This is part of the How To…series on describing sedimentary rocks – mass transport deposits in outcrop.
The images shown here illustrate some of the sedimentary facies, the soft-sediment deformation structures, and associated turbidite facies commonly encountered in MTDs.
Mass Transport Deposit, or MTD is the term given to slumps, slides and debris flows, mostly generated on relatively high angle slopes between the shelf or platform margin, and deep-water settings at the base-of-slope and beyond. The term is generally reserved for sediment packages that move and deform en masse under the influence of gravity, commonly in multiple events. Note that debris flows are included because many – most involve cohesive sediment mixes, where the mechanics of emplacement are akin to plastic flow. Turbidites (and turbidity currents) are not included because they evolve from single event turbulent suspensions of sediment (viscous fluids). This may seem a bit arbitrary, given that some debris flows lack cohesion, develop stratification and may also represent single depositional events (a couple of examples shown below). However, it is also generally recognised that debris flows and turbidity currents represent a continuum of depositional processes.
There is a close association between MTDs and autochthonous slope deposits (mud-dominated) and turbidites in submarine fans. MTD packages commonly overlie undisturbed turbidite assemblages, and in turn are overlain or draped by them. Slump, slide and creep components of MTDs generally consist of deformed turbidites and related depositional assemblages.
MTDs develop via a range of emplacement mechanisms and mechanical processes; most sediments will be ‘soft’, unconsolidated or only mildly so, and have high interstitial fluid contents (usually seawater). Sedimentary layers may bend and fold as hydroplastics under modest strain rates, or break like brittle materials under high strain rates (faults and fractures). Liquefaction is common, where sediment becomes fluidal. All these mechanisms may occur in the same structure. The deforming sediment package may also generate sediment gravity flows such as debris flows and turbidites.
There are many excellent publications that detail MTDs; their formation, facies associations, and their significance in sedimentary basin evolution and tectonics. A few of my favourites are listed below.
More images of MTDs and related facies can be accessed in the:
The first two diagrams show some basic sediment descriptors and terminology, and a typical stratigraphic column drawn from outcrop data. The third graph shows the basic Stress-Strain Rate rheology for different flow types. These are your starting points for describing and interpreting sedimentary rocks and sedimentary structures in outcrop, hand specimen, and core.
P.R. King, B.R. Ilg, M. Arnott, G.H. Browne, L.J. Strachan, M. Crundwell, and K. Helle. 2011. Outcrop and seismic examples of mass transport deposits from a Late Miocene deep-water succession, Taranaki Basin, New Zealand. In R.C. Shipp, P Weimer, and H.W. Posamentier Eds.), Mass-Transport Deposits in Deepwater Settings. SEPM Special Publication Volume 96. Fantastic coastal exposures of MTDs, along the North Taranaki coast.
T. Mulder, and J. Alexander; 2001, “The physical character of subaqueous sedimentary density flows and their deposits”; Sedimentology: 48, 269-299
H.W. Posamentier and O.J. Martinsen. 2011. The character and genesis of submarine Mass Transport Deposits: Insights from outcrop and 3D seismic data. In R.C. Shipp, P Weimer, and H.W. Posamentier Eds.), Mass-Transport Deposits in Deepwater Settings. SEPM Special Publication Volume 96.
R.C. Shipp, P Weimer, and H.W. Posamentier Eds.), 2011. Mass-Transport Deposits in Deepwater Settings. SEPM Special Publication Volume 96 Most of the papers in this volume are free access.
D. Stow and Z. Smillie, 2020 Distinguishing between deep-water sediment facies: Turbidites, Contourites, and Hemipelites. Geosciences, v. 10,. Open Access.
The Atlas, as are all blogs, is a publication. If you use the images, please acknowledge their source (it is the polite, and professional thing to do).
Stratigraphy is a cornerstone (sic) of the earth sciences. With it, we unravel earth’s history, the sequence of events and processes that have given us the world we live in. It is the story, written in rocks and fluids, of the physical, chemical, and biological world. Perhaps we should now include the social and psychological spheres of our existence, as part of the latest geological period, the Anthropocene – layer upon layer of human thought, actions, consequences.
Unconformities are a fundamental part of Stratigraphy. They are that part of the rock record in which time and rock are missing – periods of time in which rocks either did not form, or if they did form were subsequently removed. In both cases, the “missing” information tells us that something happened; the ‘something’ may have been local, confined to our own backyard, or of global extent such as extinction events, the construction of mountains or destruction of oceans. So, geologists who find unconformities don’t throw up their hands in despair; they rub their hands in glee at the promise of so many possible explanations.
What better example to begin with than one of James Hutton’s classic localities on Arran, west Scotland (image above). This is the unconformity at Lochranza where Carboniferous sandstone overlies Late Precambrian Dalradian schist. The unconformity here represents about 240 million years of time, seemingly missing, and yet it also represents a period of mountain building, where deeply buried metamorphic rocks were uplifted many kilometres, exposed and worn down by the vagaries of ancient weather systems, and buried by sand shed from the rising mountains. This tale of the evolving earth is encapsulated in the seemingly innocuous contact between the two different groups of rock.
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An uncluttered view of Hutton’s unconformity at Lochranza (same location as the image above)
Basal conglomerate of the Carboniferous succession that onlaps Dalradian schist at Lochranza. Hammer is at the unconformity.
The unconformity between Archean metavolcanic and plutonic rocks at Cobalt, Ontario, and the Proterozoic Gowganda Formation, is marked by a regolith of blocky granodiorite and granite, that is overlain by diamictites deposited during Early Proterozoic glaciation.
Portskerra: Old Red Sandstone (ORS) on Moine schists, north Scotland
The ORS is a mixed bag of sedimentary rocks, mostly Devonian, but extending into the late Silurian and early Carboniferous. Their importance lies in the direct association with Caledonide tectonics, where sediment was shed from the rising mountains into adjacent foreland basins. The ORS is sometimes compared with the younger Molasse foredeep successions of Europe. The unconformity at Portskerra is an erosional surface, where the ORS fills paleotopographic lows and drapes the intervening highs.
Numbered sites refer to the thumbnail images below.
Sites 1 (left) to 4 as shown in the general view above. Moine rocks were exposed during Caledonian uplift and subsequent erosion that removed many kilometres of overlying rock. Much of this sediment was deposited as ORS.
A coarse ORS breccia, consisting almost entirely of fragmented Moine schist, overlies the unconformity.
The ORS beds contain shallow trough crossbeds and ripples, and occasional pebble-cobble lags that mark the base of channels.
Rippled sandstone in beds a metre above the unconformity.
Typical, strongly foliated Moine schist.
The NW coast, towards Portskerra and the distant Orkney archipelago.
Loch Assynt, northwest Scotland
Lewisian gneisses and migmatites (Archean) are overlain unconformably by Torridonian sandstone (Proterozoic). The roadcut adjacent Loch Assynt is west of the Moine Thrust complex; both rock assemblages are part of the ancient Laurentian continental block. The three thumbnail images below are from the same general location. At this locality there is subdued paleotopographic relief on the unconformity.
Expedition Formation, Canadian Arctic
The Campanian to Middle Eocene Eureka Sound Group on Ellesmere and Axel Heiberg Islands represents the last gasp of sedimentation in a thermally subsiding Sverdrup Basin. In the central part of the basin, The Expedition Formation contains two stratigraphic sequences separated by a disconformity where most of the Maastrichtian is missing. Along the basin margins Sequence 1 is commonly missing such that Sequence 2 onlaps Paleozoic bedrock.
The Campanian-Lower Paleocene unconformity at Hot Weather Creek, Ellesmere Island. Throughout the basin, the base of the Paleocene is characterised by thick quartz-rich sandstones deposited in estuaries, sandspits and bars.
Lower Paleocene Sequence 2 along the basin margins commonly onlaps Paleozoic rocks – here Ordovician carbonates. The earliest sediments infilled a karst paleotopography. Mt. Moore, Ellesmere Island.
This Lower Paleocene – Ordovician unconformity has a well developed regolith in the carbonates. Mt Moore area.
Left: Lower Paleocene Sequence 2 on Devonian sandstone-limestone. The trace of the unconformity coincides with the stream (lower right). Right: Lower Paleocene Sequence 2 on Permian limestones-grainstones near Canon Fiord. The trace of the unconformity coincides with the stream (center).
Buchanan Lake Formation, Canadian Arctic
This is the youngest formation in the Eureka Sound Group. Its deposits record inversion and dismembering of Sverdrup Basin by thrust-dominated tectonics during the Middle Eocene. Deposition took place in several foredeeps, that also were involved in the deformation.
Syntectonic, Middle Eocene Buchanan Lake strata disconformably overly Lower-Mid Eocene delta deposits (Iceberg Bay Fm, Sequence 4). Sediment was derived from uplifted Late Paleozoic and Triassic rocks. They were subsequently overthrust by Late Paleozoic anhydrite and Permian mudstone-sandstone. North of Whitsunday Bay, Axel Heiberg Island.
Syntectonic Buchanan Lake conglomerate (brown hues) overlies unconformably Triassic sandstone. Stang Bay, Axel Heiberg Island.
New Zealand Paleogene-Neogene basins
The Plio-Pleistocene Wanganui Basin occupies a position between the Hikurangia subduction zone and the Late Cretaceous – Miocene rift-passive margin succession comprising Taranaki Basin. Along its eastern margin, Wanganui Basin strata onlap much older greywacke-greenschist basement, shown above at Otupae Station (about 30km SE of Waiouru, along the west flank of the Ruahine Ranges.
Marine terraces eroded into Middle Pliocene Tangahoe Mudstone are exposed on the south Taranaki coast. Here there are excellent examples of shallow, shore platform channels and potholes, filled by pebbly sand of the Rapanui Formation. Pollen assemblages indicate that shallow marine-beach and dune deposition took place during interglacial conditions in the late Pleistocene.
The Late Eocene-Oligocene Te Kuiti Group (New Zealand) contains cool-water carbonates and associated mudrocks, that accumulated on a broad platform during a period of relative crustal stability. The deposits gradually onlapped eroded greywacke basement (Torlesse-Waipapa terranes), as shown in this quarry, west of Te Kuiti town. The limestone unit is the Otorohanga Limestone. This stratigraphic pinchout is unconformably overlain by Early Miocene, deeper water Mahoenui mudstone.
Waitemata Basin
The Lower Miocene Waitemata Basin extends from greater Auckland into Northland, New Zealand. The fill is dominated by turbidites deposited at bathyal water depths. The basin mainly overlies Mesozoic greywacke. In what is a remarkable contrast in water depth, the basal few metres consists of conglomerate, fossiliferous sandstone and limestone that were deposited in shallow shelf and pocket beach settings. The pre-Miocene surface has considerable paleotopographic relief. Along the Early Miocene coastline this was manifested as greywacke islands, sea cliffs and sea stacks.
The cartoon below shows a rough reconstruction of the Early Miocene environment (drawn more than 30 years ago). Panels a and b show shoreline, beach, subtidal facies, complete with cliff rock-falls and landslides. Panel c depicts the early stages of draping and blanketing by bathyal turbidites and debris flows.
The unconformity in the shore platform below Leigh Institute of Marine Sciences. Intensely deformed greywacke below the red line, is overlain by flat-lying, shallow water calcareous and fossiliferous sandstone. Fossils include abundant barnacles, bivalves (including large oysters), gastropods, solitary corals, bryozoa, calcareous algae (Lithothamnion rhodoliths), foraminifera, and trace fossils.
The unconformity at Matheson’s Bay. The steep paleosurface (just left of hammer) is overlain by angular boulders and cobbles of greywacke. Some boulders contain evidence of pre-Miocende weathering.
Paleo-seastacks of greywacke that, following rapid subsidence to bathyal depths, were draped by turbidites. Left: North end of Matheson’s Bay. This sea-stack has remnant pholad borings (bivalves that bore into hard rock). Right: Omana Bay, south Auckland. Here, drape folds over greywacke sea-stacks have been exhumed in the modern shore platform.
Panorama of lower Waitemata Basin strata, looking south from Takatu Point. The unconformity on the small island is overlain by boulder conglomerate and well bedded calcareous sandstone.
Kariotahi, Pleistocene dune-barrier bar complex
There are several very large barrier island-bar systems along the North Island west coast. during the Pleistocene, they effectively straightened the coastline, blockading harbours and estuaries with shallow marine and subaerial dune sands, with entrance and egress of water through narrow tidal inlets.
The coastal exposure at Kariotahi beach, west of Auckland city, contains a nice example of an ancient valley cut into older dune sands, that was subsequently filled with a new generation of dune sands and stream deposits, only to be exhumed much later in the Pleistocene. The unconformity between the original valley margin and the infilling dunes is shown below. The unconformity also shows signs of old soils and weathering.
The valley margins (outlined) are overlain by younger dune sands. The present valley has cut into both of generations of Pleistocene dunes. Kariotahi, west Auckland.
Closer views of the Pleistocene valley unconformity. The older (brown) deposits occur below the steeply dipping surface; the younger dunes above. The irregular, rust-coloured resistant layers are iron-pan; iron oxides that have precipitated during groundwater seepage. Kariotahi, west Auckland.
Typical dune cross bedding in the younger valley fill. The muddy, concave layer near the bottom of the image is thought to have formed in an interdune pond. Kariotahi, west Auckland.
Syntectonic sediments – sediments associated with active tectonism
The Atlas, as are all blogs, is a publication. If you use the images, please acknowledge their source (it is the polite, and professional thing to do).
This category is a bit different to the other Atlas collections. It does not refer to a specific environmental state, like fluvial or submarine fan, but to erosion, deposition, and deformation associated with active tectonics. This includes uplift, folding, faulting, the erosion of landscapes created by each of these, and subsequent deposition. Syn-tectonic deposits may be constrained in time to specific events (e.g. faulting), or to periods of mountain building, or other modes of deformation along plate boundaries. Classic examples include the Molasse of central Europe, and basins outboard of the Cordilleran fold and thrust belt in western Canada.
Most of the images here are inferred to have been associated with specific tectonic events. Conglomerate facies are common in fluvial and alluvial settings in close proximity to active faults and uplifts (Eurekan Orogeny in the Canadian Arctic, Alberta Foreland Basin, evolving transform faults in Ridge Basin, and active extension – strike slip faulting in Death Valley), to deep marine turbidites that were also influenced by active (Waitemata) basin tectonics. There’s also a few shots of coastal exposure of an active accretionary prism on New Zealand’s east coast.
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The images:
Diabase sills intrude Jurassic through Permian successions in the Arctic Sverdrup Basin. Unroofing of these older rocks during the Eurekan Orogeny (climaxing about mid Eocene) provided large volumes of coarse sediment to alluvial fans, braided and high sinuosity rivers. In these two examples the Stolz Thrust is at the base of slope, with tectonic transport to the right (east). Here, the older rocks have been thrust over the syntectonic deposits (Buchanan Lake Fm.). Axel Heiberg Island.
Stolz Thrust at Geodetic Hills (the site of the Middle Eocene Fossil Forest). Left: Diabase sills are thrust over syntectonic conglomerate. Right: Upturned and sheared Triassic rocks in the hanging wall; the fault trace is located in the depression (upper left).
Detail of shear and boudinage of Triassic sandstone-mudstone in Stolz Thrust zone, Geodetic Hills. Location is the right image above.
Stolz Thrust, with Permo-Triassic rocks in the hanging wall (including slivers of anhydrite), over middle Eocene syntectonic conglomerate and sandstone (Buchanan Lake Fm.) North of Whitsunday Bay, Axel Heiberg Island. Coarse-grained sediment was shed from the uplifted older rocks, and subsequently over-ridden by continued thrusting.
Intensely deformed anhydrite in the hanging wall of Stolz Thrust, Axel Heiberg Island. It is likely anhydrite debris was shed with the coarse sediment, but did not survive the first cycle of transport and deposition.
Left: Syntectonic conglomerate (Buchanan Lake Fm.) over-thrust by Ordovician limestone (that also contributed debris to the conglomerate), Franklin Pierce Bay, Ellesmere Island. Right: Syntectonic conglomerate-sandstone braided river deposits that accumulated outboard of faulted uplifts. Boulder Hills, Ellesmere Island.
Panorama of Jurassic-Triassic rocks above Stolz Thrust over syntectonic conglomerate at Geodetic Hills (Buchanan Lake Fm.), Axel Heiberg Island (left), and a compositional unroofing sequence in conglomerate (right). The lighter coloured deposits near the base of conglomerate were derived from Jurassic sandstones. the progressive change upward to darker brown conglomerate reflects access to deeper, older Triassic sandstone and diabase sills in the eroding hanging wall.
Aerial views of Middle Eocene, syntectonic alluvial fan – braidplain conglomerate outboard of thrusted uplands. Left: Emma Fiord, Ellesmere Island. Right: Geodetic Hills, Axel Heiberg Island.
Small thrust fault through proximal, bouldery, syntectonic conglomerate, Geodetic Hills, Axel Heiberg Island. Hammer lower center. Boulders to 50cm wide.
Syntectonic boulder-cobble (mostly diabase) proximal alluvial fan deposits, with scattered sand wedges, Geodetic Hills, Axel Heiberg Island. At the time of deposition, they would have been close to the uplifted source rocks.
Thick, crudely bedded debris flows and sheet flood alluvial fan conglomerates, probably close to sediment source. Diabase clasts up to a metre wide. Middle Eocene, Geodetic Hills, Axel Heiberg Island.
Lower Paleozoic carbonates have been thrust over Upper Cretaceous foreland basin strata (approximately east-dipping bedding visible at top right), Kananaskis, Alberta Basin. The U. Cretacous units accumulated during an earlier phase of thrusting, farther west, and then subsquently over-ridden.
Left: older foreland basin deposits (Kootenay Gp), overlain by conglomerate, shed from a renewed phase of thrusting and folding (resistant units at top) – The Lower Cretaceous Cadomin Fm. interpreted variously as braidplain, alluvial fan, and pediment. Right: Trough crossbedded, pebbly sandstone, Cadomin Fm.
Lower Cretaceous foreland basin strata involved in a later phase of thrusting. View is to the north of Highwood Pass. Lewis Thrust charges down the valley beyond. Front Ranges, Alberta Foreland basin.
Iconic views of the Front Ranges, Kananaskis. Left: Upturned Lower Paleozoic carbonates and sandstones, and in the valley, recessive Jurassic-Lower Cretaceous foreland basin strata. Right: Probably one of the most photographed fold pairs in Canada – Lewis Thrust terminates at the base of this fold pair. Kananaskis Highway.
The northern segment of Lower Miocene Waitemata Basin (Auckland) developed atop a moving slab of obducted lithosphere – the Northland Allochthon. The Allochthon, now fragmented, consists of ophiolite (including possible seamounts), marls, terrigenous clastics and limestones. Allochthon rocks, like those shown here (Algies Bay) commonly are intensely deformed. Movement of the Allochthon is implicated in some of the syn-sedimentary – weak rock deformation in Waitemata Basin itself. This view shows thrusted marls, north of Algies Bay.
Examples of intense shearing in Northland Allochthon marls and mudstones. Left: multiple generations of fracturing. Right: Boudinage and shear of siderite nodules in the mudrocks (above). Algies Bay, Auckland.
Sedimentary dyke through Northland Allochthon mudrocks. The dyke contains fragments of Lower Miocene Waitemata Basin sandstone and mudstone, attesting to the dynamic relationship between the two. The dyke in turn is fractured by later deformation. Algies Bay, Auckland.
Examples of soft and weak-rock deformation – slumping in Waitemata Basin turbidites, possibly dynamically linked to Northland Allochthon deformation. Left: Thrust-folds near Waiwera. Right: Recumbent isoclinal folds, and rotated boudins in sandstone, Army Bay.
Intensely folded and faulted turbidites above an undeformed glide plane, south of Orewa Beach, possibly dynamically linked to Northland Allochthon deformation.
Violin Breccia, Ridge Basin, California. fault plane talus, and or debris flows, adjacent San Gabriel Fault, a Late Miocene splay of the evolving San Andreas transform. Breccia clasts are mainly gneiss. The breccia extends many km along the fault strand, but only about 2km down-dip into the basin.
Left: Lacustrine shoreface – delta sandstone, and stringers of Violin Breccia. Right: detail of the left image, showing crossbedded sandstone and grit-pebble sized material from the Violin Breccia. Ridge Basin, California.
Left: down dip view of dissected Panamint Range alluvial fan, Death Valley. The coarse fan deposits reflect erosion of the uplifted Panamint metamorphic core complex. The fan canyon-head is shown in the right image.
Hole in the Wall, Death Valley. Here, lacustrine sands and muds contain sporadic debris flows (resistant unit). Right image shows debris flow scours. They accumulated during Miocene-Pliocene extension that resulted in Death Valley basin subsidence. Subsequent deformation took place as the Furnace Creek strike-slip fault created an en echelon stack of fan deltas and associated lacustrine deposits.
Hole in the Wall, Death Valley. Discordant packages of lacustrine shoreface and prodelta mudstone-sandstone, and pebble conglomerate. The debris flow in the images above can be traced from the lower right to the central part of the cliff.
Hole in the Wall, Death Valley. Lacustrine silt and clay, in prodelta or basin floor. The right image shows small grit-filled scours from periodic influxes down the prodelta slope.
Coastal exposure of an active accretionary prism, Waimarama, eastern North Island. The accretionary prism here consists of telescoped slivers of sea-floor sediment, above Hikurangi subduction zone. Left: Thrusts and associated shearing in bentonitic mudrocks, sandstones, and marls (arrows), looking north. Right: Looking south at similar lithologies, and the modern expression of sedimentation associated with the deformation – a cobble beach.
Closer view of thrusts and intensely sheared mudstone-sandstone melange, Waimarama, eastern North Island.
Sheared and stretched sandstone (left), and sheared bentonitic melange (right), within thin, accretionary prism thrust sheets, Waimarama, eastern North Island.
A lozenge of resistant cherty mudstone within the softer bentonitic melange, detached during thrusting, Waimarama, eastern North Island.
Deformation of sediment while it is soft or semi-consolidated
The Atlas, as are all blogs, is a publication. If you use the images, please acknowledge their source as indicated below (it is the polite, and professional thing to do).
Deformation of sediment while it is soft or semi-consolidated, is common. The rock record is replete with folded and slumped strata, strata that slid in coherent packages, strata that lose their coherence during liquefaction or fluidization, displacement by faults where soft or plastic sediment seemingly acts like its brittle rock counterparts, or dyke-like injections where sediment is locally overpressured.
The term syn-sedimentary tends to be used rather loosely, as deformation that takes place during or soon after deposition; the ‘soon’ is the loose part of this broad definition. Sediment begins to compact almost immediately following deposition, where framework grains begin to move closer together. Interstitial water is expelled, and this process in itself can deform the sediment. Water expulsion in compacting deeper strata can also increase local pore pressures that in turn reduce sediment shear strength. Other common triggers are gravitational instability and seismic tremors. Coastal storm surges can produce instability in sea floor sediments caused by rapid fluctuations in pore pressure.
This link will take you to an explanation of the Atlas series, the ownership, use and acknowledgment of images. There, you will also find links to the other categories.
Click on the image for an expanded view, then ‘back page’ arrow to return to the Atlas.
Five of the images shown in this tranche also appear in the Submarine fans and channels category; there are several more examples of soft- or syn-sedimentary structures on the Submarine fans page.
Sediment deposited rapidly will have a high water content. Immediately following deposition and incipient compaction, excess water will be forced towards the sea floor. Muddy sediment, like a turbidite will present natural permeability barriers to water expulsion, resulting in either deformation of laminae and other structures, or formation of dewatering pipes, or pillars. Water escaping at the sea floor will deposit fine sediment that it has picked up along its trajectory, and deposit this as small mud-silt pimples or volcanoes. This example (Omarolluk Fm, Proterozoic, Belcher Islands) shows the mud volcanoes on bedding, and in cross-section, thin whitish pillars that represent water escape routes – they are white because the muddy matrix has been removed.
Dewatering pillars can occur in sheets within single beds, in this case a Proterozoic turbidite. The position of sheets within a bed is probably associated with permeability barriers. Omarolluk Fm. Belcher Islands (1.8-1.9 billion years). The black patches are calcite concretions; pillars pass through the concretions.
Calcite concretions in turbidites, Omarolluk Fm, Belcher Islands, formed during very early stages of burial. This very early stage of diagenesis was shallow enough for the concretions to be reworked in submarine channels.
Dish structures are another product of dewatering. Water that escapes though narrow conduits, will drag sand laminae upwards; laminae between adjacent dewatering pillars will appear concave upwards, or dish-shaped. Left is from Lower Miocene Waitemata Basin, Musick Point; Right is from the Rosario Group, San Diego.
Fluvial trough crossbeds here have been turned on end during early compaction and dewatering, producing what are commonly called ball and pillow structure. Proterozoic Loaf Fm. Belcher Islands.
Ripples and bed contacts in this sandstone-mudstone unit have been deformed by liquefaction, and in places pulled apart. Evidence from nearby strata indicates a possible seismic event has jostled these beds (see image below). Fairweather Fm, Belcher Islands, about 2 billion years old.
This sandstone dyke terminates in, and probably breached shallow intertidal deposits. The surrounding layers have been dragged upwards during sand intrusion. Structures like this commonly form during earthquakes when soft sediment is liquefied. Fairweather Fm, Belcher Islands, about 2 billion years old.
Detached load casts in laminated, locally rippled volcaniclastics. Flaherty (volcanic) Fm, Belcher Islands, about 2 billion years old.
A sandstone dyke that originated from deformed – slumped sandy turbidites; the dyke intrudes a slope mudstone-siltstone succession, and extends about 40m up the exposed face. Both the slumping and sandstone intrusion are thought to have formed during a seismic event. Upper Jurassic, Tsatia Mt, Bowser Basin.
Dololutite beds deformed while in a plastic state, are interbedded with undeformed crossbedded (dolomitic) grainstone. These folds probably formed as packages of sediment were moved during karstification. Some layers have detached from one another, forming voids that were eventually filled by aragonite-fibrous calcite – subsequently converted to dolomite. Both images from the Rowatt Fm, Belcher Islands, about 2 billion years old.
Detached folds in ice-contact glacial outwash. Elevated pore pressures and deformation were probably caused by ice loading. Late Pleistocene, Ottawa.
Classic folded, faulted, and detached turbidite beds, caused by sliding, slumping, syn-depositional faulting, and some liquefaction. Left; Lower Miocene Waitemata Basin, Army Bay, Right: Lower Miocene Waitemata Basin Manly Beach, Auckland.
Classic folded, faulted, and detached turbidite beds, caused by sliding, slumping, synsedimentary faulting, and local liquefaction. Left; Lower Miocene Waitemata Basin, Takapuna Beach , Auckland. Right: highway roadcut, Albany, Auckland.
Small, detached slump fold carried along the base of a turbidity current. Lower Miocene Waitemata Basin, Cockle Bay, Auckland
Detached slump folded dololutite-calcilutite. These thin carbonate beds were deposited on a Proterozoic slope (Costello Fm. Belcher Islands), outboard of really large, platform stromatolite reefs.
Folded, and possibly thrust faulted turbidites, above which are undisturbed beds. Lower Miocene Waitemata Basin, Pukenihinihi Point, north Auckland.
Slump folds in Late Miocene Castaic Fm, Ridge Basin turbidites, probably initiated by seismic events on the bounding San Gabriel strike-slip fault, that was an offshoot of the evolving San Andreas transform system. Left: a fold pair. Right: folding, pull-apart, and small accommodation faults.
Folding and intrusion of liquefied sand in the Rosario Group, San Diego
Large recumbent slump fold in a Late Miocene basin floor submarine fan, Mt. Messenger Formation, North Taranaki, New Zealand.
Seriously deformed and detached slumps, boudinage, and slides in Late Miocene, basin floor submarine fan, Mt. Messenger Formation, North Taranaki, New Zealand. Strata below the detachment are not deformed.
Detail of deformation associated with slumping – here, boudinage and tight recumbent folds in dark brown sandstone layers. Late Miocene, basin floor submarine fan, Mt. Messenger Formation, North Taranaki, New Zealand.
The iconic ‘Jam Roll’ slump in Late Miocene, basin floor submarine fan, Mt. Messenger Formation, North Taranaki, New Zealand. Folded sandstone-mudstone almost completely encloses the structure.
Detail of liquefaction and dewatering structures in the Jam Roll slump. Left: a modest size mud volcano. Right: Highly fluid mud layers that were squeezed during liquefaction. Late Miocene, basin floor submarine fan, Mt. Messenger Formation, North Taranaki, New Zealand.
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Beyond the slope (continental slope or delta slope) is the deep ocean floor, at depths usually measured in 100s to 1000s of metres. Sediment that has bypassed the shelf is transported through submarine canyons and gullies by turbulent flows of mud and sand (turbidites), or debris flows that are capable of moving a much greater range of clast sizes, from pebbles to chunks of rock or dislodged sediment having dimensions in the 10s to 100s of metres. A lower sea floor gradient at the base of the slope, plus frictional forces along the sea floor and overlying water, causes these flows to decelerate. The sediment accumulates in submarine fans, that have dimensions measured in 10s to 100s of kilometres.
The earliest models of submarine fan construction and architecture in the late 60s early 70s (e.g. Walker, Normark, Mutti and Ricci Luchi), and the plethora of model variations since, are based primarily on reconstructions from the rock record, with a smattering of new, actualistic observations. All these models have certain commonalities – in terms of their stratigraphic and geomorphic architecture, they contain elements of proximal to distal components of fan lobes, submarine channels, channel levees and overbank, and dislocation of slope, fan or channel sediment packages by slumping and sliding. Sediment dispersal is generally attributed to turbulent flows (turbidity currents), debris flows (ranging from highly fluid to plastic), and grain flows (less common), against a background of normal oceanic traction currents and pelagic-hemipelagic sedimentation. I have tried to illustrate as many of these attributes as possible in the images that follow.
Ancient submarine fan deposits illustrated here include: the Lower Miocene Waitemata Basin near Auckland, New Zealand; the Paleocene of Point San Pedro, Upper Cretaceous Pigeon Point, and Dana Point successions, all in California; and Proterozoic examples from Belcher Islands (about 1800-1900 Ma).
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The images:
Typical exposure of Waitemata Basin strata around Auckland coastal cliffs: Left; mid-fan turbidites at Takapuna Beach. Right; thick, proximal submarine fan-channel capped by thinning-upward overbank facies, north end of Goat Island Marine Reserve.
Waitemata Basin turbidites near the base of the succession, folded by compaction over paleotopographic highs on Jurassic-Permian metagreywacke basement. Omana Beach, south Auckland
Thick, proximal to mid-fan turbidites and possible channel overbank, Waitemata Basin, Goat Island Marine Reserve.
The thicker, upper unit is is a laminated Tb Bouma interval with mudstone rip-up clasts, and a partly eroded-disrupted Td interval at the top – traced laterally this unit becomes composite. The thick mudstone beds are probably a combination of Td,e intervals. Takapuna Beach, Auckland.
Turbidite beds, well developed Bouma Tb-d intervals, with oversteepened and convoluted ripple drift (Tc interval), Lower Miocene Waitemata Basin, Cockle Bay, Auckland.
A thin Bouma Tb layer (at the coin) is overlain by a thin, rippled Tc (just above the coin), that subsequently was eroded by a thin, but coarse-grained sandy flow that ripped up local mudstone slabs and wafers. The middle grey mudstone is mostly Te (hemipelagic) with small bottom-current ripples redistributing sand across a thin layer. Waitemata Basin, Cockle Bay, south Auckland.
Convoluted siltstone-fine sandstone, truncated by the next flow unit, in which there is a thin, gritty Ta interval. Waitemata Basin, Cockle Bay, south Auckland.
A composite flow unit with well developed Tb laminations (lowest), and near the top a scour surface formed by the succeeding flow. Waitemata Basin, north end of Goat Island Marine Reserve.
Thick, coarse-grained laminated Tb interval, Musick Point, Auckland.
Thick Bouma Ta-b composites; most of the intervening, skinny Td mudstone (center) has been eroded. Waitemata Basin, Cockle Bay.
Dewatering of this turbidite (during very early burial) is indicated the concave-up dish structures, and small synsedimentary faults that terminate just above the dish structures. Waitemata Basin, Musick Point,
Coalified wood fragment (outlined), intensely bored by Miocene Toredo-like marine worms, Waitemata Basin, Goat Island Marine Reserve.
Very think, composite debris flows containing abundant pebbles, cobbles and boulders of basalt, and subordinate sedimentary and mafic igneous clasts. Interpreted provenance of the clasts varies between two extremes: an active, early Miocene volcanic arc on the western margin of Waitemata Basin; and more recently as debris from oceanic islands (see Shane et al, 2010, Geochemistry, Geophysics, Geosystems, open access). Left: Motuihe Island, Auckland. Right: an iconic outcrop at Waiwera, north Auckland. Lower flow units have large rafts of locally derived, deformed mudstone. The debris flow is overlain by thick, proximal fan turbidites.
Mixed matrix-supported and some clast-supported textures in Waitemata Basin debris flows. Left: Waiwera (same as the left image above); Right: Karekare, Auckland west coast.
A massive raft of columnar-jointed basalt, a remnant of either a lava flow of dyke from an oceanic island somewhere west of the basin. The weight of the block and compaction have pushed it into the underlying turbidite beds. Waitemata Basin, Army Bay, Auckland.
Probably the most photographed slump fold in Waitamata Basin, Army Bay. The recumbent structure is detached from strata below along a relatively undisturbed glide plane. The lower limb is also cut by small faults.
Left: Classic slump folded turbidites, confined to a specific interval; strata above and below are relatively undeformed. Fold sandstone limbs are partly detached or pulled apart, and some mudrocks have been fluidized, Waitemata Basin, Takapuna, Auckland. Right: Broken soft-sediment fold, with partially fluidized mudrock below the central detached limb. Waitemata Basin, Little Manly Beach.
Isoclinal folding in thin-bedded mudstone-sandstone (left center), and a sandy turbidite bed deformed by rotated boudins (upper right). All these structures formed while the sediment was at a transition from relatively soft to weakly indurated. Waitemata Basin, Army Bay, north Auckland.
Soft sediment deformation in Waitemata Basin, includes small thrusts (fault plane indicated by arrows), with folded strata in the hanging wall, and small drag folds in the footwall. Waiwera, north Auckland.
Intensely folded turbidites on a horizontal, undeformed glide plane, Waitemata Basin, Orewa Beach, Auckland.
Paleocene turbidites, Point San Pedro, California.
Left: Successive cycles of thinning upward and thin bedded, distal fan turbidites, Point San Pedro, California. Right: Cyclic, thinning upward interchannel facies, Paleocene Point San Pedro, California.
Small slump package in thinly bedded distal fan facies, Point San Pedro, California.
Submarine channel sandstone overlain by thin sandy turbdites and overbank mudstone. Point San Pedro, California.
Thick submarine fan channel and overbank, Point San Pedro, California.
Classic outcrops of pebbly mudstone – matrix-supported debris flows, that probably accumulated in proximal fan channels. Upper Cretaceous Pigeon Point, California.
A variation on the debris flow theme, with well stratified conglomerate and commonly clast-supported frameworks, that are inferred to have formed from more fluid flows than their pebbly mudstone counterparts. Upper Cretaceous Pigeon Point, California.
A broader view of stratified, possibly surging debris flows in proximal fan channels. Upper Cretaceous Pigeon Point, California.
Slump folded, and partly fluidized turbidites in Upper Cretaceous Pigeon Point, California.
Thin Bouma Tb-c flow units, Pebble Beach, California. the middle unit has developed some excellent flame structures. the lower unit contains sand-filled burrows, and detached load casts.
Dish structures and pillars indicating dewatering (fluid expulsion) during early burial by the overlying sandy turbidites. Rosario Group, San Diego.
Stacking of sandstone and conglomerate-filled submarine channels in the Miocene Capistrano Formation, Dana Point, California.
Submarine channel sandstones and overbank facies exposed at Wheeler Gorge, California.
Bedding style in the Omarolluk Fm. turbidite succession, Proterozoic, Belcher Islands (about 1800-1900 Ma). On the left, mid fan channel sandstone and overbank; on the right more proximal sandstone facies.
A paper on the Omarolluk Formation: Ricketts, B.D. 1981: A submarine fan – distal molasse sequence of Middle Precambrian age, Belcher Islands, Hudson Bay; Bulletin Canadian Petroleum Geology, v. 29, p. 561-582.
Channel overbank facies containing thin graded sandstone, thin sandstone beds with ripples and starved ripples, and Bouma Td-e mudstones. Omarolluk Fm. Proterozoic, Belcher Islands
Four incomplete Bouma cycles, each Tb with thin Tc. The whitish patches are very early diagenetic concretions. Omarolluk Fm. Proterozoic, Belcher Islands.
Thin Bouma Tc-d mid-fan cycles, with ripple drift, flame structures, and a small scour. Omarolluk Fm. Proterozoic, Belcher Islands.
A Bouma Tb-c cycle with well developed and oversteepened ripple drift, overlain by a thicker Tb cycle with only a thin Td cap. Omarolluk Fm. Proterozoic, Belcher Islands
A view of Bouma Tc-d intervals and convoluted laminae. Omarolluk Fm. Proterozoic, Belcher Islands
Sole structures beneath sandy turbidites. On the left, flute casts are superposed on grooves. On the right, large flute casts are slightly deformed (block is about a metre across). Omarolluk Fm. Proterozoic, Belcher Islands.
Large flute cast, paleoflow to top right. Omarolluk Fm. Proterozoic, Belcher Islands
Dewatering of turbidites, soon after deposition, produced thin fluid-escape pillars (left, cross-section view), and on bedding planes, small sand-mud volcanoes. Right image is a bedding view. Omarolluk Fm. Proterozoic, Belcher Islands
Oblique views of thick Bouma Tb units, and sheets of dewatering pillars formed during very early burial and compaction. Segregation of sheets through the sandstones is a function of different permeabilities between successive flow layers. Dark globular shapes on left image, and white patches in the middle image, are early diagenetic calcite concretions (see images below). Omarolluk Fm. Proterozoic, Belcher Islands
Left: Proximal submarine channel conglomerate consisting almost entirely of reworked calcite concretions. Right: Detail of the channel conglomerate clasts. Elongate clasts are concretions that formed in laminated and rippled Tc intervals; the ovoid and spherical concretions are coarser grained and formed in Ta or Tb Bouma intervals. Omarolluk Fm. Proterozoic, Belcher Islands.
Stacked event beds, mostly in Td intervals in this view, with significant detachment of convoluted-folded very thin sandstone beds. Subvertical, wrinkled conduits, 2-3 mm wide, are dewatering pillars formed by escaping fluids during early compaction. These units are associated with inter- lava flow turbidites in the volcanic Flaherty Fm, Proterozoic Belcher Islands (Flaherty volcanics overlie the Omarolluk Fm.),
