欧洲中部地区晚更新世及全新世的泉华沉积

PLEISTOCENE AND HOLOCENE SINTER SEDIMENTATION IN CENTRAL EUROPE

在中欧地区的河谷、洪积扇、山坡坡麓及湖底常零星分布着更新世及全新世的碳酸盐沉积物。不少学者把碳酸盐沉积当作气候变化的产物并划分出其在中欧沉积的若干时期。笔者通过德国中部Ｌｅｉｎｅ河流域新老石灰泉华的详细研究对泉华沉积与气候直接联系的观点提出了新的见解。运用不同方法测年验证，得知研究区的石灰泉华沉积始于１１０００ａＢ．Ｐ，随后石灰泉华在研究区不同地点连续沉积。岩芯上沉积的变化和石灰泉华层的消失应是由地貌过程所引起的泉水出露位置改变所致。

Pleistocene and Holocene freshWater carbonate is often scattered in valleys, on alluvial fans, at the foot of mountain slopes and the bottom of lakes in Central Europe. Since the beginning of this century, a large number of different names have been given to this kind of deposit, such as sinter, calc-sinter, travertine, tufa or calctufa, Sinterkalk, Wiesenkalk, Dauch and Quellkalk. Fundamentally all the different terms are used in a general meaning as well as in more restricted contexts to distinguish between different freshwater carbonate deposits on grounds of porosity,genesis and location. Quite a few researchers have used carbonate deposits as paleoclimatic indication and have divided into many different episodes for these deposits, in Central Europe.In order to clarify the mechanism of carbonate deposition in the maritime climate zone of Central Europe, the authors have made detailed investigations into calc- sinters in the area of Leine River (southern forer Saxony, Germany). Many drillings have presented sinters with a thickness commonly between 5 cm and 150 cm. For the first time, a broad layer of sinter has ben discovered under the Gande alluvial fan which is located five kilometers northeast of Einbeck (51 °50' N, 9°55' E). Leine River deposits intervene in the alluvial fan originating from the Gande tributary. From bottom to top, the stratigraphy of a typical core is: sand and gravel under the depth of 480～500 cm; alluvial clay upwards until the depth of 255 cm; and then a thin palaeosol; 40 cm thick sinter, upper palaeosol, and fluvial silt and sand with variable characters in the top section. With the 14C dating techniques, the palaeosol under the sinter is dated to be 8 976±245a B. P. and the palaeosol above to be 8800±80a B.P.The peat in the bottom of a borehole nearby displays a Preboreal pollen spectrum.In this case, it is worth to question which factors caused the sinter sedimentation for such a short period. The climatic warming at the end of Pleistocene may be responsible for the start of deposition. But its termination can not arise from climatic factors. The lack of tectonic movement during the Holocene in the research area means it is unlikely that tectonic rising caused surface water to flow underground. It makes sense to presume that the geomorphological processes may be the cause. A landslide might fill up the headwaier region so that the water could not flow out from the same site any more.Drawing the parallels between the divided cores reveals a 150 cm thick sinter layer which is 200～300 cm below the valley bottom in the upper reach of the small Gande catchment area. Under the sinter there are some peat and a large area of carbonate-rich mud with a thickness of one to three meters. Beneath it is glaciofluvial gravel from the last ice age. Above the sinter is a ca 40 cm thick palaeosol covered by slope deposits with a thickness between 100 cm and 300 cm. This palaeosol is ab-sent in some cores. Examined with the 14C-dating /AMS method, the sample from the bottom of the sinter has shown an age of 11 360±100 a B. P., and from the top given an age of 2065±65 a B. P. The results of pollen analysis verify principally the 14C data. Based on these facts, the average deposition rate is estimated at 0.15 nun per year.In many other sites, the authors have also studied carbonate deposits and indirectly got the ops by stratigraphic correlations. Some sinter deposits occurred during human history or even at present time. The evidence of human activities suggest that a layer of sinter in Alfeld (51°58' N, 9°43' E). was formed at the end of the 11th century and at the beginning of the 12th century. Active deposition is observed .in many places, such as Goettingen. On the slope of Westhoefer Valley (51°58' N,10°7' E) active sinter deposition covers the whole surface. These deposits are graywhite-coloured, porous carbonates containing plant remains. Sinter deposition forms terrace-like landscape on steep sections and builds porous carbonate stone and small sinter terraces on slopes of moderat