Post-glacial Sea-level Change Research Articles

РАЗРУШЕНИЕ ДЕЛЬТЫ РЕКИ ТУМАННОЙ В ГОЛОЦЕНОВОЕ ВРЕМЯ И ФОРМИРОВАНИЕ ПРИПОВЕРХНОСТНЫХ СКОПЛЕНИЙ ГАЗА НА ШЕЛЬФЕ ЗАПАДНОЙ ЧАСТИ ЗАЛИВА ПЕТРА ВЕЛИКОГО (ЯПОНСКОЕ МОРЕ)

The results of bathymetric and seismoacoustic studies of the shelf in the western part of Peter the Great Bay are presented. Five flooded coastlines formed in the Late Pleistocene-Holocene were identified on the shelf. It was found that a significant part of the shelf is occupied by a zone of irregular sedimentation, which is underlain by an erosion surface buried under sediments of ebb-tidal deltas in areas of active sedimentation and exposed on the seabed within the area of active modern erosion. The processes of abrasion and formation of an irregular sedimentation zone on the shelf intensified about 11500–11700 years ago. Acoustic anomalies associated with the presence of gas in sediments and gas flares in the water column were found on the shelf of the Bay. Anomalies were classified by types, and a map of their areal distribution was compiled. It is concluded that the trigger mechanism that ensures the migration of gas into sediments and water column is associated with a group of factors: postglacial sea level change, abrasion processes, meteorological and hydrological regimes.

Imprints of post-glacial sea-level changes in the Visakhapatnam Bay (VB) basin: first documentation from multibeam bathymetry data

Imprints of post-glacial sea-level changes in the Visakhapatnam Bay (VB) basin: first documentation from multibeam bathymetry data

ONSHORE-OFFSHORE TRENDS IN THE TEMPORAL RESOLUTION OF MOLLUSCAN DEATH ASSEMBLAGES: HOW AGE-FREQUENCY DISTRIBUTIONS REVEAL QUATERNARY SEA-LEVEL HISTORY

Abstract Surficial shell accumulations from shallow marine settings are typically averaged over centennial-to-millennial time scales and dominated by specimens that died in the most recent centuries, resulting in strongly right-skewed age-frequency distributions (AFDs). However, AFDs from modern offshore settings (outer shelf and uppermost continental slope) still need to be explored. Using individually dated shells (14C-calibrated amino acid racemization), we compared AFDs along an onshore-offshore gradient across the southern Brazilian shelf, with sites ranging from the inner shelf, shallow-water (< 40 m) to offshore, deep-water (> 100 m) settings. The duration of time averaging is slightly higher in deeper water environments, and the AFD shapes change along the depositional profile. The inner shelf AFDs are strongly right-skewed due to the dominance of shells from the most recent millennia (median age range: 0–3 ka). In contrast, on the outer shelf and the uppermost continental slope, AFDs are symmetrical to left-skewed and dominated by specimens that died following the Last Glacial Maximum (median age range: 15–18 ka). The onshore-offshore changes in the observed properties of AFDs—increased median age and decreased skewness, but only slightly increased temporal mixing—likely reflect changes in sea level and concurrent water depth-related changes in biological productivity. These results suggest that on a passive continental margin subject to post-glacial sea-level changes, the magnitude of time-averaging of shell assemblages is less variable along the depositional profile than shell assemblage ages and the shapes of AFDs.

Human observations of late Quaternary coastal change: Examples from Australia, Europe and the Pacific Islands

In the aftermath of the last ice age, when sea level rose along most of the world's coastline, the activities of coastal peoples were impacted by coastal submergence, land loss and sometimes isolation as offshore islands formed. In some parts of the world, there is clear evidence that people encoded their observations of postglacial sea-level rise into oral traditions that were communicated across hundreds of generations to reach us today in an intelligible form. In other contexts, people's observations of rising sea level are likely to have formed the foundations of ‘legends’ about undersea places and the peoples inhabiting them.For a selection of coastal sites in Australia and northwest Europe, this study discusses a range of contrasting situations in which culturally-grounded stories about coastal submergence, land loss and isolation plausibly recollect the nature and effects of postglacial sea-level rise. Using science-based histories of postglacial sea-level change, minimum ages are determined for each group of site-specific stories; in the case of Australia, these range from 7000–11,500 BP, for northwest Europe from 5500 to 9500 BP. For selected sites in the Pacific Islands, where human settlement about 3000 years BP post-dated the end of postglacial sea-level rise, localized submergence is recalled in traditional stories of local people.It is argued that studies of late Quaternary coastal evolution can often be filled out by adding details from stories preserved in local cultures, something which leads to a clearer picture of the human-societal impacts of coastal submergence and land loss than can be obtained from palaeoenvironmental reconstructions and geological evidence alone.

Late and postglacial sea-level changes in The Kattegat: The consequences to different coastal aquifers (on the islands Zealand and Anholt)

Fluctuations in sea level influence the condition of coastal groundwater aquifers. In this paper the palaeo-hydrology of Anholt and part of Zealand and its dependence on the sea level history of Kattegat will be analyzed.The Late and Postglacial Sea-Level Changes in Kattegat are outlined and the consequences analyzed for Late and Postglacial ice movement and for two different coastal aquifers: a simple unconfined aquifer at the island Anholt, and a complex confined Limestone aquifers around Roskilde on Zealand.Data are presented which provide a description of how sea level changes have influenced and formed the island Anholt. This geological history can be used to provide information on the development of the salt-fresh groundwater interface under a sand island. The center of Anholt was covered by the sea at 6 ka and has now an ideal Ghyben-Herzberg freshwater lens. This means that the present equilibrium between the saltwater and freshwater has been established in less than 6000 years.Limestone aquifers on Zealand show no ideal Ghyben- Herzberg freshwater lens. Detailed 3-D mapping of a study area, around Roskilde- and Isefjord, has revealed how low sea-levels (around 50–30 ka) cause development of karst structures and deep erosion channels in the limestone (later filled with high permeable sand and gravel). These channels drain the groundwater to subsea springs, working as natural pumps, resulting in a freshwater “lens” much thinner than the equilibrium.

Quantifying the sensitivity of post-glacial sea level change to laterally varying viscosity

Quantifying the sensitivity of post-glacial sea level change to laterally varying viscosity

Predicted bounds on peak global mean sea level during marine isotope stages 5a and 5c

Estimates of marine isotope stage (MIS) 5c and 5a global mean sea level (GMSL) based on marine terraces and coastal indicators range from 15–37 m and 9–30 m below present, respectively. Tectonic displacement and glacial isostatic adjustment (GIA) complicate efforts to refine this range. We revisit this issue using numerical predictions of post-glacial sea-level change and updated estimates of site-specific tectonic signals based upon these predictions. Laurentide and Cordilleran peripheral bulge dynamics and variations in the gravitational effect of these ice masses dominate the GIA signal along the east and west coasts of North America. Published compilations suggest that MIS 5 sea-level indicators extending from Virginia to the Caribbean lie on the outer flank of the peripheral bulge, while those along a transect from Oregon to Baja California sit on the inner flank of the bulge. Our GIA modeling reconciles these data by adopting a significantly weaker (i.e., lower viscosity) upper mantle in analyzing data on the Pacific coast relative to the Atlantic, an inference supported by seismic tomography. We present a sensitivity analysis that compares the observed elevation of globally distributed high stand markers to a suite of GIA simulations that vary the Earth model and GMSL from the Last Interglaciation (MIS 5e, ∼130-115 ka) to 70 ka. We conclude that GMSL peaked at −8.5 ± 4.6 m (1σ) during MIS 5a and −9.4 ± 5.3 m during MIS 5c. A more restrictive analysis yields slightly wider bounds corresponding to −10.5 ± 5.5 m and −11.1 ± 6.6 m, respectively.

Carbon isotope gradient of the Ediacaran cap carbonate in the Shennongjia area and its implications for ocean stratification and palaeogeography

The geochemistry and paleogeography of the Doushantuo succession in the Shennongjia area have been insufficiently studied. Here, we report on the carbon and oxygen isotope compositions of Ediacaran Doushantuo cap carbonates from four sections (Longxi, Muyu, Yazikou and Songluo) in the Shennongjia area. A large C-isotopic gradient (~5‰) between the Longxi and Songluo sections, here identified for the first time, is inferred to have been dynamically maintained by photosynthesis in surface waters and anaerobic oxidation of dissolved organic carbon (DOC) in deep waters. Spatial variation in C-isotope chemostratigraphy among the four sections was related to Marinoan post-glacial sea-level elevation changes. At Longxi, a positive δ 13Ccarb shift below the horizon containing tepee-like structure resulted from intense photosynthesis during early regression. A negative δ 13Ccarb shift within the tepee-horizon was triggered by sulfate reduction and freshwater mixing with 13C-depleted dissolved inorganic carbon (DIC) during late regression. A positive δ 13Ccarb excursion in the uppermost part of the cap carbonate was related to enhance primary productivity and organic matter burial during early transgression. At Muyu, the carbon isotopic variation tendency, which is similar to that at Longxi, may have been mildly influenced by the surface water environment. At Songluo, the positive δ 13Ccarb excursion, up to -4‰ in the lower part of the cap carbonate, was probably associated with methanogenesis in deep waters during late transgression to early regression and subsequently disappeared due to decomposition of methane hydrate during late regression. At Yazikou, the consistently stable δ 13Ccarb values around -4‰ indicate that the cap carbonate may have deposited at intermediate water depths. As evidenced by diagnostic sedimentary characteristics of the study sections, the palaeogeographic framework of the Shennongjia area exhibited deepening from SE to NW during the Early Ediacaran Period in the aftermath of Snowball Earth.

Middle to late-Holocene decreased fluvial aggradation and widespread peat initiation in the Ishikari lowland (northern Japan)

This study investigated the influence of sea-level and climate changes on the decreased fluvial aggradation and subsequent widespread peat initiation in the middle to late-Holocene in the Ishikari lowland, which is a coastal floodplain formed in response to the postglacial sea-level change. By introducing a new approach to separately evaluate the rates of organic and clastic sediment input, we demonstrated that the peat began to form when the fluvial sedimentation rate was significantly decreased (less than 0.6 mm/yr), while plant macrofossil analysis suggested that lowering of water level is also important to the peat initiation. Such changes in sedimentary environment may be associated with the abrupt abandonment of crevasse splays. The concentrated ages of the peat initiation around 5600–5000, 4600–4300, and 4100–3600 cal. BP suggest that an allogenic control promoted the abandonment of crevasse splays, and different onset ages can be explained by different fluvial responses of the Ishikari River and its tributaries. The abandonment of crevasse splays could result from sea-level fall or decreased precipitation. While submillennial sea-level fluctuations coincident with the peat initiation have not been reported in coastal lowlands of Japan, the close comparison of the onset ages and decreased precipitation recorded in a stalagmite from China, which represents the strength of the East Asian summer monsoon (EASM), suggests that decrease in precipitation led to the abandonment of crevasse splays. Our results may indicate that similar fluvial responses might be common in other coastal floodplains affected by the EASM.

Cap carbonate platform facies model, Noonday Formation, SE California

The Neoproterozoic outcrop belt of the Death Valley region, California, preserves an oblique cross section of the Noonday Formation, a mixed carbonate-siliciclastic platform that hosts distinctive basal Ediacaran cap carbonate−affiliated sedimentary structures, stromatolite textures, and δ^(13)C_(carb) values. The Noonday platform encompasses two depositional sequences that reveal two cycles of relative sea-level change within strata conventionally considered to record a single, rapid, postglacial sea-level rise. In updip localities, facies of the first depositional sequence record the transition from a carbonate ramp to a stromatolite-bearing, “tubestone”-textured, reef-rimmed platform; downdip, localities seaward of the reefal escarpment variably preserve a thin and condensed onlapping foreslope wedge. Base-level fall exposed the reef crest to karstic dissolution and propagated submarine incised valleys into the seaward margin of the reef. Overlying strata record the backfilling of a submarine incised valley and reestablishment of a back-stepping, carbonate-dominated ramp prior to a second subaerial exposure event that defines the contact between the Noonday and Johnnie formations. We address the relative contributions of syndepositional tectonism and recovery from low-latitude deglaciation in dictating Noonday platform architecture and the intra−Noonday Formation sequence boundary. Noonday Formation deposition coincided with extension of the Laurentian margin during disaggregation of the Rodinian supercontinent. Within this framework, previous work has suggested that the intra−Noonday Formation sequence boundary records growth faulting that reinforced differential topography, uplifting reef-rimmed horsts—exposing the reef crest to karstic dissolution—and downdropping grabens. However, we trace the intra−Noonday Formation sequence boundary seaward of the reef crest and demonstrate that, for a time, wave base was situated downdip of the reef escarpment on putatively downdropped fault blocks. Thus, if the Noonday margin were undergoing extension, then the creation of the intra−Noonday Formation sequence boundary required a concomitant decrease in accommodation due, perhaps, to postglacial isostatic uplift attendant with low-latitude deglaciation. We speculate that Noonday Formation sequence architecture records (1) immediate deglacial flooding, (2) shoaling and exposure due to isostatic rebound induced by either a hiatus in meltwater flux or rapid ice-sheet collapse against a background of global deglaciation, and (3) resumed flooding following complete deglaciation. As rift-related tectonism could amplify or counter glacial isostasy, inferences of the amplitude of local postglacial sea-level change will require robust estimates of syndepositional extension across the Noonday margin.

Postglacial relative sea level change at Fildes Peninsula, King George Island (West Antarctic)

Analysis and integration of data obtained in our field and laboratory investigations of 2008–2012 together with results of previous paleogeographic studies were conducted to reveal parameters and factors of the post-glacial changes in the relative sea-level on the Fildes Peninsula and the King George Island. Results of dating of organic material taken from cross-sections of Quaternary deposits, data on morphology of marine landforms as well as on bottom sediments in lakes were used to construct a curve of changes in the relative sea-level. Our research has shown that the rapid rise of relative sea level in the area (since the beginning of the Holocene) decelerated about 8000 years BP, achieving its maximum about 7000 years BP. This was followed by the fall of relative sea-level (the land elevation) by 18–20 m in total, and it was characterized by relatively high rate of fall during periods of 6000– 5000 years BP, 4000–2500 years BP, and during the last 1500 years; the rate decreased in 5000–4000 years BP and 2500– 1600 years BP. The changes in relative sea level in this region were determined by the following factors: the eustatic component of the global changes in sea-level and, possibly, oscillations in the global sea level of another nature; local parameters of the Last glacial maximum; a course of the Peninsula deglaciation; regional physical characteristics of the Earth's crust and the mantle substances; local tectonic processes, including the isostatic rebound. Since the beginning of the Holocene up to about 7000 years BP, the main contribution to changes of the relative sea-level in this area was made by the global eustatic factor. The subsequent fall of the relative sea-level (elevation of the Peninsula surface) proceeded under condition of reduced role of the eustatic factor and predominance of other factors.

Formation of subsurface shallow gas accumulations in Amurskiy Bay (Peter the Great Bay, Sea of Japan) as a result of postglacial sea-level change, paleoceanographic conditions and hydrological activity

We present new data on the study of subsurface gas accumulations in the sediments of Amurskiy Bay (the Sea of Japan). Geophysical research (single-channel continuous seismic profiling with airguns and high-resolution acoustic investigations with a high-frequency GeoPulse profiler) shows that the bay depression is filled by Pre-Quaternary sediments that are at least 0.8s (TWT) thick and overlaying Late Pleistocene–Holocene sediments that are up to 30m thick. The Pre-Quaternary deposits are possibly represented by coal-containing Mesozoic and Cenozoic rocks. Gas-related acoustic anomalies were found in the Late Pleistocene–Holocene silty sediments in the northern part of the bay. These gas-related anomalies have been divided into blanket column, turbidity and pillar anomalies. A single pockmark was also observed in the bottom relief of the bay. The gas accumulation area in the sediments is 19km long and 12km wide. The degassing of the Pre-Quaternary coal-containing deposits is assumed to be the major cause of gas. The formation of most of the gas anomalies in the Late Pleistocene–Holocene sediments and the trigger mechanism of gas migration may be associated with sea-level changes, paleoceanographic conditions, sedimentation features and the hydrodynamic regime in the bay. Increases in the number of diatoms and the presence of aberrant forms of some silicoflagellates have been observed in areas with high gas contents. Areas with numerous small underwater elevations or mounds were distinguished in the bay. In the northern part of the bay, the mounds correspond to ostraceous reefs or other local shellfish colonies. In the southern part of the bay, the elevations could be related to methane-derived authigenic carbonates, which formed pavements for the fixation of shellfish colonies and construction of reefs.

A new glacial isostatic adjustment model of the Innuitian Ice Sheet, Arctic Canada

A reconstruction of the Innuitian Ice Sheet (IIS) is developed that incorporates first-order constraints on its spatial extent and history as suggested by regional glacial geology studies. Glacial isostatic adjustment modelling of this ice sheet provides relative sea-level predictions that are in good agreement with measurements of post-glacial sea-level change at 18 locations. The results indicate peak thicknesses of the Innuitian Ice Sheet of approximately 1600 m, up to 400 m thicker than the minimum peak thicknesses estimated from glacial geology studies, but between approximately 1000 to 1500 m thinner than the peak thicknesses present in previous GIA models. The thickness history of the best-fit Innuitian Ice Sheet model developed here, termed SJD15, differs from the ICE-5G reconstruction and provides an improved fit to sea-level measurements from the lowland sector of the ice sheet. Both models provide a similar fit to relative sea-level measurements from the alpine sector. The vertical crustal motion predictions of the best-fit IIS model are in general agreement with limited GPS observations, after correction for a significant elastic crustal response to present-day ice mass change. The new model provides approximately 2.7 m equivalent contribution to global sea-level rise, an increase of +0.6 m compared to the Innuitian portion of ICE-5G. SJD15 is qualitatively more similar to the recent ICE-6G ice sheet reconstruction, which appears to also include more spatially extensive ice cover in the Innuitian region than ICE-5G.

Space geodesy constrains ice age terminal deglaciation: The global ICE‐6G_C (VM5a) model

AbstractA new model of the last deglaciation event of the Late Quaternary ice age is here described and denoted as ICE‐6G_C (VM5a). It differs from previously published models in this sequence in that it has been explicitly refined by applying all of the available Global Positioning System (GPS) measurements of vertical motion of the crust that may be brought to bear to constrain the thickness of local ice cover as well as the timing of its removal. Additional space geodetic constraints have also been applied to specify the reference frame within which the GPS data are described. The focus of the paper is upon the three main regions of Last Glacial Maximum ice cover, namely, North America, Northwestern Europe/Eurasia, and Antarctica, although Greenland and the British Isles will also be included, if peripherally, in the discussion. In each of the three major regions, the model predictions of the time rate of change of the gravitational field are also compared to that being measured by the Gravity Recovery and Climate Experiment satellites as an independent means of verifying the improvement of the model achieved by applying the GPS constraints. Several aspects of the global characteristics of this new model are also discussed, including the nature of relative sea level history predictions at far‐field locations, in particular the Caribbean island of Barbados, from which especially high‐quality records of postglacial sea level change are available but which records were not employed in the development of the model. Although ICE‐6G_C (VM5a) is a significant improvement insofar as the most recently available GPS observations are concerned, comparison of model predictions with such far‐field relative sea level histories enables us to identify a series of additional improvements that should follow from a further stage of model iteration.

Toward a luminescence chronology for coastal dune and beach deposits on Calvert Island, British Columbia central coast, Canada

The Quaternary geology of the central coast of British Columbia contains a rich and complex record of glacial activity, post-glacial sea level and landscape change, and early human occupation spanning the last ∼10,000 years. At present, however, this region remains a largely understudied portion of coastal North America. This study describes the luminescence characteristics of quartz and K-feldspar from coastal dune and beach sands on Calvert Island and develops a suitable optical dating protocol that will allow for a more rigorous chronology for post-glacial landscape evolution and human occupation on British Columbia's central coast. Luminescence signals from Calvert Island quartz are dim, and appear to lack the so-called “fast” component that is most desirable for optical dating. K-feldspar signals are sufficiently bright for optical dating. We test and refine a single-aliquot regenerative-dose (SAR) protocol for K-feldspar specific to Calvert Island samples through a series of dose recovery and preheat plateau tests. Two approaches for correcting a sample age for anomalous fading are compared and a correction for phototransfer is introduced and applied. Measured fading rates vary from sample to sample implying that, in this region, it is not sufficient to rely on two or three representative fading rates as has sometimes been done elsewhere. Refined age estimates show consistency with independent radiocarbon dating control and help identify radiocarbon-dated organic-rich sediments that have been reworked.

Refining Estimates of Polar Ice Volumes during the MIS11 Interglacial Using Sea Level Records from South Africa

Abstract Peak eustatic sea level (ESL), or minimum ice volume, during the protracted marine isotope stage 11 (MIS11) interglacial at ~420 ka remains a matter of contention. A recent study of high-stand markers of MIS11 age from the tectonically stable southern coast of South Africa estimated a peak ESL of 13 m. The present study refines this estimate by taking into account both the uncertainty in the correction for glacial isostatic adjustment (GIA) and the geographic variability of sea level change following polar ice sheet collapse. In regard to the latter, the authors demonstrate, using gravitationally self-consistent numerical predictions of postglacial sea level change, that rapid melting from any of the three major polar ice sheets (West Antarctic, Greenland, or East Antarctic) will lead to a local sea level rise in southern South Africa that is 15%–20% higher than the eustatic sea level rise associated with the ice sheet collapse. Taking this amplification and a range of possible GIA corrections into account and assuming that the tectonic correction applied in the earlier study is correct, the authors revise downward the estimate of peak ESL during MIS11 to 8–11.5 m.

Stratigraphy of late Quaternary deposits using high resolution seismic profile in the southeastern Yellow Sea

High-resolution (Chirp and Sparker system) seismic profiles were analyzed to investigate the sequence stratigraphy of late Quaternary deposits in the southeastern Yellow Sea. Approximately 1560 line-km data of chirp and sparker profiles were acquired, together with 11 piston cores. Two previous long drill cores (YSDP-102 and 103) were used for comparison with seismic data. High-resolution seismic profiles image the Holocene mud deposits and the complex sedimentary structure in this area. Sequence analysis of high-resolution seismic profiles reveals that the shelf deposits form a succession of high-frequency (five-order) sequences consisting of one depositional sequence developed during the late Quaternary. The depositional sequence includes five sedimentary units, each with different seismic facies and geometry: (1) incised channel fill and lowstand deltaic wedge (unit SY1), (2) sand ridges (unit SY2), (3) estuarine/deltaic mud (unit SY3), (4) redeposited mud (unit SY4), and (5) recent distal mud (unit SY5). Based on the interpretation of high-resolution seismic records and correlation with the YSDP-102, 103 long cores and piston cores, late Quaternary deposits in the southeastern Yellow Sea consists of a set of the lowstand (unit SY1), early transgressive (unit SY2), middle transgressive (unit SY3), late transgressive (unit SY4), and highstand systems tract (unit SY5) formed since the last-glacial period. The rather unusual stratigraphic architecture including three systems tracts is largely controlled by the postglacial sea-level changes and regionally circulation pattern associated with sediment erosion and redeposition. The results of this study present firstly clear seismic evidence that the southeastern Yellow Sea mud belt (SEYSM) can be divided into three stratigraphic units (units SY3, SY4, and SY5) bounded by distinct bounding surfaces.

Post-glacial sea-level change along the Pacific coast of North America

Sea-level history since the Last Glacial Maximum on the Pacific margin of North America is complex and heterogeneous owing to regional differences in crustal deformation (neotectonics), changes in global ocean volumes (eustasy) and the depression and rebound of the Earth's crust in response to ice sheets on land (isostasy). At the Last Glacial Maximum, the Cordilleran Ice Sheet depressed the crust over which it formed and created a raised forebulge along peripheral areas offshore. This, combined with different tectonic settings along the coast, resulted in divergent relative sea-level responses during the Holocene. For example, sea level was up to 200 m higher than present in the lower Fraser Valley region of southwest British Columbia, due largely to isostatic depression. At the same time, sea level was 150 m lower than present in Haida Gwaii, on the northern coast of British Columbia, due to the combined effects of the forebulge raising the land and lower eustatic sea level. A forebulge also developed in parts of southeast Alaska resulting in post-glacial sea levels at least 122 m lower than present and possibly as low as 165 m. On the coasts of Washington and Oregon, as well as south-central Alaska, neotectonics and eustasy seem to have played larger roles than isostatic adjustments in controlling relative sea-level changes.

Rising waters: New geoarchaeological evidence of inundation and early agriculture from former settlement sites on the southern Yangtze Delta, China

New pollen, phytolith, charcoal and diatom data from 14C AMS-dated sediments from three clusters of former occupation sites on the southern Yangtze Delta – Liangzhu, Majiabang and Chuodun – reveal that hydrological conditions were a key factor influencing early food production on the southern Yangtze Delta. At least two episodes of inundation are recognized, the first occurring at c. 7200–5700 cal. yr BP and a second from c. 4700 cal. yr BP. The first involved increasing salinity of surface waters, likely associated with marine intrusion linked to post-glacial sea-level change (meltwater pulse (MWP) 2). The second appears to have been freshwater in nature and driven at least in part by extreme meteorological events of high levels of precipitation in combination with impeded drainage. These two episodes had profound impacts on Neolithic settlement and farming. Further hydrological changes, presumably linked to changes in sedimentary regime, geomorphology and drainage of the Taihu depression, recorded at the Chuodun site after c. 3000 cal. yr BP, appear to have had a major effect on technologically relatively advanced food production systems. While environmental pressures appear to have played an important role in shaping human activities and settlement on the southern Yangtze Delta, people responded by adopting strategies that included an increased reliance on food production, migration to more clement locations and implementation of new technologies, which possibly included the construction of flood defence works.

Post-glacial filling of a semi-enclosed basin: The Arguin Basin (Mauritania)

Semi-enclosed basins are not very common features in the world and are most frequently the result of tectonic movements. Studies of their filling are usually based on the micropaleontological analyses of sediment cores (Torgersen et al., 1988; Reeves et al., 2007) or seismic analyses (Lykousis et al., 2007; Cagatay et al., 2009; Van Daele et al., 2011). The morphology of semi-enclosed basins is generally simple and bowl-shaped, and their edges are marked by one or more sills. Their depths range from a few dozen to several thousand meters. Semi-enclosed basins are however present in some regions in the world. The semi-enclosed basin of the Golfe d'Arguin (Northwest Africa) is present on a wide, shallow shelf, bordering the Sahara desert, in a stable tectonic context. Its sedimentary filling took place during the end of the post-glacial transgression. The current knowledge on sedimentary filling of semi-enclosed basins is rather limited and inadequate to fully understand the processes at play. Three campaigns have allowed the creation of the first morpho-bathymetric map of the Golfe d'Arguin, shedding new light on its large-scale morphology. A series of rocky shoals (Banc d'Arguin), interrupted by two sills in the north and south, divides the shelf into two parts, the inner and outer. The inner part of the Golfe d'Arguin, called the Arguin Basin, forms a shallow semi-enclosed depression. The basin is situated on the stable West African margin and the lack of any vertical tectonic movement provides an ideal situation for studying the progradation/regression variations and the sediment depositional conditions caused by the post-glacial sea level changes. Based on the analysis of very high-resolution seismic data, seven units were identified. The sedimentary sequence of deposition of the Arguin Basin was interpreted in relation to the bedrock morphology, the sea-level rise and the climatic changes. Their chronology was established in comparison to the regional sea-level curve, basin physiography and unit distribution. The Arguin Basin is interpreted as a land-locked freshwater lake during the post-glacial sea-level rise, corresponding to wet climatic conditions. The inner part was flooded ca. 8.7 ka BP when the sea level reached the sills. The filling then corresponded to a marine–estuarine environment. The climatic aridification and the sea-level stabilization from 6.5 ka BP onwards allowed the deposition of the last units, which are composed of aeolian sand combined with a significant marine biogenic carbonate fraction. Bedrock morphology plays a major role in determining the depositional sequence architecture. It controls the available accommodation space and, in conjunction with climate changes, influences the environmental processes that shape the deposit geometry.