Late Pleistocene Sea-level Changes Research Articles

Late Pleistocene sea level change and tectonism control on the formation of the Old Red Sand along the southeastern coast of China

The Zhe-Min Uplift (ZMU) has undergone tectonic subsidence, which has been associated with a notable transgression in the northern marginal seas of China since the middle Pleistocene. However, its uplift history during the late Quaternary is still inadequate. The Old Red Sand (ORS) is a late Pleistocene deposit that is widely distributed along the southeastern coast of China. The ORS consists of partially-cemented fine- to medium-grained sand. In this paper, we focus on mud-rich ORS deposits of the Liushui area, Pingtan Island, Fujian Province, and report optically stimulated luminescence (OSL) ages, and new datasets of grain size, mineralogy (detrital zircon, clay and detrital minerals) and organic carbon and nitrogen isotope profiles to improve understanding of chronology, provenance, palaeoenvironmental evolution and tectonic infuence. Based on the OSL data, we hypothesize that the development of the ORS was associated with lower sea levels, with most deposition occurring within MIS4. Based on comparison of detrital zircon UPb ages, the coarse fraction of the Liushui ORS was mainly derived from the Minjiang River, with modest input from weathering of coastal granites. The East Asian Winter Monsoon contributed some materials from the East China Sea shelf during the last glacial period, as indicated by the fine-grained nature of the Liushui ORS, low K-feldspar/plagioclase ratios, high dolomite content and the frequency of Neoproterozoic and Palaeoproterozoic detrital zircons. The deposition of the ORS was influenced by both the East Asian Winter Monsoon and sea level changes. The clay minerals in the mud layers of the Liushui ORS were dominated by kaolinite and illite, with little chlorite and no smectite, indicating that they originated from the Minjiang River. The TOC/TN ratios of the mud layers, as well as their isotope characteristics, indicate the organic matter was derived from marine sources, presumably during the transgression event in MIS5. The average uplift rate of the ORS was about 0.03 mm/yr. The uplift of the ORS provided new insights into the geological records of the ZMU, which differed from the subsidence observed in the northern region of the Minjiang River during the late Pleistocene.

Stable isotope geochemistry of Gwebin mammalian fauna with implications for late Neogene paleoenvironmental changes in central Myanmar

To explore the paleoenvironmental changes in SE Asia during the late Neogene, we examined the stable carbon and oxygen isotope compositions of tooth enamel from mammals of the late Pliocene/earliest Pleistocene Gwebin area in central Myanmar and compared the results with those of the latest Miocene Chaingzauk mammals in Myanmar. The stable carbon isotope values (δ13C) of Gwebin mammals indicate that they inhabited mosaic environment ranging from woodland to grassland. The relative abundance of C3-browsing versus C4-grazing bovids as well as other C3-consuming anthracotheriids, porcupine, rhinoceroses, suids, and stegodontids suggest the dominance of wooded environment. In central Myanmar, it is assumed that floral transition from C3 to C4 plants has occurred since the latest Miocene to Early Pliocene relating to the Himalayan Orogeny. However, stable isotope data at present indicate that paleoenvironment of central Myanmar did not change considerably in the Pliocene and served as a refugium for several forest/woodland dwellers at least until the early Pleistocene. The development of the proto-Ayeyarwady and proto-Chindwin drainage systems in the late Neogene of Myanmar induced the riparian environment, probably buffering against the rain shadow effect of the Indo-Myanmar Ranges. The onset of the present day aridification in central Myanmar is probably related to the Middle to Late Pleistocene sea-level changes in SE Asian region, which have had a major impact on climate, vegetation and megafauna of SE Asia.

Late Pleistocene sea-level changes and the formation and fill of bent valleys incised into the shelf of the western South China Sea

During times of lowered sea level, Mekong River and Red River incised valleys into the ancient coastal plains of the exposed shelves of the western South China Sea. The deglacial fill history of the incised valley was investigated by seismic surveys and sediment cores. The channels mainly exhibit a low-sinuosity course, but some channel segments are bent. The oldest part of the channel-bend fill exhibits shingled reflectors in Parasound seismic records documenting lateral channel migration typical of meandering rivers. Above, vertically stacked reflectors, which extend from the inner-bend side onto the cut-bank side document that the river-mouth channel turned to a mainly depositional mode. Vertical aggradation started when sea level was ~ 1–2 m below river water-level. During this phase, about two-third of the channel depth was filled by “fluvial-to-estuarine” mud having negative log(Ti/Ca) values as evidenced in XRF core scan data. Typically estuarine conditions developed when river water-level was approximate to sea level. Today channel bends form in estuaries within the zone of bedload convergence. Therefore, it is suggested that the studied channel bends represent antecedent, inherited features that formed during phases of prolonged phases of lowered, but relatively stable sea level to allow bends morphologically to develop. In fact, the bends occur not only in the western South China Sea but also in other areas of the world within a depth range that corresponds to times of retarded sea-level fall during MIS 5b, 5d, 4, and 3.

Phylogeography of Noah’s giant clam

Noah’s giant clam (Tridacna noae), recently resurrected from synonymy with T. maxima, occurs from Christmas Island to the Northern Line Islands and from the Ryukyu Islands to New Caledonia. We used mitochondrial and microsatellite markers to investigate the phylogeographic structure and demographic history of T. noae over most of its geographical range. Results from the two types of markers reveal a consistent population structure, partitioning T. noae into three distinct lineages: (1) eastern half of the Indo-Malay archipelago and Western Australia, (2) Melanesia and Micronesia, and (3) Central Polynesia. Demographic expansion initiated between 300,000 and 400,000 years ago, as was detected for each haplogroup. This pattern, which is congruent with other co-occurring Tridacna species, indicates a shared evolutionary history with expansion from past refuges following late-Pleistocene sea-level changes.

Late Pleistocene sea-level changes recorded in tidal and fluvial deposits from Itaubal Formation, onshore portion of the Foz do Amazonas Basin, Brazil

ABSTRACTThe Pleistocene deposits exposed in the Amapá Coastal Plain (onshore portion of the Foz do Amazonas Basin, northeastern South America) were previously interpreted as Miocene in age. In this work, they were named as "Itaubal Formation" and were included in the quaternary coastal history of Amazonia. The study, through facies and stratigraphic analyses in combination with optically stimulated luminescence (single and multiple aliquot regeneration), allowed interpreting this unit as Late Pleistocene tidal and fluvial deposits. The Itaubal Formation, which unconformably overlies strongly weathered basement rocks of the Guianas Shield, was subdivided into two progradational units, separated by an unconformity related to sea-level fall, here named as Lower and Upper Units. The Lower Unit yielded ages between 120,600 (± 12,000) and 70,850 (± 6,700) years BP and consists of subtidal flat, tide-influenced meandering stream and floodplain deposits, during highstand conditions. The Upper Unit spans between 69,150 (± 7,200) and 58,150 (± 6,800) years BP and is characterized by braided fluvial deposits incised in the Lower Unit, related to base-level fall; lowstand conditions remained until 23,500 (± 3,000) years BP. The studied region was likely exposed during the Last Glacial Maximum and then during Holocene, covered by tidal deposits influenced by the Amazon River.

Morphotectonics of the Gorringe Bank summit, eastern Atlantic Ocean, based on high-resolution multibeam bathymetry

High-resolution swath bathymetry of the Gorringe Bank, located along the Europe–Africa obliquely convergent plate boundary offshore SW Portugal, allowed investigation of its shallow-depth morphotectonic structure as a contribution to understanding the interplay of sea-level changes and active deformation of the region. Dominant ENE–WSW to NNE–WSW, and subordinate NW–SE trending morphologic alignments were mapped on the Digital Terrain Model (DTM) built from multibeam data for both the Gettysburg and Ormonde summits of the bank. Based on appraisal of regional structural and seismological data, the dominant and subordinate sets are interpreted to reflect dip-slip to left-oblique reverse faults, and normal faults or dyke-like joints, respectively. Several terrace remnants were mapped on the DTM and were grouped into five orders at depths ranging from ∼40 to ∼120 m. Morphological features suggest that the terraces were formed in a coastal environment likely during Middle–Late Pleistocene sea-level changes. The terraces are probably polycyclic, implying minor vertical tectonic motion. However, the whole terrace set (except the deeper and younger one, which was mainly shaped during the LGM lowstand) is consistently up to ∼10 m lower at Ormonde in the east relative to Gettysburg in the west, suggesting displacement across a NNE–SSW striking fault mapped in the saddle between the two seamounts. The structure assemblage is argued to represent the shallow splay system of a crustal-scale fault ramp underlying the bank. The ENE–WSW reverse faults have a southward polarity and, together with the overall northwest tilt of the bank, point to displacement toward the Horseshoe Abyssal Plain to the south at least at upper crustal levels.

Late Pleistocene to Holocene environmental changes as recorded in the sulfur geochemistry of coastal plain sediments, southwestern Taiwan

A core, drilled at San-liao-wan in the southwestern coastal plain of Taiwan, has been analyzed for total sulfur contents, isotopic values, as well as ratios of pyritic sulfur to organic carbon. Our results demonstrate a close relationship between late Pleistocene sea-level change and the proxies generated in this study. The inorganic sulfur contents indicate that at our study site, the Holocene transgression started at ∼11 ka and remained under seawater for thousands of years until the late Holocene, corresponding to a depth of 20 m in the study core. The uppermost 20 m of core shows relatively high total organic carbon (TOC) and δ 34S of inorganic sulfur, suggesting a transitional environment such as muddy lagoon or marsh, before the site turned into a modern coastal plain. In the lower part of the core, at depths of 110–145 m (corresponding ages of ∼12–30 ka), low sulfur contents are recorded, probably indicating fluvial sediments deposited during the oceanic isotope stage (OIS) 2, a sea-level lowstand. The lower part of the core, roughly within OIS 3, records at least two transgressions, although the transgressional signals may be somewhat obscured by subsequent weathering. The reworked origin of organic matter reported in previous studies is confirmed by our organic sulfur data; however, the marine organic source was periodically dominant. The modern high sulfate concentrations in pore water have no correlation to the other sulfur species in the sediments, probably indicating that the sulfate migrated into the site subsequent to early diagenesis.

Development of cassiterite-bearing sediments and their relation to late Pleistocene sea-level changes in the Straits of Malacca

Cassiterite-bearing sediments were surveyed in the central parts of the Straits of Malacca by high-resolution seismic profiling and vibrocoring. Placer deposits of cassiterite were found in the tidal scour channel of Cape Rachado and a Pleistocene river valley. According to sedimentological parameters the cassiterite derived from a local primary mineralization of granite and from long-distance fluvial transport. The basement, consisting of granites and metamorphites, is covered by four sedimentary sequences which are separated by major erosional unconformities. The last two unconformities were attributed to the regressional periods of the last and previous glaciations. Based on the distribution of the sequences deposited during periods of high sea level, the Malaysian peninsula is subsiding.

Late pleistocene sea level change in the Bahamas from mass spectrometric U-series dating of submerged speleothem

The dating of sea level events by a method independent of orbital tuning techniques and the marine foraminiferal isotopic record provides a test of both the dating of the marine record and the strength and nature of the relationship between climatic change, sea level change and Milankovitch cycles. Dating of fossil corals and submerged speleothem provides such independent information. Results of thermal ionization mass spectrometric U-series dating on layers of flowstone speleothem from Lucayan Caverns, Grand Bahama Island indicate that multiple sea level events have passed through a depth of −10 to −15 m below modern sea level during the last 300,000 years. These data are used to constrain the magnitude and timing of sea-level fluctuations during the late Pleistocene. The new sea level curve constructed from these data correlates closely with the marine isotopic record: sea level peaks occurred at around 233, 215, 125 and 100 ka BP. There is no evidence at the depth from which this speleothem was retrieved of any high sea stands at 195 or 80 ka corresponding to the foraminiferal 7a and 5a oxygen isotope peaks. There is also no evidence of a double rise around the 125 ka (5e) peak, although such an oscillation could have occurred above −10 m leaving no record in the Lucayan Caverns speleothem.

The effect of spatially non-uniform water loads on prediction of sea-level change

SUMMARY Numerical modelling of postglacial rebound predics a spatially variable pattern of sea-level change. Yet, many previous models predicting Late Pleistocene sea-level change either neglect the load of water added to the oceans, or assume a spatially uniform time-dependent load over the whole ocean. This is a poor approximation of the load near the former ice sheet, since sea-level change varies geographically. In addition, the coastline goemetry changes through time. A spectral technique has been used to solve the sea-level equation on an earth model with axisymmetric distribution of ice and oceans and also for a realistic ice-ocean configuration. The axisymmetric model is useful for demonstrating the fundamental physics involved in sea-level changes caused by changes in surface loads. In particular, it can be seen that the elastic and gravitational response to the load is spread over a great distance, whereas the viscous response is more localized. A realistic ice-ocean configuration has been used to demonstrate that, neglect of the melt-water load underestimates the amount of uplift in Fennoscandia and other regions where rebound occurs in the ocean [as previously noted by Wu & Peltier (1983) in Hudson Bay], and that movement of the coastlines and spatially varying water loads must both be included in calculations for the North Sea and other near field regions with shallow seas. Sea-level calculations including these effects and careful analysis of the sea-level and ice-melting record are required to determine modifications to the viscosity profile and ice model inferred by previous inaccurate models of the ocean load in the near field.

Late pleistocene and halocene sea-level changes in Japan: implications for tectonic histories and mantle rheology

It is very important to separate the tectonic and glacial-isostatic components in the observed Holocene and Late Pleistocene sea-level changes in tectonically active areas such as Japan for studying tectonic processes and for constraining mantle rheology. The separation can be achieved by considering the spatial dependence of the relative sea-level on the geometry of the coastline around the site where sea-level is evaluated. In fact, the relative sea-level caused by the last deglaciation at sites in the embayment such as Tokyo and Osaka has a sea-level curve with a high stand at mid-Holocene, and that site situated on the tip of peninsula has a sea-level curve culminating towards the present. The geometric effect also causes the regional difference of the sea-level variations in the late glacial phase. In the Japanese Islands, the regional difference of the predicted relative sea-level is about 5 m at 6000 years ago, 20 m at 10,000 years ago and 30 m at 18,000 years ago. Comparison between observations and predictions indicates that the observations at several sites in Japan are consistent with the predicted sea-level variations. More systematic data is required for the period 18,000 years ago to the present in order to examine tectonic processes and mantle rheology.

Palaeomangroves of Kanara coast, Karnataka, India and their implications on Late Pleistocene sea-level changes

Along the Kanara coast, some wells, show an organic clay layer, 1.5 to 7 m thick, between a layer of 2 to 6 m of coarse yellow sand above and white sand and pebbles below. The altitude of this intermediate organic clay formation is more or less at the present mean sea-level. Palynological analyses reveal that this sediment had been deposited within a mangrove environment i.e. at sea-level, while the 14 C datings give ages older than 40,000 years B. P. No proof of vertical movements after the deposit of the intermediate organic clay formation has been put forward up to now. Therefore, it can be accepted that the present elevation of this formation is more or less the same as its original altitude i.e., the present sea-level. Comparison of this altitude with the curves of global sea-level changes indicates that the period of deposition of these organic sediments should be around 125,000 years B.P., during the last Interglacial (Eemian) when the sea-level was ± the same that it is today. The main characteristics of “Eemian” flora were the same as the present. The climatic regime may have been slightly different with the less contrasting season.

KING ISLAND VISITED: An archaeological survey

Recent developments in Tasmanian prehistory have raised questions directly related to the archaeological investigation of Bass Strait islands. The discovery of human occupation in Tasmania over 30,000 years ago (Cosgrove in press) and recent research on late Pleistocene sea level changes in Bass Strait (Blom 1988) suggest that archaeological evidence of human occupation of a similar or possible even greater antiquity may yet be discovered on these islands. Stone artefacts have been recorded on Flinders Island in Bass Strait islands. Stone artefacts have been recorded on Flinders Island in Bass Straight which are reminiscent of the Kartan industry of Kangaroo Island (Lampert 1981, Orchiston 1979). Some archaeologists believe the Kartan to be an industry ancestral to the more general Australian core tool and scraper tradition although many disagree with this interpretation (Draper 1987, Lampert 1981, Tindale 1937, White and O'Connell 1982). The major focus of research on Flinders Island was however the shell middens for which the most recent date in a discrete midden area was 7,150 BP (Orchiston and Glenie 1979:131). New data on sea level changes (Blom 1988, Chappell and Shackleton 1986) and bathymetric mapping of the region have implications for archaeological evidence that had previously been interpreted as possible evidence of 'relict' prehistoric Bass Strait populations (Jones 1979, Orchiston 1979). The correlation of Bassian sea core sediment analysis with sea level curves, and the recently available bathymetric charts for the region, suggest that the dated archaeological evidence on both Flinders and King Islands could be from when they were still connected to Tasmania. The paucity of archaeological survey data on King Island suggested that it was an area of particular archaeological potential. A survey project was therefore planned which was both within the scope of an Honours thesis, and, could add to the limited knowledge of sites in the region. The primary aim of this project has therefore to locate and record sites on King Island to provide a descriptive documentation of the sites and their contexts. This was to form a basic data base from which further research questions could be formulated. From a preliminary surface survey it was hoped, that sites could be found on King Island; that the types of remains discovered would enable a tentative explanation (or alternative explanations) to be made regarding Aboriginal occupation of King Island and the relationship of this occupation to the broader context of southeast Australian prehistory; and, that sites could be found that would have the potential to test the validity of these explanations, and a future research project could be designed to facilitate this. King Island presented many logistical problems because of the remote location and transport limitations. The first reconnaissance trip to King Island to assess the feasibility of locating sites suitable for the project, indicated that the cost of carrying out the field work would be substantial. It was apparent that private sponsorship was necessary to enable this project to be carried out. Australian Geographic provided the required financial support which allowed six weeks field work to be completed during January and February in 1988. During this time twenty-two prehistoric Aboriginal sites and four historic sites were recorded. The latter included three early sealing womens' sites and one European muttonbirders' site.