Palaeolake Rehwiese, NE-Germany, Younger Dryas varved data set RW09

The first 1400-year floating varve chronology for north-eastern Germany covering the late Allerød to the early Holocene has been established by microscopic varve counts from the Rehwiese palaeolake sediment record. The Laacher See Tephra (LST), at the base of the studied interval, forms the tephrochronological anchor point. The fine laminations were examined using a combination of micro-facies and ?-XRF analyses and are typical of calcite varves, which in this case provide mainly a warm season signal. Two varve types with different sub-layer structures have been distinguished: (I) complex varves consisting of up to four seasonal sub-layers formed during the Allerød and early Holocene periods, and, (II) simple two sub-layer type varves only occurring during the Younger Dryas. The precision of the chronology has been improved by varve-to-varve comparison of two independently analyzed sediment profiles based on well-defined micro-marker layers. This has enabled both (1) the precise location of single missing varves in one of the sediment profiles, and, (2) the verification of varve interpolation in disturbed varve intervals in the parallel core. Inter-annual and decadal-scale variability in sediment deposition processes were traced by multi-proxy data series including seasonal layer thickness, high-resolution element scans and total organic and inorganic carbon data at a five-varve resolution. These data support the idea of a two-phase Younger Dryas, with the first interval (12,675 - 12,275 varve years BP) characterised by a still significant but gradually decreasing warm-season calcite precipitation and a second phase (12,275 - 11,640 varve years BP) with only weak calcite precipitation. Detailed correlation of these two phases with the Meerfelder Maar record based on the LST isochrone and independent varve counts provides clues about regional differences and seasonal aspects of YD climate change along a transect from a location proximal to the North Atlantic in the west to a more continental site in the east.

Heat flow ratios of stations from the Iberian abyssal plain (Table 1)

New heat flow observations have been made in the Iberia abyssal plain off the Galicia margin along the transeat of Ocean Drilling Program Leg 149 drill sites. in order to investigate the nature of this unusually wide and deep continet-ocean transition region. Our results indicate the presence of three separate zones. Average values of 47.5 +/- 3 mW/m in the westernmost zone III agree with predictions of standard oceanic lithospheric models for its estimated age of 126 Ma. In contrast, the heat flow within zone II is 5-15 mW/m higher than predicted. assuming that the mantle heat flow remains constant across the basin. This region of high values is coincident with the location of a major intra-crustal "S"-type reflector east of ODP Site 900. and the anomaly is consistent with the presence of 2-3 km of primarily upper continental crust above the reflector, with concentrations of radiogenic components similar to those from granodiorite samplles dredged off Galicia Bank. It is not, however, consistent with the low values of heat production measured on gabbroic sanhples from its western end at ODP Site 900. In zone I, detailed measurements across the tilted fault block south of ODP Site 901 show consistent variations which closely match predictions due to the effects of basement structure and sediment deposition. There is no evidence for variations due to vertical convective transport along the dipping basement fault block. Once corrected for these variations. measurements in zone I yield average values that agree quite well with previous measurements across Calicia Bank. indicating no systematic landward increase in heat flow with decreasing amounts of continental, extension.

Os isotope record of ODP Site 159-959

The known temporal relationship between the benthic foraminiferal d18O record and the marine Os isotope record is used to reinterpret the absolute chronology and paleoceanographic context of an episode of organic carbon burial on the West African margin Ocean Drilling Program (ODP) Site 959. Although organic-rich sediments require significant corrections for in situ decay of 187Re to 187Os, these results demonstrate the utility of the marine Os isotope record for chemostratigraphic correlation of organic-rich sediments that are devoid of age diagnostic microfossils with pelagic carbonate sequences. Revision of the ODP Site 959 chronology shifts the age assignment of an interval of biosiliceous, organic-rich sediment deposition from the Oligocene to the late Eocene and earliest Oligocene, likely culminating with the first major glaciation of the Oligocene (Oi1). We speculate that enhanced organic carbon burial over much of the West African margin may have contributed to drawdown of atmospheric carbon dioxide before and during the Oi1 event and suggest that Os isotope chemostratigraphy provides a valuable tool for further exploring this possibility.

Biogenic opal and carbonate concentration in late Neogene sediments of ODP Site 114-704

A preliminary composite depth section was generated for Site 704 by splicing Holes 704A and 704B together over the interval 0-350 mbsf (0-9 m.y.). High-resolution carbonate and opal data from the cores were correlated with the calcium and silicon signals from the GST logging run in Hole 704B to identify missing and disturbed intervals in the cores. Paleomagnetic and biostratigraphic age boundaries were then transferred to the composite depth records to obtain an age model, and sedimentation rates were calculated by linear interpolation between datums. Algorithms relating measured dry-bulk density to carbonate content and depth were generated to produce predicted values of density for every sample. Accumulation rates of bulk, carbonate, opal, and terrigenous sediment components were then computed to generate a record of sediment deposition on the Meteor Rise that has a resolution of better than 200,000 yr for the period from 8.6 to 1.0 m.y. From 8.6 to 2.5 m.y., bulk-accumulation rates on the Meteor Rise averaged less than 2 g/cm**2/1000 yr and were dominated by carbonate deposition. The first significant opal deposition (6.0 m.y.) punctuated a brief (less than 0.6 Ma) approach of the Polar Front Zone (PFZ) northward that heralded a period of increasing severity of periodic carbonate dissolution events (terrigenous maxima) that abruptly terminated at 4.8 m.y. (base of the Thvera Subchron), synchronous with the reflooding of the Mediterranean after the Messinian salinity crisis. From 4.8 to 2.5 m.y., carbonate again dominated deposition, and the PFZ was far south except during brief northward excursions bracketing 4.2-3.9, 3.3-2.9, and 2.8-2.7 m.y. At 2.5 m.y., all components of bulk-accumulation rates increased dramatically (up to 15 g/cm2/1000 yr), and by 2.4 m.y., a pattern of alternating, high-amplitude carbonate and opal cyclicity marked the initiation of rapid glacial to interglaci·l swings in the position of the PFZ, synchronous with the "onset" of major Northern Hemisphere glaciation. Both mass-accumulation rates and the amplitude of the cycles decreased by about 2 m.y., but opal accumulation rates remained high up through the base of the Jaramillo (0.98 m.y.). From 1.9 to 1 m.y., the record is characterized by moderate amplitude fluctuations in carbonate and opal. This record of opal accumulation rates is interpreted as a long-term "Polar Front Indicator" that monitors the advance and retreat of the opal-rich PFZ northward (southward) toward (away from) the Meteor Rise in the subantarctic sector of the South Atlantic Ocean. The timing of PFZ migrations in the subantarctic South Atlantic Ocean is remarkably similar to Pliocene-Pleistocene climate records deduced from benthic oxygen isotope records in the North Atlantic Ocean (Raymo et al., 1989, doi:10.1029/PA004i004p00413; Ruddiman et al., 1989, doi:10.1029/PA004i004p00353). These include northward migrations during "cold" intervals containing strong glacial isotope stages (2.4-2.3, 2.1-2.0, 1.95-1.55, 1.45-1.30 m.y. and at about 1.13 and 1.09 m.y.) and southward migrations during "warm" intervals containing weak glacial and/or strong interglacial stages (2.45-2.40, 2.30-2.10, 2.00-1.95, 1.52-1.45, 1.30-1.18, 1.11, and 1.06-0.93 m.y.). Although our preliminary composite record is not continuous (some stages are obviously missing), there is hope that future work will identify these missing intervals in the as yet incomplete Hole 704B and will extend this high-resolution Southern Hemisphere climate record back to 8.6 m.y.

Geochemistry of neritic carbonates of ODP Hole 134-831B

Drilling at Bougainville Guyot (Ocean Drilling Program Site 831), New Hebrides Island Arc during Leg 134 revealed that 727.5 m of carbonate overlies an andesite basement. The carbonate cap at Site 831 consists of 20 m of pelagic carbonate overlying 707.5 m of neritic carbonates. The neritic section consists of ~230 m of largely unaltered aragonite sediment that overlies ~497 m of totally calcitized limestone. The deeper portion of the calcitized interval has been pervasively altered by diagenesis. Prior to this study the age distribution of sediments at Bougainville Guyot was poorly known because age diagnostic fossils are sparsely and discontinuously distributed in the sequence. We have used Sr isotopes to provide temporal constraints on the deposition of carbonates at Site 831; these constraints are critical in reconstructing the vertical movement of Bougainville Guyot before its collision with the New Hebrides Island Arc. Overall, the chronostratigraphy of Bougainville Guyot can be subdivided into three intervals: (1) a Pleistocene interval (102.4 to 391.11 meters below sea floor [mbsf]); (2) a Miocene interval (410.31 to 669.53 mbsf); and (3) an Oligocene interval (678.83 to 727.50 mbsf). Strontium isotopic ages of samples increase with increasing depth in the carbonate sequence, except near the bottom of the sequence, where several samples exhibit a consistent reversed age vs. depth trend. Such age reversals are most likely the product of post-depositional rock-water interaction. Preliminary stable isotope data are consistent with diagenetic alteration in the marine and meteoric environments. Several abrupt decreases in d87Sr, and hence age, of sediments are recognized in the carbonate cap at Bougainville Guyot. These disconformities are most likely the product of subaerial exposure in response to relative sea-level fall. Indeed, Sr-isotope ages indicate that 2 to 9 m.y. of sediment deposition is missing across these d87Sr disconformities.

Concentrations and accumulation rates of platinum-group elements and rhenium in Pacific and Atlantic sediments, DSDP and ODP data

The nature of Re-platinum-group element (PGE; Pt, Pd, Ir, Os, Ru) transport in the marine environment was investigated by means of marine sediments at and across the Cretaceous-Tertiary boundary (KTB) at two hemipelagic sites in Europe and two pelagic sites in the North and South Pacific. A traverse across the KTB in the South Pacific pelagic clay core found elevated levels of Re, Pt, Ir, Os, and Ru, each of which is approximately symmetrically distributed over a distance of ~1.8 m across the KTB. The Re-PGE abundance patterns are fractionated from chondritic relative abundances: Ru, Pt, Pd, and Re contents are slightly subchondritic relative to Ir, and Os is depleted by ~95% relative to chondritic Ir proportions. A similar depletion in Os (~90%) was found in a sample of the pelagic KTB in the North Pacific, but it is enriched in Ru, Pt, Pd, and Re relative to Ir. The two hemipelagic KTB clays have near-chondritic abundance patterns. The ~1.8-m-wide Re-PGE peak in the pelagic South Pacific section cannot be reconciled with the fallout of a single impactor, indicating that postdepositional redistribution has occurred. The elemental profiles appear to fit diffusion profiles, although bioturbation could have also played a role. If diffusion had occurred over ~65 Ma, the effective diffusivities are ~10**?13 cm**2/s, much smaller than that of soluble cations in pore waters (~10**?6 cm**2/s). The coupling of Re and the PGEs during redistribution indicates that postdepositional processes did not significantly fractionate their relative abundances. If redistribution was caused by diffusion, then the effective diffusivities are the same. Fractionation of Os from Ir during the KTB interval must therefore have occurred during aqueous transport in the marine environment. Distinctly subchondritic Os/Ir ratios throughout the Cenozoic in the South Pacific core further suggest that fractionation of Os from Ir in the marine environment is a general process throughout geologic time because most of the inputs of Os and Ir into the ocean have Os/Ir ratios >/=1. Mass balance calculations show that Os and Re burial fluxes in pelagic sediments account for only a small fraction of the riverine Os (<10%) and Re (<0.1%) inputs into the oceans. In contrast, burial of Ir in pelagic sediments is similar to the riverine Ir input, indicating that pelagic sediments are a much larger repository for Ir than for Os and Re. If all of the missing Os and Re is assumed to reside in anoxic sediments in oceanic margins, the calculated burial fluxes in anoxic sediments are similar to observed burial fluxes. However, putting all of the missing Os and Re into estuarine sediments would require high concentrations to balance the riverine input and would also fail to explain the depletion of Os at pelagic KTB sites, where at most ~25% of the K-T impactor's Os could have passed through estuaries. If Os is preferentially sequestered in anoxic marine environments, it follows that the Os/Ir ratio of pelagic sediments should be sensitive to changes in the rates of anoxic sediment deposition. There is thus a clear fractionation of Os and Re from Ir in precipitation out of sea water in pelagic sections. Accordingly, it is inferred here that Re and Os are removed from sea water in anoxic marine depositional regimes.

Chemical analyses and results of sediments from different DSDP Holes from the North Atlantic

Chemical analyses of North Atlantic D.S.D.P. (Deep Sea Drilling Project) sediments indicate that basal sediments generally contain higher concentrations of Fe, Mn, Mg, Pb, and Ni, and similar or lower concentrations of Ti, Al, Cr, Cu, Zn, and Li than the material overlying them. Partition studies on selected samples indicate that the enriched metals in the basal sediments are usually held in a fashion similar to that in basal sediments from the Pacific, other D.S.D.P. sediments, and modern North Atlantic ridge and non-ridge material. Although, on average, chemical differences between basal sediments of varying ages are apparent, normalization of the data indicates that the processes leading to metal enrichment on the crest of the Mid-Atlantic Ridge appear to have been approximately constant in intensity since Cretaceous times. In addition, the bulk composition of detrital sediments also appears to have been relatively constant over the same time period. Paleocene sediments from site 118 are, however, an exception to this rule, there apparently having been an increased detrital influx during this period. The bulk geochemistry, partitioning patterns, and mineralogy of sediments from D.S.D.P. 9A indicates that post-depositional migration of such elements as Mn, Ni, Cu, Zn, and Pb may have occurred. The basement encountered at the base of site 138 is thought to be a basaltic sill, but the overlying basal sediments are geochemically similar to other metalliferous basal sediments from the North Atlantic. These results, as well as those from site 114 where true oceanic basement was encountered, but where there was an estimated 7 m.y. hiatus between basaltic extrusion and basal sediment deposition, indicate that ridge-crest sediments are not necessarily deposited during active volcanism but can be formed after the volcanism has ceased. The predominant processes for metal enrichment in these deposits and those formed in association with other submarine volcanic features is a combination of shallow hydrothermal activity, submarine weathering of basalt, and the formation of ferromanganese oxides which can scavenge metals from seawater. In addition, it seems as though the formation of submarine metalliferous sediments is not restricted to active-ridge areas.

2012-2014 sedimentation data for the Congaree River floodplain, SC, USA

This dataset contains sedimentation data that was collected for the Congaree River floodplain, SC, USA. The study sites were located at floodplain positions with varying flood frequencies and geomorphic positions. Flood frequency was determined using hydrological statistics based on data acquired from USGS gage #02169500 for the Congaree River; sites are classified as having high, intermediate, or low flood frequency. The geomorphic position classification was determined using field observations; sites are classified as abandoned channel, ridge, river margin, and swale positions. Sediment deposition was measured in centimeters and reflects the amount of sediment that was deposited on a feldspar clay pad that was installed at each of the sampling sites. The feldspar pads were installed in the summer of 2012 and cored and measured for deposition amounts in the summer of 2014. In the summer of 2012, soil samples were collected at each of the sampling sites. Each soil sample was analyzed for soil texture (percent sand, silt, and clay), major and micro-nutrients (parts per million), percent organic matter, and pH.

Topological invariance and spatial scaling of surface roughness in two highly eroded zones of Mexico: a comparative study

The Fractal Image Informatics toolbox (Oleschko et al., 2008 a; Torres-Argüelles et al., 2010) was applied to extract, classify and model the topological structure and dynamics of surface roughness in two highly eroded catchments of Mexico. Both areas are affected by gully erosion (Sidorchuk, 2005) and characterized by avalanche-like matter transport. Five contrasting morphological patterns were distinguished across the slope of the bare eroded surface of Faeozem (Queretaro State) while only one (apparently independent on the slope) roughness pattern was documented for Andosol (Michoacan State). We called these patterns ?the roughness clusters? and compared them in terms of metrizability, continuity, compactness, topological connectedness (global and local) and invariance, separability, and degree of ramification (Weyl, 1937). All mentioned topological measurands were correlated with the variance, skewness and kurtosis of the gray-level distribution of digital images. The morphology0 spatial dynamics of roughness clusters was measured and mapped with high precision in terms of fractal descriptors. The Hurst exponent was especially suitable to distinguish between the structure of ?turtle shell? and ?ramification? patterns (sediment producing zone A of the slope); as well as ?honeycomb? (sediment transport zone B) and ?dinosaur steps? and ?corals? (sediment deposition zone C) roughness clusters. Some other structural attributes of studied patterns were also statistically different and correlated with the variance, skewness and kurtosis of gray distribution of multiscale digital images. The scale invariance of classified roughness patterns was documented inside the range of five image resolutions. We conjectured that the geometrization of erosion patterns in terms of roughness clustering might benefit the most semi-quantitative models developed for erosion and sediment yield assessments (de Vente and Poesen, 2005).

(Appendix) Grain-size distribution, calcium carbonate content and proportion of cemented aggregates in ODP Site 133-820

The textural and compositional characteristics of the 400 m sequence of Pleistocene wackestones and packstones intersected at Ocean Drilling Program (ODP) Site 820 reflect deposition controlled by fluctuations in sea-level, and by variations in the rate of sediment supply. The development of an effective reefal barrier adjacent to Site 820, between 760 k.y. and 1.01 Ma, resulted in a marked reduction in sediment accumulation rates on the central Great Barrier Reef outermost shelf and upper slope. This marked change corresponds with the transition from sigmoidal prograding seismic geometry in the lower 254 m of the sequence, to aggradational geometry in the top 146 m. The reduction in the rate of sediment accumulation that followed development of the reefal barrier also caused a fundamental change in the way in which fluctuations in sea-level controlled sediment deposition. In the lower, progradational portion of the sequence, sea-level cyclicity is represented by superimposed coarsening-upward cycles. Although moderately calcareous throughout (mostly 35%-75% CaCO3), the depositional system acted in a similar manner to siliciclastic shelf depositional systems. Relative sea-level rises resulted in deposition of more condensed, less calcareous, fine, muddy wackestones at the base of each cycle. Sea-level highstands resulted in increased sedimentation rates and greater influx of coarse bioclastic material. Continued high rates of sedimentation of both coarse bioclastic material and mixed carbonate and terrigenous mud marked falling and low sea-levels. This lower part of the sequence therefore is dominated by coarse packstones, with only thin wackestone intervals representing transgressions. In contrast, sea-level fluctuations following formation of an effective reefal barrier produced a markedly different sedimentary record. The more slowly deposited aggradational sequence is characterized by discrete thin interbeds of relatively coarse packstone within a predominantly fine wackestone sequence. These thin packstone beds resulted from relatively low sedimentation rates during falling and low sea-levels, with much higher rates of muddy sediment accumulation during rising and high sea-levels. The transition from progradational to aggradational sequence geometry therefore corresponds to a transition from a "siliciclastic-type" to a "carbonate-type" depositional system.

Herbicides implicated as the cause of severe mangrove dieback in the Mackay region, NE Australia: consequences for marine plant habitats of the GBR World Heritage Area

Herbicides, particularly diuron, were correlated with severe and widespread dieback of the dominant mangrove, Avicennia marina (Forsk.) Vieth. var. eucalyptifolia (Val.) N.C. Duke (Avicenniaceae), its reduced canopy condition, and declines in seedling health within three neighbouring estuaries in the Mackay region of NE Australia. This unusual species-specific dieback, first observed in the early 1990s, had gotten notably worse by 2002 to affect > 30km(2) of mangroves in at least five adjacent estuaries in the region. Over the past century, agricultural production has responded well to the demands of increasing population with improvements in farm efficiency assisted by significant increases in the use of agricultural chemicals. However, with regular and episodic river flow events, these chemicals have sometimes found their way into estuarine and nearshore water and sediments where their effects on marine habitats have been largely unquantified. Investigations over the last three years in the Mackay region provide compelling evidence of diuron, and possibly other agricultural herbicides, as the most likely cause of the severe and widespread mangrove dieback. The likely consequences of such dieback included declines in coastal water quality with increased turbidity, nutrients and sediment deposition, as well as further dispersal of the toxic chemicals. The implications of such findings are immense since they describe not only the serious deterioration of protected and beneficial mangrove habitat but also the potential for significant direct and indirect effects on other highly-valued estuarine and marine habitats in the region, including seagrass beds and coral reefs of the Great Barrier Reef lagoon. This article reviews all key findings and observations to date and describes the essential correlative and causative evidence. (c) 2004 Elsevier Ltd. All rights reserved.