Submarine Fan Research Articles

Productivity and organic carbon trends through the Wilcox Group in the deep Gulf of Mexico: Evidence for ventilation during the Paleocene-Eocene Thermal Maximum

Deposition of the Paleocene-Eocene Wilcox Group (Gp) in the northern Gulf of Mexico (GoM) occurred during dramatic global climate and regional tectonic change. Key drivers impacting the GoM over this time were 1) significantly enhanced runoff and sediment supply from the developing Laramide hinterland, 2) intense global warming culminating in the Paleocene–Eocene Thermal Maximum (PETM) at ∼56 Ma, and 3) proposed Paleogene restriction of the GoM as Cuba docked with Yucatan-Bahamas-Florida. In this paper, we investigate biological and organic geochemical responses to these drivers across the PETM and identify spatial variations in productivity, oxygenation, and ultimately, ventilation. The PETM has been identified by calcareous nannofossil marker taxa and/or excursion taxa from the genera Rhomboaster and Discoaster that exclusively existed during the event. A calcareous nannofossil transition from cool eutrophic to warm oligotrophic assemblages occurs across the PETM broadly over the GoM suggesting that surface water nutrient supply decreased due to slowing circulation or increased sequestration of nutrients along the margins. Associated radiolarian bursts indicate additional factors, such as eustacy and runoff, may have modulated nutrient supply. Benthic habitats were impacted as agglutinated foraminifera, which were dominant in the Paleocene, disappeared at the PETM over submarine fan environments while calcareous benthic forams remained largely absent until the late Eocene. Deoxygenation may have contributed to benthic ecosystem decline as marine kerogen enrichment is noted broadly in the middle Wilcox and PETM. Total organic carbon is generally <3% except in more isolated marginal settings suggesting that deep-basin dysoxia co-existed with a variably enhanced oxygen minimum. We suggest these biotic and organic geochemical responses reflect connection to the Global Ocean during the PETM, with ventilation reduced but not eliminated by increases in salinity stratification due to runoff and reductions in deeper water entry into the GoM at gateways.

Seismic geomorphology applied to sediment dispersal patterns and an analysis of the stages of channel-lobe systems in the Yinggehai Basin, northern South China Sea

The lithostratigraphic plays in the Dongfang area of the Yinggehai Basin at the northern margin of the South China Sea consist of a Neogene multistage, thinly bedded, channel-lobe system. Integrating high-resolution 3D seismic, lithological and well log data shows that the channel-lobe system developed primarily in the lowstand system tract of the Huangliu Formation. We investigated the developmental stages of lobes based on the stacking relationships of seismic events, the degrees of channel downcutting in lobes, and the occurrences of sandstone facies observed in the stratal slices. The lobes finally identified 9 small-scale stages, which reveal a complete sedimentary cycle controlled by high-frequency sea-level fluctuations. Facies architectures such as main channels, channels and overbank deposits were identified by using seismic sedimentology and geomorphology. Seismic stratal slices display the different characteristics of the sediment dispersal patterns in the northern part (block DF-a) and the southern region (block DF-b). The northern part contains isolated lobes. The southern region mostly contains deeply incised channels and meander belts that are wider than those in the northern part. Three main sediment dispersal patterns have been recognized, namely, channel-lobe, channelized lobe and non-channelized lobe. Sea level fluctuation and topographic variations exert strong influences on spatial-temporal evolution of the sediment diffusion and are the key controlling factors for the patterns. The methodology used in this study characterizes the submarine fan development in an area with limited well control; this methodology is more accurate for reservoir-scale exploration and development compared to other uses.

Morphology and Late Pleistocene–Holocene sedimentation of the Strait of Istanbul (Bosphorus): a review

Abstract The Bosphorus (Istanbul) Strait is a natural strait that connects the Black Sea with the Aegean Sea via the Sea of Marmara and the Dardanelles Strait. It is a 31 km-long and 3.5 km-wide winding channel, with an irregular bottom morphology. It has depressions up to 110 m deep, and two sills with depths of 35 and 58 m in the south and north, respectively. Presently, a two-layer water exchange exists through the strait, with the Mediterranean and Black Sea waters forming the lower and upper layers, respectively. The Bosphorus channel extends as shelf valleys on the Black Sea and Sea of Marmara shelves. However, it operated as a river valley or an estuary during the stadial lowstand periods. The infill sedimentary succession of the Bosphorus channel is up to 100 m thick above the Paleozoic–Cretaceous basement with an irregular topography. The oldest sediments are sandy to muddy fluvial–lacustrine facies of late Pleistocene age, which are preserved only in up to 160 m-deep scoured depressions of the basement. They are overlain by mid–late Holocene estuarine–marine shelly sandy to muddy sediments with patches of bioherms and shelly lag deposits. The Bosphorus outlet areas of the Black Sea and Sea of Marmara are characterized by a submarine fan and a shelf valley, respectively. The fan system in the Black Sea started depositing c. 900 years after the initial vigorous marine water incursion at c. 8.4 14 C ka BP. On the Marmara shelf, extension of the Bosphorus channel is a sinuous shelf valley with a channel–levee complex that was deposited by the Black Sea outflow during 11–10 14 C ka BP. Catastrophic floodings of the Sea of Marmara by torrential Black Sea outflows during the Greenland Interstadial melt-water pulses, as well as the strong Mediterranean current towards the Black Sea during the interglacial periods, were responsible for carving out the Bosphorus channel and the shelf valleys, as well as removing the sediments belonging to the earlier periods.

Provenance of Late Cretaceous accretionary complex within the Yarlung–Zangpo suture zone, Bainang, southern Tibet: Implications for the subduction–accretion of the Neo-Tethyan ocean

Accretionary complexes offer important source of information for studying the subduction history and source-to-sink system and neighboring terranes. In this study, we conducted field mapping, detrital zircon U–Pb age and trace element analyses, and electronic microprobe composition analysis of detrital Cr-spinel in sandstones from the Cretaceous Bainang accretionary complex in the central part of the Yarlung–Zangpo suture zone (YZSZ). The Bainang accretionary complex is located in a structural window that is mainly composed of Xigaze ophiolite, Late Triassic–Early Cretaceous radiolarite chert with a Late Cretaceous hemipelagic siliceous shale matrix, and Late Cretaceous sandstone. The obtained detrital zircon geochronological dataset confirms two spectra. Detrital zircons from the Canggasaba and Lianxiang sections are dominated by Precambrian grains with subordinate numbers of Mesozoic grains clustering at 243–178, 164–117, and 109–91 Ma, consistent with the mélange and trench-fill Rongmawa Formation, and all the trace elements of the Mesozoic grains match continental arc affinity. Provenance analysis suggests that detritus in these sections was mainly derived from the eastern part of the Gangdese arc and the central–northern Lhasa terrane. These results confirm the existence of the ancestral Lhasa River that transports sediments from the eastern Lhasa terrane to the subduction zone and further westward along the east–west axial system parallel to the trench. Conversely, the Qiajiu section is mainly dominated by Mesozoic detrital zircon grains, representing submarine fan deposits that were sourced from the adjacent Gangdese arc and transported through a local north–south-flowing river system. Detrital Cr-spinel compositions and detrital zircon trace elements from the Qiajiu section also revealed the contribution of ophiolites. Considering the abundance of Eurasia-affinity detrital zircons, this study supports the single subduction model that was developed along the southern margin of the Lhasa terrane.

Cenozoic sequence stratigraphy and sedimentary evolution of forearc basin in Ryukyu Island Arc region

琉球弧前盆地位于菲律宾海板块北部与欧亚板块汇聚部位，发育于琉球海沟北部增生楔与琉球岛弧之间，是典型“沟-弧-盆”体系的组成单元。现利用多道地震资料，首次建立琉球弧前盆地的层序地层格架，分析其新生代层序地层特征，阐明弧前盆地沉积充填演化过程，并探讨各盆地主要物源。通过地震剖面解释分析，表明:①始新世为岛弧变质基底沉积期，晚渐新世晚期-早中新世阶段发育残余伸展盆地基底沉积，属于浅海环境，主要受岩浆活动影响，发育火山碎屑岩相；②中中新世-第四纪时期是弧前盆地的主体沉积期，盆地从半深海沉积环境向深海环境过渡，发育典型深海沉积相，局部为火山碎屑岩相；中中新世时北部的南琉球群岛是弧前盆地主要物源区；晚中新世至第四纪时期，台湾岛东北部陆区成为对该弧前盆地贡献最大的物源区，而南琉球群岛的物源供给量降为次要地位。该研究结果是对琉球岛弧及周缘构造控盆作用研究的拓展，并对台湾岛陆地与东部海域“源-汇”系统研究有重要的指导意义。;The Ryukyu forearc basin is located at the convergence of the northern Philippine Sea plate and the Eurasian plate. It is developed between the accretionary wedge in the northern Ryukyu trench and the Ryukyu Island Arc. It is a component unit of a typical 'trench-arc-basin' system. Now, based on the multi-channel seismic data, the sequence stratigraphic framework established for the first time in the study area is used to analyze the Cenozoic sequence stratigraphy and sedimentary evolution characteristics, and discuss the main source of sediment. According to the characteristics of seismic reflection and the contact relationship of reflection layer group, it is revealed that the Cenozoic in the study area experienced the process of shallow marine facies, semi-deep marine facies and deep-sea facies. It is considered that island arc metamorphic basement sedimentation developed in Eocene, and the basement sedimentation period of residual extensional basin from Late Eocene to Early Miocene belongs to the basement sedimentation period of fore arc basin, which is a shallow sea environment and mainly develops pyroclastic lithofacies; The Middle Miocene to Quaternary is the main sedimentary period of the forearc basin. It transited from the bathyal to the deep-sea sedimentary environment. The local volcanic clastic facies developed many typical sedimentary systems, such as gravity flow, turbidite fan, underwater delta and turbidite channel. It is inferred that the South Ryukyu Islands in the northern part of the Middle Miocene was the main provenance in the forearc basin period. Since the Late Miocene, the land area in the northeast of Taiwan Island has become the largest provenance, and the South Ryukyu Islands is in the second place. The results are an extension of the study on the basin control of the Ryukyu Island Arc and its surrounding structures, and have important guiding significance for the study of the 'source-sink' system of the land and eastern sea area of Taiwan Island.

Sedimentary environment and tectonic setting of the clastic formation of the Tanjianshan Group in the Tuomoerrite area, North Qaidam

柴北缘构造带断续出露的寒武-奥陶纪滩间山群火山-沉积岩系是早古生代时期原特提斯洋俯冲造山作用的产物，也是中国西部块状硫化物和造山型金矿床的重要含矿岩系。前人已对滩间山群火山岩组开展了大量的地球化学和同位素年代学研究，而碎屑岩组的沉积序列和沉积相研究相对薄弱。我们在柴北缘托莫尔日特地区地质填图过程中，对该地区的滩间山群碎屑岩组开展了系统的沉积组合序列和沉积相研究。托莫尔日特地区滩间山群碎屑岩组是由富含火山碎屑物质的含砾砂岩、砂岩、粉砂岩、泥岩、沉凝灰岩、硅质凝灰岩、硅质岩及少量砾岩共同组成。可分为下岩性段和上岩性段，其中下岩性段为一套形成于海底扇外扇环境以沉凝灰岩为主的沉积组合；上岩性段包含海底扇内扇、中扇和外扇沉积，且以中扇环境的沉积为主。垂向上，它们呈现出粒度向上逐渐变细特征；空间上，具有向北西方向火山物质成分逐渐增多、砾岩和砂岩厚度变薄且砾岩消失的变化特征。砂岩主要为岩屑长石杂砂岩，其中岩屑主要是安山岩和少量玄武岩、英安岩、凝灰岩；长石主要为斜长石；石英碎屑相对缺失。砾岩中砾石以安山岩和硅质岩为主，并含有少量灰岩和凝灰岩砾石。底冲刷面、正粒序、平行层理和波纹层理等沉积构造普遍发育，呈现出典型的浊流沉积特征；同时在局部露头见有滑塌构造和波痕。区域上，这套沉积组合序列位于寒武-奥陶纪岛弧火山岩的南侧；古水流分析显示，它们的碎屑物质主要来自于其北东方向。这些结果表明，柴北缘构造带东段的滩间山群碎屑岩组是一套成熟度极低且与寒武-奥陶纪岛弧火山活动密切相关的沉积组合。;Volcano-sedimentary system of the Cambrian-Ordovician Tanjianshan Group in the northern margin of Qaidam basin was formed by the subduction of the Proto-Tethys Ocean during Early Paleozoic and hosted massive sulfides and orogenic gold deposits in western China. Much attention had been paid to geochemistry and isotopic dating of the volcanic Formation of the Tanjianshan Group, but the sedimentary sequence and facies of the associated clastic rocks received less care. Systemic studies on the sedimentary sequence and facies in the processes of the geological mapping demonstrate that the clastic Formation in the Tuomoerrite area consists of pebbly sandstone, sandstone, siltstone, mudstone, tuffite, siliceous tuff, chert and minor conglomerate. This formation can be subdivided into two lithologic units. The lower unit is mainly dominated by tuffite deposited in the lower submarine fan environment, whereas the upper unit is deposited in the upper, mid, and lower fan environments. In contrast, the rock assemblages of the upper unit are mainly composed of the mid-fan deposits. The upper unit is characterized by fining-upward sequence and increasing abundance of volcanic composition northwestward, but the thickness of sandstones decreases and conglomerate disappears to northwest. Sandstones mainly comprise lithic greywacke. Lithic fragments contain andesite, basalt, dacite, and minor tuff and limestone. Feldspar fragments are dominated by plagioclase grains, and less monocrystalline quartz grains with an igneous origin occur in several samples. Clasts of conglomerates are dominated by angular andesite, chert and minor limestone and tuff. Irregular basal erosional surface, normal grading, parallel laminations and ripples are widespread show typical of turbidite. Slumping folds and wave marks can also be observed in the local outcrops. Regionally, volcano-clastic rocks distributed in the southern margin of Cambrian-Ordovician Keke island arc with a southwestward paleocurrent. These results demonstrate that the clastic formation is closely related to the Cambrian-Ordovician island arc.

Вік та умови нагромадження палеоценових відкладів Скибового покриву Карпат на основі мікропалеонтологічних та седиментологічних даних

The results of micropaleontological and sedimentological studies of the Paleocene sediments such as the Upper Member of the Stryi Formation and the Yamna Formation located in the Skyba Nappe in the Ukrainian Outer (Flysh) Carpathians are represented. Sedimentological features of the flysch successions (including the sedimentary succession along the Prut River in the city of Yaremche) proved that the Upper Member of the Stryi Formation is represented mainly by turbidites; the lower part of the Yamna Formation (variegated Yaremcha Horizon) is composed of red and green clay hemipelagites and turbidites, and the upper part of the Yamna Formation (Yamna sandstone) consists of deposits of high-density turbidite currents and grain flows. The calcareous nannoplankton: NP1, NP2, NP3 and NP4 zones as well as the foraminifera: planktonic Globoconusa daubjergensis Zone (Danian Stage) and benthic Rzehakina epigona Subzone of Rzehakina fissistomata Zone, s. l. (the early Paleocene) are identified in the Upper Member of the Stryi Formation. The calcareous nannoplanktonic NP4, NP5, NP6 zones are distinguished in the Yaremcha Horizon and NP6, NP8, NP9 zones are identified in the Yamna sandstone. The agglutinated foraminifera including Rzehakina fissistomatа, Rz. epigona, Caudammina ovula, Hormosina velascoense, Glomospirella grzybowskii, Saccammina placenta, Paratrochamminoides irregularis are dominated in the Yamna Formation. The age of the Stryi Formation (Upper Member) is established as Danian–partly Zealandian, and the age of the Yamna Formation is Zealandian–Thanetian based on nannoplankton and foraminifera data. Deep-water agglutinated foraminifera (DWAF) belonging to the genera Rhabdammina, Hyperammina, Dendrophrya, Ammodiscus, Glomospira, Hormosina, Reophax, Haplophragmoides, Recurvoides, Trochamminoides, Paratrochamminoides, Spiroplectammina, Karreriella are dominated in the background hemipelagic clay deposits and make up to 100% of the tests in the microfaunal associations, that suggests the lower bathyal-abyssal depths of the sedimentary paleobasin The channel deposits (Yamna sandstone) and interchannel sediments (Upper Member of the Stryi Formation) of the ancient deep-sea fan are identified in the Paleogene flysch.

Controls on submarine canyon morphology along a convergent tectonic margin. The Southern Caribbean of Colombia

Submarine canyons are major conduits for sediment transfer from continental shelf to deep marine environments. Mass failures and faults play a key role in the initiation and evolution of submarine canyons along convergent tectonic margins, in addition to continental sediment supply. Here we analyze high-resolution bathymetry and seismic data from the Colombian southern Caribbean to investigate the controls on submarine canyon morphology along a convergent tectonic margin. We propose three end-member types of canyons: Type I canyons have a direct connection to a major river associated with high sediment supply. These canyons are highly erosive and cut topographic barriers created by tectonic deformation. Type II canyons are associated with faults at the canyon's head, where the location, orientation, and sinuosity are controlled by fault strike. Also, the presence of faults is related to an increase in the occurrence of mass failures from the steep canyon borders, increasing the depth and width asymmetry. Finally, Type III canyons evolve toward the continental shelf edge through retrogressive mass failures. These mass failures produce erosional scars that merge downslope to create submarine canyons in early stages of development, which later evolve to wider but shallow canyons due to the progressive basinward merging. We argue that the morphology of each canyon type is controlled by the interaction between continental sediment supply, mass failures, shelf width, and fault occurrence. We also demonstrate that seafloor topography influences the size of submarine fan deposits at the mouths of canyons. We identified large fan deposits (>650 km2) on the continental rise, whereas in piggyback sub-basins we found smaller fans (<60 km2). Our analysis of downdip canyon morphology and associated deposits can be used to predict the development of submarine canyons and associated fans in convergent tectonic margins worldwide.

Modelling the dynamic response of shallow methane hydrates to simultaneous sea level and bottom water temperatures variations since the last glacial maximum on the Amazon Deep-Sea Fan, Brazil

In marine sediments, methane hydrate can occur within the methane hydrate stability zone (MHSZ), which extends from the seafloor to a certain depth below it, within which the conditions of pressure and temperature are such that allow their formation and stability. Variations in sea level and in bottom water temperatures (BWTs) have opposite effects on the stability zone: a sea level rise leads to higher hydrostatic pressure, which tends to enlarge the MHSZ, while an increase in temperature tends to shrink it, and vice-versa. When the MHSZ shrinks, methane hydrate dissociates, releasing water and gaseous methane into the sediment pores. If the gaseous methane reaches the seafloor, it will be released into the ocean. In this study, we use numerical modelling to investigate the dynamic response of shallow methane hydrates at 550, 575, 600, 625, 650, 700 and 750 m water depth (mwd), on the Amazon Deep-Sea Fan, Equatorial Atlantic Ocean (near the northern coast of Brazil), to simultaneous sea level and BWTs increases, since the Last Glacial Maximum (LGM) up to the present. These water depths lie on the feather edge of the MHSZ, where hydrates are most sensitive to pressure and temperature perturbations. The results suggest that the methane hydrate stability decrease caused by the BWTs increases has completely overcome the increase in stability owing to sea level increase, for 550 and 575 mwd. For these two water depths, the MHSZ disappeared in the models and all the hydrate initially present has dissociated. The modelling results indicate that gaseous methane started to be released into the ocean at ca. 17,500 y BP for 550 mwd and at ca. 16,000 y BP for 575 mwd. For the other water depths considered, hydrate stability decrease caused by the BWT increase has only partly overcome the increase in stability due to pressure increase, so that the MHSZs have shrank, but have not totally disappeared in the models. Gaseous methane was released into the ocean from ca. 14,000 y BP to 7000 y BP for 600 mwd. For 625, 650, 700 and 750 mwd, no gaseous methane has been released into the ocean. Methane release amounts and flowrates are maximum limits for each depth, as no methane consumption processes, such as anaerobic oxidation, are modeled in this study.

Particle shape trends across experimental cohesive and non‐cohesive sediment gravity flow deposits: Implications for particle fractionation and discrimination of depositional settings

AbstractFractionation of particles in deep‐water sediment gravity flows is an important factor in the resulting deposit and for discriminating sedimentary environments, but remains poorly understood. Quantitative characterization of particle shape was performed for more than ten‐thousand particles of experimental gravity flow experiments (both of cohesive and non‐cohesive nature) made using coal and kaolin particles. Eleven particle shape parameters were calculated and their distribution and trends within the experimental basin were evaluated. Results indicate the existence of non‐normal distributions and observable correlations between particle shape parameters. Shape parameters such as circularity and roundness are dominant controls on shape variation. Strong correlations exist between mean shape parameters and along‐flow distance from the source for particles in non‐cohesive flow experiments. Important differences were observed between shape parameter distributions of particles sampled at different areas within the experimental basin, which can be grouped based on their depositional setting (proximal or distal) using multivariate statistical analysis, especially for the non‐cohesive flow experiments. A tendency for more elongated and irregularly‐shaped particles at the more distal and marginal areas of the studied experimental basin was observed and validated by previous field studies in real‐world deep‐marine deposits. Besides, fractionation of particles is less‐pronounced in cohesive flows compared with non‐cohesive ones suggesting the soundness of discrimination of depositional settings based solely on particle shape characteristics is strongly dependent on parent flow characteristics. Yet, results highlight the potential of particle shape analysis in revealing spatial particle shape trends due to hydrodynamic fractionation and discriminating different depositional settings within submarine fans. This methodology may be applied to seafloor and subsurface samples to help identify the flow process and depositional environment.

Timelapse of the geomorphologic and stratigraphic evolution of a Late Cretaceous deep-sea fan, northern Santos basin, Brazil

Deep-sea fans are the terminal sinks of clastic sediment, nutrients and pollutants produced in continental landmasses. They are also major targets for oil and gas on continental margins. Several recent studies have applied seismic geomorphology to delineate deep-sea fans, however, most of them describe a relatively short period of the geologic time, disfavoring the observation of long-term geomorphologic changes and the resulting depositional architecture. We analyzed the geomorphologic evolution and architecture of the Maastrichtian, deeply buried, Maricá deep-sea fan in northern Santos Basin, offshore SE Brazil. Using three-dimensional seismic data and logs from three wells, we mapped five horizons (stratal slices), including fan base, fan top and three internal horizons. The examination of lobes and channel networks on each horizon resulted in a timelapse that capture major geomorphologic transformations of the deep-sea fan from inception to abandonment. The Maricá deep-sea fan is a sand-rich system deposited directly onto the irregular topography of the Maricá mass-transport deposit, and its geometry is also influenced by structural highs uplifted by active halokinesis. Six lobes were mapped, which present variable growing patterns and associated stratigraphic signatures indicative of aggradation, progradation, retrogradation, and lateral switching. Four types of channel morphology were identified (straight, sinuous, meandering, and braided-like). Channel length and sinuosity tend to increase with time in the whole fan and within individual lobes. Amplitude maps and well-log motifs suggest that sandy sediments occur mainly as channel-fill deposits and that different channel morphologies produce contrasting stratigraphic architectures and reservoir heterogeneities. Our results show that channel network and sand-body architecture evolve in a predictive fashion mostly controlled by fan aggradation. However, the interaction with the underlying topography causes morphologic changes at the lobe and depositional element scale that often deviate from the overall trend and affect sand distribution across the fan surface.

Source-to-sink characteristics of the channelized submarine fan system of the Huangliu formation in the Dongfang block, Yinggehai basin, south China sea

Under the guidance of the source-to-sink system model, we conducted multi-scale research, characterizing the provenance features, transport pathway, convergence mode, sand body architecture, and controlling factors of the channelized submarine fan developed in the Huangliuformation, Dongfang block, Yinggehai basin by combining both macro and micro methods. Zircon U–Pb dating, heavy minerals, and source area lithologic geological analysis confirmed that the provenance input for the upper member of the Huangliuformation mainly originated from a northwest mixed provenance system, which includes the Red River, Lam River, and Ma River drainage area. Based on 3D seismic and well logging data, seismic interpretation and sand body tracking were performed to further reveal that the ancient delta sediments were transported along the Yingxi slope and converged on the seafloor in the central depression to form a submarine fan. Detailed seismic sedimentological analysis also confirmed that the submarine fan is characterized by a strong gravity flow channelization. The thickness of the sand body varies significantly and its spatial structure is highly heterogeneous. The channels in the area were divided into four types: main channel, medial channel, migrated channel, and distal channel, according to genetic type and morphological characteristics. The submarine fan system was divided into six stages, exhibiting various channel and lobe developments and distributions. The evolution of the multi-stage channelized submarine fan was closely related to the sediment provenance, sea level rise and fall, and paleogeomorphology. Our research is important for the natural gas field exploration and sand body reservoir evaluation in DongFang block,and have typical case value for deep-water channelized submarine fan deposition in the South China Sea.

Facies architecture, modal analysis and geochemistry of the Early Ediacaran turbiditic series in the Skoura inlier (Central High Atlas, Morocco): Implications for provenance and geotectonic setting.

A multidisciplinary approach based on lithostratigraphy, petrography, modal composition and geochemistry was performed for the first time, to study the Early Ediacaran Skoura Turbidites (EEST) of the Skoura inlier, Central High Atlas. It represents widely distributed turbidite successions up to 8 km in thickness. A total of twelve lithofacies types have been distinguished, spread in four profiles, and grouped in three major depositional environments: shallow delta complex (FA1), submarine channel (FA2), and deep-sea fan (FA3). The paleogeographic distribution of the EEST may indicate basin depth changes related to the onset of convergence.Petrographic and modal analyses of EEST reveal greywacke and lith-arenite lithologies displaying similar clast composition, mainly comprising quartz and lithic fragments. Volcanic, plutonic, and metamorphic rocks have been exposed in the source areas feeding the Skoura basin. On Q-F-L diagram, EEST have characteristics of a recycled orogen, suggesting their derivation from an active arc setting. Geochemical data of EEST samples display similar SiO2 and Al2O3 abundances, with relatively intermediate compositions. Most of the studied samples demonstrate their derivation from a composite of oceanic island and continental arc systems providing felsic and mafic to intermediate detritus to the Skoura basin. Rare-earth element patterns show features similar to those of sandstones in modern active margin zones. The EEST rocks are similar with other Early Ediacaran sediments of the Saghro Group in the Anti-Atlas belt. This architecture suggests deposition of the EEST in an orogenic basin developed in a back-arc setting during the Early Ediacaran time.

Lateral, longitudinal, and temporal variation in trench-slope basin fill: examples from the Neogene Akitio sub-basin, Hikurangi Margin, New Zealand

ABSTRACT The fill of trench-slope basins is complex, varying temporally, laterally, and longitudinally. New data from the Neogene stratigraphy of the Akitio Sub-basin, Wairarapa, are presented to investigate such fill variation. The preserved basin fill spans an area 70 km long by 10 km wide, representing deposits from a trench-slope basin. Integration of sedimentological, micropalaeoentological, and geological mapping data charts basin fill evolution. Over 15 km of strata were logged, defining 17 lithofacies associations, which were mapped across the basin; these are interpreted to represent both shallow and deep-water environments. The deep-water strata show a temporal evolution from ponded turbidite deposition, to a period of basin spill via conduits connecting to downstream basins, development of aggradational channel-levees, and finally unconfined submarine fan deposition. Shallow marine deposits mostly developed on the up-dip basin margin occur contemporaneously with basinal mass-transport deposits, and in association with the growth of basin bounding structural ridges. Comparison with the evolution of the offshore, actively filling Akitio Trough highlights controls on trench-slope basin fill: a first-order influence of external controls, e.g. tectonism to create the basin; a second-order progression from under- to overfilled; and third-order lateral variation reflecting autogenic process and the effects of local structures on seafloor gradients. These factors combine to vary sedimentation in trench-slope-basins spatially and temporally.

Proximal to distal grain‐size distribution of basin‐floor lobes: A study from the Battfjellet Formation, Central Tertiary Basin, Svalbard

AbstractThe grain‐size distribution of sediment particles is an important aspect of the architecture of submarine fans and lobes. It governs depositional sand quality and reflects distribution of particulate organic carbon and pollutants. Documenting the grain‐size distribution of these deep‐marine sedimentary bodies can also offer us an insight into the flows that deposited them. Submarine lobes are commonly assumed to linearly fine from an apex, meaning there should be a proportional relationship between grain size and distance from the lobe apex. However, not much detailed quantitative work has been done to test this hypothesis. Exposure of a 5 km long dip‐section of basin‐floor lobes in Clinoform 12, Battfjellet Formation, Spitsbergen, enable the study of basinward grain‐size evolution in lobe deposits. Furthermore, the dataset allows testing if there are any documentable grain‐size differences between lobe sub‐environments. For this purpose, the palaeogeography of Clinoform 12 was reconstructed and the youngest lobe, which was exposed in all collected logs, chosen to be evaluated for its grain‐size trends. Photographed thin sections of 66 rock samples were analysed to obtain quantitative grain‐size distributions. The results show that fining of lobe deposits occurs predominantly in the most proximal and most distal parts of the lobe, while the intermediate lobe, which is dominated by lobe off‐axis deposits, is characterised by a relatively consistent grain‐size range. Lobe sub‐environments show statistically distinct grain‐size distributions from lobe axis to lobe fringe. An explanation for these trends is the interplay of capacity and competence‐driven deposition with the grain‐size stratification of the flows. The outcomes of this study help to better understand the proximal to distal evolution of turbidity currents and their depositional patterns. They also provide important insights in reservoir potential of basin‐floor fans at lobe scale.

Facies Analysis, Depositional Environments and Geochemistry of the Late Ladinian-Early Carnian Ashin Formation, (Central Iran)

The present study aims to investigate the petrographic, geochemical features, and depositional facies of the Late Triassic Ashin Formation (Nakhlak Group, central Iran). For this purpose, 100 thin sections, and 13 samples of fine-grained sedimentary rocks were analyzed for their petrographic and geochemical characteristics, taken from a 330-m thick section of this formation. The petrographic types identified in this formation include sandstone, siltstone and limestone. This study suggests limestone facies are deposited in upper parts of the distal submarine fan towards the shore, sandstone facies are deposited in the middle part of the distal submarine fan, and the shale facies are deposited in lower parts of the distal submarine fan towards the abyssal plain by turbidity currents. The plotting of petrographic data on ternary diagrams for compositional classification illustrate their composition as litharenites, sub-litharenites, and a few litharenite-feldspathic and shales. Discrete diagrams refer to a tectonic setting of a continental arc complex and the active continental margin. The results of the modal analysis and geochemical data indicate the orogenic re-cycling for these deposits. CIA and CIW indexes indicate moderate weathering of the source area under semi-arid to semi-humid climates.

Statistical characterization of a confined submarine fan system: The Pennsylvanian Lower Atoka Formation, Ouachita Mountains, USA

AbstractCurrent knowledge of submarine fan deposits has historically relied heavily on qualitative field and subsurface observations and interpretations, but recent studies using statistical analyses have enhanced the understanding of submarine fan sub‐environments, including the degree of confinement, stratigraphic patterns and potential control factors. The purpose of this study is to improve the quantitative understanding of synorogenic submarine fan deposition at foreland basin settings with a statistical approach. A suite of statistical methods is integrated and developed (Hurst Statistics/rescaled range analysis, bed thickness frequency distribution analysis, Markov Chains and time‐series analysis), and applied to the well‐understood Pennsylvanian lower Atoka submarine fan system in the Ouachita Mountains, United States, for this purpose. The results of the Hurst Statistics and bed thickness analyses corroborate qualitative interpretations that: (i) the lower Atoka is lobe‐dominated; and (ii) the south‐eastern (wedge top) portion of the system is more strongly confined than the northern (foredeep) portion. The Markov Chains and time‐series analyses reveal the prevalence (56% of the measured sections) of stratigraphic orderliness and cyclicity; these results are used to discuss potential control signals, which are otherwise difficult to distinguish, on the turbidite sandstone recurrence cycles. The results of this study demonstrate that these integrated statistical methods can be utilized to quantify depositional interpretations and extract hidden information using outcrops with limited exposures.

Geology and sedimentary environment of the Surma Group of rocks, Bandarban anticline, Bandarban, Bangladesh

The study illustrates the effect of tectonics, climate, and relative sea-level change on the depositional process of the Miocene Bhuban and Boka Bil Formation of Bengal Basin. Outcrop sediments of five transverse sections exposed along the axial zone of Bandarban anticline were studied. Twelve lithofacies such as Gm, Gms, Sm, ST, Sp, Sr, Sl, Sf, Sll, Fw, Fl and Fm have been identified within the successions and grouped into (i) turbidite generated, (ii) outer fan distal lobe basin plain and (iii) tide-influenced facies association. The analyses reveal that the Bhuban Formation was turbidite- generated that deposited below the continental shelf-slope environment. The Lower Bhuban Member consists of gray to brownish-gray calcareous sandstone with shale deposited under the channelized lobe of submarine fan. The Middle Bhuban Member dominated by black shale-siltstone deposited in distal turbidite lobe due to change the flow regime. The Upper Bhuban Member consists of yellow to yellowish gray, coarse to medium-grained sandstone-siltstone with black shale that deposited under channelized to nonchannelized lobes of submarine fan. The increasing sedimentation during the formation of the Upper Bhuban Member can be caused by increased the intensity of the Asian Monsoon that carried huge sediment from the Himalaya. The Boka Bil Formation was deposited under estuary to tidal flat environment. The area was uplifted during and/or after subduction of the Indian Plate beneath the Burmese Plate. The monsoonal intensity enhances sedimentation that moved prograding delta towards the south. These processes shifted depositional environment from continental shelf-slope to marginal shallow marine during deposition of the Boka Bil Formation. The continental slope aligned east-west direction and sediments likely derived from the Himalaya and Trans-Himalaya in the present geographical setup during deposition of the sediments.

Depositional and geomorphic patterns of mixed calciclastic‐siliciclastic systems on a deep‐water Equatorial Margin

AbstractDistal slope and basin depositional systems in deep waters of the Pará‐Maranhão Basin, Equatorial Brazil, are investigated using a high‐resolution 3D seismic volume, borehole data and multispectral satellite imagery. A Neogene calciclastic submarine fan and a series of channel‐levee systems are analysed at water depths of 100–3,500 m. Channel‐levee systems have sinuous and straight morphologies and are of different sizes. Their origin is related to turbidity flows sourced and funnelled from the carbonate shelf to submarine canyons and gullies, as well as from areas with marked slope instability. A mixed calciclastic‐siliciclastic sediment input is recognised with autochthonous calcarenites and calcilutites comprising the bulk of sediment on the mid and outer continental shelf. Minor amounts of siliciclastic sediment sourced from small rivers occur on the inner shelf. Sedimentation processes of a distally steepened carbonate ramp are discussed considering a general depositional setting dominated by fluctuations in relative sea‐level. Cross‐sectional and planar parameters of mixed calciclastic‐siliciclastic channel‐levee systems are compared to their siliciclastic counterparts. Morphological results show similarities between calciclastic and siliciclastic channel‐levee systems. As a corollary, three types of channel‐levee systems are described: (a) channels related to calciclastic submarine fans, (b) low‐sinuosity, aggradational channels, and (c) high‐sinuosity channels.

Submarine geomorphology

Abstract Submarine geomorphology underwent significant development in the second half of the twentieth century, largely thanks to advances in technology by the military, navigation and hydrocarbon industry, which were later transferred to the academic and commercial sectors. In this chapter we summarize the development of the key methods used in submarine geomorphology between 1950 and 2000, which include sidescan sonar, multibeam echo sounder, reflection seismology, seafloor sampling and marine robotic systems. We then highlight the progress in our understanding of seafloor processes and landforms made using these methods, focusing on continental shelf landforms, slope instability, submarine canyons, submarine fans and channels, and current-controlled landforms.