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The Hare Indian Formation (HIF) is a late Eifelian to Givetian organic-rich mudstone constituting the lower portion of the Horn River Group (HRG), which has been minimally scrutinized in the literature. This paper proposes depositional environments and a sequence stratigraphic framework for the HIF. Using composition data collected via energy-dispersive X-ray fluorescence, geochemical proxies inform detrital input, silica source, and paleoredox conditions. Cross-plots and chemostratigraphic profiles of detritally sourced Al, Ti, and K and redox-sensitive Mo and V inform depositional and stratigraphic constraints. Silica proportions vary, indicating that sediment was derived from detrital and biogenic sources. Al, Ti, and K distributions increase upwards, showing increased continentally sourced minerals. Redox-sensitive metals are highest in the Bluefish Member (BM), suggesting intermittent euxinia. Based on the presence of continental and pelagic sediments, the sedimentary environment is interpreted as proximal- to mid-shelf. These proxies guide systems tract interpretations. Si and redox-sensitive metal concentrations peak higher in the BM, accompanied by lowered concentrations of Al, Ti, and K, suggesting a maximum flooding surface. At the top of the Prohibition and Bell Creek members, redox-sensitive enrichments are lower with higher concentrations of Al, Ti, and K, suggesting a maximum regressive surface. Transgression occurred during the initial deposition of the BM, followed by regression for the remainder of the HIF. The sedimentology of the HIF can be difficult to decipher; the use of chemostratigraphy supports its geological history (including sedimentation trends and a local record of relative sea level) using methods that may be applied to other finegrained successions. Key words: chemostratigraphy, Hare Indian Formation, Horn River Group, Devonian, Givetian, mudstone, fine-grained, sequence stratigraphy, geochemistry, Northwest Territories, Central Mackenzie Valley, Mackenzie Mountains, XRF, X-ray fluorescence. La Formation de Hare Indian (FHI) est un mudstone tardi-eifelien a givetien riche en matiere organique constituant la partie inferieure du Groupe de Horn River (GHR), qui a fait l'objet de peu d' etudes publiees. Le present article propose des milieux de depot et un cadre de stratigraphie sequentielle pour la FHI. A la lumiere de donnees de composition obtenues par fluorescence X a dispersion d' energie, des variables substitutives geochimiques apportent des precisions sur les apports detritiques, les sources de silice et les conditions d'oxydoreduction passees. Des graphiques de correlation et des profils chimiostratigraphiques de l'Al, du Ti et du K de source detritique et du Mo et du V, qui sont sensibles aux conditions d'oxydoreduction, mettent en lumiere des contraintes stratigraphiques et de sedimentation. Les proportions de silice varient, indiquant que les sediments proviennent de sources detritiques et biogenes. Les concentrations d'Al, de Ti et de K augmentent vers le haut, indiquant une augmentation de mineraux de source continentale. Les proportions des metaux sensibles a l'oxydoreduction sont les plus grandes dans le membre de Bluefish (MB), laissant croire a un euxinisme intermittent. Etant donne la presence de sediments continentaux et pelagiques, un milieu sedimentaire de plateforme proximale a mediale est interprete. Ces variables substitutives guident l'interpretation des corteges de depot. Les concentrations de Si et de metaux sensibles a l'oxydoreduction atteignent un maximum plus haut dans le MB, accompagne de concentrations moindres d'Al, de Ti et de K, ce qui indiquerait une surface d'inondation maximum. Au sommet des membres de Prohibition et de Bell Creek, les enrichissements de metaux sensibles a l'oxydoreduction sont plus faibles et les concentrations d'Al, de Ti et de K, plus grandes, ce qui indiquerait une surface de regression maximum. Une transgression s'est produite durant le depot initial du MB, suivie d'une regression pour le reste de la FHI. La sedimentologie de la FHI peut etre difficile a etablir; l'utilisation de la chimiostratigraphie appuie son histoire geologique (y compris les tendances de sedimentation et un registre local du niveau relatif de la mer) en faisant appel a des methodes qui pourraient etre appliquees a d'autres successions a grains fins. [Traduit par la Redaction] Mots-cles : chimiostratigraphie, Formation de Hare Indian, Groupe de Horn River, Devonien, Givetien, mudstone, a grains fins, stratigraphie sequentielle, geochimie, Territoires du Nord-Ouest, vallee centrale du fleuve Mackenzie, monts Mackenzie, fluorescence X., Introduction Unconventional reservoirs have become increasingly prevalent in the energy industry and, as such, organic-rich mudstones have become common targets of exploration and production in basins across North America. This [...]

Ninety per cent of marine organic matter burial occurs in continental margin sediments, where a substantial fraction of organic carbon escapes oxidation and enters long-term geologic storage within sedimentary rocks. In such environments, microbial metabolism is limited by the diffusive supply of electron acceptors. One strategy to optimize energy yields in a resource-limited habitat is symbiotic metabolite exchange among microbial associations (1,2).Thermodynamic and geochemical considerations indicate that microbial cometabolisms are likely to play a critical part in sedimentary organic carbon cycling (3-5). Yet only one association, between methanotrophic archaea and sulphate-reducing bacteria, has been demonstrated in marine sediments in situ (6,7), and little is known of the role of microbial symbiotic interactions in other sedimentary biogeochemical cycles (8). Here we report in situ molecular and incubation-based evidence for a novel symbiotic consortium between two chemolithotrophic bacteria--anaerobic ammonium-oxidizing (anammox) bacteria and the nitrate-sequestering sulphur-oxidizing Thioploca species--in anoxic sediments of the Soledad basin at the Mexican Pacific margin. A mass balance of benthic solute fluxes and the corresponding nitrogen isotope composition of nitrate and ammonium fluxes indicate that anammox bacteria rely on Thioploca species for the supply of metabolic substrates and account for about 57 ± 21 per cent of the total benthic [N.sub.2] production. We show that Thioploca-anammox symbiosis intensifies benthic fixed nitrogen losses in anoxic sediments, bypassing diffusion-imposed limitations by efficiently coupling the carbon, nitrogen and sulphur cycles., Interspecies metabolite exchange is an effective strategy for harvesting potential energy in resource-limited environments. In organic-rich marine sediments, which are characterized by a strong deficit of electron acceptors, symbiotic microbial [...]

Larval settlement of the infaunal spionid polychaetes Polydora cornuta and Streblospio benedicti is mediated by sediment-associated microorganisms. To investigate if larval preference for certain sediment is guide by individual sediment-associated bacteria, 13 bacterial isolates (5 phyla) obtained from the natural habitat of adult polychaetes (Wadden Sea, Germany) in 2008 were screened in still-water, no-choice settlement assays. Two isolates (α-Proteobacterium-Strain DF11 and Flavobacterium-Strain 54) significantly triggered larval settlement in comparison with sterile sediment. In still-water, multiple-choice settlement assays comprising natural and sterile sediment and sediment re-inoculated with isolates DF11 and 54, significant preferences for natural sediment and sediment containing bacterial isolates at [10..sup.8] cells [g.sup.-1] were observed. Larval settlement was influenced by bacterial abundance in sediment but the correlation was not strictly positive; thus, maximum larval settlement in response to single bacterial species may occur at certain optimum densities. Non-viable or suspended bacteria and water-soluble bacterial products did not induce larval settlement, suggesting that sediment-associated bacterial settlement cues for P. cornuta and S. benedicti were either produced in situ and/or consisted of heat-labile bacterial products., Introduction Marine biofilms, agglomerates of attached bacteria, benthic diatoms, fungi, and protozoa stimulate or inhibit settlement of benthic invertebrate larvae on hard substratum (Qian et al. 2007). It is well [...]

It all started when Dan Lizarralde went to the gulf of California in 2002 to explore a spreading center at the bottom of the Guaymas basin where two of Earth's [...]

Recent studies suggest that as much as half of the organic carbon (OC) undergoing burial in the sediments of tectonically active continental margins may be the product of fossil shale weathering. These estimates rely on the assumption that vascular plant detritus spends little time sequestered in intermediate reservoirs such as soils, freshwater sediments, and river deltas, and thus only minimally contributes to the extraneously old [sup.14]C ages of total organic matter often observed on adjacent shelves. Here we test this paradigm by measuring the [DELTA][sup.14]C and [delta][sup.13]C values of individual higher plant wax fatty acids as well as the [delta][sup.13]C values of extractable alkanes isolated from the Eel River margin (California). The isotopic signatures of the long chain fatty acids indicate that vascular plant material has been sequestered for several thousand years before deposition. A coupled molecular isotope mass balance used to reassess the sedimentary carbon budget indicates that the fossil component is less abundant than previously estimated, with pre-aged terrestrial material instead composing a considerable proportion of all organic matter. If these findings are characteristic of other continental margins proximal to small mountainous rivers, then the importance of petrogenic OC burial in marine sediments may need to be reevaluated.

This manuscript describes a new protocol for determination of Pa/Th/U in marine sediments. It is based on microwave-assisted digestion and represents an important reduction of working time over conventional hot-plate digestion methods, and the use of HCl[O.sub.4] is avoided. Although Th and U are completely dissolved with a first microwave step, around 40% of [sup.231]Pa remains undissolved, and a short hot-plate step with reverse aqua regia is required to achieve total digestion and spike equilibration. Next, the method involves a separation of these elements and a further purification of the Pa fraction using Dowex AG1-X8 resin. Separation with Bio-Rad and Sigma-Aldrich resins was compared; although both perform similarly for Th and U, Pa yields are higher with Bio-Rad. Finally, samples are measured using a Nu instruments multiple collector inductively coupled plasma mass spectrometer (MC-ICPMS). Overall chemical yields range around 50% for Pa, 60% for Th, and 70% for U.

Bottom trawling not only erodes the sea bed, but also reduces its carbon-storage capacity. Bottom trawling not only erodes the sea bed, but also reduces its carbon-storage capacity., Author Affiliations: Dragging nets and other fishing gear across the sea floor can cut the amount of carbon stored in sediments. Credit: Alamy Fishing boat / Trawler on the North [...]

We compared near-bottom seston and surface sediment composition in Cape Cod estuaries receiving different N loads to determine whether eutrophic-driven changes in seston and sediment composition occur in tandem and what implications such coupling has for the quantity and quality of particles available as food for benthic consumers. [[delta].sup.15]N signatures in seston and sediment increased with increasing N loads to estuaries and linked particles in nearshore seston and sediment to land-derived wastewater sources. [[delta].sup.13]C signatures in seston and sediment reflected C inputs primarily from microalgae. Sediments, however, were consistently lighter in [[delta].sup.15]N and heavier in [[delta].sup.13]C compared with seston among our estuaries and in other estuaries worldwide, which suggests a seston-sediment biogeochemical coupling that may be independent of estuary-specific differences. In Cape Cod estuaries, N enrichment increased microalgal production in seston and sediment in nearshore areas, and higher N loads decreased C : N in sediments, but not in seston. The biogeochemical coupling reflected in isotopic signatures in seston and sediment persisted despite these changes associated with N enrichment and differences in grazer abundance, salinity, and flushing times across estuaries. Differences in isotopic signatures in benthic algae compared with phytoplankton were consistent with isotopic differences in sediment compared with seston, and microalgal production was the only aspect of composition that responded similarly to N loading in both seston and sediment across estuaries. The consistent coupling between seston and sediment composition, therefore, was likely related to differences in microalgal composition and, in turn, the type and quantity of particles available as food to consumers at the sediment-water interlace.

Diatomaceous deposits in the Miocene--Pliocene Pisco Formation contain abundant whales preserved in pristine condition (bones articulated or at least closely associated), in some cases including preserved baleen. The well-preserved whales indicate rapid burial. The 346 whales within ~1.5 [km.sup.2] of surveyed surface were not buried as an event, but were distributed uninterrupted through an 80-m-thick sedimentary section. The diatomaceous sediment lacks repeating primary laminations, but instead is mostly massive, with irregular laminations and speckles. There is no evidence for bioturbation by invertebrates in the whale-bearing sediment. Current depositional models do not account for the volume of diatomaceous sediments or the taphonomic features of the whales. These taphonomic and sedimentary features suggest that rapid burial due to high diatom accumulation, in part by lateral advection into protected, shallow embayments, is responsible for the superb preservation of these whales, leading to a higher upper limit on phytoplankton accumulation rates than previously documented. Keywords: taphonomy, diatoms, Pisco Formation, Miocene, Pliocene, Cetacea, sedimentation rates.

Cool-water shelf carbonates differ from tropical carbonates in their sources, modes, and rates of deposition, geochemistry, and diagenesis. Inorganic precipitation, marine cementation, and sediment accumulation rates are absent or slow in cool waters, so that temperate carbonates remain longer at or near the sea bed. Early sea-floor processes, occurring between biogenic calcification and ultimate deposition, thus take on an important role, and there is the potential for considerable taphonomic loss of skeletal information into the fossilised record of cool-water carbonate deposits. The physical breakdown processes of dissociation, breakage, and abrasion are mediated mainly by hydraulic regime, and are always destructive. Impact damage reduces the size of grains, removes structure and therefore information, and ultimately may transform skeletal material into anonymous particles. Abrasion is highly selective amongst and within taxa, their skeletal form and structure strongly influencing resistance to mechanical breakdown. Dissolution and precipitation are the end-members of a two-way chemical equilibrium operating in sea water. In cool waters, inorganic precipitation is rare. There is conflicting opinion about the importance of diagenetic dissolution of carbonate skeletons on the temperate sea floor, but test maceration and early loss of aragonite in particular are reported. Dissolution may relate to undersaturated acidic pore waters generated locally by a combination of microbial metabolisation of organic matter, strong bioturbation, and oxidation of solid phase sulphides immediately beneath the sea floor in otherwise very slowly accumulating skeletal deposits. Laboratory experiments demonstrate that surface-to-volume ratio and skeletal mineralogy are both important in determining skeletal resistance to dissolution. Biological processes on the sea floor include encrustation and bioerosion. Encrustation, a constructive process, may be periodic or seasonal, and can be reversed. It produces both information and material. Bioerosion, in contrast, is destructive and permanent. In temperate areas bioerosion may destroy even very large shells during their long residence at the sea floor, on the order of hundreds to thousands of years. Overall, processes on the temperate sea floor may combine to destroy more carbonate than they produce, and the preservation potential of temperate shelf carbonate into the rock record may be significantly affected. Where preservation does occur in such a destructive regime, the effects of early sea-floor processes will be key determinants of the deposit, resulting in a 'taphofacies' characteristic of temperate shelf carbonate sediments. Keywords: Early diagenesis; Taphonomy; Cool-water carbonates; Abrasion; Breakage; Dissolution; Cementation; Encrustation; Bioerosion; Sediments

The Yellow Sea has been extensively studied for the understanding of dispersal patterns and limits of sediments from neighboring countries including China and Korea. Although sedimentological, mineralogical, and geochemical approaches have been tried to solve the problems, especially including the identification of sediment sources in and around the Yellow Sea, the published results are not enough for understanding them. Suggestions on sediment origins, budgets, sediment accumulation rates, mineralogical, and geochemical compositions are not coincident to each other and sometimes even controversial; for example, conflicts on the distribution patterns of smectite and calcium carbonate, the provenance of the southeastern Yellow Sea mud and sedimentation rates in there, the ratios of V/Al and Mn/Al in Korea and China river sediments, the origin of Ba and Pb in sandy sediments of the northeastern Yellow Sea, and so on. Various geochemical indicators from the literature for the provenance discrimination in the Yellow Sea are reviewed here in depth, and corresponding discussions are described separately. Research topics for the future study, also, are suggested for the proper access to the understanding of the origin and dispersal patterns of the Yellow Sea sediments, especially focusing on the geochemical approaches. Keywords: Provenance discrimination; Yellow Sea; Sediment; Geochemistry

Tsunami events with extreme effects on sedimentary transport or considerable alterations of the coastal configuration are rather rare regarding human history, but considering geological timescales they occur frequently. At least 100 megatsunami in different parts of the world have been recorded in the past 2000 years--but presumably far more have failed to be noticed during historical times and are not mentioned either in written or oral ancient records. Therefore, the topic of paleotsunami requires inevitable sedimentological and geomorphological research. However, field research concerning paleotsunami is astonishingly rare within the scientific approach and only 5% of the existing tsunami literature is related to this subject. Future efforts in paleotsunami research should focus on the geological evidence of these mega-events to clarify their contribution to coastal forming processes. This paper reviews the state-of-the-art knowledge of sedimentologic and geomorphic imprints of tsunami along the world's coastlines in order to highlight the need for more detailed studies of paleotsunami depositional and geomorphological traces. Keywords: Tsunami; Onshore tsunami deposits; Field evidences

Submarine-flank deposits of Hawaiian volcanoes are widely recognized to have formed largely by gravitationally driven volcano spreading and associated landsliding. Observations from submersibles show that prominent benches at middepths on flanks of Mauna Loa and Kilauea consist of volcaniclastic debris derived by landsliding from nearby shallow submarine and subaerial flanks of the same edifice. Massive slide breccias from the mature subaerial tholeiitic shield of Mauna Loa underlie the frontal scarp of its South Kona bench. In contrast, coarse volcaniclastic sediments derived largely from submarine-erupted preshield alkalic and transitional basalts of ancestral Kilauea underlie its Hilina bench. Both midslope benches record the same general processes of slope failure, followed by modest compression during continued volcano spreading, even though they record development during different stages of edifice growth. The dive results suggest that volcaniclastic rocks at the north end of the Kona bench, interpreted by others as distal sediments from older volcanoes that were offscraped, uplifted, and accreted to the island by far-traveled thrusts, alternatively are a largely coherent stratigraphic assemblage deposited in a basin behind the South Kona bench. Keywords: volcanic processes, volcano spreading, landslides, Mauna Loa, Hawaii.

Shelf-margin or shelf-edge deltas are a common constituent of Quaternary shelves, where their genetic link to falling and lowstand sea level has been well established, but they are rarely reported from older successions. Recognition of this delta type in the ancient record is nevertheless important, because (1) it helps to position the fossil shelf edge, (2) it provides insight into how sand budgets were partitioned between shelf edge, slope and basin-floor settings, and (3) it can contribute to the debate concerning three versus four systems-tract systematics and the positioning of a sequence boundary. Shelf-margin deltas create wide (tens of kilometers), high (hundreds of meters) and steep (3-6[degrees]) clinoforms, because they build across the relatively deepwater shelf margin. Such bodies tend to form strike-elongate wedges that initially thicken basinwards, attaining a maximum thickness of 50-200 m just outboard of the shelf edge, then thin on the middle/lower slope, whereas they commonly pinch out landwards by lapping back onto shelf shales. Prior to reaching the shelf edge, small-scale (tens of meters), tangential foresets (usually < 3[degrees] slope) of the shelf delta downlap onto the preexisting outer-shelf surface, whereas below the shelf edge, the shelf-margin deltaic foresets become longer, steeper (3-6[degrees]) and more turbidite prone, and they downlap onto the preexisting slope of the shelf margin. The top of the shelf-edge delta package is a sharp, planar to incised surface that truncates the delta increasingly landwards, merging eventually with the basal downlap surface. The clinoform series created by this transition from outer-shelf to shelf-margin deltas tends to have a horizontal-to-downward trajectory and, eventually, in the most distal bundles, an aggrading to backstepping trajectory as relative sea level begins to rise. The key facies association in shelf-edge deltas is the mouth bar-to-delta front association. Mouth-bar facies, landwards of the shelf edge, consist mainly of thick, clean, flat to low-angle and tipple-laminated medium to fine sands. Basinwards from the shelf edge, such sands commonly alternate with heterolithic slumped unit, creating characteristic slumped to laminated couplets. Because the delta front is superimposed on a preexisting, steep and extended shelf margin, it commonly contains (beyond the mouth bars) thick successions (up to many tens of meters) of sandy, slope turbidites. Shelf-margin deltas differ from inner shelf deltas in showing: (1) an order of magnitude higher clinoforms (hundreds instead of tens of meters), and strike-elongated, locally pod-like sand bodies commonly affected and augmented by growth faulting; (2) paleoecological evidence of abrupt shallowing (foreshortened stratigraphy); (3) turbidite-prone delta-fronts; (4) larger scale and greater abundance of slope-controlled soft-sediment deformation and (5) the general absence of a paralic 'tail' along the trailing edge of the delta front. Shelf-margin deltas can be classified into two types. Stable shelf-margin deltas are usually tens of meters thick and are not associated with shelf-edge incision or major slope collapse/disruption features. Slope turbidites are common and occur as unconfined sheets and lobes. Such deltas form when relative sea level falls no lower than the level of the shelf platform or, after longer sea-level falls, when rivers reestablish at the shelf edge on the rise. Unstable shelf-margin deltas are associated with large-scale slope collapse, listric growth faults and sometimes with salt diapirs. Slides are common on the upper slope, whereas imbricated sediment packages and compressional ridges affect the slope toe. Slope turbidites can be ponded within structurally controlled mini-basins on the slope. Such deltas are often related to unusually great sand influx to the shelf edge, or simply to prolonged or large fall of relative sea level below the shelf edge. The diachronous erosional unconformity atop the shelf-to-shelf-edge deltaic wedge is viewed by some researchers as the most easily recognizable and persistent surface on the shelf and slope. This surface contrasts with the downlap erosional surface developed from the beginning of sea-level fall, which is viewed by other researchers as the key boundary surface within this complex. It should be noted that sea level can fall for a long period of time (tens of thousands of years) before deltas even reach the shelf margin and, therefore, before significant volumes of sand are delivered across the shelf break. Hence, the time of incision of the shelf edge and emplacement of deepwater sand is commonly long after the initial fall so the time of (maximum) relative lowstand of sea level may be a more practical choice for the timing of the sequence boundary. Recognition of shelf-margin deltas and analysis of their architecture help in the prediction of presence or absence of basin-floor fans. Deltaic complexes that are aggradational to backstepping, downlap onto disrupted or complex slopes, and overlie an incised shelf and shelf edge, predict that there should be basin-floor fans present. In contrast, delta complexes that show a prolonged and preserved progradational to downstepping architecture implies the presence of turbidite accumulations on the slope but not on the basin floor. Keywords: Shelf-margin delta; Forced regression; Depositional systems tract; Sequence boundary; Basin-floor fan

Environmental hypoxia and the release of reduced manganese (Mn) are often combined stress factors in marine sediments. Previous investigations have shown that hypoxia induces variable responses in the concentration of the respiratory pigment haemocyanin (Hc) of crustaceans. A recent study demonstrated that the magnitude and direction of the changes was dependent on the initial level of Hc in individuals of the Norway lobster Nephrops norvegicus. The changes also took place within 24 h rather than days as suggested by previous studies. In this present study we investigated changes of Hc in individual N. norvegicus in uncontaminated sea water after exposure to and release from realistic hypoxic stress (P[O.sub.2] = 6.0 kPa). Furthermore we investigated how concomitant exposure to realistic concentrations of manganese (20 mg [l.sup.-1]) modified the responses we observed. We confirmed a between-individual variation in response and a change in Hc towards an optimum level after hypoxia, but also showed that changes that took place post-hypoxic exposure occurred over a timescale similar to that of the hypoxic response itself. Manganese exposure resulted in no significant changes in Hc whereas Mn exposure combined with hypoxia resulted in a significant decrease (15%) in all individuals independent of initial Hc. N. norvegicus was thus unable to compensate for the effects of hypoxia by synthesis of Hc after exposure to naturally occurring Mn concentrations.

Marine organisms have occupied hard substrates since the Archaean. Shells, rocks, wood and sedimentary hardgrounds offer relatively stable habitats compared to unconsolidated sediments, but the plants and animals which inhabit them must develop means to gain and defend this premium attachment space. Hard substrate communities are formed by organisms with a variety of strategies for adhering to and/or excavating the substrates they inhabit. While mobile grazers, organically attached and even soft-bodied organisms may leave evidence of their former presence in ancient hard substrate communities, a superior fossil record is left by sessile encrusters with mineralised skeletons and by borers which leave trace fossils. Furthermore, encrusters and borers are preserved in situ, retaining their spatial relationships to one another and to the substrate. Spatial competition, ecological succession, oriented growth, and differential utilisation of exposed vs. hidden substrate surfaces can all be observed or inferred. Hard substrate communities are thus excellent systems with which to study community evolution over hundreds of millions of years. Here we review the research on modern and ancient hard substrate communities, and point to some changes that have affected them over geological time scales. Such changes include a general increase in bioerosion of hard substrates, particularly carbonate surfaces, through the Phanerozoic. This is, at least in part, analogous to the infaunalisation trends seen in soft substrate communities. Encrusting forms show an increase in skeletalisation from the Palaeozoic into the Mesozoic and Cenozoic, which may be a response to increasing levels of predation. Hard substrate communities, considering borers and encrusters together, show a rough increase in tiering through the Phanerozoic which again parallels trends seen in soft substrate communities. This extensive review of the literature on living and fossil hard substrate organisms shows that many opportunities remain for large-scale studies of trends through time at the community and clade levels. Palaeontologists will especially benefit by closer integration of their work with that of neontologists, particularly in aspects of ecology such as larval recruitment, competition and succession. Keywords: Hard substrates; Encrusters; Borers; Bioerosion; Ecology; Palaeoecology; Evolution

[1] Subsidence of Lima Basin, part of the Peruvian forearc, is controlled by tectonic erosion by the subducting Nazca plate. Multichannel seismic reflection data coupled with age and paleowater depth constraints derived from Ocean Drilling Program (ODP) coring now allow the rates of erosion to be reconstructed through time. In trenchward locations the forearc has experienced limited recent relative uplift (700-850 m) likely due to preferential basal erosion under the center of Lima Basin. Long-term subsidence driven by basal tectonic erosion dominates and is fastest closest to the trench. Since 47 Ma (Eocene) up to 148 km of the plate margin have been lost at an average rate of up to 3.1 km [myr.sup.-1]. Appoximately 110 km of that total appears to be lost since 11 Ma, implying much faster average rates of trench retreat (10 km [myr.sup.-1]) since collision of the Nazca Ridge with the Lima Basin at 11 Ma. Although there is no clear subsidence event at ODP Site 679 during the time at which Nazca Ridge was subducting beneath this part of the forearc (4-11 Ma), the more trenchward ODP Sites 682 and 688 show significant deepening after 11 Ma indicating that subduction of the ridge accelerates tectonic erosion. Long-term rates of crustal erosion in the region of Lima Basin are greater than estimates of regional arc magmatic productivity, implying that such margins are net sinks of continental crust. INDEX TERMS: 3025 Marine Geology and Geophysics: Marine seismics (0935); 3040 Marine Geology and Geophysics: Plate tectonics (8150, 8155, 8157, 8158); 8015 Structural Geology: Local crustal structure; 0935 Exploration Geophysics: Seismic methods (3025); KEYWORDS: Peru, subduction, tectonics, subsidence. Citation: Clift, P. D., I. Pecher, N. Kukowski, and A. Hampel, Tectonic erosion of the Peruvian forearc, Lima Basin, by subduction and Nazca Ridge collision, Tectonics, 22(3), 1023, doi:10.1029/2002TC001386, 2003.

The O, S, and Sr isotope compositions were determined for 17 samples of gypsum that replaced anhydrite in the sheeted-dike complex of the Macquarie Island ophiolite. Elevated [delta][sup.34]S (26.2 [per thousands]-29.0 [per thousands]) and [delta][sup.18]O values (12.5 [per thousands]-14.4 [per thousands],) of gypsum compared to those of seawater sulfate are the result of microbial sulfate reduction. Low organic carbon contents and little sulfate reduction in sediments, plus a large basaltic Sr component in the gypsum ([sup.87]Sr/[sup.86]Sr = 0.70446-0.70524), indicate that the sulfate source was not pore waters in the overlying sediment. Low [delta][sup.34]S values of sulfide in basalt lavas are consistent with microbial reduction of seawater sulfate within the volcanic rocks. Tectonic activity at the slow-spreading ridge allowed evolved formation waters to enter hot sheeted-dike complex basement, resulting in heating and precipitation of anhydrite. Results show that microbes can leave geochemical tracers of their activity in oceanic basement and that anhydrite can be preserved in oceanic crust and may be of significance for the oceanic sulfur budget. Keywords: sulfates, hydrothermal processes, bacteria, biosphere, mid-ocean ridges.

The Nankai hydrate field, Japan, is an example of gas-hydrate deposits associated with an active subduction zone. In order to determine the origin of gas hydrates in this area, [sup.129]I/I ratios together with halogen concentrations were measured in a set of pore-water samples collected from two boreholes in the Nankai hydrate field. Iodine concentrations are between 100 and 230 [micro]M, i.e., strongly enriched compared to seawater, while CI concentrations were found to he close to that of seawater. Except for one sample, [sup.129]I/1 ratios are between 180 and 520 x [10.sup.-15], giving minimum ages between 24 and 48 Ma. Because these ages are considerably older than present host sediments ( Keywords: gas hydrates, I-129 dating, Nankai Trough, pore waters, marine sediments.

Pore-water solute transport processes acting in addition to molecular diffusion affect sediment biogeochemistry and benthic exchange fluxes. Given the relatively few direct measurements of enhanced transport intensities, there is a need for predictive relationships to calculate enhanced transport parameters from more readily available information. Here, enhanced diffusion coefficients and nonlocal mass transfer coefficients are obtained by comparing total and molecular diffusion fluxes of oxygen across the sediment--water interface. Semiempirical relationships for these coefficients are derived as functions of benthic oxygen uptake. According to these relationships, enhanced solute transport significantly affects sediment--water column exchanges in regions with large benthic oxygen fluxes, typically on the continental shelves. On a global scale, enhanced transport contributes approximately one third of the total benthic flux of oxygen and more than half of that of phosphate.

A new morphosedimentary map of the Gulf of Cadiz is presented, showing the contourite depositional system on the gulf's middle slope. This map is constructed from a broad database provided by the Spanish Research Council and the U.S. Naval Research Laboratory. Our map shows that this contourite depositional system comprises five morphosedimentary sectors: (1) proximal scour and sand ribbons; (2) overflow sedimentary lobe; (3) channels and ridges; (4) contourite deposition; and (5) submarine canyons. The Gulf of Cadiz contourite depositional system stems directly from the interaction between Mediterranean Outflow Water and the seafloor; its morphosedimentary sectors are clearly related to the systematic deceleration of the Mediterranean Outflow Waters westward branches, bathymetric stress on the margin, and the Coriolis force. The slope's depositional system can be considered as a mixed contourite and turbidite system, i.e., a detached combined drift and fan. Keywords: contourite depositional system, middle slope, drifts, channels, diapirs, Gulf of Cadiz.

Sediment cores as long as 20 m, dated by [sup.14]C, [sup.14]Pb, and [sup.137]Cs methods and pollen stratigraphy, provide a history of diatom productivity and sediment-accumulation rates in Chesapeake Bay. We calculated the flux of biogenic silica and total sediment for the past 1500 yr for two high-sedimentation-rate sites in the mesohaline section of the bay. The data show that biogenic silica flux to sediments, an index of diatom productivity in the bay, as well as its variability, were relatively low before European settlement of the Chesapeake Bay watershed. In the succeeding 300-400 yr, the flux of biogenic silica has increased by a factor of 4 to 5. Biogenic silica fluxes still appear to be increasing, despite recent nutrient-reduction efforts. The increase in diatom-produced biogenic silica has been partly masked (in concentration terms) by a similar increase in total sediment flux. This history suggests the magnitude of anthropogenic disturbance of the estuary and indicates that significant changes had occurred long before the twentieth century. Keywords: Chesapeake Bay, biogenic silica, sediments, sedimentation, dating, nutrients.

The Indian monsoon system, as recorded by ocean-floor biota (benthic foraminifera) at Ocean Drilling Program Site 758 in the eastern equatorial Indian Ocean, has varied dramatically over the past 5.5 m.y., long after the onset of the monsoons at 10-8 Ma. Benthic foraminifera that thrive with high productivity year-round were common before the formation of Northern Hemisphere continental ice sheets ca. 3.1-2.5 Ma, indicating that the summer (southwest) monsoon had high intensity and long seasonal duration. Ca. 2.8 Ma benthic faunas became dominated by taxa that flourish with a seasonally strongly fluctuating food supply, indicating that the northeast (winter) monsoon, during which primary productivity is relatively low, increased in duration and strength to form a system similar to that of today. The change occurred coeval with the initiation of the Northern Hemisphere glaciation, documenting a close link between the development of the Indian monsoon and Northern Hemisphere glaciation. Keywords: monsoons, Indian Ocean, productivity, benthic foraminifera, Pliocene, Ocean Drilling Program.

Volcanic strata on southwest Isla Tiburon define the age of interstratified marine rocks and, through revision of existing correlations, the age of the proto-Gulf of California marine incursion. A 5.7 [+ or -] 0.2 Ma ash flow was emplaced at the base of the marine section. A rhyodacite dike and its related lava flow, dated as 11.2 [+ or -] 1.3 Ma, 3.7 [+ or -] 0.9 Ma, and 4.2 [+ or -] 1.8 Ma, intrudes and overlies, respectively, the marine rocks. The 11.2 Ma age, which was the core datum for a middle Miocene proto-Gulf of California origin for the underlying rocks, is discordant with all other isotopic and microfossil ages. An alternative interpretation, utilizing all available geologic and geochronologic data except this discordant age, is that marine strata on Isla Tiburon are latest Miocene to early Pliocene age. Reinterpretation of these strata supports a simplified history of marine incursion into the Gulf of California. Marine rocks as old as 8.2 Ma in the southern Gulf of California indicate an early marine incursion, perhaps flooding a region of more intense proto-Gulf of California continental extension. Flooding of the entire basin by 6.5-6.3 Ma correlates to the sudden onset of significant Pacific-North American plate-boundary motion within the Gulf of California. Keywords: Gulf of California, Salton Trough, Mexico, marine sediments, rifting.

A molecular isotopic study in cold-seep sediments from Kazan mud volcano in the eastern Mediterranean Sea indicates that a significant proportion of methane released in this environment is incorporated into biomass in methane-supported chemosynthetic microbial communities. Furthermore, extremely [sup.13]C depleted biomarkers (as much as -111%[per thousand] Vienna Pee Dee Belemnite (VPDB)) have revealed pathways of methane-derived carbon flow through the microbial community and into eukaryotic biomass. Specifically, we are able to trace the flow of methane-derived carbon through anaerobic methane-oxidizing archaea into sulfate-reducing bacteria, as well as into aerobic methane-oxidizing bacteria. The methane-derived carbon is then incorporated into eukaryotic biomass through heterotrophy by bacterivorous ciliates.

Measurements are reported of sediment pickup rates from rippled beds in an oscillatory-flow water tunnel. Two maxima in pickup rate are observed in each half-cycle: The first corresponds to the sediment entrained at flow reversal, and the second occurs close to maximum flow velocity. Additionally, fluid velocities were measured with a laser doppler anemometer in the mobile layer over both rippled and plane beds. These measurements confirm the finding of Zala Flores and Sleath that the flow in the mobile layer is quasisteady at low values of the acceleration parameter S= [rho][U.sub.O]w/([[rho].sub.s] - [rho])g. The velocity and pickup measurements are used to calculate sediment transport rates. The maximum transport rate over the crest that occurs soon after maximum flow velocity is in good agreement with the Meyer Peter and Muller formula, provided the calculation is based on the shear stress at the crest. However, the maximum transport rate that occurs in the vicinity of flow reversal does not agree with this formula. Alternative formulas are derived. DOI: 10.1061/(ASCE)0733-950X(2002)128:6(228) CE Database keywords: Oscillatory flow; Bed ripples; Sediment transport; Transport rate.

Widespread populations of obligate marine bacteria belonging to a new actinomycete taxon from ocean sediments show distinguished morphological features, small-subunit rRNA nucleotides, and their requirement for seawater for growth. Data indicate that they are distributed worldwide.

A method is described for the determination of methylmercury and butyltin compounds in marine sediment and tissue using microwave-assisted acid extraction or digestion and solid-phase microextraction (SPME) followed by analysis using gas chromatography with microwave-induced plasma atomic emission spectrometric detection (GC-MIP-AES). Using the SPME-GC-MIP-AES method, enrichment factors for methylmercury and butyltin compounds of 50-100 were achieved, as compared to the typical hexane extraction, and measurements in marine tissue and sediment matrixes were possible at 1-2 [micro]g/ kg (methylmercury) and 10-100 ng/kg (butyltins). The SPME-GC-MIP-AES method was validated using several marine sediment and tissue matrix certified reference materials (CRMs) with certified values for methylmercury and butyltin compounds. The SPME-GC-MIP-AES method was used to measure methylmercury in four marine tissue CRMs ranging from oyster tissue at 13.0 [+ or -] 1.0 [micro]g/kg to fish tissue at 397 [+ or -] 13 [micro]g/kg (as Hg dry mass). Results from the SPME-GC-MIP-AES method were used in conjunction with results from other techniques to assign certified values for methylmercury in oyster, mussel, and fish tissue CRMs. Mono-, di-, and tributyltin were measured in three sediment CRMs at concentration levels of (0.08 [+ or -] 0.03)-(0.35 [+ or -] 0.05) mg/kg (as Sn dry mass).

Particulate nitrogen, particulate organic carbon, sediment community composition and oxygen consumption were measured for the North Pacific Subtropical Gyre. Findings showed that measurements peaked during September, and that the region's organic carbon supply meets 65% of the food demand.

Research on marine sediments from the Arabian Sea indicate that chlorin concentration variations are strongly correlated to water depth for surface sediments, and that chlorins exponentially decay downcore. Implications for chlorins as a tool to gauge paleoproductivity are discussed.

Deep-sea sediment samples collected from the northeastern Atlantic Ocean yielded significant positive exponential correlations between DNA synthesis and bacterial numbers, and sediments and percentages of particulate organic carbon and total nitrogen in phytodetritus. Implications for research on surficial sediments are also discussed.

Deep-water syntectonic deposits and angular unconformities record the denudation and deformation history of the middle Cretaceous Aitzeta structure, interpreted here as a monoclinal syncline associated with the high-angle reverse Mutriku fault (Basque-Cantabrian basin, northern Spain). Sedimentological and structural analyses, combined with a precise chronostratigraphy based on ammonites, permit us to document in detail the history of this syncline during ~0.53 m.y. (Late Albian, Callihoplites auritus Subzone). Tectonism occurred during two major and two minor short-lived pulses. The sedimentary signatures of these pulses include unconformities and resedimented deposits derived from the uplifted rocks, showing inverted clast stratigraphy. In contrast, intervening phases of tectonic calm were characterized by gentle hemipelagic sedimentation. The major tectonic pulses were characterized by strong rotation and uplift of the syncline limb. The two major pulses coincided with the lower and upper limits of the auritus Subzone, respectively, and resulted in the following limb-rotation and uplift values: 42[degrees] and 250 m in the first pulse and 66[degrees] and 100-140 m in the second pulse. A maximum duration of 0.12 m.y. for each major pulse has been calculated, from which limb-rotation and uplift rates of 0.35[degrees]/k.y. and 2.08 m/k.y. (first pulse) and 0.55[degrees]/k.y. and 0.83-1.16 m/ k.y. (second pulse) are estimated. Growth strata and angular unconformity geometries, temporal variation of deformation rates, and bedding-parallel faulting indicate folding by progressive limb rotation and associated flexural slip. Local northwest-southeast compression is deduced in formation of the Aitzeta syncline. The presence of bedding-parallel oblique faulting and minor drag folds suggests a component of right-oblique movement along the Mutriku fault. Keywords: Albian, Basque, folding, rates, sedimentation, transpression.

Research on marine sediments off the coast of New Jersey indicates that sediment plays a key role in determining biodiversity and colonization patterns of benthic populations. Muddy-site sediment trays demonstrated a higher level of diversity than sandy-site trays.

Research on Long Island Sound sediments indicates that dissolution of calcium carbonate predominates during the winter, resulting in large fluxes of F(-), Sr(2+), and Ca(2+) out of the ocean floor. Approximately 90% of calcium carbonate precipitated annually is dissolved.

A reaction-diffusion model of the Atlantic Ocean's northeastern continental slope demonstrates that the degradation rate constants for total organic carbon and total hydrolyzable amino acids decrease with greater water depth. Findings also confirm that mineralization of organic matter within lateral and vertical transport, coupled with downslope accumulation, transport and sorting, result in a higher level of organic matter degradation.

The sorption of manganese(2+) in natural marine sediments is explored, along with rate-determining factors, in the Iberian margin of the Atlantic Ocean. Research shows that adsorbed Mn(2+) plays an important role as a significant redox intermediate between pore water Mn(2+) and Mn oxide, and enhances sediment column retention.

Three algorithm-based models are presented for oceanic particle cycling, one deterministic, one simulated annealing and one genetic algorithm. The models can recover a minimum of two parameters but the deterministic method gradient requirement is problematic.

A model is presented for demonstrating the paleoceanographic data obtained from the nitrogen content of marine sediments. The trophic chain model depicts the isotropic signal in detritus, zooplankton, phytoplankton and nutrients, with higher delta(15)N values indicating long cell length scenarios, or high sea levels, and lower delta(15)N values indicating short cell length scenarios, or low sea levels.

Research on Thalassia testudinum seagrass populations in Texas' Laguna Madre and Corpus Christi Bay indicate that plant tissue production through carbon fixation is linked to sediment nitrogen levels. In low nitrogen conditions, above-ground growth is diminished while below-ground growth is enhanced, while high nitrogen conditions enhance above-ground production.

A study of terrigenous organic matter in offshore surface sediments in the Gulf of Mexico revealed that offshore sediments originate from grassland soils in the Mississippi River drainage basin and that nearshore sediments derive from coastal forests and swamps. The study examined the chemical and stable isotope signatures of oxidation from lignins in the organic matter. It enabled researchers to differentiate between matter which originated from plants which use the C4 mechanism in photosynthesis and those which use the C3 mechanism. These results significantly expand knowledge of the nature and fraction of terrigenous organic carbon in marine sediments.

The role of nematodes in the marine sediment community is not yet fully understood. The density of nematode communities decreases from the shelf to the abyssal plains, a change which has been attributed to food supply. A new study investigating nematode density in ocean margin sediments of the Goban Spur in the northeast Atlantic shows that it is positively and linearly related to sediment geochemistry. Details of the study are presented.

Gas in solution in the pore water or in its free form is found in many marine sediments around the world. The presence of gas may influence and alter the properties of the host soil, and could, in some cases, jeopardize the stability of foundations of marine structures. The outcome of a pilot laboratory study on the effects of gas on the undrained static and cyclic strength of sand is presented in this paper. The test results indicate that the presence of gas may strongly influence the undrained strength of sand. The extent of the effect is, among other things, a function of the gas type, the amount of gas, and the pore pressure level.

Two sequential extraction methods, an acid-gradient and a 'Tessier-type' scheme, were used to elucidate the mode of formation of the uniquely colored trace metal enriched fronts with a six-fold Cu-enrichment, which are seen in the interbedded pelagic-turbiditic sediments from the Madeira Abyssal Plain. Type-1 fronts, associated with the oxidation fronts that emerged after deposition of turbidites, are mainly black and enriched in Cu, Ni, Zn and Co. Type-2 fronts, associated with sulfur, are purple and highly enriched in Cu.

An examination of the sediment trap samples, collected between Dec 1, 1986, and Apr 30, 1987, at 1020 and 4120 m below the northeast subtropical Atlantic Ocean surface, contained particulate fluxes of copper, iron, aluminium, cobalt, manganese, cadmium, lead, zinc, vanadium, phosphorus and nickle. An analysis of the elemental composition and flux rates suggests that the major contributor of these elements to depositing material are brought by the northeast trade winds.

An analysis of the distribution and the biochemical composition of organic matter in surface sediments (0-15 cm) of 22 continental and bathyal stations reveals that disparties in labile organic matter, total organic matter, bacterial density and biomass were related to the benthic bacterial populations and to environmental conditions. It was also found that due to the high percentage of labile organic matter and bacterial density, deep sea sediments of the Eastern Mediterranean Sea are not entirely bereft of nutritional value.

A three-level bioassay-directed chemical analysis was used to determine the amount of genotoxic components in marine sediments off the coast of Barcelona, Spain. The research study employed gel permeation chromatography, normal-phase liquid chromatography and reversed-phase liquid chromatography. The samples analyzed revealed 140 aromatic compounds, 57 of which were mutagenic or belonged to mutagenic chemical classes.

The petrography and geochemistry of marine magnesian calcite cements recovered from the sea floor on the lower-thermocline lower slope of Little Bahama Bank address three issues concerning inorganic carbonates: (1) crystal habit of marine magnesian calcite cements, (2) cation composition of marine precipitates, and (3) origins of cathodoluminescence in calcite. Bladed and blocky limpid spar cements formed contemporaneously within the same intraparticle pore, as shown by banded cathodoluminescence traced without interruption through both cement habits. Bladed and blocky cements exhibit a positively covariant linear relationship for Mg and Sr, having low proximal (early formed) compositions and high distal (late formed) compositions. Linear covariance of Mg and Sr is interpreted to indicate that the concentrations of these cations were controlled by kinetic effects as they formed, with early precipitation occurring more rapidly than later precipitation. Precipitation rates apparently did not affect cement habit. Limpid, isopachous, bladed spar cements, the distal third of which are brightly cathodoluminescent, have a wide range of Mg and Sr compositions, which is almost completely spanned by both distal cathodoluminescent and proximal noncathodoluminescent parts of cements occurring within the same pore. Mg and Sr do not have a linear relationship. These cements are interpreted to have recrystallized in deep, cool sea water. During recrystallization, magnesium was lost, and in some cases, manganese, the principal cathodoluminescence excitor, was presumably gained.