Late Quaternary fire regimes of Australasia

We have compiled 223 sedimentary charcoal records from Australasia in order to examine the temporal and spatial variability of fire regimes during the Late Quaternary. While some of these records cover more than a full glacial cycle, here we focus on the last 70,000 years when the number of individual records in the compilation allows more robust conclusions. On orbital time scales, fire in Australasia predominantly reflects climate, with colder periods characterized by less and warmer intervals by more biomass burning. The composite record for the region also shows considerable millennial-scale variability during the last glacial interval (73.5–14.7 ka). Within the limits of the dating uncertainties of individual records, the variability shown by the composite charcoal record is more similar to the form, number and timing of Dansgaard–Oeschger cycles as observed in Greenland ice cores than to the variability expressed in the Antarctic ice-core record. The composite charcoal record suggests increased biomass burning in the Australasian region during Greenland Interstadials and reduced burning during Greenland Stadials. Millennial-scale variability is characteristic of the composite record of the sub-tropical high pressure belt during the past 21 ka, but the tropics show a somewhat simpler pattern of variability with major peaks in biomass burning around 15 ka and 8 ka. There is no distinct change in fire regime corresponding to the arrival of humans in Australia at 50 ± 10 ka and no correlation between archaeological evidence of increased human activity during the past 40 ka and the history of biomass burning. However, changes in biomass burning in the last 200 years may have been exacerbated or influenced by humans.     

Control of Carbonate Sedimentation and Reef Growth in Llandovery Sequences on the Northwestern Margin of the Yangtze Platform, South China

The later Telychian (late Llandovery, Silurian) sea-level highstand was a suitable setting for global carbonate deposition and reef growth in epeiric seas. However, evidence from the northwest margin of Yangtze Platform indicates that small carbonate platforms developed in rapidly-subsiding small basins and were principally controlled by muddy clastic input. In particular, sediments of the Ningqiang Formation, late Telychian, usually more than 2000 m thick, are mostly shales, but eight major units of discontinuous (15 km maximum width) and relatively thin (120 m maximum thickness) reef-bearing carbonates, which developed when the sedimentation rate apparently lessened, occur within a relatively short time interval. This interval is between upper griestonensis to spiralis-grandis graptolite biozones, estimated as a c. 2 Ma duration. More than 30 small- to medium-scale patch reefs occur in several parts of the sequence, but only within the carbonate units. Shelly faunas common throughout the sequence reveal water depth to have been shallow during deposition of the Ningqiang Formation equivalent to BA2–3, which has a depth range from low intertidal to the base of the photic zone. BA3 is interpreted as being no more than 60 m deep (Boucot, 1975), which is above normal wave base, frequently affected by storms (Chen et al., 1996), and is regarded as optimum depth for high diversity of Silurian faunas (Boucot, 1975; Brett, 1991). Thus, the rate of sediment accumulation kept pace with basement subsidence, and was a substantial factor for limiting reef growth. Sharp contacts between carbonate units and shales indicate that carbonate units are constrained by frequent inputs of terrigenous debris, as the major cause for termination of carbonate deposition. Therefore, carbonate platforms, and reefs they contained, formed during times when sediment input to the basin lessened and ended when it increased; present evidence does not allow correlation to modeled dry episodes, and we interpret the control to be principally tectonic. Overall, sedimentation in the region was terminated by the end of Telychian time by tectonic uplift of the Yangtze Platform; the southwestward migration of palaeocoastline shows this progression. Sedimentation ceased until Middle Devonian time. Ludlow marine transgression has been recognized in the offshore area of Ningjiang Bay.     

Late Quaternary environmental change and human impact around Lake Bolac,western Victoria,Australia

The late Quaternary history of the Lake Bolac region is reconstructed from sedimentary and pollen analysis of lake and swamp sequences and is supported by archaeological remains from lunette sediments. Freshwater deposits recovered from lake Turangmoroke appear to date from the last glacial period, when the vegetation was composed of herbfield and grassland. Subsequent dry conditions at the end of the Pleistocene caused the deflation of some accumulated sediments. On refilling, the lake had become saline. As moisture availability increased, casuarina woodland, dominated by Allocasuarina verticillata, became the regional vegetation cover. Domination by casuarina ended ca. 8000–7000 yr BP, probably as a result of rising saline ground-water tables. Casuarinas were replaced to some degree by eucalypts, augmented by the development of a riverine Eucalyptus camaldulensis woodland. Swamp deposition commenced in the channel of neighbouring Fiery Creek at ca. 4000 yr BP, most likely as the result of a reduction in stream flow with decreased precipitation. Despite suggestions of significant impact on the vegetation by Aboriginal people from other sites in southeastern Australia, there is no evidence of any alteration here from periods of occupation dated to around 13000 yr BP and after 3500 yr BP. The period of European occupation, though, is marked by significant changes in fire patterns, reduced tree cover, loss of floristic diversity, increased erosion rates and salinity levels, and decreased water levels.     

The Global Stratotype Section and Point （GSSP） for the base of the Holocene Series/Epoch （Quaternary System/Period） in the NGRIP ice core

The Greenland ice core from NorthGRIP （NGRIP） contains a proxy climate record across the Pleistocene-Holocene boundary of unprecedented clarity and resolution. Analysis of an array of physical and chemical parameters within the ice enables the base of the Holocene, as reflected in the first signs of climatic warming at the end of the Younger Dryas/Greenland Stadial 1 cold phase, to be located with a high degree of precision.     

华南奥陶纪生物礁时空分布的控制因素(英文)

华南奥陶纪生物礁主要分布于三个层位 ,选择了数个生物礁实例分析当时的古地理格局对礁相地层时空分布的控制作用。涉及到的生物礁赋存层位自下而上为 :特马道克晚期扬子地台中部宜昌分乡组和同时代的扬子地台南缘皖南的仑山组 ;阿伦尼克早期分布于地台中部至南缘的红花园组 ;阿什吉尔中期浙赣边区下镇组和三衢山组。研究结果表明 ,礁相地层的的发育与否及其生物和沉积结构在时空上表现出的分异 ,明显受控于与古地理背景的变迁相关的诸多因素 ,如海平面升降、碳酸盐岩台地的规模以及沉积区间的抬升等     

Sedimentary and biotic evidence of a warm-water enclave in the cooler oceans of the latest Ordovician glacial phase, Yangtze Platform, South China block

Abstract   During the Hirnantian period, the Yangtze Platform was situated in the western part of the South China block (SCB) before its later rotation, in the middle–low paleolatitudes of the southern hemisphere in the northeast side of peri-Gondwana. It is part of the Kosov faunal province as indicated by the Hirnantia fauna. Sedimentary evidence shows the domination of cool ventilated marine water from its offshore ramp and shelf. Hirnantian shallow-water carbonate facies (Kuanyinchiao Bed) overlie earlier Ashgill graptolitic black shales (Wufeng Formation) as a result of marine regression. In the Yangtze Platform, however, we have found local areas of intertidal to nearshore facies that lack the typical highly diverse Hirnantia fauna. Some warm-water features (radial oolites, peloids, diverse solitary rugose corals and other benthic shelly fauna) occur commonly in some limited shallow areas, forming grainstones and packstones. Although interglacial episodes within the Hirnantian glaciation could be responsible for these features, their limited occurrence within the interior of the platform leads us to interpret the deposits as indicating that cold-water currents from the southeastern high latitudes were partly excluded from the nearshore area of the Yangtze Platform. The landmass of the eastern SCB in the Hirnantian epoch prevented access to some areas of the cold marine water masses that flowed from higher latitudes of Gondwana; the result was a persistence of warm-water shallow marine facies in some areas.