查看更多>>摘要：? 2022The approach and results of our 2019 paper (Brooke et al., 2019) have been criticised by Dougherty (2022). We examined the sensitivity of a tropical, coarse sand strandplain to changes in relative sea level as expressed through beach-ridge morphology and the elevation of beach berms preserved in the succession of cyclone-generated beach ridges at Cowley Beach, Queensland, Australia. Rather than presenting a new sea-level curve for this region as suggested by Dougherty, our 2019 study of the Cowley Beach strandplain revealed that when compared with the modelled Holocene relative sea-level record and sea-level indicator data for north-eastern Queensland, the strandplain morphology and stratigraphy provide a first-order representation of sea-level position. Importantly, Dougherty (2022) has overlooked the processes involved in the formation of beach ridges at this site and the spatial coverage of our analysis of the strandplain morphology. Both these factors are fundamental to the approach and conclusions of our 2019 paper. We reiterate here that the Cowley Beach strandplain morphology and succession of beach-berm deposits have elevation patterns that match well the broad trend in the regional relative sea-level model for the past 7 ka. We highlight those key beach-ridge formative processes and data limitations neglected in the Dougherty Comment. Finally, we note the challenges and opportunities for further research into the sedimentary records preserved in this distinctive type of tropical strandplain.
查看更多>>摘要：? 2022 Elsevier B.V.The Sansha Yongle Blue Hole (SYBH) is the deepest (301.19 m) blue hole known in the world and is a water-filled karst opening in the intertidal reef flats of the eastern Yongle Atoll, Xisha Islands, South China Sea. It is differentiated from the surrounding environment by its deep blue colour as observed when viewed from above. The SYBH exhibits extremely rare karst networks and speleothems and differs from the blue holes of the Bahamas and Bermuda, indicating a different development process. Here, we present the morphology and U[sbnd]Th ages of the SYBH, which document the evolution of the coastal cave over time. Morphology and lithostratigraphy indicate that the hole resulted from dissolution via ascending acidic water/gas followed by subsequent collapse. The adjacent volcanoes surrounding the eastern Yongle Atoll are the most likely source of these ascending fluids. U[sbnd]Th ages of the cemented carbonate sand underlying the entrance constrain an upper limit of the opening time of the SYBH to be up to 111.7 ± 9.5 kyr BP. Deeply submerged speleothems at ?116 m determine the lower collapse time of the SYBH to be 29.16 ± 0.17 kyr BP. The SYBH probably formed due to the upward release of volcanogenic acid water/gas through low-lying unconsolidated carbonate sediments, followed by buoyant collapses due to a 40-m fall in the sea level during 31–29 kyr BP. As the sea level rose to ?15 m in the early Holocene, corals grew in the cave opening since 8.58 kyr BP and surrounded the entrance for the SYBH.
查看更多>>摘要：? 2022 The AuthorsAkko/Acre, a UNESCO World Heritage site since 2001, is one of the oldest continuously inhabited sites in the eastern Mediterranean. Tel Akko was a major maritime centre of the southern Levant from the Middle Bronze to the Late Persian period. The city was then moved 1500 m to the west on the Akko promontory where the ‘Old City’ of Saint-Jean d'Acre is located. The natural and anthropogenic evolution of Tel Akko area is reflected by persistent geographical and habitation pattern changes. We combine sedimentological and faunal analyses of radiocarbon dated cores as well as identification of ceramic sherds found in the cores with ground penetrating radar investigations to propose an up-to-date palaeogeographical reconstruction of landscape/environmental changes of the Akko coastal plain in order to understand the extent to which environmental pressures have played a role on the position of anchorage and habitation patterns. We highlight how the local population make use of the natural advantages of the area and adapted to environmental pressures. Following a constant sedimentary input and simultaneous coastal progradation of the Akko coastal plain the main anchorage areas where forced to move. While the 2nd Millennium BCE anchorage was on the southern area of the tell, the late-1st Millennium BCE (Phoenician-Persian) anchorage was relocated on the western area. Vicissitudes in settlement pattern noted in archaeological excavations and surveys on Tel Akko have, most likely, been the consequence of the changes in the position of the coastline.
查看更多>>摘要：? 2022 Elsevier B.V.The geomorphology of the Amazon Continental Margin (ACM) is highly heterogeneous and includes a variety of reef-like formations found in deep-water along the shelf-slope transition. The ACM has been divided into three Sectors (Northern, Central and Southern) according to the distribution of the carbonate producers and the ‘reefs’, influenced by the Amazon River plume. Here, we characterize these structures that were sampled with a manned submersible and multibeam surveys to depths of up to 230 m, exploring their relationship with the Amazon river plume and changing sea level following the Last Glacial Maximum (LGM). The shelf-slope transition and a deeper shelf break in the Northern Sector of the Brazilian portion of the ACM carry a series of prominent high-relief structures (HRS) that experience a strong fluvial influence. The tops of these features are between 110 and 165 m depths and seem to have originated during lowstands, through erosion of Pleistocene sandstones. Siliciclastic and carbonate deposits accumulated on the tops of these features in shallow waters during the LGM and early deglaciation and were gradually submerged by rising sea level and subsidence. A thin layer of encrusting organisms, coralline algae, sponges, bryozoans and serpulids presently colonizes most of these surfaces at the sites sampled and contributes to the aggregation of thin fine-grained siliciclastic deposits. The Central Sector, off the river mouth, is associated with long-term sediment accumulation and lacks a shelf break. Nevertheless, living benthic communities occur on rock outcrops. The Southern Sector is less influenced by the river plume and includes a shallower shelf-break and a prominent canyon. The surveyed outcrops of Pleistocene carbonate and siliciclastic rocks at 180 m carry thin covers of a benthic community dominated by sponges and coralline algae, which is responsible for the accumulation of a thin (up to a few centimeters) deposit of carbonate bioclasts, quartz sand and mud on the rocky substrate. Thus, the ‘reefs’ of the outer shelf and mesophotic Amazon margin are typically eroded older rocks, colonized by encrusting organisms during the LGM and deglaciation forming a carbonate veneer, which now support a mesophotic community.
Angulo R.J.de Souza M.C.da Camara Rosa M.L.C.Caron F....
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查看更多>>摘要：? 2022 Elsevier B.V.Rocas Atoll is a remote place and the only atoll in the southwestern Atlantic Ocean. This study presents new paleo-sea level reconstructions and a new interpretation on former ones. The new data indicate that sea level was higher at the Late-Holocene than it is at present and that the hydrodynamic factors overlap with sea-level changes, precluding more precise paleo-sea level reconstructions. According to previous works, the Rocas Atoll presents one of the most conspicuous paleo-sea level indicators, represented by reef remains. But, in this paper, these supposedly reef remains are reinterpreted as algal-reef boulders detached from the atoll reef-front by high-wave energy events and deposited over the reef rim, where they remain detached or are cemented and, sometimes, mushroom shaped. It is considered that the bigger boulders may have been deposited in their current position by the cumulative effects of past energetic wave events. Furthermore, the use of beachrocks as paleo-sea level indicators in former studies is discussed, leading to the conclusion that they actually indicate beach progradation and lateral accretion resulting from a positive sand budget. Finally, a schematic morphological evolution of the atoll during the Late-Holocene is proposed. At the atoll, leveling with RTK and imagery with laser scanner were collected, and eleven radiocarbon ages were measured by accelerator mass spectrometry (AMS).
查看更多>>摘要：? 2022 Elsevier B.V.Ancient hydrothermal vent complexes have released large volumes of greenhouse gases in the past causing global warming, and similar modern vent structures are potential geohazards. In the NE Atlantic, thousands of hydrothermal vent complexes were formed during the Paleocene-Eocene Thermal Maximum. In Java, Indonesia, the erupting Lusi sediment-hosted geothermal system caused the displacement of 40,000 people. In order to determine how ancient and modern hydrothermal venting systems are related, we map a well-defined buried hydrothermal vent complex offshore mid-Norway using 3D seismic reflection data and then compare it to the active Lusi eruption (since 2006) and the neighboring inactive Porong Structure. These are characterized using 2D seismic reflection data, borehole data and field observations. The venting structures are subcircular in plan-view and a few kilometers in diameter. They are funnel-shaped in profiles, with inward-dipping beds surrounding the conduits. The hydrothermal vent complex offshore mid-Norway reveals five seismically-distinct vent fill facies units. Importantly, two of the facies units are separated by an angular unconformity, clearly indicating that the depositional events within the vent fill were distinct. Hydrothermal fluids are interpreted to have led to the fluidization of mud-rich sediments which were erupted and deposited in and around the vent complex. Interpretation of a seismically transparent body along the conduit of the Norwegian venting structure, and the abrupt widening of the conduit at the Porong Structure, are interpreted to be caused by changes in fluid-flow dynamics as the fluids rise and get released from the host-rock. The hydrothermal venting systems in Java and offshore mid-Norway are found to be morphologically similar and are interpreted to form as the result of the transport and eruption of fluidized sediments.
查看更多>>摘要：? 2022 The AuthorsLarge river deltas serve as globally important archives of terrestrial and shallow marine biogeochemical signatures and because of rapid sedimentation have the potential to impact global biogeochemical cycling. The Ayeyarwady Delta in Myanmar ranks as the world's third largest river delta in terms of sediment supply; however, modern increases in regional anthropogenic impacts risk severe alteration to sediment and TerrOC loads within this major system. By investigating modern sediment and terrestrial organic carbon (TerrOC) accumulation within the offshore Ayeyarwady Delta this study estimates baseline sediment and TerrOC budgets for this understudied mega-delta. Using 210Pb geochronology of 27 sediment cores collected from the continental shelf, we estimate that 405 (+52/-47) Mt of sediment, or ~70-80% of fluvial sediment discharged from the Ayeyarwady and Thanlwin rivers (the main inputs to the delta), accumulates there annually. Sediment not retained on the shelf is likely partitioned between the Ayeyarwady floodplain, shoreline accretion, and minor deep-sea export. Estimates of TerrOC (based on δ13C mixing models) were coupled with modern sediment accumulation rates to determine an annual burial of 1.93 (+1.09/-0.15) Mt C on the shelf, with TerrOC burial fluxes being highest in the foreset beds of the subaqueous delta, coincident with the area of highest sediment accumulation rate. Based on estimates of the Ayeyarwady and Thanlwin rivers' TerrOC delivery, an apparent ~100% of TerrOC input is preserved on the continental shelf. However, an across shelf trend of increasing TerrOC degradation with distance offshore is also observed, indicating that while the shelf has high apparent TerrOC sequestration, carbon remineralization is also occurring prior to deposition within the subaqueous delta. Based on these conflicting outcomes, we suggest that input of TerrOC from additional sources other than the Ayeyarwady and Thanlwin rivers roughly balance the observed carbon remineralization. Main additional sources of TerrOC include the Sittang and several smaller rivers, and the Ayeyarwady delta plain below the river gauging station. As anthropogenic development within the Ayeyarwady and Thanlwin watersheds continues to increase, these sediment and TerrOC budgets provide a baseline from which future changes within the offshore Ayeyarwady Delta can be monitored.
查看更多>>摘要：? 2022 Elsevier B.V.An improved understanding of the resilience capacity of salt-marsh environments, which are recognized as one of the most vulnerable yet valuable coastal morpho-sedimentary systems is important for enhancing adaptation to ongoing and future sea-level rise. The aim of this study is to provide a long-term (multi-centennial) context to the capacity of response of saltmarsh environments to relative sea-level rise and extreme wave events by reconstructing the accretion histories of two microtidal back-barrier (one aggradational and one transgressive) saltmarshes in the Bay of Gaspé (Québec, Eastern Canada) over the last centuries. Particular emphasis is put on coarse minerogenic sedimentation and the role it played in the response of the two marshes to relative sea-level changes. To do so, lithostratigraphic, geochronological, and geochemical analyses are carried out on sedimentary cores taken in the back-barrier marsh areas. The accretion histories and the chronology of coarse deposition upon the marshes are reconstructed and yield the following two main results: (1) Coherent yet contrasting records of coarse sedimentation histories are obtained for the two sites, which relate to the distinct configurations and functioning of the fronting barrier systems. The coarse sedimentation time-series of both marshes carry pluri-decadal periodicities typical of atmospheric and intra-oceanic modes of variability, as well as periodicities of 18.0 to 18.5 years, which are interpreted as the expressions of the influence of the 18.6-year nodal tidal cycle. (2) We observe intra- and inter-site variations in the accretionary behavior of the two systems as well as in their respective histories of coarse minerogenic deposition. We show that coarse sedimentation at the surface of the two marshes has been crucial for maintaining accretion rates both in minerogenic and organogenic environments, and thus for allowing saltmarshes to build a resilience capacity in a regime of relative sea-level rise.
查看更多>>摘要：? 2022 Elsevier B.V.The Qiongdongnan Basin (QDNB) is a petroleum-bearing basin in the northern margin of the South China Sea (SCS). Provenance analysis is an important tool in petroleum exploration and is helpful in predicting the distribution of good reservoirs in areas with less drilling. However, the provenance of the QDNB remains controversial, and further research is needed. Here, we apply whole-rock geochemistry, petrography, and heavy minerals combined with published detrital zircon U-Pb ages to constrain the provenance of Oligocene to middle Miocene sandstones in the QDNB and the tectonic environment of their deposition. The Oligocene to middle Miocene sandstones from the QDNB are geochemically immature. These sandstones were derived from a weakly weathered source area characterized by dominantly felsic igneous rocks, with a particular slight addition from recycled sedimentary sources. And the Lingshui Formation underwent less weathering than the upper and lower strata. The tectonic setting of the sandstones in the basin belongs to a continental island arc (CIA) or an active continental margin (ACM). Heavy mineral assemblages and detrital zircon U-Pb ages reveal sediment input from multiple sources. Hainan Island was a major and continuous source area contributing to the basin from the early Oligocene to the middle Miocene. In addition, intrabasinal uplift regions could have supplied material to local areas. While these sedimentary source patterns appear to have changed very little in the late Oligocene, a provenance from central Vietnam was explicitly discerned in the western QDNB in the late Oligocene. It is possible that the paleo-Pearl River supplied large volumes of sediment to the eastern QDNB from the late Oligocene to the early Miocene.
查看更多>>摘要：? 2022 Elsevier B.V.Estuaries are typical depositional systems of transgressive coasts; however, depositional systems with similar geometry also occur on regressive coasts. Such “regressive estuaries” are found in areas of Asia, South America, and Australia that have experienced relative sea-level lowering since the middle Holocene. Regressive estuaries form in incised valleys that were drowned by the last deglacial sea-level rise and receive relatively little riverine sediment discharge. The largest estuary in Japan, with a length of 120 km and a width of 10 km, is in the Paleo-Kinu Bay region. A partly unfilled wave-dominated estuary developed in this region prior to the artificial diversion of the Tone River during the 17th century. In this study, we document the Holocene filling of the Paleo-Kinu Bay on the basis of 14 sediment cores and 171 radiocarbon dates. Unfilled wave-dominated estuary at 7–4 ka has more pronounced wave-built morphologic elements than at 4–0 ka. As a result of sea-level lowering and weakening of tidal currents at 4–0 ka, the bay mouth became narrowed by lateral accretion of sandy tidal river sediments and the central basin was filled by progradation of muddy bayhead delta sediments. The acceleration of the bay mouth narrowing and central basin infilling similar to what happened during 4–0 ka in the Paleo-Kinu Bay region have not been identified in transgressive estuaries, but are common features of regressive estuaries.
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