摘要
在辽东半岛东部的大孤山一带，面向海岸平原的沟谷埋藏泥炭十分发育。通过对11个沟谷进行钻孔调查，确认了在被切割的丘陵台地的沟谷中，埋藏泥炭广泛地发育在海拔2-10余米的不同高度；并对钻孔样品做硅藻分析，明确了基底海拔高度在4-2m的泥炭层之下的沉积物为海生种硅藻占优势的海相层，因而取得了海水广泛侵入大洋河平原并直达沟谷深处的微体古生物方面的证据。进一步对3个代表性的小沟谷平原从沟头到沟口连续钻孔取样以及地质剖面分析，研究沟谷埋藏泥炭在横向上的分布特征表明：沟谷埋藏泥炭是全新世高海面期以后，随着海水的退却而形成的沼泽和湖沼等环境下的溺谷型泥炭；位于沟谷中沟头位置的海拔4m左右的泥炭底部的标高，大致代表了该区全新世最高海面期海水（平均高潮线）曾达到的位置和高度，其泥炭在沟头开始形成的时期大致代表该区全新世最高海平面期；研究区约6000-5500年前达到全新世最高海面，当时海面高度比现在约高出1.7m。
Diatom analysis and AMS-14^C chronology of peat samples from the valleys in the Dagu Mountain area revealed the history of palaeoenvironment change and sea-level change of that area in Holocene. Comparing with detailed results of coast plains in Japan, a new tectogenesis is adopted to explain the environment change history of the research area. The formation of Dagu Mountain shell-accumulations is believed to be the indicator of the highest sea-level in Holocene.
Core sampling was carried out at 11 valleys in the Dayang rivermouth plain in the East Liaoning peninsula, to investigate peat locations as well as palaeoaltitudes. Diatom analysis revealed that the valley peats below 4m altitude were marine facies sediments because marine diatoms dominated, and the sediments above 4m altitude were of terrestrial formation yielding no marine diatom.
In order to figure out the distribution and the uppermost altitude of the marine sediment in the valleys, a series of core sampling was conducted at 3 valleys. In the profile of core samplings, the thickness of valley peats decrease from top to mouth of the valleys and finally black clay lamina appears at the mouth, suggesting that the altitude of valley peats descend from the top of valleys, about 4m altitude, to the mouth of valleys. Diatom analysis from the cores LD and DK reveals that the place where marine facies beneath the valley peats were deposited was a transition zone, with the number of marine species decreases while that of freshwater species increases.
There is conformity contact between valley peats and the underlain marine facies sediments. The forming of peat indicates such a process that seawater firstly exited which was followed by the growing of plants. As a result, then the bottom of the top layer of valley peat represents the highest sea level. The shell samples for dating were collected from the lower part of the peat near the mouths of valley at the cores LD and DK as well as from marine facies sediments at the coastal plain. The 14^C dating for those shells indicates that the maximum Holocene transgression is around 6000 - 5500cal. aB. P., with the altitude of sea-level at around 4m （the average level for high-tide）. It is believed to be about 1.7m higher than the current sea-level. Neither the peat layer which is 8m above the sea-level at the valley of Huantukan, nor the shell-accumulations at 7 - 10m in the west of Dagu Mountain can indicate highest Holocen sea-level because the sediments underlying the valley peats are not of marine facies and the shell-accumulation is formed by shell-tumulus.
Evidence for coastal rise such as paleo-coastal erosion and paleo-coatal terrace in Holocene was not observed.Besides, the consistency of the age and the maximum altitude of sea-level in Holocene between the study area and the coastal plains of descending or stable in Japan, Dayang River plain in Dagu Mountain area is not the uplifting area but the descending or stable area in Holocene.
出处
《第四纪研究》
CAS
CSCD
北大核心
2007年第5期797-805,共9页
Quaternary Sciences
基金
日本笹川研究助成金项目(批准号:11-393M)资助
