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1.
《Marine and Petroleum Geology》2012,32(1):53-69
The objectives of our study were to assess the thickness, lateral extent, organic richness and maturity of the potential source rocks in Hungary and to estimate the volumes of hydrocarbons generated, in order that potential shale gas and shale oil plays could be identified and characterised.The Upper Triassic Kössen Marl in south-west Hungary could represent the best potential shale gas/shale oil play, due to its high organic richness, high maturity and the presence of fracture barriers. The area of gas- and oil-generative maturity is around 720 km2 with the unexpelled petroleum estimated to be up to 9 billion barrel oil-equivalent.The Lower Jurassic sediments of the Mecsek Mountains and under the Great Plain contain fair quality gas-prone source rocks, with low shale gas potential, except for a thin Toarcian shale unit which is richer in organic matter. The latter could form a potential shale gas play under the Great Hungarian Plain, if it is thicker locally.The Lower Oligocene Tard Clay in north-east Hungary could represent the second best potential shale oil play, due to its organic richness, favourable maturity and large areal extent (4500 km2) with around 7 billion barrel oil-equivalent estimated in-place volume of petroleum.Middle Miocene marine formations could represent locally-developed shale gas plays; they have fair amounts of organic matter and a mixture of type II/III kerogen, but their vertical and lateral variability is high.The Upper Miocene lacustrine Endrőd Marl contains less organic matter and the kerogen is mainly type III, which is not favourable for shale gas generation. The high carbonate and clay content, plus the lack of upper and lower fracture barriers would represent additional production challenges. 相似文献
2.
Xiaochen Liu Yangbo Lu Yongchao Lu Lei Chen Yiquan Ma Chao Wang 《Marine Geophysical Researches》2018,39(3):421-439
Based on cores, well logs and seismic data, we established the isochronous sequence stratigraphic framework of the Lower Silurian Longmaxi Formation and predicted the shale lithofacies distribution within the sequence stratigraphic framework using geostatistical inversion. The results of our study show that the Lower Member of the Longmaxi Formation is a third order sequence that includes a transgressive systems tract (TST), an early highstand systems tract (EHST) and a late highstand systems tract (LHST). Four lithofacies units have been recognized, specifically siliceous shale, argillaceous shale, calcareous shale and mixed shale. The results of geostatistical inversion reveal that the TST is characterized by flaky siliceous shale and some sparsely distributed calcareous shale. The EHST is dominated by mixed shale with minor amounts of siliceous shale, which occurs in only a small area. Moreover, in the LHST, argillaceous shale occupies almost the entire study region. Comparing to traditional geological research with geophysical research, the vertical resolution of the predictive results of geostatistical inversion could reach 1–2 m. Geostatistical inversion effectively solves the problem of precisely identifying the lithofacies in the Fuling shale gas field and predicting their spatial distribution. This successful study showcases the potential of this method for carrying out marine shale lithofacies prediction in China and other locations with similar geological backgrounds. 相似文献
3.
The pore size classification (micropore <2 nm, mesopore 2–50 nm and macropore >50 nm) of IUPAC (1972) has been commonly used in chemical products and shale gas reservoirs; however, it may be insufficient for shale oil reservoirs. To establish a suitable pore size classification for shale oil reservoirs, the open pore systems of 142 Chinese shales (from Jianghan basin) were studied using mercury intrusion capillary pressure analyses. A quantitative evaluation method for I-micropores (0–25 nm in diameter), II-micropores (25–100 nm), mesopores (100–1000 nm) and macropores (>1000 nm) within shales was established from mercury intrusion curves. This method was verified using fractal geometry theory and argon-ion milling scanning electron microscopy images. Based on the combination of pore size distribution with permeability and average pore radius, six types (I-VI) shale open pore systems were analyzed. Moreover, six types open pore systems were graded as good, medium and poor reservoirs. The controlling factors of pore systems were also investigated according to shale compositions and scanning electron microscopy images. The results show that good reservoirs are composed of shales with type I, II and III pore systems characterized by dominant mesopores (mean 68.12 vol %), a few macropores (mean 7.20 vol %), large porosity (mean 16.83%), an average permeability of 0.823 mD and an average pore radius (ra) of 88 nm. Type IV pore system shales are medium reservoirs, which have a low oil reservoir potential due to the developed II-micropores (mean 57.67 vol %) and a few of mesopores (mean 20.19 vol %). Poor reservoirs (composed of type V and VI pore systems) are inadequate reservoirs for shale oil due to the high percentage of I-micropores (mean 69.16 vol %), which is unfavorable for the flow of oil in shale. Pore size is controlled by shale compositions (including minerals and organic matter), and arrangement and morphology of mineral particles, resulting in the developments of shale pore systems. High content of siliceous mineral and dolomite with regular morphology are advantage for the development of macro- and mesopores, while high content of clay minerals results in a high content of micropores. 相似文献
4.
According to palaeoenvironmental analysis on the fossil fauna dominated by Foraminifera and Ostracoda, core QC2 contains 8 marine transgressive beds, called (from up to bottom) Transgressive Beds Ⅰ,Ⅱ, Ⅲ, …,Ⅷ respectively. Together with dating data, the transgressive sequence since 1. 7 Ma B. P. has been established, indicating that the core went through middle and late Early Pleistocene, early and late Middle Pleistocene, early and late (Substages A and B) Late Pleistocene and the Holocene transgressions. Within these 8 transgressions, late Middle Pleistocene, early Late Pleistocene and the Holocene transgressions-had rather strong activities proved by shallow sea (of 50 or 20-50 m water depth) deposits in the prime, while 2 of the 8, during middle Early Pleistocene and late Late Pleistocene (Substage A), were much weaker only with supratidal deposits. The transgressive cycles also differ from each other. Transgressions in the Holocene and in Substage B of late Late Pleistocene are made up of 3 and 相似文献
5.
High-frequency sequences composed of mixed siliciclastic-carbonate deposits may exhibit either vertical or horizontal changes between siliciclastics and carbonates. Vertical facies shifts occur between systems tracts and define a ‘reciprocal sedimentation’ pattern, typically consisting of transgressive/highstand carbonates and forced regressive/lowstand siliciclastics, although variations from this rule are common. Mixed systems with lateral facies change, usually typifying transgressive and/or highstand systems tracts, may exhibit proximal siliciclastics and distal carbonates or vice-versa, although variations may also occur along depositional strike. The marked variability of mixed siliciclastic-carbonate sequences makes the definition of a universal sequence stratigraphic model impossible, as the composition and geometries of systems tracts may change considerably, and sequence stratigraphic surfaces and facies contacts may vary in terms of occurrence and physical expression. However, some resemblance exists between siliciclastic sequences and mixed sequences showing lateral facies changes between siliciclastics and carbonates. In particular, these mixed sequences display 1) a stratal architecture of the clastic part of the systems tracts that is comparable to that of siliciclastic deposits, 2) a dominant role of the inherited physiography and of erosional processes, rather than carbonate production, in shaping the shelf profile, and 3) a local lateral juxtaposition of siliciclastic sandstones and carbonate bioconstructions due to hydrodynamic processes. These observations are helpful in predicting the location of porous and potential sealing bodies and baffles to fluid flow at the intra-high-frequency sequence scale, and ultimately they are useful for both petroleum exploration and production. 相似文献
6.
The Middle Triassic Botneheia Formation of eastern Svalbard (Edgeøya and Barentsøya) comprises an organic carbon-rich, fine-grained clastic succession (∼100 m thick) that makes the best petroleum source rock horizon in the NW Barents Sea shelf. The succession records a transgressive–regressive interplay between the prodelta depositional system sourced in the southern Barents Sea shelf (black shale facies of the lower and middle parts of the Muen Member) and the open shelf phosphogenic system related to upwelling and nutrient supply from the Panthalassic Ocean (phosphogenic black shale facies of the upper part of the Muen Member and the Blanknuten Member). The relationships between organic matter, authigenic apatite, and pyrite in these facies allow to characterize the relative roles of redox conditions and oceanic productivity in the organic carbon preservation. The accumulation of terrestrial and autochthonous marine organic matter in the black shale facies occurred under dominating oxic conditions and increasing-upward productivity related to early transgressive phase and retrogradation of the prodelta system. The phosphogenic black shale facies deposited in an oxygen-minimum zone (OMZ) of the open shelf environment during the late transgressive to regressive phases under conditions of high biological productivity, suppressed sedimentation rates, and changing bottom redox. The phosphatic black shales occurring in the lower and upper parts of the phosphogenic succession reveal depositional conditions indicative of the shallower part of OMZ, including high input of autochthonous organic matter into sediment, oxic-to-dysoxic (episodically suboxic and/or anoxic) conditions, intense phosphogenesis, and recurrent reworking of the seabed. The massive phosphatic mudstone occurring in the middle of the phosphogenic succession reflects the development of euxinia in the deeper part of OMZ during high-stand of the sea. High input of autochthonous organic matter in this environment was coupled with mineral starvation and intermittent phosphogenesis. In mature sections in eastern Svalbard, the petroleum potential of the Botneheia Formation rises from moderate to good in the black shale facies, and from good to very good in the phosphogenic black shale facies, attaining maximum in the massive phosphatic mudstone. 相似文献
7.
The seismic analysis of the sedimentary infill of the Ría de Vigo reveals that the infill comprises of a fifth order sequence (18 ky) bounded by a major discontinuity surface. Within the Holocene sequence, several seismic units have been identified; the oldest one originated after the Würm glaciation and the origin of its top discontinuity was eroded during the regression (sea level at − 120 m) of this last glacial episode (isotopic stages 2 to 4), 18 ky B.P.
In some places below this ría infill, another sequence can be identified. This older sequence is associated with the pre-existing faults and troughs in the deepest parts of the ría, and it was deposited during the Würm glaciation (Miocene–Pleistocene). Eroded sediments were moved from the rías area to deeper zones, where they accumulated in the lowstand system tract. The next sea level rise occured in two steps, producing two transgressive units separated by an hiatus surface. This cycle was interrupted by the next sea level fall (to − 55 m) marked on the seismic records by another recognizable boundary. The next sea level rise took place in several steps (back-stepping) with some stillstands, generating another transgressive system tract in the ría. From that time on, the relative sea level continued rising, depositing the most recent unit which represents the highstand system tract. Separating the highstand system tract and the transgresive unit below there is a consensed section.
The analysis of 29 cores provides groundtruthing for our hypothesis. The identified main lithologic units show a transgressive sequence: a granitic rock base, an overlying second unit-locally wedge shaped- and most recently, a marine muddy unit covering the present ría seafloor. 相似文献
8.
Omer Aziz Tahir Hussain Matee Ullah Asher Samuel Bhatti Aamir Ali 《Marine Geophysical Researches》2018,39(4):491-508
The exploration and production of unconventional resources has increased significantly over the past few years around the globe to fulfill growing energy demands. Hydrocarbon potential of these unconventional petroleum systems depends on the presence of significant organic matter; their thermal maturity and the quality of present hydrocarbons i.e. gas or oil shale. In this work, we present a workflow for estimating Total Organic Content (TOC) from seismic reflection data. To achieve the objective of this study, we have chosen a classic potential candidate for exploration of unconventional reserves, the shale of the Sembar Formation, Lower Indus Basin, Pakistan. Our method includes the estimation of TOC from the well data using the Passey’s ΔlogR and Schwarzkofp’s methods. From seismic data, maps of Relative Acoustic Impedance (RAI) are extracted at maximum and minimum TOC zones within the Sembar Formation. A geostatistical trend with good correlation coefficient (R2) for cross-plots between TOC and RAI at well locations is used for estimation of seismic based TOC at the reservoir scale. Our results suggest a good calibration of TOC values from seismic at well locations. The estimated TOC values range from 1 to 4% showing that the shale of the Sembar Formation lies in the range of good to excellent unconventional oil/gas play within the context of TOC. This methodology of source rock evaluation provides a spatial distribution of TOC at the reservoir scale as compared to the conventional distribution generated from samples collected over sparse wells. The approach presented in this work has wider applications for source rock evaluation in other similar petroliferous basins worldwide. 相似文献
9.
This paper presents a revision of the Eocene to Miocene rock units of al Jabal al Akhdar (northeast Libya), based on the study of several surface sections in the vicinity of Benghazi and on earlier studies. The gradual disappearance of deep water marine fauna during the Early Eocene (Apollonia Formation) combined with gradual appearances of large-sized nummulitids and coarsening upwards of allochems during the Middle Eocene (Darnah Formation) indicate a shallowing-up trend, which continued to the end of the Miocene. Upper Eocene deposits are missing in the Benghazi area. The Al Bayda Formation (Oligocene) rests disconformably on the Middle Eocene Darnah Formation. The lower part of the Shahhat Marl Member (lower member of the Al Bayda Formation) is detrital and contains reworked Eocene Nummulites together with in situ Early Oligocene N. fichteli and N. vascus. The Algal Limestone (upper member of the Al Bayda Formation) represents Wilson's facies SMF 4, 5 and 6. Cyclicity in this member is notable and it appears to be associated with the regressive and transgressive global fourth-order Cycles TA4.3 to TA4.4. The lower part of the Al Abraq Formation is attributed to the transgressive global fourth-order Cycle TA4.5 and the upper part to Cycle TB1.1. The lower and middle parts of the Al Faidiyah Formation are attributed to the Miocene transgressive Cycles TB1.4 and TB1.5, with the upper part a result of sea level lowering related to Cycle TB2.1. Wilson's facies SMF 7 and SMF 8 typify this formation. 相似文献
10.
《Marine Geology》2005,219(4):207-218
A vertical succession of five composite sequences has been identified within the upper 100 m of the outer Bengal Shelf by means of high-resolution multi-channel seismic data. Each sequence consists predominantly of up to 100 km long and some 10 m thick forced regression systems tracts. The internal reflection pattern of the regressive units show mainly prograding oblique clinoforms. Intervening transgressive systems tracts are represented by seismically transparent or chaotic layers. On the outer shelf three of the sequences cause shelf aggradation and retrogradation, and two of them cause mainly shelf progradation. Based on the hierarchy of systems tracts, their calibration by comparison with eustatic sea-level curves and reconstructed paleoshoreline positions the composite sequences are interpreted as eccentricity driven eustatic 4th order (Milankovitch) cycles with a periodicity of about 100 ky. Internal unconformities mark cycles of 5th or higher order. An average subsidence of the outer shelf is estimated to be less than 0.4 mm/year during the last 345 ky. The correlation between the shelf growth pattern and sea-level fluctuations is consistent with the enhanced deposition on the eastern Bengal submarine fan from 465 to 125 ky B.P., as was observed by other authors. 相似文献
11.
The Late Devonian to Early Mississippian Bakken Formation in the Williston basin of North Dakota, USA, shows a tri-partite subdivision: a middle mixed carbonate-siliciclastic member is sandwiched in-between two black siliciclastic mudstones, the lower and upper Bakken member shales. However, the transition from the lower shale member to the middle member does not represent a gradual coarsening but contains in places several millimeter - to centimeter-thick siliciclastic mudstones and carbonates that consist of three facies: (1) a glauconitic carbonate-rich siliciclastic mudstone, (2) a carbonate mud-to wackestone, and (3) an echinoderm wacke-to packstone with shell fragments. These three facies are present in many (all?) of the cores close and directly in the basin center in Mountrail County, North Dakota. At least one of these three facies is present in all 23 cores included in this study.This thin carbonate unit at the transition between the lower and the middle Bakken members is interpreted as representing the remnants of the transgressive systems tract. It is assumed that relative sea-level fell before deposition of the middle Bakken member establishing a proximal coarse-grained to distal fine-grained depositional transect that successively migrated into the basin. During the subsequent transgression, the siliciclastic input was low to absent, and the entire sedimentary system switched to depositing carbonates. The proximal to distal transect during this time showed coarse-grained packstones (and grainstones?) close to the shoreline, and a fining outwards towards the distal parts of the basin. This transgression also eroded what remained of the regressive and most of the subsequent transgressive sediments, leaving only the thin carbonate layer behind. Evidence for the regression, even though no sediment is directly preserved along the lower to middle Bakken member contact, comes from the fill of clastic dykes that cut through the lower Bakken member shale. The fill of the clastic dykes is partly siliciclastic and partly carbonate and not similar to any of the surrounding sediment. This indicates that these dykes must have originated before the middle Bakken member was deposited, yet the overlying sediment must have been carbonate at some point and siliciclastic another time. As it is not present anymore, this sediment must have been entirely removed by erosion.The here presented model suggests that the Bakken Formation reflects two entire sea-level oscillations. The first encompasses the lower Bakken member shale and the siliciclastic regressive portion of the lowstand only preserved as infill of the clastic dykes. The subsequent transgression deposited the carbonates now blanketing the lower to middle Bakken member transition, and the highstand and subsequent regression plus lowstand are represented by the middle Bakken member. The transgressive surface and therewith the onset of the topmost Bakken transgression is marked by the transition from the middle to the upper Bakken shale member. 相似文献
12.
The Songliao Basin is a large-scale petroliferous basin in China. With a gradual decline in conventional oil production, the exploration and development of replacement resources in the basin is becoming increasingly important. Previous studies have shown that the Cretaceous Qingshankou Formation (K2qn) has favorable geological conditions for the formation of shale oil. Thus, shale oil in the Qingshankou Formation represents a promising and practical replacement resource for conventional oil. In this study, geological field surveys, core observation, sample tests, and the analysis of well logs were applied to study the geochemical and reservoir characteristics of shales, identify shale oil beds, build shale oil enrichment models, and classify favorable exploration areas of shale oil from the Cretaceous Qingshankou Formation. The organic matter content is high in shales from the first member of the Cretaceous Qingshankou Formation (K2qn1), with average total organic carbon (TOC) content exceeding 2%. The organic matter is mainly derived from lower aquatic organisms in a reducing brackish to fresh water environment, resulting in mostly type I kerogen. The vitrinite reflectance (Ro) and the temperature at which the maximum is release of hydrocarbons from cracking of kerogen occurred during pyrolysis (Tmax) respectively range from 0.5% to 1.1% and from 430 °C to 450 °C, indicating that the K2qn1 shales are in the low-mature to mature stage (Ro ranges from 0.5% to 1.2%) and currently generating a large amount of oil. The favorable depth for oil generation and expulsion is 1800–2200 m and 1900–2500 m, respectively as determined by basin modeling. The reserving space of the K2qn1 shale oil includes micropores and mircofractures. The micropore reservoirs are developed in shales interbedded with siltstones exhibiting high gamma ray (GR), high resistivity (Rt), low density (DEN), and slightly abnormal spontaneous potential (SP) in the well-logging curves. The microfracture reservoirs are mainly thick shales with high Rt, high AC (acoustic transit time), high GR, low DEN, and abnormal SP. Based on the shale distribution, geochemical characteristics, reservoir types, fracture development, and the process of shale oil generation and enrichment, the southern Taikang and northern Da'an are classified as two favorable shale oil exploration areas in the Songliao Basin. 相似文献
13.
14.
The post-Calabrian sedimentary column of the northwestern Alboran Sea comprises three depositional sequences. The two older depositional sequences are defined by lowstand systems tracts (shelf-margin deltas, slope, base-of-slope, and basin deposits, and the Guadiaro channel-levee complex). In contrast, the most recent depositional sequence also includes transgressive (relict shelf facies) and high-stand (the Guadalmedina-Guadalhorce prodelta and hemipelagic facies) systems tracts. The stratigraphic architecture of these depositional sequences is controlled by the synchronism between high frequency sea-level changes, variations in sediment supply, and sedimentary processes. The configuration of the depositional sequences is variable and their distribution is complex, as a result of the relative importance played by sea-level changes and tectonism through the area.
The sequence boundaries are represented by polygenetic surfaces in the proximal margin, and by monogenetic surfaces in the distal margin and basin. Each polygenetic surface results from the interaction between the sequence boundary with the lowstand erosional truncation surface and the transgressive surface, both developed during the previous sea-level cycle. The monogenetic surfaces correspond to unconformities and their correlative conformities, formed during sea-level lowstands. This pattern of depositional sequences developed in the margin and basin of the northwestern Alboran Sea shows differences with the Exxon Sequence Stratigraphy Model as traditionally applied: sea-level change control is essentially recognized through lowstand systems tracts, and sequence boundary coincides with lowstand erosional truncation surface and transgressive surface, both developed during the previous sea-level cycle. 相似文献
15.
Sequence stratigraphy and syndepositional structural slope-break zones define the architecture of the Paleogene syn-rift, lacustrine succession in eastern China's Bohai Bay Basin. Jiyang, Huanghua and Liaohe subbasins are of particular interest and were our primary research objectives. Interpretation of 3D seismic data, well logs and cores reveals: One first-order sequence, 4 second-order sequences, and ten to thirteen third-order sequences were identified on the basis of the tectonic evolution, lithologic assemblage and unconformities in the subbasins of Bohai Bay Basin. Three types of syndepositional paleo-structure styles are recognized in this basin. They are identified as fault controlled, slope-break zone; flexure controlled, slope-break zone; and gentle slope.The three active structural styles affect the sequence stratigraphy. Distinct third-order sequences, within second-order sequences, have variable systems tract architecture due to structuring effects during tectonic episodes. Second-order sequences 1 and 2 were formed during rifting episodes 1 and 2. The development of the third-order sequences within these 2 second-order sequences was controlled by the active NW and NE oriented fault controlled, slope-break zones. Second-order sequence 3 formed during rifting episode 3, the most intense extensional faulting of the basin. Two types of distinctive lacustrine depositional sequence were formed during rifting episode 3: one was developed in an active fault controlled, slope-break zone, the other in an active flexure controlled, slope-break zone. Second-order sequence 4 was formed during the fourth episode of rifting. Syndepositional, fault- and flexure-controlled slope-break zones developed in the subsidence center (shore to offshore areas) of the basin and controlled the architecture of third-order sequences in a way similar to that in second-order sequence 3. Sequences in the gentle slope and syndepositional, flexure controlled slope-break zones were developed in subaerial region.Distribution of lowstand sandbodies was controlled primarily by active structuring on the slope-break zones, and these sandbodies were deposited downdip of the slope-break zones. Sand bodies within lowstand systems tracts have good reservoir quality, and are usually sealed by the shale sediments of the subsequent transgressive systems tract. They are favorable plays for stratigraphic trap exploration. 相似文献
16.
Mohamed S. Abu El Ghar 《Marine and Petroleum Geology》2012,29(1):276-292
The Middle Eocene deposits in the Fayoum Ranges are composed of complex alternative clastic (claystone and sandstone) and carbonate (limestone and dolostone) facies and dominated carbonate (limestone) facies. Facies are arranged mainly in regression and shallowing upward (emergence) cycles and sequences. Field stratigraphic and microfacies analysis of the study area permits recognition of four major sequences, reflecting 3rd-order cycles. Depositional sequences and cycles are bounded by subaerial erosive surfaces or caliche deposits, ferruginous crust, and by their correlative conformities. Sequence-1 consists of two shallowing-upward cycles (dominate carbonate facies), each of which starts with nummulitic wackestone, capped with nummulitic packstone including Globigerinatheka subconglobata subconglobata biozone. These cycles were deposited under tropical to subtropical conditions as evidenced by the carbonate nature of the rocks and the abundance of nummulites, which need warm conditions for their flourishing. Sequence-2 consists of four emergence cycles based with claystone and capped with wackestone including Morozovella lehneri biozone. The duration (Ma) of sequence-2 (Morozovella lehneri zone) is 3.05 Ma (44.25 Ma for the upper of TA3 3.3 to 41.2 Ma for the lower of TA3 3.5). Sequence-3 includes three rock units (includes Trucorotaloides rohri biozone). The lower unit involves lowstand systems tract, the middle unit contains transgressive systems tract and the upper rock unit includes highstand systems tract. The lowstand systems tract consists of emergence cycles of mixed clastic- carbonate facies, clays at the base and capped with wackestone and packstone facies. The transgressive systems tract consists of dominant carbonate facies, wackestone at the base and capped with packstone facies. Sequence 4 involves transgressive systems tract. The duration of both sequence-3 and sequence 4 has been estimated as 1.8 Ma. 相似文献
17.
Natasha Khan Khaista Rehman Sajjad Ahmad Jamil Khokher M. Iqbal Hajana M. Hanif 《Marine Geophysical Researches》2016,37(3):207-228
In this study, seismic data from two wells (Pak G2-1 and Indus Marine-1C) and age diagnostic larger benthic foraminifera (LBF) within drill cuttings has been used for the first time to identify depositional sequences within the carbonates in the Offshore Indus Basin, Pakistan. The Offshore Indus is tectonically categorized as a passive continental margin where carbonates occur as shelf carbonates in the near offshore and on volcanic seamounts in deeper waters. Seismic data analysis has indicated the presence of minor faults and carbonate buildups above the igneous basement in the south. Patterns of the seismic reflections enabled definition of three seismic facies units identified as: Unit 1 basement, represented by chaotic, moderate amplitude reflection configuration; while parallel bedding and the drape of overlying strata is typical character of Unit 2, carbonate mound facies. The younger Miocene channels represent Unit 3. The diagnosis of Alveolina vredenburgi/cucumiformis biozone confirmed the Ilerdian (55–52 Ma) stage constituting a second order cycle of deposition for the Eocene carbonates (identified as Unit 2). The carbonate succession has been mainly attributed to an early highstand system tract (HST). The environmental conditions remained favorable leading to the development of keep-up carbonates similar to pinnacle buildups as a result of aggradation during late transgressive system tract and an early HST. The carbonate sequence in the south (Pak G2-1) is thicker and fossiliferous representing inner to middle shelf depths based on fauna compared to the Indus Marine-1C in the north, which is devoid of fossils. Three biozones (SBZ 5, SBZ 6 and SBZ 8) were identified based on the occurrence of LBF. The base of the SBZ 5 zone marks the larger foraminifera turnover and the Paleocene–Eocene (P–E) boundary. The LBF encountered in this study coincides with earlier findings for the P–E boundary. Our findings indicate that the entire Ilerdian stage ranges from 55.5 to 52 Ma that was the episode of warmer water conditions on the carbonate shelves leading to the diversification of K-strategist larger foraminifera. The larger foraminiferal assemblage encountered in this study confirms the findings. The possible indication of stratigraphic-combination traps, revealed as reflection terminations, make carbonate mounds in the south a potential exploration target. 相似文献
18.
In the Chelif basin, the geochemical characterization reveals that the Upper Cretaceous and Messinian shales have a high generation potential. The former exhibits fair to good TOC values ranging from 0.5 to 1.2% with a max. of 7%. The Messinian series show TOC values comprised between 0.5 and 2.3% and a high hydrogen index (HI) with values up to 566 mg HC/g TOC. Based on petroleum geochemistry (CPLC and CPGC) technics, the oil-to source correlation shows that the oil of the Tliouanet field display the same signature as extracts from the Upper Cretaceous source rocks (Cenomanian to Campanian). In contrast, oil from the Ain Zeft field contains oleanane, and could thus have been sourced by the Messinian black shale or older Cenozoic series. Two petroleum systems are distinguished: Cretaceous (source rock) – middle to upper Miocene (reservoirs) and Messinian (source rock)/Messinian (reservoirs). Overall, the distribution of Cretaceous-sourced oil in the south, directly connected with the surface trace of the main border fault of the Neogene pull-apart basin, rather suggests a dismigration from deeper reservoirs located in the parautochthonous subthrust units or in the underthrust foreland, rather than from the Tellian allochthon itself (the latter being mainly made up of tectonic mélange at the base, reworking blocks and slivers of Upper Cretaceous black shale and Lower Miocene clastics). Conversely, the occurrence of Cenozoic-sourced oils in the north suggests that the Neogene depocenters of the Chelif thrust-top pull-apart basin reached locally the oil window, and therefore account for a local oil kitchen zone. In spite of their limited extension, allochthonous Upper cretaceous Tellian formations still conceal potential source rock layers, particularly around the Dahra Mountains and the Tliouanet field. Additionally they are also recognized by the W11 well in the western part of the basin (Tahamda). The results of the thermal modelling of the same well shows that there is generation and migration of oil from this source rock level even at recent times (since 8 Ma), coevally with the Plio-Quaternary traps formation. Therefore, there is a possibility of an in-situ oil migration and accumulation, even from Tellian Cretaceous units, to the recent structures, like in the Sedra structure. However, the oil remigration from deep early accumulations into the Miocene reservoirs is the most favourable case in terms of hydrocarbon potential of the Chelif basin. 相似文献
19.
In the mid-eastern Yellow Sea, closely spaced high-resolution seismic profiles and a 44-m-long sediment core (YSDP-104) were analyzed to reveal the internal structures and stratigraphy of the shelf ridges currently shaped by tidal currents. Three depositional sequences (sequences I, II and III in descending order) can be recognized. Sequence III, the substratum of the ridges, consists of coarse-grained sediments in the lower part (non-marine deposits) and tide-influenced muddy sediments in the upper part (probable transgressive to highstand systems tract). Sequence II represents internal ridge sediments, similar in character to sequence III, but is demarcated by an undulatory ridge topography. According to radiocarbon dating of marine muds, these sequences range in age from 47,000 to 28,000 years B.P., representing two cycles of short-term sea-level fluctuations during oxygen isotope stage 3. Sequence I consists mostly of late-Holocene transgressive sand veneer on the ridge surface. It also includes minor amounts of early-Holocene muddy sediments occasionally underlying the sand. Most of the ridges are presently undergoing erosion by tidal currents, forming widespread sand dunes on the entire surface. 相似文献
20.
Erosional shelf ridges in the mid-eastern Yellow Sea 总被引：1，自引：0，他引：1
In the mid-eastern Yellow Sea, closely spaced high-resolution seismic profiles and a 44-m-long sediment core (YSDP-104) were analyzed to reveal the internal structures and stratigraphy of the shelf ridges currently shaped by tidal currents. Three depositional sequences (sequences I, II and III in descending order) can be recognized. Sequence III, the substratum of the ridges, consists of coarse-grained sediments in the lower part (non-marine deposits) and tide-influenced muddy sediments in the upper part (probable transgressive to highstand systems tract). Sequence II represents internal ridge sediments, similar in character to sequence III, but is demarcated by an undulatory ridge topography. According to radiocarbon dating of marine muds, these sequences range in age from 47,000 to 28,000 years B.P., representing two cycles of short-term sea-level fluctuations during oxygen isotope stage 3. Sequence I consists mostly of late-Holocene transgressive sand veneer on the ridge surface. It also includes minor amounts of early-Holocene muddy sediments occasionally underlying the sand. Most of the ridges are presently undergoing erosion by tidal currents, forming widespread sand dunes on the entire surface. 相似文献