Submarine Fan Research Articles

BLACK SEA SUBMARINE VALLEYS – PATTERNS, SYSTEMS, NETWORKS

The article presents a detailed analysis of the underwater morphology of the entire Black Sea basin beyond the shelf break. The focus is on submarine valley systems on continental slope and rise zones, and partially in the abyssal plain area. The present research is among the very few studies that have undertaken a morphological analysis on a regional scale, for an entire marine basin. This achievement was possible by using the publicly available EMODnet bathymetric map of the Black Sea. The Black Sea submarine valleys networks are presented in a map-sketch. It includes 25 valley systems, 5 groups of simple first order channels, and other number of simple, not associated channels. The 25 valley systems are adding up more than 110 main channels and tributaries. Morphological description and analysis of each of the mapped systems is given – shape and plan view morphology, dimensions (length and surface) and slope gradient. Some considerations about the amount of sediments supplied by the valleys from the shelf to the basin floor, forming the deep-sea fans, are presented. For a more detailed and precise image of the Black Sea network of submarine valleys additional work would be necessary to cover the entire basin with a minimum standard network of modern bathymetric mapping and of high resolution seismic survey lines. To take into account the composition and geological structure of different sectors, as factors that influence significantly the morphology of the seabed, would be also particularly useful.

Exploring a new breadth of cyclic steps on distal submarine fans

AbstractResearch on the depositional record of submarine fans and related turbidite systems has highlighted the importance of channel, lobe and levée–overbank architectural elements as fundamental building blocks. However, many of the characteristics and processes of deposits left by flows traversing those fans remain elusive, because flows seem to be able to go unconfined for long distances. Offshore southern California (USA), the La Jolla Canyon decreases in relief to become an approximately U‐shaped channel across the basin floor of the San Diego Trough. The La Jolla Channel gradually loses confinement and transitions to a network of scours, some of which align to form incipient channels, and fields of bedforms. High‐resolution seafloor topography, CHIRP seismic‐reflection data, sediment cores and hydrodynamic flow analysis are used to explore these features. The focus is on two regions of bedforms: (i) a field of net‐depositional, concentric bedforms across the eastern levée–overbank upstream from the terminus of the La Jolla Channel; and (ii) a linear train of more erosional bedforms approximating an incipient channel adjacent to the present mouth of the La Jolla Channel. These bedforms are interpreted to be among a class of upper‐flow‐regime bedforms called cyclic steps, which were formed by densimetric Froude supercritical turbidity currents that spilled out of the present La Jolla Channel. The high‐resolution data for the La Jolla Fan provide valuable insights into the characteristics of supercritical bedforms likely common to distal submarine fans, as well as on sedimentary processes likely important for submarine fan growth into sedimentary basins. In particular, the pattern of evolution of the La Jolla Fan suggests that cyclic steps with wavelengths on the order of tens of metres to a few hundreds of metres could be fundamentally important for the evolution of the distal submarine fans with relatively low‐relief main channels.

Sedimentary provenance of the Plio-Pleistocene Nicobar Fan: Complex sourcing revealed through Raman spectroscopy heavy mineral analysis

The Nicobar Fan lies within the north-eastern Indian Ocean between the Ninety-East Ridge and Sunda Arc. The fan forms part of the Bengal–Nicobar Fan System and is among the oldest and largest submarine fans on Earth. Previous U–Pb zircon studies of the Nicobar and Bengal fans indicate the Himalaya as the dominate sediment source, making these fans a major Cenozoic sink for uplifted Himalayan sediment. However, the northwards moving Indian Plate, coupled with mid-Pleistocene collision of the Ninety-East Ridge with the Sunda Arc, has shutdown many sediment pathways linking the Himalaya and Nicobar Fan. Here we use big data Raman spectroscopy heavy mineral analysis along with U–Pb zircon data to better define sediment source regions for the Nicobar Fan during the Plio-Pleistocene following the shutdown of sediment delivery. The detrital zircon spectra for the Plio-Pleistocene Nicobar Fan from this study are consistent with previous work indicating that the original sources of these zircons can be found within both the Greater and Tethyan Himalaya, the Gangdese Arc, and the Indo-Myanmar Ranges. However, the heavy mineral data indicate that a large proportion of sediment has been derived from a more complex array of sources. This is coupled with an abundance of low- and moderate-stability minerals (e.g., amphibole, apatite, clinopyroxene), which are unlikely to have been transported large distances. Suggesting that proximal sources have delivered the majority of lower-stability heavy minerals into the Plio-Pleistocene Nicobar Fan. We show that from the Pleistocene onwards direct sediment delivery into the Nicobar Fan from the Himalaya was largely shutdown, with sediment instead shedding off the uplifting Indo-Myanmar Ranges, the Andaman–Nicobar Accretionary Ridge, and the westwards propagating Ayeyarwady River. This study shows that extensive uplift along the northern Sunda Arc is recorded in the Nicobar Fan alongside the previously reported Himalayan record.

Evaluation of hydrocarbon source rock potential: Deep marine shales of Belaga Formation of Late Cretaceous-Late Eocene, Sarawak, Malaysia

In the Sibu-Tatau region of Sarawak, the Belaga Formation (Late Cretaceous- Late Eocene turbidites) is interpreted in relation to a submarine fan model deposited in the extinct ocean basin of the proto-South China Sea. A number of clastic rocks, which include sandstone, siltstone, mudstone, and black shale, define the formation. While it is considered one of the Rajang group's extensive and well-studied formations, yet no comprehensive studies have been carried out on the shales in Sarawak, Malaysia, to interpret their importance as a source rock to oil and gas fields. The present study highlights the prominent lithofacies in addition to the detailed source rock characterization of each member of Belaga Formation to discuss the potential source rock intervals present in these Cretaceous to Eocene rock units. Four major types of shales and mudstones facies were observed in the field, i.e. (i) Variegated colored shale facies (VSF), (ii) Black “Papery” shale facies (BSF), (iii) Gray to black mudstone facies (GMF), (iv) Silty/sandy shale facies (SSF). They show hemipelagic settling in a calm environment to turbiditic deposition at levees as well as distal lobe depositional environment. In this study primary geochemical studies such as Rock-Eval pyrolysis and Total Organic Carbon (TOC) analysis were used to classify the thermal maturity, organic matter richness, and kerogen type of the studied shales. Forty-six selected shale samples were studied from the formation, including samples from members of the Layar (Upper Cretaceous), Kapit (Paleocene to Early Eocene), Pelagus (Early to Middle Eocene), Metah (Middle to Late Eocene) and Bawang (Eocene). The shales of Belaga Formation typically display low to moderate source rock potential, which is obvious by low TOC contents between 0.14 wt% and 7.22 wt% (average of about 2.97 wt%) and show a wide range of maturity (immature to over mature) evident from very low to very high Tmax values ranging from 293 °C to 610 °C. The results show that the kerogen is of type IV, with some units can be potential sources of gas.

Continuous canyon-river connection on a passive margin: The case of São Francisco Canyon (eastern Brazil)

Submarine canyons play a major role in sediment transfer to the deep sea. When connected with fluvial systems, they can produce large submarine fans, whose sandy bodies have a high potential as petroleum reservoirs. Although canyon-river connections are common on passive margins during lowstands, they are rare during highstands. So far, the only canyon in the Western South Atlantic to have exhibited continuous river connection throughout the Quaternary, regardless of sea level position, is the São Francisco Canyon (SFC) in eastern Brazil. In this study, we used multibeam and 3D seismic records integrated with previously published data to investigate the reasons for the continuous canyon-river connection in the area of the São Francisco River. The SFC comprises two compartments: The Upper and the Mid Canyon. The Upper Canyon indents 15 km of the shelf and acts as an erosive feeder trunk to the São Francisco Submarine Fan. When it emerges on the continental slope (Mid Canyon), depositional processes dominate; the canyon now begins to meander and the thalweg is bordered by numerous terraces and levees. Five stratigraphic units have accumulated in the region of the canyon head since the beginning of the Oligocene. Initially, sedimentation had a uniform aggradational character (Unit 1), which later became more discontinuous in association with the development of reef build-ups (Unit 2) and of a low-lying area around the canyon head. This depression was partially infilled by siliciclastics (Unit 3) and later incised by a precursor of the SFC (Unit 4). The depression still has a morphological expression in the shelf nowadays as a bathymetric low (BL), within which the São Francisco River has built its delta (Unit 5). We hypothesize that the origin and evolution of the SFC is associated with three main factors: (i) breaching by the canyon head of thick carbonates rimming the shelf break; (ii) development of the shelf depression referred above; and (iii) major continental drainage reorganization. Continuous canyon-river connection was ensured by this shelf depression, which helped funnel siliciclastic sediments to the canyon and precluded lateral changes to the lower river trunk. Morphological features, such as axial incision of mass movement deposits is suggestive of some, although very limited, modern canyon activity. This case study contributes to a better understanding of river-basin sediment pathways, particularly on passive margins, which are of great importance for the successful exploration of submarine fan systems.

Reconciling along-strike disparity in slip displacement of the San Andreas fault, central California, USA

Abstract The correlation of the ca. 23 Ma Pinnacles and Neenach volcanic complexes provides the most robust estimate on the timing and magnitude of Neogene right-lateral displacement on the San Andreas strike-slip fault system (California, United States). Displacement of ∼315 km has been applied rigorously along the plate margin to guide reconstruction of offset paleogeographic features. We present new detrital zircon U-Pb geochronology from the La Honda and western San Joaquin basins to document sediment provenance and reevaluate compositional constraints on a hypothesized key cross-fault tie (i.e., Castle Rock–Recruit Pass submarine fan system). Whereas the Upper Oligocene–Lower Miocene Vaqueros Formation of the La Honda basin was likely recycled from or shared a similar southern Sierra Nevada–western Mojave source with the underlying Eocene stratigraphy, we found that the Temblor Formation of the central Temblor Range (e.g., Recruit Pass submarine fan) was derived directly from Late Cretaceous northern Salinian basement. Furthermore, the Carneros Sandstone of the northern Temblor Range had a central Sierra Nevada batholith source that was likely recycled during early Miocene unroofing of the underlying stratigraphy. Conversely, strata of the southwest San Joaquin basin have provenance characteristics that match more closely with those of the La Honda basin. Our data preclude a contiguous Castle Rock–Recruit Pass submarine fan system across the San Andreas fault. These relationships are resolved by restoring the ca. 105–100 Ma basement of the northernmost Salinian block an additional ∼45 km or greater farther south relative to the Sierra Nevada batholith during late Oligocene–early Miocene time. Inconsistency in displacement along the San Andreas fault with the coeval correlation of the Pinnacles–Neenach volcanic complex is reconciled by postdepositional Miocene–Quaternary off-fault NW-SE structural shortening via major thrusts and/or transrotation of the Tehachapi block, in combination with extension of the northern Salinian block. This additional displacement reduces the need for pre–28 Ma slip on the San Andreas or predecessor faults to resolve Cretaceous through Eocene cross-fault relationships and reconciles an early Miocene discrepancy with Pacific–North America relative plate motion. This study highlights the fact that displacement histories of major strike-slip faults are divergent across changing structural domains, and recognition of slip disparities can constrain the magnitude of deformation.

E&P Notes (December 2020)

E&P Notes (December 2020)

Marine gas hydrates’ evolution after Middle Pleistocene: basin analysis of the Danube fan, Black Sea

The aim of this work is to reconstruct the variations of the total gas hydrate (GH) masses of the Danube deep-sea fan after 0.265 Ma BP. The PetroMod™ model developed in GEOMAR, Germany is for basin analysis of the Western Black Sea for 98 Ma. Geological structure is from 2D seismic of the Black Sea consortium “Geology without limits”. Results show a trend for total GH masses decrease after Middle Pleistocene and the role of the GHs as sink and source of methane.

Deep-lacustrine sediment gravity flow channel-lobe complexes on a stepped slope: An example from the Chengbei Low Uplift, Bohai Bay Basin, East China

Many stepped slopes are present at deep-lacustrine basin margins in China, especially in the Paleogene rift basin margins of East China. Sediment gravity-flow deposits on these stepped slopes have the potential to form excellent reservoir quality sediments that are targeted for hydrocarbon exploration, but still remain poorly understood. In this study we use the Ed3 member of Oligocene-aged Dongying Formation deposited over the Chengbei Low Uplift, as an example for investigating facies types, distribution and main controlling factors of sediment gravity-flow deposits on stepped slopes at deep-lacustrine basin margins. Paleotopographical reconstructions indicate that the study area displayed a three-level stepped slope that were dissected by three large canyons and many associated smaller-scale channels prior to the deposition of the Ed3 member. On the basis of facies identification, six facies associations are further distinguished: (1) fan valley fills, (2) confined channel deposits, (3) poorly confined channel deposits, (4) levee deposits, (5) interchannel deposits, and (6) lobe deposits. These facies associations are grouped into four systems, namely fan valley fills, confined channel-levee, poorly confined channel-levee and lobe systems, as architectural elements constituting two types of channel-lobe complexes in the study area, namely anastomosing channel-lobe complexes and meandering channel-lobe complexes. The interaction between paleotopography and lake level fluctuations likely represented the direct control on the morphology, pattern and spatial-temporal distribution of channel-lobe complexes in the study area. Moreover, lake level fluctuations can also influence the volume and grain size of sediment supply to the stepped slope systems. Hyperpycnal flood events, as trigger factors, caused the generation of subaqueous sediment gravity flows that fed the stepped slope systems. Climate variations appear to be a contributing driver of lake-level fluctuations, and also indirectly control sediment supply into the deep lake and development scale of the stepped slope systems. These controls therefore determined the sediment supply, trigger and spatial-temporal variations of the stepped slope systems. This study improves the understanding of facies types and their distribution across stepped slopes at deep-lacustrine basin margins, as well as the controlling factors on the development of these sediment gravity-flow deposits.

3D anatomy and flow dynamics of net-depositional cyclic steps on the world\u2019s largest submarine fan: a joint 3D seismic and numerical approach

Supercritical flows are ubiquitous in natural environments; however, there is rare 3D anatomy of their deposits. This study uses high-quality 3D seismic datasets from the world’s largest submarine fan, Bengal Fan, to interpret 3D architectures and flow processes of Pliocene undulating bedforms that were related to supercritical flows. Bengal undulating bedforms as documented in this study were developed in unconfined settings, and are seismically imaged as strike-elongated, crescentic bedforms in plan view and as rhythmically undulating, upstream migrating, erosive, discontinuous reflections in section view. Their lee sides are overall 3 to 4 times steeper (0.28° to 1.19° in slope) and 3 to 4 times shorter (117 to 419 m in length) than their stoss flanks and were ascribed to faster (high flow velocities of 2.70 to 3.98 m/s) supercritical flows (Froude numbers of 1.53 to 2.27). Their stoss sides, in contrast, are overall 3 to 4 times gentler (0.12° to 0.27° in slope) and 3 to 4 times longer (410 to 1139 m in length) than their lee flanks and were related to slower (low velocities of 2.35 to 3.05 m/s) subcritical flows (Froude numbers of 0.58 to 0.97). Bengal wave-like features were, thus, created by supercritical-to-subcritical flow transformations through internal hydraulic jumps (i.e., cyclic steps). They have crests that are positive relative to the surrounding region of the seafloor, suggesting the predominant deposition of draping sediments associated with net-depositional cyclic steps. Turbidity currents forming Bengal wave-like features were, thus, dominated by deposition, resulting in net-depositional cyclic steps. Sandy deposits associated with Bengal net-depositional cyclic steps are imaged themselves as closely spaced, strike-elongated high RMS-attribute patches, thereby showing closely spaced, long and linear, strike-elongated distribution patterns.

Subsurface basement, structure, stratigraphy, and timing of regional tectonic events affecting the Guajira margin of northern Colombia

We have combined previous data from Mesozoic-Cenozoic outcrops in the Guajira Peninsula of northern Colombia with regional gravity, bathymetric, and seismic interpretations to demonstrate the existence of a 280 km long western extension of the Great Arc of the Caribbean (GAC) along the continental margin of Colombia. Seismic data reveal an 80–100 km wide domal-shaped basement high that exhibits internal chaotic seismic facies. This elongate and domal-shaped structure extends 1800 km from the Aves Ridge in the Caribbean Sea to the study area in offshore Colombia. The western extension of the GAC in Colombia and western Venezuela is buried by 700–3000 m of continental margin sedimentary rocks as a result of the GAC colliding earlier with the Colombian margin (Cretaceous-early Paleogene collision) than its subaerially exposed eastern extension along the Leeward Antilles ridge (late Paleogene-Neogene). Our compilation of geologic information from the entire GAC reveals that GAC magmatism occurred from 128 to 74 Ma with magmatism ages progressively younger toward the east. Six upper Eocene to recent marine seismic sequences overlying the domal basement high of the GAC have been mapped by our analysis of 2400 km of seismic lines and 12 well logs. Based on subsurface mapping correlated with well-log information and onland geology in the Guajira Peninsula, these six sequences record four major deformational events: (1) late Eocene rifting in an east–west direction produced half-grabens in the northern part of the area, (2) Oligocene transtension in the southern part of the area expressed by right-lateral Oligocene strike-slip faulting and extensional basin formation, (3) early-middle Miocene transtension, and (4) late Miocene-early Pliocene Andean uplift accompanied by rapid erosion and clastic infilling of offshore basins by the Magdalena delta and deep-sea fan. The significance of this basin framework is discussed for known and inferred hydrocarbon systems.

Characterization and geochronology of Archean metasedimentary sequences in the eastern portion of Rio das Velhas greenstone belt, Quadrilátero Ferrífero, Brazil

The Quadrilátero Ferrífero (QF) is an important, polydeformed mineral province, located in the southernmost portion of São Francisco Craton. The Rio das Velhas greenstone belt (RVGB) is an Archean meta-volcano-sedimentary succession from the QF, the Córrego do Sítio unit (CdS) being its most widely distributed sedimentary sequence. Detailed sedimentology study allied to x-ray diffraction-XRD and geochronological (LA-ICP-MS in detrital zircon) analyses provide evidence for a new interpretation of the CdS. The identified sedimentary structures of the CdS (e.g. flaser and lenticular bedding, sharp and erosional base, normal grading, mud drapes, quartz granules, syndepositional deformation, and ball & pillow) led the interpretation of these couplets as turbidity currents deposits corresponding to TA and TE facies of the classic Bouma Sequence. The CdS sequence was deposited on distal portions of an ancient submarine fan environment by turbidity current mechanisms, then it was partially reworked by tidal bottom currents. Geochronological data pointed out the main influence of the Rio das Velhas II magmatic event in the deposition of the eastern QF metasedimentary sequence, as evidenced by the maximum depositional age at 2818 ± 31 Ma. The surrounding metamorphic complexes terrains may have acted as source areas during the deposition of the sedimentary sequences, probably in a convergent to a collisional marginal tectonic setting (subduction stage).

Chasing the 400 kyr pacing of deep-marine sandy submarine fans: Middle Eocene Aínsa Basin, Spanish Pyrenees

In an attempt to understand the relative importance of climate and tectonics in modulating coarse-grained sediment flux to a tectonically active basin during what many researchers believe to be a greenhouse period, we have studied the Middle Eocene deep-marine Aínsa Basin, Spanish Pyrenees. We use orbital tuning of many spectral gamma-ray-logged fine-grained siliciclastic sections, already shown to contain Milankovitch frequencies, in conjunction with a new high-resolution palaeomagnetic study through the basin sediments, to identify polarity reversals in the basin as anchor points to allow the conversion of a depth-stratigraphy to a chronostratigraphy. We use these data, in conjunction with a new age model incorporating new biostratigraphic data, to pace the development of the deep-marine sandy submarine fans over c . 8 million years. Timing for the sandy submarine fans shows that, unlike for the fine-grained interfan sediments, coarse-grained delivery to the basin was more complex. Approximately 72% of the sandy fans are potentially coincident with the long-eccentricity (400 kyr) minima and, therefore, potentially recording changing climate. The stratigraphic position of some sandy fans is at variance with this, specifically those that likely coincide with a period of known increased tectonic activity within the Aínsa Basin, which we propose represents the time when the basin was converted into a thrust-top basin (Gavarnie thrust sheet), presumably associated with rapid uplift and redeposition of coarse clastics into deep-marine environments. We also identify sub-Milankovitch climate signals such as the c . 41.5 Ma Late Lutetian Thermal Maximum. This study demonstrates the complex nature of drivers on deep-marine sandy fans in a tectonically active basin over c . 8 Myr. Findings of this study suggest that, even during greenhouse periods, sandy submarine fans are more likely linked with times of eccentricity minima and climate change, broadly consistent with the concept of lowstand fans. However, hysteresis effects in orogenic processes of mountain uplift, erosion and delivery of coarse siliciclastics via fluvial systems to coastal (deltaic) and shallow-marine environments likely contributed to the complex signals that we recognize, including the 2–3 Myr time gap between the onset of deep-marine fine-grained sediments in the early development of the Aínsa Basin and the arrival of the first sandy fans. Supplementary Materials : Filtered records for each of the analysed gamma-ray logged sections. Anchor points, SARs tables and graphs and alternative tuning sections are available at: https://doi.org/10.6084/m9.figshare.c.5132975

Sedimentology, Provenance and Radiometric Dating of the Silante Formation: Implications for the Cenozoic Evolution of the Western Andes of Ecuador

The Silante Formation is a thick series of continental deposits, exposed along a trench-parallel distance of approximately 300 km within the Western Cordillera of Ecuador. The origin, tectonic setting, age and stratigraphic relationships are poorly known, although these are key to understand the Cenozoic evolution of the Ecuadorian Andes. We present new sedimentological, stratigraphic, petrographic, radiometric and provenance data from the Silante Formation and underlying rocks. The detailed stratigraphic analysis shows that the Silante Formation unconformably overlies Paleocene submarine fan deposits of the Pilalo Formation, which was coeval with submarine tholeiitic volcanism. The lithofacies of the Silante Formation suggest that the sediments were deposited in a debris flow dominated alluvial fan. Provenance analysis including heavy mineral assemblages and detrital zircon U-Pb ages indicate that sediments of the Silante Formation were derived from the erosion of a continental, calc-alkaline volcanic arc, pointing to the Oligocene to Miocene San Juan de Lachas volcanic arc. Thermochronological data and regional correlations suggest that deposition of the Silante Formation was coeval with regional rock and surface uplift of the Andean margin that deposited alluvial fans in intermontane and back-arc domains.

Impact of Paleosalinity, Paleoredox, Paleoproductivity/Preservation on the Organic Matter Enrichment in Black Shales from Triassic Turbidites of Semanggol Basin, Peninsular Malaysia

Turbidite-associated black shale of the Semanggol Formation is extensively distributed in the northwestern part of the Western Belt, Peninsular Malaysia. The black shale occurs as a dark grey to black and thick to medium-bedded deposit. It represents the distal part of submarine fan system (outer-fan) overlying interbedded sandstone to shale facies of the mid-fan and conglomeratic pebbly sandstone facies of the inner-fan. Field observations and its widespread occurrence have resulted in the black shale being considered as a potential analog for a source rock in offshore Peninsular Malaysia. The present study includes detailed mineralogical (XRD, SEM, and EDX analysis), inorganic geochemical (major oxides, trace elements TEs, and rare earth elements REEs), and Rock-Eval pyrolysis analyses of the black shale samples, collected from the Gunung Semanggol, Bukit Merah, and Nami areas in northwestern Peninsular Malaysia. The primary focus of this study is to investigate the provenance, paleoredox conditions, paleoclimate, sedimentary rate, paleoproductivity, and upwelling system that would be helpful to understanding the role of these parameters in the enrichment of organic matter (OM) in the black shale. The Rock-Eval analysis shows that the black shale of the Semanggol Formation comprises type-III kerogens, which suggests organic input from a terrestrial source. The black shale also contains mature to postmature organic matter. Based on the mineralogical analysis, the mineral composition of the black shale comprises illite and kaolinite, with abundant traces of quartz and feldspar as well as few traces of titanium and zircon. Inorganic geochemical data designate black shale deposition in a passive margin setting that has experienced moderate to strong weathering, semi-arid to hot arid climate, and moderate sedimentation rate. Ratios of Ni/Co, U/Th, and V/(V+Ni) along with slightly negative to positive Ce* anomalies and UEF-MoEF cross-plot unanimously indicate anoxic/dysoxic water conditions that are suitable for organic matter preservation. Geochemical proxies related to modern upwelling settings (i.e., Cd/Mo, Co vs. Mn) show that the deep marine black shale was strongly influenced by persistent upwelling, a first-order controlling factor for organic matter enrichment in the distal part (outer fan of the submarine fan system) of the Semanggol Basin. However, productivity-controlled upwelling and a high sedimentary rate, as well as high-productivity in oxygen-depleted settings without strong anoxic conditions, has played an essential role in the accumulation of organic matter.

Sedimentary architecture of the undeformed Lower Miocene Görendağı Submarine Fan deposits from Neo-Tethys Ocean (Eastern Anatolia-Turkey): Tectonic control on preservation of fan morphology

Submarine fan deposits which constitute the remnants of Neo-Tethys are widely observed throughout the Bitlis–Zagros Suture Belt. Most of these deposits are located in the Arabian-Eurasian collision zone and have been intensively deformed due to ongoing tectonic activity. In this study, the depositional characteristics and preservation processes of the undeformed, Lower Miocene Görendağı Submarine Fan deposits, associated with this zone, are studied with respect to their sedimentological and structural features. These deposits display feeder or distributary channels, overbank, and lobe sediments and classical Bouma Ta–d divisions. They are subdivided into inner, middle, and outer fan, according to sedimentological and morphological properties. Sand-rich submarine fan deposits have 39 m thickness and approximately 2 km of lateral extension.The submarine fan body is bounded to the north and the south by two reverse faults, namely the Özyurt and Göktepe faults. These faults formed an accommodation space where the fan was deposited and also caused the deepening of the basin. The position and activity of these oppositely inclined reverse faults, which form a triangular zone, are the main reason for preservation of the original fan morphology in the Görendağı Submarine Fan. Our results indicate that the Görendağı Submarine Fan represents one of the last sequences deposited before the closure of the southern branch of the Neo-Tethys Ocean and also the most well-preserved.

Diagenetic and Reservoir Quality Variation of Miocene Sandstone Reservoir Analogues from Three Basins of Southern California, USA

The Miocene sandstone deposits in the Southern California region are important hydrocarbon reservoirs. However, their development has been very challenging due to the wide variability in their reservoir quality. These sandstones have been studied from three sedimentary basins by petrographic thin section, scanning electron microscope, and X-ray diffraction to evaluate and compare the influence of diagenesis on their reservoir quality in these basins. Four petrofacies, namely P1 (sand injectite or dyke), P2 (sub-marine fan), P3 (turbidite and marine-influenced alluvial fans) and P4 (continental sandstones) have been identified. P1 and P2 characterise the sandstones in the San Joaquin forearc basin and are affected by kaolinite and extensive early calcite diagenesis. P3 and P4 delineate the sandstones in the Cajon Valley and Salton Trough strike-slip basins and are dominated by smectite, mixed illite-smectite, early calcite and late calcite diagenesis. Early calcite cement in P3 and P4 is in lower proportion than in P1 and P2. Although the dissolution of these sandstones by acidic fluids did not have a pattern, it, however, has the most considerable influence on P2 creating moldic pores which are expected to increase pore connectivity. The relatively abundant dissolution pores in P2, together with the absence of late authigenic calcite and illite clay in comparison to the other petrofacies studied are likely to make this sandstone facies the best reservoir targets in the Southern California region. These rocks are analogous to producing reservoirs in the region. However, because, petroleum accumulation in these reservoirs are compartmentalized by early calcite cement, maximum recovery using acidified fluids is recommended to dissolve the calcite-filled pores in order to increase connectivity of their pore network and enhance flow potential.

Facies models of the Achimov Formation of East-Urengoiskoe license as the basis for optimizing exploration and field development patterns

The results of sedimentological core analysis of the Achimov Formation (Upper Valanginian, Lower Cretaceous) confirm that it was formed by higher efficiency systems of submarine fans in (relatively) deep marine basin. Lithofacies models of Ach5-6 were generated, well correlation was performed based on the comprehensive analysis of core, well logging and seismic data. Distributary channels and proximal parts of depositional lobes are characterized by the best reservoir properties.

Tectonic control on mass‐transport deposit and canyon‐fed fan system in the Ulleung Basin, East Sea (Sea of Japan)

AbstractExtensive 2D multichannel seismic (~17340 km) and well data provide an opportunity to investigate the source to sink processes and triggering factors of the Late Miocene sedimentary record in the Ulleung Basin, East Sea (Sea of Japan). The sedimentary succession of the basin comprises two distinct deep‐water depositional systems, which are characterised by stacked mass‐transport deposits (MTDs) and subsequent submarine fan. Individual MTDs spread downslope over areas as large as ~9000 km2 with NW–SE or N–S flow direction. The deep‐water fan consists of distributary channel‐lobe complexes (DLCs) that are 80 km wide and 140 km long. Two major tectonic periods driven by structural deformation characterised the Late Miocene deep‐water sedimentation growth. During early to middle Late Miocene (10.3–8.2 Ma), the MTDs were sourced from degraded fold triggered by slope oversteepening and seismicity on the southeastern basin margin, where the thrust‐and‐fold belt developed. In the middle to latest Late Miocene (8.2–6.3 Ma), the DLCs were fed by canyon‐channel systems on the southwestern basin margin, where the tectonic uplift of the anticline was active. Therefore, this study suggests that strike variation in shelf‐margin erosional and depositional processes were caused principally by the locations and timings of tectonic deformation.

The role of large-scale mass wasting processes in changing the sediment dispersal pattern in the deep-water Central Canyon of the northwestern South China Sea

Large-scale mass transport complex (MTC) (usually covering hundreds to thousands of km2 with a volume of tens to hundreds of km3) resulting from slope failures, can change the overall sediment dispersal pattern in deep-water canyon. However, the causal mechanisms remain enigmatic. We investigate the large-scale MTCs in the Central Canyon that are imaged in 3D by high-resolution seismic reflection data from the northwestern South China Sea. Our results indicate that a total volume of 435.3 km3 of sediments related to large-scale mass wasting processes were dumped into the Central Canyon from its side direction between 5.7 and 4.2 Ma. This led to adjustments of the geomorphology of the thalweg slope, which changed from a simply stepped slope (2 steps separated by 1 ramp) into a complexly stepped slope (3 steps separated by 2 ramps). The adjustments are argued to be caused by the thickness variations of MTCs1-4 that also ponded the axial turbidity flows at their up-dip directions. And then, the adjusted thalweg slope controlled the formation of a multi-stage submarine fan, which is proved to be an important hydrocarbon exploration target within the Central Canyon. Besides the first step in the canyon where sediments were mainly transported downslope due to the initially large velocities of turbidity flows, the following ramps were also considered as sediment bypass zones due to the further accelerated flows. Whereas, the subsequent steps became sediment deposition dominated zones as turbidity flows decelerated abruptly. Slope overstepping resulting from high sediment supply that was controlled by the East Asia summer monsoon, together with seismicity caused by the structural inversion of the Red River Fault were responsible for the occurrences of the large-scale mass wasting processes. We highlight how the large-scale mass wasting processes change the sediment dispersal pattern in the deep-water canyon for the first time. This study is of great significant to identify the locations of hydrocarbon reservoirs and evaluate the spatial variability in depositional reservoir qualities within the deep-water canyon.