Palaeoenvironmental evolution and sea‐level fluctuations along the southeastern Pampa grasslands coast of Argentina during the Holocene

Holocene pollen and diatom analyses and complementary data from δ¹⁸O and δ¹³C, malacology and sedimentology have provided a detailed record of vegetation history and palaeoenvironmental change at arroyo Las Brusquitas, on the southeastern coast of the pampas of Argentina especially in relation to past sea levels. Holocene palaeosalinity trends were estimated by Detrended Correspondence Analysis and by salinity indexes based on pollen and diatom data. As a consequence of sea‐level rise from the postglacial an extensive wave‐cut platform formed over which Holocene infilling sequences were deposited unconformably. In these sequences, variation in pollen and diatom assemblages occurred in agreement with changes in mollusc diversity and abundance, isotope values, and sediment deposits. Between ca. 6700 and 6190 ¹⁴C yr BP (6279–6998 cal. yr BP) saline conditions predominated in an environment highly influenced by tides and salt water during the Holocene sea‐level highstand. Between ca. 6200 and 3900 ¹⁴C yr BP (4235–4608 cal. yr BP) shallow brackish water bodies formed surrounded by saltmarsh vegetation that became more widespread from 5180 ¹⁴C yr BP (5830–6173 cal. yr BP) to 3900 ¹⁴C yr BP in relation to a sea‐level stabilisation period within the regression phase. Less saline conditions marked by frequent variations in salinity predominated between ca. 3900 and 2040 yr ¹⁴C BP (1830–2160 cal. yr BP). The intertidal saltmarsh environment changed into a brackish marsh dominated by freshwater conditions and sporadic tidal influence. Halophytic vegetation increased towards ca. 2000¹⁴C yr BP indicating that saline conditions may be due to either desiccation or an unusually high tide range with rare frequency. After ca. 2000 ¹⁴C yr BP the sedimentary sequences were buried by aeolian sand dunes. Changes in Holocene vegetation and environments in Las Brusquitas area are in agreement with data obtained from various southeastern coastal sites of the Pampa grasslands. Copyright © 2005 John Wiley & Sons, Ltd.     

A late Holocene record of land-use history,soil erosion,lake trophy and lake-level fluctuations at Bjäresjösjön (south Sweden)

Land-use history, soil erosion, lake trophy and lake-level fluctuations during the last 3000 years were reconstructed through a multidisciplinary palaeolimnological study (pollen, plant macrofossils, diatoms, physical and chemical analysis, magnetic measurements and radiometric methods) of a small eutrophic lake in southern Sweden (Bjäresjösjön, Scania). There are striking responses in diatom, chemical, sediment yield and magnetic records to land-use changes documented by pollen analysis or historical sources, and to lake-level changes identified from sedimentary changes. Our multidisciplinary approach assists interpretation of the processes controlling long-term changes and separation of the effects of different factors (land-use changes, lake-level fluctuations) on individual biostratigraphical records. Climate has controlled processes in the lake indirectly, through lake-level fluctuations, from the Late Bronze Age to the Viking Age (700 BC-AD 800). Since the Viking Age, land-use controlled most of the changes observed in the lake's development and soil erosion processes. Major changes in lake development occurred during the last 200 years, due to a drastic increase in soil erosion and water eutrophication during a period of agricultural modernization.     

THE SPREAD OF AGRICULTURE IN CHINA

At pressent, China has about 100 million ha of farmland and 1.1 billion inhabitants, of which, about 80% are still engaged in agriculture. In geographical distribution, primitive shifting cultivation was at first mainly scattered in small patches in Eastern Monsoon China, especially concentrated in the middle and lower reaches of the Huanghe (Yellow) River and the Changjiang (Yangtze) River. The ratio of agriculture to industry in production value changed from 7:3 in the early 1950s to 3:7 in the middle 1980s. Agricultural Regionalization is based upon agricultural development as well as physical regionalization in China. Seven first-level agricultural regions might be identified.     

On the First Anthropic Argument in Astrobiology

We consider the little-known anthropic argument of Fontenelledealing with the nature of cometary orbits, given a year before the publication of Newton'sPrincipia. This is particularly interesting in view of the rapid development of therecently resurgent theories of cometary catastrophism and their role in the modern astrobiologicaldebates, for instance in the ``rare Earth' hypothesis of Ward and Brownlee.     

A Holocene and latest Pleistocene pollen record from Lake Poukawa, Hawke's Bay, New Zealand

Lake Poukawa is a small, shallow lake lying in the middle of extensive peatland in the Poukawa depression, central Hawke's Bay. Holocene peats (10 m at deepest point) overlie more than 200 m of sand, silt, clastic debris and infrequent thin peats and lacustrine sediments deposited during the late Pleistocene. Pollen analyses are presented for: a peat possibly dating to a late stage of the last interglacial or a warm interstadial of the last glacial; cool climate last glacial sediments; and a Holocene peat. The last interglacial or interstadial peat records a cool climate Nothofagus podocarp forest. During the last glacial, sparse shrubland and grassland grew within the depression under much drier and colder conditions than now. There is no pollen record for the Late Glacial and early Holocene period as conditions remained too dry for peat formation. Avian fossils indicate scrub and grassland persisted through until at least 10,600 years BP, and scrub or open forest may have prevailed until c. 6500 years BP. Closed podocarp broadleaved forest (Prumnopitys taxifolia dominant) occupied the depression from at least 6500 years BP until its destruction by Polynesian settlers after 800 years BP. Water levels rose from 6500 to 4500 years BP, culminating in the establishment of the present fluctuating lake-peatland system. Dry conditions in the Late Glacial and early Holocene may reflect a predominant northwesterly air flow, and a change to more easterly and southerly air flow in the mid- to late Holocene resulted in increased rainfall.     

天再旦日食的根据与计算——对Keenan质疑的注释

作者由“天再旦”日食说证实西周懿王元年为公元前 899年。夏商周断代工程以此为支点之一 ,得到西周年代表。针对读者的质疑 ,在历史文献的可靠性、天光视亮度的表达和计算方法、地球自转长期参数等方面做了进一步的阐述。     

Detailed paleoseismic history of the Hinagu fault zone revealed by the high-density radiocarbon dating and trenching survey across a surface rupture of the 2016 Kumamoto earthquake,Kyushu, Japan

The NE-trending Hinagu fault zone, length 81 km, is one of the major active faults in Kyushu, Japan. From north to south, it is divided into three segments based on geomorphic features and paleoseismic behavior: the Takano-Shirahata, Hinagu, and Yatsushiro Sea segments. The 2016 Kumamoto earthquake produced a 6-km-long surface rupture with a dextral strike-slip displacement on the northern part of the Takano-Shirahata segment. Surface rupture, a faint east-side-up flexure with a vertical offset of less than 8 cm, was observed near the middle of the Takano-Shirahata segment. To examine past surface-rupturing earthquakes on the Takano-Shirahata segment, including rupture frequency and timing, we conducted a paleoseismic study with boring and trenching at Yamaide. A trench across the surface rupture exposed multiple fault strands associated with multiple surface-rupturing events that deformed several strata of fine-grained sediments. By structural and stratigraphic interpretation, high-density radiocarbon dating and tephra analysis, and Bayesian modeling, we constrained the timing of seven events, Events 1–7, to 0.84–1.25, 1.31–7.06, 9.99–11.0, 10.8–12.1, 12.0–13.0, 14.2–15.1, and before 14.8 kcal BP. Slip during Events 1–6 was obviously larger than the 2016 slip. The estimated average recurrence interval was about 2596–2860 years, but the interval between Events 2 and 3 was much longer than other intervals. Moreover, the vertical throw associated with Event 2 was larger than that of other events. This implies that the Takano-Shirahata segment has a period with rare larger earthquakes and a period with frequent smaller earthquakes. Some events might have produced ruptures on both the Takano-Shirahata and the northern part of the Hinagu segments simultaneously or in a short time. The variety of recurrence intervals suggests that the seismic activity has been affected by one or both activities of the Futagawa fault zone and the Hinagu segment.     

日本福岛7.3级地震区域震害分析与对比

基于近实时区域震害评估系统RED-ACT,对2021年2月23日发生在日本福岛县东部海域的7.3级地震开展了震中附近区域的地面运动破坏力分析,包括典型强震记录分析、震中附近台站周围的建筑震损、人体感受和滑坡风险分析。基于实际震害调查结果,对比了RED-ACT系统、日本NIED-CRS系统和美国PAGER系统的震害评估结果准确性。结果表明:RED-ACT系统的评估结果与实际情况较为接近,能够为震后应急响应提供重要参考。     

油气成藏年代学研究进展及发展趋势

成藏年代学是当代石油地质学的一个前沿领域。80年代以来，随着油藏地球化学、流体包裹体方法、同位素测年法、油气水界面追溯法等多种新方法或新技术的引入，成藏年代学研究取得了重要进展，实现了由传统的间接向直接研究、宏观向微观研究，以及定性向定量（或定期向定年）研究的重要转变。间接研究与直接研究相结合、宏观与微观研究相结合、定性与定量（或定期与定年）研究相结合，已成为现代成藏年代学研究发展的重要趋势，这对于叠合盆地的成藏年代与成藏史研究尤为必要。就各种成藏年代学研究方法的应用及其存在的问题进行了简要分析和讨论。     

深层油气研究现状及进展

随着油气勘探工作的日益深入，渴望在盆地中浅层取得大的突破已越来越困难。近年来世界油气勘探的一个重要发展趋势是向盆地深部拓展。国内外均广泛发现的超过油气稳定温度和深度下限的深层油气藏的存在，对传统的油气成因理论提出了严峻的挑战，用传统的油气成因理论对深层油气勘探中出现的一系列新问题难以作出合理的解释。系统总结了近年来国内外在深层油气方面的研究现状及最新进展。并从深层油气的温度、深层油气的分布、深层油气形成的物质基础、深层油气的稳定性以及深层油气的储集空间等方面论述了沉积盆地深层仍具有形成工业油气藏的条件和基础。理论研究和实际勘探结果均表明，烃源岩在较高的热演化阶段仍具有形成工业油气藏的成烃潜力。深部地层裂缝和微破裂带是不封闭的，流体可以沿此为通道发生运移并储集，深部有形成大型烃类矿藏的条件。