History Of Sediment Accumulation Research Articles

Detecting detrital carbonate in shale successions - Relevance for evaluation of depositional setting and sequence stratigraphic interpretation

The Portwood Member of the New Albany Formation is a dolomitic black shale succession that was deposited in the western portion of the Appalachian Basin. Correlative of the Tully Limestone interval found to the northeast in the Appalachian Basin and slightly more than 5 m thick, it nonetheless consists of three erosion-bounded stratal packages that record Late Givetian eustatic sea-level variations. Detailed petrographic study shows that its carbonate interbeds, though readily interpreted as transgressive in nature, are largely detrital, and represent lowstand deposits eroded from the Cincinnati Arch in the west. Petrographical inspection showed abundant silt-sized detrital carbonate within the black shales, as well as a range of other key features, such as mud-dominated composite particles and agglutinated benthic foraminifera, that shed a new and much differentiated light on depositional setting and history of sediment accumulation. Whereas earlier recognized internal erosion surfaces still anchor the sequence stratigraphic framework, reinterpreting carbonate beds as lowstand deposits, and identifying condensed intervals and maximum flooding surfaces via distinct glauconite maxima, supports a reassessment of system tracts that is in agreement with petrographic constraints. Thin section based microfacies analysis identified multiple sedimentary settings, ranging from comparatively shallow (10's of meters, suboxic to dysoxic, tempestites) to very shallow (meters, dysoxic to oxic, wave and current action), and enabled subdivision of the Portwood into a series of upwards shallowing parasequences. This study demonstrates that petrographic due diligence is essential to correctly identify the origin of shale hosted carbonate intervals, and as an added benefit yields a sophisticated understanding of depositional conditions and long-term depositional trends that rivals what is possible for sandstone or carbonate successions.

Absence of evidence of climate-driven cycles in Carboniferous deposits of Joggins, Nova Scotia, Canada: influence of salt withdrawal tectonics on deposition and pedogenesis

ABSTRACT During the Late Paleozoic Ice Age, the fault-bounded equatorial Cumberland Basin of Nova Scotia experienced rapid subsidence, accumulating kilometer-thick fluvial sedimentary units derived from two highlands to the northwest and southeast. Major variations are recorded in the paleosols exposed at the Joggins Fossil Cliffs, ranging from oxidized and well-drained paleosols with recognizable vertic features to highly reduced organic-rich paleosols. These different soil lithologies suggest alternating conditions between well-drained floodplain environments and water saturation associated with overall poor soil development. Although halokinetic subsidence of the Cumberland Basin is known to have been operative during deposition of these units, previous research favored glacio-eustatic processes as the primary forcing mechanism of sedimentation. A total of 474 fluvial aggradational cycles were identified within a kilometer-thick interval and show a fluctuating accommodation history with a very abrupt nature. The series of fluvial aggradational cycles was used to develop threshold autoregressive models based on 1) their thickness, 2) their paleosol thickness, 3) their sandstone content, and 4) their paleosol-to-sandstone ratio. For each model, results suggest no evidence of statistically significant cyclicity, contradicting the hypothesis that fluvial sedimentation was mainly driven by glacio-eustatic cyclothems. Additionally, a total of 7 lithologies were recognized through 1,655 beds. Evaluation of 8 spherical semivariograms suggests no evidence for cyclicity in the frequency, order, or distribution of the data based on lithologies, although some covariance was found at distances between 550 and 750 m suggesting similar processes controlling sedimentation in the lower and upper Joggins Formation. The Cumberland Basin is known to have been rapidly subsiding, mainly because of ductile deformation of salt deposits in the deeper basinal units. Our results suggest that Joggins records tectonically induced ponding of a part of the sedimentary basin, allowing more extensive preservation of abundant coal and organic-rich units, as well as still-standing fossil forests exposed along the cliffs. These new results suggest that tectonic subsidence of the Cumberland Basin during the Late Paleozoic Ice Age was a more important driver of fluvial sedimentation than previously thought. This novel application of the TAR methodology provides a mathematical description of the sediment accumulation history of terrestrial basins when applied to conformable sedimentary successions, along with the means of linking paleosol development to climatic processes.

Li-isotope exchange during low-temperature alteration of the upper oceanic crust at DSDP Sites 417 and 418

The record of the Li-isotopic composition of ancient-seawater has the potential to provide important insight into the Earth system. However, we still have an incomplete understanding of the controls on the magnitude and isotopic compositions of the fluxes of Li into and out of the ocean. An important sink for Li from seawater is through low-temperature hydrothermal alteration of the upper oceanic crust. Here we present a detailed study of three adjacent drill cores in 120 Myr old Atlantic crust (Holes 417A, 417D and 418A) that had very different sedimentation histories. Samples from Hole 417A, drilled on a topographic high and exposed to seawater for >20 Myr before sediment started to accumulate, have much higher Li contents (up to ∼70 ppm) than samples from the other sites where sediment began accumulating immediately after crustal accretion (up to ∼20 ppm). Despite this difference in Li content, the δ7Li of the altered basalts in all cores increases with depth over the upper ∼40 m from around −1‰ at the lava-sediment interface to 6 ± 2‰ at ∼40 m depth, remaining roughly constant with depth after this. If the uppermost lavas equilibrated with seawater, with a bulk fractionation factor of ∼0.980 ± 0.003, then the isotopic composition of seawater 120 Myr ago was ∼19 ± 3‰, within the range of other estimates for Cretaceous seawater. Fluid-rock reaction models, with the hydrological regime varying as a function of depth and sediment accumulation history, can explain the observed rock compositions. However, modelling shows that complexities related to the time-varying hydrological regime, along with the possibility of time-varying δ7Li of seawater, mean that the Li-isotopic composition of altered oceanic lavas cannot be uniquely interpreted. The bulk Li content and isotopic composition of the well-sampled 120 Myr crust in Holes 417A, 417D and 418A suggest that Cretaceous upper oceanic crust was a sink for ∼4×109 mol yr−1 of Li. Surprisingly, the bulk Li-isotopic composition of the lavas sampled at these sites (∼6‰) is not much higher than that of fresh MORB, and within uncertainty of that of high-temperature hydrothermal vent fluids; i.e., high- and low-temperature alteration processes approximately balanced one another for Li-isotopes in the late Cretaceous. This could be fortuitous; alternatively, if the ocean was at steady state the main source of Li to the ocean at this time may have had a δ7Li similar to that of high-temperature hydrothermal fluids.

Relative sea-level trends in New York City during the past 1500 years

New York City (NYC) is threatened by 21st-century relative sea-level (RSL) rise because it will experience a trend that exceeds the global mean and has high concentrations of low-lying infrastructure and socioeconomic activity. To provide a long-term context for anticipated trends, we reconstructed RSL change during the past ~1500 years using a core of salt-marsh sediment from Pelham Bay in The Bronx. Foraminifera and bulk-sediment δ13C values were used as sea-level indicators. The history of sediment accumulation was established by radiocarbon dating and recognition of pollution and land-use trends of known age in down-core elemental, isotopic, and pollen profiles. The reconstruction was generated within a Bayesian hierarchical model to accommodate multiple proxies and to provide a unified statistical framework for quantifying uncertainty. We show that RSL in NYC rose by ~1.70 m since ~575 CE (including ~0.38 m since 1850 CE). The rate of RSL rise increased markedly at 1812–1913 CE from ~1.0 to ~2.5 mm/yr, which coincides with other reconstructions along the US Atlantic coast. We investigated the possible influence of tidal-range change in Long Island Sound on our reconstruction using a regional tidal model, and we demonstrate that this effect was likely small. However, future tidal-range change could exacerbate the impacts of RSL rise in communities bordering Long Island Sound. The current rate of RSL rise is the fastest that NYC has experienced for >1500 years, and its ongoing acceleration suggests that projections of 21st-century local RSL rise will be realized.

Atmospheric oxygenation driven by unsteady growth of the continental sedimentary reservoir

Atmospheric oxygen concentration has increased over Earth history, from ∼0 before 2.5 billion years ago to its present-day concentration of 21%. The initial rise in pO2 approximately 2.3 billion years ago required oxygenic photosynthesis, but the evolution of this key metabolic pathway was not sufficient to propel atmospheric oxygen to modern levels, which were not sustained until approximately two billion years later. The protracted lag between the origin of oxygenic photosynthesis and abundant O2 in the surface environment has many implications for the evolution of animals, but the reasons for the delay remain unknown. Here we show that the history of sediment accumulation on continental crust covaries with the history of atmospheric oxygen concentration. A forward model based on the empirical record of net organic carbon burial and oxidative weathering of the crust predicts two significant rises in pO2 separated by three comparatively stable plateaus, a pattern that reproduces major biological transitions and proxy-based pO2 records. These results suggest that the two-phased oxygenation of Earth's surface environment, and the long delays between the origin of life, the evolution of metazoans, and their subsequent diversification during the Cambrian Explosion, was caused by step-wise shifts in the ability of the continents to accumulate and store sedimentary organic carbon. The geodynamic mechanisms that promote and inhibit sediment accumulation on continental crust have, therefore, exerted a first-order control on the evolution of Earth's life and environment.

The Bengal fan: External controls on the Holocene Active Channel turbidite activity

The eastern levee of the Active Channel in the Bengal fan has been investigated in order to better understand the history of turbidite activity in this channel during the Holocene in the context of Ganges-Brahmaputra ‘source-to-sink’ system. A robust 14C-based chronostratigraphy provides high temporal resolution for reconstructing sediment accumulation history on the eastern levee of the Active Channel. Integration of this study with previous work in the area suggests that the Bengal fan has remained continually connected with the Ganges-Brahmaputra fluvial system through the Holocene, feeding through the main canyon, the Swatch of No Ground (SoNG). An intense turbidite activity occurred during a transgressive wet period from 14.5 to 9.2 ka cal. BP, followed by an abrupt shift in sedimentation at 9.2 ka cal. BP, probably due to the high sea level leading to a partial disconnection between massive river discharges and the deep turbidite system. During the last 9.2 ka cal. BP, turbidite activity is still present but irregular, likely modulated by a combination of various forcings such as monsoon variability and river migration. In total, three phases are distinguishable during this period: 9.2–5.5, 5.5–4, and 4 ka cal. BP to modern, according to the turbidite record. Unexpectedly, the Indo-Asian monsoon does not appear to be the only predominant forcing on the establishment of the Bengal fan during the Holocene because of the combination of different forcings directly affecting transfers between the Ganges-Brahmaputra and the Bengal fan as well as river migrations, delta construction, and potentially anthropogenic impact.

Re‐defining the natural range of Scots Pine (Pinus sylvestrisL.): a newly discovered microrefugium in western Ireland

AbstractAimNativePinus sylvestrisbecame extirpated in Ireland, during a massive population decline experienced throughout Europe. It was extensively replanted in Ireland during the 18th century from Scottish stock. We test the hypothesis thatP. sylvestrisin Rockforest Co. Clare did not become extirpated during theP. sylvestrisdecline, and persisted to present day independent of 18th century plantations.LocationRockforest, Co. Clare in Ireland.MethodsFossil pollen was counted from a terrestrial core. Radiocarbon dates and age‐depth modelling was used to ascertain the core chronology. Loss‐on‐ignition was carried out to investigate sediment accumulation history. Pollen was also counted from moss polster pollen traps to explore the deposition ofP. sylvestrispollen in the surrounding landscape. Historical maps were consulted to investigate the longevity of other nearbyP. sylvestrispopulations.ResultsA continuous record ofP. sylvestrisis reported. The core extends through the last two millennia, and reports a clear decline ofP. sylvestrisatc. 1550 calbp. TheP. sylvestrispollen curve recovers quickly after the decline event and persists at high levels up until the present day. The loss‐on‐ignition data reveal a stable accumulation of sediment with no major erosion events. The moss polster pollen traps show the core site is a suitable location for collecting pollen from the RockforestP. sylvestrispopulation. Historical maps demonstrate that none of the other nearbyP. sylvestrispopulations extends further back than plantations in the early 18th century.Main conclusionsThe population ofP. sylvestrisin Rockforest Co. Clare survived the regionalP. sylvestrisdecline, recovered and persisted right up to the present day, independent of introduction by human agency. Hence, we identify this microrefugium population of native Irish stock outside of the current understanding of the native range for this tree species.

Relative sea-level change in Connecticut (USA) during the last 2200 yrs

We produced a relative sea-level (RSL) reconstruction from Connecticut (USA) spanning the last ∼2200 yrs that is free from the influence of sediment compaction. The reconstruction used a suite of vertically- and laterally-ordered sediment samples ≤2 cm above bedrock that were collected by excavating a trench along an evenly-sloped bedrock surface. Paleomarsh elevation was reconstructed using a regional-scale transfer function trained on the modern distribution of foraminifera on Long Island Sound salt marshes and supported by bulk-sediment δ13C measurements. The history of sediment accumulation was estimated using an age-elevation model constrained by radiocarbon dates and recognition of pollution horizons of known age. The RSL reconstruction was combined with regional tide-gauge measurements spanning the last ∼150 yrs before being quantitatively analyzed using an error-in-variables integrated Gaussian process model to identify sea-level trends with formal and appropriate treatment of uncertainty and the temporal distribution of data. RSL rise was stable (∼1 mm/yr) from ∼200 BCE to ∼1000 CE, slowed to a minimum rate of rise (0.41 mm/yr) at ∼1400 CE, and then accelerated continuously to reach a current rate of 3.2 mm/yr, which is the fastest, century-scale rate of the last 2200 yrs. Change point analysis identified that modern rates of rise in Connecticut began at 1850–1886 CE. This timing is synchronous with changes recorded at other sites on the U.S. Atlantic coast and is likely the local expression of a global sea-level change. Earlier sea-level trends show coherence north of Cape Hatteras that are contrasted with southern sites. This pattern may represent centennial-scale variability in the position and/or strength of the Gulf Stream. Comparison of the new record to three existing and reanalyzed RSL reconstructions from the same site developed using sediment cores indicates that compaction is unlikely to significantly distort RSL reconstructions produced from shallow (∼2–3 m thick) sequences of salt-marsh peat.

Seafloor geomorphology and submarine landslide hazards along the continental slope in the Carnarvon Basin, Exmouth Plateau, North West Shelf, Australia

3D exploration seismic data were interpreted to investigate the locations and characteristics of submarine slope failures along the continental slope in the offshore Carnarvon Basin on Australia’s North West Shelf. Seisnetics™, a patented genetic algorithm was used to process the 3D seismic data to extract virtually all trough and peak surfaces in an unbiased and automated manner. The extracted surfaces were combined in the 3D visual database to develop a seafloor digital terrain model that extends from the continental slope to the Exmouth Plateau. The 3D data were used to map the subsurface extent and geometry of landslide failure planes, as well as to estimate the thickness and volumes of slide deposits. This paper describes the geomorphic characteristics of five of the survey areas. Geomorphic mapping shows the presence of slope failures ranging from small (20 km across) mass transport complexes (MTC). The features are associated with debris flow chutes, turbidity flow channels, and debris fields. Analysis of failure planes show prominent grooves or striations related to the mobilisation of slide material down both the continental slope and Exmouth Plateau and into the Kangaroo Syncline. Submarine slope failures can occur at the continental shelf break in about 200–300 m of water and run out to the Exmouth Plateau surface in about 1,100–1,400 m water depths. The largest individual slides in the survey areas have widths of 30 km and minimum run-out lengths of 75 km, though associated turbidity flow deposits likely extend much further. The subsurface expression of the large MTCs illustrates a history of sediment accumulation along the mid-slope followed by repeated slope failure and debris run-out. Sediment accumulation and slope failure processes are actively occurring along the continental slope and submarine landslides thus are a major driver of hazard to subsea infrastructure development. Smaller more frequent slides may pose a greater hazard than large infrequent MTCs.

The 2.6 Ma depositional sequence from the Challenger cold-water coral carbonate mound (IODP Exp. 307): Sediment contributors and hydrodynamic palaeo-environments

During IODP Expedition 307, the first complete sequence through a cold-water coral carbonate mound (a bio-geological seafloor feature created through successive stages of cold-water coral mediated sediment accumulation) was successfully acquired. The full recovery of the Challenger Mound, one of the large (ca. 155 m high) coral carbonate mounds along the NE Atlantic continental margin (Belgica mound province, eastern Porcupine Seabight) facilitates for the first time the study of the entire development of a coral carbonate mound and, hence, allows the identification of the environmental conditions driving and maintaining the entire build-up of these remarkable seafloor habitats. In this study, the different sediment contributors to the Challenger Mound are identified and assessed throughout its entire 2.6 Ma long development. High-resolution siliciclastic particle-size end-member modelling and its ground-truthing (XRD, quartz-sand surface microtextures) indicate the influence of an all dominant contour-current system, operating in variable energetic modes, for most of the sediment accumulation history of the Challenger Mound. Only local, short-distance current-controlled sediment re-dispersal is evidenced, while iceberg rafting is identified as an important depositional mechanism throughout the whole mound development period. Furthermore, evidence for icebergs repeatedly reaching the eastern Porcupine Seabight continental margin, even in the early stages of Northern Hemisphere glacial expansion, is preserved in the mound sequence. Supporting the existing coral-stratigraphy, the Challenger Mound depositional sequence reveals a two-phase development, separated by a significant hiatus. The lower mound-phase (M1; 2.6–1.7 Ma) indicates a semi-continuous, steadily changing, fast accumulating current-controlled depositional environment. The condensed upper mound-phase (M2; 998–1.5 ka) bears witness of a distinct shift to a more glacially-influenced, low accumulation environment, most likely resulting from a reduced capacity to deposit and/or preserve sediments. Cold-water coral density at the site of deposition is assumed to play an essential role in sediment deposition and preservation on Challenger Mound. It enabled the preservation of a unique, higher resolution record in the lower M1 sequence in the otherwise erosive/non-depositional Early-Pleistocene environment along the NW European continental margin. The potential of coral carbonate mounds as intermediate water depth, continental margin, (Plio-)Pleistocene palaeo-archives is thereby showcased.

Reconstructing the history of sediment accumulation in the Yesa reservoir: an approach for management of mountain reservoirs

Navas, A., B. Valero-Garcés, L. Gaspar and J. Machín. 2008. Reconstructing the history of sediment accumulation in the Yesa reservoir: an approach for management of mountain reservoirs. Lake Reserv. Manage. 25:15–27. The Aragón River was impounded at the foothills of the Pyrenean Internal Depression in 1959; since then sediments accumulations have decreased the reservoir storage capacity. In this work, we interpreted the history of the sediment accumulation in the Yesa reservoir based on the detailed study of two sediment cores collected at the more stable area in the reservoir. The identification of main sedimentological facies together with the analysis of the grain size distribution of the materials accumulated at the bottom of the reservoir was used for interpretations of the sedimentary dynamics. These data were compared with records of known flood events to derive a tentative chronology of the infilling process by assigning main changes observed in the facies types and sediment components to specific years. In addition to grain size data of sediments accumulated in the river channels, suspended sediments from representative sites of the Aragón Basin to the Yesa reservoir were collected during high and low waters and analysed. Grain size data and sediment composition (organic matter, carbonates) were used to assess the characteristics and the pattern of the sediment transport through the Aragón River network and the role played by lithology and land use. The results provide information on the sediment transport. This approach can be used to assess the siltation processes in Mediterranean mountain reservoirs to improve the management of water bodies by preventing their infilling.

Northwest African Continental Margin: History of sediment accumulation, landslide deposits, and hiatuses as revealed by drilling the Madeira Abyssal Plain

ODP drill sites in the Madeira Abyssal Plain reveal sequences of organic‐rich turbidites derived from the northwest African margin, in which each turbidite has a volume of tens to hundreds of cubic kilometers. The frequency of turbidite emplacement has been combined with core and seismic data to show the volume of redeposited sediment. The basin began to fill about 22 Ma with numerous small turbidites, up to 100 per million years, each with volumes of a few cubic kilometers. The total volume of turbidites deposited increased between 16 and 11 Ma, as did their individual volumes, and then declined to 7 Ma. At 7 Ma, there was a dramatic increase in the amount of turbidite input to 768 km3/Myr and a rise in the average volume of each unit to 59 km3. These high values have been maintained to the present day. The variations in the amount of redeposited sediment most likely reflect the rates of sedimentation on the northwest African margin since high sedimentation leads to oversteepening of the slopes and eventual mass wasting. The dramatic changes at about 7 Ma may be due to a large increase in upwelling off northwest Africa caused by circulation changes associated with increased glaciation of the poles. Up to 20% of sediment may be remobilized by landslides, with each event leaving a hiatus. Each of these hiatuses extends over an average area of ∼4800 km2 and represents removal of sediment layers several tens of meters thick and of several hundred thousand years duration.

Early to middle Tertiary foreland basin development and the history of Andean crustal shortening in Bolivia

A >2.5-km-thick succession of Tertiary strata in the Eastern Cordillera of southern central Bolivia consists of predominantly fluvial and lacustrine deposits. The age of the base of the succession is middle Paleocene, and its upper part (which is erosionally truncated) is probably late Oligocene-early Miocene. The lower 50-130 m of the succession consists of interbedded fluvial sandstone and mudstone (including minor paleosols) of the Santa Lucia Formation. These strata are overlain by up to 50 m of pervasively pedogenically altered mudstone and sandstone in the upper part of the Santa Lucia Formation and lower part of the Impora Formation that may represent much of late Paleocene-Eocene time. Above the paleosol zone is a thin zone (∼10 m) of lacustrine carbonate and clastic rocks in the uppermost Impora Formation, and this in turn is overlain by a >2000-m-thick, upward-coarsening succession of clastic fluvial deposits in the Cayara, Camargo, and Suticollo Formations. Paleocurrent data indicate that fluvial channels that deposited the Santa Lucia, Impora, and Cayara Formations flowed mainly westward, whereas channels responsible for the Camargo and Suticollo Formations flowed generally eastward. Modal sandstone petrographic data show a long-term evolution from subarkosic (during Santa Lucia deposition) to quartz-arenitic (during Impora and Cayara deposition) to sublitharenitic (during Camargo and Suticollo deposition) compositions. We argue that the lithofacies and sediment-accumulation history of this succession are most consistent with deposition in an eastward-migrating foreland basin system. E -mail: decelles@geo.arizona.edu. Critical to this interpretation is the zone of extreme stratigraphic condensation in the lower Impora Formation, the inferred upper Paleocene-Eocene part of the succession. The abrupt decrease in sediment accumulation represented by this zone is difficult to reconcile with the leading alternative model in which continuous, postrift thermal subsidence resulted in a gradual, continuous decay of early Tertiary sediment-accumulation rates. Stratigraphic condensation is, however, consistent with passage of the forebulge through the region, an interpretation that also can be reconciled with the record of foreland basin development in the Altiplano to the west and gross sediment accumulation patterns in the Subandean zone and modern foreland basin to the east. Simple flexural modeling and palinspastic reconstruction of the complete Cenozoic migration history of the foreland basin system suggest that ∼1000 km of foreland lithosphere has been underthrust westward beneath the Andean orogenic belt at the latitude of southern Bolivia. The amount of middle and lower crust that would have been added to the Andean infrastructure is sufficient to explain the present crustal thicknesses in Bolivia.

Radiocarbon Dating, Chronologic Framework, and Changes in Accumulation Rates of Holocene Estuarine Sediments from Chesapeake Bay

Rapidly accumulating Holocene sediments in estuaries commonly are difficult to sample and date. In Chesapeake Bay, we obtained sediment cores as much as 20 m in length and used numerous radiocarbon ages measured by accelerator mass spectrometry methods to provide the first detailed chronologies of Holocene sediment accumulation in the bay. Carbon in these sediments is a complex mixture of materials from a variety of sources. Analyses of different components of the sediments show that total organic carbon ages are largely unreliable, because much of the carbon (including coal) has been transported to the bay from upstream sources and is older than sediments in which it was deposited. Mollusk shells (clams, oysters) and foraminifera appear to give reliable results, although reworking and burrowing are potential problems. Analyses of museum specimens collected alive before atmospheric nuclear testing suggest that the standard reservoir correction for marine samples is appropriate for middle to lower Chesapeake Bay. The biogenic carbonate radiocarbon ages are compatible with 210Pb and 137Cs data and pollen stratigraphy from the same sites.Post-settlement changes in sediment transport and accumulation is an important environmental issue in many estuaries, including the Chesapeake. Our data show that large variations in sediment mass accumulation rates occur among sites. At shallow water sites, local factors seem to control changes in accumulation rates with time. Our two relatively deep-water sites in the axial channel of the bay have different long-term average accumulation rates, but the history of sediment accumulation at these sites appears to reflect overall conditions in the bay. Mass accumulation rates at the two deep-water sites rapidly increased by about fourfold coincident with widespread land clearance for agriculture in the Chesapeake watershed.

Abrupt deglaciation events and Holocene palaeoceanography from high-resolution cores, Cartwright Saddle, Labrador Shelf, Canada

The uppermost Quaternary sediments in Cartwright Saddle, Labrador Shelf, are acoustically laminated, with reflectors that can be traced over long distances. Two piston cores from the saddle record changes in sediment and meltwater delivery from the northeast margin of the Laurentide Ice Sheet (LIS) during deglaciation. Variations in sediment properties indicate a similar history of sediment accumulation over the last 12 kyr. The temporal sampling interval reaches decadal resolution in the last deglacial period 7–9 ka. Analyses of total carbonate content, sediment magnetic variables, foraminiferal species and stable isotope measurements on planktic foraminifers show that abrupt changes occurred ca. 10.9, 9.2, 8.8, 7.9 and 7 ka (with 450 yr correction). There was no distinct change in sediment character during much of the Younger Dryas chronozone. In the δ18O record, the 8.8 ka event is a dramatic 1‰ shift toward lower values, which we associate with the Noble Inlet glacial event within Hudson Strait. We do not see the pronounced low δ18O event at 7.1 ka reported off Nova Scotia, but surprisingly, neither the Nova Scotia records nor other records in the Labrador Sea capture the impressive 8.8 ka change. Serious consideration must be given to the final collapse of the LIS as the cause of the 8.2 cal. ka cold event recorded in Greenland and northwest Europe. Copyright © 1999 John Wiley & Sons, Ltd.

100 Years of Sediment Accumulation History of Organic Halogens and Heavy Metals in Recipient and Nonrecipient Lakes of Pulping Industry in Finland

Rate of sediment accumulation of extractable organic halogen (EOX) and of 12 trace elements (As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Sn, V, and Zn) were analyzed retrospectively over 100 years in the recipient area of pulp mills in Lake Saimaa and in two nonrecipient forest lakes in southeastern Finland. The sediments were dated by 210Pb and 137Cs activities. From 1880s to 1940s, <1 mg of EOX−Cl accumulated m-2 year-1 in the sediment of southeastern Lake Saimaa, but accumulation increased to 1350 mg of EOX−Cl m-2 year-1 from the 1950s to the 1980s at 3 km and to 500 mg at 5 km from the discharge point of bleaching pulp mills. Abandoning elemental chlorine in bleaching and adopting biological treatment for wastewaters in the 1990s associated with a decreasing the sediment accumulation of EOX to <400 mg of EOX−Cl m-2 year-1 at both sites. The deposition rates of inorganic elements were similar in all three lakes from 1880s to 1940s, 5−40 mg m-2 year-1 for Mn and Zn, 1−5 mg m-2 year-1 for Cr, Cu, Ni, Pb, Sn, and...

Long-term sediment accumulation in the Middle Jurassic–early Eocene Cordilleran retroarc foreland-basin system

Research Article| July 01, 1996 Long-term sediment accumulation in the Middle Jurassic–early Eocene Cordilleran retroarc foreland-basin system P. G. DeCelles; P. G. DeCelles 1Department of Geosciences, University of Arizona, Tucson, Arizona 85721 Search for other works by this author on: GSW Google Scholar B. S. Currie B. S. Currie 1Department of Geosciences, University of Arizona, Tucson, Arizona 85721 Search for other works by this author on: GSW Google Scholar Geology (1996) 24 (7): 591–594. https://doi.org/10.1130/0091-7613(1996)024<0591:LTSAIT>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation P. G. DeCelles, B. S. Currie; Long-term sediment accumulation in the Middle Jurassic–early Eocene Cordilleran retroarc foreland-basin system. Geology 1996;; 24 (7): 591–594. doi: https://doi.org/10.1130/0091-7613(1996)024<0591:LTSAIT>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The late Middle Jurassic–early Eocene (∼ 120 m.y.) sediment-accumulation history of the Cordilleran foreland basin in northern Utah exhibits a sigmoidal pattern on a rate vs. time plot, with moderate rates of accumulation during late Middle Jurassic, very low net rates during Late Jurassic–earliest Cretaceous, increasingly rapid rates during Early-middle Cretaceous, and low rates during Late Cretaceous–early Eocene time. This pattern is consistent with deposition in a prograding foreland-basin system that comprised integrated back-bulge, forebulge, foredeep, and wedge-top depozones. The upper Middle Jurassic represents the back-bulge depozone; the Upper Jurassic was deposited on the eastern flank of a flexural forebulge; the basal Cretaceous unconformity is the result of eastward migration of the forebulge; the thick, Lower-middle Cretaceous succession represents the foredeep depozone; and the Upper Cretaceous–early Eocene embodies the syndepositionally deformed wedge-top depozone. Previous models that explain Middle-Late Jurassic stratigraphic patterns in terms of foredeep subsidence (alone) and a Late Jurassic hiatus in crustal shortening in the Cordilleran orogen are shown to be neither necessary nor supported by evidence from the Cordilleran hinterland. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Phase change and thermal subsidence of the Williston basin

SUMMARY A mechanism of subsidence for the Williston basin is proposed and tested. The mechanism combines cooling and thermal contraction of the lithosphere with a phase transformation in the lower crust. The cooling and the phase boundary movement following a sudden change in the thermal boundary condition at the base of the lithosphere are calculated; isostatic adjustments and sea-level variations are included to determine subsidence and sediment accumulation at the basin's centre, which are compared with the data. The subsidence record could not be explained by temperature boundary conditions. The calculations show that: (1) the heat-flow boundary condition explains the long duration (more than 350 Myrs) of subsidence of the Williston basin and (2) the delay of the phase-change subsidence (about 40Myrs) explains an acceleration of subsidence in the early stages of the basin's evolution. When isostatic adjustments and the effect of sea-level variations are included, the calculated sediment accumulation history fits well the sediment record of the Williston basin.

Phase changes and thermal subsidence in intracontinental sedimentary basins

A model of tectonic subsidence is developed to explain the late acceleration of subsidence observed in some intracratonic sedimentary basins. The proposed mechanism combines the effect of thermal contraction of an initially hot lithosphere with the effect of a subcrustal phase transformation that moves under changing pressure and temperature conditions. The subsidence following a sudden change in temperature at the base of the lithosphere is calculated. The calculations show that: (1) phase changes, if present and activated, contribute substantially to the subsidence of sedimentary basins; (2) because the effect of phase change is delayed, subsidence accelerates after a time on the order of 20 Myr; and (3) the duration of the subsidence is on the order of 100 to 150 Myr. During the late stages of subsidence, the phase change is the dominating mechanism. An application to the Michigan basin is presented. The calculated sediment accumulation history fits the record well when the effect of sea-level changes is included in the model.

Williston in the Family of Cratonic Basins: ABSTRACT

The Williston basin is one of a clan of subcircular to elliptical elements in the interiors of all cratons; such basins are distinguished by characteristics common to all. In each, the basement consists of continental crust and each basin is surrounded by areas of continental crust. Subsidence rates are typically low, so that conditions near depositional base level prevailed during much of the history of sediment accumulation. Episodic subsidence occurred over time spans of 107-108 years; major episodes of subsidence are broadly concurrent on all cratons. Tectonic tempo and mode of subsidence evolved synchronously on all cratons; therefore, similar isopach and facies patterns (and similar oil or gas maturation, migration, and trap potentials) occur o all cratons. All members of the clan exhibit a range of individual variations imposed by latitude and climate. Intraplate tectonism and volcanism, approach to or distance from source areas, and distribution paths of detrital sediment. Nevertheless, facts and concepts developed by intensive study of basins with high-density documentation (outcrop and subsurface) are commonly applicable to basins such as the Williston, which is in a less mature stage of exploration. End_of_Article - Last_Page 867------------