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The reservoir architecture analysis of braided rivers, especially falling-silt seam forms, has played a key role in predicting remaining oil distributions. However, no studies have used architecture analyses that document braided river outcrops and researched the tapping of the few remaining oil distributions based on outcrops in the Songliao basin, northeast China. In this paper, the architecture characteristics and remaining oil distribution of braided river reservoirs are studied using a combination of an outcrop, modern deposition and subsurface well data. The new 8–13 m thick Lower Cretaceous Quantou Formation outcrop of the Songliao basin is a braided fluvial succession arranged in one large fining-upward cycle. Eight facies (Gt, St, Sm, Sh, Sp, Sw, Fl and Fm), four architecture elements (CH, DA, LV, and FF), and three orders of bounding surfaces (third-, fourth-, and fifth-order) are recognized. A new distribution pattern of falling-silt seams and a braided river architecture model are presented according to the analysis of the outcrop. In the mid-channel bar, the falling-silt seams thin from the mid-bar to the bar tail following the flow direction. Each falling-silt seam is oriented tangentially to the basal surface of the mid-channel bar, and the upper falling-silt seam extends farther than the lower one. In a Daqing Oilfield exploitation block in the Songliao basin, while channels and bars are the main reservoir units, they have different remaining oil distribution patterns. For bars, water injection wells located at the mid-bar, zonal injection technology, the drilling of horizontal wells, and proper well patterns are proposed. Fourth-order bounding surfaces, single braided channels, stacking patterns, and the lateral blocking of levees and floodplains are the key factors affecting the remaining oil distribution in channels.

The sandbodies within braided fluvial deposits are important reservoirs for the oil fields in China, and they usually have complex sedimentary architecture. A lot of research has been concentrated on characterizing the architecture of the sandbodies. Based on the observation that muddy deposits are commonly well preserved in fluvial deposits, we find that understanding the contact relationship between the muddy deposits and surrounding sand bodies can help characterize the depositional process of sandy braided fluvial systems. We have determined the effectiveness of this idea by characterizing a well-exposed outcrop of sandy braided fluvial system in the Datong Basin, Shanxi Province of China. We first define six muddy lithofacies by integrating the thickness of the muddy deposits, the morphology of the muddy deposit, and the lithofacies of surrounding sand deposits. The six muddy lithofacies include floodplain muddy deposits between intermittent channel complex, lateral covering muddy deposits and fall-silt seam muddy deposits between migrated bar complex, muddy gravel deposits in erosional bar complex, and channel-fill muddy deposits and gully-fill muddy deposits in abandoned bar complex. We then analyze the depositional environments according to the defined muddy lithofacies. We finally build the architecture of the outcrops by integrating the lithofacies of sand deposits and evolution of the depositional environments deduced from the muddy lithofacies.

Take the lacustrine delta in the second member of Paleogene Shahejie Formation in block Wang43, Dongying depression, Bohai Bay Basin as an example, the deposition architectural characteristics of lacustrine deltaic sand bodies controlled by syn-depositional faults in complex fault blocks of rift basin are examined from the aspect of the tectonic-deposition response, using cores, well logs and three-dimensional seismic data. The small-scale syn-depositional faults in complex fault blocks are dense and different in dip, the activity along the strike of syn-depositional fault varies in different positions, and all these control the sedimentary process of deltaic sand bodies. Influenced by syn-depositional faults, the deltaic distributary channel is more likely to pass through the position with weak fault activity, and be deflected or limited at the position with strong fault activity. In downthrown side of a single syn-depositional fault or micro-graben areas, sand bodies increase in thickness and planar scale, and sand bodies of multiple stages are likely to stack over each other vertically. In micro-horst areas controlled by syn-depositional faults, the sand bodies decrease in abundance, and appear in intermittent superimposed pattern vertically. This study can provide new research ideas and theoretical basis for exploration and development research in complex fault blocks.

The limited knowledge of Late Cretaceous terrestrial environments and their response to tectonic events in mid-latitudes can be addressed through continental basin deposits such as paleosols. Paleosols have been discovered in the Late Cretaceous Yaojia Formation in the southern Songlaio Basin and are recognized by evidence of soil structures controlled by pedogenesis. Sedimentary facies research on red paleosols was conducted on the Late Cretaceous Yaojia Formation in the outcrop of the southern Songliao Basin to interpret the depositional environments and tectonic significance of red paleosols during the greenhouse period. Mudflat, lake margin, and shallow lake depositional environments in a semi-arid climate are interpreted from the outcrops based on sedimentary descriptions and interpretation as well as geochemical and micromorphological analyses of paleosols in outcrops. We reconstructed the paleoenvironmental and paleoclimatic conditions through the paleosols in the mudflats and lake margin. The red paleosols in the mudflats and lake margin deposits formed in a stable landscape influenced by the tectonic uplift of the Songliao Basin, which is considered as new important evidence for tectonic uplift influenced by the collision of the Okhotomorsk Block with East Asia. The tectonic uplift process in East Asia is identified from the evolution of the depositional environments and drainage conditions inferred from different types of paleosols. Thus, the paleosols-bearing red bed deposits in outcrops provide an important contribution of the Late Cretaceous terrestrial paleoclimate and the tectonic setting research.

Shallow water delta developed during the Late Cretaceous greenhouse climate depositing in the red bed succession of the Yaojia Formation in the Southern Songliao Basin, NE China. The shallow water delta deposits provide an opportunity to understand the influence of high discharge variability in a semi-arid climate on the fluvial patterns, internal sedimentary details, and reservoir quality of distributary channels. The sedimentary process of the shallow water delta in the Yaojia Formation was controlled by a dual-stage process, including a high-flow stage and a low-flow stage within a semi-arid paleoclimate. During the high-flow stage, crevasse channels formed through avulsion of major distributary channels on the delta plain. Subaqueous terminal distributary channels and mouth bars formed at the delta front during progradation of the delta. During the low-flow stage after flood events, crevasse channels were abandoned and frequently exposed becoming reddish in color. This process can be reason for the classification for two main types of distributary channels: major distributary channels and crevasse channels in the delta plain. Sand bodies in distributary channels are distinguished by sedimentary structures indicate critical and supercritical flow conditions. Based on well logs and 3D seismic data, the sand distribution of was analyzed from the sandstone isopach map of the 2nd sand bed in the first member of the Yaojia Formation. The framework sand belts develop coincides with distribution of the major distributary channels. Based on detailed observational and reservoir test data from cores, the distribution of major distributary channels revealed a belt of high-quality reservoirs in the shallow water delta. This study provides a new perspective on the sedimentary pattern of distributary channels in shallow water deltas with high discharge variability, which has important implications for reservoir exploration in lacustrine basins.

Based on outcrop, core, logging and mud logging data, and modern deposition analog, the sandbodies genetic types and spatial distribution in different facies belts of the shallow water delta in the first Member of Cretaceous Yaojia Formation (K2y1) of Qian'an area in Changling sag of southern Songliao Basin were analyzed, and the sedimentary model of shallow water delta was established according to deposition process. Active channel sandbodies, point bar sandbodies and bifurcation bar sandbodies in distributary channels and complex sandbodies formed the main sandbodies in the delta plain, while terminal distributary channels and mouth bar sandbodies formed the main sandbodies in the delta front. The delta prograded gradually under the construction of river mouth and reconstruction of river erosion, the early delta front evolved into delta plain and was reformed by distributary channels, and new delta fronts were formed at the river mouth ahead constantly. Under the control of the above deposition process, the size of main distributary channels in delta plain-delta front declined, while mouth bars developed increasingly. The sandbodies of different genetic types formed framework of river-dominated shallow water delta. The point bar and active channel sandbodies in main distributary channels of the delta, with the best reservoir quality, are lithologic reservoir targets in future exploration. Key words: Songliao Basin, Cretaceous, Yaojia Formation, shallow water delta, sandbody type, sedimentary model

Formed in extensional structural system, syndepositional faults are widely distributed in rift basins. Large basinal scale syndepositional faults play important roles in controlling the development and dispersion of depositional systems in rift basins. When it comes to the intensively developed small-scale syndepositional faults related to those large basinal scale syndepositional faults in complex fault blocks, the controlling effects to sedimentary architecture in the finer scale are still not well understood in the depositional systems. Thus, commonly used sedimentary models without considering small-scale syndepositional faults related paleogeomorphology are difficult to apply in complex fault blocks of rift basins. In this study, using the interpretation of 3D seismic profiles, wire-line log curves, and cores, patterns of small-scale syndepositional faults and their related finer scale stratigraphic sequences are described in the upper Es2 member, Shahejie Formation of the W43 complex fault block area, Dongying Depression, Bohai Bay Basin. The syndepositional faults are intensively distributed in the W43 complex fault block area. Based on the interpretation of sequence boundaries, four types of syndepositional faults related paleogeomorphology units were identified. They are named the micro slope break belt, micro-horst belt, and the micro-graben belt. The stacking patterns and development scale of individual deltaic sand bodies in the parasequences are controlled by activity of the syndepositional faults. In the hanging wall area near the syndepositional fault of the micro-step and micro-graben, thickened multi-stage continuously individual sand bodies are deposited controlled by low topography during the depositional period with sufficient sediment supply. In the footwall area of single micro syndepositional fault and micro-horst belt, individual sand bodies became thinner and less aggraded in vertical direction. The small-scale syndepositional fault-related paleogeomorphology is a new important factor that controls the sedimentary architecture of the shallow water deltaic sand bodies in the rift basin. This study provides insights into tectonic control of finer-scale sedimentary architecture and hydrocarbon reservoirs development in continental rift basins.

Sediment routing in deep-water settings can be significantly different in lacustrine basins from their well-studied marine counterparts, which has been largely overlooked during the past decades. The seismically well-imaged lacustrine clinothems in the Eocene Dongying Depression provide a good opportunity to bridge the deep-water sediment partitioning with clinothem architecture and shelf-edge trajectories, which have been studied through the integration of 3D seismic data and well-logging data. In the study area, the Eocene delta-complexes are architecturally manifested as alternating aggradation dominated (AC) and progradation dominated clinothems (PC). The Eocene Dongying clinothem architecture has been documented in terms of shelf–edge trajectory angle (θsht), edge-to-toe distance (ETT), aggradation height (Ah), progradation distance (Pd) and maximum foreset angle (γmfa). Aggradation dominated clinothems are characterized by ascending shelf-edge trajectories with thick and widespread sand-prone bottomsets, suggesting higher efficiency of sediment delivery into the outlying lake floor. Progradation dominated clinothems, in contrast, are characterized by flat to slightly descending trajectories and generally by a lack of bottomsets. Alternations of rising and flat to slightly descending trajectories accompanied with different clinothem types probably indicate frequent relative lake level changes (on time-scales of 100s of kyr). Further analysis of seismic images and extensive well-logs suggest the distal aggradational bottomsets are generally consist of sub-lacustrine channel-lobe systems, whereas sediment slide, slump blocks occur in slope to slope toe areas of progradation dominated clinothems, which indicate varied processes of deep-water sediment transport associated with different clinothem types and shelf-edge trajectories. Lake-level, sediment supply, water salinity and density change induced by humid-arid climate cycle are suggested to be main factors controlling clinothems stacking pattern and sediment dispersal into deep-lacustrine. Humid climate are considered to be related with strongly aggradational clinothems, during which sediment can be directly transported to the distant bottomset areas due to increased sediment concentration and energy in river discharge. Whereas during dry periods, progradation dominated clinothems start to build under stillstand or falling lake level conditions, sediment generally accumulates at river mouth and collapses due to sediment overload or fault activity. Therefore, a relationship between deep-lacustrine depositional process and climatic signature was established which may provide new thoughts in both the study of deep-water sequences and deep-water exploration in lacustrine basins.

The Eocene lacustrine carbonates in the western Dongying Depression, Bohai Bay Basin were examined based on integrated analysis of 3D seismic data, cores, thin-sections, and geochemical testing. Seismic profiles and geomorphological mapping revealed a landmass-attached (semi-isolated) carbonate platform restricted by marginal syn-sedimentary faults and surrounded by three deep sags. 3D topographic analysis of the platform revealed six districts characterized by variable buried depths, topographic gradient, and fault combinations, including two flat-topped areas (PFW and SD; topographic gradient