Catastrophic Deposition Research Articles

Initiation of turbidity currents: outcrop evidence for Eocene hyperpycnal flow turbidites

The most widely used, although not as widely documented, explanation for initiation of turbidites is the conversion of catastrophic sediment failures into turbidites. Such instantaneous sediment failures generate short-lived surge-type flows that deposit turbidite beds described as Bouma sequences. In this communication, we present data from the Eocene Central Basin of Spitsbergen that shows turbidite systems that are volumetrically dominated by thick ungraded and laminated sandy turbidite beds, deposited by gradual aggradation from sustained flows. Sustained flows are long-lived and more or less continuous. They can be generated by a variety of mechanisms, e.g.: (1) instability during volcanic eruptions and the consequent remobilisation of unconsolidated material; (2) seismically triggered subaerial sliding within the drainage; (3) storm surges; (4) retrogressive slope failure; (5) breaching; and (6) hyperpycnal flows. Our database shows that in the Eocene Central Basin, the sustained flows were generated by hyperpycnal flows, i.e., by direct river effluent. The hyperpycnal flow turbidites have been recognized on the basis of (1) physical connection between fluvial and turbidite channels at the shelf edge, (2) abundance of thick turbidite sandstone beds, (3) sand-prone nature of the turbidite systems, (4) downslope changes of individual thick, sandy turbidite beds, and their collapsed pinch-out segments, (5) great abundance of continental material (leaves, coal fragments) in turbidite beds, (6) low abundance of associated slumped or debris-flow beds, and (7) the occurrence of turbidites in systematically accreted shelf-margins. These features strongly suggest that hyperpycnal flow, generated by direct river effluent, deposited significant number of turbidite beds in the documented slope and basin-floor turbidite successions. We also argue that the hyperpycnal flows are preferentially fed into the deepwater slopes beyond the shelf edge during the falling stage and lowstand of relative sea level. The turbidite beds were studied in the context of seismic-scale (1×15 km), dip-oriented outcrops by measuring detailed vertical sections, following individual beds and packages of beds downslope for distances over 5 km, lateral mapping, and helicopter-taken photomosaics.

A depositional record of deglaciation in a paleofjord (Late Carboniferous [Pennsylvanian] of San Juan Province, Argentina): The role of catastrophic sedimentation

Research Article| March 01, 2004 A depositional record of deglaciation in a paleofjord (Late Carboniferous [Pennsylvanian] of San Juan Province, Argentina): The role of catastrophic sedimentation Ben Kneller; Ben Kneller 1School of Earth Sciences, University of Leeds, Leeds LS2 9JT, UK Search for other works by this author on: GSW Google Scholar Juan Pablo Milana; Juan Pablo Milana 2CONICET e Instituto de Geología, Universidad Nacional de San Juan, San Juan, Argentina Search for other works by this author on: GSW Google Scholar Clare Buckee; Clare Buckee 3School of Earth Sciences, University of Leeds, Leeds LS2 9JT, UK Search for other works by this author on: GSW Google Scholar Omar al Ja'aidi Omar al Ja'aidi 3School of Earth Sciences, University of Leeds, Leeds LS2 9JT, UK Search for other works by this author on: GSW Google Scholar GSA Bulletin (2004) 116 (3-4): 348–367. https://doi.org/10.1130/B25242.1 Article history received: 15 Aug 2002 rev-recd: 18 Feb 2003 accepted: 14 Apr 2003 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Ben Kneller, Juan Pablo Milana, Clare Buckee, Omar al Ja'aidi; A depositional record of deglaciation in a paleofjord (Late Carboniferous [Pennsylvanian] of San Juan Province, Argentina): The role of catastrophic sedimentation. GSA Bulletin 2004;; 116 (3-4): 348–367. doi: https://doi.org/10.1130/B25242.1 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 SocietyGSA Bulletin Search Advanced Search Abstract The combination of high sediment supply rates and ample accommodation within fjords provides high-resolution records of deglaciation. Ancient fjord fills provide the potential for three-dimensional views of the evolution of depositional environments in response to changing sediment supply and base level through the deglacial process. We describe the fill (Jejenes Formation) of a well-exposed Late Carboniferous (Pennsylvanian) glacial valley and its tributaries; these deposits record the progressive marine flooding and infilling of topography by glacially derived sediments. The geometry of the valley and its tributaries is controlled by the underlying lower Paleozoic lithologies: a deep valley with steep sides exists where the bedrock is massive limestones, and a broader, shallower valley exists where the bedrock is generally a fine-grained olistostrome. The valleys are locally floored with diamictites, including both in situ tillites and remobilized diamictites. In the trunk valley these are locally overlain by a small, shallow-water delta. The major part of the valley fill consists of a ≤150-m-thick mudstone-dominated succession (probably generated by plumes of glacial outwash) containing numerous dropstones that decrease in abundance down the fjord. The mudstones contain numerous thin sandstone and conglomerate turbidites that were supplied laterally via subaqueous gravel fans feeding in from the tributary valleys, each of which has a distinctive clast suite related to the local subcrop. The entire succession is overlain by >300 m of sandy turbidites, of which the upper part includes large mass-transport complexes.Intercalated within the succession in the trunk valley are structureless, graded, silty mudstones lacking dropstones but with abundant large wood fragments. Close to the steep western margin of the trunk valley, each of these massive mudstones is underlain by a slump or debris flow, locally containing meter-scale blocks of Ordovician limestone from the valley side. We interpret these as a consequence of rockfalls from the steeper valley sides, triggering debris flows on the subaqueous fjord slopes. We suggest that large solitary waves were generated as the rockfalls entered the water, traveling along the fjord and stripping vegetation from the shoreline. Large amounts of mud and silt were thrown into suspension during these events and subsequently settled from suspension to form the structureless graded beds. These deposits, and other mass-flow deposits within the succession, emphasize the potential importance of catastrophic sedimentation within deglacial successions. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

MACROBENTHIC RECOVERY PROCESSES FOLLOWING CATASTROPHIC SEDIMENTATION ON ESTUARINE SANDFLATS

Land use can exacerbate the rate of sediment delivery to estuaries. In particular, for catchments with steep terrain and heavy, sporadic rainfall, changes in land use can increase the risk of catastrophic deposition of terrestrial sediment. One of the key issues in assessing the ecological significance of catastrophic sedimentation events is determining the rate of recovery of the macrobenthic community and understanding how physical and biological processes influence the recovery rate in different locations. We conducted a field experiment over 212 days to assess the impact of terrestrial sediment deposits at six sites on the intertidal sandflats of Whitianga Harbour (New Zealand). Differences in the sedimentary habitat as a result of the deposition of terrestrial sediment lasted for ∼50 d, although these effects varied between different sediment properties and between sites. The deposition of terrestrial sediment had an immediate and negative effect on resident macrofauna, although complete defaunation of the experimental plots did not occur. Macrobenthic recovery lagged behind the recovery of the sediment properties. Based on multivariate analysis, three sites never recovered over the duration of the experiment, while based on univariate analysis four sites never recovered. Macrofaunal assemblages living deep (2–15 cm) within the sediment were generally slower to recover than those found in the top 2 cm. A meta‐analysis of recovery rates for macrofauna was conducted on information generated in this study and in two similar experiments carried out in other New Zealand estuaries. This analysis revealed a consistent negative relationship between the magnitude of disturbance generated by the terrestrial sediment layer and the recovery of the macrobenthos. Measures of recovery at the community level emphasized the importance of site environmental factors reflecting increased wave disturbance, flow velocity, and the wetting and drying of the deposited terrestrial sediment in speeding recovery. Overall, our results indicate that the long‐term effects of catastrophic sediment disturbance are influenced by local hydrodynamic conditions and the composition of resident macrofauna living in sediments adjacent to disturbed areas. Given the long time scale of recovery from these experiments they indicate the potential for catastrophic sediment deposition to result in broad‐scale degradation of estuarine macrobenthic communities.

Catastrophic deposits in the Bulgarian Lower Cretaceous

Catastrophic deposits in the Bulgarian Lower Cretaceous

Soft sediment as a constraint on the spread of the zebra mussel in western Lake Erie: Processes and impacts

The zebra mussel (Dreissena), inadvertently introduced to the Great Lakes in 1986, has since expanded to cover most of the shallow-water, hard substrates in Lakes Erie and Ontario. Colony densities exceed 300,000 per m2 in some bedrock areas of western Lake Erie. The objective of this study was to investigate the spread of zebra mussel onto soft sediment areas of the western basin of Lake Erie and to identify natural controls on the large-scale colonization of such sediments. Combined side scan sonar, underwater video imagery, and direct diver observation showed three modes of viable zebra mussel colonies in soft substrates: 1) attachment to zebra mussel shell debris deposited in linear troughs (stripes); 2) attachment to shells built up over hard substrates intermittently covered by soft sediments (footballs); and 3) as isolated clumps (druses) attached to dropstones, unionid clams, or their shells. Their spatial distribution suggests that zebra mussel expansion onto soft sediments is supplied primarily by nearby hard substrate areas. Zebra mussel populations living on soft sediment have the normal size distribution as those found on hard surfaces, often with a bimodal or trimodal character, representing cohorts of different ages. At the sites studied, there was a large proportion of dead shells, suggesting colonization over an extended period, as well as a relatively high mortality rate due to burial by periodic catastrophic sedimentation after storms. This vulnerability and the need to be near to source areas make it unlikely that the zebra mussel (D. polymorpha) will continue to expand into areas of soft sediment remote from hard substrate areas. The impact of the zebra mussel colonies on important textural properties of the substrate was not dramatic, but median grain diameter was significantly finer, organic carbon significantly higher, and sediment consistency more clayey below zebra mussel mats. Metal content was generally higher in the samples below zebra mussel mats, but the differences were statistically significant only in the case of iron and maganese. However, the sediment concentrations of metals at all sites were much greater than those at the remote Mid-basin site that was barren of zebra mussels, suggesting an overall metal enrichment near zebra mussel colonies.

Early diagenetic processes in coastal marine sediments disturbed by a catastrophic sedimentation event

Following a catastrophic flash flood in July 1996, as much as 50 cm of post-glacial clays were deposited in less than 2 days in the upper reaches of the Saguenay Fjord (Quebec, Canada), disrupting the normal sedimentation and diagenetic regimes. We report detailed geochemical analyses of sediments (porosity, Eh, organic and inorganic carbon, Fe and Mn reactive solid phases, and acid volatile sulfide) and porewaters (salinity, dissolved organic carbon (DOC), Fe(II), Mn(II), nitrate, ammonium, and sulfate) for seven stations located in the Saguenay Fjord. Three of these (SAG-05, SAG-09, and SAG-30) were visited in 1996 and once per year thereafter to document the chemical evolution of the sediment toward a new steady state. The flood deposits contain less organic carbon and more inorganic carbon than the indigenous fjord sediments. The flood deposit modified the distribution patterns of reactive Mn and Fe as a result of the reduction of Mn and Fe oxides delivered with the deposit and those concentrated at the now buried former sediment-water interface. Most of the Mn(II) migrated to the new sediment-water interface, where a Mn-rich layer was formed. In contrast, much of the Fe(II) was precipitated as sulfides and remained trapped at or close to the old interface. A nitrate peak developed in the porewater at the old sediment-water interface, possibly because of the oxidation of ammonia by Mn oxides. The distributions of porewater DOC within the flood deposit correlate with the distributions of dissolved Mn(II) and Fe(II), suggesting that adsorbed DOC was released when metal oxides were reduced.

Sedimentology of magmatically and structurally controlled outburst valleys along rifted volcanic margins: examples from the Nuussuaq Basin, West Greenland

ABSTRACT After a period of early Palaeocene faulting and uplift of the Nuussuaq Basin, West Greenland, two valley systems were incised into the underlying sediments. Incision of the older Tupaasat valley took place during a single drainage event of large water masses, which resulted in catastrophic deposition. The valley was cut along early Palaeocene NW‐ to SE‐trending normal faults, clearly showing that the trend and the relief of the valley were structurally controlled. The valley fill is up to 120 m thick and consists of a lower part of sandstones and conglomerates deposited from catastrophic flows characterized by very high concentrations of suspended coarse‐grained sediment load. Catastrophic deposition was followed by rapid decrease in flow discharge and the establishment of a lacustrine environment within the valley characterized by the deposition of heterolithic sediments. The younger Paatuutkløften valley system was mainly cut into the Tupaasat valley fill, which was completely or nearly completely eroded away in many places. The younger valley is 1–2 km wide and up to 190 m deep. Incision of the Paatuutkløften valley probably reflected renewed tectonic activity and uplift of the basin. This phase was shortly followed by rapid major subsidence. The valley‐fill deposits comprise a uniform succession of fluvial and estuarine sandstones. The valley fill is topped by shoreface sandstones, which are succeeded abruptly by offshore mudstones deposited shortly before and during the initial extrusion of a thick hyaloclastite succession. The Paatuutkløften valley fill is attributed to a very rapid rise in relative sea level contemporary with extensive volcanism. It is suggested that this sequence of events coincided with the arrival of the North Atlantic mantle plume. In several respects, the early Palaeocene valley‐fill deposits of the Nuussuaq Basin are different from idealized facies models for incised valley systems and represent very special cases of incised valleys. Major differences from published examples include the dominance of catastrophic deposits and indications of large changes in relative sea level of several hundreds of metres taking place rapidly in less than 1 Myr. These changes were governed by the rise of the North Atlantic mantle plume.

Coastal landsliding and catastrophic sedimentation triggered by Cretaceous-Tertiary bolide impact: A Pacific margin example?

We report here the first-recognized Pacific margin stratigraphic sequence containing evidence for catastrophic landsliding attributed to bolide impact–related seismic shocking at the Cretaceous-Tertiary (K-T) boundary. The K-T boundary is not commonly preserved in stratigraphic sequences of the Pacific margin, but we have discovered it within a coastal paleovalley in Baja California, Mexico (near El Rosario). This 5-km-wide, 15-km-long, and 200-m-deep coastal paleovalley formed by massive gravitational collapses and rapidly filled with coastal (shallow marine and lesser fluvial) gravels and sands, as well as slide sheets of marine mudstone that range from meters to kilometers in length. We infer that seismic shocking caused liquefaction and extremely rapid sedimentation of the gravels and sands, simultaneous with unleashing of slide sheets. Laser-heating 40Ar/39Ar data for biotite, hornblende, and plagioclase (single crystal and bulk step heating) on a 20-m-thick pumice lapilli tuff in the middle of the valley fill give an age of 65.5 ± 0.6 Ma; this is indistinguishable from the age of Haitian tektites dated by the same laboratory. Our new Pacific margin sequence, like many K-T boundary sequences in the Gulf of Mexico–Caribbean region, provides evidence of giant landslides and catastrophic sedimentation 1800 km from the bolide impact site.

Seafloor imagery from the BIG'95 debris flow, western Mediterranean

Seafloor backscatter data are used to image the product of one of the youngest major mass-wasting events in the northwestern Mediterranean Sea: a 26 km3 debris-flow deposit that covers 2000 km2 of the Ebro continental slope and base of slope, offshore Spain. Backscatter images provide unprecedented insights on debris-flow dynamics in the deep sea. A pattern of low-backscatter patches represents large sediment blocks that moved while keeping their internal coherence. High-backscatter alignments restricted to topographic lows that represent coarse sediment pathways separate the blocks. The results presented prove the occurrence of large catastrophic sediment failures near heavily populated coastal areas even in continental margins considered to be geodynamically quiet, such as those of the northwestern Mediterranean.

Mantle plumes and sequence stratigraphy; Late Maastrichtian- Early Paleocene of West Greenland

The sedimentary history of the upper Maastrichtian–Paleocene succession underneath the extensive Paleocene flood basalts in central West Greenland supports models for the generation of flood basalt provinces in response to rising, hot mantle plumes. The rise of the North Atlantic mantle plume was associated with deposition of at least three sedimentary sequences; each associated with incision of submarine canyons and valleys. Relative sea-level changes were caused by plumerelated tectonics and generation of sequence boundaries was in general associated with catastrophic sedimentation and very rapid development of sequences. As such the late Maastrichtian–early Paleocene sequences record a spectacular and significant but rare geological event.

Sea level changes and the continental freeboard concept: general principles and application to the Precambrian

Eustatic sea level changes reflect variation in ocean water or ocean basin volume, or changes to the hypsometric curve, which is in itself geographically and chronologically variable. Freeboard, the elevation of a continent above mean sea level, is closely related to changes in both sea level and this curve. Relative sea level change occurs due to tectonism, sediment supply, compaction, and eustatic movements. Hydroisostatic compensation modifies first-order sea level variation by about one-third. Short term and localised change in sea level may be ascribed to waves and tides, storm winds, hurricanes, tsunamis and catastrophic sediment slumps. Wide, gently sloping shelves with more uniform circulation systems, inferred for the Precambrian, may have enhanced tide and wave-induced sea level changes. Salinity and water temperature, mutually dependent, affect eustatic and relative sea levels; elevated water temperatures postulated for the early Precambrian would have been offset partly by enhanced evaporation and increased salinity. Longer term changes in sea level, regional or eustatic, may result from orogenesis, volcanism, sediment supply, compaction and loading, isostasy, and thermal mechanisms. Glacioeustatic changes, compounded by related salinity variations, moderated by glacioisostatic effects and modified by hydroisostasy, reach ca 150 m. Isostatic rebound in interglacial episodes will produce rapid and marked sea level drops up to ca 250 m; this is a localised effect and contrasts with the global enhancement of sea level during interglacials. However, evidence for glaciation in the geological record is limited, also for most of the Precambrian; sea level oscillations in non-glacial episodes may reflect flexure of tectonic plates (change up to ∼100 m) or changes to Earth's geoid (∼250 m). Eustasy up to ∼350 m will result from change to ocean basin volume, due to variation in mid-ocean ridge volume and spreading rates, also related to supercontinent amalgamation and breakup. Intra-plate hot spots and oceanic plateaus will change eustatic sea level more slowly, up to ∼100 m. Higher heat flow in the Archaean and concomitant enhanced volcanism suggest that these were important influences on Precambrian sea levels. The exponential elevation-age relationship observed for Phanerozoic oceanic lithosphere may have been more significant in the Precambrian. As continental crust grew from ca 4.0 Ga, declining heat flow and concomitant deepening of the ocean basins maintained an approximately constant freeboard during the Archaean. Although still hotly debated, there is strong support for episodic growth models inferring rapid formation of continental crust near the Archaean–Proterozoic boundary. This would imply constant freeboard conditions after 2.5 Ga as well. The constant freeboard model, however, is one based on average global conditions. Freeboard was still subject to geographic and chronologic variation, and these potential changes lie within the bounds of eustatic and relative sea level change. Continental crustal growth, the freeboard concept and sea level changes are thus interdependent variables in Precambrian geology.

Distribution and fractionation of heavy metals in the surface sediments of the Ganges- Brahmaputra-Meghna river system in the Bengal basin

The lower Ganges-Brahmaputra-Meghna (G-B-M) drainage basin occupies the total Bengal Basin, which is one of the unique basins of the world because of its location and size, density of population, and catastrophic deposition of sediments. The increased heavy metal concentration in the 63 m fraction of surface sediments shows similarity among major segments of the G-B-M system in the basin, which reflects the homogenization of lithologic and chemical diversity of the greater denudation regime by the river processes. The differences in heavy metal concentation in the lower G-B-M system with that of its upper and middle counterpart is mainly related to the contrast between Himalayan rivers and the other major South Asian rivers, and may be due to the geological differences of their denudation regime. Heavy metals in the Lower G-B-M system have an affinity towards the clay fraction of the sediments. The correlation matix of heavy metals in the lower Brahmaputra and Meghna suggests the importance of Fe-Mn oxyhydroxides in their accumulations. Iron, Ti and Mn are higher in the Meghna main channel, Zn is higher in the Meghna tributaries, and Cr is higher in both the Brahmaputra and Meghna compared to the value for standard shale. The enrichment factor is ≤1 for most of the metals except Mn which is relatively higher in the Meghna and lower Ganges main channels. The geoaccumulation index (Igeo) for most of the heavy metals lies below grade zero, suggesting unpolluted sediment quality. The lower Ganges system shows relatively higher concentration in the nondetrital fraction of heavy metals, probably due to the presence of petroleum refinery, industrial and mining effluents, and agricultural runoff in the drainage basin. The relative uniformity in concentration of heavy metals in vertical profiles may be due to the uniformity in sediment grain size and catastrophic deposition of sediments, where the time period represented by the vertical sediment column is not enough to reflect the cultural accumulation of heavy metals. The Bengal basin thus represents a relatively unperturbed alluvial basin with regards to heavy metal pollution.

CRITICAL DATA REQUIREMENTS FOR PREDICTION OF EROSION AND SEDIMENTATION IN MOUNTAIN DRAINAGE BASINS1

ABSTRACT: The potential for understanding and, where necessary, managing sedimentation in humid mountain drainage basins increases with awareness of the conditions that lead to shallow landsliding, debris flows, and catastrophic sedimentation in stream channels. Progress in understanding has involved: improved recognition of source areas and the potential for downstream effects of slope failure; improved understanding of hydrological conditions required for failure; and a general theory of slope stability in shallow colluvium, including the role of plants, fires, timber harvest, and other disturbances. The theory acknowledges spatial variability in topographic and geotechnical terrain characteristics, the stochastic nature of climatic triggering events such as forest fires and rainstorms, and the integrating nature of channel networks in modulating the cumulative effects of transient processes within a basin. Anthropogenic fire regimes, road effects, and timber harvest can readily be included. Continued application and modification of the theory over an expanded geographical range require improvements in field data and their systematic storage in spatial databases. Improvements in digital topographic data for mountain basins, systematic network‐wide surveys of channel conditions, and new technology for rapid documentation of soil depths in landslide source areas would enhance the prediction of mass failure, its consequences for channel habitat, and the basin‐wide or regional distribution of hillslope and channel conditions. Computations of the probabilities of transient effects throughout basins could then form the basis of ecological risk analyses. Large‐scale spatial data sets of a few critical variables are required before this next level of understanding can be developed and applied to sedimentation impacts on ecosystems and other resources.

Sedimentary response to mantle plumes: Implications from Paleocene onshore successions, West and East Greenland

The uplift history of the Upper Cretaceous–Paleocene sedimentary successions underneath the extensive Tertiary flood basalts of West and East Greenland supports recently described models for the generation of flood basalt provinces in response to rising, hot, mantle plumes. However, the sedimentary development indicates that the period of plume-related uplift prior to eruption of volcanic rocks was very short (<5 m.y.). Substantial regional uplift and faulting took place in West and East Greenland in the early Paleocene to earliest(?) late Paleocene, resulting in a basinwide unconformity. In West Greenland, the uplift was associated with fluvial peneplanation, valley incision, and catastrophic deposition; in East Greenland, it was associated with fluvial peneplanation. The cumulative uplift in West Greenland is probably on the order of several hundred meters, whereas in East Greenland, the observed uplift cannot be quantified. In both West and East Greenland, this phase was shortly followed by rapid, major subsidence associated with extensive volcanism. It is suggested that this sequence of events reflects the arrival of the North Atlantic mantle plume or plumes.

Sea-level –and gas-hydrate–controlled catastrophic sediment failures of the Amazon Fan

The architecture and Quaternary history of the massive and highly structured Amazon Fan has been reconstructed using sediment recovered by Ocean Drilling Program Leg 155. Huge regional mass-transport deposits make up a significant component of the Amazon Fan. These massive mass-transport deposits each cover an area over 15,000 km{sup 2} (approximately the size of Jamaica), reach a maximum thickness of 200 m, and consist of {approx}50,000 Gt of sediment. Analysis of both benthic foraminiferal fauna and the sediments indicates that the mass-transport deposits originated at a water depth of between 200 and 600 m on the continental slope, which is at least 200 km lateral to and 1500 m above their present position. Each mass-failure event was formed by the catastrophic failure of the continental slope and has been dated and correlated with climate-induced changes in sea level. Two different mechanisms initiated these catastrophic slumps: (1) Rapid drops in sea level destabilized continental slope gas hydrate reservoirs, causing slope failure and the glacial mass-transport deposits, and (2) deglaciation of the Andes and the consequent flushing of Amazon River sediment to the continental slope caused over-burdening and the deglacial mass-transport deposits.

Taphonomy of a Living Fossil: The Lingulide Brachiopod Glottidia palmeri Dall from Baja California, Mexico

Glottidia palmeri Dall, a Recent lingulide brachiopod, inhabits intertidal flats of the Colorado Delta plain in Baja California, Mexico. Live lingulides occur in patches across the intertidal zone. Patches are dominated by single cohorts with unimodal size-frequency distributions. The oldest cohorts appear to be between four and five years old. Dead specimens of G. palmeri occur in three modes: (1) In situ shells remaining after death in their burrows. These undergo decay and maceration, and blacken, soften, and eventually disintegrate. They persist up to at least a year and represent a slightly time-averaged, but strictly in place record of a single patch: (2) Surface shells removed from their burrows be-. fore or soon after death. These are deposited on the surface as single valves and undergo quick mechanical disintegration. They disappear within days, or at most weeks, and are a synchronous but spatially mixed record of different patches coexisting on the flat: (3) Beach shells represented by dried shells with mummified soft bodies. These specimens are washed out by storms and deposited on supratidal beach ridges. They disappear within weeks to months and are a synchronous, but spatially mixed record of different patches. This study offers criteria for the recognition and interpretation of preservation modes in fossil lingulides. Moreover, it confirms previous notions that Recent lingulide brachiopods have a very low fossilization potential and suggestions that high to catastrophic sedimentation rates are needed to preserve them. Thus, large-scale aspects of lingulide history (e.g., global taxonomic diversity, stratigraphic ranges) must be poorly recorded in the fossil record. At the same time, extensive time-averaging or significant transport of lingulide shells are highly unlikely. Therefore, on those rare occasions when lingulide shells are preserved, they record outcropscale, short-term aspects of their history with high fidelity. The literature on the Paleozoic lingulides suggests that they had a higher fossilization potential than their post-Paleozoic relatives. Thus, this study is most applicable to Mesozoic and Cenozoic lingulides. Most importantly, this study suggests that the fossil record of the lingulides may be affected by a taphonomic megabias-their decrease in diversity and ecologic importance after the Paleozoic may be, in part, a taphonomic artifact.

Turbidite Systems and Their Relations to Catastrophic Fluvial Sedimentation: ABSTRACT

Turbidite Systems and Their Relations to Catastrophic Fluvial Sedimentation: ABSTRACT

Catastrophic Sediment Related Disaster due to Debris Flows and Landslides associated with July 19-21 Heavy Rainfall in Kingdom of Nepal

Catastrophic Sediment Related Disaster due to Debris Flows and Landslides associated with July 19-21 Heavy Rainfall in Kingdom of Nepal

Ordovician marine volcanic and sedimentary record of rifting and volcanotectonism: Snowdon, Wales, United Kingdom

Research Article| November 01, 1992 Ordovician marine volcanic and sedimentary record of rifting and volcanotectonism: Snowdon, Wales, United Kingdom PETER KOKELAAR PETER KOKELAAR 1Earth Sciences Department, University of Liverpool, P.O. Box 147, Liverpool, L69 3BX, United Kingdom Search for other works by this author on: GSW Google Scholar GSA Bulletin (1992) 104 (11): 1433–1455. https://doi.org/10.1130/0016-7606(1992)104<1433:OMVASR>2.3.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation PETER KOKELAAR; Ordovician marine volcanic and sedimentary record of rifting and volcanotectonism: Snowdon, Wales, United Kingdom. GSA Bulletin 1992;; 104 (11): 1433–1455. doi: https://doi.org/10.1130/0016-7606(1992)104<1433:OMVASR>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 SocietyGSA Bulletin Search Advanced Search Abstract Wales was part of a continental convergent plate margin for ∼50 m.y. during Ordovician time. The crustal stress regime was one of sinistral transtension, due largely to oblique subduction. Early uplift and subsequent growth of subaerial arc volcanoes were followed by development of a broad, fault-bound, marine basin (>150 km wide) in an infra-arc or back-arc setting. Within the basin, relatively narrow grabens became sites of pronounced subsidence and bimodal (basalt-rhyolite) volcanism. The grabens developed in fault-splays above steep, crust-penetrating discontinuities that focused extension and plumbing of magmas at these sites. At Snowdon, the Bedded Pyroclastic Formation records submarine and island basaltic volcanism with associated sedimentation at the site of an active rhyolitic caldera volcano. The volcanoes formed on the axis of the Snowdon Graben, and the basaltic succession, which contains several unconformities due to marine abrasion at sea level, shows a complex history of alternate uplift and subsidence. The uplift is attributable to resurgence of rhyolitic magma and was >336 m in total. Subsidence, due mainly to crustal extension, was >500 m at a rate of ≥500 m/m.y.The Bedded Pyroclastic Formation shows clear evidence of tectonic influence in the timing, location, and style of basaltic magmatism. Repeated reactivation of magmatic plumbing systems demonstrates fault- or fault-intersection controlled channeling of magmas in the upper crust. Episodes of relatively vigorous subsidence preceded copious magmatism, and both intrusive and extrusive basalt magmas exploited contemporaneously active normal faults. Pronounced topographic ponding of extrusive products, and highly variable trends of fault-block subsidence and rotation evident from the volcanogenic sedimentary deposits, testify to chaotic (piecemeal) displacements on faults spaced commonly at < < 500 m. Diverse marine volcaniclastic systems developed in response to active volcanism and/or faulting with attendant littoral abrasion and current reworking. The systems defined include (1) progradational repose-slope volcanic piles and sedimentary fans with associated slope-foot aprons, (2) transgressive shoreline sedimentary aprons reflecting erosion of island volcanoes, and (3) a fault-controlled, emergent-shoreline, sedimentary apron complex. All of the aprons formed pre-dominantly by deposition from high-density turbidity currents; most show evidence of deposition above wave base. Catastrophic sediment supply, rapid aggradation, extreme variability in hydraulic properties of clasts, and considerable vertical displacements led to development of lithofacies and lithofacies associations that are unlike those of broadly analogous nonvolcanic systems. 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.