Buried Canyon Research Articles

Rectangular drainage pattern of a submarine canyon controlled by extensional tectonic structures: Case study of the Afam Incision Surface (Tortonian, Niger Delta, Nigeria)

Submarine canyons are a key element of the growth of continental margin depocentres such as the Niger Delta, the progradation of which is commonly influenced by syn-sedimentary processes of gravity-driven tectonism. In such setting, canyons commonly constitute combined stratigraphic-structural traps because of: (i) their clayey infilling and, (ii) the incision of marine reservoirs. Nevertheless, most of the time, their drainage network and/or the external factors leading to their formation are poorly characterized, which is also the case in other settings when the resolution of geophysical dataset is less accurate. Here we use 3D seismic reflection data from the onshore eastern Niger Delta to study the morphology of a buried canyon system in relation to extensional tectonic structures, which are E-W trending growth-faults and roll-over anticlines. We map the Afam Incision Surface (AIS), which cuts up to 1000 m into subjacent Eocene-Miocene deltaic and continental series. In planform, the AIS is organized in 6 stream orders. The Afam Canyon which has the highest stream order is globally NNW-SSE oriented and is locally controlled by E-W oriented grabens, which give it right-angle changes of direction. It perpendicularly captures 5th and 4th order tributaries, each of which has an asymmetric cross-sectional profile controlled by one major growth-fault. In the southern area, the western tributaries all include an upstream part that drains in the opposite direction to the regional slope, leading to bayonet-shaped paths in planform. Whatever the stream order of the tributary considered; its increase is controlled by growth-faults. Therefore, the AIS planform network has the characteristics of a rectangular pattern. Erosion of the AIS as a submarine canyon system is consistent with its more than one-kilometer depth, preserved knickpoints within the thalweg of the main canyon; and the many erosional terraces boarded by arcuate scarps located along the main canyon and its tributaries. The formation of the AIS is correlated to the 50 m Tor2 sea-level fall at 9.5–9.2 my, and may have been initiated by by-pass currents that acted in tandem with retrogressive erosion. The latter greatly contributed to deepening and widening of the canyon and its tributaries whatever the orientation of the local slope. Erosion of the AIS was favored by the high-density of growth-faults. During the final excavation phases, the channelization of longshore drift currents by the canyon and its tributaries probably contributed to the destabilization of their upper margins.

Initiation and evolution of an isolated submarine canyon system on a low-gradient continental slope

Submarine canyons are important conduits transferring large volumes of sediment, nutrients, and pollutants from the continental shelf to deep-water basins. However, the mechanisms initiating submarine canyons and the factors influencing their evolution are still poorly understood. Here, we use multibeam bathymetry and two-dimensional seismic reflection data to investigate the origin and development of a submarine canyon system on the northern South China Sea margin. Our results show a submarine canyon system lying at a water depth of 400–1200 m on a relatively low-gradient (<0.5°), open continental slope. At the bottom of this canyon system, buried canyons undercut a mass-transport complex (MTC 1), whose top surface is early Pliocene in age. No other modern or buried canyons, channels and gullies are observed outside the area spanned by MTC 1. Such an observation demonstrates that pre-existing slide scars can capture gravity flows by providing accommodation space for sediment transported onto the lower continental slope, thus facilitating the development of pre-existing channels above MTCs. Lateral accretion packages identified on the southwest walls of several submarine canyons suggest they migrated northeastward due to the influence of contour currents. In addition, the presence of several basal erosional surfaces and smaller-scale MTCs in the canyons confirms they have undergone multiple cut-and-fill cycles, which were likely controlled by relative sea-level changes. The relative high sea level recorded at present ultimately led to the preservation of the studied canyon system on the continental slope. The results not only demonstrate the crucial role of submarine landslides in the initiation of submarine canyons, but also highlight how relative changes in sea level influence the evolution of submarine canyons on low-gradient continental slopes.

Erratum to: A buried submarine canyon in the northwest South China Sea: architecture, development processes and implications for hydrocarbon exploration

Erratum to: A buried submarine canyon in the northwest South China Sea: architecture, development processes and implications for hydrocarbon exploration

Genome Sequencing of the Endangered Kingdonia uniflora (Circaeasteraceae, Ranunculales) Reveals Potential Mechanisms of Evolutionary Specialization.

SummaryKingdonia uniflora, an alpine herb, has an extremely narrow distribution and represents a model for studying evolutionary mechanisms of species that have adapted to undisturbed environments for evolutionarily long periods of time. We assembled a 1,004.7-Mb draft genome (encoding 43,301 genes) of K. uniflora and found significant overrepresentation in gene families associated with DNA repair, underrepresentation in gene families associated with stress response, and loss of most plastid ndh genes. During the evolutionary process, the overrepresentation of gene families involved in DNA repair could help asexual K. uniflora reduce the accumulation of deleterious mutations, while reducing genetic diversity, which is important in responding to environment fluctuations. The underrepresentation of gene families related to stress response and functional loss of ndh genes could be due to lack or loss of ability to respond to environmental changes caused by long-term adaptation to a relatively stable ecological environment.

Gas venting that bypasses the feather edge of marine hydrate, offshore Mauritania

Methane can be released from the vast marine hydrate reservoirs that surround continents into oceans and perhaps the atmosphere. But how these pathways work within the global carbon cycle now and during a warmer world is only partially understood. Here we use 3-D seismic data to identify what we interpret to be a gas venting system that bypasses the hydrate stability zone (HSZ) offshore of Mauritania. This venting is manifested by the presence of the acoustic wipe-out (AWO) across a densely faulted succession above a salt diapir and a set of morphological features including a substantial, ∼260 m wide and ∼32 m deep, pockmark at the seabed. The base of the HSZ is marked by a bottom simulating reflector (BSR) which deflects upwards above the diapir, rather than mimicking the seabed. We use a numerical modelling to show that this deflection is caused by the underlying salt diapir. It creates a trapping geometry for gas sealed by hydrate-clogged sediment. After entering the HSZ, some methane accumulated as hydrate in the levees of a buried canyon. Venting in this locality probably reduces the flux of gas to the landward limit of feather edge of hydrate, reducing the volume of gas that would be susceptible for release during a warmer world.

Canyon-confined pockmarks on the western Niger Delta slope

Fluid flow phenomena in the deepwater Niger Delta are important for the safe and efficient exploration, development and production of hydrocarbons in the area. Utilizing 3D seismic data from the western Niger Delta slope, we have identified pockmarks that are confined within a NE–SW oriented submarine canyon system that has been active since the early Quaternary. The pockmarks, subdivided into ‘canyon-margin’ pockmarks and ‘intra-canyon’ pockmarks, on the basis of their plan-form distribution patterns, are found to be spatially and stratigraphically related to stratigraphic discontinuities created by erosion cuts associated with the submarine canyon system.We infer that stratigraphic discontinuities provided pathways for fluid migration within the buried canyon system, allowing fluids from deeper parts of the basin to reach the seafloor as indicated by abundant pockmarks above the partly buried canyon. The transportation of fluids from deeper parts of the basin into the buried segment of the canyon system was facilitated by carrier beds expressed as high amplitude reflection packages and by extensional normal faults. The prevalence of the ‘canyon margin’ pockmarks over the ‘intra-canyon’ pockmarks is attributed to the direct connection of the buried canyon margins with truncated reservoir facies in hydraulic connection with deeper reservoir facies. The formation of the ‘intra-canyon’ pockmarks is interpreted to have been limited by fluid flow disconnection often caused by stratigraphic alternation of sand-rich and shale-rich channel deposits that constitute the canyon fill. Muddy canyon fill units act as baffles to fluid flow, while connected sandy infill units constitute pathways for fluid migration. Occurrence of pockmarks throughout the length of the submarine canyon system is an indication of shallow fluid flow within buried reservoir facies. Systematic alignment of seafloor pockmarks are clues to buried reservoirs and provide insights into reservoir architecture which could be crucial in frontier exploration of buried deepwater canyons reservoirs and for risk assessment of development activities on top of submarine canyons. A single mega pockmark linked by a gas chimney to a deeper anticlinal structure was discovered to the north of the canyon system. This structure may be indicative of subsurface geo-pressures close to the fracture gradient, highlighting a significant drilling hazard in this part of the study area.

Tectonic control of Yarlung Tsangpo Gorge revealed by a buried canyon in Southern Tibet.

The Himalayan mountains are dissected by some of the deepest and most impressive gorges on Earth. Constraining the interplay between river incision and rock uplift is important for understanding tectonic deformation in this region. We report here the discovery of a deeply incised canyon of the Yarlung Tsangpo River, at the eastern end of the Himalaya, which is now buried under more than 500 meters of sediments. By reconstructing the former valley bottom and dating sediments at the base of the valley fill, we show that steepening of the Tsangpo Gorge started at about 2 million to 2.5 million years ago as a consequence of an increase in rock uplift rates. The high erosion rates within the gorge are therefore a direct consequence of rapid rock uplift.

Tibetan gorge avoids a tectonic aneurysm

Geomorphology![Figure][1] Tsangpo Gorge, Tibet PHOTO: FENG WEI PHOTOGRAPHY/GETTY IMAGES Rapid tectonic uplift was responsible for the immense Tsangpo Gorge on the eastern edge of the Tibetan plateau 2.5 million years ago. Wang et al. found a buried canyon upstream from the gorge along the

Influence of stratigraphic setting and simple shear on layer-bound compaction faults offshore Mauritania

We have used three-dimensional seismic data to examine the geometry of layer-bound compaction faults on the Mauritanian continental margin. The faults deform a fine-grained Neogene unit which mantles buried canyons. Above the canyons, most layer-bound faults strike perpendicular to the canyon axes, whereas adjacent to the canyons the faults are omni-directional and intersect bedding planes in polygonal patterns. On the flanks of a large structural high, faults also strike perpendicular to the slope direction, displaying a concentric pattern. Faults that show preferential alignment are located in areas with increased bedding dip, and most aligned faults are antithetic to the bedding dip. Where the bedding dip is greater than ∼1°, the synthetic faults dip more steeply than the antithetic faults. This discovery was unexpected because the stress tensor due to the effect of gravity on a dipping margin would cause the antithetic faults to form with steeper dips, which we show theoretically. We hypothesise that the layer hosting the faults has been subjected to simple shear of ∼20° or more, with the top of the layer displaced downdip by ∼100 m relative to its base. A potential application of these, and similar, observations is to assess slope stability on continental margins.

Resolving near-seabed velocity anomalies: Deep water offshore eastern India

Imaging in deep-water environments poses a specific set of challenges, both in data preconditioning and velocity model building. These challenges include scattered, complex 3D multiples, aliased noise, and low-velocity shallow anomalies associated with channel fills and gas hydrates. We describe an approach to tackling such problems for data from deep water off the east coast of India, concentrating our attention on iterative velocity model building, and more specifically the resolution of near-surface and other velocity anomalies. In the region under investigation, the velocity field is complicated by narrow buried canyons ([Formula: see text] wide) filled with low-velocity sediments, which give rise to severe pull-down effects; possible free-gas accumulation below an extensive gas-hydrate cap, causing dimming of the image below (perhaps as a result of absorption); and thin-channel bodies with low-velocity fill. Hybrid gridded tomography using a conjugate gradient solver (with [Formula: see text] vertical cell size) was applied to resolve small-scale velocity anomalies (with thicknesses of about [Formula: see text]). Manual picking of narrow-channel features was used to define bodies too small for the tomography to resolve. Prestack depth migration, using a velocity model built with a combination of these techniques, could resolve pull-down and other image distortion effects in the final image. The resulting velocity field shows high-resolution detail useful in identifying anomalous geobodies of potential exploration interest.

Amplitude anomalies in a sequence stratigraphic framework: Exploration successes and pitfalls in a subgorge play, Sacramento Basin, California

The Sacramento Basin is part of the Great Valley, a prolific hydrocarbon province that is the remnant of a late Mesozoic-early Cenozoic forearc basin in California. A series of buried submarine canyons extend seaward from the eastern margin of the forearc. These “gorges” formed during multiple episodes of relative sea-level fall during the Tertiary, truncating Late Cretaceous through Eocene marine and nonmarine sandstones. Mud-stones dominate the canyon fills, creating lateral and top seals for numerous gas reservoirs.

Discussion on mantle plume uplift in the sedimentary record: origin of kilometre-deep canyons within late Neoproterozoic successions, South Australia

Scientific editing by Nick Rogers. Nicholas Christie-Blick writes: Kilometre-deep buried canyons in the upper Neoproterozoic successions of South Australia are unusual by any standard, and any viable explanation for their origin will probably involve an unusual set of circumstances. ⇓Williams & Gostin (2000) review published geological constraints and competing hypotheses, and suggest a role for uplift and crustal deformation associated with the passage of a mantle plume. On the basis of available evidence, I continue to favour an alternative explanation—that they are due to the short-lived evaporative drawdown of sea level in a marine embayment that became temporarily isolated from the global ocean (⇓von der Borch et al. 1989; ⇓Christie-Blick et al. 1990; ⇓Christie-Blick 1998). ### Spatial and temporal distribution of erosion Canyons more than 1 km deep in the Wonoka Formation of the Adelaide fold belt and up to 700 m deep in the subsurface of the eastern Officer basin are reasonably interpreted as coeval and of common origin, with a length scale of order 1000 km. Comparable erosional features are found nowhere else in Australia, even in the Kimberley region and western Officer basin (⇓Coats & Preiss 1980; ⇓Walter et al. 1994, ⇓1995), where flood basalts of possible plume origin are widespread (⇓Bultitude 1976; ⇓Jackson & van de Graaff 1981). ⇓Bender (2000) independently noted the distribution of late Neoproterozoic to early Palaeozoic magmatism in Western Australia, and analyzed the possible role of plume-related uplift and erosional thinning of the crust in early Palaeozoic subsidence of the Canning basin. However, that basin is some 2000 km to the northwest of the Adelaide fold belt, where the canyons are best known. A rather thornier problem is that in the Adelaide fold belt prominent erosion surfaces are present at three other horizons above the level of Marinoan glaciation and below Cambrian strata. …

Sequence stratigraphy and the interpretation of Neoproterozoic earth history

The application of sequence stratigraphy to Neoproterozoic successions is important for improving the resolution of time-correlation within individual sedimentary basins and potentially at a global scale. The methodology is illustrated in this paper by reference to two contrasting examples from the Flinders Ranges (Adelaide geosyncline) of South Australia, where the younger part of the Neoproterozoic to earliest Cambrian succession (∼ 770 Ma to ∼ 540 Ma) has been divided into thirteen unconformity-bounded depositional sequences. One of the most prominent sequence boundaries, at or near the base of the Wonoka Formation, is characterized by a series of buried canyons as much as 1 km deep. High-resolution sequence-stratigraphic studies at Umberatana syncline continue to support the view that the canyons were cut subaerially and filled by fluvial and shallow-water sediments. In contrast to the Wonoka canyons, sequence boundaries interpreted at the base of the Nuccaleena Formation/Seacliff Sandstone and near the top of the ABC Range Quartzite are relatively subtle, with only limited evidence for erosion and valley incision. Four sequence boundaries, at the level of the Sturtian and Marinoan (Varanger?) glacial deposits and in the vicinity of the Precambrian-Cambrian boundary, are thought to correlate with surfaces in the Amadeus basin of central Australia. Other prominent sequence boundaries, including the Wonoka canyons and surfaces within the upper part of the Wonoka Formation and at the base of the Ediacara Member of the Rawnsley Quartzite, correspond with a relatively condensed section in the Amadeus basin, and their lateral persistence beyond the Adelaide geosyncline is therefore difficult to evaluate. Given the lack of precision in biostratigraphy and isotope geochemistry in Neoproterozoic rocks, and in a marked departure from Phanerozoic practice, we recommend placement of a terminal Proterozoic GSSP at a sequence boundary. A prime candidate in Australia is the sequence boundary at the base of the Nuccaleena Formation/Seacliff Sandstone, immediately above the Marinoan glacial rocks in the Adelaide geosyncline, and its likely correlative at or near the base of the Gaylad Sandstone in the Amadeus basin.

Submarine canyon initiation by downslope-eroding sediment flows: Evidence in late Cenozoic strata on the New Jersey continental slope

Multibeam bathymetry and seismic reflection profiles of the New Jersey continental slope reveal a series of abandoned and now-buried submarine canyons that have apparently influenced the development of modern canyons. The buried canyons are infilled along nine slope-wide unconformities separating upper-middle Miocene to Pleistocene sediments that thin downslope. Canyons infilled during the Miocene occur in the southwest part of the study area where Miocene sediments are thickest. Other canyons, infilled during the Pleistocene, occur in the northeast part of the study area where Pleistocene sediments are thickest. When followed downslope, each of the buried canyons arrives at a confluence with a modern canyon, usually where the downslope-tapering sediment cover has failed to smooth over the buried canyon, leaving a sea-floor trough. Sea-ward of the confluences, the modern canyons have exhumed the buried canyons and use the older valleys to reach the base of the slope. Re-use of the lower slope reach of the buried canyons appears to have begun when the sea-floor troughs over the buried canyons captured sediment flows initiated along the upper slope and shelf break and confined them to follow the former path of the buried canyons to the base of the slope. The downslope erosion caused by the sediment.flows is proposed to have initiated the modern canyons, which eventually excavated and deepened the former routes of the buried canyons seaward of the sites of sediment flow capture. The occurrence of buried canyons where strata thickens alongslope suggests that infilling of the buried canyons occurred seaward of shelf-edge depocenters. The heightened sediment input to the slope in these regions may have also led to the initiation and growth of modern-day canyons. The temporal relation between modern canyon formation, sediment supply, and sea level, however, remains to be established.

Middle to late Miocene canyon cutting on the New Jersey continental slope: Biostratigraphic and seismic stratigraphic evidence

We have identified and dated a major Miocene erosional surface (M1) on the New Jersey continental slope. This surface was penetrated at Deep Sea Drilling Project (DSDP) Site 612, which was drilled near the thalweg of a buried V-shaped canyon. Biostratigraphic data at Site 612 firmly constrain the age of strata above the buried canyon surface as Zones CN7 (=NN9) and N16 (lowermost upper Miocene); the upper Miocene surface at Site 612 lies above lowermost Oligocene strata because of coalesced unconformities. We traced the M1 erosional surface to the COST B-3 well where upper middle Miocene strata underlie it. Biostratigraphic studies of other New Jersey continental slope boreholes (ASP 14, ASP 15) suggest that elsewhere the sediments immediately below the M1 surface encompass the Globorotalia fohsi robusta Zone (= Zone N12-earliest N13; middle middle Miocene). The best age estimate is that M1 was eroded between 11.5 and 10.0 Ma. This erosional event apparently correlates with a similar event on the Irish and Florida continental margins and with oxygen-isotope evidence for a glacio-eustatic lowering.

Growth fault on insular slope/rise of western Iceland; comparison with SE Greenland canyons and slumps

A recently active normal fault and extensional crevasse on the western insular slope/rise boundary of Iceland adjoins a rotational slump that moved as the lower block of an active growth fault. A slump off SE Greenland is contrasted to the western Iceland slope/rise feature in translational movement and slump morphology. Bergschrund-like extensional cracks and valleys at the heads of slumps serve as troughs channeling gravity flows into established canyons on the midrise. Distinctive characteristics of buried canyons and levees may be confused with slump or slide surfaces and related subbottom features that have similar seismic reflection qualities. Examples are defined forGrowth Fault/Rotational Slumps, andTranslational Displacement Slumps.

Early Cretaceous Buried Canyon: Influence on Accumulation of Hydrocarbons in Helez Oil Field, Israel

A fossil canyon, known as Gevaram canyon and postulated to be of submarine origin, exists in the southern coastal plain of Israel. This canyon was excavated in rocks of Middle Jurassic age which unconformably underlie strata of Early Cretaceous age. The canyon runs in a northwest direction into the old Tethys through the Helez oil field and is at least 16 km long and 7 km wide. The canyon widens west of Helez. Maximum canyon depth is nearly 1,000 m; sediment fill consists mostly of dark-gray shale of the Gevaram Formation. Several sandy beds are present in the central part of the channel and limestone breccia derived from the wall rock fills the base. After the canyon was filled and buried, clastic beds of the Helez Formation accumulated in the southwestern part of the area; gray shale of the Gevaram Formation accumulated in the northwest. An embayment formed in the Helez area as a result of local subsidence caused by compaction of the shale that filled the buried canyon. Through that embayment the source beds of the Gevaram Formation reached the area in which the reservoir beds of the Helez Formation were deposited. Contact between reservoir beds and source beds thus was established, resulting in accumulation of oil in the Helez field.

Polygenetic Origin of Monterey Submarine Canyon

Monterey Submarine Canyon, one of the world's largest and deepest, heads immediately offshore in Monterey Bay on the central California coast. Starke (1956) reported the presence of a deep buried canyon inland from, and aligned with, the head of the submarine canyon. Cumulative well records, gravity surveys, and field investigations strongly suggest that the buried ancestral canyon was eroded by fluvial processes, and that the present submarine canyon originated, at least in part, by the fluming out of the ancestral canyon by dominantly submarine processes. Other submarine canyons off unstable coasts may also be polygenetic in origin. The presence of the ancestral canyon provides additional information on the deformational history of this part of the central California coast.

Seismic Investigation of Eel Submarine Canyon, Humboldt County, California: ABSTRACT

Prior to and during the early 1960s several sparker and conventional survey lines were run across the head of Eel Canyon, which lies 7 miles west of the mouth of the Eel River, Humboldt County, California, and on the adjacent shelf area. The data from the surveys were utilized to discover if a canyon exists below the shelf sediments. Interpretation of the seismic records indicates that a buried canyon does extend shoreward from the present-day canyon. Furthermore, this buried canyon consists of two branches; one branch is oriented toward Arcata Bay in the north Humboldt Bay area and the other branch is oriented toward South Bay in the south Humboldt Bay area. End_of_Article - Last_Page 648------------