摘要
通过氧、碳同位素和岩石化学的系统测试,采用聚类分析和对应分析及最优分割等方法,依据地球化学的演变规律及其所对应的沉积环境以及化学地层学原理,揭示了淮南群的地球化学特征,重新厘定了其内部“组”一级单位的划分。研究结果表明:淮南群中Na、Ca、和K的地球化学特征,与沉积旋回特征相比较,具有明显的相似性,而Mg和Ca、Na元素的分布特征,则又指示出四顶山组形成的古气候已转为干燥,并与δ^(18)O,δ^(13)C测温的结果(29.42℃)具有明显的对应性;依据化学地层学对淮南群内部“组”一级单位的划分结果,与前人依据岩石地层学所划分的结果相比较,显示了较大的一致性,特别是九里桥组的顶界,在地球化学演变和古海水温度变化梯度及古气候变迁等方面,均具有明显的一级划分性;淮南群中δ^(13)C演变曲线特征显示,其下部与燕山地区晚元古代青白口系上部的层位相重叠,进而增加了二者对比、衔接的可行性,更填补了我国中、晚元古代δ^(13)C演变曲线中在900～650Ma左右时间段上的此类资料的空白;淮南群中碳酸盐岩形成时的古海水温度,由老至新有2个最高值,即刘老碑组45.13℃,奶奶庙组35.42℃,显示了时代越老水温越高的趋势,并且似乎还具有150～200Ma的周期性变化;据淮南群及其上覆地层δ^(13)C与δ^(18)O演变特征推测,?
After systematic analyses of oxygen and carbon isotopes and lithochemistry by means of assembling analysis, correspondent analysis and the optimal section and according to the geochemical evolution and its correspondent principles of depositional environment and chemical stratigraphy, this paper shows geochemical characteristics of the Huainan Group and redivides 'formation' units in the Huainan Group.The results suggest that Na, Ca and K geochemical characteristics have similar evolution to depositional cycles in the Huainan Group.Distributional features of Mg.Ca and Na elements indicate that palaeoclimate for the Sidingshan Formation had changed into being dry, which is apparently supported by the results (29.42℃ )of <δ18O and δ13C temperature determination. Division of ' formation' units by means of chemical stratigraphy shows similarity to the previous devision by lithostratigraphy in the Huainan Group, especially at the top of the jiuliqiao Formation where divisional features are obviously shown by geochemical evolution.change gradient of the marine water temperature and palaeoclimate change. Features of δ13C evolutional curve in the Huainan Groupindicate that the lower part can be correlated with the upper part of the Qinbeikou System of late Proterozoic in the Yanshan region.This fills a previous blank of middle and late Proterozoic (650-900Ma)δ13C evolutional curves. In time sequence, marine water temperature during deposition of carbonatites in the HuainanGroup had two peaks,i.e.45.13,℃ for the Liulaobei Formation and 35.42℃ for theNainaimiao Formation. They show a rising tendency of the marine water temperature with ages and seem having a periodical change of 150-200Ma. According to δ13C and δ18O evolutional features of the Huainan Group and. its above.marine water temperature for deposition of the Liulaobei Formation was higher(45.13℃) At that time, the marine was not quite fluent and its middle and upper levels were appropriate to breeding of floatable mega-algae and some metazoan. In contrast. marine water temperature for deposition of the Jiuliqiao Formation was lower (13.37℃),at which time the marine was fluent,shallow and appropriate to vast breeding of bottom-dwelling and floatable life. These results are consistent with those of palaeoecological studies in the Huainan fauna and flora
基金
国家自然科学基金资助项目(4870089)成果之一
关键词
淮南群
化学地层学
地球化学
Norlhem Jiangsu and Anhui, Late Precambrian, Huainan Group, Chemicalstratigraphg
