淮北白浆土发育与晚第四纪古地理环境变化

DEVELOPMENT OF ALBIC SOILS IN HILLS AND MOUNDS BETWEEN SHANDONG AND JIANGSU PROVINCES, CHINA AND LATE QUATERNARY ENVIRONMENTAL CHANGES

本文从淮北白浆土的剖面二段性出发，根据土壤性质的剖面变化，剖析了这种土壤中存在着的土壤发生间断性，并通过化学成分、粘土矿物组成、铁锰结核的地球化学、土壤薄片及石英颗粒形态、抱粉以及年龄等分析、鉴定和测定，结合土壤与地貌的关系，揭示了这种土壤上、下部土体间不同的发育状态。研究表明，淮北白浆土的形成并非全新世以来某种单一成土过程的结果，而是本区晚第四纪以来不同阶段地貌演变和气候变化造成的土壤演变的外在表现，它还记录了本区多次抬升－剥蚀－堆积－土壤发育的交替演变。

There are over 100 000 hactares of albic soils in hills and mounds betweenShangdong and Jiangsu Provinces.Their average profile is constituted by two parts.The upper part includes a gray, silt sandy and weakly structured anthropic epipedonand underlying albic soils,locally with bottom gravels cemented with dark brownoxyhydrates, and the lower part is generally brownish clay with well developed prismatic structure, transiting to weathered metamorphic rocks, dominantly gneiss. Theformation of albic soils used to be attributed to reduction-bleaching of water detained by the impermeable lower part. Nevertheless, pseudo-conformability withinprofiles and lack of reduction phenomena imply that the formation of albic soilswas a discontinuous process, which could be related to Quaternary environmentalchanges.Analyses of particle size, placer minerals and main chemical compositions revealthe discontinuity of sedimentation and pedogenesis between the upper and lowerparts in albic soil-bearing profiles. The surface morphology of quartz grains showsthat the upper part originated from younger sediments and the lower part from older in situ weathered rocks. The TL dating of quartz further shows that the upperwas deposited at the end of the last glacial and the lower part formed in the interglacial period between the Lushan glacial and the Dan glacial. Soils in the upperpart contains abundant ferrugineous concretions, especially at the bottom, consists ofdetrital minerals dominated by hydromica (illite), is weak both in weathering andin differentiation and gelatification. On the other hand, soils in the lower partcontains only a few ferric nodules, consists of clay minerals from illite to kaolinite(in some places, dominated by kaolinite with heamatite), and is varying in weathering and strong in differentiation and gelatification.According to geomorphic data, in combination with our field observation, soils'in the lower part is the erosion residue of paleosols formed during the period ofMiddle Pleistocene to Late Pleistocene. The erosion took place during the end ofLate Pleistocene. Then the residual paleosols was again covered by sediments afterthe last glaciation (soils in upper part). Several pedogenic phases related to Quaternary environment were established in albic soil-bearing profiles:(A) Relatively hot and humid climate and development of red earth beforeabout 130 000 a B. P.;(B) Uplifting and erosion of red earth from 130 000 a B. P. to Late Pleistocene;(C) Warm and humid climate and development of brown earth from 65 000 aB.P.to 45 000 a B. P.,corresponding to Late Pleistocene;(D) Uplifting and differentiated erosion of brown earth from 45 000 a B. P.(the end of late Pleistocene) to 10 000 a B. P.;(E) Cold and dry climate and accumulation of young sediment after about10 000 a B. P.;(F) Warm and wet climate and pedogenesis associated with formation of ferruginous concretions in about 7 500 a B. P.These phases are largely comparable to those main environmental change eventsof Late Quaternary established by other researchers studying North China's loess.Thus, the albic soils in the region was not simply due to pedogenesis but a composite product of pedogenesis together with soil evolution responded to climatic changes