Fan Facies Research Articles

Deconstruction of the Franciscan Complex Central Terrane Mélange and re-evaluation of Franciscan mélanges and architecture of the northwestern San Francisco Bay Area, California, USA

Various mélange types occur within the Franciscan accretionary Complex of western California. The largest mélange body, called the Central Belt Mélange (or similar names) served earlier as the type example for the orogen-long, subduction channel model, yet in the northwestern San Francisco Bay Area the name does not accurately reflect the geology. The mélange designation was commonly applied where resistant exotic and native blocks of rock are scattered across a relatively smooth terrain. Detailed mapping shows that many blocks experienced post-accretion transport. Areally large rock masses previously designated as Central Belt Mélange consist of multiple units and less than 30% of the tectonostratigraphy is mélange. Weakly metamorphosed sandstone–mudrock broken to dismembered formational units and similarly deformed sandstone–mudrock submarine fan facies dominate the tectonostratigraphy. Subordinate mélanges of the northwestern San Francisco Bay Area are of tectonic or sedimentary origin. The sedimentary bodies represent submarine mass flow deposits. Tectonic mélanges mark Mesozoic subduction-zone faults or Cenozoic strike-slip faults. Discriminating between mélange types and their origins, and reconstructing tectonostratigraphic columns for major fault blocks, clarifies the primary accretionary complex architecture and reveals significant along-strike variations in the Franciscan subduction accretionary Complex.

Depositional architecture of early rift non-marine systems and implications for reservoir development: Oligocene to Miocene Al Wajh Formation, Midyan Basin of Red Sea, Saudi Arabia

Exhumed early rift alluvial fan and braided fluvial fan systems are rare and consequently understanding facies distribution, stratal architecture, reservoir connectivity, and controls on stratigraphic development of these systems is quite difficult. The outcrops of early Oligocene to early Miocene Al Wajh Formation in the Red Sea region of Saudi Arabia provide an opportunity to investigate the depositional architecture and reservoir potential of an early rift alluvial to fluvial system. Eleven lithofacies (F1-F11) and four facies associations (alluvial fan facies association (FA1), braided fluvial fan facies association (FA2), floodplain facies association (FA3) and delta front facies association (FA4)) are identified in four subbasins (Maqna 1–2, Sukk and Ifal), suggesting deposition in an alluvial-braided fluvial fan system. FA1 (36–100%) and FA4 (9–13%) have higher relative proportion and widely distributed in the northern subbasins (Sukk and Ifal subbasins) while the relative proportion of FA2 (50–82%) and FA3 (18%) increases towards southern subbasins (Maqna-1 and Maqna-2 subbasins). Distribution of facies associations, relative reduction in the clast diameter, and general southward paleoflow direction suggest that the northern subbasins (Sukk and Ifal) represent the proximal settings and southern subbasins represent medial (Maqna-1 subbasin) and distal settings (Maqna-2 subbasin) of a large alluvial-braided fluvial fan environment. Stratal architecture of proximal conglomeratic channel deposits highlight that despite reasonable thickness and spatial connectivity (several meters), these deposits may have marginal reservoir quality because of poor sorting and high matrix content. Sandstone beds occurring in medial settings have a higher potential to act as hydrocarbon reservoirs by displaying excellent reservoir properties on the account of their significant thickness (up to few meters), coarse grain sizes, better sorting, considerable spatial connectivity (10s of meters) and lower proportion of interbedded mudstone.

Sedimentary evolution and sequence stratigraphic model of Neogene–Quaternary terrestrial foreland basin in Southwest Tarim

Based on the research results of stratigraphic sedimentary facies, plane maps of sedimentary facies for four periods of the Neogene terrestrial foreland basin in Southwest Tarim were compiled. Research results conclude that the Neogene Miocene developed alluvial fan facies, fan delta facies, and lacustrine facies successively from the piedmont belt to the Maigaiti Slope. During the sedimentation of the Miocene Anju’an Formation, the lake range expanded to its maximum. According to the new division scheme for five-order sequences in prototype sedimentary basin, the stratigraphic sequence of a terrestrial foreland basin was divided and compared, and a sequence development and evolution model was established. Research results show that: (1) the Neogene–Quaternary is a typical type I sedimentary sequence with huge thickness; (2) the Neogene is a period of tectonic compression and flexural subsidence sedimentation in the foreland basin; with the maximum lake flooding surface at the top of the Miocene Anju’an Formation as the boundary, the lower part is a second-order super-sequence of the lacustrine transgression system tracts (TST), the upper part is a second-order super-sequence of the highstand system tracts (HST), and the Quaternary is a second-order super-sequence of the lowstand system tracts (LST) in forced lacustrine regression caused by the Late Himalayan tectonic movement; (3) the classic sequence stratigraphy made an error in establishing the theoretical model of marine type I sequences, as it placed the LST in the wrong position. The corrected type I sequences are in the order of TST, HST, and LST. (4) Finally, two examples were applied to demonstrate the development position of the LST, indicating that whether it is a marine or terrestrial prototype sedimentary basin, the LST was developed during the late stage of tectonic compression and uplift in a basin, and is the sedimentary sequence at the top of the prototype sedimentary basin.

The Sequence Stratigraphy and Sedimentary Evolution of the Guantao Formation in the Binxian Uplift Area, Bohai Bay Basin, China

Due to the influence of multiple tectonic movements in rift basins, the sequence and sedimentary filling modes of continental petroleum reservoirs are complex, which makes it difficult to establish isochronous stratigraphic frameworks and thus affects the accuracy of subsequent predictions of effective sand bodies. Taking the Guantao Formation of the Binxian uplift and the surrounding areas as an example, this study established the sequence stratigraphic framework of the Guantao Formation and discussed the controlling effect of sequence stratigraphy on sedimentary filling. According to a combination method of seismic data, well log data, the wavelet transform technique (WTT), and Integrated Prediction Error Filter Analysis (INPEFA) methods, the Guantao Formation in the study area can be divided into 1 long-term cycle (LNG), 4 mid-term cycles (MNG1–MNG4, from bottom to top), and 11 short-term cycles (SNG1–SNG11, from bottom to top). Based on comprehensive analysis of geological and seismic data, three sedimentary facies can be classified: alluvial fan facies, braided fluvial facies, and meandering fluvial facies. The sequence stratigraphic style of the study area has a significant controlling effect on sedimentation and sand body distribution. Different levels of cycles have different impacts on sedimentary facies/microfacies types, the development degree of each sedimentary microfacies, and sand body distribution. The long-term cycle controls the distribution of sedimentary facies, while the mid-term and short-term cycles control the distribution of sedimentary microfacies. The bottom interface of the Guantao Formation (T1) served as the dominant migration channel in the study area, connecting the reservoir and source rocks. When the base-level was in the low stage (MNG1), a large amount of sand bodies developed, forming favorable reservoirs for petroleum. The interlayers at the top of the long- and mid-term cycles served as seal layers to prevent oil and gas from escaping. The MNG1 cycle has a good combination of reservoir and seal, resulting in the accumulation of oil and gas in the MNG1 strata, which became the main oil- and gas-producing layer in the area. These study results can provide effective guidance for future prediction of the distribution of sand bodies and high-quality reservoirs.

Intermontane erg environment and arid climate indicated from associated eolian and alluvial fan facies during the Late Cretaceous, South China

Late Cretaceous eolian sandstones found in several basins in South China were previously interpreted as indicators of desert environments. To better understand the environment and climate conditions of that period more accurately, a comprehensively in-depth study of the eolianites was undertaken across multiple basins. Two primary lithofacies were identified within the eolianite-bearing sequences. The eolian facies is classified into four subfacies, namely dune, interdune, sand-sheet, and Gobi, while the alluvial fan facies are categorized into three subfacies, i.e. ephemeral channel, sheet flood, and debris flow. These two facies signify recurring interactions of eolian and water-laid systems, highlighting instances of eolian dune migration and deflation in conjunction with the intrusion of alluvial flows. The coexistence of the two facies in conjunction with the spatial distribution and morphometric characteristics associated with paleowind directions, suggests the following: 1) Eolian sandstones were formed within local intermontane ergs confined to narrow basins, negating their formation in broadly expansive desert or sand sea environments; 2) The alluvial fan facies evolved under localized ephemeral arid conditions; 3) South China experienced a relatively prolonged arid climate during the middle Late Cretaceous period, as opposed to the alternating humid and arid conditions. It is argued that the paleowind directions, recovered from the azimuths of cross-beddings in eolianites are reflective of the planetary wind system that was present in South China at that time, given their consistence with the strikes of basins and tectonic axial orientations.

Sedimentary infill of Early-Middle Jurassic in the southeastern Tarim Basin and its constraints on the evolution of the Altyn Tagh Fault in the Northeast Tibet Plateau

The Altyn Tagh Fault (ATF) is the boundary between the Tarim Basin and the Tibetan Plateau, which is crucial for the tectonic evolution and uplift of the Tibetan Plateau. However, the Mesozoic tectonic evolution of the ATF remains controversial. This study reconstructed the Early-Middle Jurassic palaeogeographic pattern of the southeast depression of the Tarim Basin (SDTB) and revealed potential source-sink relationships between the SDTB and its adjacent mountains to constrain the Mesozoic tectonic evolution of the ATF based on sedimentology and provenance analyses. The results indicated that the SDTB was infilled with alluvial fan facies during the Early Jurassic and the late Early Jurassic, giving rise to the braided-river delta to lacustrine facies. During the Middle Jurassic, the lacustrine basin expanded with the wide development of lacustrine facies, and the lacustrine basin contracted and was primarily infilled with braided delta facies in the late Middle Jurassic. The Jurassic sedimentary center, the SDTB situated in front of the Altyn Tagh Mountain and East Kunlun Mountain, played a crucial role in the development of three types of hydrocarbon source rocks: charcoal mudstone, coal beds, and dark mudstone. Combined with seismic reflection data interpretations, the Early Jurassic the STDB is a rift basin that underwent a rift-depression transition in the late Early Jurassic, solidifying the characteristics of the depression basin in the Middle Jurassic. The extensional environment in the SDTB resulted from the tectonic effects of slab break-off following the closure of the Tethys Ocean and the spreading of the distal stress field of the Bangonghu–Nujiang Ocean. The analyses of gravel component and heavy mineral indicated that the Jurassic source of the basin was traced back to the ancestral Altyn Mountains, the East Kunlun Mountains, and the internal palaeo-uplift of the basin, which demonstrated that the SDTB and Western Qaidam Basin (WQB) shared a common lacustrine basin during the Jurassic, suggesting that the ATF did not initiate strike-slip movements during this period. This study significantly enhanced our understanding of the Mesozoic tectonic evolution in Northwest China, providing valuable insights into exploring Mesozoic oil-bearing basins in the northern Tibetan Plateau. Furthermore, it served as a useful reference for constraining the timing of the initial slip of similar plate boundary strike-slip faults.

Mid-Holocene climate-glacier relationship inferred from landforms and relict lake sequence, Southern Zanskar ranges, NW Himalaya

The geomorphological disposition of (para/peri) glacial landforms, elemental geochemistry, and optical chronology of the relict lake sediment in the Southern Zanskar ranges, northwest Himalaya are used to understand the relationship between glacial dynamics and the lake sedimentation during the mid-Holocene climate variability. Following the Last Glacial Maxima (LGM), pulsating deposition of outwash gravels until the early Holocene overwhelmed the Zanskar valley. The obstruction of Tsarap Chu (chu = river) by alluvial fans during the mid-Holocene led to the development of Padum Lake. In the present study, cirque glacier moraines representing three minor glacial advances were mapped along with sedimentological details and dated using Optically Stimulated Luminescence (OSL) dating technique. The oldest cirque glacier advance - Padum Cirque moraine-3 (PDCm-3) is dated to 11.4 ± 0.9 ka. The succeeding advance (PDCm-2) is dated to 5.3 ± 0.6 and 4.8 ± 0.8 ka whereas, the younger cirque glacier advance (PDCm-1) remains undated. The mid to late Holocene climate variability inferred using major and trace element geochemistry of the relict Padum lake sediments supported by optical chronology indicates six centennial to millennial-scale climatic phases. The prominent warmer phases are represented by decreased mineralogical fine grain flux (low K/Ti, Fe/Si, and Al/Si) with a corresponding increased coarse grain flux (higher Ti/Al and Sr/Al ratios). These phases are dated between 5.9 and 5.5 ka (phase-I), 3.8 and 3.4 ka (phase-IV), and 2.8 and 2.5 ka (phase-VI). The increased mineralogical finer fraction (higher K/Ti, Fe/Si, and Al/Si) between 5.5 and 5.1 ka (phase-II) and 3.4 and 2.8 ka (phase-V) indicate reduced meltwater flux during cooler phases. The intervening phase-III (5.1–3.8 ka) is characterized by increased mineralogical coarse grain flux (decreasing K/Ti, Fe/Si, Al/Si) suggesting gradual warming. The oscillatory climate at millennial scale was further used to understand glacier dynamics. The PDCm-2 advance in the lake record corresponds to the first major cooling (5.5 and 5.1 ka; phase-II) and continued until ∼3.8 ka. Using geochemical data of lake record, a major recession is inferred after 3.8 ka that persisted until around 3.4 ka (phase-IV). Similarly, the undated younger cirque glacier advance (PDCm-1) is assigned to the second cooling event (3.4 and 2.8 ka; phase-V). Thereafter, the cirque glaciers receded, most likely under increasing dryness and fluctuating climate (2.8–2.5 ka, phase-VI). After ∼2.6 ka, the development of ice-wedge pseudomorphs indicates the onset of permafrost conditions that degraded after ∼2.5 ka implying an increase in air temperature. The lake sedimentation terminates with the deposition of multiple younger alluvial fan facies. The climate variability shows a close correspondence with regional climate records suggesting that marginal glacier advancements were triggered by enhanced moisture via atmospheric rivers and cooler winter temperatures. The study highlights the potential of relict lake sediment in association with para- and peri-glacial landforms to reconstruct the pattern of minor glacier responses to climate variability during the Holocene.

Depositional and diagenetic controls on the reservoir quality of Early Miocene syn-rift deep-marine sandstones, NW Saudi Arabia

Understanding the distribution of sedimentary facies, their texture and diagenetic alterations in deep-marine rift systems are critical for improved reservoir quality predictions in the subsurface. Syn-rift deep-marine sandstones of the Miocene Burqan Formation, deposited by various sediment gravity flow types in the Midyan Basin (Red Sea, Saudi Arabia) are characterized using detailed sedimentological and petrographic analyses. Six distinctive lithofacies (F1-F6) have been identified within the Burqan Formation and grouped into three broad facies associations namely proximal, medial, and distal facies of a submarine fan. The proximal fan facies consists of disorganized conglomerate (F1) and structureless sandstone (F2) . The medial fan facies are represented by graded bedded and channelized sandstone (F3) and sandstone dominated heterolithics (F4) . Deposits of distal fan facies consist of mudstone dominated heterolithics (F5) and structureless mudstone (F6) . The sandstones are predominantly arkoses and lithic arkoses with a low degree of diagenetic modification (Eo- and Telo-diagenesis; ≤ 2 km and ≤ 70 °C temperature) and low to moderate volumes of carbonate cement (mean = 7%). The structureless sandstone (F2), sandstone dominated heterolithics (F4) and mudstone dominated heterolithics (F5) have poor reservoir quality due to the presence of authigenic cement and matrix. Graded bedded and channelized sandstone (F3) lithofacies consists of excellent reservoir sandstone due to the least proportion of cement and virtual absence of detrital clay. The observed variability in composition and textural parameters within Burqan Formation indicates that sedimentological transport processes control the depositional reservoir quality which in turn dictates diagenetic modification in deep-marine sandstones with important implications for prediction of reservoir quality in deep-marine systems.

The Effects of Porosity on The Anisotropy Parameters of The Slope Fan Facies Sand Reservoirs in The Deepwater Kutai Basin, East Kalimantan, Indonesia

For good interpretation and modelling, knowledge about the effects of anisotropy and its relationship with reservoir properties is needed. Related to this issue, this study evaluated the effects of porosity on the anisotropy parameters for sand reservoirs deposited in the upper slope fan facies. The study objects are obtained from core plug samples of sand reservoirs in the deep-water Kutai Basin. Core plug samples were collected from 13602.5 ft to 13704.5 MD depth. The ε, γ, δ, and η anisotropy parameters data were obtained by ultrasonic measurements, and porosity data were obtained by laboratory measurement with Coreval 700 apparatus and Boyle’s law. The analysis results show that the relationship of the anisotropy parameters with porosity appears when high-porosity sandstone and low-porosity sandstone are separated. The plots of anisotropy ε, γ, and δ, show trends for greywacke, with increasing anisotropy value the porosity increases. The effect of porosity on the high porosity (29%-37%) sandstone shows a steeper change than on the lower porosity (12%-13%) sandstone. The analysis also shows that the higher composition of lithic mineral grain reduces the effect of anisotropy on porosity.

Sedimentological study of Bima sandstone in Dumne and Environs, Yola Sub-basin, Upper Benue Trough, Northeastern Nigeria.

Field mapping was carried out on Bima sandstone from Dumne and its environs with the aim to understand the geology and determine the paleoenvironment of deposition. The integrated (outcrop study with granulometric and pebble morphometric) studies were used to achieve this aim. Based on outcrop studies, nine (9) lithofacies were identified from the proximal alluvial fan facies to the mid-fan braided river: massive, matrix-supported, gravel-dominated facies (Gmm); matrix-supported gravel (Gmg); clast-supported gravel stratified (Gh); gravel stratified trough cross-bedded sandstone (Gt); trough cross-bedded sandstone (St); planar cross-bedded sandstone (Sp); ripple cross-laminated sandstone (Sr); massive sandstone (Sm) and silt and mud (Fsm). The outcrop sampled materials were subjected to granulometric and morphometric analyses. The result of the granulometric shows that the Bima sandstones of the study area have an average graphic mean (Mz) of 0.82 (coarse grains), an inclusive graphic standard deviation (δi) of 1.33 (poorly sorted), a graphic kurtosis (K) of 1.11 (leptokurtic), and an inclusive graphic skewness (Ski) of 0.17 (positive skewed). The result of the pebble morphometrics shows that the grains have an average elongation ratio (ER) of 0.80, coefficient of flatness (FI) of 60.6%, oblate–prolate index (OPI) of 0.35, maximum projection sphericity index (MPSI) of 0.77 and roundness (ρ) of 0.43. The roundness versus elongation ratio plot indicates a fluvial to transitional environment. Several bivariate and ternary plots that include the granulometric and pebble morphometric data suggest a river environment for the Bima sandstone in the studied area.

Alluvial fan and fan delta facies architecture recording initial marine flooding in the Mio‐Pliocene syn‐rift sequence of the Fish Creek‐Vallecito Basin, southern California

AbstractThe timing and character of the initial marine flooding of extensional basins has implications for their tectonic history. Yet, the recognition of such flooding is difficult along rift basin margins due to the dominance of coarse‐grained systems and the lack of marine fauna. This study conducts detailed facies and stratigraphic analysis of a Mio‐Pliocene alluvial fan and fan‐delta succession in the Fish Creek Vallecito Basin in southern California. Our goal is to characterize the marine flooding surface, determine the paleogeographic position of the shoreline and estimate the magnitude of relative base‐level rise that occurred during the marine incursion associated with the opening of the Gulf of California. Our results show that the flooding of the Elephant Trees alluvial fans is often marked by an abrupt lithologic and facies change from meter‐scale boulder‐rich subaerial debrites (proximal alluvial fan facies association) to centimetre‐scale granule‐rich subaqueous debrites, ripple‐laminated sandstones and mudstones (prodelta facies association). By delineating the zone of transition between the subaerial and subaqueous facies, we place the initial flooding paleo‐shoreline 4 km up the alluvial fan's paleo‐depositional slope. Considering alluvial fan slope gradients between 1° and 5°, this 4 km transgression would require an estimated 70–350 m of water depth during the initial marine incursion. Interfingering of fan‐delta deposits with subaqueous marine and planktonic‐rich evaporites suggests that the basin was below sea‐level after, and perhaps even before, the marine flooding. Subaerial subsea‐level basins exist in Death Valley and the Salton Trough today within similar extensional and transtentional tectonic regimes. This subaerial subsea‐level interpretation might explain the high magnitude and abrupt relative base‐level rise recorded by the facies transitions in the Fish Creek Vallecito Basin. These results suggest that the Fish Creek Vallecito Basin underwent significant extension during its early and nonmarine depositional phase, allowing it to reach subsea‐level elevations. The tectonic history of the Fish Creek Vallecito Basin maybe similar to other extensional basins where rapid subsidence allows the accumulation of nonmarine strata below sea‐level prior to the marine flooding, then restricted and deep marine strata immediately after flooding.

Study on the Early Cretaceous fluvial-desert sedimentary paleogeography in the Northwest of Ordos Basin

Abstract Early Cretaceous desert sedimentary system was developed in Northwest Ordos Basin. At present, the research degree of desert sedimentary paleogeography is low. The research on paleogeographic environment of Early Cretaceous sedimentary sandstone has guiding significance for the exploration of uranium resource and underground water resource in Northwest Ordos Basin. Based on the previous basic geological data of the lower Cretaceous in the Northwest of Ordos, through field geological survey, drilling core observation, and paleocurrent measurement, the sedimentary paleogeographic environments in different periods of Early Cretaceous had been studied. The results show that the lower Cretaceous in Northwestern Ordos Basin can be divided into two sedimentary cycles, the lower sedimentary cycle composed of Luohe Formation and Huachi-Huanhe Formation, and the upper sedimentary cycle composed of Luohandong Formation and Jingchuan Formation. Alluvial, Aeolian, and desert lake depositional systems were developed. The main sedimentary facies were alluvial fan, braided river, sand dune, dry valley, and dry lake. Alluvial fan and braided river facies had mainly developed in Luohe Formation. Braided fluvial facies mainly had developed in Huachi-Huanhe Formation, and alluvial fans locally developed around it. The deposits in Luohandong Formation were mainly aeolian sandstone, and the alluvial fan facies were inherently developed at Western and Northern margins. The depositional environment of Jingchuan formation is mainly river and lake. The tectonic evolution of lower Cretaceous had controlled the development of paleogeographic environment, and sedimentary facies had controlled the development of aquifer system. The paleogeographic environment of Early Cretaceous is conducive to the reduction and enrichment of uranium and the development of metallogenic units.

Seismic reservoir characterization of the syn-rift lower Miocene Rudeis Formation in the July oilfield, Gulf of Suez basin, Egypt: Implication for reservoir quality assessment

The Lower Miocene Rudeis Formation is among the most potential oil-bearing sedimentary sequences in the Gulf of Suez (GOS), representing the main producer of Egyptian oil. This study concerns primarily with revealing the reservoir characteristics and facies distribution, as well as the implication of the predominant diagenetic factors on the quality of the Lower Miocene syn-rift Rudeis reservoir in the July oilfield. Therefore, this study integrates 2D seismic, and wireline logs, as well as conventional and special core analyses to determine the reservoir characteristics and facies distribution. The interpreted data elucidate four different seismic facies in the Rudeis Formation with a net pay thickness ranging from 29 to 233 m in the studied wells of 16.3% average porosity, 62.9% average oil saturation, and 9.3% average shale volume. Four seismic facies (SF1-SF4) were interpreted and correlated with the Rudeis clastic deep-water turbiditic succession. The 3D static property models revealed that the best reservoir facies in terms of low shale content and water saturation, as well as high porosity, coincide with the submarine channels and fans containing coarse-grained, clean sandstones. From the core analysis, the Lower part of the Rudeis sequence is subdivided into five reservoir rock types (RRTs). The RRT1 is characterized by the best reservoir quality; it is composed of quartz arenites, sublithic arenites, and subfeldspathic arenites. In contrast, the RRT5 represents the lowest reservoir quality; it consists of very coarse siltstone, laminated glauconitic siltstone, and highly compacted dolomitic and calcareous quartz arenites. The poor reservoir characteristics of the RRT5 are attributed to tight compaction, cementation, and early dolomitization phase, whereas the highest quality of the RRT1 is related to fracturing and dissolution processes. The RRT1 rocks are mostly associated with the submarine channel and fan facies, whereas the poor quality RRT5 sediments were accumulated as hemipelagic/background. This integrated workflow study can be applied to further case studies in the Middle East, Africa, and the other analogues all over the world.

Facies association and sequence stratigraphic analysis of the lower Cretaceous Bima Formation in Yola arm of the Upper Benue Trough, Northeastern Nigeria

The Lower Cretaceous Bima Formation is the oldest sedimentary rock in the Upper Benue Trough. This research is aimed at understanding the facies, facies association, and sequence stratigraphic framework of the continental Bima Formation. Detail field mapping, lithostratigraphic studies, petrography, and paleocurrent analysis revealed that the formation is composed of three facies associations; gravel facies association FAI (gravelly dominated), sandstone facies association FAII (sand-sandstones dominated), and fine-grained facies association FAIII and four facies successions; proximal alluvial fan facies succession, braided river facies succession, fluvio-lacustrine facies succession, and flood plain facies association. The Bima Formation is punctuated by three major bounding surfaces, these provide the means of subdividing the Bima Formation into four depositional sequences namely; SQ1, SQ2, SQ3, and SQ4. Four system tracts were also identified within the Bima Formation; aggradational and high accommodation system tracts represent positive accommodation/sediments supply, and low accommodation system tract-A and B suggest negative accommodation/sediment supply. The overall sedimentation processes in the Bima Formation are controlled by climate, tectonic subsidence, and uplift. The paleocurrent data from the northern part of the study area suggest a unidirectional flow in NNW while the southern part of the study area shows SSW direction.

Sedimentary Characteristics of Denglouku third member in the south of Shuangcheng area, Songliao Basin

Based on sedimentary theory and high-resolution sequence stratigraphic theory, Denglouku third member in the south of Shuangcheng area is finely divided into a long-term reference surface cycle, 3 medium-term reference surface cycles and 20 short-term reference surface cycles. Denglouku third member is divided into three sand groups from top to bottom according to the medium-term reference surface cycles, and 6 layers, 6 layers, 8 layers in the groups respectively. Through fine observation of rock cores and data analysis of nearly one hundred wells, it is believed that alluvial fan facies, fluvial facies and delta facies are developed in the study area, which can be further divided into 6 subfacies and 12 microfacies. After the analysis to the plane distribution and vertical evolution characteristics of sedimentary facies, it is found that Denglouku third member in the south of Shuangcheng area shows a water-transgression sedimentary cycle from bottom to top which reflects the sedimentary process of water body gradually deepening.

Syn-rift sedimentary response to growth folding along a rift-margin transfer zone: An example from the early Miocene of the Gulf of Suez, Egypt

Growth folds developed at rift margin transfer zones are mostly studied for their structural style and stratal architecture. The influence of the growth of these folds on the syn-rift sedimentary facies development, however, remains less documented. To address this, we investigated the syn-rift facies of the Lower Miocene Rudeis Formation in relation to the growth of structures within the North Baba transfer zone at the eastern margin of the Suez rift. Sedimentological analysis defined seven facies associations in three successive depositional systems: (i) gravel-rich submarine fans with up-dip thinning geometry, comprising upper, middle and lower fan facies associations, (ii) a gravitationally modified Gilbert-type fan delta, with tangential foreset and bottomset. Both fan systems pass gradationally into basinal marl-dominated facies, and (iii) shoreface-to-offshore. Paleocurrent measurements and the spatial facies variability indicate that the North Baba transfer zone was acting as the main sediment fairway conveying the sediments southwards from the adjacent rift shoulder to the Baba hangingwall syncline. Mapping of key stratal surfaces and growth structures helped in distinguishing four lower Rudeis stratal units, which provide a framework for studying the spatial and vertical relationships among the recognized facies. Deposition of these stratal units was influenced by progressive steepening and localized faulting of a fault-tip growth monocline above the North Baba transfer zone and a submerged intrabasinal high. These structures controlled the hangingwall gradient, bathymetry, flow pathways and facies relations, triggered multiple gravity flows and slumps, and created terraces on which patch reefs and localized shoreface deposits intermittently developed. This study reveals that the transfer zone was still acting as growth monocline even during the rift-climax. The coeval deposits were mainly sourced from a hinterland drainage catchment rather than local footwall scarps. They form progressively tilted clastic wedges that onlap and pinch out up-dip toward the growth monocline, unlike those observed at faulted margins where the facies commonly thicken toward the fault.

Preliminary analysis of sedimentary characteristics and facies model of M-II layer in Kazakhstan Oilfield A

The lithologic melange accumulation of areskum formation in akshabluk area is one of the key strata in exploration. Its basement inheritance controls the whole process of Jurassic sedimentation, and the filling and leveling gradually reduces the terrain elevation difference; After the late Jurassic deformation, the flat paleogeomorphology was changed and the deposition of Early Cretaceous strata was controlled. Under the control of marker beds, sedimentary cycles are divided according to the cycle characteristics of logging curves. Under the control of cycle interface (standard layer), according to the cyclicity of logging curve (GR), combined with core and seismic data, it is divided step by step according to the cycle level, from large to small, that is, it is divided step by step according to “oil bearing series → oil reservoir group → small layer → sedimentary unit”, and a layered system is established. Vertically, M-I and M-II groups are developed from bottom to top. M-II group is divided into m-ii-1 and m-ii-2. M - II - 1 is subdivided into four sub layers: m - Ⅱ - 1A, M - II - 1B, M - II - 1c and M - II - 1D. Based on the comprehensive analysis of sedimentary background and paleostructural characteristics, according to the sedimentary location and sedimentary environment of oilfield a, and referring to core data and seismic data, it is determined that oilfield a develops three sedimentary facies: alluvial fan facies, fluvial facies and lacustrine facies. According to the seismic attribute slice and logging data, predict the sandstone thickness contour map of each sedimentary unit, divide the single well logging facies, study and divide the sedimentary subfacies and sedimentary microfacies according to the sedimentary model.

Research on sedimentary facies of Guantao Formation in Shanjiasi area of Dongying depression, China

Alluvial fan and Fluvial facies sand bodies are important reservoirs for oil and gas resources. In this study, the sedimentary characteristics and evolutionary patterns of Alluvial fan and fluvial deposits in the Neogene Guantao Formation of the Dongying Sag, Bohai Bay Basin were analyzed using cores, well logs and three-dimensional seismic data, and the quantitative information of the sand bodies in different deposits were characterized with dense well-net constraints. Through the calibration between the core and wireline logging data, the developmental characteristics of the sand bodies in the Alluvial fan and fluvial deposits were clearly defined base on sedimentary microfacies and seismic facies interpretation. Using the RMS amplitude attribute and reconstructed Wave Impedance Inversion, the sand bodies of Guantao Formation in this area were carefully described and studied, and the effective reservoir range was predicted on the basis of fully understanding the oil test data. Results: The top and bottom interface of Guantao Formation are characterized by strong continuous reflection on seismic section, exist within the guantao on seismic section three continuous or intermittent peaks, from bottom to top respectively represent the interface between Ng4 and Ng3 sand group, the interface between Ng3 and Ng2 sand group,the interface between Ng2 and Ng1 of the Guantao Formation, and Ng4 sand group of the Guantao Formation is the key layer; The boundary Growth Fault and Binxian high jointly controlled the deposition of Guantao Formation. The sedimentary thickness of the strata decreased on the north and west sides of the sag, and increased from the core to the edge of the Binxian high; The sedimentary facies of Guantao Formation in the study area can be divided into three types: alluvial fan facies, braided river facies and meandering river facies, and various corresponding subfacies and microfacies can be subdivided into different types. Ng4 sand group of the Guantao Formation is identified as alluvial fan-braided river model; Based on the analysis of the distribution and physical properties of alluvial and fluvial facies sand bodies in the study area, it is considered that the effective reservoir of Ng4 sand group of the Guantao Formation is mainly developed in the nose structure around Binxian high, and is semicircular in distribution.

Organic Geochemical Characteristics of Mudstone and Marl from Western Hoh Xil Basin of Tibet

The mudstone and marl from western Hoh Xil basin, located in Tibet of the west of China, were deposited in Tertiary lacustrine environment. Investigation of organic geochemistry, sedimentary characteristics, and 13C in kerogen was conducted to analyze the sedimentary environment, biomarkers, paleoclimate, and source of organic matter during deposition. The Cenozoic sedimentary facies of the basin included upper lacustrine facies and lower alluvial fan facies, which belong to Miocene Wudaoliang Formation and Oligocene Yaxicuo Group, respectively. The Miocene marl-sandstone-mudstone from Wudaoliang Formation was analyzed. Maceral composition was dominated by amorphous organic matter. T max values indicated that the mudstones were thermally immature-low maturity with mainly type II and III organic matter, while organic matter in marlite belongs mainly to type I-II1 with low maturity-maturity stage. The biomarkers showed the characteristics of odd-over-even predominance of long-chain n-alkanes, higher proportion of C27 sterane in most of the samples, heavy δ13Corg composition, low Pr/Ph ratios (0.11-0.36), and so on. Organic geochemistry indicated that the organic matter originated from bacteria, algae, and higher plants. The rocks were formed in reducing environments with stratified water column and high productivity. The paleoclimate became more humid during depositional stage in the western Hoh Xil basin.

Seismic reservoir characterization of gas-sand deposits in the Kutei basin, Indonesia

Kutei Basin has the second largest hydrocarbon reserve in Indonesia. In addition to the Miocene inversion related structural traps, slope-fan and channel stratigraphic traps are also important traps in this basin. To guide stratigraphic traps explorations in the basin, the seismic stratigraphy, attributes, and AI inversion methods are integrated to identify and map the reservoir seismic facies, porosity, and pore-fluid. Well data indicates that the studied reservoirs are filled by gas. Seismic data shows that there are two main gas-sand reservoirs corresponding to strong amplitude anomaly. Seismic stratigraphy analysis, guided by seismic attributes, shows that these gas-sand reservoirs were deposited in the channel and local fan facies. The AI inversion is applied to identify and map the porosity and pore-fluid of these two sand reservoirs. Future well locations are identified by integrating the facies, porosity, and pore-fluid maps.