Fan Bodies Research Articles

Application of Seismic Sedimentology in Identifying Submarine Fan Bodies

Abstract The research area is located in the Yenisai Hatanga Basin of Russia, which is a transitional facies sedimentary rock between sea and land. Oil and gas are mostly concentrated in turbidite sand bodies of the low level domain submarine fans of Lower hutt formation in the Lower Cretaceous, and locally developed in the slope fan sand bodies of the high postion domain. which is good oil and gas reservoir, however, due to limitations of geological research conditions and data, the sedimentary characteristics and planar distribution of the submarine fan sand bodies are not clear in research area. This article conducts research on the identification and plane distribution prediction of submarine fan bodies using seismic sedimentology methods, By combining sequence stratigraphy, seismic profile, and RGB fusion technology, the sand bodies of submarine fans are analyzed. Through the correlation analysis of seismic profiles and seismic facies, corresponding relationship between sedimentary microfacies and typical seismic wave patterns is established. The study shows that the study area mainly develops continental shelf slope facies, submarine fans, and shallow to semi deep marine facies. Sediments formed a turbidite submarine fan composed of sandstone siltstone mudstone in the ancient trough. There are 5 sand groups developed in the Hutt Formation under the main target layer in the study area. Among them, the IV oil group is the main oil-bearing layer. The 0, Ⅰ, and Ⅱ sand groups have limited distribution and poor sand body connectivity. The Ⅲ sand group is mainly developed in the study area. In the north, it is distributed in the middle of the study area on the plane. The IV sand group is widely developed and distributed in the middle of the study area on the plane. Seismic sedimentology can provide technical support for prediction research of reservoirs.

Postglacial outsize fan formation in the Upper Rhone valley, Switzerland – gradual or catastrophic?

AbstractOutsize fans are characterized by seemingly disproportionately small feeder catchments in relation to their fan area. Often having escaped rigorous scientific inquiry, the formative processes of these landforms remain inconclusive, supposedly ranging from catastrophic mass‐wasting processes to gradual fluvial formation. Here we apply a multi‐method approach, combining morphometric analysis with geophysical subsurface surveys and cosmogenic radionuclide exposure dating, to three outsize fans with hitherto unknown formation history in the Upper Rhone valley, Switzerland. Their feeder catchments are cut into bedrock hillslopes with a lack of indication of both pre‐existing catchment structures and/or unconsolidated material that was available after deglaciation.Focusing our study on the largest of these fans, our findings suggest a fan formation in three phases: In Phase 1, commencing after deglaciation at c. 10 ka and ceasing with full catchment development c. 6.0 ka, bulk fan bodies were established by deposits of massive high‐energy, high‐magnitude debris flows exporting sediment with average yields of up to 73 kt km−2 yr−1. In Phase 2, feeder basins were affected by comparatively lower‐magnitude debris flows that distributed a sedimentary facies of debris flow channels, snouts and large boulders across the initial fan. Over time, deposition rates quickly decayed and finally ceased c. 0.8 ka, when the system entered the present Phase 3, during which the fan‐surface consolidated and fan aggradation terminated. Low gradient and abundant still‐water deposits upstream of the fan still attest to the disruption of longitudinal sediment connectivity in the trunk valley.We conclude that outsize fan formation by massive debris flows in the Upper Rhone valley was rapid and massive, but incremental and non‐catastrophic. Given the delivery of material at extremely high rates, outsize fans are capable of having a sustained impact on geomorphic systems and, during phases of activity, potentially endangering human livelihoods.

The Main Controlling Factors of Glutenite Development and Their Impacts on Oil Energy Extraction

The glutenite reservoirs discovered in the Jiyang depression in Bohai Bay contribute greatly to proven oil and gas resources, which have reached 1.27 billion cubic meters. Both insufficient studies on the glutenite distribution and incomplete understanding of the corresponding geology restrict further oil energy extraction. Hence, it is necessary to study the controlling factors of glutenite development. Sedimentation, tectonic faults, geophysical data, etc., was used in this paper to study these factors. Four main controlling factors involved in the development of glutenite fan bodies have been studied and summarized: the fault ramp controls the glutenite fan, the fault characteristics control the glutenite acreage, the fault throw controls the thickness of the glutenite, and the dimensions of the incised valleys control the glutenite transport capacity. Based on this geological understanding, this paper analyzes the relationship between oil productivity data and the factors controlling conglomerate development. With this, the reservoir in the study area is divided into a high production area, medium production area, and low production area. The C913 well was deployed in the predicted high production area. The daily oil production reached 88 t/d, and the energy exploitation effect was good. Therefore, this study provides important guidance for the further extraction of oil energy.

E&P Notes (December 2020)

E&P Notes (December 2020)

Three-dimensional Simulation and Analysis of Spray Structure inVertical MOCVD Reaction Chamber

In the vertical spray MOCVD reactor, a spray structure composed of fan bodies was proposed. CFD was used to simulate the gas deposition process in GaN-MOCVD reactor. The characteristics of changing the concentration of reaction gas above the substrate surface with the height of the fan, the distance between the spray nozzle and the substrate surface, and the substrate rotation speed were given. Compared with the traditional spray structure, the cylindrical spray structure composed of fan body can effectively reduce the premixing problem of reaction gas sprayed from the spray nozzle before entering the reaction chamber and reaching the substrate surface. At the same time, the simulation structure shows that when other conditions are fixed, with the increase of the fan height, the increase of the distance between the spray nozzle and the substrate surface and the acceleration of the substrate rotation speed, the uniformity of GaN deposition on the substrate surface can be better under the same isolation effect, so that the utilization rate of TMG can be as high as possible under the condition that the uniformity is satisfied.

Lower Cretaceous stratigraphic characteristics and tectonic control of the eastern depression, North Yellow Sea Basin, North China

The Lower Cretaceous of the eastern depression in the North Yellow Sea Basin is a set of residual strata that can be divided into K1sq1 and K1sq2 sequences. There are four lithology–lithofacies architectures summarized in the third-order sequences of wells W5, W3, W1, W9, W16, W7, W8, and W10, and they are the coarse–fine–coarse, asymmetric coarse–fine, asymmetric fine–coarse, and interbedded coarse and fine. F1, F4, F6, and F7, which are strike-slip faults, were dominant during the Early Cretaceous, and controlled the eastern depression to undergo right-lateral movement from transtension to transpression. The tectonic movement controlled different stratigraphic structure in different areas, and the fan bodies deposited along the basin margin and progradated into the basin center. The sequence models under extensional and strike-slip setting were established respectively. The transtension–transpression movement controlled the development of the sandstones in the Lower Cretaceous and improved the quality of the reservoir rocks.

Sedimentary sequence and architecture analysis by integrating multi-discipline data — An example of a sandy conglomerate reservoir in Qie12 block, Qaidam Basin, NW China

Understanding the sedimentary sequence and architecture is important for planning the development strategy. We illustrate a case study of analyzing the sequence and architecture of a sandy conglomerate reservoir by integrating geology, petrophysics, seismic, and development data. The analysis indicates that the depostional environment of the target lower part of the Ganchaigou Formation is an alluvial fan. We defined eight lithofacies according to the core analysis and five sedimentary microfacies by integrating the core and petrophysical data. We next propose four sedimentary architectural models by integrating the lithofacies result, microfacies analysis, and high frequency sequence models. The four architecture models include the extensively connecting body sandwiched with intermittent channels, the composite channel formed by the overlapping and separation of stable channels, the lateral alternated braided channel and sheet flow sediment, and the runoff channel inlaid in flood plain mudstone. We finally build an architecture model for the alluvial fan. The model of the alluvial fan overall shows an upward-fining grain-size features and this feature indicates that the alluvial fan belongs to a retrograding sequence. The built model consists of six alluvial fan bodies that migrates from north.

The structure, depositional style and accumulation characteristics of continental margin with diachronous breakup in the northern South China Sea

ABSTRACT A typical diachronous breakup developed in the South China Sea (SCS); the breakup has been unequivocally identified, and gradually decreases in age from NE to SW. To illustrate the influence of a diachronous breakup on hydrocarbon accumulation, we used seismic profiles from CNOOC, and analysed crustal extension characteristics, sedimentary style and source rock accumulation. The main conclusions are as follows: (1) Because of the diachronous breakup in the SCS, various tectonic units developed in different positions on the northern continental margin with different degrees of extension. The Pearl River Mouth Basin (PRMB) is closer to the central sea basin of the SCS and has been affected by regional tension stress for a longer time. Tectonic units of proximal domain, necking zone, and distal margin types developed, and the crust structure thinned from the land towards the sea. The Qiongdongnan Basin (QB) is closer to the Southwest Sub-basin. There are symmetrical proximal domains on the southern and northern sides of the QB, with a necking zone in the central part. It presents as an abandoned passive continental margin. (2) The PRMB exhibited rifted cells first, followed by canyon type extensional faulting and horizontal axial transportation, and then by a longitudinal shelf-slope sedimentary style. But the QB has only rifted cells and canyon type faulting stages, no longitudinal shelf-slope sedimentary stage. The major source rocks in the northern SCS become younger from east to west, and the sedimentary facies change from lacustrine facies to marine-continental transitional facies. (3) The diachronous breakup process ultimately affecting oil and gas migration and accumulation process. The PRMB is dominated by deep-water shelf break accumulation with deep-water fan reservoir bodies. The QB is dominated by canyon type accumulation with channels.

The Hypanis Valles delta: The last highstand of a sea on early Mars?

One of the most contentious hypotheses in the geological history of Mars is whether the northern lowlands ever contained an oceanic water body. Arguably, the best evidence for an ocean comes from the presence of sedimentary fans around Mars' dichotomy boundary, which separates the northern lowlands from the southern highlands. Here we describe the palaeogeomorphology of the Hypanis Valles sediment fan, the largest sediment fan complex reported on Mars (area >970 km2). This has an extensive catchment (4.6×105 km2) incorporating Hypanis and Nanedi Valles, that we show was active during the late-Noachian/early-Hesperian period (∼3.7 Ga). The fan comprises a series of lobe-shaped sediment bodies, connected by multiple bifurcating flat-topped ridges. We interpret the latter as former fluvial channel belts now preserved in inverted relief. Meter-scale-thick, sub-horizontal layers that are continuous over tens of kilometres are visible in scarps and the inverted channel margins. The inverted channel branches and lobes are observed to occur up to at least 140 km from the outlet of Hypanis Valles and descend ∼500 m in elevation. The progressive basinward advance of the channellobe transition records deposition and avulsion at the margin of a retreating standing body of water, assuming the elevation of the northern plains basin floor is stable. We interpret the Hypanis sediment fan to represent an ancient delta as opposed to a fluvial fan system. At its location at the dichotomy boundary, the Hypanis Valles fan system is topographically open to Chryse Planitia – an extensive plain that opens in turn into the larger northern lowlands basin. We conclude that the observed progradation of fan bodies was due to basinward shoreline retreat of an ancient body of water which extended across at least Chryse Planitia. Given the open topography, it is plausible that the Hypanis fan system records the existence, last highstand, and retreat of a large sea in Chryse Planitia and perhaps even an ocean that filled the northern plains of Mars.

Late Pleistocene dune–sourced alluvial fans in coastal settings: Sedimentary facies and related processes (Mallorca, Western Mediterranean)

Aeolian-alluvial sedimentary interaction results in the formation of deposits characterized by typical alluvial sedimentary structures, but is composed of conspicuous amounts of aeolian sediments. The literature on this topic is limited and most works relate more with continental aeolian dunes or fluvial dune interference with fan bodies. Furthermore, there is a lack of examples of aeolian-alluvial sedimentary interference in coastal settings. In the western Mediterranean, there are many Pleistocene alluvial fan deposits built up partly by sediment originating from coastal dunes dismantled by alluvial streams. Very often, these deposits show a continuous sedimentary sequence through which we can derive the contribution and predominance of coastal, alluvial-colluvial and aeolian processes and their controls on landscape formation. This is an outstanding feature within coastal systems since it shows marine sediments reworked and integrated within coastal dune fields by aeolian transport, and the latter built up into alluvial fan bodies. In this sense, aeolian-alluvial interaction is the geomorphic–sedimentary expression of the coexistence and overlapping of alluvial and aeolian environments resulting in deposits sharing sedimentary features from both environments. The aim of this paper is to unravel the contribution of coastal dunes in the construction of alluvial fans bodies and identify the main sedimentary facies that constitute these deposits, as well as their climatic controls. For this reason, Es Caló fan (northern Mallorca) has been selected due to its well-exposed deposits exhibiting the alternation of aeolian, alluvial and colluvial deposits. Sedimentological and stratigraphic analyses based on 33 logs and complementary analyses demonstrate that most of the facies constituting the fan body are made up completely of marine bioclastic sands. These deposits record an alluvial fan sedimentary environment characterized by sediments inputs that do not proceed from non-alluvial/fluvial/colluvial systems. In fact they relate with a marine source. Chronologies on aeolianites of northern Mallorca indicate that up to four periods of aeolian deposition took place during cooling stages and marine regressions over the last 100 kyr. Moreover, the alternation of short warming-cooling fluctuations between the cooling stages may have provided the conditions necessary to generate stormy weather in the western Mediterranean, resulting in aeolian-alluvial interactions. Additionally, the dynamics of this sedimentary environment were only possible because during the Last Glacial Maximum, the sea level remained low enough to allow for the formation of coastal dune fields and fans.

塔木察格盆地南贝尔凹陷西部次凹下白垩统沉积和石油地质特征

蒙古国塔木察格盆地南贝尔凹陷西部次凹的发育主要受北东向同生正断层控制，叠加有基底地形起伏和北东东–近东西向剪切变换构造的影响。早白垩世早期为断陷阶段，相发育在西部次凹全区经历了统一–分异–再统一的完整旋回。铜钵庙组和南屯组主要发育扇三角洲相、近岸水下扇和湖泊相，扇体展布及其亚相发育受东、西两侧的物源区控制。西南侧的“临时性”物源区造成铜钵庙组沉积期南洼槽的沉降中心与沉积中心不一致。因厚度、岩性和岩相空间变化较大，源岩和储层发育因地而异。南洼槽烃源岩发育好，有机质以II2型为主，热演化经历了未成熟、成熟和生油高峰3个阶段。砂体发育在中–北洼槽较好，现有资料表明以特低孔–超低渗型储层为主。 The evolution of the West Sub-Sag, South Buir Sag of Tamtsag Basin in Mongolia is mainly controlled by extension of the contemporaneous NE-orientated faults. In addition, it is superimposed with the influences of the base-mental relief and the transferring of NEE- /near WE-orientated shear fracture. The early Early Cretaceous was a fault-depressing stage of the West Sub-Sag’s tectono-sedimentary evolution, and the facies developing experienced a complete cycle of universal- differentiation-re-universal. In the Tongbomiao and Nantun Formations, the major sedimentary facies-types are fan delta, inshore underwater fan and lacustrine facies. The distribution of fan bodies and each sub-facies occurring of fan delta and inshore underwater fan should be constrained by the source regions to both the eastern and western sides. To the southwestern side of the South Hollow, there existed a “temporary” source region, which resulted in the subsidence center being not superposition with the depocenter during the sedimentary period of the Tongbomiao Formation. Owing to spatial changes of the thickness, lithology and petrofacies, the source rocks and reservoirs in the West Sub-Sag display distinct inhomogeneity. In the South Hollow, the source rocks are better occurred, with the organic materials being mainly II2-type. The organic thermal evolution can be divided into three stages: unmatured, matured and oil-generating peak stages. The sand bodies are better developed in the Central-North Hollow. The available data demonstrate the reservoir’s physical property being relatively poor, namely, the majority being reservoir with extra-lower porosity and super-lower permeability.

The use of seismic attributes for fan and reservoir definition in the Sea Lion Field, North Falkland Basin

Fan bodies in the North Falkland Basin, including those that comprise the reservoir in the Sea Lion Field, have been defined seismically with the aid of several seismic attributes. This has provided a greater understanding of their geomorphology, potential reservoir variations and distribution, and has helped illuminate the full extent of some fans as well as the internal architectural detail of others. The attributes used include reflectivity attributes on full-stack and part-stack three-dimensional (3D) seismic data, impedance attributes on inverted seismic data, isochron attributes, and geometric attributes such as coherence, dip, curvature and spectral decomposition. The combination of spectral decomposition and high-resolution visualization techniques has greatly aided the identification and interpretation of some of the fans. Colour blending, where separate colours relating to different frequency ranges are blended into a single image, can reveal additional detail within the fan systems. Specific colour blends are seen to highlight separate sand bodies, as well as thickness variations, and have helped to resolve stratigraphic and petrophysical heterogeneity. Seismic attribute responses have been quantified with the integration of well data from the 18 wells within the 3D data set. This has resulted in a detailed reservoir characterization and definition of geological features within some of the fan bodies. This detailed use of seismic attributes on the North Falkland Basin 3D data set has been of benefit for both the appraisal and development of the Sea Lion Field, and has also helped to define future exploration targets and well locations within the basin.

Characteristics and origin of abnormally high porosity zones in buried Paleogene clastic reservoirs in the Shengtuo area, Dongying Sag, East China

There are three abnormally high porosity zones developed in buried Paleogene nearshore subaqueous fan and sublacustrine fan clastic reservoirs at 2,800–3,200 m, 3,250–3,700 m and 3,900–4,400 m, respectively, within the Shengtuo area of the Dongying Sag. Here the porosity of reservoirs buried deeper than 4,000 m can still be greater than 20%. Investigation of these three abnormally high porosity (AHP) zones in the 3rd to 4th member of the Paleogene Shahejie Formation in the Shengtuo area was carried out with utilization of core observation, thin section identification, SEM observation, image analysis, core physical property testing and other technical methods. The results show that, the AHP zones in 2,800–3,200 m and 3,250–3,700 m are visible pores primary AHP zones dominated by significant primary intergranular pores (more than 50% of the total porosity), while secondary pores and micropores in authigenic clays may develop in some reservoirs. AHP reservoirs in the AHP zone of 3,900–4,400 m are dominated by micropores in matrix, visible pores are mainly grain dissolution pores but with low absolute content (< 1%), so this zone belongs to the micropores primary AHP zone. The genesis of the three AHP zones was studied to distinguish between porosity enhancement and porosity preservation. Our research shows that, in deeply buried clastic reservoirs in the Shengtuo area, mineral dissolution occurred in a relatively closed diagenetic system with high temperature and high salinity. Reservoir rocks underwent extensive feldspar dissolution, while detrital carbonate grains and carbonate cements show no evidence of extensive dissolution. Although significant feldspar dissolution pores developed, feldspar dissolution enhanced porosity only a little due to the precipitation of almost isovolumetric dissolution products in the nearby primary intergranular pores in forms of authigenic clays and quartz cements. Net enhanced porosity originating from feldspar dissolution is generally less than 0.25%. Thus, the subsurface dissolution has little impact on the mid-deep buried high porosity reservoirs. Reservoirs in braided channels of middle fans in sublacustrine fans and reservoirs in the middle-front of fan bodies of nearshore subaqueous fans provide the basis for the development of AHP zones. The shallow development of fluid overpressure and early hydrocarbon emplacement have effectively retarded compaction and carbonate cementation, so that the high porosity in the superficial layers is preserved in the mid-deep layers. These are the main controlling factors in the development of AHP zones.

冲积扇扇体沉积特征与形态的刻画

准噶尔盆地西北缘二叠系中晚期地层大面积发育砾岩、砂质砾岩、砂质小砾岩等粗粒碎屑岩。通过对钻井、测井、录井、地震等资料的分析，认识到五八区上乌尔禾组主要发育冲积扇相及扇三角洲相，其中冲积扇相可分为扇根、扇中、扇端三个亚相，进一步细分为十个微相。通过对单个扇体的刻画，可以清晰认识到扇体的分布及叠置关系，这样结合“一扇一藏”理论对扇体进行油气的勘探与开发有很好的指导意义。 There widely exist coarse granular detrital rocks, such as conglomerate, sandy gravels, in middle- late permian series of northwest edge of Junggar Basin. Based on the analysis of the data on well drilling, logging and seism, we have recognized that alluvial fan and fan delta facies are widely developed in upper-WuErHe group of 5-8-area. Alluvial fan facies can be divided into three subfacies (fan-root, fan-middle and fan-terminal) and ten micro-facies. According to the detection of each fan body, the distribution and superimposed relationship of fan bodies can be well detected. As the traditional saying goes, “where there is alluvial fan, there is oil or gas”, it plays an important role in hydrocarbon exploration and production.

Tectonic evolution and its control over deposition in fault basins: A case study of the Western Sag of the Cenozoic Liaohe Depression, eastern China

The main petroliferous basins in eastern China are Cenozoic fault basins, most of which have experienced two-stage tectonic evolution, i.e., rifting subsidence in the Paleogene and post-rifting thermal subsidence in the Neogene-Quaternary. The episodic tectonic evolution and syndepositional faulting had significant influence on the fault basins in terms of accommodation space, deposition rate, and depositional facies zones. In this study, the tectonic deformation characteristics and the tectonic-depositional evolution of the Western Sag of the Cenozoic Liaohe Depression were investigated by comprehensive analysis of the available geological and geophysical data using the modern theory of tectonic geology and the balanced section technique. The tectonic deformation of the Cenozoic fault basin was characterized by superimposed faults and depression. In addition, there existed relatively independent but still related extensional tectonic systems and strike-slip tectonic systems. The tectonic evolution of the fault basin involved five stages, i.e., initial rifting stage (E2s4), intense faulting stage (E2s3), fault-depression transition stage (E3s1–2), differential uplifting stage (E3d), and depression stage (N-Q). According to the characteristics of tectonic development and evolution of the Western Sag, the depositional evolution in the Cenozoic fault basin was divided into two stages, i.e., multi-episodic rifting filling in the Paleogene and post-rifting filling in the Neogene-Quaternary. The former rifting stage was further subdivided into four episodes with different characteristics of depositional development. The episodic faulting controlled the filling process and filling pattern of the Cenozoic Western Sag as well as the development and spatial distribution of associated depositional systems, whereas the syndepositional faults that developed in multiple stages in various tectonic positions controlled the development of depositional systems and sand bodies in the Western Sag. That is, the fault terraces on steep slopes controlled the development of sand bodies, the fault terraces on gentle slopes controlled the development of low-stand fan bodies, and the fault terraces or fault troughs in the central basin controlled the development of fluxoturbidite bodies.

Anatomy of a subaqueous ice‐contact fan and delta complex, Middle Pleistocene, North‐west Germany

AbstractThis paper presents a detailed analysis of the high‐resolution facies architecture of the Middle Pleistocene Porta subaqueous ice‐contact fan and delta complex, deposited on the northern margin of glacial Lake Weser (North‐west Germany). A total of 10 sand and gravel pits and more than 100 wells were examined to document the complex facies architecture. The field study was supplemented with a ground‐penetrating radar survey and a shear‐wave seismic survey. All collected sedimentological and geophysical data were integrated into a high‐resolution three‐dimensional geological model for reconstructing the spatial distribution of facies associations. The Porta subaqueous fan and delta complex consist of three fan bodies deposited on a flat lake‐bottom surface at the margin of a retreating ice lobe. The northernmost fan complex is up to 55 m thick, 6·2 km wide and 6·5 km long. The incipient fan deposition is characterized by high‐energy flows of a plane‐wall jet. Very coarse‐grained, highly scoured jet‐efflux deposits with an elongate plan shape indicate a high Froude number, probably &gt;5. These jet‐efflux sediments are deposited in front of a large ∼3·2 km long, up to 1·2 km wide, and up to 25 m deep flute‐like scour, indicating the most proximal erosion and bypass area of the jet that widens and deepens with distance downstream to the region of maximum turbulence (approximately five times the conduit diameter). Evidence for subsequent flow splitting is given by the presence of two marginal gravel fan lobes, deposited in front of 1·3 to 2·5 km long flute‐like scours, that are 0·8 to 1 km wide and 7 to 20 m deep. In response to continued aggradation, small jets developed at the periphery of these bar‐like deposits and filled in the low areas adjacent to the original superelevated regions, locally raising the depositional surface and characterized by large‐scale trough cross‐stratified sand and pebbly sand. The incision of an up to 1·2 km wide and up to 35 m deep channel into the evolving fan is attributed to a catastrophic drainage event, probably related to a lake outburst and lake‐level fall in the range of 40 to 60 m. At the mouth of this channel, highly scoured jet‐efflux deposits formed under hydraulic‐jump conditions during flow expansion. Subsequently, Gilbert‐type deltas formed on the truncated fan margin, recording a second lake‐level drop in the range of 30 to 40 m. These catastrophic lake‐level falls were probably caused by rapid ice‐lobe retreat controlled by the convex‐up bottom topography of the ice valley.

Alluvial fan development and morpho‐tectonic evolution in response to contractional fault reactivation (Late Cretaceous–Palaeocene), Provence, France

ABSTRACTAlong‐strike variability within a Late Cretaceous to early Palaeocene contractional growth structure and associated alluvial fan deposits is documented at the northern margin of the Arc Basin (Provence, SE France). This contribution shows that alluvial fans can be used as high‐resolution proxies to reconstruct structural segmentation and palaeo‐geomorphological evolution of a source/basin margin system. Facies‐based reconstruction allows the spatial and temporal distribution of alluvial fan bodies to be mapped. Relationships between fan area and catchment size from modern alluvial fan systems were used to estimate palaeo‐catchment size. Combining alluvial fan morphologies with catchment area, pebble provenance analysis and growth structure reconstruction, we show that: (1) fan distribution and related depositional processes were strongly influenced by intrinsic parameters such as drainage basin evolution, local structural inheritance and lateral facies changes in source area lithologies; (2) Inherited structures trending N100 effectively controlled the first‐order location of the fold and thrust structures (Montagne Sainte‐Victoire Range) and adjacent depositional areas (Arc Basin); (3) Syn‐sedimentary faults trending N010‐030 influenced the source/basin margin development and interacted with developing growth structures; (4) Facies changes in Jurassic carbonates controlled fold development and consequently the structural evolution of the source area; and (5) the N010‐030 faults and along‐strike variability of the source/basin margin system were ultimately controlled by basement structures that controlled where Late Cretaceous deformation nucleated. The overall architecture of the source/basin margin system reflects segmentation and strain partitioning along strike, as demonstrated by diachronous alluvial fan distribution.

Tertiary alluvial fans at the northern margin of the Ebro Basin: a review

Abstract Tertiary alluvial fan deposits along the margin of the Ebro foreland basin north of Huesca, Spain, are remarkable for the range of sedimentological and tectonic features preserved within them. The fan deposits formed after the southern Pyrenean thrust front (the Guarga Thrust) was established in this area, forming steep topography at the basin margin in the mid-Oligocene. Some shortening continued during deposition of the earliest fans resulting in synsedimentary faults, folds and unconformities. Clast compositions in the fan conglomerate beds record unroofing of the thrust front and also reveal differences in bedrock provenance between adjacent, coeval fan deposits. Bedrock provenance also influenced processes of deposition, with fans built up of detritus derived from areas rich in gypsum and mudrock showing more evidence of debris-flow processes. Deposition by debris flows also dominated the smallest fan body, but the majority of the fans were the products of sedimentation from unconfined or poorly confined traction currents. These resulted in sheets of conglomerate in the more proximal areas. Within individual fan bodies the proportion of sandstone increases over a distance of up to 5 km to where the distal fan facies are seen as thin sandstone and mudstone beds. The fringes of the fan bodies interfinger with lacustrine and fluvial facies, which indicate a temperate-semi-aric palaeoclimate. Vertical aggradation of the fan deposits due to rising base level in the Ebro Basin in the Oligocene and early Miocene was followed by deep incision following a late Miocene base level-fall. This led to the partial erosion of the fan deposits and their spectacular exposure in the modern landscape.

Basin-floor fans of the Central Tertiary Basin, Spitsbergen: relationship of basin-floor sand-bodies to prograding clinoforms in a structurally active basin

Abstract Lower Eocene shelf-slope clinoforms are exposed in 1 × 10 km mountainside outcrops in the Central Tertiary Basin, Spitsbergen. Where clinoforms are sand-prone they include a deepwater sand complex. Submarine fans represent an early, basin-floor aggradational phase of clinoform growth, whereas later growth of the same clinoform involves a phase of shelf-margin accretion. Individual fans, within stacked series, can be distinguished when traced towards the slope, where a thickening wedge of mudstones separates successive fan bodies. The sand-prone parts of basin-floor fans are some 15–60 m thick and extend into the basin by up to 10–12 km. The lower levels of any fan consist of ripple- to parallel-laminated thin-bedded turbidites interbedded with some thick-bedded turbidites. This association changes irregularly upwards to a succession dominated by thick beds that are structureless and parallel-laminated. The thin-bedded facies are interpreted as turbidite sheets that formed as channel-mouth sandy lobes, sandy levees and crevasse splays. The erosively based, thick-bedded facies are interpreted as constructional channel-fill sandstones. The shallow channels fed sheet-complexes both laterally and distally. The apparent short basinward extent and longitudinal palaeocurrents for the youngest fans suggest that downslope sediment transport became longitudinally deflected by anticlinal topography once sediment reached the basin floor.

Evidence of iceberg‐ploughing in a subaqueous ice‐contact fan, glacial Lake Rinteln, NW Germany

The Coppenbrügge subaqueous ice‐contact fan complex of early Saalian age is about 10 km long and up to 10 km wide and is composed of offset‐stacked fan clinothems that are transgressive‐regressive sequences formed during an overall lake level rise. The individual fan bodies consist of coarse gravel in the ice‐proximal part, passing distally into sandy facies and showing large‐scale foreset bedding. The iceberg scour recognized in an open‐pit outcrop is up to 1.5m deep, up to 2m wide and cut in undisturbed mid‐fan deposits. The scour‐fill can be traced laterally for about 15m and consists of sheared sand and, in the frontal zone, of downbent overlying strata surrounded by a zone of deformed sediments. The deformed sediment produced by the iceberg keel's shearing of the trough walls is a sand mass containing angular soft‐sediment clasts that show internal folds and fractures. The basal surface of the deformed sediment is a nearly horizontal shear plane, steepening up laterally as a discrete thrust and showing a flat‐ramp‐flat geometry. The scour was formed by the iceberg keel's ploughing the substrate and pushing the sediment sideways and frontally, forming a ridge of deformed sediments at the trough end. This ridge was concurrently eroded by an accompanying meltwater underflow which apparently developed a horseshoe system of scouring vortices around the grounded iceberg. The current's scour was filled with massive, non‐stratified sand deposited rapidly from turbulent suspension. The iceberg eventually broke up and its keel part was buried. As these ice fragments gradually melted, the space was closed by normal faulting and downbending of overlying strata. The collapsing scour‐fill became partly liquified, and the resulting water‐escape structures cut the normal faults and the overlying deposits. Though produced chiefly by tangential shear strain, iceberg‐ploughing features are readily distinguishable from other glaciotectonic deformations. They can serve as a diagnostic criterion for glaciolacustrine or glaciomarine environments and the distinguishing of ice‐contact subaqueous fans from ice‐contact deltas in the stratigraphic record.