关于下蜀组沉积初期自然环境面貌的初步推断

下蜀组在长江下游分布很广,与农副业生产关系密切,是许多大型工程建筑的地基持力层。虽然几十年来许多地层古生物学工作者做了大量的研究,使之成为晚新生界的典型层位,但对其成因和代表的环境等尚存在分歧看法。本文讨论一例五十年代可能发现于下蜀组底部的、近年来生境研究得十分清楚的生物化石,认为下蜀组沉积初期的环境可能是温湿、低平、多水域的,沉积成因类型可能是水成的。在生物证据不多的情况下,哪怕增加一点点说明问题的生物线索都显得异常珍贵,因为往往生物反映的环境面貌比较地全面和具体。     

洛川黄土剖面的粉砂与粘粒比值及粒度旋回

洛川黑木沟黄土剖面发育了一套完整的黄土地层。据剖面百余块标本粒度资料阐述了Kd=(粉砂(0.05-0.01mm％))/(粘粒(<0.005mm)％)的地质及物理意义。它反映了受风化的粉尘粒组与次生粒组之间的消长关系,Kd值变化既受风尘来源区干湿状况或生物气候条件的制约,又受风化成壤作用的制约。因此,Kd值可视为黄土、古土壤生成环境的一个指标。据Mφ(平均值)由粗到细的变化划为一个粒度旋回,全剖面共分11个旋回。每个旋回反映了一定的岩性地层组合及生物气候环境的变化。     

Niveo-aeolian deposits and denivation forms,with special reference to the great Kobuk Sand Dunes,Northwestern Alaska

The geomorphology, lithology and chronostratigraphy of extensive, late Pleistocene inland and river dune sands, aeolian sand sheets (‘cover sands’) and loess deposits of periglacial origin in northwestern Europe are well known. However, the idea that some of these aeolian sediments result from niveo-aeolian processes is still an open question, as no diagnostic sedimentary features have yet been reported. Moreover, actual niveo-aeolian sediments and related denivation forms, reported from various cold-climate regions, are not suitable analogues. Recent observations in active dune fields in northwestern Alaska indicate that interstratification of wind-driven snow and sand preferentially occurs on slip faces of transverse, barchanoid or parabolic dune ridges. Annual denivation forms develop: e.g. snow ramparts, sinkholes, snow hummocks, snow meltwater fans and tensional cracks. The surface consists of a cracked wet sand layer with a dimpled surface and spongy structure. Although the preservation potential of these features is low in this specific case, similar features may be observed in ancient sediments elsewhere and provide useful palaeoclimatic indicators. The niveo-aeolian concept should therefore not specifically be related to late Pleistocene cover sand deposition in northwestern Europe, as previously assumed.     

Stratigraphy,geochemistry, and thermoluminescence ages of lower Mississippi Valley loess

Four periods of loess deposition in the Lower Mississippi Valley can be identified on the basis of geochemical and mineralogical criteria, radiocarbon dating, and thermoluminescence dating. These are designated Loess Units 1,2,3, and 4 in order of increasing age. Carbonate-rich Unit 1 loess comprises more than 70 per cent of the thickness of the loess profiles. ¹⁴C and TL dates indicate this loess was deposited between 9 000 and 20 000 years ago. A maximum sedimentation rate of 2.17 mm yr^?1 has been recorded near Vicksburg just after the last Laurentide glacial maximum, between 17 190 and 15 580 years ago. The Unit 2 loess, which is thin and partly decalcified, was deposited slowly between about 25 000 and 20 000 years ago. The Unit 3 and Unit 4 loess formations, which are both highly weathered, have yielded TL ages of 76 000–85 000 years and 119 000- > 132 000 years, suggesting they were deposited during the Altonian Substage of the early Wisconsinan and the Illinoian glacial stage respectively. The four loess units are stratigraphically equivalent to the Peoria, Farmdale, Roxana, and Loveland loess formations previously recognized in Illinois. The source of dust in both areas was glacial outwash in the Mississippi Valley. During interglacials and interstadials, when the supply of glacial debris was reduced and the Mississippi River changed from a braided to a meandering regime, dust sedimentation in southern Mississippi virtually ceased, allowing weathering and pedogenesis to proceed.     

Late quaternary monsoon patterns on the Loess Plateau of China

China's Loess Plateau was formed under special conditions. The tectonic movement, topographical characteristics, and monsoon patterns combined to create a favourable environment for the accumulation of thick loessic deposits. The Loess Plateau itself is part of the ‘Monsoon Triangle’ of China, a region very susceptible to climatic changes. Throughout the Upper Pleistocene the palaeoenvironment on the Loess Plateau alternated from steppe, to deciduous forest and coniferous forest, in response to shifts in the atmospheric circulation. Three monsoon patterns appear to be indicated: (1) a full glacial monsoon pattern (18000–15000 yr BP) which induced a cold and dry climate favouring loess accumulation in steppe conditions; (2) an interglacial monsoon pattern (last interglacial and Holocene) in which a warm humid climate prevailed with deciduous forests, leaving palaeosols interbedded within the loess sequence; and (3) a transitional or interstadial monsoon pattern (50 000–23 000 yr BP) in which the climate was cold and humid in the Loess Plateau, encouraging the development of coniferous forest.     

FACTORS CONTROLLING DIFFERENTIATION OF SELENIUM ECONVIRONMENT IN THE LOESS PLATEAU

ItisataskofNationaScienceandTechnologyProjectNo.75-62-03-05and06forthe7thFive-YearPlanperiod.InvestigationsinGansuandShanxiwereundertakenbyInstituteofGeography,CAS,whiiethatinShaanxiwascarriedoutbyNortllwestInstitllteofWaterandSoilConservation,CAS.**OthermembersintheGroupofEndemicDiseaseandEnvironment,InstituteofGeograpl1y,CASare:YangLinsheng,ZhaoYuanwei,ZhaoNaiqin,LiDezhu,WangLizhenandTanJianan.I.IntrodIlcti01llthasbeenreported[21thattwoendemics,KeshanandKaschin-Beck,arecl…     

遥感技术在黄土高原土地利用现状调查中的应用研究

本研究选取黄土高原典型丘陵沟壑区——陕西省米脂县为试验区,用TM磁带、TM假彩色合成影像、SPOT多光谱影像和彩色红外航空像片同时对试区进行土地利用现状分类与制图的比较研究。通过对土地利用现状分类系统、TM图像计算机增强处理与自动分类、TM最佳波段组合、三种影像的目视判读与制图、以及遥感信息源的综合评价等多方面的试验研究,为遥感技术在黄土高原1:5万土地利用现状调查制图中的应用提供了一套技术数据及可行的方法。     

(Re) deposition of loess in southern Limbourg,the Netherlands 3. Field evidence for conditions of deposition of the middle and upper silt loam complexes,and landscape evolution at Nagelbeek

This paper is about conditions and processes during the accumulation of the Upper Pleniglacial Middle and Upper Silt Loam complexes at Nagelbeek, Limbourg, a Weichselian stratigraphical type locality. The complexes correlate with Hesbayan and Brabantian loesses in Belgium, formed between 28,000 and 12,400 yrs BP. They are characterized by sediment features (cracks, mass deformations, and cut-and-fill features) that are ascribed to a cryogenic regimen. The main Middle Silt Loam subunit contains contraction cracks deformed and further modified by masswasting. Intra-Upper-Pleniglacial pedogenic intervals are inferred from three greyish bands, from a truncated weathered zone surmounting the Middle Silt Loam, and from an aeolian-cumulic palaeosol at the base of the Upper Silt Loam. Latter two zones and an intervening erosional unconformity were cryogenically reworked, less than 22,000 yrs BP, to form a complex stratigraphical marker-zone: the ‘Horizon à Langues de Nagelbeek’. Morphological variants of the marker-zone are described. The geomorphic evolution of the Nagelbeek upland, from Saalian to Holocene times, is summarized in unconformity maps and a time diagram.     

浅议中国黄土磁化率的物理意义

中国的陆相黄土地层连续地记录了第四纪以来的古气候变化。基于中国黄土磁化率曲线与深海氧同位素记录具有可比性这一事实，磁化率作为一种气候替代性指标在黄土研究中得到广泛的应用。但是，磁化率的物理意义仍不清楚。本文作者对陕西榆林蔡家沟剖面末次间冰期以来的风成沉积作了研究，指出黄土、古土壤的磁化率差异不仅与前人提出的碳酸盐淋失、空隙度变化、“就地”新生成磁性矿物等作用有关，而且还可能与有机质有重要关系。有机     

Soil erosion and management on the Loess Plateau

1 Introduction The Loess Plateau situated in northern China covers the drainage basins in the middle reaches of the Yellow River. It starts from the western piedmont of Taihang Mountains in the east, reaches the eastern slope of the Wushao and Riyue mountains, connects the northern part of the Qinling Mountains in the south and borders the Great Wall in the north, covering an area of about 380,000 km2 (Figure 1). The region is overlain extensively by Quaternary loess in great thickness, …