Evolution of Tere-Khol lake and the holocene dynamics of the environment in the southeastern part of the Sayan-Tuva highland
А. В. ПанинM. A. BronnikovaO. N. UspenskayaИрина АржанцеваЕ. А. КонстантиновА. В. КошурниковE. V. SeleznevaYu. N. FuzeinaE. D. Sheremetskaya
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ABSTRACT Unconsolidated carbonate sands and cobbles on Kapapa Island, windward Oahu, are 1.4-2.8 (± 0.25) m above present mean sea level (msl). Agreeing with Stearns (1935), we interpret the deposit to be a fossil beach or shoreline representing a highstand of relative sea level during middle to late Holocene time. Calibrated radiocarbon dates of coral and mollusc samples, and a consideration of the effect of wave energy setup, indicate that paleo-msl was at least 1.6 (± 0.45) m above present msl prior to 3889-3665 cal. yr B.P, possibly as early as 5532-5294 cal. yr B.P., and lasted until at least 2239-1940 cal. yr B.P. Hence, the main phase of deposition on Kapapa Island lasted a minimum of c. 1400 yr and possibly as long as c. 3400 yr. No modern samples have been recovered from the fossil beach on Kapapa Island, and samples from potential source sites offshore of the island show modern ages, indicating that sediments on the island are not deposited by modern-era storm and tsunami overwash. Because antecedent sediments are uncommon offshore but common on the island, deposition must have been time-transgressive rather than related to a single event. Radiocarbon ages of coral and mollusc clasts from a breccia lining an emerged (1.4 ± 0.25 m msl) intertidal notch, cut into emerged coralline-algal carbonate of presumed last interglacial age, on south Mokulua Island (15 km to the southeast of Kapapa Island) correlate to the history recorded on Kapapa Island. Calibrated ages range from 2755-2671 to 3757-3580 cal. yr B.P. (averaging c. 3100 cal. yr B.P.) suggesting that a higher than present sea level formed the notch prior to 3757-3580 cal. yr B.P. A storm or tsunami origin for the features on Kapapa and south Mokulua islands is highly unlikely. Their age and elevation indicate, instead, a history of higher relative sea level (and subsequent fall) on windward Oahu during the middle to late Holocene. This history is consistent with geophysical models of postglacial geoid subsidence over the equatorial ocean first predicted by Walcott (1972) and later refined by Clark et al. (1978) and Mitrovica and Peltier (1991).
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The Chinese Loess Plateau has been demonstrated to be one of the most sensitive areas to large-scale climate changes.The reconstruction of paleoclimatic changes in this region is expected to significantly improve our understanding of the mechanisms and processed of large-scale climate changes.Pollen data from 24 sites in the Chinese Loess Plateau were reviewed to document regional patterns of Holocene vegetation and climate change.Vegetations at bedrock mountain and valley switched forest,while,vegetation in the Yuan and the transitional zone between loess and desert changed between steppe and desert steppe and there was no natural forest.Considerating of uncertainties in the chronologies,those pollen data,in spite of differ area,suggested that the similar climatic characteristics during Holocene,e.g.,arid on early and late Holocene while warm and humid on the middle Holocene.
Steppe
Bedrock
Loess plateau
Holocene climatic optimum
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Up to six regressive terraces occur on the Holocene raised reef tract and up to 15 occur on late Pleistocene raised reef tracts along 40 km of coastline at Huon Peninsula, Papua New Guinea. We suggest that the regressive terraces represent repeated episodic uplift caused by great earthquakes. Ages of Holocene coseismic uplift events are established by radiocarbon dating; the late Pleistocene events are bracketed by U series ages of the raised reef tracts on which they occur. The mean recurrence interval of great earthquakes that caused the uplift events is 970 to 1165 years in the Holocene and probably the same in the late Pleistocene; the interval ranged from about 200 to 1900 years. The uplift rate increases parallel to the coast from northwest to southeast, and the amplitude of coseismic uplifts generally increases similarly, although some events produced uplift with little shore‐parallel tilting. The mean amplitude of coseismic uplifts throughout the study area is ∼3 m in for both Holocene and late Pleistocene sequences. Large, late Quaternary landslides are numerous, and some probably were triggered by the great earthquakes that caused coseismic uplift. There appears to be no continuum between historical large earthquakes at Huon Peninsula of magnitudes >7 that produced no or only minor uplift, and the great earthquakes represented by meter‐scale coseismic uplifts and very large landslides. Two tectonic subregions are recognized, which were uplifted together by some Holocene events but not by others. There is no surface trace of Holocene faulting between the subregions, and a buried fault is thought to separate them.
Tectonic uplift
Peninsula
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Abstract This paper summarizes the present knowledge on the variation of summer temperatures in the European Alps throughout the Holocene by combining the results of an extraordinary archaeological find with the information gathered from glacier and tree-line movements. As it turns out, there were several distinct periods were the glaciers were smaller than today, allowing in some periods the growth of trees in areas, which even now are still covered with ice. On average, the first half of the Holocene was warmer than the second half, with temperatures starting to decrease around the time of the Iceman some 5000 yr ago. One of the coldest periods during the Holocene, the so-called Little Ice Age (LIA), lasted from about AD 1300 to 1850. It is well known that since then the Alpine glaciers have been receding, most likely amplified by anthropogenic impact. The study of temperature variations before human influence may help to eventually disentangle natural and anthropogenic causes for the global warming of our time.
Tree line
Holocene climatic optimum
Ice core
Little ice age
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The late Holocene activity of a restraining bend of the northern strand of the North Anatolian Fault in Izmit Bay was investigated by a sedimentological, geochemical, and paleoecological analysis of sediment cores from Hersek coastal lagoon, NW Turkey. The sediment cores show a succession of sedimentary sequences composed of three units separated by gradual transitions. The first unit is composed of a thin layer of shell debris-rich sediment in abrupt contact with the underlying organic-rich deposits. This unit is overlain by a thick foraminifera-rich mud deposit, and the sequences are capped by an organic-rich mud unit. These sequences are interpreted as silting up, shallowing upward deposits, typical of a lagoon becoming isolated from the sea. We suggest that they represent the sedimentary signature of coseismic subsidence, which was caused by reverse slip at the Hersek bend, and tsunamis in Izmit Bay. Our radiocarbon-dated paleoseismological record indicates (1) the atypical collapse of the hanging wall during the 740 earthquake and (2) subsidence of the footwall during the 987, 1509, and 1719 earthquakes. This study contributes to the understanding of the dynamics of restraining bends, and it highlights the potential of coastal sediments for reconstructing past earthquakes and tsunamis in regions dominated by strike-slip deformations.
North Anatolian Fault
Paleoseismology
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Synthetic analyses on sedimentology and geochemistry of a sediment core with high deposition rate collected under the Tsushima Warm Current (TWC) axis on the southwestern slope of East/Japan Sea were carried out,in order to discuss the formation and evolution of TWC during the Holocene. Based on them,we got very similar results to those from paleoceanographical method in nearby areas. Thus,sedimentological and geochemical methods were offered for the future study on TWC evolution in the study area. Totally,there were five main evolution periods of TWC recorded in the study core. In the early Holocene,that is 9.6 kaBP,TWC began to weakly enter into the East/Japan Sea,together with the East China Sea Coast Water (ECSCW) enriched in nutrient matter,which led to the transfer of bottom environment from anoxic to oxic. At 6.5 kaBP,the modern current mode dominated by TWC in the southern East/Japan Sea finally formed,whereas the influence of ECSCW almost disappeared. After that,TWC obviously weakened. At 3.0 kaBP,TWC strengthened again to almost reach its present level,since then the circulation structure has been relatively stable,except for a weak depression of TWC during 2.0~0.7 kaBP.
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ABSTRACT Scalloped and planar erosion surfaces are developed at numerous stratigraphic levels above prograded tidal flat fenestral limestones and beneath more open marine skeletal limestones in the Middle Ordovician limestone sequence, Virginia. Scalloped surfaces consist of smooth curved basins (10 cm to over 1 m wide) with intervening steep, locally overhanging walls and sharp ridges. Relief is up to 30 cm. The scalloped surfaces pass laterally into planar erosional contacts. Erosional surfaces truncate grains and cements and rare incipiently brecciated (vadose) fabrics. Fossiliferous breccias occur rarely above contacts. Some contacts are bored locally and encrusted by calcareous algae and bryozoans. Erosional contacts between fenestral limestones and overlying skeletal beds are extremely s arp and there is no burrowing across the contacts. Locally, submarine hardgrounds converge onto scalloped/planar erosional contacts. The erosion surfaces are believed to have formed initially as exposed karst on supratidal, prograded, early lithified tidal flat limestones, as indicated by vadose features beneath some contacts. Further erosion in tidal rock platform environments is indicated by position of erosion surfaces beneath open marine carbonates, organic encrustation of contacts, local marine cements beneath some contacts, local bored contacts, and by reported higher rates of tidal erosion compared to subaerial erosion in the Recent. These surfaces do not appear to have been documented to any extent in ancient carbonate sequences. However, the abundance of such surfaces along modern coasts and in karst terrains, and in the Middle Ordovician limestones of Virginia, suggests that they might be more abundant elsewhere. Finally, these surfaces might be useful in defining paleoshorelines in the absence of tidal flat deposits.
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