Low Uplift Research Articles

Formation and characteristics of large-medium buried-hill hydrocarbon reservoirs in Bohai Sea

There had been a long history of the buried-hill hydrocarbon reservoirs exploration operation in Bohai Sea. Between 1970s and 1990s, based on the onshore exploration experiences in eastern China, many boreholes were drilled in order to detect large-scale carbonate buried-hill hydrocarbon reservoirs in Bohai Sea, but no prominent discoveries was achieved. In-depth re-evaluation and examination were conducted upon these exploration failures, a new understanding that Bohai Sea had unique geological characteristics of buried hills was concluded. Bedrocks on the uplifts of Bohai oil province were mainly granites and migmatitic granites of Archean, Proterozoic and Mesozoic, as well as minor Lower Paleozoic carbonates. Proterozoic algae dolomite was most favorable for buried-hill hydrocarbon reservoirs however which were not developed in Bohai Sea. A large number of faults in Bohai oil province were developed and faults activities were intense in the late period. Thus, conventionally, reservoirs and preservation conditions of the buried hills were believed to be poor in Bohai Sea, and were not favourable for formation of large-scale buried-hill hydrocarbon reservoirs. Through the long-term practices and deep analyses, the coupling between granites, migmatitic granites and intense bedrock faults was favorable for buried-hill reservoirs with high test production and relatively low core recovery rate. Geophysical data could be used for accurate predictions of bedrock lithology and faults. The monadnock buried hills on the low uplifts adjacent to hydrocarbon-rich sags were covered by shallow to semi-deep lacustrine shale, which was favorable for buried-hill hydrocarbon reservoirs. Under the guidance of a series of innovative understandings, the re-exploration of buried hills in Bohai Sea achieved two largest granite buried-hill oil and gas fields with 100 million tons of reserves. The understanding and practice processes might also inspire exploration of other areas.

Past environmental change and seawater intrusion into coastal Lake Lilaste, Latvia

Diatoms, organic matter and magnetic susceptibility in a 10-m-long sediment sequence from coastal Lake Lilaste, Latvia, were analysed to evaluate Holocene environmental changes related to past sea-water intrusions. Lake Lilaste is located ~1 km from the present sea coast in an area with a low uplift rate and a threshold altitude of 0.5 m a.s.l. It was thus considered to be an appropriate site to study the influence of past sea level fluctuations on the lake and its sediments. Variations in diatom community composition, along with sediment lithostratigraphy, show that a shallow, nutrient-rich freshwater lake existed there during the early Holocene. The first brackish-water diatoms appeared concurrent with a sea level rise ca. 8700 ± 50 cal a BP, but long-term, intermittent inputs of brackish water were observed between 6700 ± 40 and 4200 ± 80 cal a BP. During those time spans, diatoms indicate increased nutrient concentrations and high conductivity, a consequence of occasional mixing of brackish and freshwater that promoted biological productivity. Lilaste was isolated from the sea at 4200 ± 80 cal a BP, after which a stable freshwater environment, dominated by planktonic diatoms such as Aulacoseira ambigua, A. granulata, A. islandica and A. subarctica, was established. At 400 ± 50 cal a BP, planktonic diatoms were gradually replaced by Fragilaria spp., indicating the beginning of anthropogenic impact. The reconstructed relative water-level curve from the lake coincides with the eustatic sea level curve from 6800 ± 40 cal a BP onwards. There was a distinct increase in abundance of brackish-water diatoms when the sea level reached the threshold of Lilaste, which at that time was probably about 3 m lower than the present sea level. According to radiocarbon-dated shifts in the diatom community composition, the Litorina Sea transgression was a long-lasting event (ca. 2200 years) in the southern part of the Gulf of Riga, where the land uplift rate was near zero. It culminated more than 1000 years later than at other sites with higher uplift, in the northern part of the Baltic Sea.

辽西低凸起中北段潜山油气藏泥岩盖层封闭能力评价

为综合评价辽西低凸起泥岩盖层封闭能力，统计分析了辽西低凸起中北段潜山基础井资料，表明辽西低凸起潜山盖层主要由东营组和沙河街组泥岩盖层组成，其中以东营组泥岩盖层为区域性盖层，沙一段沙二段和沙三段泥岩盖层在JZ20-2、JZ25-1S潜山有分布，为局部盖层。选取泥质含量、突破压力、超压压力系数等参数研究微观特征，研究表明辽西低凸起潜山盖层主要存在泥岩毛细管压力封盖和超压封盖两种类型的微观机理，其中超压封盖主要分布在低凸起中北部JZ25-1S地区与JZ20-2地区。综合评价辽西低凸起中北段泥岩盖层封闭能力。结果表明：辽西低凸起中北段盖层以中等、好为主，好盖层分布较广。通过分析盖层与已发现油气藏关系，辽西低凸起中北段已发现油气分布在中等及以上盖层区域内，表明中等封盖能力的潜山盖层就能很好的封闭潜山油气。 In order to comprehensively evaluate low bulge mudstone caprock sealing ability, the data of buried hill basic well in Liaoxi low uplift are statistically analyzed. It shows that Liaoxi low uplift buried hills cover layer is mainly composed of dongying group and the shahejie formation. Among them, mudstone caprock of Dongying formation is a regional cap rock. And Sha 1, Sha 2 and Sha 3 mudstone cover are distributed in the JZ20-2, JZ25-1s buried hill, which are partial cap rocks. The parameters of shale content, breakthrough pressure and overpressure pressure coefficient were selected to study the microscopic features. The results showed that there were mainly two types of micro-mechanisms: Mudstone capillary pressure cap and overpressure sealing system. Overpressure sealing system is mainly distributed in low rising in north-central JZ25-1s region and the JZ20-2. A comprehensive evaluation of the sealing ability of mudstone cover in the northern section of Liaoxi low uplift was made. The results showed that the top layer of the northern section of the low bulge in the Liaoxi low uplift was medium and good, and the distribution of the good cover was wide. By analyzing the relationship between cap rock and reservoir that had been found, and the oil and gas that had been found in the medium and above cover area, which showed that the buried caprocks with medium cap ability can well seal the buried hill oil and gas.

Why is there no Coastal Cordillera at the Arica Bend (Western Central Andes)?

AbstractThe architecture of the Western Andes is remarkably constant between southern Peru and northern Chile. An exception, however, is present near Arica at 18°S, where the Andes change their strike direction by ca. 50° and the Coastal Cordillera is absent over an along‐strike width of 50 km. Although this feature has been mentioned in several previous studies, no effort has been made yet to describe and explain this peculiar morphology of the Western Central Andean forearc. Here, we propose a large‐scale model to explain the Myr‐long low uplift rate of the Arica Bend concerning seismic coupling and continental wedge‐top basin evolution. New geomorphic and sedimentologic data are integrated with seismicity and structural data from the literature to interpret the post‐Oligocene pattern of uplift, erosion and sediment transport to the trench. Results show that the Arica Bend has been marked by exceptionally low coastal uplift rates over post‐Oligocene timescales. In addition, this uplift anomaly at the Arica Bend correlates with relatively high sediment discharge to the corresponding trench segment since late Oligocene time. We interpret that before 25 Ma, the forming seaward concavity of the subduction zone induced trench‐parallel extension at the curvature apex of the overriding forearc. The subsequent low uplift rate would have then triggered a feedback mechanism, where the interplay between relatively low interplate friction, low coastal uplift and relatively high sediment discharge favoured Myr‐long relative subsidence at the Arica Bend, in contrast to Myr‐long uplift of the Coastal Cordillera north and south of it.

Analysis of the interaction between neotectonic and surface processes in a low-land intracratonic setting of South America

Abstract The Quaternary sedimentary record in the continental interiors has generally been studied taking into consideration the climatic forcing. However, episodes of uplift controlling the development of landforms have often been dismissed. The interiors of continents are typically considered to have low deformation rates, lower than the rates of exogenous processes. Deformation in the middle of the Pampean plains, an intracratonic setting of South America, has been observed to have generated an elevated area surrounded by lowland plains. This elevated area is susceptible to fluvial erosion. From this fact we developed a geomorphologic modelling constrained from geomorphic markers in order to estimate the relative incidence of the different factors that control erosion in lowland landscapes. An adapted erosion code was employed, which combines fluvial incision equation (the stream power law), an uplift function spatially distributed and the hillslope diffusion equation. A low-DEM was achieved for restoring an initial non-deformed topography affected by low fluvial incision. It represents a palaeosurface chrono-stratigraphically constrained. The estimation of the model parameters was achieved by applying the inversion method. The best-fit between the numerical solution (calculated topography) and the measured topography (simulated by means a DEM) was approached by comparison of the stream longitudinal profiles. The yield numerical approach suggests that a geomorphological modelling based on the stream power law is possible to be applied in low-land landscapes. For this, a large scale change of the magnitude of the processes modelling the landscape should be expected in comparison with mountain erosional environments. Remarkably low K empirical values ( K = 5 × 10 −6 –6 × 10 −6 yr −1 ) suggest that the extremely low slopes exert a larger influence on the stream power in low-land landscapes. Also the diffusion coefficient D values resulted largely lower (3 × 10 −4 –1.9 × 10 −3 cm 2 /yr) than presented in tectonically active landscapes (>0.03 cm 2 /yr). Regional uplift rates can be higher (0.35 mm/yr) than it is generally expected in low uplift rate settings (0.1–0.25 mm/yr). These estimations evidence highly dynamic surface and tectonic processes controlling the landscape evolution over intermediate time scales in an intracratonic setting.

Seismic reflection characteristics and evolution of intrusions in the Qiongdongnan Basin: Implications for the rifting of the South China Sea

The Qiongdongnan Basin (QDNB) is situated in the extensional zone at the vertex of the V-shaped northwest sub-basin, non-volcanic northern margin of the South China Sea (SCS). From north to south, the thickness of the continental lithosphere decreases from 22 km on the northern continental shelf to 17 km at the deepest area of the central depression. A sharp change on the crustal structure is of importance to hydrocarbon exploration yet the dynamic causes remain unknown. A comprehensive study including (1) interpretation of seismic profiles, (2) P-wave velocity data modeling, and (3) magnetic anomalies analysis reveals that there are some high-density intrusions along the lithospheric thinning belt. Chaotic reflections can be found in the southwest of the QDNB, with a low velocity ( 6 km/s) suggest the existence of igneous diapirs. Diapirism differentiation are primarily achieved through analysis of the contact relationship and the thickness variations in the surrounding strata. The first phase of diapirism along the Songnan low uplift occurred in the Late Mesozoic, and the second phase of diapirism in a form of subsequent gas movement remained active until the Late Quaternary. The distribution and the evolution of the diapirs would have major implications for post-rift emplacement.

Evolutionary history and controlling factors of the shelf breaks in the Pearl River Mouth Basin, northern South China Sea

The migration history of shelf breaks in the stratigraphy of a basin contains significant information about sediment-budget partitioning into the deep water area, which is thus important in predicting the distribution and quality of deepwater reservoirs. Previous studies primarily focused on the sedimentary-dominated shelf breaks (e.g., progradational-type), which are controlled by sediment supply and relative sea-level changes. The location and migration pattern of structure-controlled shelf breaks are comparatively less well documented.The evolutionary history of shelf breaks in the Pearl River Mouth Basin from 30 Ma to present is examined here. Shelf breaks are picked from 280 2-D depositional dip-oriented seismic profiles in the forced regressive systems tracts of 20 3rd-order sequences (SQ 1-20) in four super sequences (SSQ 1-4). Planview distribution maps indicate these shelf breaks can be divided into two groups of different character. Shelf breaks in SSQ 1 (30–23.8 Ma) have migrated progressively and considerably basinward (∼50 km) along with the progradation of shelf-margin deltas, which were propelled by a very strong sediment supply even under the background of relative sea-level rise. They are consequently classified as sedimentary-dominated types. In contrast, shelf breaks in SSQ 2-4 have stayed fairly close (∼20 km) to the boundary between the Panyu Low Uplift and the Baiyun Sag, which is identified as a tectonic hinge zone across which subsidence rate increased abruptly basinward. Shelf breaks were close to the hinge zone even in SQ 11 and 12, in which the depositional shoreline breaks were located ∼80 km further landward. They are classified as structure-controlled types. Our study indicates that through the evolutionary history of the Pearl River Mouth Basin, the locations and migration pattern of the shelf breaks were mainly sediment-supply controlled during 30–23.8 Ma but changed to structure-controlled (i.e., tectonic hinge zone) during 23.8 Ma-Present.

Active tectonic deformation along rejuvenated faults in tropical Borneo: Inferences obtained from tectono-geomorphic evaluation

The island of Borneo is enveloped by tropical rainforests and hostile terrain characterized by high denudation rates. Owing to such conditions, studies pertaining to neotectonics and consequent geomorphic expressions with regard to surface processes and landscape evolution are inadequately constrained. Here we demonstrate the first systematic tectono-geomorphic evaluation of north Borneo through quantitative and qualitative morphotectonic analysis at sub-catchment scale, for two large drainage basins located in Sarawak: the Rajang and Baram basins. The extraction of morphometric parameters utilizing digital elevation models arranged within a GIS environment focuses on hypsometric curve analysis, distribution of hypsometric integrals through spatial autocorrelation statistics, relative uplift values, the asymmetry factor and the normalized channel steepness index. Hypsometric analysis suggests a young topography adjusting to changes in tectonic boundary conditions. Autocorrelation statistics show clusters of high values of hypsometric integrals as prominent hotspots that are associated with less eroded, young topography situated in the fold and thrust belts of the Interior Highlands of Borneo. High channel steepness and gradients (>200m0.9) are observed in zones corresponding to the hotspots. Relative uplift values reveal the presence of tectonically uplifted blocks together with relatively subsided or lesser uplifted zones along known faults. Sub-catchments of both basins display asymmetry indicating tectonic tilting. Stream longitudinal profiles demonstrate the presence of anomalies in the form of knickzones without apparent lithological controls along their channel reaches. Surfaces represented by cold spots of low HI values and low channel gradients observed in the high elevation headwaters of both basins are linked to isolated erosional planation surfaces that could be remnants of piracy processes. The implication of our results is that Borneo experiences active folding of the Rajang Group fold–thrust belt to present and these events reactivated old major faults and minor related dislocations. From geomorphic analysis associated with sedimentary record, we posit that the terrain could have undergone high uplift rates since 5Ma or multi-phased uplift with periodic intermittent pulses of high and low uplift rates.

Geochemistry, origin and accumulation of natural gases in the deepwater area of the Qiongdongnan Basin, South China Sea

The Qiongdongnan Basin, South China Sea has received huge thickness (>12 km) of Tertiary-Quaternary sediments in the deepwater area to which great attention has been paid due to the recent discoveries of the SS22-1 and the SS17-2 commercial gas fields in the Pliocene-Upper Miocene submarine canyon system with water depth over 1300 m. In this study, the geochemistry, origin and accumulation models of these gases were investigated. The results reveal that the gases are predominated by hydrocarbon gases (98%–99% by volume), with the ratio of C1/C1-5 ranging from 0.92 to 0.94, and they are characterized by relatively heavy δ13C1 (−36.8‰ to −39.4‰) and δDCH4 values (−144‰ to −147‰), similar to the thermogenic gases discovered in the shallow water area of the basin. The C5-7 light hydrocarbons associated with these gases are dominated by isoparaffins (35%–65%), implying an origin from higher plants. For the associated condensates, carbon isotopic compositions and high abundance of oleanane and presence of bicadinanes show close affinity with those from the YC13-1 gas field in the shallow water area. All these geochemical characteristics correlate well with those found in the shales of the Oligocene Yacheng Formation in the Qiongdongnan Basin. The Yacheng Formation in the deepwater area has TOC values in the range of 0.4–21% and contains type IIb–III gas-prone kerogens, indicating an excellent gas source rock. The kinetic modeling results show that the δ13C1 values of the gas generated from the Yacheng source rock since 3 or 4 Ma are well matched with those of the reservoir gases, indicating that the gas pool is young and likely formed after 4 Ma. The geologic and geochemical data show that the mud diapirs and faults provide the main pathways for the upward migration of gases from the deep gas kitchen into the shallow, normally pressured reservoirs, and that the deep overpressure is the key driving force for the vertical and lateral migration of gas. This gas migration pattern implies that the South Low Uplift and the No.2 Fault zone near the deepwater area are also favorable for gas accumulation because they are located in the pathway of gas migration, and therefore more attention should be paid to them in the future.

Coastal uplift west of Algiers (Algeria): pre- and post-Messinian sequences of marine terraces and rasas and their associated drainage pattern

The North Africa passive margin is affected by the ongoing convergence between the African and Eurasian plates. This convergence is responsible for coastal uplift, folding, and reverse faulting on new and reactivated faults on the margin. The active deformation is diffuse and thus rather difficult to locate precisely. We aim to determine how a coastal landscape evolve in this geodynamic setting and gain insights into active tectonics. More particularly, we evidence and quantify coastal uplift pattern of the Chenoua, Sahel, and Algiers reliefs (Algeria), using sequences of marine terraces and rasas and computing several morphometric indices from the drainage pattern. Upper and Middle Pleistocene uplift rates are obtained by fossil shoreline mapping and preliminary U/Th dating of associated coastal deposits. Extrapolation of these rates combined to analyses of sea-level referential data and spatial relationships between marine terraces/rasas and other geological markers lead us to tentatively propose an age for the highest coastal indicators (purported the oldest). Values of morphometric indices showing correlations with uplift rate allow us to analyze uplift variation on area devoid of coastal sequence. Geological and geomorphological data suggest that coastal uplift probably occurred since the Middle Miocene. It resulted in the emergence of the Algiers massif, followed by the Sahel ridge massif. The Sahel ridge has asymmetrically grown by folding from west to east and was affected by temporal variation of uplift. Compared to previous study, the location of the Sahel fold axis has been shifted offshore, near the coast. The Chenoua fault vertical motion does not offset significantly the coastal sequence. Mean apparent uplift rates and corrected uplift rates since 120 ka are globally steady all along the coast with a mean value of 0.055 ± 0.015 mm/year (apparent) and of 0.005 ± 0.045 mm/year (corrected for eustasy). Mean apparent coastal uplift rates between 120 and 400 ka increase eastward from 0.045 ± 0.025 to 0.19 ± 0.12 mm/year (without correction for eustasy) or from 0.06 ± 0.06 to 0.2 ± 0.15 mm/year (with correction for eustasy). In addition, the combination of structural and geomorphic data suggests a low uplift rate for the southern part of the Algiers massif.

Dibenzothiophenes and benzo[b]naphthothiophenes: Molecular markers for tracing oil filling pathways in the carbonate reservoir of the Tarim Basin, NW China

Dibenzothiophenes (DBTs) and benzo[b]naphthothiophenes (BNTs) are the main sulfur-containing heterocyclic aromatic compounds in crude oils and sedimentary rock extracts. Because of the relatively higher electronegativity and an unshared pair of electrons in the outer shell orbital of the sulfur atom, hydrogen bonds can be formed between the sulfur and hydrogen atoms of the surrounding medium in carrier beds. Therefore, DBTs and BNTs are potential geochemical markers for tracing oil filling pathways. A correlation of oils in the Halahatang Oilfield of the Tabei Uplift in the Tarim Basin (NW China) shows that the molecular marker compositions of all oils are quite similar, implying that these oils have been sourced from the same source kitchen and belong to a same oil family. Using molecular indicators relative to DBTs and BNTs, namely, 4-/1-MDBT (4-/1-methyldibenzothiophene), 4,6-/(1,4+1,6)-DMDBT (4,6-/(1,4+1,6)-dimethyldibenzothiophene), (2,6+3,6)-/(1,4+1,6)-DMDBT ((2,6+3,6)-/(1,4+1,6)-dimethyldibenzothiophene), and [2,1]BNT/([2,1]BNT+[1,2]BNT) (benzo[b]naphtho[2,1-d]thiophene/(benzo[b]naphtho[2,1-d]thiophene+benzo[b]naphtho[1,2-d]thiophene)), this paper traces the oil migration orientation and filling pathways in this oilfield. The isopleth maps of these molecular indicators unequivocally reveal an overall oil migration, filling points, and preferred filling pathways orientation from south to north. Based on this, a potential source kitchen is predicted in the southern part of the Halahatang Depression, most probably at the Manxi (Shuntuoguole) Low Uplift, just between the Awati and Manjiaer depressions. The southern part of the Halahatang Depression, along the oil charging pathways, is predicted to be the most promising region for oil exploration.

Evolution regularity of the Neogene shallow water delta in the Laibei area Bohai Bay Basin, northern China

According to the characteristics of sedimentary microfacies, unique vertical depositional sequences and well logging response, the authors propose that a shallow water delta was widely developed in the Neogene of the Laibei area, Bohai Bay Basin of northern China. Based on seismic minimum amplitude slices, well logging data, test analytical data and so forth, detailed research on the evolution of the shallow water delta of the Neogene Lower Member of Minghuazhen Formation was conducted. The results indicate that the third-order sequence base level controls sandbody types. During a period of low base level, a distributary channel sandbody of shallow water deltaic plain was developed. With base level rising, the sandbody type gradually changed into a subaqueous distributary channel sandbody and a sheet sand can be found as well. The fourth-order sequence base level controls medium–short term evolution of the sandbody. Within a sequence, due to the rising and falling of base level, the sandbody assemblages are identified as an upward-coarsening type, an upward-fining and a compound type respectively. Regionally, from the Laibei Low Uplift to the Huanghekou Sag, the shallow water delta evoluted from a dendritic shape, to a cuspate shape and finally to a sheet shape.

Neotectonic characteristics along the eastern flank of the Central Range in the active Taiwan orogen inferred from fluvial channel morphology

The tectonic activity of the Taiwan orogenic belt has been studied by different methods over various timescales. Constraints on tectonic characteristics over timescales of 103–105 years, however, are rather limited. To further understand the tectonic forcing over this timescale, we analyzed 20 major river basins along the eastern flank of the Central Range, the mountainous core of the orogen. The results of river steepness index (ksn) values and the distribution patterns of knickpoints are consistent with the patterns of tectonic evolution in Taiwan. On both ends of the orogen, the rivers have low ksn values that indicate low uplift rates throughout the area. In the central part of the island where the orogen is under rapid collisional processes, the rivers are steeper and are characterized by many tectonic knickpoints. Our results show different patterns from both short-term and long-term uplift and denudation rate patterns. This suggests that these rates change temporally and spatially. Moreover, the steepness indexes of rivers in the Taiwan orogen show the same increasing trend with erosion rates as those in other active orogens but correspond to significantly higher erosion rates. This is likely produced by the frequent debris flow and landslide events in Taiwan, a character that makes the island distinctive from other active orogens in the world.

Difference in full-filled time and its controlling factors in the central canyon of the Qiongdongnan Basin

Based on the interpretation of high resolution 2D/3D seismic data, sedimentary filling characteristics and fullfilled time of the Central Canyon in different segments in the Qiongdongnan Basin of northwestern South China Sea have been studied. The research results indicate that the initial formation age of the Central Canyon is traced back to 11.6 Ma (T40), at which the canyon began to develop due to the scouring of turbidity currents from west to east. During the period of 11.6–8.2 Ma (T40–T31), strong downcutting by gravity flow occurred, which led to the formation of the canyon. The canyon fillings began to form since 8.2 Ma (T31) and were dominated by turbidite deposits, which constituted of lateral migration and vertical superposition of turbidity channels during the time of 8.2–5.5 Ma. The interbeds of turbidity currents deposits and mass transport deposits (MTDs) were developed in the period of 5.5–3.8 Ma (T30–T28). After then, the canyon fillings were primarily made up of large scale MTDs, interrupted by small scale turbidity channels and thin pelagic mudstones. The Central Canyon can be divided into three types according to the main controlling factors, geomorphology-controlled, fault-controlled and intrusionmodified canyons. Among them, the geomorphology-controlled canyon is developed at the Ledong, Lingshui, Songnan and western Baodao Depressions, situated in a confined basin center between the northern slope and the South Uplift Belt along the Central Depression Belt. The fault-controlled canyon is developed mainly along the deep-seated faults in the Changchang Depression and eastern Baodao Depression. Intrusion-modified canyon is only occurred in the Songnan Low Uplift, which is still mainly controlled by geomorphology, the intrusion just modified seabed morphology. The full-filled time of the Central Canyon differs from west to east, displaying a tendency of being successively late eastward. The geomorphology-controlled canyon was completely filled before 3.8 Ma (T28), but that in intrusion-modified canyon was delayed to 2.4 Ma (T27) because of the uplifted southern canyon wall. To the Changchang Depression, the complete filling time was successively late eastward, and the canyon in eastern Changchang Depression is still not fully filled up to today. Difference in full-filled time in the Central Canyon is mainly governed by multiple sediment supplies and regional tectonic activities. Due to sufficient supply of turbidity currents and MTDs from west and north respectively, western segment of the Central Canyon is entirely filled up earlier. Owing to slower sediment supply rate, together with differential subsidence by deep-seated faults, the full-filled time of the canyon is put off eastwards gradually.

RECENT GEOMORPHOLOGIC REGIMES OF THE URAL

The territory of the Ural neotectonic structural zone consists of several areas with highly different recent geomor-phologic regimes. For the mountainous regimes of the North and Polar Ural the typical are high values of neotectonic 4* 83 uplift, deep and dense erosion dissection, high gradients of elevations, glacial landforms. The regimes of plain type are characterized by insignificant dissection under condition of low uplift; they occupy Pai-Khoi, the eastern margin of the Ural and Transural plateau. The intermediate regimes have intermediate values of neotectonic uplift, elevations, and erosion dissection, but high intensity of karst and landslides, and large amount of woodland; they are situated on the west slope of the North and Middle Ural and in the NW part of the South Ural. The Ural is usually classified as a single mountain morphostructural type with subtypes. We suppose there should be three or at least two mor-phostructural types: the properly mountain, the transitional, and platform plain types of morphostructure within the Ural neotectonic region (the last two may possibly be merged into one transitional type). These types manifest the different stages or different intensity of the Ural's rejuvenation (or regeneration). The distribution of recent geomor-phologic regimes is governed not only by the Hercynian meridional tectonic structures but by the latitude climatic zones and neotectonic features as well.

Plio–Pleistocene palaeogeography of the Llanura Costera del Caribe in eastern Hispaniola (Dominican Republic): Interplay of geomorphic evolution and sedimentation

This paper aims to reconstruct the palaeogeographic evolution of the Llanura Costera del Caribe (LCC) in eastern Hispaniola (Dominican Republic) during the Pleistocene, adding new insights to published information on Pliocene–Early Pleistocene deposits. The LCC is a generally flat region comprising the unfolded sedimentary cover of the Cordilleras Central and Oriental. Within this cover, the Pliocene–Early Pleistocene Yanigua Formation,mainly consisting of marl, changes seawards to the mainly limestone Los Haitises Formation. Both units formed in a shallow-water platform rimmed by a reef barrier at least in the latest depositional stages. The overlying Pleistocene La Isabela Formation consists of two major offlapping reef terraces, in which a reef core enclosed a lagoon, and prograded over forereef bioclastic debris. Two belts in LCC's morphostructure directly reflect its sedimentary evolution. The Inner Belt extends over the marly substrate of the Yanigua Formation and the Coastal Belt comprises three major surfaces corresponding to the depositional top of the Los Haitises Formation (Upper Surface), and to the Upper and Lower terraces of the La Isabela Formation (Intermediate and Lower Surfaces, respectively). The MIS 5e age of the 10–20 m high Lower Terrace implies a low uplift rate of 0.033–0.068 mm/yr for the Lower Surface. The Pliocene–Early Pleistocene platform was emergent in the Early–Middle Pleistocene. The Early Pleistocene reef barrier separated endorheic watersheds extending over the former shelf lagoon from the open ocean. Reefs built the Upper Terrace of the La Isabela Formation during one or several Middle Pleistocene highstands and the Lower Terrace during MIS 5e and previous highstands. Siliciclastic deposits in this terrace record the opening to the Caribbean Sea of watersheds in the eastern LCC. The Lower Terrace emersion and opening of the large drainage systems of the western and central LCC took place after MIS 5e. Relative sea level fall and emersion of a large area did not imply increased terrigenous sedimentation in the adjacent marine basin. Development of endorheic watersheds over most of the emergent surface delayed the diachronic arrival of siliciclastics into the marine basin for hundreds of thousands of years.

Application of an odd/even predominance of n-alkanes in oil–source rock correlation: taking the lower Paleozoic strata of the Tarim Basin as an example

The composition and distribution of n-alkanes carbon numbers reflect the source of kerogenic organic matter, sedimentary environment, and maturity of the rocks. The comparison results of the n-alkanes GC (gas chromatography) chromatograms in the Tazhong Low Uplift show that the n-alkanes of the source rocks in Upper Ordovician display an odd carbon number predominance. At the same time, Cambrian–Lower Ordovician exhibit an even carbon number predominance. The correlation between oil and source rock illustrates that crude oils in the fields of well TZ10-12 and well TZ24 stem from the Upper Ordovician source rocks. The origins of the crude oils in the fields of well TZ161-162 and well TZ45 are Cambrian–Lower Ordovician. The strata corresponding to the crude oils with odd/even carbon number predominance match the oil–source rock correlation. Thus, the characteristics of odd/even carbon number predominance in n-alkane compounds are effective for oil–source rock correlation in the Tazhong Low Uplift, Tarim Basin.

Kinetics and model of gas generation of source rocks in the deepwater area, Qiongdongnan Basin

In order to investigate the hydrocarbon generation process and gas potentials of source rocks in deepwater area of the Qiongdongnan Basin, kinetic parameters of gas generation (activation energy distribution and frequency factor) of the Yacheng Formation source rocks (coal and neritic mudstones) was determined by thermal simulation experiments in the closed system and the specific KINETICS Software. The results show that the activation energy (E a) distribution of C1–C5 generation ranges from 50 to 74 kcal/mol with a frequency factor of 2.4×1015 s−1 for the neritic mudstone and the E a distribution of C1–C5 generation ranges from 49 to 73 kcal/mol with a frequency factor of 8.92×1013 s−1 for the coal. On the basis of these kinetic parameters and combined with the data of sedimentary burial and paleothermal histories, the gas generation model of the Yacheng Formation source rocks closer to geological condition was worked out, indicating its main gas generation stage at R o (vitrinite reflectance) of 1.25%–2.8%. Meanwhile, the gas generation process of the source rocks of different structural locations (central part, southern slope and south low uplift) in the Lingshui Sag was simulated. Among them, the gas generation of the Yacheng Formation source rocks in the central part and the southern slope of the sag entered the main gas window at 10 and 5 Ma respectively and the peak gas generation in the southern slope occurred at 3 Ma. The very late peak gas generation and the relatively large gas potential indices (GPI: 20×108–60×108 m3/km2) would provide favorable conditions for the accumulation of large natural gas reserves in the deepwater area.

The Characteristic of Oil and Gas Accumulation and Main Factors of Reservoir Enrichment in SZ36-1 Region

The hydrocarbon reservoirs which have been found in SZ36-1 region are located in Liaoxi low uplift and dominated by structural traps. The principle source rock is the first and the third member of the Neogen Shahejie Formation and the main reservoir type is delta sand body which mainly located in the second member of Shahejie Formation. Oil reservoirs are mostly in normal pressure and are possess characteristic of late hydrocarbon accumulation. Hydrocarbon accumulation is mainly controlled by fault,reservoir-cap rock combination, and petroleum migration pathways. Lateral distribution of hydrocarbon reservoirs is mostly controlled by reservoir rocks, while the vertical distribution is controlled by fault.

Study on classification and characteristics of crude oils in Baiyun deep-water Sag

The geochemical characteristics of about 30 crude oil samples collected from Baiyun Sag were studied. These oil samples can be divided into two classes: class A and B, and 5 subclasses (A1.A2.A3.B1.B2). Samples in class A are located in the northern part of the sag, adjacent to Panyu Lower Uplift; samples in class B are located in the eastern part of the sag. Crude oils in Baiyun Sag indicate an oxidizing type of depositional environment, with a notable higher plant input, and mainly reflecting the lacustrine facies sedimentary characteristics. Oil samples are mature-high mature oil, with aromatic hydrocarbons having a wider range of chemical kinetics than saturated hydrocarbons, aromatic hydrocarbon maturity parameters are well pronounced and provide an effective means of measuring maturity compared to saturated hydrocarbon maturity parameters. In this study, based on integrated analysis of various parameters, the crude oils show mature-high mature oil characteristics, whereas class A has a high maturity compared to B.