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1.
The sedimentary history of Kachchh offshore (central western Indian margin), especially since the eruption of the Deccan Traps (∼65 Ma), has remained scantily studied despite an area with promising resource potential. Of late, new marine surveys combined with industrial drilling along the Kachchh shelf are beginning to elucidate the depositional history of this region. Here, we attempt to synthesize interpretation of new offshore seismic data, along with borehole information and long-term sea-level variations to provide a coherent sedimentological and lithostratigraphic framework over the past ∼65 Ma in this area.  相似文献   

2.
东海陆架区中北部前第三系基底综合地球物理研究   总被引：6，自引：0，他引：6  
从地震、钻井资料出发,结合周边地质特征,推断东海陆架区中北部存在中生界和古生界地层。结合地震资料,正演消除了海底和新生界密度不均匀在重力场上的影响,定量反演重、磁力异常并求取了重力基底和磁性基底。重力基底的特征在东西分带的大背景下表现出“靠陆侧南北分块,靠洋侧东西分带”的特点。西湖凹陷区的磁性基底与重力基底埋深大致相同,不一致地方可能是受岩体的影响。西湖凹陷以西地区,包括海礁凸起等单元,总体出现磁性基底埋深比重力基底埋深深2km左右,初步解释为古生界地层的反映。中生界地层厚度的分布也具有东西分带和南北分块特点。西湖凹陷西缘的中生界地层厚度大,其中带中生界虽然含有一定的火山岩或火山碎屑岩,但沉积岩更多,这对下一步的油气勘探有利。  相似文献   

3.
Whilst the relationship between stratigraphic development and carbonate cementation within siliciclastic succession has been documented through a number case studies, these studies have been generally restricted to observations upon individual sequences and/or limited sub-surface data. In this paper, long-term (5 million years), large-scale (>200 km) stratigraphic controls on carbonate cementation patterns are documented from the Upper Cretaceous Panther Tongue Member, Blackhawk Formation and Castlegate Sandstone exposed in the Book Cliffs in Utah and Colorado, USA. Together, these comprise eight progradational wedges of sandstones, which interfinger with the Mancos Shale, deposited within the Western Interior Seaway foreland basin. Petrographic analyses of ferroan dolomite cement bodies within these sandstone wedges show that the ferroan dolomite cements are all early, relative to burial diagenesis within the host sandstones. Stable isotope analyses indicates that a significant meteoric component was present in precipitating fluids and this is consistent with the observation that cements, are always present down-dip of sequence boundaries and/or leached whitecaps beneath coals. In addition, the lateral distribution of cement bodies increases consistently up-succession from less than 5 km in extent in the older sequences, to 30 km in extent in the youngest sequences. These changes in distribution are in response to the increased progradation and increased and more aerially extensive sequence-boundary development in younger sequences. The implications of these data are that whilst localized spatial patterns of diagenesis, and in particular carbonate cementation, are predictable and controlled by the nature and presence of individual stratal surfaces, systematic diagenetic alteration patterns are also present at the sedimentary basin scale and controlled by the nature of larger-scale stratigraphic development and basin evolution. This evolution may be driven by eustatic shifts, or through tectonic or climatic driven base-level shifts. These observations allow an improved insight into the basin-scale processes that control the macroscopic diagenetic properties of sedimentary successions and sub-surface hydrocarbon reservoirs.  相似文献   

4.
The pre-Cenozoic northern South China Sea(SCS) Basin basement was supposed to exist as a complex of heterogeneous segments, divided by dozens of N-S faulting. Unfortunately, only the Hainan Island and the northeastern SCS region were modestly dated while the extensive basement remains roughly postulated by limited geophysical data. This study presents a systematic analysis including U-Pb geochronology, elemental geochemistry and petrographic identification on granite and meta-clastic borehole samples from several key areas. Constrained from gravity-magnetic joint inversion, this interpretation will be of great significance revealing the tectono-magmatic evolution along the southeastern margin of the Eurasian Plate. Beneath the thick Cenozoic sediments, the northern SCS is composed of a uniform Mesozoic basement while the Precambrian rocks are only constricted along the Red River Fault Zone. Further eastern part of the northern SCS below the Cenozoic succession was widely intruded by granites with Jurassic-to-early Cretaceous ages. Further western part, on the other hand, is represented by meta-sedimentary rocks with relatively sporadic granite complexes. To be noted,the western areas derived higher-degree and wider metamorphic zones, which is in contrast with the lowerdegree and narrower metamorphic belt developed in the eastern region. Drastic collisions between the Indochina Block and South China continent took place since at least late Triassic, resulting in large-scale suturing and deformation zones. At the westernmost part of the northern SCS, the intracontinental amalgamation with closure of the Meso-Tethys has caused fairly stronger and broader metamorphism. One metamorphic biotite granite is located on the suturing belt and yields a Precambrian U-Pb age. It likely represents the relict from the ancient Gondwana supercontinent or its fringes. Arc-continental collision between the Paleo-Pacific and the southeast China Block, on the other hand, results in a relatively narrow NE–SW trending metamorphic belt during the late Mesozoic. Within the overall geological setting, the Cenozoic SCS oceanic basin was subsequently generated from a series of rifting and faulting processes along the collisional-accretionary continental margin.  相似文献   

5.
A seismic refraction survey along nine profiles has been carried out on the Norwegian continental shelf in the area between Andøya and Fugløybanken (69°–71°N). In all but one of the profiles the shelf is found to be covered with layered sediments. Average velocities are 1.85, 2.20, 2,55, 3.25, and 3.90 km/s probably representing sediments of Cenozoic and Mesozoic ages. An average velocity of 5.25 km/s represents a basement, which probably is the seaward continuation of the onshore Caledonian rocks. Except for an apparent depressional area just north of Andøya the sedimentary layers appear to dip towards the shelf edge. On the outer part of the shelf the 2.20 km/s layer appears at the sea-floor while more complex structures are found on the inner part of the shelf.Publication No. 3 in NTNF's Continental Shelf Project.  相似文献   

6.
The effects of the ocean coast on magnetotelluric (MT) data have been studied and results are described in this article. MT soundings from various sites along coastal plains of Kachchh were acquired where volcanic rocks overlie Mesozoic sediments having potential resource prospects. The region of our study lies in the proximity of Gulf of Kachchh and Arabian Sea. This article describes the effects the presence of a conductive body on the acquired MT data. With the help of synthetic MT modelling and induction arrows we demonstrate the influence of shallow conductive body on the MT data. The modelling results when compared to the field observations show that much of the high frequencies are unaffected by the coast, however low frequencies of the data do seem to be distorted by onshore–offshore resistivity contrasts. The least affect on high frequencies can be attributed to very shallow water depth as well as to the fact that the onshore–offshore resistivity contrasts are not large enough to influence the high frequency data badly. The results presented here report for the first time the effect of the coast on the analysis on MT data from Kachchh. Due to several academic as well as industrial onshore–offshore MT experiments presently being carried out to explore its hydrocarbon potential, our results have an important bearing on designing and acquisition of future MT surveys in this region.  相似文献   

7.
本文根据反射地震、折射地震、磁力等资料,结合周边地质,探讨冲绳海槽南段基底组成。在海槽周边的东海陆架盆地、台湾褶皱带和琉球岛弧褶皱带,均出露不同程度变质的晚古生代、中生代和早第三纪地层。多道反射地震表明,海槽南段沉积盖层由上第三系和第四系组成,声学基底由下第三系及更老地层构成。邻近海槽的折射地震揭示,除第四系-中新统速度层之外,还存在纵波速度分别为4．7～5．3km／s和6．3km／s的下第三系和中生界速度层。磁异常分析和正反演拟合计算结果表明,海槽磁性基底主要由变质岩系构成,次为燕山期中酸性岩浆岩和喜山期中基性岩浆岩,磁性基底大部分相当声学基底。综合分析表明,海槽南段基底主要由不同程度变质的下第三系、中生界和上古生界构成;在海槽某些构造部位,已有喜山期基性岩浆岩形成。  相似文献   

8.
In 2001 and 2002, Australia acquired an integrated geophysical data set over the deep-water continental margin of East Antarctica from west of Enderby Land to offshore from Prydz Bay. The data include approximately 7700 km of high-quality, deep-seismic data with coincident gravity, magnetic and bathymetry data, and 37 non-reversed refraction stations using expendable sonobuoys. Integration of these data with similar quality data recorded by Japan in 1999 allows a new regional interpretation of this sector of the Antarctic margin. This part of the Antarctic continental margin formed during the breakup of the eastern margin of India and East Antarctica, which culminated with the onset of seafloor spreading in the Valanginian. The geology of the Antarctic margin and the adjacent oceanic crust can be divided into distinct east and west sectors by an interpreted crustal boundary at approximately 58° E. Across this boundary, the continent–ocean boundary (COB), defined as the inboard edge of unequivocal oceanic crust, steps outboard from west to east by about 100 km. Structure in the sector west of 58° E is largely controlled by the mixed rift-transform setting. The edge of the onshore Archaean–Proterozoic Napier Complex is downfaulted oceanwards near the shelf edge by at least 6 km and these rocks are interpreted to underlie a rift basin beneath the continental slope. The thickness of rift and pre-rift rocks cannot be accurately determined with the available data, but they appear to be relatively thin. The margin is overlain by a blanket of post-rift sedimentary rocks that are up to 6 km thick beneath the lower continental slope. The COB in this sector is interpreted from the seismic reflection data and potential field modelling to coincide with the base of a basement depression at 8.0–8.5 s two-way time, approximately 170 km oceanwards of the shelf-edge bounding fault system. Oceanic crust in this sector is highly variable in character, from rugged with a relief of more than 1 km over distances of 10–20 km, to rugose with low-amplitude relief set on a long-wavelength undulating basement. The crustal velocity profile appears unusual, with velocities of 7.6–7.95 km s−1 being recorded at several stations at a depth that gives a thickness of crust of only 4 km. If these velocities are from mantle, then the thin crust may be due to the presence of fracture zones. Alternatively, the velocities may be coming from a lower crust that has been heavily altered by the intrusion of mantle rocks. The sector east of 58° E has formed in a normal rifted margin setting, with complexities in the east from the underlying structure of the N–S trending Palaeozoic Lambert Graben. The Napier Complex is downfaulted to depths of 8–10 km beneath the upper continental slope, and the margin rift basin is more than 300 km wide. As in the western sector, the rift-stage rocks are probably relatively thin. This part of the margin is blanketed by post-rift sediments that are up to about 8 km thick. The interpreted COB in the eastern sector is the most prominent boundary in deep water, and typically coincides with a prominent oceanwards step-up in the basement level of up to 1 km. As in the west, the interpretation of this boundary is supported by potential field modelling. The oceanic crust adjacent to the COB in this sector has a highly distinctive character, commonly with (1) a smooth upper surface underlain by short, seaward-dipping flows; (2) a transparent upper crustal layer; (3) a lower crust dominated by dipping high-amplitude reflections that probably reflect intruded or altered shears; (4) a strong reflection Moho, confirmed by seismic refraction modelling; and (5) prominent landward-dipping upper mantle reflections on several adjacent lines. A similar style of oceanic crust is also found in contemporaneous ocean basins that developed between Greater India and Australia–Antarctica west of Bruce Rise on the Antarctic margin, and along the Cuvier margin of northwest Australia.  相似文献   

9.
During TAiwan Integrated GEodynamics Research of 2009, we investigated data from thirty-seven ocean-bottom seismometers (OBS) and three multi-channel seismic (MCS) profiles across the deformation front in the northernmost South China Sea (SCS) off SW Taiwan. Initial velocity-interface models were built from horizon velocity analysis and pre-stack depth migration of MCS data. Subsequently, we used refracted, head-wave and reflected arrivals from OBS data to forward model and then invert the velocity-interface structures layer-by-layer. Based on OBS velocity models west of the deformation front, possible Mesozoic sedimentary rocks, revealed by large variation of the lateral velocity (3.1–4.8 km/s) and the thickness (5.0–10.0 km), below the rift-onset unconformity and above the continental crust extended southward to the NW limit of the continent–ocean boundary (COB). The interpreted Mesozoic sedimentary rocks NW of the COB and the oceanic layer 2 SE of the COB imaged from OBS and gravity data were incorporated into the overriding wedge below the deformation front because the transitional crust subducted beneath the overriding wedge of the southern Taiwan. East of the deformation front, the thickness of the overriding wedge (1.7–5.0 km/s) from the sea floor to the décollement decreases toward the WSW direction from 20.0 km off SW Taiwan to 8.0 km at the deformation front. In particular, near a turn in the orientation of the deformation front, the crustal thickness (7.0–12.0 km) is abruptly thinner and the free-air (?20 to 10 mGal) and Bouguer (30–50 mGal) gravity anomalies are relatively low due to plate warping from an ongoing transition from subduction to collision. West of the deformation front, intra-crustal interfaces dipping landward were observed owing to subduction of the extended continent toward the deformation front. However, the intra-crustal interface near the turn in the orientation of the deformation front dipping seaward caused by the transition from subduction to collision. SE of the COB, the oceanic crust, with a crustal thickness of about 10.0–17.0 km, was thickened due to late magmatic underplating or partially serpentinized mantle after SCS seafloor spreading. The thick oceanic crust may have subducted beneath the overriding wedge observed from the low anomalies of the free-air (?50 to ?20 mGal) and Bouguer (40–80 mGal) gravities across the deformation front.  相似文献   

10.
Aeromagnetic data collected over the Offshore Mahanadi Basin along the Eastern margin of India display high amplitude magnetic anomalies. The presence of a Cretaceous volcanic sequence masks the seismic response from the underlying basement and results in poor quality seismic data. In this study spectral analysis of the aeromagnetic data collected over this part of the Offshore Mahanadi Basin was carried out. Results of this analysis indicate the presence of a high density, highvelocity (6.45 km/s) mafic layer within the crystalline basement varying from 4–6 km depth. This intra-basement layer seems to have been affected by a number of lineaments, which have played a role in the evolution of the Mahanadi Offshore Basin. The western part of the offshore basin is affected by the volcanism related to the 85°E Ridge, whereas the intense anomaly band (900 nT) offshore Puri, Konark and Paradip is interpreted as a combined effect of crystalline Precambrian basement overlain (i) by Cretaceous volcanic rocks of variable thickness (25–860 m) and (ii) by a mafic layer within the basement.  相似文献   

11.
The western South Korea Plateau in the East Sea (Sea of Japan) is occupied by rifted continental fragments formed in association with the early phase of back-arc opening. The present study focuses on the seismic stratigraphy of the sedimentary succession and the underlying acoustic basement in this region, based on closely spaced multichannel seismic reflection profiles. The sedimentary succession occurs mainly within a series of subparallel basement troughs (grabens or half grabens) bounded by faulted continental blocks (horsts) or volcanic ridges, and commonly floored by extrusive volcanic rocks showing hyperbolic reflectors. These features are strongly suggestive of continental rifting accompanied by normal faulting, volcanic activity and high rates of basin subsidence. The sedimentary succession can be subdivided into four seismic units. Unit 1 is characterized by short and irregular high-amplitude reflectors and interpreted as a syn-rift deposit consisting of a non-marine volcanics/sediment complex in topographic lows. Units 2 and 3 formed in an open marine environment during the Middle Miocene to Early Pliocene, characterized by an onlap-fill and later draping marine sedimentary succession dominantly composed of hemipelagic sediments and turbidites with frequent intercalation of mass-flow deposits. Along the western margin of the plateau, these units were deformed under a compressional regime in the Early Pliocene, associated with the back-arc closing phase. Unit 4 (deposited since the Early Pliocene) comprises hemipelagic sediments and turbidites with evidence of sporadic slides/slumps.  相似文献   

12.
As the Mesozoic sediments contribute most of the oil and gas reserves of the world, we present an integrated interpretation approach using magnetotellurics (MT) and surface geochemical prospecting studies to demarcate hydrocarbon prospective Gondwana (Mesozoic) formations underneath the Deccan flood basalts of Late Cretaceous age across Narmada-Tapti rift (between Bhusawal and Barwah) in Central India. The MT interpretation shows deep (∼5 km) basement structure between southern and central part of the MT profile however, it gradually becomes shallower to either ends of the profile with a predominant basement depth reduction in the northern end compared to the southern end. The geophysical results suggest thick (2-3.5 km) Mesozoic sediments in the area characterized by deep basement structure. The geochemical analysis of the near surface soil samples indicate higher concentrations of light gaseous hydrocarbons constituents over the area marked with thick sub-basalt Mesozoic formations. Analyses of the geochemical data imply that these hydrocarbons are genetically related, generated from a thermogenic source and these samples fall in the oil-producing zone. The temperature-depth estimations in the region supports favorable temperature conditions (80-120 °C) for oil generation at basement depths.  相似文献   

13.
The northern and central parts of the Okhotsk Sea form an epiMesozoic platform. The hetero-aged acoustic basement is represented by deformed geosynclinal rocks from Cretaceous to Precambrian in age. The slightly deformed sedimentary cover levelled the uneven surface of the acoustic basement, and this Upper Paleogene—Neogene cover filled up the system of the structural basins. The general NW—SE and W—E extensions of the taphrogenic horsts and grabens of the acoustic basement were formed due to extension and subsidence of the earth's crust during the late Paleogene—Neogene.  相似文献   

14.
This study presents the modelling of 2-D and 3-D wide-angle seismic data acquired on the complex, volcanic passive margin of the Vøring Plateau, off Norway. Three wide-angle seismic profiles were shot and recorded simultaneously by 21 Ocean Bottom Seismometers, yielding a comprehensive 3-D data set, in addition to the three in-line profiles. Coincident multi-channel seismic profiles are used to better constrain the modelling, but the Mesozoic and deeper structures are poorly imaged due to the presence of flood basalts and sills. Velocity modelling reveals an unexpectedly large 30 km basement high hidden below the flood basalt. When interpreted as a 2-D structure, this basement high produces a modelled gravity anomaly in disagreement with the observed gravity. However, both the gravity and the seismic data suggest that the structure varies in all three directions. The modelling of the entire 3-D set of travel times leads to a coherent velocity structure that confirms the basement high; it also shows that the abrupt transition to the slower Cretaceous basin coincides in position and orientation with the fault system forming the Rån Ridge. The positive gravity anomaly over the Rån Ridge originates from the focussed and coincident elevation of the high velocity lower crust and pre-Cretaceous basement. Although the Moho is not constrained by the seismic data, the gravity modelled from the 3-D velocity model shows a better fit along the profiles. This study illustrates the interest of a 3-D acquisition of wide-angle seismic over complex structures and the benefit of the subsequent integrated interpretation of the seismic and gravity data.  相似文献   

15.
The Berkine and Illizi basins are Palaeozoic–Mesozoic intraplate depressions that preserve an over 7000 m thick sedimentary rock record and contain world-class petroleum systems with over 39 BBOE EUR hydrocarbon reserves. Regional seismic transects and a wealth of well data are used to review the tectonostratigraphic evolution of the area. The Gondwana (Palaeozoic) and Tethys (Mesozoic) supercycles make up the bulk of the Phanerozoic succession. These 1st order cycles record extensional basin formation, followed by a protracted period of overall net subsidence, and conclude with basin inversion and regional uplift during the Hercynian and Alpine orogenies respectively. Structural styles were dictated by transpressional or transtensional reactivation of mostly NNE oriented basement structural grain of Late Proterozoic–Ea.Cambrian (Pan-African) age and vertical movement of long wavelength regional highs and lows. Local tectonism is considered to be the far-field effect of plate-tectonic processes that affected the North African plate-boundaries, such as the Caledonian and Hercynian Orogenies, the opening of the Tethys and Atlantic oceans, and the Alpine Orogeny. These were accompanied by localised thermal mantle processes.  相似文献   

16.
The Agulhas Bank, which forms the continental margin on the southern tip of Africa, consists of a thick Meso-Cainozoic sedimentary sequence (up to 6.2 km) resting on and behind pre-Mesozoic continental acoustic basement. The stratigraphy of this sequence is outlined and its history and facies variations mentioned where they are known. Refraction seismic velocity and bottom sample data indicate a basic three-fold subdivision of the Mesozoic sequence, which can be correlated with the onshore succession in the Algoa Basin. It is separated by a major hiatus from the Cainozoic sediments, which consist of a Palaeogene and Neogene sequence subdivided by another well-defined level of erosion. Various formations within the Cainozoic are defined and named. An outline of the bathymetry of the eastern Agulhas Bank is also given.  相似文献   

17.
The analysis of 2D deep-seismic-reflection profiles across the slope and abyssal plain of the Angola oceanic basin reveals the existence of a significant and formerly unknown depocentre beneath the giant Cenozoic Congo deep-sea fan, between 7000 m and 9000 m depth, deposited directly onto the Aptian oceanic crust. The unit, which is up to 2.5 km thick and extends for more than 200 km basinwards of the Continent-Ocean boundary, is probably aged Albian–Turonian. Its radial fan-shaped depocentre is centred on the present-day Congo River outlet and contains at least 0.2 Mio km3 of sediments. These observations and the results from flexural modelling indicate that (1) the location of the Congo River's outlet has remained fairly stable since the Late Cretaceous, and (2) the basal unit was indeed sourced by a palaeo-Congo River probably located nearby the present-day one. Thus, the Atlantic sedimentary system related to the exoreism of the Congo River is much older than previously thought. Thermal modelling indicates that the maturation history of this upper-Cretaceous deposits is highly influenced by the interaction between the initial high heat flow of the young oceanic crust and further increase in sediment supply due to the progradation of the overlying Tertiary deep-sea fan during the Miocene. Hence, despite low present-day heat-flow values, should the unit have source rock potential, its basal section may be currently generating hydrocarbons.  相似文献   

18.
Cenozoic eastward migration of the Caribbean plate relative to the South American plate is recorded by an 1100-km-long Venezuela-Trinidad foreland basin which is oldest in western Venezuela (65-55 Ma), of intermediate age in eastern Venezuela (34-20 Ma) and youngest beneath the shelf and slope area of eastern offshore Trinidad (submarine Columbus basin, 15.0 Ma-Recent). In this study of the regional structure, fault families, and chronology of faulting and tectonic events affecting the hydrocarbon-rich Columbus foreland basin of eastern offshore Trinidad, we have integrated approximately 775 km of deep-penetration 2D seismic lines acquired by the 2004 Broadband Ocean-Land Investigations of Venezuela and the Antilles arc Region (BOLIVAR) survey, 325 km of vintage GULFREX seismic data collected by Gulf Oil Company in 1974, and published industry well data that can be tied to some of the seismic reflection lines. Top Cretaceous depth structure maps in the Columbus basin made from integration of all available seismic and well data define for the first time the elongate subsurface geometry of the 11-15 km thick and highly asymmetrical middle Miocene-Recent depocenter of the Columbus basin. The main depocenter located 150-200 km east of Trinidad and now the object of deepwater hydrocarbon exploration is completely filled by shelf and deepwater sediments derived mainly from the Orinoco delta. The submarine Darien ridge exhibits moderate (20-140 m) seafloor relief, forms the steep (12°-24°), northern structural boundary of the Columbus basin, and is known from industry wells to be composed of 0.5-4.5 km thick, folded and thrust-imbricated, hydrocarbon-bearing section of Cretaceous and early Tertiary limestones and clastic rocks. The eastern and southern boundaries of the basin are formed by the gently (1.7°-4.5°), northward-dipping Cretaceous-Paleogene passive margin of South America that is in turn underlain by Precambrian rocks of the Guyana shield.Interpretation of seismic sections tied to wells reveals the following fault chronology: (1) middle Miocene thrusting along the Darien ridge related to highly oblique convergence between the Caribbean plate and the passive margin of northern South America; continuing thrusting and transpression in an oblique foreland basin setting through the early Pleistocene; (2) early Pliocene-recent low-angle normal faults along the top of the Cretaceous passive margin; these faults were triggered by oversteepening related to formation of the downdip, structurally and bathymetrically deeper, and more seaward Columbus basin; large transfer faults with dominantly strike-slip displacements connect gravity-driven normal faults that cluster near the modern shelf-slope break and trend in the downslope direction; to the south no normal faults are present because the top Cretaceous horizon has not been oversteepened as it is adjacent to the foreland basin; (3) early Pliocene-Recent strike-slip faults parallel the trend of the Darien ridge and accommodate present-day plate motions.  相似文献   

19.
台湾海峡地区新生代的构造演化   总被引：9，自引：1，他引：9  
根据采集反射剖面,结合区域地质资料,分析了晋江凹陷、九龙江凹陷、新竹凹陷、台中凹陷和台湾凹陷为半地堑结构。新竹凹陷和台中凹陷下拗,演变为前陆盆地。晋江凹陷和九龙江凹陷因岩石圈上隆,其沉积较薄。这种模式决定了在台湾海峡地区,西部的生油气层为下第三系,而东部的生油气层为下第三系和上第三系。  相似文献   

20.
Several exploration wells have intersected a Cenozoic coal-bearing, fluvial-deltaic mudstone and sandstone succession in the northeastern Vietnamese part of the Malay Basin, and have successfully tested seismically identified direct hydrocarbon indicators (DHIs). The oil and gas/condensate discovery well 46-CN-1x encountered a ∼55 m thick section of lacustrine mudstones having considerable potential as an oil source. Vitrinite reflectance (VR) measurements from these alginite-bearing rocks introduce several problems in thermal maturity evaluation, including associated VR suppression and delineation of cavings and bitumens. Reliable thermal maturity gradients, however, may be established using a combination of conventional VR measurements and ‘equivalent VR’ (EqVR) values derived from the fluorescence alteration of multiple macerals (FAMM) technique. These measurements, performed on dispersed organic matter (DOM) in cuttings from 46-CN-1x, allow separation of low-reflecting bitumens and vitrinite in cavings from indigenous vitrinite and the FAMM results indicate VR suppression of 0.14% in an alginite-bearing mudstone with a high Hydrogen Index value. On the basis of available ‘raw’ VR data, a highly irregular maturity trend is determined, with the deepest sample (2675–2680 m) having a VR of ∼0.4%Ro. The EqVR value, however, for the deepest sample is 0.70%. The maturity trend determined from the FAMM data (and VR data, omitting samples having suppressed VR) indicates that the top of the oil window (VR of 0.75%Ro) is located at about 2800 m depth. Modelling the geothermal gradient using the EASY%Ro algorithm yields ∼40 °C/km for both of the two maturity profiles; this is in the low end of the range for the Malay Basin. Modelled temperature histories indicate onset of hydrocarbon generation for the uppermost Oligocene source rocks between 2 Ma and present-day, which post-dates trap formation. Seismic facies patterns suggest that lacustrine oil-prone units are in the oil window in the same graben complex a few km NW of the investigated well, and these rocks are likely to be the source of the hydrocarbons found in the well. A more widespread occurrence of hydrocarbons sourced from this kitchen is indicated by other discoveries and mapping of DHIs in the area.  相似文献   

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