Miocene Unconformity Research Articles

Seismic Imaging of Strata Truncating to Base Miocene Unconformity Integrated with Petrophysical Analysis of Mianwali Re-entrant, Pakistan: a Case Study from the Upper Indus Basin of Pakistan

Seismic Imaging of Strata Truncating to Base Miocene Unconformity Integrated with Petrophysical Analysis of Mianwali Re-entrant, Pakistan: a Case Study from the Upper Indus Basin of Pakistan

Miocene sequences and depocentres in the Roer Valley Rift System

AbstractThe Miocene sequence in the Roer Valley Rift System consists of alternating open‐to‐shallow marine, coastal and fluvio‐deltaic deposits. In this study, well logs, bio‐chronostratigraphy and seismostratigraphy are used to characterize major units and their bounding unconformities and to infer sediment dispersal patterns. Three major unconformities occur in the sequence: the early, middle and late Miocene unconformities (EMU, MMU and LMU). The EMU formed due to tectonic motions related to the Savian phase. After formation of the EMU, a broad depocentre developed in the south‐eastern part of the Roer Valley Graben (RVG). Sediment accumulation increased during this period and peaked in the middle Langhian, after which it diminished again to a low level during the late Serravallian. The decrease in sediment accumulation coincided with a period of tectonic subsidence along the major bounding fault zones (i.e. the Peel Boundary Fault System, the Feldbiss Fault System and the Veldhoven Fault System). The resulting transgression caused sediment starvation in the central RVG. Subsequently, global sea‐level fall during the early Tortonian caused large‐scale erosion, and formation of incised valleys on the highs adjacent to the RVG (Peel Block and Campine Block), as well as the south‐eastern RVG, forming the MMU. However, sedimentation continued during this period in the central part of the RVG where no erosional hiatus developed. From the Tortonian onwards, accumulation rates increased again. The depocentre shifted towards the north‐west and clinoforms developed in the RVG. During the latest Miocene, the depocentre was concentrated along the south‐western margin of the RVG. Meanwhile, the depositional environment of the entire RVRS gradually shallowed as the LMU was formed.

Multi-phase subsidence history of the Sarawak continental margin and its regional significance

Subsidence analysis of Sarawak Basin using stratigraphic data from a selection of exploration wells revealed a multi-phase history of crustal extension (rifting), subsidence and uplift. A relatively rapid subsidence during the early rift phase from Eocene to Oligocene (ca. 37–28 Ma) was followed by a gradual decrease in subsidence rate as the extended lithosphere underwent post-rift thermal relaxation (ca. 28–22 Ma). A second phase of extension during the Early Miocene (ca. 22–17 Ma) resulted in an increase in subsidence rate, which coincided with a major episode of compressional deformation, uplift and localised erosion. This deformation event culminated in a major unconformity dated ~16 Ma, known as the Middle Miocene Unconformity (MMU), which is recognised throughout the Bunguran Trough and North Luconia regions of Sarawak Basin as a major stratigraphic hiatus spanning the Early to Middle Miocene. Since the Late Miocene, there had been an increase in the subsidence rate, probably due to progradation of the Sarawak shelf to its present-day configuration. The complex subsidence history of Sarawak Basin is similar to those reported from other parts of the South China Sea margin. The subsidence histories indicate a common, underlying tectonic factor which is probably related to rifting and sea-floor spreading in the southwestern prong of the South China Sea oceanic basin.

THE ZECHSTEIN Z2 HAUPTDOLOMIT PLATFORM IN THE SOUTHERN UK MID NORTH SEA HIGH AND ITS ASSOCIATED PETROLEUM PLAYS, POTENTIAL AND PROSPECTIVITY

The Mid North Sea High (MNSH) region represents one of the least explored areas for the Late Permian Zechstein Hauptdolomit play in the Southern Permian Basin although some of the first offshore wells drilled in the UK were located here. In other parts of the basin such as onshore Poland, the Hauptdolomit Formation (“Hauptdolomit”) is an active and attractive exploration target, with oil and gas production from commercial‐sized fields. In the UK, the play has been overshadowed by drilling campaigns in areas to the south of the MNSH which tested plays in the underlying Rotliegend and Carboniferous successions. However, with these areas now in decline, there is increased exploration interest in the Hauptdolomit in the MNSH region, particularly since 2019 when 3D seismic data were acquired and the first hydrocarbon discovery was made at Ossian (well 42/04‐01/1Z). Geochemical data from the latter discovery have pointed to the presence of a prolific petroleum system with the potential for Hauptdolomit reservoirs to be charged both by Zechstein‐generated oils and Carboniferous condensate/gas. With regard to hydrocarbon migration and preservation in the southern MNSH, a detailed evaluation of the effects of the Mid Miocene Unconformity has allowed for a greater understanding of the main factors controlling hydrocarbon preservation and remigration. Reservoir characterization of the Hauptdolomit play has been achieved by integrating petrographic microfacies analyses, core data and petrophysical interpretations. The most important factors controlling reservoir quality are the presence and extent of anhydrite cementation and the presence of high energy shoal facies. Thicker and coarser grained shoal facies are expected to occur along the yet‐to‐be explored Orchard platform margin where numerous prospects have been mapped and refined using recently acquired 3D seismic data.

Flexural Response to Erosional Unloading of Continental Margins: An Example From the Bering Sea, USA

AbstractThe geodynamic response of continental margins to erosion may reveal current and past changes in the location of the continental slope. We model the three‐dimensional isostatic response to erosion along the retreating Beringian Margin to test the hypothesis that the margin and its canyons were dominantly eroded during the Pleistocene. Our results predict 900 m of flexural uplift, though evidence for this magnitude of uplift is not observed in Pleistocene and younger deposits, suggesting a substantial amount of margin erosion occurred pre‐Pleistocene. Uplift of this magnitude may be represented by a Late Miocene unconformity across the Bering Shelf and upwarped subsurface units at the base of the Beringian Margin. The distribution of uplift from varying canyon incision and margin retreat scenarios has implications for the extent of geodynamic response during erosional periods.

Extensional structures of the Nan′an Basin in the rifting tip of the South China Sea: Implication for tectonic evolution of the southwestern continental margin

Nanan Basin is a giant hydrocarbon basin, but its tectonic division scheme and associated fault systems has not been well understood. Based on newly acquired seismic data from the southwestern margin of the South China Sea, this study analysed the structural units, tectonic feature and geodynamics of the sedimentary basin. The new data suggests that the Nanan Basin is a rift basin oriented in the NE-SW direction, rather than a pull-apart basin induced by strike-slip faults along the western margin. The basin is a continuation of the rifts in the southwest South China Sea since the Late Cretaceous. It continued rifting until the middle Miocene, even though oceanic crust occurred in the southwest subbasin. However, it had no transfer surface at the end of spreading, where it was characterized by a late middle Miocene unconformity (reflector T3). The Nanan Basin can be divided into eight structural units by a series of NE-striking faults. This study provides evidences to confirm the relative importance and interplay between regional strike-slips and orthogonal displacement during basin development and deformation. The NE-SW-striking dominant rift basin indicates that the geodynamic drivers of tectonic evolution in the western margin of the South China Sea did not have a large strike-slip mechanism. Therefore, we conclude that a large strike-slip fault system did not exist in the western margin of the South China Sea.

Fossilized silica diagenetic fronts: Implications for palaeoceanographic evolution across the Falkland/Malvinas plateau

A set of newly collected 2D seismic reflection data allows the mapping of two distinct cross-cutting reflectors across the Falkland/Malvinas Plateau. Reflector XR-F/MB in the Falkland/Malvinas Basin appears as a bottom simulating reflector that mimics the geometry of the present seafloor, whereas reflector XR-F/MT in the Falkland/Malvinas Trough is a non-bottom simulating reflector that mimics a shallower reflector representing the Early-Middle Miocene unconformity. The discordant geometry of these two reflectors with respect to the host-stratigraphy is argued to be associated with Opal-A to Opal-CT diagenesis, which is primarily a function of temperature. However, the estimated temperature at the present depth for reflector XR-F/MB lies below the minimum temperature for the onset of silica diagenesis. Based on their geometry and seismic characteristics, the two reflectors are interpreted to be fossilized silica diagenetic fronts, formed under palaeo-thermal conditions different from today. We hypothesize that the erosional action of intensified deep and bottom water masses subsequent to Antarctic glaciations during the Early-Middle Miocene may have driven the fossilization of the diagenetic front in the study area. It is estimated that erosion of a minimum of 270 m of overburden would account for the temperature drop driving the fossilization of the silica diagenetic fron.

A history of the latest and Neogene unconformities, offshore Palawan and the southern South China Sea

The age and character of the main unconformities offshore Palawan is resolved, and their history reviewed. Some very deep and very shallow unconformities have insufficient well data, but from the Oligocene to Late Miocene times a series of unconformities can be dated, characterised and correlated regionally to help develop a new tectono-stratigraphic framework. This framework does not support the widely cited idea of Early Miocene subduction of a Proto-South China Sea plate followed by collision over a plate suture.The absence or very weak expression of a Base Miocene Unconformity (c. 24 Ma), so strongly expressed across northern Borneo, also suggests a major revision of tectonic models is required. In spite of many cited reports, there is no evidence for an unconformity in the later Early Miocene (c. 17 to 15 Ma), which was a period of gradually increasing compression and uplift. The main mid-Neogene seismic unconformity is the Red Unconformity dated at about 12–13 Ma (equivalent to the DRU of Sabah). This was when the uplift of a foreland over-thrust system paused, and a locally erosional surface was rapidly transgressed.This review describes the neglect of analytical sciences that remain a crucial part of basic geological studies.

Re-examination of the Base Miocene Unconformity in west Sabah, Malaysia, and stratigraphic evidence against a slab-pull subduction model

This review chiefly examines data on the regionally important Base Miocene Unconformity , confirming its age and expression in west Sabah, then integrates this with data on the tectono-stratigraphic development of the broader Sabah to Palawan region. The two unconformities described (the Base Miocene Unconformity and the younger Deep Regional Unconformity) were both produced when deformation abruptly stopped, leaving erosional surfaces that were then transgressed. The ages of these two events are c. 24 and 12–13 Ma respectively, and the areas affected by the prior uplift and erosion can be mapped. The results are incompatible with widely cited plate tectonic models that describe closure of a postulated Proto-South China Sea [PSCS]. These prior models had assumed plate drift ended with collision at plate docking over a PSCS suture in about mid Early Miocene times. However, stratigraphic data shows that Early Miocene times were a period of quiescence across Sabah, with mostly mild subsidence . It is therefore proposed that plate drift in the SCS could not have been linked to any type of subduction process anywhere around western Sabah. The absence of any plate docking or any Oligocene through Middle Miocene compression around northern Palawan is a further anomaly to the old subduction based tectonic model.

The Celebes Molasse: A revised Neogene stratigraphy for Sulawesi, Indonesia

• Review of Neogene stratigraphy of Sulawesi based on new field and laboratory work. • Celebes Molasse includes sediments of different age and depositional environment. • Early Miocene unconformity marks collision of the Sula Spur microcontinent. • Younger unconformities not related to collisions but due to extension. • Extension mainly resulted from subduction rollback. Over the past century, a wide variety of poorly dated sediments that unconformably overlie pre-Neogene rocks in Sulawesi have been assigned to the Celebes Molasse and interpreted as post-orogenic rocks deposited after a major collision. New data from fieldwork and laboratory studies, including mineralogical, palaeontological and zircon geochronological analyses, provide the basis for a new Neogene stratigraphy and show that sediments assigned to the Celebes Molasse have significant variations in age, environment of deposition, composition and sedimentation history. Identified unconformities in the (1) Early Miocene (c. 23 Ma), (2) Middle Miocene (c. 15 Ma), (3) Mio-Pliocene (c. 6–5.3 Ma), and (4 and 5) Pleistocene (c. 1.8 and 0.1 Ma) separate Lower Miocene, Middle to Upper Miocene, Pliocene, Pleistocene and Holocene mega-sequences. These mega-sequences resulted from Early Miocene collision followed by extension, driven by subduction rollback, causing both uplift and subsidence, in contrast to previous interpretations of multiple collisions.

The crustal structure and evolution of the Bunguran Trough, offshore Sarawak, Malaysia

The Bunguran Trough is a deep Tertiary basin depocentre in the West Luconia Delta Province, Sarawak Basin, offshore Malaysia. At the centre of the trough, the top of the acoustic basement is ∼15 km deep, buried beneath a thick pile of Late Eocene to Quaternary coastal-deltaic sediments of the proto-Rajang-Lupar River delta system. Sediment thickness, bathymetry and gravity data were utilized to re-construct the crustal structure of the West Luconia Delta and the Bunguran Trough. The results indicate an average crustal thickness of 5.3 km beneath the Bunguran Trough, which is extremely thin compared to the extended continental crust (∼15–22 km) beneath the adjacent West, Central and North Luconia provinces. Extreme crustal thinning is confined to the Bunguran Trough, which appears to have steeply faulted boundaries, but the nature of the faults is obscured by the thick sedimentary pile.Structural evidences from reflection seismic data suggest widespread extensional faulting throughout Sarawak Basin although some major tectonic lineaments may have had significant strike-slip movements due to later reactivation and basin inversion. Both extensional and strike-slip faulting may have contributed to the formation and subsidence of the Bunguran Trough. West Balingian Line is a major fault zone that seems to have had a significant strike-slip displacement history and probably had an important role during basin initiation. Seismic data suggests that this fault zone extends from the Balingian and Tatau provinces into West Luconia as a major strike-slip fault with a releasing bend along which the Bunguran Trough may have developed. Crustal extension in a pull-apart basin may have been initiated by sinistral motion along the fault during Late Eocene-Oligocene. Alternatively, the widespread normal faulting indicates that the Bunguran Trough may have developed as a rift basin which experienced at least two phases of extension before a major inversion event which is marked by the Middle Miocene Unconformity (MMU). The main phase of subsidence in the Bunguran Trough had occurred during the active extensional phase before the MMU.

Surficial redistribution of gold and arsenic from the Rise and Shine Shear Zone, Otago, New Zealand

ABSTRACT The historic Come-In-Time gold mine was developed in a ∼100*100 m area of the >7 km long orogenic Rise and Shine Shear Zone in Otago Schist. The oxidation of hydrothermal ankeritic and auriferous arsenopyrite and pyrite-bearing Otago Schist beneath a regional Miocene unconformity resulted in replacement of sulphides and ankerite by arsenic (As)-bearing ferric oxyhydroxide. The As-bearing ferric oxyhydroxide is mainly concentrated in and near the original mineralisation sites, especially shears, but mobilisation into post-mineralisation joints and fractures has redistributed As on a metre scale. Gold was liberated from sulphides during oxidation and aggregated by supergene oxidation processes into a smaller number of larger particles (mm scale) that are intimately intergrown with As-bearing ferric oxyhydroxide, especially in shears. Eluvial gold in proximal immature debris includes variably rounded supergene particles eroded from nearby, and some externally derived detrital flakes from previously overlying Miocene sediments. Some eluvial gold is trapped in fine sediments by lichen on outcrops. The hydrothermal As-Au relationship has therefore been broadly maintained through oxidation of rocks at the metre scale but Au concentrations have been locally enhanced in the surficial environment.

Evidence for rapid large-amplitude vertical motions in the Valencia Trough (Western Mediterranean) generated by 3D subduction slab roll-back

The mechanisms controlling the Cenozoic subsidence of the Valencia Trough, located in the Western Mediterranean, are poorly understood. The Cenozoic geodynamic evolution of the Western Mediterranean is complex comprising subduction, slab roll-back, back-arc extension, collision, and lithosphere delamination. We investigate the subsidence of a regionally observed unconformity, here referred to as the Miocene Unconformity, which separates Mesozoic from latest Palaeogene to Neogene sediments. Using a dense grid of seismic reflection data, well data and 3D flexural backstripping, we show that the Miocene Unconformity in the SW Valencia Trough subsided by more than 1.5 km to the present day at an average rate of 90 m/Myr. The absence of Cenozoic extensional faults affecting the basement shown by seismic data indicates that this rapid subsidence is not caused by Cenozoic rifting or remaining Mesozoic post-rift thermal subsidence. Neither can this subsidence be explained by subduction dynamic subsidence or flexural loading related to the thin-skin Betic fold and thrust belt which only affects subsidence observed near the deformation front.We interpret the 1.5 km subsidence of the Miocene Unconformity as the collapse of a back-arc transient uplift event. Erosion during this uplift, resulting in the formation of the Miocene Unconformity, is estimated to exceed 4 km. Transient uplift was likely caused by heating of back-arc lithosphere and asthenosphere, combined with mantle dynamic uplift, both caused by segmentation of Tethyan subduction resulting in slab tear. Subsidence resulted from thermal equilibration and the removal of mantle flow dynamic support Tethyan subduction slab roll-back. We propose that our observations and interpretation of rapid back-arc km-scale uplift and collapse have global applicability for other back-arc regions experiencing subduction segmentation and slab tear during subduction slab roll-back.

Physical controls on the formation of halophytic saline substrates near Alexandra, Central Otago, New Zealand

ABSTRACT Soil-free saline substrates near Alexandra have developed from evaporated marine aerosols dominated by NaCl. The salts accumulate on impermeable substrates where there is minimal chemical interaction between water and rock. Most of the known saline sites occur on outcrops of clay-altered schist exposed immediately below the regional Miocene unconformity, and on clay-rich sediments eroded from altered schist. The unconformity zones that host these saline sites occur linearly along structurally controlled depressions. These unconformity zones have been major targets for placer gold mining, and most of the saline sites occur in abandoned mines where impermeable rocks were exposed by historic excavations. Native salt-tolerant plants (halophytes) have colonised parts of the saline substrates, especially on actively-forming clay pans derived from nearby steep mine cuts. Saline sites are ephemeral, as salt is readily removed in water, sediments can bury the surfaces, and incursion of adventive plant species encourages further sedimentation. Erosional disturbance can overcome these effects temporarily, and surface erosion to bare ground along the strike of the structurally controlled schist unconformity zones may also create new saline sites.

Sequence biostratigraphy of the late Oligocene to Miocene succession in the northern Song Hong Basin, offshore Vietnam

The Cenozoic sedimentary succession of the Song Hong Basin, offshore North Vietnam is poor in marine microfossils, especially in the early Miocene and Oligocene and subsequently is poorly dated. However, it is rich in terrestrially derived pollen, spores, and freshwater algae. Biostratigraphic assemblages from two wells, termed Well A and B, have been evaluated using the approach of sequence biostratigraphy. The Oligocene fluvio-lacustrine succession through the Dinh Cao Formation displays multiple transgressive-regressive cycles comparable with those reported from the Cuu Long Basin to the south. By applying the local Cuu Long Oligocene palynological zonation (CLO zones), these cycles can be correlated directly with the cycles from the Cuu Long Basin, showing that sedimentation began during sequence 19, at about 29 Ma or a little earlier off-structure, over basement. The deepest interval within Well A yielded abundant pollen of the montane tree Alnus, and with the position of the basin within the northern tropics at 20oN, this suggests that in the mid Oligocene, the basin was intermontane, with Alnus widespread in swamps after the lake shallowed, at an altitude of at least 1000 m. The Miocene succession has been interpreted by reference to SEA (‘Southeast Asia’) depositional cycles following Morley et al. (2021). The evaluation suggests a complete early Miocene succession, varying from fluvial with low sedimentation rates for the youngest part of the Dinh Cao and Phong Chau Formations to shallow marine with increased sedimentation rates after 17 Ma through the Phu Cu Formation which correlates to the middle Miocene climatic optimum. There was a significant period of non-deposition from 13.8 to 9.5 Ma in Well A and from 13.5 to 11.8 Ma in well B, corresponding to the middle Miocene unconformity seen in other nearby basins.

Stratigraphic evolution of deep-water Dangerous Grounds in the South China Sea, NW Sabah Platform Region, Malaysia

The onshore and shallow marine conventional hydrocarbon resources around the world are mostly at the maturation phase and hence, exploration activity globally, showing increasing interest into progressively deeper water hydrocarbon prospects such as South China Sea basins. However, a comprehensive understanding of basin tectonics, depositional history, and petroleum systems of the basin is required to deduce the exploration prospectivity of these deeper reservoirs. The Sabah Basin is a prolific hydrocarbon province in Southeast Asia and has a significant economic impact on this part. Recent discoveries in the deep-water hydrocarbon prospects in the NW Sabah Trough prompted a comprehensive investigation of the surrounding area, e.g., Dangerous Grounds for hydrocarbon prospectivity. Previous studies in the Dangerous Grounds mainly focused on the sparse 2D seismic and gravity-magnetic data analysis. A systematic review of stratigraphic evolution has not been presented thus far in the published literature. In this paper, recently acquired high-resolution 3D seismic data with the core and cuttings and conventional well log data from the adjacent areas have been combined to characterize the stratigraphic evolution of the Dangerous Grounds in the NW Sabah Platform. Seven horizons interpreted from the 7570 sq. km 3D seismic data, calibrated with the global sea - level curve and geological time scale, to establish the stratigraphic evolution in the study area. Based on distinct structural and seismic characteristics, and calibrated with the adjacent regions well data, two mega-sequences, namely, lower syn-rift and upper post-rift mega-sequences, have been identified and evaluated. The Paleocene to Early Oligocene syn-rift sequence consists of clastic sedimentary fill in grabens and half-grabens is overlain by Late Oligocene to recent post-rift sedimentary successions represented by siliciclastic and carbonates deposits. Major depositional units within these two mega-sequences, including carbonate, channel, mass transport deposits, and turbidites have been identified and evaluated. During Late Oligocene to Middle Miocene, the area has witnessed the deposition of carbonate platform and reefs on top of pre-existing structural highs. Late Oligocene to Middle Miocene channel-levee complexes with convex upward sand filling features is prominent in the seismic data. Mass Transport Deposits and turbidites have also been observed above the Middle Miocene Unconformity with distinct seismic characteristics. The pelagic and hemipelagic nature of the sedimentary succession deposited from Pliocene to recent in a passive margin condition have also been interpreted from their unique seismic features. Paleocene-Early Oligocene syn-rift siliciclastic hydrocarbon play, Late Oligocene-Middle Miocene carbonate play, and Late Miocene turbidite play within the study area have been interpreted.

Upper Oligocene lithostratigraphic units and the transition to the Miocene in North Belgium

The presence of Chattian deposits in Belgium was confirmed in the early 20th century by correlation of their mollusc faunas with the type Chattian in Germany. Consequently, the Voort Formation in the Campine Basin and the Boncelles Sand on the northeastern Ardennes were established and assigned a Chattian age. Contacts with underlying Rupelian and overlying Burdigalian formations are marked by hiatuses, linked mainly to end-Oligocene Savian tectonics and reactivation of the Roer Valley Graben (RVG). On the Campine Block, only the lower part of the Chattian, the Voort Sand is deposited, increasing in thickness in the direction of the RVG and including a geophysically traceable clayey marker horizon allowing the mapping of this unit in the Campine Basin, into the Netherlands and even possibly link it to the hydrostratigraphic subdivision of the Chattian in the Lower Rhine Graben. Lithologically, these uppermost Paleogene Chattian deposits form the base of the Neogene sequence along the Southern Bight of the North Sea, characterised by predominantly glauconite-bearing sand. The Chattian sediments rapidly become thicker in the strongly subsiding RVG, resulting in a more continuous sedimentation with the development above the Voort Sand of a clay unit and another sand unit, forming together the Veldhoven Formation. In Belgium such sequence is only found in the RVG without biostratigraphic data. However, it can be demonstrated that lithostratigraphically this sequence is comparable to the better-studied Veldhoven Formation in the Netherlands where biostratigraphy revealed that the Veldhoven Formation grades into the Aquitanian to Burdigalian, crossing the Paleogene–Neogene boundary and separated from middle Miocene deposits by the Early Miocene Unconformity (EMU). It is proposed to harmonise Belgian and Dutch stratigraphic nomenclatures, making the more complete Veldhoven Formation applicable both in the Campine Basin and the Roer Valley Graben, and further north in the Netherlands. Within this scheme, the Belgian Voort Formation becomes the Voort Member as the lower part of the Veldhoven Formation, of which the middle Wintelre clayey and upper Someren sandy members are only recognised in the graben.

Stratigraphy and palaeontology of the lower Miocene Kiel Sand Member (Berchem Formation) in temporary exposures in Antwerp (northern Belgium)

The stratigraphic position of the lower Miocene Kiel Sand Member of the Berchem Formation in the Antwerp area (northern Belgium) is not well constrained and its depositional environments are poorly known. Due to a spatial limited decalcification front, the Kiel Sand Member is completely decalcified in southern Antwerp and gradually becomes fossiliferous to the north-east of the city. The stratigraphy and palaeontology of the fossiliferous sediments in three temporary exposures are presented. The dinoflagellate cyst analysis of fossiliferous horizons shows the relative progress of a transgression in the southern North Sea Basin during the early–middle Burdigalian, that probably initiated in the late Aquitanian. The Kiel Sand Member contains an important mollusc fauna, with several species reported for the first time from this member. The taphonomy and fauna of the shell beds indicate a shallow marine, high energetic depositional environment, strongly influenced by storms, currents, waves and a rather low sedimentation rate. The climate was warm-temperate to subtropical. In all studied sections, the Kiel Sand Member could be clearly distinguished from the Antwerpen Sand Member: similarities and differences are discussed. Moving to the north of Antwerp, the erosive base of the Antwerpen Sand Member cuts deeper into the Kiel Sand Member. The Early Miocene Unconformity (EMU) is suggested at this contact.

Neotectonic evolution of Northeastern Venezuela . Geomorphological and seismic analysis in the Monagas Fold and Thrust Belt

In Northeastern Venezuela, since 10 Ma, the tectonic setting is dominated by the eastward translation of the Caribbean Plate accommodated mainly by the E-W El Pilar strike-slip fault. However, to the south, in the Monagas Fold and Thrust Belt (MFTB), evidence of active compression has been identified in the southern limit of the Urica dextral fault. The objective of this study is to integrate geomorphological, dating terraces and 2D-3D seismic data in four zones of the MFTB: Tarragona, Punta de Mata, Jusepín, and Amarilis to understand the tectonics relationship between surficial and deep deformation in the area. These zones show surface deformations such as topographic uplifts, tilted, folded and faulted terraces, and drainage anomalies.The age of the river terraces obtained through 10Be and 26Al methods indicates that these terraces were formed in the late Pleistocene. The oldest terrace, located in the Tarragona zone, has a maximum exposure age of 90 ± 5 ka and the youngest, located in the Punta de Mata zone of 15 ± 5 ka. Additionally, we calculated an uplift rate of 0.3–0.4 mm/y for Plio-Pleistocene units using the deformation of the Late Miocene Unconformity (LMU). This rate coincides with the vertical deformation rate average calculated from terraces dating, which suggests that the deformation rate in the MFTB has not changed significantly for the last 5.3 Ma.The ridges observed at the surface and the structural highs interpreted from seismic sections indicate that the uplifting has been active up to the present through the activation of deep thrusts. We propose that the deformation on the surface is linked to the Tarragona, Pirital, Furrial thrusts, and the Amarilis backthrust activity and the youngest thrusts developed in the Carapita Formation. However, this surface deformation decreases towards the SSE away from the Urica fault; therefore, the neotectonic deformation is believed to be caused by the horsetail termination activity at the southern limit of the Urica fault.

Seismic attribute analysis of deep-water Dangerous Grounds in the South China Sea, NW Sabah Platform region, Malaysia

The Sabah Basin is a prolific hydrocarbon province in Southeast Asia and has a significant economic impact on this part. Recent discoveries in the deep-water hydrocarbon prospects in the Northwest Sabah Trough prompted a comprehensive investigation of the surrounding area, e.g., Dangerous Grounds for hydrocarbon prospectivity. Previous studies in the Dangerous Grounds mainly focused on the sparse 2D seismic and gravity-magnetic data analysis. A systematic review of detailed depositional history has not been presented so far in the published literature. To achieve this, recently acquired high-resolution 3D seismic data and well information have been used for seismic attribute analysis to establish the structural features and depositional pattern from the Paleocene to recent age. Two major sedimentary sequences have been evaluated from the seismic data, which include syn-rift and post-rift sequence. The pre-rift sequence considered to be the acoustic basement is overlain by syn-rift sequence, deposited during the Paleocene to Early Oligocene age. Spectral decomposition analysis demarcates paleo-lows/depocenters, consist of siliciclastic sedimentary fills in grabens and half grabens with the syn-sedimentary deformation. Geobody interpretation helps to understand the different phases of syn-sedimentary faulting with the presence of antithetic faults in the grabens. Late Oligocene to Middle Miocene carbonate platform and reefs has been observed on top of the pre-existing structural highs. Sweetness attributes enable to appraise the reef structure to demarcate lithofacies boundaries. Variance and amplitude extraction maps reveal the development of reefs on top of the carbonate platform. Amplitude extraction map reflects the Late Oligocene to Middle Miocene channel-levee complex with the convex upward unconsolidated sand filling pattern. Sweetness map helps to delineate the meandering channel boundary, channel geomorphology with ox-bow lake, point bar, and west to east channel shifting. Carbonate and clastic dominated areas have been differentiated in the southwest part. Slides and debris flow Mass Transport Deposits, Late Miocene turbidites have been observed above the Middle Miocene Unconformity and evaluated based on their distinct seismic characteristics. During the Pliocene to recent, the basin has witnessed the deposition of thick pelagic-hemipelagic sediments in the outer-neritic to the bathyal environment in the passive margin condition.