Eustatic Sea-level Drop Research Articles

On the nature of the Talysh-Vandam Mesozoic uplift and the West Caspian tectonic fault (in the order of discussion)

On the basis of seismostratigraphic studies, the nature of the Talysh-Vendam gravity maximum and the West Caspian deep fault has been revised, and a number of interesting results have been obtained. Thus, in the interval from the end of the Cretaceous to the end of the Sabunchu Formation of the Lower Pliocene, a sharp discrepancy between the geological sections of the basins of the Lower and Middle Kura, when (from the end of the Miocene) the level of erosion of the former decreased to 1800 m, in the latter remained above sea level until the end of the Surakhan (lower Pliocene) formations. Based on the results of seismostratigraphic studies, it was proposed to use the term Mingachevir-Saatly-Talysh Mesozoic uplift zone as tectonic elements instead of the Talysh-Vendam gravity maximum, Kurdamir-Saatly and Mingachevir-Goychay Mesozoic uplifts. Although in the basin of the Lower Kura there was a deepening up to 1800 m, corresponding in age to the Messinian eustatic drop in sea level, the subsidence of the bottom of a basin of this magnitude was associated with bending processes. The results of seismostratigraphic studies state that the Mingachevir-Saatly-Talysh zone of the Mesozoic uplift divides the Kura sedimentary basin into two blocks, such as the Lower and Middle Kura depressions, and not the West Caspian deep fault. The results of seismic studies on a regional scale once again confirmed that the West Caspian Fault does not occur in the geological section of the territory of Azerbaijan, at least in its Cenozoic interval.

Quaternary evolution of the Meiji Atoll (Mischief Reef) in the southern South China Sea

This paper describes the Quaternary evolution of Meiji Atoll (also known as Mischief Reef) in the southern South China Sea. Findings are based on a sedimentological and paleontological investigation of the uppermost 150 m of core NK-1. Through the Quaternary, open-lagoon sediments initially developed from ca. 2.6 to 1.6 Ma, which were succeeded by backreef sediments from 1.6 to 1.1 Ma, and subsequently by reef-flat sediments from 1.1 Ma to present, as the atoll evolved. The deepest depositional environments occurred between 2.0 and 1.6 Ma as a result of significant rates of subsidence in the Dangerous Grounds area. Coral abundance steadily increased during the Quaternary due to the secular eustatic sea-level drop and continuous high temperatures in the southern South China Sea. After the start of the Mid-Pleistocene Transition from 1.25 Ma, there was an increase in the amplification of short-eccentricity glacio-eustatic cycles, which resulted in two impacts. First, more frequent exposure horizons developed over the atoll due to an increase in amplitude of short-term sea-level fall events. Second, the occurrence of the thickest coral framestone units developed at around 0.8 Ma, perhaps linked to prominent short-term sea-level highstands (i.e., 125-ka cycle) and moderate subsidence rates. In summary, we document the Quaternary evolution of the Meiji Atoll, and show how variations in sea surface temperature, eustatic sea level, and tectonics have influenced its development. These findings have broader implications for understanding the Quaternary evolution of similar tropical carbonate atolls in the region.

Evidence for enhanced aridification since 13 Ma in the Qom back-arc basin, Central Iran

The Iranian Plateau was once occupied by the Neotethys Sea, which connected with the Indian Ocean in the southeast and the proto-Mediterranean in the west during most of the Cenozoic era. However, the Neotethys Sea has undergone a stepwise retreat, and the Tethyan Seaway also closed in the Miocene driven by both Arabia-Eurasia collision and global eustatic sea-level drop. Changes in the land-sea distribution and uplift of the Zagros Mountain belt must have affected paleoclimatic changes in Iran. To date, a high-resolution paleoclimatic record is lacking for Iran. In this paper, we present new environmental magnetic and color parameter data for terrestrial sediments in the Qom back-arc basin, Central Iran from the middle to late Miocene (17–11.5 Ma). All of our parameters indicate an abrupt climatic change at ∼13 Ma. We suggest that the less reddish color and a shift in environmental magnetic parameters after ∼13 Ma implies weakened chemical weathering under a colder/drier climate. Enhanced aridification was mainly controlled by closure of the Tethyan Seaway and shrinkage of the Neotethys Sea after ∼13 Ma, which greatly reduced moisture transport to the downwind Central Iran by westerlies, whereas the rain shallow effect of the initially uplifted Zagros Mountain belt and reduced seawater evaporation related to lower sea-surface temperatures after the Mid-Miocene Climatic Transition only played minor roles. Therefore, our results provide a window to discuss relationships between plate tectonic movements, land/sea distribution, and climatic change in a tectonically active region during the late Cenozoic.

Relative sea level changes during the Last Glacial Maximum and deglaciation (33–15 ka) inferred from the δ18O records of planktic foraminifera from the Sea of Japan

The Sea of Japan, located in the humid zone, was subjected to significant freshening of surface waters and a decrease in ventilation of deep waters during the glacial eustatic drop in relative sea level (RSL) and a decrease in water exchange with Pacific due to the shallowness of its straits. As a result, the δ18O values of planktic foraminifera (δ18Opf) decreased by several ppm, in contrast to the increase of ones in the Red Sea, depending on the degree of RSL drop.The good preservation of planktic foraminifera in the sediments of the Sea of Japan during the Last Glacial Maximum (LGM) and deglaciation allows us to significantly refine and supplement the available evidences of the global sea level changes over the 33–15 ka. Based on the obtained and published records of δ18Opf of five cores from different parts of the sea and the general chronology of the accumulation of dark layers in the sediments of the Sea of Japan, we calculated the δ18Opf stacks with high and low resolution (0.13 kyr for two cores and 0.5 kyr for other three cores) for the time 33–15 ka.Both stacks showed significant RSL falls at the onset of LGM (32–29 ka), during 21.8–20.3 ka, and an abrupt rise at 17 ka consistently with previously published data. The higher resolution stack additionally showed two phases of RSL falls at the onset of the LGM followed by a slow decrease until 22 ka, with a short and abrupt descent at around 25 ka. According to both stacks the lowest sea level around 18.5–17.5 ka was preceded by a short rise just before 19 ka. A significant RSL rise at 17 ka was followed by an abrupt and short fall at nearly 16.5 ka and then prolonged rise since around 16.2 ka.

Magnetostratigraphic Age Control of the Timing of Tectonic Deformation and the Shifting Depositional Environments in the Dezful Embayment, Iran

AbstractThe timing of tectonic deformation in the Zagros foreland basin provides important information about the tectonic propagation process driven by the Arabia‐Eurasia convergence. The chronology of growth strata is one of the most important methods to delimit the history of folding and thrusting within the foreland basin. In this study, we report integrated analyses of sedimentology, magnetostratigraphy, and biostratigraphy of Miocene strata in the Dezful Embayment in the SW Zagros foreland basin. The new results indicate that deposition of the northern limb of the Gach‐e Moh Anticline was between 14.6 and 8.6 Ma; that includes the Upper Gachsaran Formation (14.6–13.8 Ma), the Mishan Formation (13.8–12.8 Ma), and the Agha Jari Formation (12.8–8.6 Ma). Based on magnetostratigraphic and sedimentary evidence, the transition from marine to non‐marine was at ∼12.8 Ma. Analysis of temporal lithofacies‐stacked patterns shows there were seventeen transgression‐regression cycles during the Middle Miocene Climatic Transition with a ∼100‐Kyr Earth eccentricity cycle, suggesting that the cyclic marine transgressions and regressions were mainly driven by eustatic sea level fluctuations; but tectonic‐induced basin subsidence also contributed marine transgressions in the Upper Mishan Formation. The final seawater retreat was at 12.8 Ma driven by both the global eustatic sea level drop and the enhanced south‐westward progradation of sediments eroded from the High Zagros. The base of the growth strata in the footwall of the Mountain Front Fault was at ∼11 Ma, suggesting that tectonic deformation caused by the Arabia‐Eurasia collision had propagated to the Dezful Embayment by that time.

Deep-time climate legacies affect origination rates of marine genera

Biodiversity dynamics are shaped by a complex interplay between current conditions and historic legacy. The interaction of short- and long-term climate change may mask the true relationship of evolutionary responses to climate change if not specifically accounted for. These paleoclimate interactions have been demonstrated for extinction risk and biodiversity change, but their importance for origination dynamics remains untested. Here, we show that origination probability in marine fossil genera is strongly affected by paleoclimate interactions. Overall, origination probability increases by 27.8% [95% CI (27.4%, 28.3%)] when a short-term cooling adds to a long-term cooling trend. This large effect is consistent through time and all studied groups. The mechanisms of the detected effect might be manifold but are likely connected to increased allopatric speciation with eustatic sea level drop caused by sustained global cooling. We tested this potential mechanism through which paleoclimate interactions can act on origination rates by additionally examining a proxy for habitat fragmentation. This proxy, continental fragmentation, has a similar effect on origination rates as paleoclimate interactions, supporting the importance of allopatric speciation through habitat fragmentation in the deep-time fossil record. The identified complex nature of paleoclimate interactions might explain contradictory conclusions on the relationship between temperature and origination in the previous literature. Our results highlight the need to account for complex interactions in evolutionary studies both between and among biotic and abiotic factors.

Early post-rift confined turbidite systems in a supra-detachment basin: Implications for the early to middle Miocene basin evolution and hydrocarbon exploration of the Pannonian Basin

Understanding the interplay of sedimentation and deformation style is essential to develop an adequate model of the evolutionary history of an extensional sedimentary basin. Due to their volume and temporal extent, late post-rift deposits are often in the focus of research; however, early post-rift deposits are less studied. The aim of the study is to reconstruct the tectono-sedimentary evolution of a syn -rift to early post-rift succession in the hanging wall of a low-angle detachment zone and to recognize the effects of this deformation style on turbidity current pathways and depocenters. The small Őri sub-basin of the western part of the Miocene Pannonian basin is used as a study area where the oldest early post-rift turbidites of ~15–12.8 Ma occurred. These sediments were deposited in a supradetachment setting, where inherited and actively forming structures controlled the sediment pathways and accommodation of both the distally and locally sourced marine turbidites. Seismic data, well logs and core information were integrated to identify and analyze unconformities, structural elements, and turbidite deposits. Syn-rift, early post-rift and late post-rift system tracts were identified. The syn -rift/post-rift unconformity is a result of combined eustatic sea level drop and the change in deformation intensity. The main low-angle detachment fault, orthogonal hanging wall transfer faults and related folds together controlled the complex synformal shape of the basin, which was related to major corrugations of the footwall detachment. Four turbidite phases were distinguished based on upward increasing sand content, areal extent, reservoir quality, and degree of confinement as the turbidity currents reached the basin margins. (1) Small fans deflected by transfer faults developed, followed by (2) an axial turbidite system that reached an anticline and was deflected by it. (3) Lateral confinement by the anticline increased significantly and thick sandstone bodies with abrupt pinch-outs formed, while the influence of smaller faults diminished. (4) The axial turbidite systems covered the basin floor and their interaction with basin margins created continuous sand bodies of confined character. The sand fairways and types of confinement of a supra-detachment basin differ from high-angle normal fault systems. The exhumed metamorphic rocks provided the sediment, and the extension-parallel antiformal and synformal corrugations acted as lateral confinement. The gentle back-tilt of the detachment hanging wall block exerted a frontal confinement for the extensive turbidite system at the distal part of the basin, but the gentle NE-ward dip over the detachment still permitted long run-out distances. • Combination of eustasy and tectonics leads to syn-rift-early post-rift unconformity. • Corrugation fold of a detachment creates an intricate topography for sediment flows. • Deformation activity decreases during deposition of early post-rift turbidites. • Lateral, frontal confinement of turbidity currents controls reservoirs quality. • Differences between sand fairways in high- and low-angle extensional systems.

Metallogenic mechanism of large manganese deposits from Permian manganese ore belt in western South China Block: New mineralogical and geochemical evidence

The Permian manganese (Mn) ore belt lies in western South China Block, and contains many large-medium Mn deposits. However, the genesis and metallogenic mechanism of these deposits remains a matter of debate. Here we shed light on this issue based on new mineralogical, geochemical, and Sr isotope data from the Changgou Mn deposit in the Zunyi orefield (Guizhou, SW China). The Mn orebodies occur as lenses and layers, and are hosted in carbonaceous-siliceous limestone, carbonaceous mudstone, and tuffaceous claystone. The ores show a variety of structures (e.g., detrital, brecciated, massive, and banded) and complex mineral compositions (e.g., galena, sphalerite, siegenite, molybdenite, barite, rutile, and monazite). The ore samples are characterized by chalcophile and siderophile element enrichments, low Al2O3/TiO2 ratios (mean 10.36), high and varying Mn/Fe ratios (1.26–4.71), distinctly high REY (rare earth and yttrium) contents (mean 766.46 ppm), and high La/Ce (mean 1.04) and low Y/Ho (mean 28.17) ratios. The footwall and ore samples have 87Sr/86Sr ratios of 0.706897 to 0.707093. Integrated mineralogical and geochemical signatures indicate that the ore-forming fluids were most probably originated from hydrothermal activities related to early-stage Emeishan Large Igneous Province (ELIP) subaqueous volcanism. Redox proxies reveal that sedimentary conditions evolved from euxinic-anoxic (footwall deposition), through anoxic-suboxic (Mn mineralization), to oxic (hanging-wall deposition). Such changes were probably resulted from a coeval eustatic sea-level drop and enhanced seawater oxygen supply. Manganese was likely initially enriched in form of Mn2+, and subsequently precipitated with oxidation, and then transformed into Mn carbonate during sediment diagenesis. To conclude, the tectono-hydrothermal activities and major environmental redox changes led by the ELIP volcanism have provided a favorable source-migration-sink system for the Mn mineralization.

Timing and forcing mechanism of the final Neotethys seawater retreat from Central Iran in response to the Arabia-Asia collision in the late early Miocene

The Iranian Plateau lies in the middle of the Neotethys tectonic domain; to the east it connects with the Tibetan Plateau, and to the west with the Anatolian Plateau and the Alpine orogenic belts. In the Cenozoic it underwent land/sea changes and tectonic uplift in response to the Arabia-Asia plate collision. One of the most prominent geological consequences of the collision was the disappearance of an epicontinental sea in Central Iran, which was a northeastern branch of the Neotethys seaway in the Oligocene-early Miocene. The timing of the final seawater retreat from Central Iran and its forcing mechanism are important for understanding the effects of Arabia-Asia plate collision as well as global eustatic sea-level changes. In this paper we present new magnetostratigraphy, UPb ages of one tuffaceous bed, and stable isotopic records of carbonates. The results of this multidisciplinary study indicate that a shallow open sea in the Qom back-arc basin ended at 17 Ma, but the final seawater retreat from a restricted marine environment was at 16.8 Ma. The final regression was just before the Middle Miocene Optimum, implying that it was not related to a climatic factor, but driven by the Arabia-Asia plate collision. Moreover, the δ18O record of fine-grained lacustrine carbonates indicates an isotopic shift towards more positive isotopes after 13 Ma, suggesting an enhanced aridification in Central Iran. This climatic deterioration was a response to reduced transport of moisture by westerlies from a retreating Neotethys Sea driven by a global eustatic sea-level drop in response to the East Antarctica ice-sheet expansion after the middle Miocene Optimum.

Tectonic controls on the Maastrichtian-Danian transgression in the Magallanes-Austral foreland basin (Chile): Implications for the growth of the Southern Patagonian Andes

The Maastrichtian-Danian transgression was one of the most extensive Atlantic-derived marine incursions in Patagonia. This study examines its stratigraphic record and origin in the Magallanes-Austral Basin, revealing an interplay of sedimentation, tectonism, and base-level changes, which contribute to our understanding of foreland basin dynamics. We present a multidisciplinary approach from a relatively poorly documented sector (51°38′-53°50′S) of the basin. This approach includes facies and provenance analysis, palynology, sequence stratigraphy, and U-Pb geochronology. These techniques enable us to evaluate the role of climate, tectonics, and eustasy on the transgression, as well as providing insight into the growth of the Southern Patagonian Andes. A first shallowing-upward cycle (late Campanian to late Maastrichtian) is represented by the transition from outer shelf and upper slope deposits (Fuentes and Tres Pasos formations) to shoreface and deltaic environments (Rocallosa and Dorotea formations), favoured by high erosion rates in the fold-thrust belt and eustatic sea-level drop. A subsequent deepening-upward cycle (late Maastrichtian to Paleocene) records the Atlantic transgression, manifested by estuarine deposits in an incised valley (uppermost Dorotea Formation) and deep-water turbidites (Chorrillo Chico Formation and Cabo Naríz beds). Palynological results suggest a temperate palaeoclimate (~6–17 °C) during the Maastrichtian-Danian, which agrees with significant cooling of the South Atlantic Ocean at this time. Therefore, relative climatic optima are not a driver of marine ingression. The stratigraphic and tectonic evolution of the succession studied suggests that flexural and dynamic subsidence promoted marine incursion into the Magallanes-Austral Basin. Provenance data indicate sediment input to the basin from the Southern Patagonian Batholith, Rocas Verdes Basin remnants, Tobífera Formation, and metamorphic terranes exposed in the hinterland of the Southern Patagonian Andes during the early Maastrichtian. However, by the Paleocene, sediments derived from the hinterland had been structurally dammed during basinward propagation of the fold-thrust belt.

Microbial-dominated carbonate depositional systems: a biosedimentary and stratigraphic reconstruction in the Late Triassic of Western Tethys (northern Calabria, Italy)

The northern Calabria Norian-Rhaetian carbonate platform system is characterized by three depositional units: early-middle Norian Corvino Unit (CU), middle-late Norian Vaccuta Unit (VU) and late Norian-Rhaetian Grisolia Unit (GU). The CU presents a deep barrier reef consisting of an oligotypic framebuilder community of sponges, serpulids, algae, and stromatolitic microbialites. The intra-supratidal facies mainly comprise flat to low-relief, frequently subaerial-exposed, stromatolites and thrombolites, whereas subtidal facies include high-relief stromatolites and skeletal packstones. In the outer shelf, debrites, turbidites, mudstones, and slumped layers are present. In the VU, bioclastic sand-barriers, inhabited by monospecific bivalve clusters (Isognomon exilis) and low- to high-relief small-scale stromatolites, protected a peritidal domain characterized by flat to high-relief thrombolites and stromatolites. The outer-ramp facies include laminated mudstones and tempestites interbedded with sporadic flat stromatolites. Finally, tempestites and marlstones, characterizing the GU shelf, overlie all previous shallow- to deep-water facies, testifying a terrigenous input and the end of the previous carbonate factory. The Norian oligotypic fossil associations of the CU and VU imply anoxia and eutrophy, likely due to limited water circulation, related to basin isolation from the open ocean. During the whole Norian-Rhaetian interval syn-depositional down-faulting pulses was accompanied by gradual eustatic sea-level drop, inducing episodes of isolation and opening of the basin. Tectonic pulses influenced the sequence stratigraphic architecture creating an atypical system-tracts succession characterized by retrogradation of the CU and progradation followed by retrogradation for the VU and GU.

Application of HadCM3@Bristolv1.0 simulations of paleoclimate as forcing for an ice-sheet model, ANICE2.1: set-up and benchmark experiments

Abstract. Fully coupled ice-sheet–climate modelling over 10 000–100 000-year timescales at high spatial and temporal resolution remains beyond the capability of current computational systems. Forcing an ice-sheet model with precalculated output from a general circulation model (GCM) offers a middle ground, balancing the need to accurately capture both long-term processes, in particular circulation-driven changes in precipitation, and processes requiring a high spatial resolution like ablation. Here, we present and evaluate a model set-up that forces the ANICE 3-D thermodynamic ice-sheet–shelf model calculating the four large continental ice sheets (Antarctica, Greenland, North America, and Eurasia) with precalculated output from two steady-state simulations with the HadCM3 (GCM) using a so-called matrix method of coupling both components, whereby simulations with various levels of pCO2 and ice-sheet configuration are combined to form a time-continuous transient climate forcing consistent with the modelled ice sheets. We address the difficulties in downscaling low-resolution GCM output to the higher-resolution grid of an ice-sheet model and account for differences between GCM and ice-sheet model surface topography ranging from interglacial to glacial conditions. Although the approach presented here can be applied to a matrix with any number of GCM snapshots, we limited our experiments to a matrix of only two snapshots. As a benchmark experiment to assess the validity of this model set-up, we perform a simulation of the entire last glacial cycle from 120 kyr ago to present day. The simulated eustatic sea-level drop at the Last Glacial Maximum (LGM) for the combined Antarctic, Greenland, Eurasian, and North American ice sheets amounts to 100 m, in line with many other studies. The simulated ice sheets at the LGM agree well with the ICE-5G reconstruction and the more recent DATED-1 reconstruction in terms of total volume and geographical location of the ice sheets. Moreover, modelled benthic oxygen isotope abundance and the relative contributions from global ice volume and deep-water temperature agree well with available data, as do surface temperature histories for the Greenland and Antarctic ice sheets. This model strategy can be used to create time-continuous ice-sheet distribution and sea-level reconstructions for geological periods up to several million years in duration, capturing climate-model-driven variations in the mass balance of the ice sheet.

РЕГИОНАЛЬНОЕ ЗНАЧЕНИЕ И ОБЪЕМЫ ПЕРЕРЫВОВ/НЕСОГЛАСИЙ В ПАЛЕОГЕНОВЫХ ОТЛОЖЕНИЯХ СЕВЕРНОЙ ТЕТИЧЕСКОЙ ОБЛАСТИ

РЕГИОНАЛЬНОЕ ЗНАЧЕНИЕ И ОБЪЕМЫ ПЕРЕРЫВОВ/НЕСОГЛАСИЙ В ПАЛЕОГЕНОВЫХ ОТЛОЖЕНИЯХ СЕВЕРНОЙ ТЕТИЧЕСКОЙ ОБЛАСТИ

Lithostratigraphy and depositional environments of the upper cretaceous deposits in the central Taurides (S Turkey)

The study area is located in the Central Taurides (southern Turkey), which is bounded by the Kirkkavak fault to the west and Ecemis fault to the east. The sequences are studied in detail based on measured sections composed of the rocks deposited during the Cenomanian–Maastrichtian and located within different tectonic units previously described in the Taurides. The study materials include 217 thin section data from seven Cenomanian–Maastrichtian sequences of outcropping in different parts of the Central Taurides. The sediments deposited during the Cenomanian–Maastrichtian period in the Central Taurides are subdivided into eight units based on their lithological, paleontological, and textural properties. The lower boundaries of the upper Santonian and Campanian are unconformable contacts. The Upper Cretaceous sequence starts with the middle Cenomanian and represents a continuation of the Lower Cretaceous tidal flat and shelf lagoon sequence. Upper Turonian–Coniacian sediments are not observed due to the eustatic sea level drop. The second main transgression period of the Upper Cretaceous platform took place in the Santonian. This unit is represented by limestones composed of wackestones/packstones containing benthic foraminifera and rudist fragments, which are deposited in tidal flats and subtidal environments. The late Campanian starts with a transgression, and the environment transformed transitions into slope facies from inner platform facies, as a result of the thrust of ophiolitic rocks. In the following period, slope front and basin plain environments were dominant due to the increasing slope. Slumped pelagic limestones were deposited on the slope. Planktonic foraminiferal pelagic limestones were unconformably deposited on plaque limestone in the slope front environment depending on the increase in slope gradient and local faulting. As a result of decreasing tectonic activity, the sediments were deposited onto a stable basin plain. They were initially fed from the nearby carbonate platform and then by siliciclastic turbidites derived from the thrusted ophiolitic rocks. In this study, the lithostratigraphic properties of the Cenomanian–Maastrichtian units outcropping in various parts of the Central Taurides are described. The sedimentary deposits described here suggest different basinal conditions in the region.

Orbital-scale changes in redox condition and biogenic silica/detrital fluxes of the Middle Jurassic Radiolarite in Tethys (Sogno, Lombardy, N-Italy): Possible link with glaciation?

Orbital forcing has been shown to be a fundamental driver of climate change through both icehouse and greenhouse periods. To reveal the impact of orbital-forcing on the oceanic environment through a greenhouse-icehouse transition, we established ~4Myr-long cyclostratigraphy of the Bajocian-Callovian (Middle Jurassic; ~160Ma) Basal Radiolarites at the Torre De Busi and Corre Di Sogno sections in the Lombardian Basin, N-Italy. Stratigraphic changes in chert abundance (chert/shale thickness ratio) and color (darkness) of Radiolarites show hierarchal periodicities of 8cm, 16cm, 40cm, 160cm, and ~4m, corresponding to ~20kyr, 40kyr, 100kyr, 400kyr, and ~1Myr cycles based on the biostratigraphic age model. Black cherts in intervals with high chert abundance might reflect oxygen-depleted conditions due to orbital-scale high productivity. On the other hand, black cherts in intervals with low chert abundance (high detrital input) might reflect oxygen-depleted conditions, probably due to orbital-scale sea-level drop and stratification. On 40kyr and 100kyr cycles, the anoxic condition occurred in low chert abundance intervals across ~8m above (~2Myr after) the base of the Radiolarites. These results imply that the formation of the restricted basin resulted from tectonic and/or eustatic sea-level drop, which is consistent with increased black chert deposition and redox-sensitive elements abundances (Mo/TOC, Mo/U). Their out-of-phase relationships on the 405kyr cycle throughout the sequence (~4Myr-long) with increasing amplitude above −8M level would be caused possibly by tectonic activity, or more likely by glacio-eustatic sea-level changes reported from sequence stratigraphy, similar to those of the Oligocene to Pliocene glacial cycles, but probably with less amplitude.

Coincidence or not? Interconnected gas/fluid migration and ocean–atmosphere oscillations in the Levant Basin

A growing number of studies on shallow marine gas/fluid systems from across the globe indicate their abundance throughout geological epochs. However, these episodic events have not been fully integrated into the fundamental concepts of continental margin development, which are thought to be dictated by three elements: tectonics, sedimentation and eustasy. The current study focuses on the passive sector of the Levant Basin on the eastern Mediterranean continental margin where these elements are well constrained, in order to isolate the contribution of gas/fluid systems. Single-channel, multichannel and 3D seismic reflection data are interpreted in terms of variance, chaos, envelope and sweetness attributes. Correlation with the Romi-1 borehole and sequence boundaries constrains interpretation of seismic stratigraphy. Results show a variety of fluid- or gas-related features such as seafloor and subsurface pockmarks, volumes of acoustic blanking, bright spots, conic pinnacle mounds, gas chimneys and high sweetness zones that represent possible secondary reservoirs. It is suggested that gas/fluid migrate upwards along lithological conduits such as falling-stage systems tracts and sequence boundaries during both highstands and lowstands. In all, 13 mid-late Pleistocene sequence boundaries are accompanied by independent evidence of 13 eustatic sea-level drops. Whether this connection is coincidental or not requires further research. These findings fill gaps between previously reported sporadic appearances throughout the Levant Basin and margin and throughout geological time from the Messinian until the present day, and create a unified framework for understanding the system as a whole. Repetitive appearance of these features suggests that their role in the morphodynamics of continental margins is more important than previously thought and thus may constitute one of the key elements of continental margin development.

Links between paleoclimate and prehistorical human dispersal in Sri Lanka: a critical view

Sri Lanka represents rich sources of prehistorical archaeological data such as the earliest: 1) Homo sapiens fossils; 2) geometric microliths in South Asia. Climatic and geological events were considered with known archaeological evidences that provide opportunities for comparative research. The author proposed that climatic transition from Marine Isotope Stage (MIS) 4 to MIS 3 and MIS 3 to MIS 2 could probably identify as main traverse periods of prehistoric modern Homo sapiens into Sri Lanka. Glacial eustatic sea-level drops create possible prehistoric migration routes between India and Sri Lanka across the Palk Strait during a number of phases under semi-arid climate. The interglacial sea-level rise had opened supplementary routes towards tropical inland rainforests along river valleys. The early-middle to late Holocene sea-level highstands can be recognised as the latest geographic isolation of island Sri Lanka.

Links between paleoclimate and prehistorical human dispersal in Sri Lanka: a critical view

Sri Lanka represents rich sources of prehistorical archaeological data such as the earliest: 1) Homo sapiens fossils; 2) geometric microliths in South Asia. Climatic and geological events were considered with known archaeological evidences that provide opportunities for comparative research. The author proposed that climatic transition from Marine Isotope Stage (MIS) 4 to MIS 3 and MIS 3 to MIS 2 could probably identify as main traverse periods of prehistoric modern Homo sapiens into Sri Lanka. Glacial eustatic sea-level drops create possible prehistoric migration routes between India and Sri Lanka across the Palk Strait during a number of phases under semi-arid climate. The interglacial sea-level rise had opened supplementary routes towards tropical inland rainforests along river valleys. The early-middle to late Holocene sea-level highstands can be recognised as the latest geographic isolation of island Sri Lanka.

Formative mechanisms, depositional processes, and geological implications of Furongian (late Cambrian) reefs in the North China Platform

The Cambrian Series 3–Furongian successions of the North China Platform contain various microbial–metazoan and microbial reefs. This study focuses on Furongian reefs of the platform in order to understand formative processes and the evolution of the reefs during Cambrian Epoch 3 and the Furongian. Three types of Furongian reefs were differentiated in the Shandong region, China: maceriate reefs, columnar stromatolitic reefs, and small-scale microbial reefs. Maceriate reefs show dm- to m-scale domal or flat-bedded geometry, and consist of cm-scale maze-like maceria structures made of siliceous sponges and microbial components (microstromatolites, Girvanella, and Tarthinia). Columnar stromatolitic reefs are characterized by stromatolite columns of 10–100cm in height and 5–50cm in diameter. They consist dominantly of Girvanella, with less conspicuous, poorly preserved sponge spicule networks. Small-scale microbial reefs commonly show cm- to dm-scale, domal macrostructures, and were constructed mainly by calcimicrobes, Girvanella and Renalcis. These three types of Furongian reefs were deposited in various shallow-marine settings in response to relative sea-level changes.The Furongian reefs are markedly different, in terms of macro- and micro-fabrics, from the Cambrian Series 3 reefs that are dominated by thrombolites and dendrolites and were constructed mainly by Epiphyton in the Shandong region. This difference is also recognized in the Beijing region, ca. 500km away. The abrupt transition from the Cambrian Series 3-type to Furongian-type reefs, coincidently with a decrease in calcified microbe diversity, was most likely due to global euxinic oceanic conditions and a possible eustatic sea-level drop, rather than the highly diachronous, platform-wide drowning event (i.e., drowning of the Cambrian Series 3 carbonate platform). The abundant occurrence of sponge spicule networks in the Furongian reefs suggests that metazoan reef builders (i.e., sponges) resurged and became actively involved in the reefal systems prior to the Great Ordovician Biodiversification Event. This study may provide an important basis for further investigation into the evolution of reefal systems during the middle to late Cambrian when metazoan reef-builders were known to be scarce.

Future surface mass balance of the Antarctic ice sheet and its influence on sea level change, simulated by a regional atmospheric climate model

A regional atmospheric climate model with multi-layer snow module (RACMO2) is forced at the lateral boundaries by global climate model (GCM) data to assess the future climate and surface mass balance (SMB) of the Antarctic ice sheet (AIS). Two different GCMs (ECHAM5 until 2100 and HadCM3 until 2200) and two different emission scenarios (A1B and E1) are used as forcing to capture a realistic range in future climate states. Simulated ice sheet averaged 2 m air temperature (T2m) increases (1.8–3.0 K in 2100 and 2.4–5.3 K in 2200), simultaneously and with the same magnitude as GCM simulated T2m. The SMB and its components increase in magnitude, as they are directly influenced by the temperature increase. Changes in atmospheric circulation around Antarctica play a minor role in future SMB changes. During the next two centuries, the projected increase in liquid water flux from rainfall and snowmelt, together 60–200 Gt year−1, will mostly refreeze in the snow pack, so runoff remains small (10–40 Gt year−1). Sublimation increases by 25–50 %, but remains an order of magnitude smaller than snowfall. The increase in snowfall mainly determines future changes in SMB on the AIS: 6–16 % in 2100 and 8–25 % in 2200. Without any ice dynamical response, this would result in an eustatic sea level drop of 20–43 mm in 2100 and 73–163 mm in 2200, compared to the twentieth century. Averaged over the AIS, a strong relation between \(\Updelta\)SMB and \(\Updelta\hbox{T}_{2{\rm m}}\) of 98 ± 5 Gt w.e. year−1 K−1 is found.