of the periodicities within the Milankovitch frequency bands.

Location, intervals and thickness of Cretaceous sections in Indian Ocean DSDP and ODP sites (Table 2)

The Indian Ocean covers approximately 73.5 * 10**6 km**3 from 25°N to 67°S and from 20° to 120°E. Several legs of the Deep Sea Drilling Project (DSDP) and the Ocean Drilling Program (ODP) have operated in its waters, many penetrating the Cretaceous. Most of the scientific drill sites are DSDP related and thus pre-dated modern biostratigraphic conventions. Foraminifers and calcareous nannoplankton were by far the dominant fossil groups studied in the earlier work, supplemented occasionally by studies of other fossil groups, The results of the Ocean Drilling Project phase are yet too young to be fully integrated but have been based on a broader range of techniques and fossil groups. During most of the Cretaceous, the proto-Indian Ocean basin lay in middle to high latitudes. Thus, it is unrealistic to expect successful routine application of low-latitude zonations. No planktonic foraminifer zonal scheme has been developed for the Indian Ocean basin for several reasons. There are no sections with complete or even significant partial sections to allow development of such a zonation. Carbonate compensation depth (CCD) effects have been marked in most sections, and significant intervals are devoid of planktonic foraminifers. The Indian Ocean now covers a great latitudinal range from tropics to polar regions and, at first glance, no scheme can be expected to be applicable over that entire range. In the Cretaceous the area was much smaller, though expanding progressively, and the paleolatitude range was quite small. Calcareous nannoplankton have proved valuable in dating Indian Ocean Cretaceous sediments and have, perhaps in contrast with the foraminifers, been consistently a more reliable means of applying zonal schemes developed elsewhere. For the Albian-Aptian, zonations based on well-known benthic foraminifer lineages (Scheibnerova, 1974) have been useful when nothing else was available or effective. Palynology has been used little, but where used, has proved excellent. It has the added value of providing valuable information on nearby terrestrial vegetation as the fossils were resistant to dissolution. Normally, when different fossil groups have been applied to a section, the results have been compatible or compatible to an acceptable degree. There are a few instances where incompatibility is noteworthy, and Site 263 is a classic example, as even two calcareous nannoplankton studies show irreconcilable differences here. All groups gave different results, but one benthic foraminifer analysis agreed with one calcareous nannoplankton study.

(Table 1) Results from XRD analysis as well as sediment type and selected results from ring shear experiments

The location of the seaward tip of a subduction thrust controls material transfer at convergent plate margins, and hence global mass balances. At approximately half of those margins, the material of the subducting plate is completely underthrust so that no accretion or even subduction erosion takes place. Along the remaining margins, material is scraped off the subducting plate and added to the upper plate by frontal accretion. We here examine the physical properties of subducting sediments off Costa Rica and Nankai, type examples for an erosional and an accretionary margin, to investigate which parameters control the level where the frontal thrust cuts into the incoming sediment pile. A series of rotary-shear experiments to measure the frictional strength of the various lithologies entering the two subduction zones were carried out. Results include the following findings: (1) At Costa Rica, clay-rich strata at the top of the incoming succession have the lowest strength (µres = 0.19) while underlying calcareous ooze, chalk and diatomite are strong (up to µres = 0.43; µpeak = 0.56). Hence the entire sediment package is underthrust. (2) Off Japan, clay-rich deposits within the lower Shikoku Basin inventory are weakest (µres = 0.13-0.19) and favour the frontal proto-thrust to migrate into one particular horizon between sandy, competent turbidites below and ash-bearing mud above. (3) Taking in situ data and earlier geotechnical testing into account, it is suggested that mineralogical composition rather than pore-pressure defines the position of the frontal thrust, which locates in the weakest, clay mineral-rich (up to 85 wt.%) materials. (4) Smectite, the dominant clay mineral phase at either margin, shows rate strengthening and stable sliding in the frontal 50 km of the subduction thrust (0.0001-0.1 mm/s, 0.5-25 MPa effective normal stress). (5) Progressive illitization of smectite cannot explain seismogenesis, because illite-rich samples also show velocity strengthening at the conditions tested.

Coral reef habitat maps derived from a high-spatial-resolution multi-spectral satellite image using object based image analysis

Coral reef maps at various spatial scales and extents are needed for mapping, monitoring, modelling, and management of these environments. High spatial resolution satellite imagery, pixel <10 m, integrated with field survey data and processed with various mapping approaches, can provide these maps. These approaches have been accurately applied to single reefs (10-100 km**2), covering one high spatial resolution scene from which a single thematic layer (e.g. benthic community) is mapped. This article demonstrates how a hierarchical mapping approach can be applied to coral reefs from individual reef to reef-system scales (10-1000 km**2) using object-based image classification of high spatial resolution images guided by ecological and geomorphological principles. The approach is demonstrated for three individual reefs (10-35 km**2) in Australia, Fiji, and Palau; and for three complex reef systems (300-600 km**2) one in the Solomon Islands and two in Fiji. Archived high spatial resolution images were pre-processed and mosaics were created for the reef systems. Georeferenced benthic photo transect surveys were used to acquire cover information. Field and image data were integrated using an object-based image analysis approach that resulted in a hierarchically structured classification. Objects were assigned class labels based on the dominant benthic cover type, or location-relevant ecological and geomorphological principles, or a combination thereof. This generated a hierarchical sequence of reef maps with an increasing complexity in benthic thematic information that included: 'reef', 'reef type', 'geomorphic zone', and 'benthic community'. The overall accuracy of the 'geomorphic zone' classification for each of the six study sites was 76-82% using 6-10 mapping categories. For 'benthic community' classification, the overall accuracy was 52-75% with individual reefs having 14-17 categories and reef systems 20-30 categories. We show that an object-based classification of high spatial resolution imagery, guided by field data and ecological and geomorphological principles, can produce consistent, accurate benthic maps at four hierarchical spatial scales for coral reefs of various sizes and complexities.

Location and ages of terrestrial peatlands located on continental shelves and in coastal sediments

This synthesis dataset contains records of freshwater peat and lake sediments from continental shelves and coastal areas. Information included is site location (when available), thickness and description of terrestrial sediments as well as underlying and overlying sediments, dates (when available), and references.

Isotope analysis and heat flow measurements of Maria S. Merian cruise MSM21/4 on the western Svalbard margin

Methane hydrate is an ice-like substance that is stable at high-pressure and low temperature in continental margin sediments. Since the discovery of a large number of gas flares at the landward termination of the gas hydrate stability zone off Svalbard, there has been concern that warming bottom waters have started to dissociate large amounts of gas hydrate and that the resulting methane release may possibly accelerate global warming. Here, we can corroborate that hydrates play a role in the observed seepage of gas, but we present evidence that seepage off Svalbard has been ongoing for at least three thousand years and that seasonal fluctuations of 1-2°C in the bottom-water temperature cause periodic gas hydrate formation and dissociation, which focus seepage at the observed sites.

Sedimentological analysis of eight cores from the Amundsen Sea

Recent palaeoglaciological studies on the West Antarctic shelf have mainly focused on the wide embayments of the Ross and Amundsen seas in order to reconstruct the extent and subsequent retreat of the West Antarctic Ice Sheet (WAIS) since the Last Glacial Maximum (LGM). However, the narrower shelf sectors between these two major embayments have remained largely unstudied in previous geological investigations despite them covering extensive areas of the West Antarctic shelf. Here, we present the first systematic marine geological and geophysical survey of a shelf sector offshore from the Hobbs Coast. It is dominated by a large grounding zone wedge (GZW), which fills the base of a palaeo-ice stream trough on the inner shelf and marks a phase of stabilization of the grounding line during general WAIS retreat following the last maximum ice-sheet extent in this particular area (referred to as the Local Last Glacial Maximum, 'LLGM'). Reliable age determination on calcareous microfossils from the infill of a subglacial meltwater channel eroded into the GZW reveals that grounded ice had retreated landward of the GZW before ~20.88 cal. ka BP, with deglaciation of the innermost shelf occurring prior to ~12.97 cal. ka BP. Geophysical sub-bottom information from the inner-, mid- and outer shelf indicates grounded ice extended to the shelf edge prior to the formation of the GZW. Assuming the wedge was deposited during deglaciation, we infer the timing of maximum grounded ice extent occurred before ~20.88 cal. ka BP. This could suggest that the WAIS retreat from the outer shelf was already underway during or even prior to the global LGM (~23-19 cal. ka BP). Our new findings give insights into the regional deglacial behaviour of this understudied part of the West Antarctic shelf and at the same time support early deglaciation ages recently presented for adjacent drainage sectors of the WAIS. If correct, these findings contrast with the hypothesis that initial deglaciation of Antarctic Ice Sheets occurred synchronously at ~19 cal. ka BP.

Geochemical analysis at ODP Site 207-1259 from the Demerara Rise in the western equatorial Atlantic

Organic carbon-rich shales deposited during the Coniacian-Santonian Oceanic Anoxic Event 3 were drilled during ODP Leg 207 at Demerara Rise. We present integrated high-resolution geochemical records of core intervals from ODP Sites 1259 and 1261 both from nannofossil biozone CC14. Our results reveal systematic variations in marine and detrital sediment contribution, depositional processes, and bottom water redox conditions during black shale formation at two locations on Demerara Rise in different paleo-water depths. A combination of redox proxies (Fe/S, P/Al, C/P, redox-sensitive/sulfide-forming trace metals Mn, Cd, Mo, Ni, V, Zn) and other analytical approaches (bulk sediment composition, P speciation, electron microscopy, X-ray diffraction) evidence anoxic to sulfidic bottom water and sediment conditions throughout the deposition of black shale. These extreme redox conditions persisted and were periodically punctuated by short-termed periods with less reducing bottom waters irrespective of paleo-water depth. Sediment supply at both sites was generally dominated by marine material (carbonate, organic matter, opal) although relationships of detrital proxies as well as glauconitic horizons support some influence of turbidites, winnowing bottom currents and/or variable detritus sources, along with less reducing bottom water at the proposed shallower location (ODP Site 1259). At Site 1261, located at greater paleo-depth, redox fluctuations were more regular, and steady hemipelagic sedimentation sustained the development of mostly undisturbed lamination in the sedimentary record. Strong similarities of the studied deposits exist with the stratigraphic older Cenomanian-Turonian OAE2 black shale sections at Demerara Rise, suggesting that the primary mechanisms controlling continental supply and ocean redox state were time-invariant and kept the western equatorial Atlantic margin widely anoxic over millions of years.