Timing and duration of growth hiatuses in mid Holocene massive Porites corals from the northern South China Sea

Growth hiatuses in massive corals are usually indicative of past ecological or environmental stresses. Among 37 fossil Porites colonies surveyed from the reef flat of Dadonghai fringing reef at Sanya, Hainan Island, northern South China Sea, seven of them were found to show clear evidence of past mortality, representing a population of ～19%. Among these samples, two of them (SYO‐13 and SYO‐28) display clear growth hiatuses reflecting mortality followed by subsequent recruitment, and five others exhibit a well‐preserved mortality surface and no subsequent recruitment. The growth hiatuses were dated using high‐precision thermal ionisation mass spectrometry U‐series techniques. The age results suggest all the dated corals formed and died in the mid Holocene. Multiple dates below the growth hiatuses suggest that SYO‐13 and SYO‐28 died at 6298 ± 11 and 6929 ± 19 a BP (i.e. years before AD 1950), respectively. Multiple dates above the growth hiatuses indicate that growth in SYO‐13 and SYO‐28 resumed at 6257 ± 14 and 6898 ± 20 a BP, respectively. The calculated durations of growth hiatuses are therefore 41 ± 18 a for SYO‐13 and 31 ± 28 a for SYO‐28, respectively, implying growth resumed within decades after the mortality events. U‐series dating of four other samples with dead heads suggests that they died at 6035 ± 53, 6059 ± 23, 6127 ± 22 and 6474 ± 24 a BP, respectively. In addition, using solution inductively coupled plasma mass spectrometry (ICP‐MS), monthly resolution Sr/Ca and Mg/Ca ratios were determined for the annual growth bands below and above the growth hiatuses for three of the dated samples. The Sr/Ca and Mg/Ca profiles indicate that the three corals probably died in different seasons (from spring to autumn), and the mortality appears to be unrelated to anomalous sea surface temperature‐induced bleaching. Copyright © 2010 John Wiley & Sons, Ltd.     

Late Pleistocene and Holocene terrestrial geomorphodynamics and soil formation in northeastern Germany: a review of geochronological data

ABSTRACT

This study is based on 616 geochronological ages from aeolian and colluvial sediments as well as paleosols, representing the largest database of geochronological data from northeastern Germany available to date. Cumulative probability density functions for radiocarbon data and kernel density estimates for luminescence data were created covering the last 15 ka. The data analysis aimed at the identification of changes and their drivers in geomorphodynamics and soil formation. The ages representing aeolian activity cluster in the Late Glacial, the Early Holocene, and the Late Holocene, where the first two clusters are assumed to result mostly from climatic impact with only a minor share of human impact triggering the mobilization of aeolian sediments. The third cluster is considered to result mainly from human impact. The Late Glacial to Early Holocene activity phase is interrupted by a phase of surface stability around 11.5–12.7 ka, which is indicated by the occurrence of initial soil formations of Finow and Usselo types. Colluvial sedimentation predominantly occurred during the last 7 ka and clearly accelerated since the last 1000 a. According to the ages of specific paleosol types, related soil-forming processes started already in the Late Glacial and were completed in the Holocene.     

江苏建湖地区全新世孢粉组合及其地质、古地理意义

对江苏建湖地区若干全新世剖面进行了系统的孢粉分析，划分出６个孢粉组合带，恢复了本地区自早全新世以来的古植被演替与古气候古环境变迁，探讨了本区全新世地层时代划分与对比     

青海喇家遗址地层划分及齐家文化废墟覆盖层成因分析

对喇家遗址进行了全面的野外考察,在其北部发现完整连续的全新世黄土-古土壤地层剖面。通过系统采样、粒度和磁化率等多种指标测试,结合OSL技术测年断代,建立了完整的土壤地层序列。深入分析土壤沉积物性质与地表过程,揭示了覆盖齐家文化废墟的沉积物的成因。研究结果表明:喇家遗址土壤沉积物地层层序自地表向下依次为:现代土壤(MS,0～1.50 ka B.P.)→全新世晚期风成黄土(L0,1.50～3.10 ka B.P.)→全新世中期古土壤(S0,3.10～8.50 ka B.P.)→全新世早期过渡性风成黄土(Lt,8.50～11.50 ka B.P.)→晚更新世晚期马兰黄土(L1,>11.50 ka B.P.)。其中全新世中期黑垆土古土壤(S0)被3组红色粘土质泥流(RC3、RC2和RC1)和山洪沙土(FFD)沉积层穿插分隔为4个亚层(S0上、S0中上、S0中下和S0下)。这证明黑垆土发育过程中,在OSL年龄3.96～3.65ka,对应于14C年龄3.85～3.60 ka B.P.出现一个山洪泥流盛行期,来自于盆地北侧沟谷的大规模暴雨山洪泥流,在大红山前古洪积扇前沿溢出沟槽、扩散覆盖了黄河...     

基于MapObjects的中国洞穴石笋信息管理系统

以中国洞穴石笋信息管理系统的设计与实现为例,讨论如何运用GIS组件MapObjects（MO）与可视化编程语言VisualBasic相结合这一开发模式,进行应用型的二次开发。并介绍了该系统的一些功能和数据库的设计,对系统中关键技术做了总结,通过该系统实现对能反映古气候的石笋信息的有效管理,为系统的后续功能拓展和维护积累了经验。     

浙江象山海滩岩的发现及其意义

作者于浙江象山爵溪首次发现了全新世海滩岩,并对其岩石学特征、同位素年龄、形成环境等进行了初步研究。爵溪海滩岩目前是我国分布位置最北的全新世海滩岩,据14C年龄测出该地3400多年来海岸的相对沉降速率为0.51mm/a     

Using microcomputed tomography (μCT) to count varves in lake sediment sequences: Application to Lake Sagtjernet,Eastern Norway

Varved lake sediments are one of the most important natural archives that allow annual resolution paleoclimate reconstructions. Conventional varve counting techniques use thin sections to manually identify lamina. However, this technique is destructive, labour intensive and limited to a 2D representation of complex 3D features which may lead to misidentification of varve boundaries. This study presents the use of microcomputed tomography (μCT) scans in constructing varve chronologies, utilizing scanning resolutions of ∼50 μm (binned to ∼200 μm) for core sections up to 150 cm long. To evaluate this method, we cored and analysed Lake Sagtjernet in Eastern Norway — revealing a 593 cm-long sediment record of the past 10274 (⁺²²⁰/_-329) years, with continuous laminations from 84 to 533 cm depth (75% of the sediments). Through limnological monitoring and microfacies analyses we demonstrate that the laminations are rare ferrogenic varves, with an annual deposition pattern comprised of seasonal changes in biogenic production superimposed on seasonal precipitates of iron and manganese hydroxides. The floating μCT-counted varve chronology presented here is the first non-glacial varve chronology in Norway and covers 4023 ⁺¹¹³/_-185 years. We find that μCT scans allow for a very fast and non-destructive way of counting varves with sufficient detail of varve boundaries. In the few sections where varve boundaries are too vague to resolve, we recommend using complimentary techniques such as thin sections in parallel. The varve chronology is in good agreement with the 95% confidence interval of the independent radiocarbon chronology based on 16 ¹⁴C dates, and ²¹⁰Pb and ¹³⁷Cs activity peaks, indicating that the varve chronology can be equated to calendar age.     

Late Pleistocene to Holocene eruptive activity of Pico de Orizaba,Eastern Mexico

The Late Pleistocene to Holocene eruptive history of Pico de Orizaba can be divided into 11 eurptive episodes. Each eruptive episode lasted several hundred years, the longest recorded being about 1000 years (the Xilomich episode). Intervals of dormancy range from millenia during the late Pleistocene to about 500 years, the shortest interval recorded in the Holocene. This difference could reflect either changes in the volcano's activity or that the older stratigraphic record is less complete than the younger. Eruptive mechanisms during the late Pleistocene were characterized by dome extrusions, lava flows and ash-and-scoria-flow generating eruptive columns. However, in Holocene time plinian activity became increasingly important. The increase in dacitic plinian eruptions over time is related to increased volumes of dacitic magma beneath Pico de Orizaba. We suggest that the magma reservoir under Pico de Orizaba is stratified. The last eruptive episode, which lasted from about 690 years bp until ad 1687, was initiated by a dacitic plinian eruption and was followed by effusive lava-forming eruptions. For the last 5,000 years the activity of the volcano has been gradually evolving towards such a trend, underlining the increasing importance of dacitic magma and stratification of the magma reservoir. Independent observations of Pico de Orizaba's glacier early this century indicate that some increase in volcanic activity occurred between 1906 and 1947, and that it was probably fumarolic.     

Robust chronologies for landform development

Obtaining chronological control for geomorphological sequences can be problematic due to the fragmentary and non‐sequential nature of sediment and landform archives. The robust analysis of ¹⁴C ages is often critical for the interpretation of these complicated sequences. This paper demonstrates a robust methodology for the ¹⁴C dating of geomorphological sequences using a case study from the lower Ribble valley, northwest England. The approach adopted incorporates using greater numbers of ages, targeting plant macrofossils, obtaining replicate measurements from single horizons to assess the extent of reworking and the use of Bayesian approaches to test models of the relative order of events. The extent of reworking of organic materials and space‐time dynamics of fluvial change means that it is critical that chronological control is sufficiently resourced with ¹⁴C measurements. As a result Bayesian approaches are increasingly important for the evaluation of large data sets. Assessing the conformability of relative order models informed by interpretation of the geomorphology can identify contexts or materials that are out of sequence, and focuses attention on problem materials (reworking) and errors in interpretation (outlier ages). These relative order models provide a framework for the interrogation of sequences and a means for securing probability‐based age estimates for events that occur between dated contexts. This approach has potential value in constraining the sequence of geomorphological development at scales that vary from individual sites to a catchment or region, furthering understanding of forcing and change in geomorphological systems. Copyright © 2008 John Wiley & Sons, Ltd.     

Holocene Rockwall Retreat in Svalbard: A Triple-Rate Evolution

Volumetric calculations of slope deposits, direct measurements of rockwall retreat and chronological control based on lichenometry provide a wide range of rockwall retreat rates in Svalbard (0–1580 mm ka⁻¹) that appears consistent with previous evaluations from other Arctic areas. In northwest and central Spitsbergen (79°N), a triple-rate rockwall retreat is suggested for the last two millennia: very slow biogenic flaking (2 mm ka⁻¹), moderate retreat due to frost shattering (100 ka⁻¹) and rapid retreat associated with post-glacial stress relaxation (c. 1000 mm ka⁻¹). Examination of the distribution of various processes indicates that the Holocene retreat of most rockwalls has not exceeded one or two metres. Bedrock conditions appear to be the main control on retreat rates. The massiveness of igneous and metamorphic outcrops, widespread in Arctic shield areas, largely accounts for the slowness of rockwall retreat, which on these lithologies is primarily due to chemical and biological processes. More rapid rates are usually associated with stress relaxation following glacial surges or with local frost susceptibility of bedrock, often where faulting has induced high joint density. At such sites, rockwall retreat rates are of the same order of magnitude as those reported from Alpine areas (1000–3000 mm ka⁻¹) where both bedrock weakening due to tectonic stresses and the greater height of steep rockwalls account for the more rapid rockwall retreat rate. © 1997 by John Wiley & Sons, Ltd.