Younger Sequence Research Articles

Structural framework of the Caswell Sub-basin, North West Shelf, Australia

The Caswell Sub-basin, situated within the Browse Basin in the North West Shelf constitutes one of Australia’s primary hydrocarbon producing regions, with notable gas-condensate producing fields including Ichthys and Prelude. Jurassic syn-rift sandstones are extensively distributed across the basin and serve as one of the major reservoirs. However, reservoir sequences are typically intensely faulted and exhibit heterogeneity in thickness and lithofacies, with some areas experiencing localised erosion on uplifted fault blocks (e.g. Northern Caswell Sub-basin). Hence, understanding the nature of the 3D fault patterns and their growth history is crucial for evaluating the reservoir characteristics for field development and additional exploration activities. This study, therefore, aims to evaluate the structural framework and the tectonic evolution of the Caswell Sub-basin. Detailed structural interpretation of Paleozoic and younger sequences was conducted using multiple 3D seismic datasets extending over Ichthys, Prelude, Lasseter, and Crown fields. Our study focuses mainly on Mesozoic faulting patterns and kinematics evaluated from interpreted structural maps, thickness changes of each stratigraphic interval and fault throw profiles of major bounding faults. The extensional phase during the Early–Middle Jurassic triggered the development of NE–SW trending faults and the deepening of the Brewster Graben. While, from the Late Jurassic to the Early Cretaceous, the development of E–W trending faults in the north of the Crown and Lasseter fields indicate a shift in the regional stress regime. We highlight the importance of evaluating the structural linkage from basement to cover sequences to achieve a comprehensive understanding of reservoirs and associated petroleum systems.

Quaternary stratigraphic architecture of the Pearl River Mouth continental shelf, northern South China Sea: Unraveling stratigraphic imprints of tectonism, paleoceanography, and climate change

The complexity of continental shelf stratigraphy is determined by the interactions among various global or local factors. However, their specific roles are still poorly understood. Using a newly-acquired grid of single-channel seismic reflection profiles, combined with piston cores, shallow boreholes, and industrial wells, this study investigates the sequence stratigraphic architecture and evolution of the Quaternary continental shelf offshore the Pearl River Mouth (PRM), northern South China Sea (SCS). Three types of bounding surfaces have been identified according to their stratal terminations: erosional surfaces (ESs), flat-lying surfaces (FSs), and locally dipping surfaces (LDSs). Given the limited extent of LDSs, we utilized ES/FS couplets to subdivide the upper Quaternary section into six high-frequency sequences (SQ6–SQ1) and their corresponding systems tracts. Within each sequence, regional progradational clinoforms (RPCs) prevail across the entire shelf and are accompanied by downstepping shoreline trajectories, which we interpreted as deposits of falling-stage systems tract. RPCs are interrupted by intercalated sheeted units (ISUs) characterized by high-amplitude and continuous seismic reflections, which may consist of transgressive and lowstand deposits. In younger sequences particularly SQ2 and SQ1, progradational-aggradational clinoforms (PACs) with ascending shoreline trajectories are well developed but confined to the shelf margin, indicating efficient sedimentation during lowstand.Our results revealed significant spatial and temporal variability in stratigraphic architectures of the PRM shelf. Along the SW–NE direction, the stratigraphic pattern changes from progradation to retrogradation and back to progradation, resulting in three sectors with distinct shoreline trajectories. Retreating shoreline trajectories and retrogradational stacking patterns are preferentially present in areas adjacent to the Dongsha Rise, which are jointly influenced by several local factors such as tectonism and intense marine processes. Temporally, a dramatic change in stratigraphic patterns can be observed across a key surface ES4, dated ca. 0.8 Ma. Below ES4, fluvial incisions are scarce and RPCs are overall low-angle and capped with relatively thick ISUs. Also, no lowstand PACs were observed. Above ES4, large-scale incised valley networks appear, together with increased scale and dominance of RPCs and PACs. This stratigraphic imprint is attributed to the Mid-Pleistocene Transition (MPT), which caused a noticeable increase in periodicity, amplitude, and asymmetry of glacio-eustatic cycles. The increased scale of RPCs and PACs after the MPT may reflect increased sediment input due to high denudation rate under intensified monsoon climate.

Morphotectonic Processes in Seismic Zones of Moderate Intensity, Argentina

This study deals with the neotectonic deformation in seismic zones of moderate intensity in some areas of the Sierras Pampeanas, Santa Bárbara System and Chaqueña Plain of Argentina. In the study region, the location of earthquakes of ≥ three, ≥ four, and ≥ six Richter magnitudes agree with the traces of regional faults, evidencing their neotectonic activity. Seismic energy is generally transmitted over inherited faults, such as in the Metan basin. Minor new faults occur in Quaternary terraced deposits,and others move, taking advantage of the Neogene sedimentary strata. The folds are generally buried, but the younger sequences are gently undulating. The seismic energy dissipated through fewer cohesion materials that form the valleys' fill, developing discrete fault scarps and strongly folded conglomerate strata. The foothills deposits and basins absorbed most of the seismic energy released during the reactivation of the faults. Tectonic activity is deforming 630 BP deposits in the Cumbres Calchaquíes piedmont. Considering deformation values, neotectonic deformation in the outcrops and seismic profiles evidence, it is possible to interpret that the seismic activity in the study area from the Pleistocene to the present remained between the current records. This seismic activity, sustained over time, is sufficient to produce deformation in the foothills, reactivate pre-existing faults with small displacements and generate minor new faults in recent conglomeratic deposits. Many faults are blind. However, the deformation of the landscape and the modification of the drainage network are direct indicators of the activity of these structures.

Cadomian to Cenerian accretionary orogenic processes in the Alpine basement: the detrital zircon archive

New whole-rock geochemical and detrital zircon U–Pb and Lu–Hf data of metasedimentary sequences of the Silvretta Nappe, Orobic Alps, Strona-Ceneri Zone, Gotthard Massif and Venediger Nappe are presented. These units seem to share a common early to middle Paleozoic geological record, which has alternatively been interpreted as the result of intraplate or orogenic processes. Detrital zircon data mainly indicate late Ediacaran to early Ordovician maximum sedimentation ages for the studied sequences, suggesting that they were intimately related to Cadomian and Cenerian orogenic processes along the northwestern Gondwana margin. The common presence of late Ediacaran to Cambrian Cadomian ages associated with variable subchondritic to suprachondritic Lu–Hf compositions points to recycling processes of Cadomian sequences, further supported by geochemical data indicating a relatively low to moderate maturity of sedimentary protoliths. The occurrence of Cenerian arc-related intrusions in Austroalpine and South Alpine basement unit points to an arc/back-arc position in the early Paleozoic Cenerian orogen, except for the Strona-Ceneri Zone, which was likely located closer to the forearc region, as indicated by the presence of high-pressure metamorphism. Younger sequences, such as the Landeck Quartz-phyllite, document post-Cenerian sedimentation, whereas those of the Venediger Nappe more likely record the early stages of Variscan subduction, as indicated by Devonian maximum deposition ages.

The Secondary Minerals from the Pillow Basalt of Salsette-Mumbai, Deccan Volcanic Province, India

Secondary minerals occur within the tholeiitic basalts of Salsette Island in the greater Mumbai region, as well as in other localities in the Deccan Volcanic Province (DVP). However, the secondary minerals of Salsette Island show remarkable differences with respect to their mineral speciation and precipitation sequence, which are both due to their unique geological environment. The greater Mumbai region is built up by the Salsette subgroup, which represents the youngest sequence of the DVP. It formed subsequently to the main phase of DVP activity in Danian time (62.5 to 61.5 Ma), in the course of the India–Laxmi Ridge–Seychelles breakup. The main part of the Salsette subgroup consists of tholeiitic basaltic flows with pillows, pillow breccia, and hyaloclastite, which formed in contact with brackish and fresh water in a lagoonal environment. In some places, intertrappeans are represented by fossiliferous shallow water sediments. On the top, trachytic and rhyolitic subaqueous volcaniclastics occur, and some dioritic bodies have intruded nearby. Due to differing fluid rock interactions, several distinctly different secondary minerals developed in the void spaces of the hyaloclastite breccia of the interpillow matrix and in the pillow cavities. The highly permeable hyaloclastite breccia formed an open system, where pronounced precipitation occurred in the early phase and at higher temperatures. In contrast, the pillow cavities were a temporally closed system and contained, for example, more low-temperature zeolites. The genesis of the secondary minerals can be summarized as follows: During initial cooling of the volcanic rocks at about 62 Ma, the first mineralization sequence developed with chlorite, laumontite I, quartz, and calcite I. Ongoing magmatic activity caused reheating and the main phase of precipitation at prehnite–pumpellyite facies conditions. During generally decreasing temperatures, in the range of 270–180 °C, babingtonite, laumontite II, prehnite, julgoldite, yugawaralite, calcite II, ilvaite, pumpellyite, and gryolite developed. The fluid contained SiO2 + Al2O3 + FeO + MgO + CaO, and minor MnO and Na2O, and was predominately mineralized by the decomposition of basaltic glass. Further temperature decreases caused zeolite facies conditions and precipitation of okenite I, scolecite, heulandite, stilbite, and finally chabazite I, in the temperature range of 180 °C to less than 100 °C. As FeO, MgO, and MnO were then absent, an interaction of the fluid with plagioclase is indicated. According to Rb-Sr and K-Ar ages on apophyllite-K, a third phase of precipitation with apophyllite-K, okenite II, and chabazite II occurred in the late Eocene to early Oligocene (30–40 Ma). The new hydrothermal fluid additionally contained K2O, and temperatures of 50–100 °C can be expected.

Meso-Neoproterozoic arc-related sediments of the Xiahe Group in the Qinling block, central China: Implications for the paleogeographic reconstruction of Rodinia

The Meso-Neoproterozoic Rodinia supercontinent formed a coherent large landmass, which was later dispersed over all current major continents and a number of microcontinents. The Qinling block is a Precambrian continental mass, located in the Qinling orogenic belt, which marks the junction of the North China and South China cratons. In this paper, we present a systematic study of the petrology, whole-rock geochemistry and geochronology of metasedimentary rocks from the Xiahe Group, which is a key unit of the Precambrian basement in the Qinling block, to constrain the paleogeographic reconstruction of Rodinia. The studied metasedimentary rocks have detrital zircon ages of 3054–1082 Ma that peak at 1172 Ma and 1582 Ma. The protoliths of the metasedimentary rocks are mainly shales and wackes with maximum depositional ages from 1147 to 1082 Ma, representing a part of a continental arc-related sedimentary sequence. Combining our results with existing data, we propose that their protoliths constituted a sedimentary series including an older sequence of basement and a younger sequence with depositional ages between 1262 and 840 Ma. The detritus that is older than 1266 Ma was sourced from the continental margin of the Indian craton, which was part of the Columbia supercontinent. There was a Paleo-Mesoproterozoic continental nucleus in the Qinling block that split from the margin of the Indian craton during the breakup of Columbia. The source rocks for the younger detritus were arc magmatic rocks in the Qinling block, which formed in a continental arc by oceanic lithosphere subduction during the assembly of Rodinia. A sequence of oceanic subduction beneath the continental nucleus of the Qinling block (1262–981 Ma), arc-continent collision between the continental nucleus and the Indian craton (981–911 Ma), continuous subduction of oceanic crust beneath the block with formation of a mature volcanic arc (929–833 Ma), and continental rifting (833–774 Ma) during the formation of the Qinling block was identified. The block faced the Neoproterozoic ocean during the assembly of Rodinia, and finally rifted off the supercontinent during its breakup to form an isolated arc terrane

Insights into the structure and surface geology of balanced and retrodeformed geological cross sections from the Nizampur basin, Khyber Pakhtunkhwa, Pakistan

The current research work is an attempt to apply the basic geological procedures, methods of geological mapping, surface and subsurface interpretation and restoration of balanced and retrodeformed cross sections from the Nizampur basin, Khyber Pakhtunkhwa, Pakistan. The work also includes the documentation of several surface structural features, i.e., anticlines, synclines and different types of folds and faults exposed in the vicinity of study area. Four central thrust faults were recognized named as Kahi Thrusts along the cross sections. These thrust faults carried the older sequences of rocks over the younger sequences in different portion along the measured cross section. The folded and faulted rocks in the area show that stratigraphic framework comprises of Eocene, Paleocene, Cretaceous and Jurassic succession of rocks. There are Eocene rocks existing in the extreme South of the mapped area with addition of older Cretaceous and Jurassic succession and contains simple and large-scale folds, faults and back thrust. Two structural transect were mapped which encounter different folds and faults, i.e., X-sections AB oriented NS and CD oriented NE-SW. Restoration of the structural transects was calculated and assumed that at the formation of Main Boundary Thrust, the study area was exposed to the tectonic forces which prognosticated 19.5% shortening in rock sequences from Jurassic to Eocene succession along the measured cross section A_B.

High-precision abundances of elements in solar-type stars

Aims. Previous high-precision studies of abundances of elements in solar twin stars are extended to a wider metallicity range to see how the trends of element ratios with stellar age depend on [Fe/H]. Methods. HARPS spectra with signal-to-noise ratios S/N ≳ 600 at λ​ ∼ ​6000 Å were analysed with MARCS model atmospheres to obtain 1D LTE abundances of C, O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Sr, and Y for 72 nearby solar-type stars with metallicities in the range of −0.3 ≲ [Fe/H] ≲ +0.3 and ASTEC stellar models were used to determine stellar ages from effective temperatures, luminosities obtained via Gaia DR2 parallaxes, and heavy element abundances. Results. The age-metallicity distribution appears to consist of the following two distinct populations: a sequence of old stars with a steep rise of [Fe/H] to ∼​ + 0.3 dex at an age of ∼​7 Gyr and a younger sequence with [Fe/H] increasing from about −0.3 dex to ∼​ + 0.2 dex over the last 6 Gyr. Furthermore, the trends of several abundance ratios, [O/Fe], [Na/Fe], [Ca/Fe], and [Ni/Fe], as a function of stellar age, split into two corresponding sequences. The [Y/Mg]-age relation, on the other hand, shows no offset between the two age sequences and has no significant dependence on [Fe/H], but the components of a visual binary star, ζ Reticuli, have a large and puzzling deviation. Conclusions. The split of the age-metallicity distribution into two sequences may be interpreted as evidence of two episodes of accretion of gas onto the Galactic disk with a quenching of star formation in between. Some of the [X/Fe]-age relations support this scenario but other relations are not so easy to explain, which calls for a deeper study of systematic errors in the derived abundances as a function of [Fe/H], in particular 3D non-LTE effects.

Temporal and spatial evolution of the Neogene age Breiðdalur central volcano through 39Ar/40Ar and U-Pb age determination

The volcanic sequences in eastern Iceland provide a cross-section of magmatic activity from the Iceland rift system throughout the Miocene. This study focuses on a high precision age determination campaign of a single Miocene volcanic system, the Breiðdalur central volcano and associated dyke swarm, in order to quantify its evolution. The central volcano consists of: a lower flank of mafic lavas erupted onto a basement of plateau basalts; an upper flank of intermediate and mafic lavas; an 8–10 km wide caldera with associated infill formations; and a summit sequence of lavas and tuffs. This study indicates that the central volcano had a lifespan of around 1 My, from 10.2–9.1 Ma, and started with mafic magmatism. Intermediate magmatism began around 10.04 Ma and the caldera formed between 9.8 and 9.5 Ma, evolving via multiple nested-caldera collapses. Effusive silicic magmatism was predominantly in the youngest sequences between 9.5 and 9.1 Ma. After 9.1 Ma the activity at the central volcano effectively ceased. The volcano became buried by plateau basalt sequences predominantly derived from eruptions at the associated Breiðdalur dyke swarm. Activity on the dyke swarm began around 9.9 Ma and continued to until 7.8 Ma, an additional 1.3 My.

The age–chemical abundance structure of the Galaxy I: evidence for a late-accretion event in the outer disc at z ∼ 0.6

ABSTRACT We investigate the age–chemical abundance structure of the outer Galactic disc at a galactocentric distance of r > 10 kpc as recently revealed by the SDSS/APOGEE survey. Two sequences are present in the [α/Fe]–[Fe/H] plane with systematically different stellar ages. Surprisingly, the young sequence is less metal rich, suggesting a recent dilution process by additional gas accretion. As the stars with the lowest iron abundance in the younger sequence also show an enhancement in α-element abundance, the gas accretion event must have involved a burst of star formation. In order to explain these observations, we construct a chemical evolution model. In this model, we include a relatively short episode of gas accretion at late times on top of an underlying secular accretion over long time-scales. Our model is successful at reproducing the observed distribution of stars in the three-dimensional space of [α/Fe]–[Fe/H]–age in the outer disc. We find that a late-time accretion with a delay of $8.2\,$Gyr and a time-scale of 0.7 Gyr best fits the observed data, in particular the presence of the young, metal-poor sequence. Our best-fitting model further implies that the amount of accreted gas in the late-time accretion event needs to be about three times the local gas reservoir in the outer disc at the time of accretion in order to sufficiently dilute the metal abundance. Given this large fraction, we interpret the late-time accretion event as a minor merger presumably with a gas-rich dwarf galaxy with a mass $M_*\lt 10^{9}\, \mathrm{ M}_{\odot }$ and a gas fraction of ∼75 per cent.

U-Th dating of a Paleolithic site in Guanyindong Cave, Guizhou Province, southwestern China

Guanyindong Cave in southwestern China has received considerable attention in the investigation of Paleolithic hominin origins and evolution in China, due to its rich archaeological finds composed of thousands of stone artifacts and a unique fauna with 23 species of mammalian fossils found. However, despite earlier extensive excavations and descriptive studies, debates still centre around the conflict between previous radiometric age data and evidence from biostratigraphic correlations. In this study, we carried out detailed field investigations and sampling, and obtained 35 U-Th dates on flowstone layers and other datable materials from the cave. The age results from materials in stratigraphic context provide a robust chronological framework of the cave. The data suggest that the deposition of Group B sediments and fossil assemblages widely distributed within the cave should have occurred after ~370 ka but before ~70 ka, with the bulk of the sediments and associated fossils laid down during 200–140 ka. Our new U-Th dates of in situ flowstone layers intercalated with one rhinoceros tooth and several other fossil fragments near the Hall at the centre of the cave constrain the deposition ages of these mammalian fossils to the period between 469 ± 37 and 336 ± 7 ka. Combined our U-Th data with recent OSL dates of Hu et al. (2019), we suggest that Group A sediments and associated fossils were likely deposited episodically from ca. 90 ka to <40 ka. Overall, our data indicate that the cave development started >469 ± 37 ka ago, whilst the cave system framework took shape as we see today >340 ± 10 ka ago. Subsequently, the cave might have experienced several flooding and washout events, resulting in recycling and mixing of older sediments and fossils into younger sequences, a hypothesis consistent with tight clustering of both U-Th ages of speleothems in this study and the OSL dates of clastic sediments (Hu et al., 2019). This would reconcile the contradiction between the great antiquity of mammalian fossils inferred from biostratigraphic correlation and the much younger radiometric dates of materials in stratigraphic context, and explain the lack of technological advance despite an apparently long presence of the “Guanyindong culture”, as well as the presence of the Levallois technologies. In this regard, our U/Th age data, combined with other recent studies, have resulted in an improved understanding of Paleolithic hominid evolution and stone technologies in south China.

Tracking the key parameters stimulating organic carbon productivity, accumulation rate and preservation based on foraminiferal proxies in the subsurface Miocene sediments in north Sinai, Egypt

Productivity, redox conditions and sedimentation rate constrain the enrichments of organic matters and under suitable conditions they can trigger larger enrichments. These parameters are tracked in the subsurface Miocene sediments in four wells on east to west transect across north Sinai. These wells are Abu Roda-1, Misfaq-1, Teffah-1 and Einab-1. The Miocene sections cover the Aquitanian, Burdigalian, Langhian, Serravalian and Tortonian. The tracking is based on the proxies of planktonic and benthic foraminifera that offer many solutions in the application of the equations used to calculate these parameters. The first of these parameters is the sedimentation rate which is calculated for different time segments based on the planktonic foraminifera bioevents. The sedimentation rates are correlated throughout the basin. The second parameter is the water depth that is obtained from conversion of the scores of component 1 resulted during the routine statistical analysis of the benthic foraminifera by cluster and principal component analyses. These analyses are used also in assessment of redox condition and eutrophication. The sedimentation rates and water paleobathymetry alongside the measured Corg are used to calculate the paleoproductivity and to determine four stratigraphic sequences (Seq1, Seq2, Seq3 and Seq4). The tracking of these parameters reveal higher productivity levels in the Seq1 (Aquitanian and Burdigalian) accompanied with dysoxic and mesotrophic conditions, however the lower sedimentation rates are not optimum to stimulate enough burial efficiency that reduced values of Corg. In the younger sequences (Seq2-4), the higher sedimentation rates increase the burial efficiency and values of Corg despite the lower paleoproductivity and oxic oligotrphic conditions.

New insights into the structure of the South Caspian Basin from seismic reflection data, Gorgan Plain, Iran

This research presents an integrated study of 2D seismic reflections and calibrated well data to outline the structural development of the Gorgan Plain on the border of the South Caspian hydrocarbon basin, in the Alborz and Kopeh-dagh ranges of northeast Iran. Eight seismic horizons, including two unconformities, have been identified, ranging in age from Early Jurassic to Quaternary. Analysis and interpretation of geophysical data provide an understanding of the structural geology of the Gorgan Plain, crucial for investigation of structural traps. Seismic interpretation indicates structural features such as deep reverse listric faults (inverted normal faults) for older formations; strike-slip and normal faults in younger sequences; dome and basin interference patterns of folding for all the top formations. Well data demonstrate the occurrence of a disconformity at the base of Upper Cretaceous beds and an angular unconformity at the base of Paleogene. Evidence identified in well and seismic-reflection data proves a complex pattern of tectonic phases since the Early Jurassic. It seems reasonable to suppose that these structural patterns are related to a change in direction of tectonic compression, which in turn has produced structural hydrocarbon traps in crests of domes in the Gorgan area.

Carbonate production, accumulation and sea-level change in fault-block platform setting: a case study on the Albian sequences in Central Tunisia

The Albian series have been deposited on both sides of a major E–W paleogeographic fault, which was inherited in the early stages of the Tethyan-rifting phase. To the south of this fault, a shallow platform domain (footwall block or horst) occurred and is relayed northward by a slope-deep shelf setting (hanging wall block or graben). The platform to basin transition was analyzed northward of this fault nearby M’rhila Mountains. A detailed sedimentological study, coupled with a tectonic analysis, indicates that the Albian sedimentary deposits consist of four third-order depositional sequences. The three lower ones are only present in the deep-shelf setting and include substantial carbonate accumulations. The latter deposits are generally arranged into alternating mud-rich-bedded limestone and conglomeratic levels. Most of this material was exported from the adjacent shallow platform by mass flow and suspension transport processes. In the studied series, the maximum carbonate accumulation is recorded in the deep shelf during the moderate transgressive increasing and the late highstand decreasing rates of sea-level rise. However, the minimum carbonate sedimentation is thought to be linked to both the minimum lowstand and the maximum transgressive sea-level rise. The uppermost depositional sequence—which occurs on both sides of the major fault, is different from the three lower ones as it includes only scarce thin re-sedimented limestone beds. The youngest sequence is related to an important interplay between a pulse of tectonic subsidence and the major see level rise that happened during the upper Albian (100–98.9 Ma), resulting in a regional collapse of the substratum and the drowning of the carbonate factory situated southward. Therefore, the uppermost sequence is considered as a tectonically originated depositional sequence rather than a “pure” eustatic one. The organic-rich deposits associated to this sequence south and north of the major fault correlate well with the global anoxic events. The present study case represents a good example illustrating the role of local tectonics and global eustatic fluctuations in controlling not only the facies and thickness distribution but also the carbonate production and accumulation.

Sedimentology, stratigraphic context, and implications of Miocene intrashelf bottomset deposits, offshore New Jersey

Drilling of intrashelf Miocene clinothems onshore and offshore New Jersey has provided better understanding of their topset and foreset deposits, but the sedimentology and stratigraphy of their bottomset deposits have not been documented in detail. Three coreholes (Sites M27–M29), collected during Integrated Ocean Drilling Program (IODP) Expedition 313, intersect multiple bottomset deposits, and their analysis helps to refine sequence stratigraphic interpretations and process response models for intrashelf clinothems. At Site M29, the most downdip location, chronostratigraphically well-constrained bottomset deposits follow a repeated stratigraphic motif. Coarse-grained glauconitic quartz sand packages abruptly overlie deeply burrowed surfaces. Typically, these packages coarsen then fine upwards and pass upward into bioturbated siltstones. These coarse sand beds are amalgamated and poorly sorted and contain thin-walled shells, benthic foraminifera, and extrabasinal clasts, consistent with an interpretation of debrites. The sedimentology and mounded seismic character of these packages support interpretation as debrite-dominated lobe complexes. Farther updip, at Site M28, the same chronostratigraphic units are amalgamated, with the absence of bioturbated silts pointing to more erosion in proximal locations. Graded sandstones and dune-scale cross-bedding in the younger sequences in Site M28 indicate deposition from turbidity currents and channelization. The sharp base of each package is interpreted as a sequence boundary, with a period of erosion and sediment bypass evidenced by the burrowed surface, and the coarse-grained debritic and turbiditic deposits representing the lowstand systems tract. The overlying fine-grained deposits are interpreted as the combined transgressive and highstand systems tract deposits and contain the deepwater equivalent of the maximum flooding surface. The variety in thickness and grain-size trends in the coarse-grained bottomset packages point to an autogenic control, through compensational stacking of lobes and lobe complexes. However, the large-scale stratigraphic organization of the bottomset deposits and the coarse-grained immature extrabasinal and reworked glauconitic detritus point to external controls, likely a combination of relative sea-level fall and waxing-and-waning cycles of sediment supply. This study demonstrates that large amounts of sediment gravity-flow deposits can be generated in relatively shallow (~100–200 m deep) and low-gradient (~1°–4°) clinothems that prograded across a deep continental shelf. This physiography likely led to the dominance of debris flow deposits due to the short transport distance limiting transformation to low-concentration turbidity currents.

High-Frequency Sequences in the Quaternary of Pelotas Basin (coastal plain): a record of degradational stacking as a function of longer-term base-level fall

ABSTRACT: The aim of this work was to analyze the sedimentary record of the coastal plain of Pelotas Basin, placing it in the context of temporal and spatial scales, and proposing a stratigraphic hierarchical framework. The coastal plain, located in southern Brazil and in northern Uruguay, is mainly formed by four Quaternary barrier-lagoon systems. Three of these systems were studied through the integration of surface and subsurface data (geomorphological and topographical mapping, outcrops description, geoprocessing, dating and Ground Penetrating Radar - GPR - records) and interpreted as the preserved, onshore portion of depositional sequences mainly controlled by glacioeustatic cycles of about 100 kyr. The stacking pattern comprising these sequences is progradational with seaward downsteping (highest sea-levels measured: 9.5, 8 and 3 m, respectively), comprehending a degradational sequence set, or the regressive/falling stage systems tract of a higher order depositional sequence identified in seismic sections, with about 0.5 Ma. The youngest sequence has diachronous systems tracts - while some sectors have already transitioned from the transgressive to the highstand/falling stage systems tract, others are still under a transgressive context. It indicates that, in this time and scale, the sea level is not the main control of coastal evolution, and autogenic factors are fundamental in the run of geological record.

The Black Sea level from the Last Glacial Maximum to the present time

Construction of the Black Sea level curve in the interval from the Last Glacial Maximum (LGM) to the present is the main purpose of this article. This curve was created on the basis of seismostratigraphic analysis and data from other investigations. Existing seismostratigraphic subdivisions have been corrected. The seismic sections of the uppermost part of the Upper Pleistocene and the Holocene display two sequences (cycles). Highstand normal regressive, forced regressive, lowstand normal regressive, and transgressive genetic units within the older sequence have been distinguished, i.e., all system tracts. The lowstand normal regressive tract in the younger sequence was not recognized in the seismic sections. This fact evidences catastrophic inundation of the brackish Black Sea from the Mediterranean (Marmara) salt waters during the Early Holocene. Synchronization between sea-level changes and climatic variations is shown. The Black Sea level in relation to the World Ocean level, the Marmara Sea level, and the Caspian Sea level have been examined. For this end, the ways and time of formation of the recognized subunits in seismic sections from the Dardanelles Strait, Marmara and Aegean Seas were explained. Juxtaposition between the results of this study and solutions of other investigations and hypotheses concerning the Black Sea level changes is done as a discussion. The chemical aragonite intercalations in the base of the sapropel mud, the seismostratigraphic analysis, and 14C dating prove redepositions over vast areas of seabed. The constructed Black Sea level curve is consistent with all data of different nature (e.g., sedimentological, climatic, biostratigraphic, seismostratigraphic, and 14C dating).

Sources and provenance of the Neoproterozoic placer deposits of the Northern Kazakhstan: Implication for continental growth of the western Central Asian Orogenic Belt

We present results of in situ analysis of zircon U-Pb ages, Hf isotopic compositions for detrital zircons combined with whole-rock Nd isotopic data for the Neoproterozoic quartzites and zircon-rutile placer deposits in quartzite-schist sequences of the Kokchetav, Ishkeol'mes and Erementau-Niyaz terranes of the Northern Kazakhstan and discuss possible provenances and position of these terranes in Mesoproterozoic. Concordia ages of detrital zircons from the Northern Kazakhstan part of the Central Asian Orogenic Belt (CAOB) demonstrate age peaks in intervals ca. 1.13–1.46, 1.65–1.78, 1.86–1.92, 2.70 and 2.84 Ga. Obtained data indicate that Mesoproterozoic, latest Paleoproterozoic (Staterian), late Paleoproterozoic '(Orosinian) and Neoarchean rocks were the sources of these metasediments. Hf-in-zircon and Nd whole rock data show that the Mesoproterozoic and latest Paleoproterozoic rock complexes were originated from mainly short-lived juvenile and mixed crustal-juvenile sources that imply their derivation in subduction-related oceanic and continental arc setting or from mafic underplating. Rocks with ages of ca 1.65–1.78, 1.86–1.92, 2.70 and 2.84Ga have not been recognised previously in the western CAOB. It is possible that these rocks were completely eroded or overlapped by younger sequences and composed the buried basement of Precambrian terranes of the western CAOB. Comparison of Meso-Paleoproterozoic age patterns for the Northern Kazakhstan, Tian Shan and Tarim craton demonstrate that the crustal basement of the Northern Kazakhstan is similar to the Chinese Central Tian Shan terrane and different from the Archean basement formation of the Tarim Craton. Age peaks at ca. 1.92–1.86, 1.78–1.65 and 1.46–1.13Ga, identified for detrital zircons from Neoproterozoic zircon-rutile placer deposits of the Northern Kazakhstan correspond to the formation and breakup of the Columbia/Nuna supercontinent and assembly of the Rodinia supercontinent or large continental domain.

Holocene palaeoenvironmental evolution of the Ebro Delta (Western Mediterranean Sea): Evidence for an early construction based on the benthic foraminiferal record

Major Mediterranean deltas began to develop during a period between 8000 and 6000 yr BP when the rate of fluvial sediment input overtook the declining rate of sea-level rise. However, different authors have argued that the Ebro Delta primarily formed during the late Middle Ages as a consequence of increased anthropogenic pressure on its river basin and these arguments are supported by the scarcity of previous geological studies and available radiocarbon dates. To reconstruct the environmental evolution of the Ebro Delta during the Holocene, we used micropalaeontological analysis of continuous boreholes drilled in two different locations (Carlet and Sant Jaume) on the central delta plain. Different lithofacies distributions and associated environments of deposition were defined based on diagnostic foraminiferal assemblages and the application of a palaeowater-depth transfer function. The more landward Carlet sequence shows an older and more proximal progradational delta with a sedimentary record composed of inner bay, lagoonal and beach materials deposited between 7600 and &gt;2000 yr BP under rising sea-level and highstand conditions. This phase was followed by a series of delta plain environments reflected in part by the Carlet deposits that formed before 2000 yr BP. The Sant Jaume borehole is located closer to the present coastline and contains a much younger sequence that accumulated in the last 2.0 ka during the development of three different deltaic lobes under highstand sea-level conditions. The results of this study reinforce the idea that the Ebro Delta dates to the early Holocene, similar to other large Mediterranean deltas.

The sedimentary infill of incised valley systems on the southeast coast of Australia: a tectonically stable coastal margin

Integrated sedimentological and micropaleontological (foraminifers and ostracods) analyses of two 55 m long borehole cores (S3 and S4) drilled in the subsurface of Lesina lagoon (Gargano promontory—Italy) has yielded a facies distribution characteristic of alluvial, coastal and shallow-marine sediments. Stratigraphic correlation between the two cores, based on strong similarity in facies distribution and AMS radiocarbon dates, indicates a Late Pleistocene to Holocene age of the sedimentary succession.Two main depositional sequences were deposited during the last 60-ky. These sequences display poor preservation of lowstand deposits and record two major transgressive pulses and subsequent sea-level highstands. The older sequence, unconformably overlying a pedogenized alluvial unit, consists of paralic and marine units (dated by AMS radiocarbon at about 45–50,000 years BP) that represent the landward migration of a barrier-lagoon system. These units are separated by a ravinement surface (RS1). Above these tansgressive deposits, highstand deposition is characterised by progradation of the coastal sediments.The younger sequence, overlying an unconformity of tectonic origin, is a 10 m-thick sedimentary body, consisting of fluvial channel sediments overlain by transgressive–regressive deposits of Holocene age. A ravinement surface (RS2), truncating the transgressive (lagoonal and back-barrier) deposits in core S4, indicates shoreface retreat and landward migration of the barrier/lagoon system. The overlying beach, lagoon and alluvial deposits are the result of mid-Holocene highstand sedimentation and coastal progradation.