Eustatic Sea-level Fluctuations Research Articles

Sequence stratigraphic architecture and depositional evolution of the early Eocene-early Miocene Al Jabal Al Akhdar carbonate successions, N Cyrenaica Promontory, NE Libya – Interplay of tectonics and eustasy

The interactions of tectonics and eustasy on the stratigraphic architectural evolution of the early Eocene-early Miocene Al Jabal Al Akhdar carbonate sedimentary successions were evaluated. This evaluation was achieved through detailed analyses of microfacies, depositional interpretation, and sequence stratigraphic framework of five measured sections located within the Al Jabal Al Akhdar Uplift, northeast Libya. The study interval was subdivided into distinct microfacies based on lithological changes, grain size and components, sedimentary texture and structures, fossil contents, color, and vertical stacking pattern. Six major depositional settings were delineated: restricted lagoon, open marine lagoon, platform margin and shoals, platform-margin reefs, foreslope, and middle to lower slope. Four third-order unconformity-bounded depositional sequences were identified based on vertical and lateral facies distribution, variations in fossil contents, and diagenetic features. Each sequence is composed of a transgressive-regressive interval, except for the younger sequence, which only contains a transgressive unit. Four evolutionary stages are recognized: initiation, growth, high-relief platform, and subaerial exposure. Subsidence resulting from tectonism and sediment loading, coupled with rising sea-level, created the accommodation space for the sedimentation of the studied carbonates. Repeated eustatic sea-level fluctuations controlled the internal stratigraphic heterogeneity and sequence development. Tectonic uplift caused a major sea-level retreat, resulting in the emersion of the carbonate sequences. The pre-existing Mesozoic and Paleocene sequences that underwent major uplift during the Late Cretaceous-early Eocene formed a shallow-water positive-antecedent topography for the formation of the carbonate sediments. This study establishes a carbonate sequence stratigraphic hierarchy of different cyclic sedimentation orders and improves our knowledge of sedimentary and stratigraphic architectural evolution and depositional mechanisms of carbonate platforms in an inverted basin setting. This knowledge can aid in predicting the distribution of lithofacies and depositional systems of economic importance.

A middle Miocene to Quaternary sedimentary and palaeoenvironmental record from the western continental shelf of South Africa

The sedimentary record of the western South African continental shelf is condensed compared to the continental slope and contains erosional unconformities, owing to periods of non-deposition, eustatic sea-level fluctuations, episodic uplift and intensified continental aridity. Despite this, the sedimentary record of the continental shelf provides important information on the depositional history and palaeoenvironmental evolution of the region. A core retrieved from the western shelf of South Africa was analysed for its sedimentary composition, lithological variation, foraminiferal content and its relation to the palaeoenvironment of the region. Four depositional facies were identified along the core, namely quartzitic sand, sandy mud, and glauco-phosphatic sand and a glauco-phosphatic gravel. The basal facies consisting of quartzitic sand is interpreted to have been deposited between 15.90 and 14.60 Ma, corresponding to the timing of the Mid-Miocene Climatic Optimum (MMCO). The highly quartzitic nature of the sediments indicate a high terrestrial influence from fluvial sources. The overlying sandy mud facies was deposited between 14.60 and 13.90 Ma based on planktic foraminiferal biostratigraphy. Foraminiferal analyses of these two facies that were deposited in the Langhian stage of the middle Miocene point to subtropical sea surface conditions and mesotrophic benthic environments. Sea level was noticeably higher during the MMCO and part of the cooling period following the MMCO. An erosional surface that spans 10.77 Myr, equal to the late Miocene (13.90 Ma) to early Pliocene (3.13 Ma), marks the boundary between the two Langhian facies and the overlying two Pleistocene facies, consisting of coarser grained glauco-phosphatic gravelly sand units. The Pleistocene environment on the shelf is interpreted to contrast with the Langhian environment, where cooler, shallower conditions and a more eutrophic benthic environment was prevalent, during a time that Benguela upwelling intensified with higher frequency and higher amplitude sea level fluctuations. Palaeobathymetric interpretations indicate that middle Miocene sea-level in the region were up to 77 m higher than present day and 101 m lower in the Pleistocene, in-line with previous global studies. Glauco-phosphatic content that increase up-core also marks the shallowing of the environment under high productivity conditions.

Palaeoecology of calcified microfossils from the Lower Devonian (Pragian-Emsian) of Sierra Morena (SW Spain)

Lower Devonian (Pragian-Emsian) reefal deposits of Sierra Morena (SW Spain) contain locally abundant calcified cyanobacteria, calcareous algae, and various microfossils including foraminifers. Calcified cyanobacteria are represented by Girvanella spp. A–C, which form crusts and clumps of various shapes. Supposed green algae (?Dasycladales) are represented by a new genus with one new species, Bediaella hispanica gen. et sp. nov. Algospongia include Vasicekia margaritula (Saltovskaya, 1986) n. comb. Microproblematica are represented by Rothpletzella sp. The studied assemblages indicate photic and warm conditions in a shallow and well-agitated environment with normal salinity, and probably mirror episodes of shallowing due to eustatic sea level fluctuations.

Evaluation of the Neogene depositional dynamics in the Malay-Tho Chu Basin based on seismic analysis: effects of local and regional tectonism and paleoclimatic variations

Depositional environments in areas located near sea level are vulnerable to even subtle changes in both tectonism, climate and eustatic sea level. Sorting out mechanisms behind depositional changes in inner shelf-margins and epeiric seas is therefore far from straight forward. The epeiric Malay-Tho Chu Basin, located in the shallow Gulf of Thailand offshore Vietnam, contains a thick uppermost Oligocene to Recent post-rift succession. Based on 18000 km of 2D seismic profiles, the uppermost Oligocene-Recent succession is subdivided into six seismic sequences. Seismic facies mapping of each sequence complemented by information from industry completion reports of 14 wells document a gradual increase in marine influence from latest Oligocene through Middle Miocene time. The increased marine influence reflects the propagation and opening of the southwestern spreading arm of the East Vietnam Sea (South China Sea (East Sea)) combined with rapid subsidence in the Malay-Tho Chu Basin resulting from fast thermal relaxation following Oligocene rifting and amplified by mild fault-controlled subsidence in especially the western part of the area. From the latest Middle Miocene, slowed subsidence and regression occurred in association with uplift in the nearby southwestern East Vietnam Sea. From the latest Miocene, and during the Pliocene and Pleistocene, subsidence rates increased promoting marine conditions towards the East Vietnam Sea in the southeast. Meanwhile, Mekong River avulsion combined with hinterland uplift stimulated fluvial and alluvial deposition in the northern and western parts of the basin. The long-term depositional pattern was controlled primarily by tectonics, drainage evolution and climate. Meanwhile, flood- and delta plain deposits intercalated with stacked fluvial incisions, often filled by estuarine deposits, document short-lived environmental changes most likely controlled by eustatic sea level fluctuations. Such intervals developed during latest Middle Miocene to Pleistocene periods of slow subsidence or fast depositional rates and are interpreted to be the result of substantial eustatic sea level fluctuations.

Tectono-stratigraphic and sedimentological analysis of the Early to Middle Devonian Floresta Formation: Insights from the Floresta Massif, Northern Andes, Colombia

A comprehensive tectono-stratigraphic and sedimentological investigation of Early to Middle Devonian rocks was conducted in the southern Floresta Massif and adjacent regions in the Northern Andes of Colombia. A substantially reduced thickness of the Floresta Formation compared to prior studies is suggested here, attributable to pronounced stratal deformation and the prevalence of recumbent folds throughout the area. The deformation in the Floresta Formation manifests as atypical recumbent folds, diverging from the structural behavior observed in the underlying and overlying strata of the El Tibet and Cuche formations respectively, which exhibit minimal deformation. Our findings also reveal that the Floresta Formation accumulated under shallow-water platform conditions, subject to eustatic sea-level fluctuations. This resulted in distinct episodes of carbonate and siliciclastic deposition, with terrigenous sediments sourced from continental origins, potentially encompassing a combination of cratonic areas and uplifted blocks. The identification of a plausible stage of carbonate silicification signifies a post-diagenetic transformation. The sedimentary rocks of the Floresta Formation reached the upper epizone conditions, in proximity to the transition between the epizone and the upper anchizone, which suggests a maximum depth and temperature of ~5-7 km and ~300 °C, respectively. This contribution provides new insights into the geological history of the region, emphasizing the importance of scrutinizing Early to Middle Devonian rocks within the broader geological context of the Northern Andes.

Investigating the controls on architecture and facies distribution of a carbonate ramp to shelf system: Insights from stratigraphic forward modeling of the Jurassic Smackover Formation, Gulf of Mexico

To develop a better understanding of the controls on the stratigraphic architecture of carbonate systems, it is necessary to quantify the impact of the physical and chemical variables responsible. The growth, distribution, and nature of carbonate factories are dependent on various space and time-dependent variables, such as paleotopography, accommodation, sediment supply, energy and slope of the system, and water chemistry.The Upper Jurassic Smackover Formation is a heterogeneous hydrocarbon source rock and reservoir in the semi-restricted Conecuh Embayment of southwestern Alabama. It consists of a lower transgressive unit composed of microbialite and mudstone/wackestone, and an upper regressive mixed carbonate-siliciclastic unit composed of oolitic packstone-grainstone, microbialite, bioturbated to laminated carbonate mudstone, and shale. The physiographic setting of the Conecuh Embayment, along with the variability in the carbonate factory types, eustatic sea level fluctuations, and sea-water circulation presents an exceptional site for evaluating the controls on carbonate platform/shelf margin to slope architecture.Stratigraphic forward modeling using DionisosFlow, calibrated with a geologic cross-section built from well log and core data, was carried out to test the impact of antecedent topography, accommodation, and carbonate factory type on the facies distribution and architecture of the carbonate shelf. Results of our study indicate that geometries in the transgressive Smackover shelf are controlled by accommodation and rate of carbonate production, while limited accommodation controlled the stratigraphic architecture of the regressive system.

Calcareous dinoflagellate blooms during the Late Cretaceous 'greenhouse' world-a case study from western Ukraine.

The Late Cretaceous was a unique period in the history of the Earth characterized by elevated sea levels, reduced land area, and significantly high concentrations of atmospheric CO2 resulting in increased temperatures across the globe-a 'Greenhouse World'. During this period, calcareous dinoflagellate cysts (c-dinocysts) flourished and became a ubiquitous constituent of calcifying plankton around the world. An acme in calcareous dinocysts during the Albian to the Turonian coincided with the highest recorded seawater surface temperatures and was possibly linked to conditions that favored calcification and a highly oligotrophic system in European shelf seas. This study examines the potential applicability of c-dinocysts as a proxy for paleoenvironmental conditions based on their assemblage changes plotted against foraminiferal occurrences and microfacies analysis. The material was extracted from the upper Turonian chalk of the Dubivtsi region in western Ukraine. An inverse correlation was observed between species diversity and the number of c-dinocyst specimens. Nutrient availability gradients apparently determined important changes in the calcareous dinocysts distribution. These trophic changes were likely caused by the interplay of eustatic sea-level fluctuations and Subhercynian tectonic activity leading to changeable nutrient inputs from the nearby land.

The upper cretaceous carbonate sediments of the Ras Budran Field, Gulf of Suez, Egypt: stacking patterns and depositional controls

The present study interprets the carbonate stacking patterns and their depositional controls in the Upper Cretaceous strata of the Ras Budran Field in the Gulf of Suez, Egypt, on the basis of integrated well logging and a geological report provided. A set of well logs was run for two wells (RB-A2 and RB-B2), comprising gamma ray, resistivity, density, neutron, sonic, and photoelectric factor. Composite logs and geological reports were also used to help deduce the lithological and biological description of the stratigraphic units under investigation. The stacking patterns of the carbonate rocks yielded three types of electro-facies. The first facies covers the lower part of the Brown Limestone (early Campanian) and reflects a cylindrical (aggrading) stacking pattern. This facies indicates keep-up carbonate deposition in a heterogeneous facies accumulated in shallow water. The second facies covers the upper part of the Brown Limestone (late Campanian) and displays a funnel (prograding) stacking pattern. This facies indicates the depositional setting of a shallow shoreline. The third facies covers the Sudr Chalk (Maastrichtian), for which a serrated stacking pattern indicates an aggradational environment. This pattern indicates a marine depositional setting both distal and deep. Therefore, the formation and evolution of the cyclical stacking pattern of the carbonate rocks reflects variations in accommodation potential that determines the environmental changes. The evolution of these deposits is mainly attributed to a combination of eustatic sea-level fluctuations and tectonic episodes within the basin.

ENSO may have contributed to sea level changes in the Gulf of Thailand during the Late-Holocene

The Gulf of Thailand is ideal for studying eustatic sea level fluctuations in Southeast Asia due to its shallow basin and tectonic stability. However, our understanding of how this region’s relative sea level (RSL) has fluctuated over the Holocene epoch is far from complete. In this study, we used lithostratigraphy, loss on ignition, grain size, and pollen analyses to reconstruct the environmental changes in the Sam Roi Yot wetland, which was significantly influenced by seawater intrusion, driven by fluctuations in RSL in the Gulf of Thailand. Therefore, the analyzed pollen records of the sediment core from the wetland reflected variabilities in the RSL in the Gulf of Thailand. Subsequently, we found that after a sea level highstand prior to 4000 cal y BP, the RSL gradually fell with two significant regressions at c. 2950 and 1850–1450 cal y BP before rising at 1450–1050 cal y BP and declining after that. The inconsistency between RSL reconstruction based on our results and the global sea level changes simulated by the Glacial Isostatic Adjustment (GIA) model further suggests that long–term El Niño Southern Oscillations (ENSO) variabilities may have played a significant role in sea level changes in the Gulf of Thailand over the Late-Holocene period. Thus, during extended El Niño or La Niña conditions, the sea level would have been consistently lower or higher than expected from eustatic and isostatic processes alone. Overall, this study emphasizes the importance of considering regional factors such as ENSO to understand sea level changes in Southeast Asia.

Submerged reef and inter-reef morphology in the Western South Atlantic, Abrolhos Shelf (Brazil)

Submarine geomorphology is a main environmental driver defining the seascape and associated benthic habitat. In this sense, eustatic sea-level fluctuations plays a major role in shaping the morphology of the seafloor. During the last deglaciation, changes in rates of sea-level rise led to moments of stillstand and rapid rise acceleration, forming and drowning distinct shelf geomorphological features. Here, we present and discuss the morphology and associated habitats related to submerged reefs and inter-reef areas along the southern Abrolhos inner shelf (western South Atlantic, Brazil). Our aim is to discuss the morphological evidence of reef drowning and related sea-level/climate events, and the formation of distinct habitats during the post-Last Glacial Maximum transgression. Multibeam echosounder data and sub-aquatic video footage are the basic datasets. Automatic seabed classification was carried out by combining morphometric analysis, acoustic backscatter and ground-truthing. Results show the presence of two clusters of submerged reefs (14-23 m and 24-35 m deep), associated with longitudinal and transverse bedforms, banks, and shelf-incised valleys. Rhodolith beds comprise the main inter-reef benthic habitat. Distinct reef clusters defined by reef top depths indicate that reef drowning occurred in two different moments. The shallower reefs are likely related to the rapid sea-level rise associated with MWP 1C, while deeper reefs are interpreted as remanent carbonate build-ups. Habitats are strongly influenced by the marine geodiversity forming a mosaic of reef, inter-reef and bedforms classes that seem to be associated with an antecedent paleo landscape marked by shelf-incised valleys and paleochannels. Submarine geomorphology is an environmental component that drives geodiversity and is driven by distinct seafloor processes acting in different time and spatial scales, as well as being able to quantify biogenic phenomena, for example, surrogacy and provide records of sea-level changes.

Sequence stratigraphy and reservoir quality of the Gulf of Suez syn-rift deposits of the Nukhul formation: Implications of rift initiation and the impact of eustacy and tectonic on deposition

The Nukhul Formation represents the sediments deposited during the earliest phase of the syn-rift period in the Gulf of Suez rift. It is the primary hydrocarbon reservoir for fifteen fields in the region. However, the timing of rifting needs to be better constrained, and the influence of local tectonics and global eustatic sea-level fluctuations on reservoir quality and deposition is still being determined. This research aims to establish a stratigraphic sequence framework, determine the age of the Suez Rift commencement, use changes in paleobathymetry, and assess reservoir quality. The methods employed involve the analysis of four boreholes in the Abu Rudeis-Sidri field, incorporating biostratigraphy, well-logs, and 3D seismic data. The integrated paleo-structure and biostratigraphic analyses indicate that the beginning of rifting in the Gulf of Suez occurred at 23.53 Ma at the first common occurrence (FCO) of Trilobatus primordius. The paleobathymetric analysis of the Nukhul Formation reveals deeper paleo-water depths during certain intervals, indicating deposition during a phase of high subsidence and rift-climax. The Nukhul stratigraphic sequence reflects sea-level changes leading to shifts in accommodation, and facies changes, erosion, and sequence formation during the late Chattian and early Burdigalian stages. However, the reservoir characterization of the Nukhul Formation is significantly affected by various factors, including cementation, pore system properties, sediment sorting, rift system geometry, and relative sea-level fluctuations. These factors must be carefully considered in any regional exploration or development efforts. The study also reveals that tectonic activity played a role in forming fault-bounded basins, and eustatic sea-level changes influenced the rate and timing of sediment accumulation. These findings can aid in predicting the distribution of the Nukhul sedimentary deposits and improve the ability to explore and develop their resources.

Ediacaran-Ordovician tectonic and geodynamic drivers of Great Unconformity exhumation on the southern Canadian Shield

The Great Unconformity erosion surface between Paleozoic sedimentary rocks and Archean-Proterozoic basement has been related to erosion occurring during Snowball Earth glaciations, eustatic sea level fluctuations, and a range of tectonic and/or geodynamic mechanisms. Each class of mechanism predicts distinct timing and spatial patterns of exhumation. Snowball Earth glacial erosion is limited to 717-635 Ma and concentrated in narrow ice streams on continental margins. Sea-level related erosion is unconstrained in time but also spatially limited to continental margins. Tectonic and geodynamic mechanisms, in contrast, can result in exhumation distributed more broadly in time and space. We combine new zircon and apatite (U-Th)/He thermochronology data (ZHe, AHe) with independent paleodepth information from a continental interior location in southeastern Ontario, Canada to constrain the timing, magnitude, and regional pattern of exhumation associated with the Great Unconformity along a ∼650 km-long transect across the southern Canadian Shield. Here, the unconformity is defined by Middle Ordovician carbonates atop Archean-Proterozoic basement. ZHe analyses for seven basement samples display a range of dates from 960 ± 20 Ma to 37.5 ± 0.9 Ma that correlate negatively with radiation damage. AHe dates are ∼300-200 Ma and generally consistent across samples regardless of radiation damage. Independent evidence supports emplacement of both the 590 +2/-1 Ma Grenville dikes and the 577 ± 1 Ma Callander Complex in the study region at depths ≥6 km. The combined data require ≥6 km of exhumation between ca. 590-577 Ma and 470 Ma in the middle of our transect, with multi-km erosion up to ≥5 km elsewhere in the study area, well after the ca. 717-635 Ma Snowball Earth glaciations. These outcomes expand the spatial extent of an Ediacaran to early-Paleozoic exhumation signal previously inferred elsewhere across the Shield to ∼1.1 million km2. Thick Ediacaran successions on the Laurentian margins are complementary depositional signals of this erosion. The enormous spatial extent of Great Unconformity exhumation across the continental interior of the Canadian Shield is incompatible with glacial erosion and eustatic sea-level change as the primary causes. Instead, we attribute exhumation to tectonic and geodynamic mechanisms, which may include isostatic rebound, dynamic topography, plume activity associated with the Central Iapetus Magmatic Province, rifting during opening of the Iapetus Ocean, and development of the Transcontinental Arch.

Facies, cycle stratigraphy, and heterogeneity of the Clear Fork carbonates in the Eastern Shelf of the Permian Basin, Texas

The Clear Fork carbonate reservoirs at Iatan East Howard field are highly heterogeneous. Facies analysis and cycle stratigraphy are employed to characterize the Clear Fork Formation and reservoir heterogeneity at the field. One-dimensional (1-D), vertical stratigraphic analyses started from meter-scale cycles to cycle sets, system tracts, and then depositional sequences. A reverse process was followed to construct a 2-D framework from a 1-D stratigraphy. In the downdip areas, the Clear Fork Formation is dominated by subtidal facies; toward the updip, peritidal facies become more abundant and depositional facies may alternate between shallow subtidal and tidal-flat facies. Approximately 56 well-developed, meter-scale, upward-shallowing cycles were defined in the Clear Fork cores facilitated by wireline logs. Most of them have bioclast wackestone and packstone in the lower part and are capped by fenestral peloid packstone, silty to sandy dolostone, and/or dark mudrocks. Six cycle sets (high-frequency sequences) were identified, and two depositional sequences were recognized. Sequences are correlatable, but it is challenging to correlate meter-scale cycles. The Clear Fork cycles display relatively consistent thickness and facies stacking pattern plus evidence of subaerial exposure and erosion of subtidal facies, suggesting an allocyclic control and having been the result of eustatic sea-level fluctuations. Reservoir pores (porosity >4%) commonly occur in the transgressive system tracts and lower highstand system tracts (HSTs) within individual high-frequency sequences; the upper HSTs commonly consist of amalgamated peritidal deposits and are generally tight because pores (mostly fenestral and intergranular pores) have been occluded by anhydrite and carbonate cements. These new findings contrast the previous studies showing that porosity is typically higher in the cycle-set-top or cycle-top facies (mainly tidal-flat deposits) in the formation. Reservoirs are areally discontinuous and vertically compartmentalized by multiple nonporous zones. Reservoir characterization is critical to improving recovery efficiency. This case study provides an insight into complex facies and cycle stacking patterns as well as stratigraphic architecture on a carbonate platform during a waning icehouse phase and can help to better understand the controls on the distribution and quality of such carbonate reservoirs.

Coralline algal and foraminiferal records of the Pliocene paleoclimatic conditions and water-depth changes in the northern South China Sea

Detailed paleontological and sedimentological data from the Pliocene interval of core XK-1 allow for a detailed documentation of the carbonate system in the northern South China Sea (SCS). Six facies are identified. Based on a comprehensive analysis of facies changes, the paleoclimatic conditions and paleowater depths during the Pliocene in the Xisha area in the northern SCS are reconstructed. The changes in the abundance of the algal genus Sporolithon and the planktonic foraminifera species Orbulina universa, Globigerinoides quadrilobatus, Globorotalia menardii, and Globigerinoides obliquus indicate that the climate in the SCS gradually became warmer from 5.3 to 4.3 Ma and then cooled from 4.3 to 2.6 Ma, which was attributed to the changes in atmospheric pCO2. The high abundance of encrusting acervulinids and coralline algae and the low coral abundance suggest periods of elevated nutrient level, possibly linked to increases in nutrient input from the higher latitudes. Distinct changes in coralline algal and foraminiferal facies help the reconstruction of paleowater depths during the Pliocene in the Xisha area. The water depth was generally rising from 5.3 to 4.3 Ma and declining afterward, which was similar to that in the Yinggehai–Qiongdongnan Basin (located on the northern part of the Xisha area). This similarity indicates that there was a common factor controlling the long-term variation in water depth in the northern SCS. The comparison between paleowater depth changes and global eustatic sea-level fluctuations indicates that the regional tectonic subsidence was important from 5.3 to 4.7 Ma. Such subsidence was probably related to thermal subsidence after the magmatism intrusion activity beneath the basement at the initial stage of the Pliocene. This study indicates that the comprehensive analysis of algal and foraminiferal facies has great potential to reconstruct the climatic conditions and water depths in the ancient times.

Depositional processes of the mixed siliciclastic-carbonate system in the Lower Cambrian Xiannüdong Formation in the northern Sichuan Basin, South China

Mixed siliciclastic-carbonate systems contain significant heterogeneity of facies associations which complicates the interpretation of depositional environments and platform evolution. The Lower Cambrian Xiannüdong Formation in the northern Sichuan Basin was deposited in a mixed system which is characterized by the non-skeleton grain (ooids and microbialites) dominated carbonates mixed with siliciclastic sediments. Such a depositional system provides a template to decipher the facies variability of mixed depositional systems and the evolution of platform geometry. Based on the facies analysis in outcrops and drilling wells, seventeen lithofacies were identified and grouped into seven lithofacies associations which represents a shallow-marine environment dominated by wave and storm activities. The vertical stacking pattern of lithofacies in the Xiannüdong Formation archives a regressive cycle which can be subdivided into four sub-cycles (i.e., S1 to S4). All the four sub-cycles exhibit the characteristic of the shallowing-upward successions, which are overlain by a flooding unit. The spatial distribution of lithofacies suggests an eastward-inclined platform. The migrating ooid shoals together with the storm activities may prevent the platform from evolving into a rimmed shelf. The lateral and vetical distribution of the terrigenous materials indicates that the provenance of terrigenous sediments were mainly sourced from the Kangdian and Bikou massifs, which indicates that the mixed system and the provenance area were separated by the Mianyang-Changning trough. Therefore, the transport of siliciclastic materials was related to the available accommodation space on the shelf, and was controlled by the eustatic sea-level fluctuation, with increased input of siliciclastic material occurred during phases of relative sea-level rise. The input of siliciclastic sediments brings nutrition for the growth of algal–archaeocyathan mounds, and therefore the mounds were mainly developed in the lower part of Xiannüdong Formation. Moreover, high siliciclastic sediments influx would also influence the growth of ooids by serving nuclei and promoting abrasion, which resulted in smaller ooid size compared to those of the relatively pure oolite. This study provides clues to understanding the facies variability in mixed systems and servers as a valuable reference for studies of other similar platforms.

Quaternary Lowstand Prograding Wedges of the Salento Continental Shelf (Southern Adriatic Sea, Italy): Architectural Stacking Patterns and the Control of Glacio-Eustatic Sea Level Fluctuations and Foreland Tectonic Uplift

The performance of both the tectonic uplift and of the 4th-order glacial eustatic sea level fluctuations in controlling the stratigraphic architecture of Quaternary lowstand prograding wedges of the Salento continental shelf (Southern Adriatic sea, Italy) during a time interval spanning from the Middle Pleistocene to the Holocene has been pointed out through the interpretation of high-resolution seismic reflection profiles and their correlation to the curves of the isotopic stratigraphy. Three main transgressive surfaces of erosion (RS1, RS2 and RS3) punctuate the stratigraphic architecture of the Salento continental shelf, separating Quaternary lowstand prograding wedges between them. All along the Middle Pleistocene, increasing the tectonic uplift of the Puglia offshore, combining with 4th-order glacio-eustatic variations, have dealt with the pattern of a broad forced regression prograding wedge, favoring a platform progradation of approximately 15 km. The architectural stacking patterns of the overlying Late Pleistocene and Holocene prograding wedges are controlled by 4th-order glacio-eustatic sea level changes, allowing for the formation of incomplete depositional sequences. In this period, the eustatic signature overcomes the tectonic mark, implying a decline in the uplift of the Apulian foreland in the course of the final 250 ky.

The return of the Iváň Canyon, a large Neogene canyon in the Alpine-Carpathian Foredeep

The submarine Iváň Canyon oriented parallel along the front of the Western Carpathian fold and thrust belt and the foreland of the Bohemian Massif has been studied on numerous 2D seismic sections and available borehole cores. The canyon can be followed over the distance of more than 75 km indented within the sedimentary infill of the Alpine-Carpathian Foredeep from Lower Austria into the Czech Republic. Seismic data reveal up to 600 m depth of the canyon and its width of 2.5–6 km. The canyon is characterized by a low sinuosity planform architecture with an axial main channel and several tributary channels of varying dimensions. Six seismic facies were identified, separated by three erosional surfaces, which led to recognition of seven evolutional stages of the canyon.Facies analysis, clast composition and heavy mineral spectra indicate derivation from a siliciclastic source area, cannibalization of an older basin infill and an important role of sustained low-density turbidity currents in transport and deposition. The strontium isotope stratigraphy data supported by microbiostratigraphy and by foraminiferal δ18O and δ13C isotope analysis confirmed, that the depositional history of the canyon infill lasted from the upper Burdigalian/Langhian boundary up to the lower Serravalian, with the dominance of Langhian deposits in its infill.The formation and depositional history of the canyon is explained by the complicated structural and depositional history of the Alpine-Carpathian Foreland basin during the lower/middle Miocene transition and middle Miocene (Langhian) with a dominant role of tectonic subsidence and basin re-configuration accompanied by eustatic sea-level fluctuations. The Iváň Canyon as axial channel developed in the elongate foreland basin reveals several differences if compared to typical ancient submarine canyons in the passive margin settings.

Stratigraphy and depositional evolution of the terminal Ediacaran platform in the central to northern Sichuan Basin, Southwest China

The upper Ediacaran Dengying Formation in the Sichuan Basin provides well-preserved sedimentary records for investigating Precambrian microbialites and platform evolution. However, as previous studies have mainly focused on the broad platform-basin architecture, the depositional evolution of the platform has not been fully illuminated in the central to northern Sichuan Basin, where an intraplatform rift trough developed. Therefore, based on drilling wells and outcrops in the area, 20 lithofacies were identified and grouped into eight lithofacies associations indicating peritidal flat, shallow subtidal flat, lagoon, mixed tidal flat, slope, basin, coast and shallow sea environments. Moreover, two transgressive-regressive depositional cycles (Cycle 1 and Cycle 2) were recognized based on the five shallowing-upward (types A–E) and three deepening-upward (types F–H) cycle types. A ramp-like epeiric platform with a gentle slope developed in Cycle 1. The platform is dominated by shallow subtidal grainstones and peritidal microbialites, and the trough is in a slope environment without deep-water basin facies. In the transgression of Cycle 2, a siliciclastic-dominated environment comprising the coast and shallow sea developed on the shelf. Then a rimmed carbonate platform developed in the regression of Cycle 2, with the accumulation of shoal grainstone and peritidal microbialite in the platform margin, lagoonal dolomudstone in the platform interior, and steep slope rhythmite and basinal chert in the distal rift trough. Eustatic sea-level fluctuation and climatic change controlled the lithological transitions between carbonate and siliciclastic deposits. The platform configuration change is closely related to the evolution of the rift trough, which is the result of intense differential subsidence and sedimentation rates between the trough and platform under the effect of pre-existing basement rifts and coeval growth fault activities. A detailed depositional history of the Ediacaran Dengying Formation around the intraplatform rift trough was finally obtained, providing a good template for the study of the Precambrian microbialite-dominated platform with a similar tectonic setting.

OSL dating of coastal sand dunes in southeastern China provides new insights into the relationship between aeolian activity and eustatic sea-level fluctuations

The southeastern coastal region of China has coastal sand dunes, which are usually called paleo-sand dunes or “Old Red Sandstone”. The ages and geological implications of these coastal dunes have been studied for tens of years but are still controversial. In this paper, we used optically stimulated luminescence (OSL) dating to establish the chronology of the paleo-aeolian reddish sand dunes from two representative sites in the coastal region of SE China. Our results indicate that the sand dunes were mainly accumulated in three periods, including 9–6 ka (broadly corresponding to marine isotope stage (MIS) 1), 50–26 ka (MIS 3), and 110–74 ka (MIS 5). Based on the comparison between the regional aeolian dune records and the global sea-level fluctuations, we concluded that the reddish sand dunes were associated with the aeolian processes during interglacials and interstadials when sea-level were relatively higher compared with glacial maxima. We proposed a conceptual model to interpret the formation of the coastal sand dunes. We suggest that coastal dunes that formed during the glacial maxima could not be preserved in highstands above the present sea-level due to the lower altitude of sand dunes and the erosion by water waves during the subsequent marine transgression. Therefore, only aeolian sand dunes accumulated in higher altitudes during sea-level rise were preserved as in the coastal region of SE China.

Depositional environments and sequence stratigraphy of the Arab Formation, Persian Gulf, Offshore Iran

The carbonate-evaporite sequence of the Arab Formation constitutes the important reservoir unit in the Persian Gulf and adjacent area. The paper aims to present detail facies characteristics, depositional environment and sequence stratigraphic analysis of the Arab Formation in an oil field in the Persian Gulf. A total of 12 microfacies (MF) and 3 dolomitic (diagenetic) facies (DF) were identified, and are interpreted as a homoclinal carbonate ramp platform. The Arab Formation is divided into four third order sequences corresponding to main reservoir intervals (Arab-A, B, C, D). The results highly correlate with the sequences of local and regional studies in the Arabian Plate. It is probably due to the cake layer nature of the Arab Formation and high impact of the world eustatic sea-level fluctuations (global curves) on the facies stacking pattern.