Slump Complex Research Articles

Sediment creep on slopes in pelagic limestones: Upper Jurassic of Northern Calcareous Alps, Austria

Slump structures in Upper Jurassic pelagic limestones of the Northern Calcareous Alps were studied using methods of ductile structural geology. The early deformation observed cannot be explained by conventional models for slumping, commonly describing slump complexes with an extending upper and contracting lower part. Instead, the structures suggest distributed bedding-parallel surficial stretching, and folding localized by roll-over normal faulting. The initially isoclinal and recumbent folds are pervasively overprinted by stretching, causing reorientation of fold axes into the downslope direction. Transport of folds separates antiformal and synformal hinges, and the resulting isolated hinges resemble intrafolial folds in metamorphic terranes. Only folds formed late in the process of lithification allow insight in the early stages of fold evolution. We suggest that this type of early deformation represents sediment creep that may be characteristic for slump structures in pelagic carbonates.

Seismic geomorphology of cretaceous megaslides offshore Namibia (Orange Basin): Insights into segmentation and degradation of gravity-driven linked systems

This study applies modern seismic geomorphology techniques to deep-water collapse features in the Orange Basin (Namibian margin, Southwest Africa) in order to provide unprecedented insights into the segmentation and degradation processes of gravity-driven linked systems. The seismic analysis was carried out using a high-quality, depth-migrated 3D volume that images the Upper Cretaceous post-rift succession of the basin, where two buried collapse features with strongly contrasting seismic expression are observed. The lower Megaslide Complex is a typical margin-scale, extensional-contractional gravity-driven linked system that deformed at least 2 km of post-rift section. The complex is laterally segmented into scoop-shaped megaslides up to 20 km wide that extend downdip for distances in excess of 30 km. The megaslides comprise extensional headwall fault systems with associated 3D rollover structures and thrust imbricates at their toes. Lateral segmentation occurs along sidewall fault systems which, in the proximal part of the megaslides, exhibit oblique extensional motion and define horst structures up to 6 km wide between individual megaslides. In the toe areas, reverse slip along these same sidewall faults, creates lateral ramps with hanging wall thrust-related folds up to 2 km wide. Headwall rollover anticlines, sidewall horsts and ramp anticlines may represent novel traps for hydrocarbon exploration on the Namibian margin.The Megaslide Complex is unconformably overlain by few hundreds of metres of highly contorted strata which define an upper Slump Complex. Combined seismic attributes and detailed seismic facies analysis allowed mapping of headscarps, thrust imbrications and longitudinal shear zones within the Slump Complex that indicate a dominantly downslope movement of a number of coalesced collapse systems. Spatial and stratal relationships between these shallow failures and the underlying megaslides suggest that the Slump Complex was likely triggered by the development of topography created by the activation of the main structural elements of the lower Megaslide Complex.This study reveals that gravity-driven linked systems undergo lateral segmentation during their evolution, and that their upper section can become unstable, favouring the initiation of a number of shallow failures that produce widespread degradation of the underlying megaslide structures. Gravity-driven linked systems along other margins are likely to share similar processes of segmentation and degradation, implying that the megaslide-related, hydrocarbon trapping structures discovered in the Namibian margin may be common elsewhere, making megaslides an attractive element of deep-water exploration along other gravitationally unstable margins.

Slope failure of chalk channel margins: implications of an Upper Cretaceous mass transport complex, southern England

The importance of mass transport and bottom currents is now widely recognized in the Upper Cretaceous Chalk Group of Northern Europe. The detailed dynamics and interaction of the two phenomena are difficult to study as most evidence is based on seismic data and drill core. Here, field observations provide evidence for recurring margin collapse of a long-lived Campanian channel. Compressionally deformed and thrust chalk hardgrounds are correlated to thicker, non-cemented chalk beds that form a broad, gentle anticline. These chalks represent a slump complex with a roll-over anticline of expanded, non-cemented chalk in the head region and a culmination of condensed hardgrounds in the toe region. Observations strongly suggest that the slumping represents collapse of a channel margin. Farther northwards, the contemporaneous succession shows evidence of small-scale penecontemporaneous normal faulting towards the south, here interpreted as gravitational settling of the chalk immediately adjacent to the channel margin. Detailed biostratigraphic studies and sedimentological observations provide evidence for at least two discrete collapse events and suggest the slumping to be the result of channel margin oversteepening rather than evidence for a regional tectonic phase. The described example thus serves as an analogue for processes commonly only inferred from subsurface data.

Catastrophic flank collapses and slumping in Pico Island during the last 130 kyr (Pico-Faial ridge, Azores Triple Junction)

The Pico Island constitutes the easternmost sub-aerial domain of a steep WNW-ESE volcanic ridge, which has developed within the Nubia-Eurasia diffuse plate boundary (Azores Triple Junction). The island comprises three volcanic systems, from older to younger: the Topo Volcano, the Fissural System, and the Pico Stratovolcano. From a high-resolution Digital Elevation Model (10m), and new bathymetric, stratigraphic, structural, and high-precision K-Ar data, we reconstruct the main successive stages of growth and partial destruction of the island over the last 200 kyr. We especially concentrate on the central sector of the island, which has recorded gradual movements through slumping and catastrophic flank collapses since ca. 130 kyr. The remmants of the Topo Volcano are partly exposed on Pico's SE flank, and are here dated between 186±5 and 115±4ka. Topo was significantly destroyed by N- and S-directed large-scale flank collapses between ca. 125 and 70ka. On Pico’s N flank, collapse seems to have removed all the unstable material, but in the S the collapse structure is composite, including a major flank collapse and a remnant slump complex that is still active. A first episode of deformation occurred between ca. 125 and 115ka along the master fault of the slump. Between ca. 115 and 69ka, most of the unstable material was removed by a major flank collapse, leaving behind a still considerable volume of unstable material that comprises the active slump. This first collapse was catastrophic and generated a large debris deposit recognized on the high-resolution bathymetry, with a minimum run-out of ca. 17km. The scar was partially filled by volcanic products erupted from volcanic cones developed within the slump depression, and possibly also from the early WNW-ESE Fissural System. Subsequent deformation in the slump area affected in part the filling units, leading to the individualization of secondary curved faults. Younger volcanic products have gradually masked the mass-wasting scars. Unlike the well-known Hilina slump (Hawaii), Pico's slump evolution might be controlled by an active regional tectonics.

The structural evolution of the Messinian evaporites in the Levantine Basin

The Levantine Basin in the South-eastern Mediterranean Sea is a world class site for studying the initial stages of salt tectonics driven by differential sediment load, because the Messinian evaporites are comparatively young, the sediment load varies along the basin margin, they are hardly tectonically overprinted, and the geometry of the basin and the overburden is well-defined. In this study we analyse depositional phases of the evaporites and their structural evolution by means of high-resolution multi-channel seismic data. The basinal evaporites have a maximum thickness of about 2 km, precipitated during the Messinian Salinity Crisis, 5.3–5.9 Ma ago. The evaporite body is characterized by 5 transparent layers sequenced by four internal reflections. We suggest that each of the internal reflection bands indicate a change of evaporite facies, possibly interbedded clastic sediments, which were deposited during temporal sea level rises. All of these internal reflections are differently folded and distorted, proving that the deformation was syn-depositional. Thrust angles up to 14° are observed. Backstripping of the Pliocene–Quaternary reveals that salt tectonic is mainly driven by the sediment load of the Nile Cone. The direction of lateral salt displacement is mainly SSW–NNE and parallel to the bathymetric trend. Apparent rollback anticlines off Israel result rather from differential subsidence than from lateral salt displacement. In the south-eastern basin margin the deposition of the Isreali Slump Complex (ISC) is coeval with the onset of salt tectonic faulting, suggesting a causal link between slumping processes and salt tectonics. The superposition of ‘thin-skinned’ tectonics and ‘thick-skinned’ tectonics becomes apparent in several locations: The fold belt off the Israeli Mediterranean slope mainly results from active strike-slip tectonics, which becomes evident in faults which reach from the seafloor well below the base of the evaporites. Owing to the wrenching of the crustal segments which are bounded by deep-rooted fault lines like the Damietta–Latakia, Pelusium and Shelf Edge Hinge line the setting is transpressional south of 32°N, where the fault lines bend further towards the west. This adds a component of ‘thick-skinned’ transpression to the generally ‘thin-skinned’ compressional regime in the basin. Above 1.5 km of evaporites, a mud volcano is observed with the mud source seemingly within the evaporite layer. At the eastern Cyprus Arc, the convergence zone of the African and the Anatolian plates, deep-rooted compression heavily deformed the base of the evaporites, whereas at the Eratosthenes Seamount mainly superficial compression affecting the Post-Messinian sediments and the top of the evaporites is observed.

Growth and collapse of Waianae Volcano, Hawaii, as revealed by exploration of its submarine flanks

Wai‘anae Volcano comprises the western half of O‘ahu Island, but until recently little was known about the submarine portion of this volcano. Seven new submersible dives, conducted in 2001 and 2002, and multibeam bathymetry offshore of Wai‘anae provide evidence pertaining to the overall growth of the volcano's edifice as well as the timing of collapses that formed the Wai‘anae slump complex. A prominent slope break at ∼1400 mbsl marks the paleoshoreline of Wai‘anae at the end of its shield‐building stage and wraps around Ka‘ena Ridge, suggesting that this may have been an extension of Wai‘anae's northwest rift zone. Subaerially erupted tholeiitic lavas were collected from a small shield along the crest of Ka‘ena Ridge. The length of Wai‘anae's south rift zone is poorly constrained but reaches at least 65 km on the basis of recovered tholeiite pillows at this distance from the volcano's center. Wai‘anae's growth was marked by multiple collapse and deformation events during and after its shield stage, resulting in the compound mass wasting features on the volcano's southwest flank (Wai‘anae slump complex). The slump complex, one of the largest in Hawai‘i, covering an area of ∼5500 km2, is composed of several distinct sections on the basis of morphology and the lithologies of recovered samples. Two dives ascended the outer bench of the slump complex and collected predominantly low‐S tholeiites that correlate with subaerial lavas erupted early during the volcano's shield stage, from 3.9 to 3.5 Ma. Pillow lavas from the outer bench have Pb, Sr, and Nd isotopic values that overlap with previously published subaerial Wai‘anae lavas. On the basis of the compositions of the recovered samples, the main body of the slump complex, as represented by the outer bench, probably formed during and shortly after the early shield stage. To the southwest of the outer bench lies a broad debris field on the seafloor, interpreted to have formed by a catastrophic collapse event that breached the outer bench. A dive within the debris field recovered subaerially derived volcaniclastic rocks; analyzed glasses are tholeiitic and resemble early shield stage compositions. The breach may have then been filled by slumping material from the main volcanic edifice. Finally, atop the northern main body of the slump is a rotated landslide block that detached from the proximal part of Ka‘ena Ridge after the volcano's late shield stage (3.2 to 3.0 Ma). From the inner scarp of this block we recovered subaerially erupted tholeiitic pillow breccias and hyaloclastites that are systematically higher in alkalis and more fractionated than those collected from the outer bench. These rocks correlate compositionally with late shield‐stage subaerial Kamaile‘unu lavas. None of the collected slump complex samples correlate with alkalic subaerial postshield lavas. Volcaniclastic rocks and glass disseminated in pelagic sediment, collected from north of Ka‘ena Ridge, originated from Wai‘anae's postshield stage and Ko‘olau's shield stage, respectively.

Slope-instability processes caused by salt movements in a complex deep-water environment, Bryant Canyon area, northwest Gulf of Mexico

Halokinetic and slope-instability processes have sculpted numerous morphological features on the flanks of the intraslope basins in the Bryant Canyon area. High-resolution geophysical data and long sediment cores (as much as 20 m [66 ft] long) were used to define the time and spatial evolution of sediment failures and their relationship to halokinetic processes. Two episodes of increased salt-tectonic activity are defined: (1) The first acted at the beginning of interglacial oxygen isotope stage 5 as salt adjusted to the abandoned environments of the Bryant and Eastern Canyon systems, and (2) the second occurred during the last glacial period and is characterized by the seaward propagation of salt masses. Three types of slopes are recognized in the intraslope basins: (1) highly inclined slopes with low-relief morphologic features resulting from shallow, translational slump complexes, (2) highly inclined slopes with high-relief morphologic features resulting from deep, rotational slump complexes, and (3) highly inclined slopes dissected by high-relief canyonlike landslide troughs resulting from channelized rotational slumps. The first two slope types occur mainly on the northern flanks of the basins, whereas the third type occurs on the southern flanks. We propose that the slump complexes on types 1 and 2 slopes were triggered by the oversteepening of the flanks by the seaward mobilization of underlying salt masses. The channelized rotational slumps on type 3 slopes are interpreted to result from the development of salt diapir bulges that lead to locally increased gradients on the basin flanks. Most of the sediment failures have been transformed into debris flows and led to the most recent phase of infilling of the basin floors.

Large-scale mass wasting on the north Spitsbergen continental margin, Arctic Ocean

Closely spaced, single-beam bathymetric and side-scan sonar investigations on the northern slope of the western Svalbard insular platform have revealed the presence of a Late Quaternary slump complex forming a hanging-wall slump canyon near the head of the Malene Bukta (Malene Bay) bathymetric embayment in the northern continental margin. Repeated slump erosion may be responsible for development of this young feature and the Malene Bukta Embayment. Focusing of the slumping may be due to the trapping of gas at shallow sea-floor depths by gas hydrate, with the consequent formation of subjacent gas-rich, low shear-strength decollement zones. Faults have likely controlled the upward migration of gas into the younger sedimentary prism.

Sediments and sedimentation at the NE Faeroe continental margin; contourites and large-scale sliding

High-resolution seismic profiles of the NE Faeroe continental margin show a wedge-shaped sedimentary sequence of up to 2 km thickness on top of lower Tertiary basaltic basement. The sedimentary section can be divided into four major seismic sequences separated by unconformities. The uppermost upper slope deposit is interpreted as a contourite which formed later than the Mid-Miocene by the southerly flow of bottom water along the margin of the SW Norwegian Sea, which is subsequently deflected to the east by the NE Faeroe continental margin and Fugloy Ridge. A scoured channel about 85–90 m deep at about 1000 m water depth associated with the contourite partially follows and modifies a preexisting slump scar. Large-scale slumping and sliding of the middle and lower continental slope below 1500 m water depth have affected sediments of presumably Miocene, Pliocene and Quaternary age. A TOBI deep-tow side-scan sonar mosaic composed of ten lines recorded in 1995 semi-parallel to the slope, shows that mass flow deposits are partially covered by recent contourite sediments on the middle slope. The slump complex at the middle/lower continental slope is younger and has a steep, 250–300 m, irregular, deep main scarp and very large, sometimes rotated blocks near the main scarp. At the base of the slide, numerous 10–15 km long, narrow tracks with individual blocks at the end are found. Several types of debris flows have been mapped, some with a longitudinal flow fabric.

Large submarine slides on the NE Faeroe continental margin

Abstract High-resolution seismic profiles of the NE Faeroe margin show large-scale slumping and sliding of the middle and lower continental slope, affecting sediments of presumed Miocene, Pliocene and Quaternary age. Mass-flow deposits on the upper slope are partially covered by more recent deposits, presumed to be contourites. A TOBI deep-tow side-scan sonar mosaic, in combination with deep-towed penetrating echosounder results, shows that the slump complex on the upper slope consists of a buried slide scar, bottleneck slides, debris-flow lobes and a number of shallow slides. Sliding at the middle and lower continental slope seems more recent and shows a steep, irregular main slump scar and very large, intact, angular blocks. The base of the slide at the lower continental slope shows numerous narrow and diverging tracks, 10–15 km length, that end at individual blocks. Several types of debris flows have been mapped, some with longitudinal flow fabrics.

Late Pleistocene landslide-dammed lakes along the Rio Grande, White Rock Canyon, New Mexico

Massive slump complexes composed of Pliocene basaltic rocks and underlying Miocene and Pliocene sediments flank the Rio Grande along 16 km of northern White Rock Canyon, New Mexico. The toe area of at least one slump complex was active in the late Pleistocene, damming the Rio Grande at least four times during the period from 18 to 12 {sup 14}C ka and impounding lakes that extended 10-20 km upriver. Stratigraphic relationships and radiocarbon age constraints indicate that three separate lakes formed between 13.7 and 12.4 {sup 14}C ka. The age and dimensions of the ca. 12.4 ka lake are best constrained; it had an estimated maximum depth of {approx}30 m, a length of {approx}13 km, a surface area of {approx}2.7 km{sup 2}, and an initial volume of {approx}2.5 x 10{sup 7} m{sup 3}. The youngest landslide-dammed lakes formed during a period of significantly wetter regional climate, strongly suggesting that climate changes were responsible for reactivation of the slump complexes. We are not certain about the exact triggering mechanisms for these landslides, but they probably involved removal of lateral support due to erosion of the slope base by the Rio Grande during periods of exceptionally high flood discharge or rapid incision;more » increased pore pressures associated with higher water tables; higher seepage forces at sites of ground-water discharge; or some combination of these processes. Seismic shaking could also have contributed to triggering of some of the landslides, particularly if aided by wet antecedent conditions. 54 refs., 19 figs., 3 tabs.« less

Lacustrine chronology links late Pleistocene climate change and mass movements in northern New Mexico

Well-dated lacustrine deposits in northern White Rock Canyon, New Mexico, record damming of the Rio Grande by at least four separate failures of a slump complex between about 17.5 and 12.4 ka ({sup 14}C), linking mass movements to a period of rapid climate change in the western United States. Failure of metastable slumps probably resulted from removal of lateral support during down-cutting and erosion by the Rio Grande and from a decrease in resisting forces due to increased pore pressures. Our chronology suggests that the lake that formed between 17.5 and 15.0 ka may record effects of both glacial melt and pluvial activity (mainly enhanced rainfall); the youngest lake (neary 12.4 ka) may record pluvial runoff; and the intermediate lakes (13.7 to 13.1 ka) may record pluvial and minor melt-water activity. We have not found lacustrine deposits younger than about 12.4 ka. The record of geomorphic response along the Rio Grande suggests that late Pleistocene climatic changes may have triggered similar mass movements elsewhere in the southwest. 27 refs., 4 figs.

Slump structures in the Late Tertiary of the Porcupine Basin, offshore Ireland

A large Late Tertiary slump complex from the Porcupine Basin, offshore western Ireland is described. It occurs in deep water, probably mud-prone, sediments on the south-west margin of a thermal subsidence basin overlying a pre-Cretaceous synrift succession. The slump consists of head, body and toe regions, each with diagnostic internal characteristics. The head region contains extensional features, whereas the toe region suffered compression. The main body acted as a relatively rigid unit in the southern zone of the slump complex, while in the north it suffered gravity-driven internal duplex thrusting. A series of elongate channels, infilled with material eroded from the crestal parts of the toe and body regions, comprise a prominant chute zone. Local reworking of the basinward edge of the toe region also occurred. A period of local turbidite deposition towards the centre of the basin appears to be coeval with the slumping. The slump movement was probably influenced by a complex combination of fault-induced earthquake movement, facies and slope variations and by the local presence of an overpressured mud horizon which acted as a décollement surface.

Use of high-frequency (3.5–12 kHz) echograms in the study of near-bottom sedimentation processes in the deep-sea: A review

During the past 15 years in creasing numbers of studies have demonstrated that continuous echograms recorded on high-frequency (3.5–12 kHz) precision depth recorders aboard surface ships provide a valuable tool for the study of near-bottom sedimentation processes on the deep-sea floor. By constructing an echo character map of the various types of bottom echoes recorded in a region and combining this information with additional data (cores, bottom photographs, nephelometer, hydrographic and temperature), it is often possible to determine the types and regional influence of the various sedimentation processes (e.g., contour currents, turbidity currents, slumps and debris flows) which have shaped that region. The types and distributions of bottom echoes from most of the basins of the Atlantic as well as for several regions of the western Indian Ocean and the western Pacific have now been classified and mapped on a regional scale. Each of these regions returns several discrete types of echoes; most types are similar from basin to basin as well as ocean to ocean. In this paper a few examples of previous echo character studies are reviewed in order to illustrate how high-frequency echograms can be utilized to study near-bottom processes. (1) Regional echo-character maps often reveal the distribution and abundance of sediments deposited by down-slope processes such as turbidity currents. Three echo types which are widespread throughout most basins of the world show a qualitative correlation with the relative abundance of coarse, bedded turbidites (silt, sand, and gravel) in the upper few meters of the sea floor: (a) distinct echoes with continuous sub-bottoms are recorded from regions with little or no coarse sediment; (b) regions with moderate amounts of silt/sand return semi-prolonged echoes with intermittent or discontinuous sub-bottoms; and (c) regions with large amounts of silt/sand return very prolonged echoes with no sub-bottoms. (2) A wide variety of hyperbolic bottom echoes are recorded from regions of the sea floor where sedimentation is controlled by deep thermohaline flow (contour currents). These hyperbolic echoes are returned by erosional/depositonal bed forms such as non-migrating sediment waves and erosional furrows. Such regions of hyperbolic echoes are often clearly distributed beneath strong near-bottom thermohaline currents such as the Antarctic Bottom Water. Thus the distributions of these types of echoes often show the regional influence of contour currents. In addition to the hyperbolic echoes, a variety of undulating, quasi-hyperbolic echoes with shifting, non-conformable or truncated sub-bottoms are also often recorded. These bedforms appear to be migrating sediment waves and are generally observed in regions affected by contour currents. In some cases, however, it appears that turbidity currents also form such migrating waves. (3) Echograms have also been of great value in revealing the presence and distribution of mass-wasting processes such as slumps, slides and debris flows. Such deposits generally appear as convex, lense-shaped transparent layers which return a fuzzy, prolonged bottom echo. Often undisturbed, well-stratified sediments are visible below the deposits as are scarps and displaced blocks at the head of the slump complex. Echograms have revealed slump/debris-flow complexes ranging from < 1 to >30,000 km 2 in size. High-frequency echograms are thus an extremely valuable tool for studying the marine geology, sediment types, and near-bottom sedimentation processes active on the sea floor. Although widely spaced data lines in many regions can only define various sedimentary processes and bedforms on a broad regional scale, such data often indicate the best locations for concentrating more detailed and quantitative studies using closely spaced surveys and sophisticated instrument packages (e.g., Deep-tow, GLORIA, submersibles, etc.). Often only the detailed studies such as these can reveal the true shapes, origins, and hydrodynamic setting of various bedforms which return specific echo types on surface-ship echograms. In addition, most echocharacter studies to date have been qualitative. In the future more sophisticated, quantitative studies will be necessary in order to fully interpret and utilize the information contained in surface-ship echograms.