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Asian deltas are densely populated and richly bio-diversified regions with significant social, economic, ecological and environmental importance across the globe. These low-lying and fertile floodplains support substantial food production. Because of sediment supply reductions, sea-level rising, subsidence, and frequent storm surges, many deltas are rapidly sinking and shrinking, which will threaten survival of millions of populations. It's of great significance to monitor the delta morphological evolution and understand the relationship between their shoreline migrations and sediment supplies. However, quantifying the delta morphological changes is challenging due to its nature of high dynamics. In this study, we developed a methodology integrated by a time-series algorithm of water frequency and a spatial analysis to track the morphological changes of 11 major Asian deltas from 1986 to 2018.The results show that the deltas of Yellow, Yangtze, Pearl, Red, Mekong, Ganges-Brahmaputra, and Chao Phraya have experienced a net land gain at the total of 1829.3 km2, with China's three major deltas accounting for 73 percent of all. The deltas of Mahanadi, Irrawaddy, Indus, and Godavari-Krishna have undergone a net land loss at the total of 295.1 km2, of which the Indus River Delta accounted for 65 percent. Most of the shorelines in the Yangtze River Delta were constantly advancing seaward at a rate of over 30 m/year, whereas, many ones in the rest of Asian deltas were significantly being eroded at a rate of over 20 m/year. These changes in delta morphology are closely related to sediment supplies and management policies. These results also suggest that rational wetland reclamation with auxiliary projects of ecological restoration can enhance the deltaic ability of sustainable development. [ABSTRACT FROM AUTHOR]

Understanding ancient climate changes is hampered by the inability to disentangle trends in continental ice volume from records of relative sea-level change. As a unique coastal deposit in tropical and subtropical regions, beachrock has been proved to be reliable for constraining the glacial meltwater signal and thus the total volume of land-based ice in Quaternary. However, beachrock is rarely recognized in the fossil record due to (a) the two-dimensional distribution of beach deposits, as opposed, for example, to extended platform sediments, and (b) the fact that specific environmental conditions are required in order to lithify sediments directly on the beach. By combining the stratigraphic architecture with petrography of characteristic carbonate cements, we demonstrate the first known occurrence of Ordovician beachrock in the Tarim Block, northwestern China. According to biostratigraphic data, a middle Katian (Upper Ordovician) palaeokarst surface is capped by carbonate conglomerate beachrock and this is suggesting a significant relative sea-level rise in late Katian. The beachrock can be correlated with widespread subaerial exposure surfaces and a pronounced stratigraphic gap within the Katian in northwestern Tarim. We suggest that the beachrock ‘fingerprinted’ a strong melt-water pulse in high latitudes after a short-lived Katian glaciation, which has not received much attention in scientific papers so far. [ABSTRACT FROM AUTHOR]

The Hirnantian period, making the end of the Ordovician with significant mass extinctions and large ice‐sheets, is a critical interval for studying paleoclimate variations. This research represents the first cyclostratigraphic study of this period, utilizing high‐resolution (1 mm sampling rate) geochemical data from the ∼7‐m thick SH‐1 drill core, capturing the latest Ordovician glaciation. Our analysis identifies the presence of Milankovitch cycles with periods of 17–21, ∼33, and ∼100‐kyr, suggesting an optimal sedimentation rate of 3.1 m/Myr. Notably, we detected signals of millennial‐scale variability, aligning with the ∼1.5‐kyr Dansgaard‐Oeschger and ∼2.4‐kyr Hallstatt heliomagnetic cycles, even in deposits lacking visible laminae alternation. This finding bolsters the hypothesis of an external origin for these millennial‐scale features. Additionally, our reconstruction of sea‐level variations, using principal component analysis and sedimentary noise modeling, reveals two intervals of sea‐level fall and one sea‐level rise, linked to an astronomical forcing cycle of ∼1.2‐Myr. The obliquity band power‐total power ratios correspond to ∼1.2‐Myr periodicities for s4‐s3 term. The synchronization of ∼1.2‐Myr cycle minimum with a sea‐level drop (low PC1 value) suggests that glacio‐eustatic variations were influenced by ∼1.2‐Myr obliquity modulation cycles. This research enhances our understanding of glacio‐eustasy during the latest Ordovician from an astronomical perspective, offering valuable insights into the interplay between orbital cycles and Earth's paleoclimate. Key Points: Millennial‐scale cycles have been detected based on five high‐resolution proxy seriesMillennial‐scale cycle preserved in the Hirnantian was linked to the D‐O and Hallstatt cycle∼1.2‐Myr PC1 filter revealed one rise and two falls of sea‐level during Hirnantian [ABSTRACT FROM AUTHOR]

The Ximing Sandstone-to-No. 9 Coal succession of the Taiyuan Formation in the Linxing gas field records a complex internal architecture of a transgressive succession developed in the western coast of the late Pennsylvanian North China epeiric sea. Facies and sequence stratigraphic analyses reveal its depositional evolution from fluvial channels through fluvial-dominated and tide-influenced inner estuaries to tide-dominated estuaries and finally to wave-dominated barrier lagoons. The evolution from fluvial- to tide-dominated deposition has been ascribed to the funnel-shaped valley coupled with an increased tidal prism induced by the upstepping and backstepping shoreline. The evolution from tide- to wave-dominated deposition has been ascribed to the wide North China epeiric seaway lacking local coastline irregularities after the incised-valley fill that provided sufficient fetch for the occurrence of large storm waves. Grain-size analysis reveals the relative importance of traction, saltation, dispersed suspension, and flocculated suspension in the development of the transgressive estuarine to lagoonal deposits. This study not only contributes to a proper understanding of coastal depositional response to the relative sea-level rise but also provides a context within which to interpret the symbiotic relationship of the superimposed sandstone–shale–coal reservoirs and predict the distribution of favorable unconventional gas production formation. [ABSTRACT FROM AUTHOR]

The Hangjiahu Plain in the lower Yangtze is one of the core areas that sustained the flourishment of the Liangzhu Civilization. This study reconstructed Holocene environmental change on the Hangjiahu Plain based on a sediment core collected from the Tangqi ZK‐3 location situated on the low‐lying Hangzhou‐Taihu region of the Yangtze Delta. We applied OSL dating, grain size analysis, pollen analysis, and magnetic susceptibility to reconstruct Holocene environmental change and compared our data with other published results. Our results showed that (i) before ~7.0 ka B.P., the ZK‐3 core recorded a strong hydrodynamic force, resulting in the widespread deposition of light grayish silt clay or clayey silt in the region. The climate was warm and humid, and the vegetation was mixed evergreen deciduous coniferous forest. (ii) Between 7.0 and 6.0 ka B.P., the hydrodynamic condition in ZK‐3 core became weaker, and the climate remained warm and humid. Although most of the Hangjiahu Plain were still covered by the light grayish silt clay or clayey silt, some higher grounds began to emerge as sea‐level rise slowed, which coincided with the development of the Majiabang culture. (iii) Between 6.0 and 4.5 ka B.P., the deposition of yellowish silty clay indicates a shallow‐water hydrological environment at ZK‐3, as the regional water level was dropping while more land was emerging, which provided a favorable physical environment for the prosperity of the Songze and Liangzhu cultures. The period experienced a drier and cooler climate, with evidence of deforestation. (iv) Between 4.5 and 3.0 ka B.P., the sediments in the ZK‐3 core were dominated by light grayish clay, indicative of a return to a deep‐water environment with a prolonged waterlogging condition. The climate remained dry and cool with further deforestation. However, the widely distributed yellowish silt clay suggests frequent floods in the region, resulting in a sharp reduction of settlement sites and the eventual decline of the Liangzhu Civilization. [ABSTRACT FROM AUTHOR]

A late Kasimovian (Pennsylvanian) coral reef is reported in the Yanbanzhai (YBZ) area, southern Guizhou Province, South China. The YBZ coral reef, with a thickness of approximately 5.5 m and a lateral exposure of nearly 50 m, is primarily composed of the colonial rugose coral Fomichevella. The fusulinids collected from the reef indicates a late Kasimovian age. Five microfacies types have been identified, including coated bioclastic grainstone, coral (Fomichevella) framestone, bioclastic wackestone, bioclastic grainstone, and peloidal grainstone. The vertical evolution of the microfacies in the YBZ coral reef indicates major sedimentary environmental changes associated with relative sea‐level changes. The growth of the reef‐builder Fomichevella was controlled by the transgression and regression. Deep water promoted the upward expansion of Fomichevella, while shallow water inhibited its growth. Published records of atmospheric pCO2 estimation and sea‐surface temperatures, combined with geochemical proxies, confirm a warm climatic period during the late Kasimovian. This is an interglacial period conducive to the growth of the coral reef. Sea‐level and climate changes associated with the Late Palaeozoic ice age (LPIA) are interpreted as significant controls of the development of the YBZ coral reef. This research of the YBZ coral reef in South China provides practical palaeobiological evidence for global sea‐level rising during the late Kasimovian period caused by the high‐latitude Gondwana delaciation. [ABSTRACT FROM AUTHOR]

While Ediacaran cap dolostones research is a hot topic, detailed sedimentological analysis of barite‐bearing cap dolostones remains scarce. Here, new data are presented from Xiangerwan in northern Three Gorges, South China, to illustrate the sedimentary characteristics, depositional environment and formation mechanism of the barite‐bearing cap dolostone. In ascending order, the succession is divided into: (i) pebbly dolostone; (ii) dolostone with unusual sedimentary structures (for example, sheet cracks and tepee structures); and (iii) barite‐bearing facies. The gravels of the pebbly dolostone record the slow relative sea‐level rise during post‐glacial transgression, with a local terrestrial influence. Sheet cracks and tepee structures represent water escape structures in the supratidal and upper intertidal zone, and gently wavy stromatolites in barite‐bearing facies are deposits typical of the upper intertidal zone. In addition, primary radial length‐slow dolomite cements were originally precipitated at the seafloor. In general, the cap dolostone was formed in a shallow‐water ramp environment. The form and sedimentary characteristics of barites indicate a primary (syngenetic) origin and help to divide the barites into bladed (Type I) and needle‐like (Type II) variants. With the ongoing melting of the Marinoan glacier and water density stratification, the cap dolostone was gradually precipitated, accompanied by exotic gravels input. The stratification persisted, and special sedimentary structures were widely developed. Phosphorus and barium ions were brought up from the deep basin by upwelling, indicated by the flourishing stromatolites and barite fan deposition. Above the sediment–water interface, the Type I barite first grew upward from substrates, then the Type II barite could grow either in the reverse 'V‐shape' cavities between and within the Type I barite clusters, forming rhythm layers with bedded dolomite, or scattered in the laminae of stromatolites or surrounding dolomite. Finally, the formation of barite fans indicates the end of cap dolostone deposition and deeper water sedimentation. [ABSTRACT FROM AUTHOR]

Coastal wetlands are key features of the Earth's surface and are characterized by a diverse array of coupled geomorphological and biological processes. However, the links between the distribution of biodiversity (for example, species and structural diversity) and the formation of coastal geomorphology are not well‐understood on a landscape scale most useful to coastal zone managers. This study describes the relationship between select geomorphological and biological mangrove community features (i.e. species composition and functional root type) in a landscape‐distributed coastal zone of Dongzhaigang Bay, north‐eastern Hainan Island, China. A total of 11 mangrove species and five functional aerial root types were encountered, with the location of species by root types being controlled by the elevation of the soil surface. Plank roots, prop roots and pneumatophores occupied the lowest intertidal elevations, while knee roots and fibrous roots of the mangrove fern, Acrostichum aureum, preferred the highest intertidal elevations. Surface sediment deposition in areas with mangroves was greater than deposition in non‐mangrove forest zones, establishing an important biological mechanism for this large‐area response because surface erosion/compaction was also more prominent within mangrove roots. Indeed, functional root type influenced the magnitude of deposition, erosion and compaction, with knee roots and pneumatophores being more effective in promoting deposition and preventing surface erosion/compaction than prop roots. These results indicate a potential role for vegetation type (especially functional root type) to influence coastal geomorphological processes at large landscape scales. While soil surface elevation is correlated to the distribution of mangrove species and functional root types, a significant feedback exists between elevation change and the capacity of those root types to influence coastal geomorphological differentiation within sustainable intertidal elevations. An enhanced understanding of geomorphological development, mangrove species distribution and functional root type may improve management to support nature‐based solutions that adjust more effectively to sea‐level rise through feedbacks. [ABSTRACT FROM AUTHOR]

Understanding coastal flooding processes in response to centennial-scale sea-level rise is essential in preparing for the challenge of present-day global warming. Mid-Holocene sea-level rise induced widespread coastal flooding along the East China coast and precipitated the collapse of the Neolithic Liangzhu Culture, the earliest known prehistoric state in East Asia. This paper presents multi-proxy analyses of sedimentology, grain size, total organic carbon (TOC), and alkaline-earth metals extracted by acetic acid (HAc) of a dated sediment core, ZK07, collected from Liangzhu City, with the aim of revealing the detailed progression of coastal flooding phases and the response of prehistoric people at the end of the associated Liangzhu Culture. A three-step succession of coastal flooding processes between ca. 4.6–4.3 cal kyr BP, brought about by relative sea-level rise, is evident in core ZK07. Initially, an increase in the local water level in response to the first phase of sea-level rise is indicated by a gradual increase in TOC at ca. 4630 cal yr BP. Subsequently, at ca. 4520 cal yr BP, a second phase of increased local water-level, consistent with further sea-level rise and salinity intrusion, is suggested by higher Sr concentrations accompanied by a sharp increase in TOC. Thirdly, at ca. 4480–4315 cal yr BP, low TOC content, high - but strongly fluctuating - Sr and Ba concentrations and coarser sediment grain size are all indicative of coastal inundation caused by both storm surges and river flooding associated with typhoon events that correspond with a concurrent phase of accelerated sea-level rise. Considering the evidence of cultural deposits preserved at Liangzhu City, it appears that the Liangzhu people were forced to respond rapidly to the inundation by abandoning the city at ca. 4480 cal yr BP. We suggest that relative sea-level rise and coastal flooding at the terminal stage of the Liangzhu Culture was the regional response to global climate warming and eustatic sea-level rise at that time. Given evidence that a contemporaneous cultural transition took place in the lower Yellow River basin, we further propose that global climate change around 4.5 cal kyr BP had a widespread impact on Neolithic cultural evolution in East China. Furthermore, the rise in local water levels and associated salinity intrusions may be considered as an early warning signal in monitoring future coastal flooding risk. • A three-step succession of coastal flooding was recognized at the end of Liangzhu Culture. • Rise in local water level and salinity intrusion could be early warning of coastal flooding. • Global climate warming and eustatic sea-level rise at ca. 4.5 ka was the major mechanism. • Contrasting Neolithic cultural evolution occurred in the lower reaches of two large rivers in East China. [ABSTRACT FROM AUTHOR]

Land subsidence is impacting large populations in coastal Asia via relative sea-level rise (RSLR). Here we assesses these risks and possible response strategies for China, including estimates of present rates of RSLR, flood exposure and risk to 2050. In 2015, each Chinese coastal resident experienced on average RSLR of 11 to 20 mm/yr. This is 3 to 5 times higher than climate-induced SLR, reflecting that people are concentrated in subsiding locations. In 2050, assuming these subsidence rates continue, land area, population and assets exposed to the 100-year coastal flood event is 20%-39%, 17%-37% and 18%-39% higher than assuming climate change alone, respectively. Realistic subsidence control measures can avoid up to two thirds of this additional growth in exposure, with adaptation required to address the residual. This analysis emphasizes subsidence as a RSLR hazard in China that requires a broad-scale policy response, utilizing subsidence control combined with coastal adaptation. Chinese coastal populations are concentrated in subsiding locations, and also subject to sea-level rise. Here the authors find that more areas, population and assets are exposed to coastal flooding by 2050 but realistic subsidence control measures can avoid additional risks. [ABSTRACT FROM AUTHOR]

Floods in river deltas are driven by complex interactions between astronomical tides, sea levels, storm surges, wind waves, rainfall‐runoff, and river discharge. Given the anticipated increase in compound flood hazards in river deltas in a warming climate, climate‐informed regional to local extreme water levels (EWLs) is thus critical for decision‐makers to evaluate flood hazards and take adaptation measures. We develop a simple yet computationally efficient stress test framework, which combines historical and projected climatological information and a state‐of‐the‐art hydrodynamic model, to assess future compound coastal‐fluvial flood hazards in river deltas. Our framework is applied in the world's largest single urban area, China's Pearl River Delta (PRD), which is also characterized by densely crossed river network. We find that extreme sea level is the dominant driver causing the compound coastal‐fluvial flood in the PRD over the past 60 years. Meanwhile, there is large spatial heterogeneity of the individual and compound effects of the typhoon intensity, local sea‐level rise, and riverine inflow on coastal‐fluvial floods. In a plausible disruptive scenario (e.g., a 0.50 m sea‐level rise combined with a 9% increase in typhoon intensity in a 2°C warming), the EWL will increase by 0.76 m on average. An additional 1.54 and 0.56 m increase in EWL will occur in the river network and near the river mouth, respectively, if coastal floods coincide with the upstream mean annual flood. Findings from our modeling framework provide important insights to guide adaptation planning in river deltas to withstand future compound floods under climate change. Plain Language Summary: Compound floods pose serious threats to the dense population living in river deltas worldwide. Climate change could increase the compound flood hazards through stronger tropical cyclones, sea level rise, higher extreme precipitation, and river flows. It is urgent to understand how the so‐called grey swan events will evolve under a changing climate in these already flood‐prone areas. Here, grey swan events are high‐consequence events that are beyond people's experience but may be foreseeable and thus can be systematically prepared for. In this study, a storyline‐based framework is proposed to assess the potential grey swan compound floods under a warming climate. We apply this framework to China's Pearl River Delta, the world's largest single urban area. In a plausible disruptive scenario (e.g., a 0.50 m sea‐level rise combined with a 9% increase in typhoon intensity in a 2°C warming), we find that extreme water levels will increase by 0.76 m on average. Our flexible and computationally efficient storyline‐based framework could guide coastal planners to prepare for the grey swan compound flood hazards under climate change. Key Points: A quantitative stress test framework is proposed to assess the compound coastal‐fluvial flood in the river delta at minimal costA state‐of‐the‐art unstructured mesh generation technology is applied to develop an objective and reproducible hydrodynamic modelCompound effects of typhoon intensity, local sea‐level rise, and river inflow on coastal‐fluvial floods are systematically investigated [ABSTRACT FROM AUTHOR]

• Monitoring mainland and island coastline variations of the Pearl River Estuary from 1978 to 2018. • Combined Otsu and Canny edge detections to extract coastline from Landsat dataset. • Reclassified coastline as biological, sandy, muddy, estuarine, rocky and artificial via visual interpretation. • Rezoned the study area into Area I-IV and analyzed coastline variations and differences among these areas. • Analyzed natural and anthropogenic factors of coastline variations of the study area. The coastline of the Pearl River Estuary (PRE) experienced significant changes due to the increasing demand for land. Previous studies have focused on coastline changes of the mainland in China; thus changes of island coastlines have not been well investigated. In this study, the coastlines of the continent and islands of the Pearl River Estuary from 1978 to 2018 were extracted and analyzed by integrating Canny edge detection and Otsu methods based on Landsat data, and the coastline was classified into six types including biological, sandy, muddy, estuarine, rocky, and artificial via visual interpretation. The coastline length, coastline change rate and change area were calculated and analyzed for the 40 years period. The precision test showed that the coastline extraction methods presented in this paper meet the accuracy standard. The coastline length of the Pearl River Estuary was found to have increased rapidly from 789 km in 1978 to 979 km in 2018. During the past four decades, a large proportion of natural coastline converted into artificial one (66% in 2018), while 577 km2 land increased in this area. The coastline of the western PRE demonstrates more rapid change rates than that of the eastern part, and more land reclamation has occurred in the western area. Between 1988 and 1997, the coastline length and area of reclamation experienced the most extensive changes. Both natural factors, including sediment transport, sea-level rise, wind, tide, as well as anthropogenic factors, such as land reclamation and dam construction, have impacted coastline variation of the Pearl River Estuary in the past four decades. In general, the western part of the study area showed more remarkable coastline change and experienced the enormous influence of land reclamation, dam construction and sediment transport, compared with the eastern part. [ABSTRACT FROM AUTHOR]

The Early-Middle Permian δ13Ccarb variations are recorded by the marine carbonates of the Luduba section in the northern margin of the South China Block. The investigated interval (~ 300 m) spans the Chihsia and Maokou formations. Preservation of the investigated micritic carbonates was evaluated by multiple petrographic and geochemical screening tools. The δ13Ccarb and δ18O values of near-primary micrites range from 2.3 to 5.0‰ (VPDB) and from − 6.4 to − 3.4‰ (VPDB), respectively, showing insignificant correlation (R2 = 0.13). Similarly, the Mn/Sr ratios show insignificant correlation with δ13Ccarb or δ18O ratios. In addition, the Al and Sr concentrations exhibit insignificant correlation, which suggests preservation of at least near-primary δ13Ccarb signatures that can be utilized to construct a reliable C-isotope profile of the equatorial eastern Paleo-Tethys for global correlations. The C-isotope profile exhibits distinct short-time negative shifts superimposed on the general long-term trend of increase in δ13Ccarb values. The long-term trend likely reflects a consistent global sea-level rise during the Early Guadalupian, which was associated with one of the largest Permian transgressions. The general sea-level rise was disrupted by few minor short-term sea-level low-stands associated with negative δ13Ccarb shifts (~ 1–2 ‰) on the C-isotope profile, which are associated with similar minor positive 87Sr/86Sr shifts (~ 0.0005 each) on the Sr isotope profile and with Al enrichment, possibly caused by the combination of global eustasy and regional tectonics in South China. Two negative δ13Ccarb shifts have been recorded in the lower and upper Chihsia Formation that can be correlated with the Early Kungurian and the Kungurian/Roadian boundary, respectively. Also, the Maokou Formation records a middle negative shift that inferred correlates with the Early Wordian. These three negative δ13Ccarb shifts are globally comparable with those documented by both the eastern Paleo-Tethys and western Panthalassa Early-Middle Permian sedimentary records and can be utilized as chemostratigraphic markers. The general increase in the δ13Ccarb values peaks at ~ 5 ‰ near the top of the Maokou Formation that resembles the Kamura event recorded in Tethy but there are issues with the origin and timing of this positive δ13Ccarb excursion. The petrological characteristics of the Luduba section carbonates support the suggested scenario of the general long-term trend of sea-level rise. [ABSTRACT FROM AUTHOR]