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1.
Visual observations of the wall of Great Bahama Canyon indicate that ledges produced by differential submarine erosion occur at depths like reflectors on high-resolution seismic profiles, suggesting lithologic changes produce acoustic impedance contrasts and therefore reflectors. Quaternary-aged sediments in a core from Little Bahama Bank exhibit changes in lithology (and presumably acoustic impedance) associated with glacial-to-interglacial transitions, which also correspond in depth to seismic reflectors. This supports the concept that reflectors on high-resolution seismic profiles of Bahamian periplatform ooze correspond directly to changes in lithology and may be associated with climate/sea level fluctuations. 相似文献
2.
Cyclic sequences occur worldwide in nearly every stratigraphic sequence; they are particularly well-developed in fluvial and
deltaic sediments that have been influenced by high-frequency eustatic sea-level fluctuations. The large data base for this
study (including 471 deep foundation borings, thousands of line kilometers of high-resolution seismic, and sedimentological
and dating analyses) represents the most complete information on high-resolution chronostratigraphy and lithostratigraphy
that is available on any modern continental shelf/upper slope. These data are used to document sedimentological characteristics
and high-resolution seismic responses during three complete sea-level cycles over the entire continental shelf/upper slope
of offshore Louisiana.
Examination of high-resolution seismic records indicates that well-defined, high-amplitude, laterally continuous reflectors
correlate with rising and high stand condensed sedimentary sequences and that the deposits laid down during falling and low-stand
periods (expanded sections) are characterized by a wide range of acoustic responses. Discontinuous reflectors with high-amplitude
variability, continuous parallel reflectors, and chaotic and amorphous zones are common acoustic responses. The association
between a particular lithofacies and a specific acoustic response on 3.5-kHz records was found to be very poor. 相似文献
3.
High-resolution seismic profiles of Eckernförde Bay and the adjacent Baltic Sea were collected, and the geoacoustic properties of sediments there were measured. Bulk densities averaged ~ 1.35 g cm–3 and ranged from ~ 1.2 to ~ 1.7 g cm–3. Compressional wave velocities in gas-free sediments averaged ~ 1460 m s–1 and ranged from ~ 1425 to ~ 1555 m s–1. In nongassy sediments, bulk density variations typically controlled changes of acoustic impedance. Impedance changes were usually too small and closely spaced to be resolved seismically, although, at certain sites, significant impedance changes are far apart enough that they correlate one-to-one with seismic reflectors. Where free gas is present, velocity decreases and wave energy is scattered, causing a prominent seismic reflector. 相似文献
4.
A synthesis of high-resolution (Chirp, 2–7 kHz) subbottom profiles in the Ulleung Basin reveals patchy distribution of shallow (<90 m subbottom depth) gassy sediments in the eastern basin plain below 1,800-m water depth. The shallow gases in the sediments are associated with acoustic turbidities, columnar acoustic blankings, enhanced reflectors, dome structures, and pockmarks. Analyses of gas samples collected from a piston core in an earlier study suggest that the shallow gases are thermogenic in origin. Also, published data showing high amounts of organic matter in thick sections of marine shale (middle Miocene to lower Pliocene sequence) and high heat flow in the basin plain sediments are consistent with the formation of deep, thermogenic gas. In multi-channel deep seismic profiles, numerous acoustic chimneys and faults reflect that the deep, thermogenic gas would have migrated upwards from the deeper subsurface to the near-seafloor. The upward-migrating gases may have accumulated in porous debrites and turbidites (upper Pliocene sequence) overlain by impermeable hemipelagites (Quaternary sequence), resulting in the patchy distribution of shallow gases on the eastern basin plain. 相似文献
5.
Distribution and expression of gas seeps in a gas hydrate province of the northeastern Sakhalin continental slope, Sea of Okhotsk 总被引：1，自引：0，他引：1
Young Keun Jin Young-Gyun Kim Boris Baranov Hitoshi Shoji Anatoly Obzhirov 《Marine and Petroleum Geology》2011,28(10):1844-1855
Multidisciplinary surveys were conducted to investigate gas seepage and gas hydrate accumulation on the northeastern Sakhalin continental slope (NESS), Sea of Okhotsk, during joint Korean–Russian–Japanese expeditions conducted from 2003 to 2007 (CHAOS and SSGH projects). One hundred sixty-one gas seeps were detected in a 2000 km2 area of the NESS (between 53°45′N and 54°45′N). Active gas seeps in a gas hydrate province on the NESS were evident from features in the water column, on the seafloor, and in the subsurface: well-defined hydroacoustic anomalies (gas flares), side-scan sonar structures with high backscatter intensity (seepage structures), bathymetric structures (pockmarks and mounds), gas- and gas-hydrate-related seismic features (bottom-simulating reflectors, gas chimneys, high-amplitude reflectors, and acoustic blanking), high methane concentrations in seawater, and gas hydrates in sediment near the seafloor. These expressions were generally spatially related; a gas flare would be associated with a seepage structure (mound), below which a gas chimney was present. The spatial distribution of gas seeps on the NESS is controlled by four types of geological structures: faults, the shelf break, seafloor canyons, and submarine slides. Gas chimneys that produced enhanced reflection on high-resolution seismic profiles are interpreted as active pathways for upward gas migration to the seafloor. The chimneys and gas flares are good indicators of active seepage. 相似文献
6.
Gas in sediments has become an important subject of research for various reasons. It affects large areas of the sea floor
where it is mainly produced. Gas and gas migration have a strong impact on the environmental situation as well as on sea floor
stability. Furthermore, large research programs on gas hydrates have been initiated during the last 10 years in order to investigate
their potential for future energy production and their climatic impact. These activities require the improvement of geophysical
methods for reservoir investigations especially with respect to their physical properties and internal structures. Basic relationships
between the physical properties and seismic parameters can be investigated in shallow marine areas as they are more easily
accessible than hydrocarbon reservoirs. High-resolution seismic profiles from the Arkona Basin (SW Baltic Sea) show distinct
‘acoustic turbidity’ zones which indicate the presence of free gas in the near surface sediments. Total gas concentrations
were determined from cores taken in the study area with mean concentrations of 46.5 ml/l wet sediment in non-acoustic turbidity
zones and up to 106.1 ml/l in the basin centre with acoustic turbidity. The expression of gas bubbles on reflection seismic
profiles has been investigated in two distinct frequency ranges using a boomer (600–2600 Hz) and an echosounder (38 kHz).
A comparison of data from both seismic sources showed strong differences in displaying reflectors. Different compressional
wave velocities were observed in acoustic turbidity zones between boomer and echosounder profiles. Furthermore, acoustic turbidity
zones were differently characterised with respect to scattering and attenuation of seismic waves. This leads to the conclusion
that seismic parameters become strongly frequency dependent due to the dynamic properties of gas bubbles. 相似文献
7.
The integration of seismic data with core data should provide ground-truth to a structural interpretation of seismic data. The main difficulty in such an integration effort is the correct translation of physical property measurements on cores to a form which can be used in seismostratigraphic interpretation. In the absence of down-hole well data and check-shots, required knowledge of the velocity structure at the drilling locations can be obtained directly from measurements of the physical properties of core samples. This involves upscaling of the data from physical properties of cores to the sample interval used in the seismic data. In the present study, three of the seven drill-sites of ODP (Ocean Drilling Program) Leg 177 in 1997/1998, located on the Agulhas Ridge in the south-eastern Atlantic (sites 1088–1090), were connected with eight seismic profiles. Physical properties data measured on the cores from the various holes at each site were combined to create a single continuous log and used to construct synthetic seismograms. The synthetics generally show a good agreement with real seismic data in terms of amplitude and waveform. Some reflections in these generated traces may have a time-shift due to sections with incomplete or spurious P-wave velocity measurements in the ODP datasets. The main reflectors identified in the real seismic data correspond to hiatuses or periods of reduced sedimentation rates, and correlate well with density variations. One particular hiatus, clearly observable in the real seismic data, was not unequivocally identifiable in the various types of core data, and tying core data to seismic data can confirm its existence in the core data, showing the benefit of including seismic data in an interpretation of core log data. On the other hand, core data provide a calibration tool for the geological timescale of seismic data and information about the lithology, needed in the interpretation of seismic data. 相似文献
8.
基于纵波地震和四分量地震的弹性波阻抗反演 总被引：3，自引：0，他引：3
为了更好地揭示崖13-1气田的泥岩夹层及剩余气分布,提高采收率,尝试了基于纵波地震和四分量地震的弹性波阻抗反演。利用常规纵波地震资料对崖13-1气田气层进行了多角度同时反演;利用四分量地震资料进行了纵波和转换横波波阻抗反演。基于常规纵波地震资料的弹性波阻抗反演剖面的分辨率较高,气层纵波波阻抗与盖层的纵波波阻抗差异大于横波,但横波波阻抗分辨率比纵波波阻抗高,对气层细节反映得更清楚。利用弹性波阻抗反演结果可以较好地发现剩余气、泥岩夹层及气水界面。转换横波地震资料的分辨率较低,基于四分量地震资料的弹性波阻抗反演的分辨率也比较低。 相似文献
9.
Roger D. Flood 《Geo-Marine Letters》1987,7(1):15-22
A high-resolution bathymetric and seismic study of sinuous midfan channels on the Amazon Fan shows that some common elements of seismic profiles across the channel/levee system may be side echoes (sideswipe) from reflective, coarse channel-floor sediments Which lie to the side of the ship track. This includes portions of a dipping zone of high-amplitude reflectors beneath the channel. If these strong echoes are side echoes rather than buried coarse sediments, there may be less coarse material present within the midfan channel/levee systems than predicted, and channel evolution is still poorly resolved. Side echoes may be common in other areas of complex deep-sea morphology. 相似文献
10.
渤海海峡及周边海域浅地层结构及地层声速的拾取 总被引：2，自引：0，他引：2
通过系统分析渤海海峡及周边海域的高分辨率浅地层剖面与3口钻孔的资料,将研究区地层自上而下划分为T0、T1、T2、T3、T4、T5、T6、T7、T8共9个反射界面及SU11、SU12、SU13、SU2、SU3、SU41、SU42、SU43、SU5共9个声学地层单元,SU1地层单元对应全新世海相沉积,其底界为一海进侵蚀面,削蚀对应晚更新世晚玉木冰期陆相沉积的SU2地层单元。SU3地层单元对应晚更新世晚玉木间冰期的海相沉积,通过侵蚀间断面与上覆SU2呈不整合接触。SU41地层单元对应晚更新世早玉木冰期晚期的陆相沉积,SU42地层单元对应晚更新世早玉木亚间冰期的海相沉积,与上覆SU41呈侵蚀不整合接触,SU43地层单元对应晚更新世早玉木冰期早期的陆相沉积,其顶界面为海进侵蚀面,与下伏地层呈不整合接触,SU5对应晚更新世玉木—里斯间冰期的海相沉积。对比分析浅地层剖面地层单元与钻孔沉积地层,确定了研究区海底面之下不同地层单元对应的平均声学速度,为后续的地层层序的研究奠定了基础。研究区"海侵-海退-海侵-海退-高水位"的沉积过程,决定了地层平均声速随深度自下而上呈现由高-低-高-低的变化模式。 相似文献
11.
Reinhardt L. Kudrass H.-R. Lückge A. Wiedicke M. Wunderlich J. Wendt G. 《Marine Geophysical Researches》2002,23(4):335-351
About 6000 km of both bathymetric and high-resolution acoustic profiles were acquired on the shelf and upper slope offshore Peru between 9° S and 14° S. Two new sediment echosounder systems – SEL-96 and SES-2000DS – provided details of the sedimentary structures of the Quaternary sequences within the Sechura-Salaverry, Huacho and Pisco Basins. To a great extent, the poleward undercurrent determines the distribution of sediments. The undercurrent has generated numerous erosional unconformities, it has winnowed hardgrounds and has created mudwaves common between 250 m and 400 m water depth. Distinct subbottom reflectors within sedimentary units represent hiatuses due to periods of intensified winnowing or non-deposition. Erosional unconformities usually marked by pronounced reflectors suggest shifts of the undercurrent system related to climatic changes and eustatic variations of sea level. On a larger scale, the stacked prograding depositional sequences reflect the sea-level cycles of the Middle Pleistocene to the Holocene. Based on the stratigraphy of our piston cores and that of Ocean Drilling Program (ODP) Site 680, the depositional sequences limited by extended unconformities were assigned to oxygen isotope stages 1 to 7. Other sedimentary structures are small straight channels that were conduits for downslope sediment transport. Deformed sediments associated with synsedimentary normal faults result from creep movements indicating beginning slope failure. 相似文献
12.
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
13.
Geotechnical data from Plio-Pleistocene sediments on the Hebrides Slope provide the basis for an analysis of potential factors controlling their acoustic character as observed on high-resolution seismic reflection profiles. Differences in acoustic signature within the sedimentary succession are related to the void index and thus to soil structure and, in turn, to the depositional history of the sediments. In this example, a correlation can be demonstrated between the seismic and geotechnical stratigraphies. 相似文献
14.
Frey Øivind Planke Sverre Symonds Phillip A. Heeremans Michel 《Marine Geophysical Researches》1998,20(4):293-311
Interpretation of deep seismic reflection data across the Gascoyne Margin reveals six distinct seismic facies units related to the tectono-magmatic breakup history. On the outer Exmouth Plateau four large scale units are identified: (1) an extensively block-faulted upper crust; (2) a middle-crustal unit of discontinuous, undulatory reflectors; (3) a reflection-free deep crustal unit; and (4) a lower-crustal band of low-frequency, high-amplitude reflectors. Two additional units are found near the continent-ocean boundary (COB); (5) seaward-dipping reflectors (SDR); and (6) landward-dipping reflectors in the lower crust below the SDR. The lower-crustal high-reflectivity band, located near the top of a high-velocity unit (Vp > 7 kms–1), is interpreted as magmatic underplating. There is a spatial correlation between the underplated area and the presence of extensive upper-crustal block-faulting and intrusive rocks in the shallow crust. The undulatory middle-crustal reflector unit is also only identified in the outer plateau area, and is interpreted as a zone in which the upper-crustal faults terminate. The inner parts of the margin consist of a deep basin showing little upper-crustal faulting and no evidence of middle crustal deformation or underplating. Theoretical modeling of the effect of rifting and magmatic underplating on crustal strength profiles suggests that the brittle-ductile transition may migrate at least 5 km upwards during several million years after the underplating event. Based on the seismic interpretation and crustal strength modeling we propose that the seismic structure of the outer Exmouth Plateau is severely modified by a transient change in the crustal rheological structure associated with magmatic underplating. 相似文献
15.
16.
Shiguo Wu Xiujuan Wang How Kin Wong Guangxue Zhang 《Marine Geophysical Researches》2007,28(2):127-138
The passive northern continental margin of the South China Sea is rich in gas hydrates, as inferred from the occurrence of
bottom-simulating reflectors (BSR) and from well logging data at Ocean Drilling Program (ODP) drill sites. Nonetheless, BSRs
on new 2D multichannel seismic reflection data from the area around the Dongsha Islands (the Dongsha Rise) are not ubiquitous.
They are confined to complex diapiric structures and active fault zones located between the Dongsha Rise and the surrounding
depressions, implying that gas hydrate occurrence is likewise limited to these areas. Most of the BSRs have low amplitude
and are therefore not clearly recognizable. Acoustic impedance provides information on rock properties and has been used to
estimate gas hydrate concentration. Gas hydrate-bearing sediments have acoustic impedance that is higher than that of the
surrounding sediments devoid of hydrates. Based on well logging data, the relationship between acoustic impedance and porosity
can be obtained by a linear regression, and the degree of gas hydrate saturation can be determined using Archie’s equation.
By applying these methods to multichannel seismic data and well logging data from the northern South China Sea, the gas hydrate
concentration is found to be 3–25% of the pore space at ODP Site 1148 depending on sub-surface depth, and is estimated to
be less than values of 5% estimated along seismic profile 0101. Our results suggest that saturation of gas hydrate in the
northern South China Sea is higher than that estimated from well resistivity log data in the gas hydrate stability zone, but
that free gas is scarce beneath this zone. It is probably the scarcity of free gas that is responsible for the low amplitudes
of the BSRs. 相似文献
17.
C. Hans Nelson Andres Maldonado Francis Coumes Henri Got Andre Manaco 《Geo-Marine Letters》1984,3(2-4):125-131
The Ebro Fan System consists of en echelon channel-levee complexes, 50×20 km in area and 200-m thick. A few strong reflectors
in a generally transparent seismic facies identify the sand-rich channel floors and levee crests. Numerous continuous acoustic
reflectors characterize overbank turbidites and hemipelagites that blanket abandoned channel-levee complexes. The interlobe
areas between channel complexes fill with homogeneous mud and sand from mass flow and overbank deposition; these exhibit a
transparent seismic character. The steep continental rise and sediment “drainage” of Valencia Trough at the end of the channel-levee
complexes prevent the development of distributary channels and midfan lobe deposits.
Margin setting represents fan and/or source area 相似文献
18.
Berit Oline Hjelstuen Haflidi Haflidason Hans Petter Sejrup Atle Nygård 《Geo-Marine Letters》2010,30(3-4):221-230
The Nyegga region, located at water depths of about 600–800 m on the NW European continental margin, contains more than 200 pockmarks. Recently collected TOPAS seismic profiles and EM1002 bathymetric records now provide high-resolution information on their seabed and shallow sub-seabed geological setting. The identified pockmarks are up to 15 m deep, between 30 m and 600 m across and reach a maximum area of ca. 315,000 m2. The pockmarks are sediment-empty features. They do not have any preferred direction of orientation and show large variations in their shape. The pockmarks are restricted to a <16.2 cal. ka old sediment unit. This unit comprises sandy mud and is characterised by sedimentation rates of ca. 1 mm/year. The pockmarks are localised over a thick late Plio-Pleistocene prograding sediment package and a polygonal faulted Miocene-Oligocene ooze-rich unit. The late Plio-Plistocene deposits host bottom simulating reflectors, indicative of gas hydrate-bearing sediments. Inspection of the newly collected high-resolution dataset, combined with previously analysed sediment cores and 2D multichannel seismic profiles, reveals that the Nyegga pockmark field does not show any strong relationship between seabed features, sub-seabed structures and the sedimentary setting. This suggests a more complex evolution history of the Nyegga pockmark field then previously thought. 相似文献
19.
Gassy sediments are detectable acoustically in subbottom profiles of Canada's Fraser Delta slope and prodelta areas. Interstitial gas is typically represented by zones of acoustic turbidity on high-resolution seismic profiles and by gas brightening on air-gun profiles. The top of the acoustically turbid zone is generally highest within the sediment column closest to the river mouths and lies within 10 ms (two-way travel time) of the sea floor in a nearly continuous area that covers over 530 km2. Most of the gas is believed to be biogenic in origin, although thermogenic gas derived from underlying Tertiary sedimentary rocks may be present in places. 相似文献
20.
Gas hydrate saturation from acoustic impedance and resistivity logs in the Shenhu area, South China Sea 总被引：4，自引：0，他引：4
Xiujuan Wang Shiguo Wu Myung LeeYiqun Guo Shengxiong YangJinqiang Liang 《Marine and Petroleum Geology》2011,28(9):1625-1633
During the China’s first gas hydrate drilling expedition -1 (GMGS-1), gas hydrate was discovered in layers ranging from 10 to 25 m above the base of gas hydrate stability zone in the Shenhu area, South China Sea. Water chemistry, electrical resistivity logs, and acoustic impedance were used to estimate gas hydrate saturations. Gas hydrate saturations estimated from the chloride concentrations range from 0 to 43% of the pore space. The higher gas hydrate saturations were present in the depth from 152 to 177 m at site SH7 and from 190 to 225 m at site SH2, respectively. Gas hydrate saturations estimated from the resistivity using Archie equation have similar trends to those from chloride concentrations. To examine the variability of gas hydrate saturations away from the wells, acoustic impedances calculated from the 3 D seismic data using constrained sparse inversion method were used. Well logs acquired at site SH7 were incorporated into the inversion by establishing a relation between the water-filled porosity, calculated using gas hydrate saturations estimated from the resistivity logs, and the acoustic impedance, calculated from density and velocity logs. Gas hydrate saturations estimated from acoustic impedance of seismic data are ∼10-23% of the pore space and are comparable to those estimated from the well logs. The uncertainties in estimated gas hydrate saturations from seismic acoustic impedances were mainly from uncertainties associated with inverted acoustic impedance, the empirical relation between the water-filled porosities and acoustic impedances, and assumed background resistivity. 相似文献