Seismic Stratigraphic Analysis Research Articles

Geology aspects and formation of the erosional structure of Upper Miocene deposits of the Western Cicaucasus

The results of regional studies of the Early Miocene deposits of the Western Ciscaucasia, carried out on the basis of seismic stratigraphic analysis, are presented. The spatial pattern of sediment accumulation is analyzed and the paleogeographic conditions during the regressive stages of the Late Miocene in the Western Ciscaucasia are clarified. Erosion incisions of several levels were identified, which developed during the fall of the erosion base level during major regressions in the studied time interval. By spatial correlation of paleochannels based on a selected series of intersecting seismic profiles, the buried river valleys of the Paleo-Don and Paleo-Donts were reconstructed and constructed at the Sarmatian‒Meotis boundaries and within the Late Meotis‒Late Pontian interval.

Structure of the basement of the near-Laptev part of the Eurasian basin according to geological and geophysical data

The near-Laptev part of the Eurasian basin is the area of transition from modern spreading to intraplate rifting. We propose an approach to the construction of a 3D model of the basement of the Laptev Sea part of the Eurasian basin based on the linkage of all currently available geological and geophysical data. The structure of the acoustic basement of the Eurasian basin is characterized by alternating troughs and highs in cross-section. The sparse seismic data do not allow us to directly trace the strike of these structures, but they can be correlated with the linearity established by gravity and magnetic data and related to the sequential opening of the basin. For the Laptev Sea part of the Eurasian basin, where linearity is no longer traceable from magnetic data, we propose a method of determining the strike of the basement structures on the basis of seismic stratigraphic analysis. The new 3D model of the acoustic basement in the studied area provided the basis for the tectonic scheme of the entire Eurasian basin. The model reflects the main stages of basin development: continental rifting up to 56 Ma, normal spreading 56–45 Ma, ultra-slow spreading 45–34 Ma, ultra-ultra-slow spreading 34–20 Ma. The southern part of the study area is overlain by a sedimentary cover with an age of 20 Ma and younger, which is associated with the cessation of spreading here no later than 20 Ma.

Seismic stratigraphy of the Cretaceous post-rift sedimentary interval in the Punta del Este Basin (offshore Uruguay) and its implications for deep-water reservoirs

The formation of the Punta del Este Basin is associated with the fragmentation of West Gondwana and consequently the opening of the South Atlantic Ocean during the Early Cretaceous. The basin comprises the Cretaceous depocentre of the Uruguayan continental margin (UCM). This study provides a seismic stratigraphic analysis of the Cretaceous post-rift sedimentary interval in the basin by defining its seismic facies, depositional sequences, shelf-edge trajectories and palaeophysiographical settings. All depositional sequences of the Cretaceous post-rift sedimentary interval represent intense basinward progradation marked by two depositional trends. The Lower Cretaceous sedimentary interval exhibits a dominant flat-to-descending shelf-edge trajectory with a migration of up to 37 km. Deposition occurred over an irregular physiography with proximal NW–SE and distal WSW–ENE trends controlled by the characteristics of the volcanic margin. The basin geometry has strong implications for understanding the deposition of a deep-water turbidite system in the UCM, with a strong analogy to the recent discovery of the Venus well in the Orange Basin, offshore Namibia. Towards the Late Cretaceous, the NW–SE depositional trend was controlled by a NE–SW slope break, indicating deposition over the south and north highs. A low-angle ascending shelf-edge trajectory was observed, with a migration of up to 16 km.

The Guangya submarine fan in the South China Sea: A distinctive channelized slope-through fan

Submarine fans play a crucial role in understanding deep-sea sedimentary processes, establishing source-to-sink linkages, and identifying deep-water hydrocarbon reservoirs. Various types of submarine fans have been documented. Here we present findings on the Guangya submarine fan in the Southwest subbasin (SWSB) of the South China Sea (SCS), by analyzing multibeam bathymetric and two-dimensional multichannel seismic data. Bathymetric data reveal that the Guangya fan, covering an area of ~22,500 km2, comprises seven leveed channels, leading to a large composite lobe off the channel mouths. Different from typical submarine fans, the Guangya fan exhibits an elongated shape, extending longitudinally from the shelf edge through the slope to the abyssal plain, while laterally confined within a trough-like morphology in the southwestern tip of the SWSB and beyond. Lacking a typical feeding canyon, the fan appears to be self-fed by the leveed channels that serve as the primary depositional element. In contrast to the radial channel pattern in typical fans, the channels within the Guangya fan form a unique braid to dendritic pattern, genetically linked to channel merging and intersecting effects. Long wavelength and low wave height cyclic steps are identified, highlighting the occurrence of energetic supercritical turbidity currents. Seismic stratigraphic analysis shows that the Guangya fan primarily consists of high-amplitude reflections, indicating its coarser-grained or sandy turbidite-dominated nature. The fan has been evolved since the Pliocene, and mainly comprises depositional elements including channel fills, levees, lobes, and mass transport deposits. The specific tectonic context at the convergence of the conjugate margins, bounding the funnel-shaped SWSB, significantly influences the development of the Guangya fan. The Guangya fan could be originated from a shelf-edge staging area predominantly fed by the Mekong River during sea-level lowstands.

Tectono-stratigraphic evolution of salt-influenced normal fault systems: an example from the Coffee-Soil Fault, Danish North Sea

We explore how the relationships between fault activity, salt movement and sediment loading affect the stratal geometry of the hanging wall throughout the evolution of a salt-influenced normal fault system. We examine a c. 65 km long portion of the Coffee-Soil Fault System in the Danish North Sea, the hanging wall of which has been partially influenced by a pre-rift unit of mobile salt. To constrain the tectono-stratigraphic evolution of this fault system, we combine structural observations with seismic stratigraphic analysis of the hanging wall growth strata. We find that the hanging wall of the Coffee-Soil Fault System shows major depocentre shifts through time, along with marked variability in the along- and across-strike stratal geometries. We explain how the development of these characteristics is influenced by: (1) the segmentation and linkage history of the fault system; (2) the evolution of the salt-cored cover monoclines above blind basement fault segments; and (3) changes in the location and rate of accommodation generated by the load-driven withdrawal of salt up the dip-slope of the hanging wall and by fault-related subsidence. Our findings have implications for structural and stratigraphic studies in salt-influenced rift basins, as well as for understanding the potential distribution of geo-storage and hydrocarbon reservoirs in such settings.

Paleo-Depositional Systems in the Krishna Godavari Basin, East Coast of India

Krishna-Godavari (K-G) basin is a continental passive marginperi-cratonic basin. It is located along the east coast of India. The basin got initiated through rift/syn-rift tectonics between Permo-Triassic to early Cretaceous periods. It consists of the deltaic plains of the Krishna and Godavari Rivers and the inter-deltaic regions. The areal extent of on land part is about 15,000 sq. km whereas the offshore area covers about 215000 sq. km up to 1,000 m isobath. The basin contains about 5 km thick sediments with several cycles of deposition, ranging in age from late Carboniferous to Pleistocene. The major geomorphologic units of the K-G basin are upland plains, coastal plains, Recent flood plain, and delta plain. Exploration for hydrocarbons in this basin was started in 1958 conducting geological mapping. Geophysical surveys using gravity and magnetic methods were started in 1964, and the seismic surveys were carried out from 1972 in the basin to identify the favourable sites of hydrocarbon accumulation. During the last four decades, 647 deep wells were drilled in different parts of the basin for exploration of oil and gas and their production activities of which 465 well are on landwhich include 85 development wells. More than 225 prospects were drilled out of which 83 are hydrocarbon bearing. 
 Cretaceous sediments having a thickness of about 6 km are known in the peri-cratonic K-G basin. Archaean basement consisting of khondalites, charnockites and some sedimentary rocks occur towards north and west of the basin. Lower Gondwana rocks overlie the basement and are exposed in a limited areas adjoining the Godavari Graben. There are several horsts and grabens in the basin. Many growth faults are also known here. The Pranhita Godavari Graben is a linear intra-cratonic rift that is in the south-central part of Peninsular India. The stratigraphic column of the basin includes older Talchir Formation of Permo-Carboniferous overlain by Barakar formations which in turn underlie the Chintalapudi sandstone of Permian age. The tectonic history of the K-G basin comprises of the Rift Stage, Syn-rift Stage, Drift Stage, and Late Drift Stage. A Petroleum System can be summarized as an independent stratigraphic compartment within which three primary requisites for hydrocarbon accumulation viz., the source, reservoir, and cap rocks occur. The basin has good hydrocarbon potential, and expletory efforts to locate oil and gas pools through seismic-stratigraphic analysis may enhance the discovery rate.

INTEGRATING DEPOSITIONAL SYSTEM TRACTS WITH MINERALOGY AND PROVENANCE OF THE MIOCENE SANDSTONES, OFFSHORE NORTH KUTEI BASIN

Vertical variation of the Miocene sandstone mineralogy in the Kutei Basin has been recognized but the reasons for this remain unsaid. Deltaic-sandstone facies, parasequence sets, detrital mineralogy, and provenance of the uppermost Middle Miocene to the Upper Miocene strata in the Anamta and Amantu areas were analyzed using twenty-three wells and selected composite 2D and 3D seismic lines. Taxon indicators were correlated to build bio- and litho-stratigraphic markers: M50, M65, M66, and M70. The mineralogy dataset was derived from core and cuttings, while the detrital minerals were described, counted, normalized, and plotted in ternary diagrams. The four key markers were tied to the 3D-seismic data for seismic-stratigraphy analysis to observe the parasequences, system tracts, and sequence boundaries that correspond to the fluctuated relative sea-level. The parasequence sets are: (1) M65 aggradation and progradation, (2) M66 progradation, forced-regression, and back to another progradation, (3) M70 progradation, which interestingly demonstrate the detrital-mineral groupings. Qt-F-L suggests a gradual change up to the younger age from subarkose to sublitharenite towards feldspathic-litharenite to litharenite. Qp-Lv-Ls demonstrates the source was derived from collision-suture and folded-thrust belt. Qm-F-Lt diagram reveals the mature rocks with stable frameworks to the recycled-orogen provenance. The sediments maturity and stability are further confirmed by the Qm-P-K ternary chart. The most important finding is a significant shift of the paleo-shelf edge during the forced regression, as it separated the mineralogy composition of the M66 to the underlying M65 parasequence sets.

Seismic Stratigraphic Analysis of the North Apsheron Trend

The Caspian Basin”s structural settings are – compared to the Southern Caspian Basin – less complex. Except for the Apsharon trend, which is a prominent overall anticlinal structure with an eastward dip of its axis, the area of investigation comprises a major northwest-southeast trending syncline and thus exhibits very limited structural potential. Structural closures are limited to the Pre-Cretaceous levels only which so far have not been tested by wells in the offshore. The Cretaceous forms anticlinal structures along the Apsharon trend. These structures appear open up-dip to the northwest with a potential culmination in the shallow water area not covered by the seismic data available. Wells on the Apsharon trend reaching the Cretaceous did not encounter a reservoir so far. The better potential is supposed to be related to stratigraphic traps. Overall three plays are defined based on the seismic stratigraphic analysis: Cretaceous reef play: Within the Cretaceous, there are good indications for buildups along a trend close to the Turkmenistan border. The definition of structural closures along the trend or potential up-dip pinch-outs along the trend requires further investigations [reprocessing] and a denser seismic grid to outline. Pontian highstand delta: The Pontian highstand delta identified in the centre of the study area is interpreted from the progradation reflection pattern and can be reasonably well delineated as a progradational body with some slumping of distinct lateral extend. The Pontian Unconformity in the area east of the incised Paleo-Volga river and north of the delta is characterized by high amplitude becoming weaker again to the N. This area can be referred to as the delta plain area on the Pontian shelf with a high probability of reservoir-quality sands. Productive Series Onlap/Pinch-out Play: With rising lake level in the South Caspian Basin the Central Caspian Basin was continuously flooded and the pre-existing relief [incised valleys, synclinal trough] became again an area of sedimentation. The relevant formations show northward onlap pinch-outs, the Pereryva pinch-out as the probably most promising reservoir was mapped in detail. The onlap positions of the higher Productive Series as well may represent further exploration potential, a detailed review of these pinch-outs.

Morphology, seismic stratigraphy, and tectonic control of the Yitong submarine canyons – fan apron system in the northern South China Sea

Submarine fans are ubiquitous in modern deep-water environments. Such systems reported in the literature are largely fed by shelf-indented canyons receiving ample fluvial or longshore drift sediment inputs, whereas those nourished by slope-confined canyons far away from terrigenous sediment sources remain poorly understood. Herein, we report such a system, the Yitong submarine canyons – fan apron system (YCFS), from the northern South China Sea. This system was studied using multibeam bathymetric and two-dimensional multichannel seismic data, combined with geological constraints from nearby International Ocean Discovery Program drilling sites. YCFS consists of approximately 12 submarine canyons confined in the lower continental slope of >1200 m water depth, which feed a fan apron in the connecting abyssal plain. The canyons are erosion-dominated, as evidenced by their V-shaped cross-sections with up to 708 m deep incisions. Canyon infillings comprise mass transport deposits and turbidites, and interfluves exhibit features such as landslides, creep-typed sediment waves, and gullies, indicating the canyons and interfluves are dominated by mass transport and turbidity-current processes. The fan apron is generally depositional, in which channels and channel-levee complexes, turbidite lobes, and mass transport deposits comprise the main depositional elements. In the canyon-to-fan transitions, supercritical turbidity current features and bedforms, including plunge pools and connected sediment mounds, cyclic steps, and antidunes, are developed, which are linked to the deceleration and hydraulic-jump effects of the high-velocity turbidity currents shedding off the canyons. Seismic stratigraphic analysis revealed that YCFS was initiated in Late Miocene. The formation and maintenance of YCFS are linked to the long-term existence of an upslope margin-parallel basement high. The latter could have maintained a steep slope condition (up to 6.5°) that favors the development of canyons and supercritical turbidity currents. Because of the blocking effect of the basement high, YCFS receives limited supply of the shallow-water sediments.

Integrated seismic stratigraphic and structural analysis of Southern main Ethiopian rift basin: implications for hydrocarbon potentials

Integrated seismic stratigraphic and structural analysis of Southern main Ethiopian rift basin: implications for hydrocarbon potentials

Evidence of the evolution of the East Antarctic Ice Sheet on the continental slope and rise sedimentary record: Insights from the Sabrina Coast, East Antarctica

Deciphering how the Antarctic Ice Sheet has responded to past climate warming is critical to understanding its sensitivity and role in current and future climate change. In this context, knowledge of the evolution of the Antarctic Ice Sheet in catchments with large potential sea-level contributions plays a key role. The Sabrina Coast of East Antarctica lies seaward of the second largest, but least known, subglacial basin on Earth, the Aurora Subglacial Basin. It is part of the East Antarctic Ice Sheet and drains to the Sabrina Coast via the Totten Glacier, the third largest drainage system in East Antarctica. Our refined, comprehensive seismic stratigraphic analysis of a large multichannel seismic data set collected in this sector of the Antarctic margin shows that sediments deposited on the continental slope and rise of the Sabrina Coast retain a well-preserved record of variations in glacial and oceanographic dynamics. Isobath and isopach maps evidence a complex, asymmetric evolution of the Sabrina slope and rise, with the western sector being the main sediment depocenter since the emplacement of the East Antarctic Ice Sheet, as indicated by the up to 4-km-thick glacial-related sequences and inferred sedimentation rates of up to 300 m/m.y. However, significant sediment accumulation also occurs in the eastern area, particularly in the western levees of the canyons. Our findings highlight the potential of this region for deep ocean drilling that will provide an unprecedented history of the dynamics of the marine-based ice sheet in the Aurora Subglacial Basin and its sensitivity to climate change under different background climate conditions.

Seismic expression and stratigraphic preservation of a coastal plain fluvial channel belt and floodplain channels on the Gulf of Mexico inner continental shelf

AbstractSubsurface fluvial deposits in coastline‐proximal settings record the spatiotemporal evolution of the coastal landscape and may be viable repositories of sediment for future coastal restoration projects. However, quantitative linkages between the geomorphic form and stratigraphic expression of coastal plain fluvial elements remain lacking, complicating coastal stratigraphic interpretations and subsurface resource assessment. This study explores the expression and preservation of fluvial coastal plain geomorphic features through outcrop‐scale seismic stratigraphic analysis of ultra‐high‐resolution chirp acoustic reflection data from the north‐western Gulf of Mexico inner continental shelf, offshore the Brazos River, Texas, USA. The chirp data exhibit decimetre‐scale vertical resolution within the upper 35 m of the shelf, evincing the preservation of two distinct types of coexisting fluvial channel‐forms: Type 1, a 1 km wide and 9 m deep single‐storey channel belt filled with sand‐rich lateral accretion deposits and channel fills; and Type 2, numerous 10 to 800 m wide and 1 to 20 m deep incisional floodplain channels filled with extensive drapes of overbank‐derived sediments. The chirp data resolve fluvial geomorphic elements including lateral accretion surfaces, levées, floodplain deposits and abandoned channel fills. Rollover of lateral accretion surfaces, widespread draping of seismic reflectors within channel fills, and quantitative comparison between the interpreted stratigraphic forms and analogous features on the nearby Texas Coastal Plain suggest near‐complete stratigraphic preservation of the geomorphic form of both channel belt and floodplain channel elements. Rapid aggradation of the coastal plain by the Brazos River in this region during the Holocene transgression is hypothesized as a mechanism for the high degree of preservation achieved. This study proposes the first recognition criteria for the seismic stratigraphic expression of coastal floodplain channels and provides direct linkages between the geomorphic and stratigraphic expression of a coastal plain fluvial landscape, promoting improved coastal stratigraphic interpretations and assessment of subsurface lithofacies distributions.

Estimating sediment transport diffusion coefficients from reconstructed rifted margin architecture: measurements in the Ogooué and Zambezi deltas

AbstractDiffusion‐based stratigraphic models are widely used to simulate sedimentary systems and margin deltas. Diffusion‐based models assume that the topographic evolution primarily depends from its slope. Limited attention has however been given to the calibration of the transport coefficients. Here, we evaluate transport coefficient values from natural examples, the Ogooué and Zambezi rifted margin deltas over the last 5 to 12 Ma respectively. We developed a method to estimate transport coefficients based on high resolution seismic stratigraphy analysis of the stratigraphic architecture of these deltas. For each stratigraphic sequence, we calibrated the sand/shale ratios of the deposits, we restored their depositional slopes, we estimated their uncompacted accumulated volumes and we calculated the transport coefficient (Kd) from the sediment flux/slope ratio. Estimated values of Kd fall within one order of magnitude (×0.1 km2/ka), a much narrower range than previously published values (×0.0001 to ×100 km2/ka). We show that the diffusion approximation is optimal at 10–100 km scale and 0.5–1 Ma time resolution, independently of the stratigraphic context. We show that the diffusion assumption is appropriate for the formation of the clinoforms (mainly gravity driven). It is however not optimal for the shelf and distal domains where additional processes (e.g., wave, flood, hemipelagic, turbidites, oceanic current), not accounted for it the diffusion assumption, significantly impact sediment transport. We documented a significant increase of Kd values after 0.9 Ma, coeval of an increase in the amplitude of eustatic variations at this time indicating that the calibration of Kd from present day sedimentary systems might not be optimal for simulations of sedimentary systems before the last million years.

Seismic-stratigraphic analysis and depositional architecture of the Cenozoic Kribi-Campo sub-basin offshore deposits (Cameroon): Seismic attributes approach and implication for the hydrocarbon prospectivity

The offshore deposits were formed the main part of the Kribi-Campo sub-basin, which is one of the three Cameroonian coastal margin basins formed during the progressive opening of the South Atlantic margin. Determination of the seismic facies and their architecture in seismic units are lacking in the Kribi-Campo sub-basin and calibration of the stratigraphic unit and the hydrocarbon prospectivity of Cenozoic offshore deposits remains unclear. Therefore, the seismic stratigraphic unit, data from five boreholes, and seismic attributes of 2D seismic data were analysed to determine the seismic stratigraphic distribution, the paleoenvironment evolution, and to assess the hydrocarbon prospectivity of the Cenozoic offshore deposits of the Kribi-Campo sub-basin. Five main seismic facies include parallel to subparallel, hummocky, chaotic, sigmoidal, and oblique, and four major seismic stratigraphic units SSU1, SSU2, SSU3, and SSU4 have been identified. The seismic stratigraphic unit has been divided into five major unconformities dated Upper Paleocene, Lower Eocene, Middle Miocene, Upper Miocene, and Pliocene to Pleistocene. The depositional environments evolve from delta to prograding continental shelves, both influenced by high and low energy processes, controlled by relative sea-level change. The offlap-breaks in the SSU4 seismic unit show the presence of both the Low Stand Systems Tract (LST) or Shelf Margin Systems Tract, and retrograding Transgressive Systems Tract (TST). The presence of potential source rocks, reservoirs, seals, and structural and stratigraphic traps throughout the studied seismic intervals highlight the prospective nature for oil and gas exploration within the offshore Cenozoic of the Kribi-Campo sub-basin.

The occurrence of a palaeo‐lithification front in an overpressured basin (Chalk Group)—Timing from clumped isotopes and seismic stratigraphic analysis

AbstractThis study proposes a unique workflow to unravel complex burial diagenetic histories of overpressured basins based on the integration of seismic and well log data, biostratigraphy, petrography, clumped isotope analyses and basin modelling. This approach is demonstrated with an example from the Chalk Group in the Danish Central Graben, where a seismic‐scale palaeo‐lithification front has been observed and studied in detail to elucidate the timing of the establishment of overpressured conditions and its relation to changing diagenetic activity. The palaeo‐lithification front separates high‐porosity chalks above, that dominantly underwent mechanical compaction and contact cementation, from low‐porosity chalk below, that dominantly underwent severe pressure dissolution and pore‐filling cementation. Analysis of chalk buried under hydrostatic conditions shows a strikingly similar lithification front between 1000 and 1200 m burial, much shallower than the lithification front in the Danish Central Graben at a current depth between 2100 and 2400 m below seafloor. The discrepancy of 1200 m is due to the establishment of overpressured conditions that limited the increase in effective stress as burial continued, finally halting burial compaction when formation fluids started to carry the lithostatic weight. Basin modelling data indicate that this occurred at the end of the Oligocene for large parts of the Danish Central Graben, which is much earlier than the Middle Miocene timing that is currently assumed. The results imply a regional occurrence of a relict lithification front in the North Sea Basin, its position guided by stratigraphy, but mainly dependent on the maximum effective stress experienced during its burial history. The study shows that the porosity bipartition is a remnant of the past and not from ongoing compaction as has previously been suggested. Since it was established before the thermal maturity of the main source rocks, chalk below the lithification front must have formed a sealing unit during hydrocarbon migration. The recognition of the lithification front is also of importance to velocity modelling and depth‐conversion since a non‐linear increase between velocity and depth is expected across this boundary. The methodology may be applied in other overpressured basins where the diagenetic state of reservoir rocks at the end of hydrostatic conditions must be constrained.

Depositional history of Lake Chala (Mt. Kilimanjaro, equatorial East Africa) from high-resolution seismic stratigraphy

Sediments deposited in Lake Chala (Kenya/Tanzania) constitute a high-resolution archive of past climate and environmental change in equatorial East Africa spanning two glacial-interglacial cycles. To correctly interpret the proxy records it contains, it is crucial to understand the evolution of lacustrine sedimentation in this volcanic crater basin. Building on previous seismic stratigraphic analysis by Moernaut et al. (2010) of a dense grid of 37 km high-resolution seismic reflection profiles with up to 270 ms two-way travel time (ca. 210 m depth) of sub-bottom penetration, this study presents a seismic-based reconstruction of the complete depositional history of Lake Chala as well as a first-order age model for the major documented stages in lake evolution. The seismic stratigraphic sequence comprises 16 distinct and finely-stratified units (U1-U16, youngest to oldest), grouped into five major depositional stages. Stage I (U16, ca. 249-212 ka) marks the initiation of sedimentation in an originally ring-shaped depositional area surrounding two central tuff cones emerging from the basin floor. Stage II (U15-U12, ca. 212-114 ka) represents the onset of basinwide sedimentation above the tuff cones, implying a gradual rise in lake depth and shift to more strictly hemipelagic sedimentation. Stage III (U11-U8, ca. 114-97 ka) represents the development of a relatively flat lake floor during a period of significantly reduced lake depth. Stage IV (U7-U4, ca. 97–20.5 ka) is again characterized by largely undisturbed hemipelagic sedimentation under mostly high lake-depth conditions. Stage V (U3-U1, 20.5 ka BP to Present) represents the establishment of the present-day, very broad and flat basin floor under fluctuating lake level. Reassessing the Moernaut et al. (2010) suggestion of a minor disconformity at ca. 100 m sub-bottom depth, we here interpret this seismic feature as a thick turbidite related to a mass wasting event. Consequently we can affirm continuity of lacustrine sedimentation in the depocenter of Lake Chala throughout the past ca. 250,000 years.

Seismic stratigraphy of the north-westernmost area of the Malta Plateau (Sicily Channel): The Middle Pleistocene-Holocene sedimentation in a tidally influenced shelf

In this study we present the results of a seismic-stratigraphic analysis of sub-bottom profiles in the north-westernmost area of the Malta Plateau in order to define the depositional mechanisms for the upper Quaternary sequences. During this interval the morphology of the Malta Plateau was characterized by a ramp and bathymetries not exceeding 200 m. Two major unconformities, related to MIS 6 and MIS 2 (the latter corresponding to the Last Glacial Maximum, LGM), characterize the upper Quaternary sequences. The geometries of the recognized seismic units indicate as depositional mechanisms were controlled by subsidence and sea-level fluctuations. In detail, deposits related to the last glacial event were recognized through their seismic pattern and have been interpreted as formed by the interaction between tide and wave dynamics. Contrary to the northern Sicilian continental margin, in the Malta Plateau ramp no LGM-related lowstand prograding wedge was recognized due to the absence of an effective shelf edge. It is considered as a consequence of the morphology and the dominant deposition processes in the Malta Plateau. Afterwards the ramp morphology allowed a rapid drowning of the Malta Plateau instead with the formation and preservation of transgressive deposits revealed as bedforms. The highstand deposits appear as prograding bodies and have been classified as infralittoral prograding wedge.

Structural evolution and sediment depositional system along the transform margin- Palar–Pennar basin, Indian east coast

Continental transform margins are characterized by sub-vertical strike-slip faults and rapid change in thermal gradient across the margin from continental to oceanic crust. The continental crust terminates abruptly along such sheared margins. Tectonic evolution associated with sedimentation in continental slope of the Palar–Pennar transform margin is inadequately understood due to limited seismic data and/or poor imaging with few well controls. Exploratory drilling attempts for hydrocarbon presence have resulted in some promising outcomes in the Palar–Pennar basin.The Palar–Pennar graben in onland is bound by steep normal rift faults, which reactivated by strike-slip movement during late syn-rift time as Antarctica separated along the NNW to ∼ N-trending Coromandal transform margin in the offshore part. The pre-existing Precambrian shear zones and lineaments in the basement have played a governing role in the basin development. The onland drainage pattern is structurally controlled as observed from its rectangular drainage pattern, tectonic index and sinuosity index. In offshore area of the basin, seismic interpretation identifies distinct pull-apart rift basin along the Coromandal transform margin with syn-rift deposits in the lower continental slope portion. Strike-slip movement uplifted the fault blocks in the southern part of the pull-apart basin. This has also reactivated some of the rift faults in the syn-rift section. Such reactivation results in early post-rift seal breach. This tectonic event has implication in the depositional sequences, which has been portrayed by seismic stratigraphic analysis and construction of chronostratigraphic section across the transform margin in this work. Thickening of post-rift deposition towards E -SE, major hiatus, large scale mass transport complexes and erosional events have been identified from such analysis. On this basis, seven distinct tectonic sequences, M1 to M5 in Mesozoic and T1 and T2 in Tertiary, have been identified. The chronostratigraphic section can help in deciphering the relative sea level changes based on the nature of stratal terminations, extent of erosion and non-deposition. This study emphasizes the tectonic-controlled drainage system and geometry as well as sedimentation pattern in onland and offshore deepwater area of Palar – Pennar basin alongside the Coromondal transform margin.

ГЕОЛОГІЧНА ПРИРОДА СЕЙСМІЧНИХ ВІДОБРАЖЕНЬ В ОСАДОВОМУ ЧОХЛІ СХІДНОЇ ЧАСТИНИ АБШЕРОН-ПРИБАЛХАНСЬКОГО ПОРОГУ

The Absheron-Prebalkhan tectonic zone, often called as the Absheron-Prebalkhan ridge, is a link between two large oil and gas basins of the world, which differ in the genetic level of the basement, i.e.: the South Caspian (SCB) and the Middle Caspian basins (MCB). The considered area has been completely covered by detailed seismic and gravity surveys over the past decades. The article presents material illustrating the information content of seismic sections in different parts of the region, which are characterized by different seismogeological conditions. As a result of the analysis of the latter, the author specified and determined four seismic horizons: SH-A (Akchagyl), SH-I (tops of RS), SH-II (horizon VIII) and SH-III (lower RS) based on the dynamic expressiveness, length, and resolution of the record. The tracking quality of these horizons is not the same. The identification of seismic intervals, which correspond to structural levels based on objectively determined seismic parameters, such as the configuration and relative position of reflections, their continuity, as well as the amplitude and frequency of seismic waves were the basis for seismic stratigraphic analysis of the wave field. The compiled schematic structural maps show the geological structure of the red-colored strata and Akchagyl deposits and the correlation of the structural plans of the latter clearly. Comparison of complex geological and geophysical materials allows to determine the character of the distribution of lithofacies features of RS deposits.

PETROPHYSICAL ANALYSIS AND SEISMIC STRATIGRAPHY INTERPRETATION TO DETERMINE HYDROCARBON RESERVOIR IN TARAKAN BASIN, BUNYU ISLAND WATERS

Tarakan Basin area of Bunyu Island Waters is known to have hydrocarbon potential with complex geological structures. This study aims to determine reservoir characterization and to obtain prospect of hydrocarbon reservoir zones based on petrophysical and seismic stratigraphy analysis with reference to Well DDS-1 and 2D seismic Line S88. Petrophysical analysis results 3 zones that have potential as hydrocarbon reservoirs. Based on petrophysical quantitative analysis, Zone 1 has values of 52.25% for shale volume, 18.48% for effective porosity, 39.84% for water saturation and 13.03 mD for permeability. Zone 2 has values of 54.66% for shale volume, 10.27% for effective porosity, 40.9% for water saturation and 1.14 mD for permeability. Zone 3 has values of 49.22% for shale volume, 9.33% for effective porosity, 56.33% for water saturation and 0.22 mD for permeability. Out of these three reservoir zones in Well DDS- 1, Zone 1 has the prospect of hydrocarbons which is supported by the net pay value. Based on seismic stratigraphy interpretation, the reservoir zone is correlated to the Tabul Formation, which comprises calcareous clay and limestone.