Subaqueous Debris Flow Deposits Research Articles

Sedimentological infill of the Middle Triassic half-graben below Mt. Vernar in Julian Alps, Slovenia

Early beginnings of the Middle Triassic extension in the areas surrounding the western embayment of the Neotethys are evidenced in formation of small half-graben basins, local emergences of the underlying platform, and/or deposition of coarse-grained breccia. The succession related to the creation and infilling of one of these half-grabens is exposed on the slopes of the base of Mt. Vernar in eastern Julian Alps, Slovenia. The lowermost exposed unit within the half-graben is the Uggowitz Breccia, which attains thickness of up to 150 m. It is followed by a few tens of meters of red nodular limestone (the informal 'Vernar member'), followed by the second, thinner Uggowitz Breccia unit, succeeded by sandstone and sandy limestone (the informal “Krma member”), rich in shallow marine foraminifers and plant material. The basin-filling succession is followed by indistinctly bedded and then massive limestone of the Schlern Formation. Late Anisian (Ilyrian) age is assumed for the sediments of the half-graben based on the clast composition and comparison with regional sequence stratigraphic schemes. Breccias likely deposited in shallow marine or marginal marine setting. Individual beds are interpreted as subaqueous debris-flow deposits.

Occurrence, Classification and Formation Mechanisms of the Organic-Rich Clasts in the Upper Paleozoic Coal-Bearing Tight Sandstone, Northeastern Margin of the Ordos Basin, China

The detailed characteristics and formation mechanisms of organic-rich clasts (ORCs) in the Upper Paleozoic tight sandstone in the northeastern margin of the Ordos Basin were analyzed through 818-m-long drilling cores and logging data from 28 wells. In general, compared with soft-sediment clasts documented in other sedimentary environments, organic-rich clasts in coal-bearing tight sandstone have not been adequately investigated in the literature. ORCs are widely developed in various sedimentary environments of coal-bearing sandstone, including fluvial channels, crevasse splays, tidal channels, sand flats, and subaqueous debris flow deposits. In addition to being controlled by the water flow energy and transportation processes, the fragmentation degree and morphology of ORCs are also related to their content of higher plants organic matter. The change in water flow energy during transportation makes the ORCs show obvious mechanical depositional differentiation. Four main types of ORC can be recognized in the deposits: diamictic organic-rich clasts, floating organic-rich clasts, loaded lamellar organic-rich clasts, and thin interlayer organic-rich clasts. The relationship between energy variation and ORCs deposition continuity is rarely studied so far. Based on the different handling processes under the control of water flow energy changes, we propose two ORCs formation mechanisms: the long-term altering of continuous water flow and the short-term water flow acting triggered by sudden events.

Timing of deposition in the Dengzhangzi and Guojiadian Basins of the Yanshan fold-thrust belt, North China

ABSTRACT The Triassic-Jurassic stratigraphy in the Yanshan fold-thrust belt is dominated by nonmarine deposits, and the division of this stratigraphy remains controversial among geologists. Age results from biostratigraphic and isotope chronological studies are inconsistent, especially for the Dengzhangzi and Guojiadian Basins in the eastern part of the Yanshan belt. We present four new detrital zircon U–Pb isotope datasets for the Triassic-Jurassic stratigraphic units and one for the Permian unit in the basins. The geochronological results show that the andesitic breccia in the Permian strata was deposited at ca. 273.78 ± 1.68 Ma, the Laohugou Formation was deposited in the Anisian-Ladinian Stage, the andesitic lava in the Shuiquangou Formation erupted at ca. 238.56 ± 0.91 Ma, and the conglomerate in the Guojiadian Formation was deposited from ca. 170 ± 5 to 163.0 ± 2.2 Ma. Field observations and facies analyses demonstrate that the Laohugou, Shuiquangou and Dengzhangzi Formations predominantly consist of subaqueous debris flow deposits, subaerial fluvial deposits, and fan delta deposits while the Guojiadian Formation is generally composed of fluvial and subaerial mass-flow deposits that formed in braided channels. Here, we propose a more precise and comprehensive Triassic-Jurassic stratigraphic division scheme based on age constraints and facies analysis. With this new stratigraphic sequence, we compare the Mesozoic stratigraphic units in the study area with those in other basins in the Yanshan fold-thrust belt in terms of the lithological associations, regional unconformities and zircon U-Pb dating results. This comparison indicates that the Indosinian and Yanshanian movements exerted a far-reaching influence on the development and evolution of the Dengzhangzi and Guojiadian Basins in the study area, forming several important regional unconformities and syntectonic conglomeratic units. These new age data on the stratigraphy are of fundamental significance for understanding the Mesozoic tectonic evolution of Yanshan.

Constraints on the nature of the Marinoan glaciation: Cyclic sedimentary records from the Nantuo Formation, South China

Detailed sedimentological investigations of the Cryogenian glacial deposits are critical for constraining the true nature of the Sturtian and Marinoan glaciations. The entire succession of the Nantuo Formation, which corresponds to the Marinoan glaciation, is well developed in South China. Here a detailed lithological and sedimentological analysis of two cores of the Nantuo Formation in Guizhou, South China, is presented in which two continuous ice advance–retreat cycles are identified. The base consists of a massive diamictite lithofacies that is representative of glacier-dominated subaqueous debris flow deposits. These proximal glaciomarine deposits are overlain by a gravel-free sandy mudstone lithofacies that is lacking in diamictites, which implies distal glaciomarine deposits. This ice advance–retreat sedimentary cycle is overlain by a weakly laminated diamictite lithofacies, which represents subaqueous debris flow deposits that formed during the second episode of ice advance. These proximal glaciomarine deposits are overlain by an interbedded sandstone–mudstone lithofacies, which is indicative of distal glaciomarine deposits that formed during another episode of ice retreat. These sedimentary cycles imply that the climate switched twice from relatively warm to extremely cold and back during the Marinoan glaciation. The global sea-level and sedimentary environments fluctuated in response to these climate changes. This co-evolution of the climate, sea-level, and sedimentary environments, which is represented by the lithofacies and sedimentary sequence of the Nantuo Formation, as well as the corresponding strata of other sections worldwide, suggests that the Marinoan glaciation is characterized by a progressive and dynamic course.

Geochronology and lithostratigraphy of the Siguiri district: Implications for gold mineralisation in the Siguiri Basin (Guinea, West Africa)

Geochronology and lithostratigraphic characterisation of the Siguiri district in the Palaeoproterozoic Birimian terrane of West Africa has provided a reappraisal of the Siguiri Basin stratigraphy. This new insight into the evolution of the central part of the basin further highlights first order controls on the location of the world class Siguiri orogenic gold district. Three metasedimentary formations occur in the Siguiri district: the Balato, Fatoya and Kintinian formations. These formations consist of fine-grained organic-rich shales, mudstone and siltstone/greywacke/limestone interbeds, decimetre- to metre-thick graded greywacke beds and debris flow deposits. The Balato Formation displays low-energy, hemipelagic marine or lake sediments, whereas the Fatoya Formation consists of distal turbidite deposits (thin-bedded turbidites and channel-fill deposits). Altogether they form a basal regressive sequence. The overlying Kintinian Formation is shale-rich, and contains a stack of polymict conglomeratic interbeds (up to 100m in thickness) around the base of the Formation in the Siguiri district. This conglomerate unit transects the whole Siguiri Basin and is interpreted to be the product of repeated subaqueous debris flow deposits and represent olistostromes (or mélanges of sedimentary origin) with various autochthonous and allochthonous clasts. The youngest detrital zircon age population for each of the Balato, Fatoya and Kintinian formations yields ages of 2113±10Ma, 2113±5Ma and 2124±7Ma respectively, thus constraining the maximum age of deposition for each of these formations. The minimum age of deposition of these sedimentary rocks is constrained by a crosscutting volcanic breccia dated at 2092±5Ma, and by the Maléa monzogranite intrusion dated at 2089±12Ma. Comparison of the sedimentary facies and geochronology of the Siguiri sedimentary rocks with other sedimentary basins in the West African Craton, suggests that the Kintinian Formation is part of the Lower Tarkwa Group, best described as “late orogenic basin” sediments. The Kintinian olistostromes are inferred to highlight the onset of renewed tectonic activity associated with the first phases of compression during the Eburnean Orogeny in the Siguiri Basin at ca. 2115Ma. The peculiar morphology of these olistostromes compared to the bulk of the Siguiri Basin sedimentary rocks, illustrates a major change in lithofacies. This change is interpreted to have developed along fundamental basement structures, controlling the early architecture of the Siguiri Basin as well as the location of world-class gold mineralisation in the Siguiri district. These fundamental structures are thought to have acted as first order fluid pathways during the E-W progressive compressional event responsible for orogenic gold mineralisation in the Siguiri district.

Late Pleistocene glaciolacustrine sedimentation and paleogeography of southeastern Michigan, USA

Abstract The geomorphic, stratigraphic and sedimentological characteristics of glaciolacustrine sediments in the metropolitan Detroit, Michigan area were studied to determine environments of deposition and make paleogeographic reconstructions. Nine lithofacies were identified and paleoenvironments interpreted based on their morphostratigraphic relationships with relict landforms. The sediments studied are found southeast of the Defiance and Birmingham moraines lying beneath a lowland characterized by a low morainal swell (Detroit moraine) and a series of lacustrine terraces that descend progressively in elevation southeastward. The glaciolacustrine sediments were deposited approximately 14.3–12.4 kA BP during the Port Bruce and Port Huron glacial phases of late Wisconsinan time, and are related to proglacial paleolakes Maumee, Arkona, Whittlesey, Warren, Wayne, Grassmere, Lundy and Rouge. The glaciolacustrine section is typically 2–4 m thick and consists of a basal unit of wavy-bedded clayey diamicton overlain by a surficial deposit of stratified and cross-stratified sand and gravel. The basal unit is comprised of subaqueous debris flow deposits that accumulated as subaqueous moraine in paleolake Maumee along the retreating front of the Huron lobe. The surficial deposits of sand and gravel were formed by traction, resulting from lacustrine wave activity and fluvial processes, in lakebed plain, beach ridge and deltaic depositional settings. Much of the lake-margin sand and gravel was derived from clayey diamicton by lacustrine wave action and winnowing, and that associated with paleolakes of the Port Huron phase is largely reworked Port Bruce sediment. Paleogeographic reconstructions show that the Defiance, Birmingham and Detroit moraines, Defiance and Rochester channels, and the Rochester delta, were deposited penecontemporaneously as paleolake Maumee expanded northward across the map area. A unique type of wavy bedform is characteristic of clayey diamicton deposited by subaqueous mass flow in the study area that is useful for differentiating sediment: 1) deposited by mass flow in subaqueous vs. subaerial settings, and 2) deposited by subaqueous mass flow vs. basal till. These bedforms are a useful tool for identifying subglacial meltwater deposits, and facilitate the mapping and correlation of glacial sediments based on till sheets. The map area provides a continental record of ice sheet dynamics along the southern margin of the Laurentide ice sheet during Heinrich event H-1. The record reveals rapid glacial retreat (∼ 0.8 km/yr) contemporaneous with the discharge of a large volume of meltwater. Evidence in the study area for subglacial meltwater is problematic, but indications that periglacial conditions persisted in the map area until ∼ 12.7 kA BP, and extended for 200 km or more south of the ice front suggest that a frozen substrate may have contributed to instability of the LIS.

The early development of an Archean submarine caldera complex with emphasis on the Mattabi ash-flow tuff and its relationship to the Mattabi massive sulfide deposit

The south Sturgeon Lake area of northwestern Ontario is underlain by an Archean submarine caldera complex which is host to six massive sulfide deposits. The complex is approximately 30 km in strike length and is partly filled by mesobreccias, subaqueous debris-flow deposits and other epiclastic rocks, as well as five major ash-flow tuff units. The most voluminous of these, the Mattabi ash-flow tuff, is up to 800 m in thickness and can be traced for more than 15 km across the caldera complex.Based on flow morphology and composition, the Mattabi ash-flow tuff is divisible into two distinct units: a bedded quartz crystal and pumice-rich unit (150-650 m thick), and a massive to poorly bedded ash unit (20-150 m thick). The bedded unit is host to the Mattabi massive sulfide deposit, as well as numerous other massive sulfide occurrences. In addition, this unit exhibits a pronounced stratigraphic and geochemical cyclicity. Individual beds (flow units) can be subdivided into basal quartz- and pumice-rich lower sections which are overlain by bedded ash tops; thicknesses of individual beds vary from 14 to 155 m. Each bed also exhibits a pronounced zonation of trace elements with high concentrations of Zr, Y, and Nb at and/or near the base gradually decreasing upward into the ash tops. The overlying massive ash unit contains no known massive sulfide mineralization and lacks any pronounced geochemical zoning.The bedded nature and geochemical zonation of individual flow units can be explained by periodic eruptions from a zoned or layered, recharged siliceous magma chamber. The difference in flow morphology between the bedded unit and the overlying massive ash-flow tuff most likely reflects the deeper submarine nature of the eruptive vents associated with the bedded deposits. The periodic and subaqueous nature of the Mattabi eruptions is indicated by the presence of exhalites and massive sulfide lenses between flow units. The ore lenses, which comprise the Mattabi deposit, formed between eruptive events from high temperature fluids whose origin may be related to processes within the magma chamber.

A thick dacitic debris flow sequence, Lake of the Woods greenstone terrane, central Canada: resedimented products of Archean vulcanian, plinian and dome-building eruptions

A 4-km thick, vertically dipping, south-facing, homoclinal, intermediate to felsic, volcaniclastic sequence in central Lake of the Woods, is underlain and overlain by subaqueous, tholeiitic basalt flows. Volcaniclastic lithologies comprise a lower tuff-breccia and lapilli-tuff assemblage, an upper turbiditic greywacke formation, and three lenticular, upward-fining, conglomerate formations interspersed within other units. Tuff-breccia and lapilli-tuff are characterized by very thick, poorly defined beds, pronounced heterogeneity, mostly angular blocks and lapilli, and a plagioclase+quartz crystal component that, in places, is incompatible with phenocryst populations in fragments. These appear to be subaqueous debris flow deposits that resulted from multistage mixing, during downslope mass transport, of fragments produced by subaerial phreatomagmatic vulcanian-type eruptions. Anomalous crystal contents represent intermixing of subaerial subplinian or plinian ash. Conglomerate formations comprise very thick, poorly defined beds composed almost entirely of well rounded, fine- to medium-grained trondhjemite. They are also subaqueous debris flow deposits but were apparently derived from wave erosion of large, flank dome complexes that periodically blocked normal transport of volcanic debris from higher on the volcano. The upper greywacke represents a shift in eruptive processes to largely plinian or subplinian eruptions.

Glaciomarine facies within subglacial tunnel valleys: the sedimentary record of glacioisostatic downwarping in the Irish Sea Basin

ABSTRACTCoastal exposures of Late Pleistocene sediments deposited after 19 000 yr BP near Dublin, Ireland, provide a window into the infill of a subglacially‐cut tunnel valley. Exposures close to the steeply dipping bedrock wall of the valley show boulder gravels within multi‐storey U‐shaped channels cut and filled by subglacial meltwaters driven by a high hydrostatic head. Gravels are truncated by poorly sorted ice‐proximal glaciomarine sediments that record the pumping of large volumes of subglacial debris along the tunnel valley to a tidewater ice sheet margin. The sedimentary succession is dominated by sediment gravity flow facies comprising interbedded diamict and massive, poorly sorted gravel facies interpreted as subaqueous debris flow deposits. Gravel beds show local inverse and normal coarse‐tail graded facies recording the restricted development of turbulent flow. Sediment gravity flow deposits fill broad (<2 km) shallow (10 m) and overlapping channels. Penetrative deformation structures (e.g. dykes) are common at the base of channels.The same subglacially‐eroded topography and glaciomarine infill stratigraphy can be identified on high resolution seismic profiles across nearly 600 km2 of the western Irish Sea. Tunnel valleys are argued to have been exposed to glaciomarine processes by the rapid retreat of a calving tidewater ice sheet margin in response to marine flooding caused by glacio‐isostatic downwarping below the last British Ice Sheet. The facies associations described in this paper comprise an event stratigraphy that may be found on other glaciated continental shelves.

Subaqueous debris flow deposits in Baffin Bay : Aksu, A.E., 1984 Geo-Marine Letts, 4(2):83–90

Subaqueous debris flow deposits in Baffin Bay : Aksu, A.E., 1984 Geo-Marine Letts, 4(2):83–90

Subaqueous debris flow deposits in Baffin Bay

Thin-bedded debris flow deposits are an important constituent of the marine Quaternary, sequence in NW Baffin Bay, covering about 30,000 km2 of sea floor. Individual debris flows traveled over a slope as low as 0.4° and a distance of several hundred kilometers. Some debris flows have generated turbidity currents. Debris flow deposits observed in the cores displayed distinctive downslope trends in grain size, bed thickness, and sorting, and showed variations in structures and sequences of sedimentary structures with poorly to moderately well-developed gravel fabric, showing the long axes of clasts aligned nearly parallel to the bedding plane.

Mélange development in the Boones Point Complex, north-central Newfoundland

The Boones Point Complex in north-central Newfoundland is a narrow mélange belt separating Roberts Arm terrain volcanic and volcaniclastic rocks to the north from Upper Ordovician westerly derived clastic rocks to the south and east. The mélange has a sedimentary matrix and contains a polymict assemblage of blocks. Limestone blocks have yielded Llanvirn–Llandeilo conodont faunas. Sedimentologic and structural analyses indicate that the complex is composed of subaqueous debris flow deposits, which are the proximal facies equivalent of the Late Ordovician clastics to the south. This debris flow material was tectonically deformed prior to the Medial Devonian 'Acadian' orogeny, probably as a result of earlier 'Taconic' thrusting.

Subaqueous debris flows of early Pleistocene age at Motunau, North Canterbury, New Zealand

Abstract Subaqueous debris flow deposits of early Pleistocene age fill a series of shallow (1–6 m deep), wide (up to more than 200 m) channels within a relatively deep-water marine mudstone sequence at Motunau, North Canterbury. Four lithotypes are distinguished; each reflects a different mechanism of debris flow. Three lithotypes (A, B, C) have in common a well-sorted fine to very fine sand with a tail of silt and clay that comprises less than 20% by weight. These reflect an interrelated spectrum of sandy debris flows, and include the first recognised example (Lithotype C) of fine-grained submarine debris flows that have been predicted by M. A. Hampton on theoretical and experimental grounds. Lithotype D is a muddy debris flow similar to others previously described in the literature. Lithotype A consists of a mixture of lithoclasts and perigenic clasts of up to boulder size, plus abundant disoriented shell fragments, all floating in the sandy matrix; stratification and grading are absent. The coarse clas...