Turbidite Deposits Research Articles

The role of buoyancy reversal in turbidite deposition and submarine fan geometry

Abstract Although recent work has shown that changing interstitial fluid density within turbidity currents is a frequently overlooked factor affecting the texture and internal architecture of turbidites, little is known about its influence on submarine fan morphology. Here we present the results of three-dimensional flume experiments of turbidity currents that clearly demonstrate the role of low-density interstitial fluid, in combination with sediment concentration and basin gradient, on submarine fan geometry. The experiments show that turbidity currents with reversing buoyancy, and their resulting deposits, are narrower than those that remain ground hugging. Furthermore, wider deposits result from increases in sediment concentration and/or basin-floor gradient. We also propose that Taylor-Görtler vortices associated with currents traveling over a break in slope may lead to the deposition of wider lobes compared with those traveling over a constant gradient.

Elemental and organic carbon proxies for redox conditions of the Oligocene formations in the Ropa Tectonic Window (Outer Carpathians, Poland): palaeoenvironmental implications

The Oligocene Grybow Succession is recognized as a counterpart of the anoxic Menilite Formation. Its comprehensive geochemical investigations are made in the key sections of the Ropa Tectonic Window (the Grybow Unit, Polish Outer Carpathians). The maceral assemblages, dominated by land-plant liptinite, vitrinite and intertinite, correspond to kerogen types II and III. A Tmax vs. HI diagram shows terrestrial kerogen type II with various additions of type III and algal kerogen type I. A variation in δ 13 C org. (from –25.21 to –27.38‰) may have resulted from variations in the composition of organic matter (the content of terrestrial vs. marine organic matter), controlled by depositional setting (turbidite vs. hemipelagic). The highest TOC contents are associated with an enhanced influx of land-derived organic matter. The redox-sensitive trace elements positively correlate with TOC and TS contents. Redox conditions varied between oxic and anoxic, as was concluded from TOC-TS, V/(V+Ni) and U/Th. The turbidity currents might have ventilated the bottom waters, especially more efficiently in the proximal zone of turbidite sedimentation. Moreover, oxygenated bottom waters may have also affected the concentration of trace metals, owing to migration of the redox interface downward within the sediments.

Nutrient Level Change Based on Calcareous Nannofossil Assemblages During Late Miocene in Banyumas Subbasin

DOI:10.17014/ijog.3.3.183-194Hydrographic situation on surface waters is more challenging to be understood, related to global and regional climate change in tropical regions. In addition, records from these tropical areas are limited compared to other areas of subtropical and polar regions. The aim of this study is to reconstruct Cenozoic paleoceanography, in particular nutrient level, using outcrop samples from Kali Pasir, Banyumas, Indonesia. This study is focused on the relationships of the relative abundance of Discoaster, coccolith size of Reticulofenestra, and lithofacies characteristics. Nutrient level is reconstructed using quantitative analysis of calcareous nannofossil by counting calcareous nannofossils on 400 fields of View (FOV) for each sample. The abundance of Discoaster and the large Reticulofenestra represent a deep thermocline and nutricline, which is a typical of oligotrophic condition. This condition also associated with the muddy facies in the early stages of Late Miocene (NN8-NN10a). Conversely, decreasing Discoaster abundance and the abundance of small Reticulofenestra indicate a shallow thermocline and nutricline, resulting strong eutrophication of surface waters in the later stage of Late Miocene (NN10b-NN11). A high nutrient content in this stage is related to classical turbidite deposits. A change in a sea surface resulted in strong eutrophication, which is in this section similar to the eastern Indian Ocean micropaleontology records during the Late Miocene (NN10). This finding shows that strong eutrophication in Kali Pasir section is probably driven by nutrient-rich terrestrial material related to the onset of Indian monsoon during the Late Miocene.

Seismic expression of depositional elements associated with a strongly progradational shelf margin: northern Santos Basin, southeastern Brazil

ABSTRACT: Seismic facies analysis and seismic geomorphology are important tools for the analysis of depositional elements in subsurface. This paper aimed to investigate the character and genesis of depositional elements and erosive features associated with an Eocene progradational shelf margin in northern Santos Basin. Identified seismic facies are interpreted as shelf-margin deltas/shoreface deposits, tangential (oblique) clinoforms, sigmoidal clinoforms, topset reflectors, mass-transport deposits and turbidites. These facies are grouped into four associations representing periods of relatively constant environmental conditions. Association 1 is composed of shelf-margin deltas/shoreface deposits, tangential clinoforms and extensive sand-rich turbidites disposed as submarine channels and frontal splays. A progressive increase in clinoform angle within this association has been identified, culminating in high-relief sigmoidal clinoforms with less voluminous turbidites of facies association 2. Association 3 is composed by subparallel to divergent topset reflectors, interpreted as continental to shelfal deposits placed during base-level rises. These are always truncated basinward by slump scars, formed as a consequence of sediment overload at the shelf margin during aggradations. Association 4 is composed of sigmoidal clinoforms, mass-transport deposits and turbidites. Early clinoforms are steeper as a consequence of the topography of the slump scars. Subsequently, dip angles become progressively gentler as the system approach to the equilibrium profile. The steep physiography was favorable for canyon incision, which played an important role in turbidite deposition. Mass-transport deposits, formed subsequent to slope collapse, are composed of mud-rich diamictites, and show strong internal deformation.

Stratigraphic and structural features of the Bas Ostriconi Unit (Corsica): Palaeogeographic implications

The palaeogeographic origin of the Bas Ostriconi Unit (Balagne area, Alpine Corsica) has long been a matter of debate. This unit is actually detached from its original basement. It is made of Late Cretaceous carbonatic turbidites with lenses of coarse-grained polymict conglomerates (Narbinco Flysch). The turbidites have a mixed siliciclastic-carbonatic composition and are affected by a polyphasic deformation. Here, based on field observations and sampling, we analyse the sedimentary, petrographic, and structural features of the Narbinco Flysch. From these analyses, we derive that the Narbinco Flysch belongs to the sedimentary cover of the Balagne ophiolite Nappe. We also show that the carbonatic turbidites are associated with mixed siliciclastic-carbonatic coarse-grained debris, which is typical of the turbidite sediments deposited during the Late Cretaceous in the Ligure-Piemontese oceanic basin close to the European Margin. Our results thus suggest that, the Bas Ostriconi Unit succession originally formed on the Ligure-Piemontese oceanic crust, then was integrated to the accretionary wedge that was thrusted on the European margin of Corsica during the Eocene collisional events.

Origin and fate of sedimentary organic matter in the northern Bay of Bengal during the last 18 ka

The Northern Bay of Bengal (NBoB) is a globally important region for deep-sea organic matter (OM) deposition due to massive fluvial discharge from the Ganges-Brahmaputra-Meghna (G-B-M) rivers and moderate to high surface productivity. Previous studies have focused on carbon burial in turbiditic sediments of the Bengal Fan. However, little is known about the storage of carbon in pelagic and hemipelagic sediments of the Bay of Bengal over millennial time scales. This study presents a comprehensive history of OM origin and fate as well as a quantification of carbon sediment storage in the Eastern Bengal Slope (EBS) during the last 18ka. Bulk organic proxies (TOC, TIC, TN, δ13CTOC, δ15NTN) and content and composition of total hydrolysable amino acids (THAA) in a sediment core (SO188-342KL) from the EBS were analyzed. Three periods of high OM accumulation were identified: the Late Glacial (LG), the Bölling/Alleröd (B/A), and the Early Holocene Climatic Optimum (EHCO). Lower eustatic sea level before 15ka BP allowed a closer connection between the EBS and the fluvial debouch, favoring high terrestrial OM input to the core site. This connection was progressively lost between 15 and 7ka BP as sea level rose to its present height and terrestrial OM input decreased considerably. Export and preservation of marine OM was stimulated during periods of summer monsoon intensification (B/A and EHCO) as a consequence of higher surface productivity enhanced by cyclonic-eddy nutrient pumping and fluvial nutrient delivery into the photic zone. Changes in the THAA composition indicate that the marine plankton community structure shifted from calcareous-dominated before 13ka BP to siliceous-dominated afterwards. They also indicate that the relative proportion of marine versus terrestrial OM deposited at site 342KL was primarily driven by relative sea level and enlarged during the Holocene. The ballasting effect of lithogenic particles during periods of high coastal proximity and/or enhanced fluvial discharge promoted the export and preservation of OM. The high organic carbon accumulation rates in the EBS during the LG (18–17ka BP) were 5-fold higher than at present and comparable to those of glacial upwelling areas. Despite the differences in sediment and OM transport and storage among the Western and Eastern sectors of the NBoB, this region remains important for global carbon sequestration during sea level low-stands. In addition, the summer monsoon was a key promotor of terrestrial and marine OM export to the deep-ocean, highlighting its relevance as regulator of the global carbon budget.

The Messinian record of Spanish onshore and offshore data (Atlantic Ocean and Western Mediterranean Sea)

Spanish territory offers a remarkable location to study the Messinian salinity crisis (MSC). So much so, that sub-basins and open margins to the Mediterranean Sea and the Atlantic Ocean can be studied from outcrop data, 2D and 3D seismic surveys, and well logs. From the analysed data, it can be determined that the Messinian sediments are involved in three third-order depositional sequences: (1) Late Tortonian–Messinian, with temperate carbonates, coral reefs and sandy turbidities; (2) Messinian, with on- and offshore deposition of shallow-marine evaporate and isotopic freshwater facies; and (3) Messinian–Early Pliocene, comprising deposits of sandy (Atlantic) and gypsum-sandy turbidites (Mediterranean) that filled incised valleys. From seismic images, the best exploration opportunities involve the lowstand systems tracts (LST), the carbonates and different facies under deep-water evaporates. For these, however, the problem is to establish the source rock, by: (a) the presence of Messinian deep-water paper shales; (b) the gas having to be biogenic in the absence of paper shales; and (c) reaching the maturity level in areas with limestone and coral reef prospects. The above possibilities come from our conception of the Messinian crisis, which was caused by two different episodes: climatic change in a restricted, but not desiccated, Mediterranean Sea, following by multiple sea-level falls and the deposition of their correlative LST turbiditic systems.

Diagenesis and reservoir quality of overpressured deep-water sandstone following inorganic carbon dioxide accumulation: Upper Miocene Huangliu Formation, Yinggehai Basin, South China Sea

Turbidite deposits, overpressure, hydrothermal fluid activity, and CO2 accumulations are the basic geologic characteristics of the Upper Miocene Huangliu Formation sandstone reservoir in the Dongfang gas field, Yinggehai Basin. This study aims to unravel the timing and origin of dissolution in sandstone and evaluate the effects of inorganic CO2 accumulation on reservoir quality. A comparative study between area DFX-1 (CO2-rich) and area DFX-2 (CO2-poor) has illustrated the differences in diagenetic alteration and the effects of CO2 accumulation on the sandstone reservoir. Diagenetic alteration of sandstones in area DFX-1 was characterised by intense dissolution and medium cementation. Dissolution of silicates following inorganic CO2 charging in the DFX-1 area created a higher percentage of dissolution porosity (41.0%–53.9% of total visible porosity), compared with minor dissolution porosity in the DFX-2 area (16.7%–29.6% of total visible porosity). Small amounts of kaolinite, authigenic quartz, ankerite, and siderite were precipitated by CO2-water-rock reactions in area DFX-1; these minerals are almost absent in area DFX-2. The carbonate cement of the Huangliu Formation sandstone in area DFX-1 is characterised by light δ13C (−3.3‰ to −1.6‰, PDB), which is consistent with formation from inorganic carbon. The timing of dissolution by inorganic CO2 is suggested to be at about 0.4 Ma based on the previous simulation experiments. In the two areas studied, overpressure was caused by pressure transmission along deep open faults and was not related to mudstone undercompaction. Overpressure did a little to contribute to porosity preservation. CO2 accumulating at low partial pressures related to hydrothermal fluid flow cannot make a net increase in porosity in the Huangliu Formation sandstone of the Dongfang gas field.

Experimental study of mud erosion at the interface of an artificial sand-mud alternate layer

Methane hydrates exist in the sand-mud alternate layers of Japan's offshore turbidite sediments. For gas production from a methane hydrate reservoir, depressurization has been considered as a promising method. When intergranular methane hydrates are dissociated, the flow of produced gas and water may cause mud erosion of turbidite sediments. The eroded mud may plug the pores near the wellbore. This research presents an experimental study for the evaluation of mud erosion at the interface between the sand and mud layers. Artificial cores consisting of sand and mud layers were made and the mass of fine particles eroded by water flow was measured. We, then, adopted a mud erosion model, which represents a linear relationship between the erosion rate of fine particles and average flow velocity in the pore, and obtained a critical flow velocity and a coefficient of the erosion rate of fines in the sand-mud alternate layer.

Compaction of smectite-rich mudstone and its influence on pore pressure in the deepwater Joetsu Basin, Sea of Japan

Pore pressure prediction is needed for drilling deepwater wildcats in the Sea of Japan because it is known from past experience that there can be drilling problems can arise due to overpressure at shallow depths. The “Joetsu Basin” area is located offshore to the southwest of Sado Island on the eastern margin of the Sea of Japan. The sedimentary succession of the Neogene is mainly composed of turbidite sediments which contained smectite-rich mudstones. The cause of overpressure in the study area is expected to be a combination of mechanical disequilibrium compaction and chemical compaction, especially from the illitization of smectite.We have constructed basin models and performed numerical simulations by using 1D and 3D PetroMod to understand clearly the history of fluid flow and overpressure development in the lower Pliocene Shiya Formation and Middle to Upper Miocene Teradomari Formations. A compaction model coupled with both mechanical and chemical compaction for smectite-rich sediments is used for pore pressure calibration. We have examined three key relationships: porosity-effective stress, porosity-permeability, and the kinetics of smectite-illite transformation. We determined the ranges for the parameter values in those relationships that allow a good fit between measured and modelled pore pressures to be obtained. Results showed that for the most likely case, high pore pressure in the Lower and Upper Teradomari developed since 8.5 Ma and 5.5 Ma, respectively. Pore pressures in studied structures have approximately doubled since 1 Ma due to the high deposition rate of the Pleistocene Haizume Formation and smectite-illite transformation in the lower Pliocene-Shiya and Middle to Upper Miocene- Lower and Upperr Teradomari formations. In three cases (high case, most likely case and low case), the overpressures in the Shiya, Upper and Lower Teradomari Formations are less than 1 MPa, 15 and 30 Ma, respectively.The results provide a basis for planning future wells in the “Joetsu Basin” area and in other basins where geological conditions are similar, i.e., deepwater, high sedimentation rate, high geothermal gradient and smectite-rich sediments.

The relationship between eruptive activity, flank collapse, and sea level at volcanic islands: A long‐term (>1 Ma) record offshore Montserrat, Lesser Antilles

AbstractHole U1395B, drilled southeast of Montserrat during Integrated Ocean Drilling Program Expedition 340, provides a long (>1 Ma) and detailed record of eruptive and mass‐wasting events (>130 discrete events). This record can be used to explore the temporal evolution in volcanic activity and landslides at an arc volcano. Analysis of tephra fall and volcaniclastic turbidite deposits in the drill cores reveals three heightened periods of volcanic activity on the island of Montserrat (∼930 to ∼900 ka, ∼810 to ∼760 ka, and ∼190 to ∼120 ka) that coincide with periods of increased volcano instability and mass‐wasting. The youngest of these periods marks the peak in activity at the Soufrière Hills volcano. The largest flank collapse of this volcano (∼130 ka) occurred toward the end of this period, and two younger landslides also occurred during a period of relatively elevated volcanism. These three landslides represent the only large (>0.3 km3) flank collapses of the Soufrière Hills edifice, and their timing also coincides with periods of rapid sea level rise (>5 m/ka). Available age data from other island arc volcanoes suggest a general correlation between the timing of large landslides and periods of rapid sea level rise, but this is not observed for volcanoes in intraplate ocean settings. We thus infer that rapid sea level rise may modulate the timing of collapse at island arc volcanoes, but not in larger ocean‐island settings.

Late Quaternary geomorphology, seabed evolution, and terrigenous sediment delivery to the Pandora and Moresby Troughs, Gulf of Papua

An integrated geology and geophysics investigation has been carried out to study the late Quaternary deepwater depositional system in the Gulf of Papua (NSF-MARGINS focus area) focusing on two contrasting depocentres, Pandora and Moresby troughs. The studies incorporate multi-beam bathymetry, sub-bottom sonar, and core data in order to define and map acoustic and lithofacies; and relate depositional processes, sediment routing, timing and geomorphic products that have developed since Marine Isotope Stage (MIS) 3, ca. 40calka. 3D seafloor visualisation is used to infer sedimentary processes responsible for observed morphology, which are then placed into a chronostratigraphic framework using recently published age models of sediment cores.The peak depositional period in Pandora Trough occurred during MIS 2. At that time a large deep-sea channel network linked the Pandora and Moresby troughs, allowing long-distance sediment transport by large turbidity currents from the Papuan mainland to the Coral Sea Basin. Near the LGM, shelf-edge failure led to emplacement of mass-transport deposits on the floor of the Pandora Trough, blocking this pathway for large turbidity currents. Intermittent turbidity currents continued to feed minibasins upslope of the MTD complex until early MIS 1 (earliest Holocene).Along the shelf edge of the Papuan Peninsula, substantial sediment delivery by turbidity currents continued until middle Holocene and perhaps later; combined with bottom currents, these flows contributed to the formation of large sediment waves of Moresby Fan. However, this Holocene turbidite sedimentation does not extend much farther into the Moresby Trough, based on negligible Holocene sediment accumulation deeper in the basin.This study has shown that sediment delivery from fluvial sources to deep basins in the GoP is controlled by a complex interplay of changing sea level, evolving basin bathymetry (influenced by depositional and tectonic processes), and oceanic transport of sediment from shelf to slope. These conditions have created highly localised conduits for shelf to slope sediment delivery that respond both to global forcing (eustatic sea level) as well as local conditions (shelf gradient, mass wasting, currents, and source proximity), resulting in a complex network of deep-sea depositional morphologies active from the Last Glacial Maximum to Holocene time.

Aligned trace fossils from the Utica Shale: implications for mode of life and feeding in the trilobiteTriarthrus beckii

The olenid trilobite Triarthrus commonly occurs in nearly monospecific assemblages within otherwise relatively barren black shales. As such, it has been proposed that these trilobites preferred dysoxic or even anoxic habitats and suggested feeding habits range from predation and particle feeding to chemoautotrophism. A unique bedding-plane assemblage of aligned traces that grade from Rusophycus to Cruziana, with associated Triarthrus beckii carcasses, are described from three localities in the Indian Castle Formation (upper Utica Shale) just below a K-bentonite bed. Although few body fossils are preserved, it is clear that the 15-cm-thick, laterally extensive Thruway K-bentonite created a unique taphonomic window that preserved the activities of numerous olenid trilobites. Rusophycus and Cruziana, consistently observed in densities above 100 trackways/m2, were excavated by the trilobites into the upper surface of a micro-graded bed, likely a distal turbidite deposit. Sedimentological and trace metal data (Mo, Mn, V and U) support dysoxic but not persistently anoxic conditions through this interval. Measurements from over 500 individual trackways have mean orientations of 259.1° (WSW) at the Myers Rd. locality and 224.59° (SW) at the Dolgeville Dam locality. These orientations are closely similar to independent sedimentological indicators of current transport direction at these sites, which indicates that the trilobites preferentially faced into the prevailing current. The trackways provide compelling evidence that Triarthrus beckii individuals were engaged in feeding, probably assisted by current transport of particles. These results do not support previous suggestions that Triarthrus may have relied upon a chemoautotrophic life habit, but are consistent with suggestions of predation or scavenging from the sediment.

An attempt to reconstruct 2700 years of seismicity using deep-sea turbidites offshore eastern Taiwan

The Taiwan area, where the Philippine Sea Plate collides with Eurasia, is one of the most seismically active areas in the world and has been consequently struck repeatedly by destructive earthquakes. To better constrain the occurrence of large earthquakes, we have conducted two cruises in 2012 and 2013 from which five piston, gravity and box-cores were retrieved from selected sites in targeted areas that contain continuous and accurate turbidite deposition offshore eastern Taiwan. Forty-seven turbidite layers deposited between 675BC and 2012AD have been described in the cores with facies varying from silty clay to coarse sand. We modeled each turbidite layer using the sedimentation rate deduced from radiocarbon age measurements performed on planktonic foraminifers. Precise dating based on 210Pb–137Cs chronology provided ages for the XXth century turbidites. Coring sites' locations, biotic association within turbidites beds and seismic calibration over the instrumental period, suggest that earthquakes are the most likely triggering mechanisms of turbidity currents over the last 2700years. Calibration of correlations between turbidites and instrumental earthquakes allowed us to determine the minimum magnitude of recorded events (Mw=6.8) and the maximum distance between the epicenter and the slope failure. Turbidites' synchroneity between cores has been tested but results showed that this criterion cannot be used in our study area because of the high level of seismicity, i.e., a M>6.8 earthquake recurrence interval much smaller than the uncertainty on radiocarbon ages. The excellent accuracy of dating allows correlating all the turbidites deposited since 1920 with instrumental earthquakes. For each core, we established a return time ranging between 112 and 147years for the period pre-1900 and ~27 and 34years for the period post-1900. The discrepancy between pre-1900 and post-1900 recurrence either suggests, that slope stability varies, with higher slope instability after 1900 possibly due to increased sediment delivery by rivers.

Seismic reflection patterns associated with continental convergent margins through time

The important role of tectonic wedging in accommodating horizontal shortening strain is increasingly recognized to occur at all scales within continental convergence zones. Wedge structures appear most common in accretionary orogens involving former passive margins with large-volume turbidite sedimentary fans or accretionary prisms. Relatively small-scale wedges can be recognized in outcrop, but crustal scale wedge geometries must be observed and analysed using seismic reflection methods. Reflection profiles now exist across a large number of accretionary orogen settings of diverse ages and continents. Similarities in seismic patterns within the major eras enable creation of a series of stylised continental margin transects for each major time period. Relatively low rock strength found in turbidite sediments rich in micas, especially when contrasted with strengths of igneous volcanic arc rocks, plays a major role because it localizes thrust faults within weaker horizons. Schematic cross sections across accretionary margins that span five geological eras summarize the principal features interpreted on numerous seismic reflection sections. Important details vary, such as the depths where tectonic wedging initiates, but tectonic wedges of diverse scales are observed in all cross sections. The percentage and degree of consolidation or metamorphism of turbiditic greywackes apparently controls the degree, depth and scale of the crustal wedging.

Rhizocorallium hamatum (Fischer-Ooster 1858), a Zoophycos-like trace fossil from deep-sea Cretaceous-Neogene sediments

Rhizocorallium hamatum (Fischer-Ooster 1858) is a trace fossil of the Zoophycos group, which is distinguished by its mostly horizontal, branched spreite lobes. It has so far, been ascribed mainly to Zoophycos, but the latter should be limited to forms having helical whorls, which are absent in R. hamatum. It has also been ascribed to Phycosiphon, which, however, shows J-shaped spreite lobes, while the lobes of R. hamatum are U-shaped. R. hamatum is very similar to R. commune var. irregulare, but the latter displays a distinctly wider marginal tunnel with respect to lobe width. R. hamatum occurs from the Turonian to Eocene, possibly from the Hauterivian to Oligocene, but mostly from Maastrichtian to Palaeocene, deep sea, mainly turbiditic sediments rich in marl. The tracemaker, probably a ‘worm’-like invertebrate, ingested an organic-rich mud of the background sediment and relocated it into the middle to deep tiers within the underlying turbiditic marl, mostly in form of faecal pellets packed within the spreite lobes, for further use as a food resource. This way of feeding was a response to food deficiency on the deep-sea floor.

Modeling of sub-bottom volume scattering from turbidite sequences

Abyssal sediments near the continental margin are often formed through turbidite deposition, which creates alternating layers of silt and mud. Modeling of reflection and sub-bottom volume scattering from turbidite sequences has been previously studied using an effective medium to model the propagation within the sediment, which is only applicable when the acoustic wavelength is much larger than the average layer thickness in the seafloor, and thus is limited to low frequencies. A volume scattering model is developed here to extend the frequency range of previous models of scattering from turbidite sequences. This model employs the Born approximation, takes into account the correct propagation physics in a layered environment, and uses a point source as an incident field. Model results will be compared to previously reported scattering data collected in the Ionian sea.

Carbonate sedimentation in an extensional active margin: Cretaceous history of the Haymana region, Pontides

The Haymana region in Central Anatolia is located in the southern part of the Pontides close to the Izmir–Ankara suture. During the Cretaceous, the region formed part of the south-facing active margin of the Eurasia. The area preserves a nearly complete record of the Cretaceous system. Shallow marine carbonates of earliest Cretaceous age are overlain by a 700-m-thick Cretaceous sequence, dominated by deep marine limestones. Three unconformity-bounded pelagic carbonate sequences of Berriasian, Albian–Cenomanian and Turonian–Santonian ages are recognized: Each depositional sequence is preceded by a period of tilting and submarine erosion during the Berriasian, early Albian and late Cenomanian, which corresponds to phases of local extension in the active continental margin. Carbonate breccias mark the base of the sequences and each carbonate sequence steps down on older units. The deep marine carbonate deposition ended in the late Santonian followed by tilting, erosion and folding during the Campanian. Deposition of thick siliciclastic turbidites started in the late Campanian and continued into the Tertiary. Unlike most forearc basins, the Haymana region was a site of deep marine carbonate deposition until the Campanian. This was because the Pontide arc was extensional and the volcanic detritus was trapped in the intra-arc basins and did not reach the forearc or the trench. The extensional nature of the arc is also shown by the opening of the Black Sea as a backarc basin in the Turonian–Santonian. The carbonate sedimentation in an active margin is characterized by synsedimentary vertical displacements, which results in submarine erosion, carbonate breccias and in the lateral discontinuity of the sequences, and differs from blanket like carbonate deposition in the passive margins.

Shelfal sediment transport by an undercurrent forces turbidity-current activity during high sea level along the Chile continental margin

Terrigenous sediment supply, marine transport, and depositional processes along tectonically active margins are key to decoding turbidite successions as potential archives of climatic and seismic forcings. Sequence stratigraphic models predict coarse-grained sediment delivery to deep-marine sites mainly during sea-level fall and lowstand. Marine siliciclastic deposition during transgressions and highstands has been attributed to sustained connectivity between terrigenous sources and marine sinks facilitated by narrow shelves. To decipher the controls on Holocene highstand turbidite deposition, we analyzed 12 sediment cores from spatially discrete, coeval turbidite systems along the Chile margin (29°–40°S) with changing climatic and geomorphic characteristics but uniform changes in sea level. Sediment cores from intraslope basins in north-central Chile (29°–33°S) offshore a narrow to absent shelf record a shut-off of turbidite deposition during the Holocene due to postglacial aridification. In contrast, core sites in south-central Chile (36°–40°S) offshore a wide shelf record frequent turbidite deposition during highstand conditions. Two core sites are linked to the Biobio river-canyon system and receive sediment directly from the river mouth. However, intraslope basins are not connected via canyons to fluvial systems but yield even higher turbidite frequencies. High sediment supply combined with a wide shelf and an undercurrent moving sediment toward the shelf edge appear to control Holocene turbidite sedimentation and distribution. Shelf undercurrents may play an important role in lateral sediment transport and supply to the deep sea and need to be accounted for in sediment-mass balances.

Conduits, timing and processes of sediment delivery across a high-relief continental margin: Continental shelf to basin in Late Quaternary, Gulf of Papua

The Gulf of Papua (GoP), between Australia and Papua New Guinea, is the receiving basin for multiple substantial rivers draining southern Papua New Guinea with collective sediment discharge >> 220 million metric tons (Mt) per year, comparable to a continental-scale river, but draining a combined catchment area of only ∼160,000 km2. This study of the deepest marginal basins in the Gulf of Papua was undertaken to build a regional late Quaternary lithofacies and stratigraphic framework to better understand processes, timing, and conduits of sediment delivery from terrestrial and shelf settings to deep marginal basins, using the GoP as a natural laboratory. Methods include observations of sediment-core stratigraphy and physical properties, accelerometer mass spectrometry (AMS) C-14 dates, core x-radiographs and thin sections.Six lithofacies across the deep water Gulf of Papua (GoP) are identified based on core visual and textural observation. Chronological constraints permit an assessment of changes in sediment supply and depositional environments across time and space, from marine isotope stage (MIS) -3 to -1, or in the last 40 cal ka. The sediment delivery to the deep water GoP is dominated by two mechanisms, gravity-driven flows down slopes and into deep sea basin primarily during lowstands in the western portions of the study area, and hemipelagic sediment accumulation during transgression and highstand. Although the sediment flux appears to be overall dominated by sediment-gravity flows, hemipelagic sediment delivery is widespread during periods of sea level highstand. In the eastern portions of the study area, off-shelf sediment delivery continued into the Holocene in sufficient local volumes to produce turbidity currents. This late, localized sediment delivery appears to have been facilitated by oceanographic processes that allowed seaward sediment transport after flooding of the shelf.A simple sediment budget comparing basinal sediment accumulation to modern estimated river-sediment discharge indicates that peak sediment accumulation in proximal basins occurred during MIS-2; and declined thereafter, generally shifting to upper slope locations, except for the eastern margin of Moresby Trough. There, turbidite deposition continued until 7.4 cal ka, well after drowning of the shelf edge. This continued Holocene deep-sea sediment delivery is likely explained by the local narrow shelf width, and the presence of oceanographic processes capable of transporting sediments from shore to shelf edge.