【摘要】 本文运用X射线衍射(XRD)的方法分析了柴达木盆地察汗斯拉图地区SG-1岩芯(38°24′35.30″N,92°30′32.70″E;长938.5m)的粘土矿物组成,重点讨论伊蒙混层结构的影响因素及其环境意义。样品取自非盐层中,取样间隔为2m。伊蒙混层矿物中的伊利石晶层含量为85%~90%,为高度有序的伊蒙混层矿物。伊利石晶层间隔层数(n)有高类型(H)和低类型(L)。主要影响因素可能是盐度和温度,盐度高的时候钾离子浓度也高,并且离子间的交换作用强,促进蒙脱石向伊利石的转化。因此,盐湖环境下H型的出现概率普遍高于咸水湖环境。盐湖环境下(2.2~2.0Ma和1.2~0.1Ma)伊利石晶层的间隔层数高,以H型为主,咸水湖环境下(2.8~2.2Ma和2.0~1.2Ma)以L型为主。钻孔中1.2~0.9Ma时期为盐湖环境,但H型出现概率却最低(4.94%),这与全球性的极冷气候有关。与粘土矿物种类相比,矿物结构的变化具有更微观的环境意义。更多还原

【Abstract】 This paper presents the structural characteristics of illite/smectite mixed minerals(I/S) and their environmental significance of the core SG-1.The 938.56m-long core(38°24′35.30″N,92°30′32.70″E) is located in the Chahansilatu subbasin,western Qaidam Basin.It was magnetostratigraphically dated to be ca.2.8Ma(938.56m) to ca.0.1Ma(0m).Lithofacies variation suggested that it evolved from a deep brackish lake into a playa since ca.2.8Ma.A total of 490 samples were sampled at about 2m intervals from non-salt layers in the core.<2μm fractions of these samples were separated from the suspension using the Stokes’ static setting method,and then made into flakes under natural,ethylene-glycol saturated and 550℃ heated conditions for X-ray Diffraction(XRD) analyses.The results show that the illite-layer percentage of I/S ranges from 85%to 90%,and all of them were highly ordered.According to the number(n) of illite-layer within two smectite layers,the structure of I/S was divided into high(H) and low(L) types.The H-type(n = 9) was dominant during the periods of 2.2~2.0Ma and 1.2~0.1 Ma,while the L-type(n = 5,6) was dominant in the rest of the core.The main influencing factors for their distribution are possibly salinity and temperature of brines or porewater.The higher salinity of brines(or porewater),the richer K~+,as a result,the stronger ion exchange actions between clay minerals and brines(or pore water),and so as to the higher temperature.The two factors play an active role on the transformation from smectite into illite,thus high number of illite-layer of I/S.Therefore,the H-type was dominant in the saline lake environments during the periods of 2.2~2.0Ma and 1.2~0.1 Ma,while the L-type was dominant in brackish lakes during the 2.8~2.2Ma and 2.0~1.2Ma.The H-type was the lowest(4.94%) in saline setting during 1.2~0.9Ma.We believe that it was due to the global extremely cold climate during the period.Compared with whole clay minerals,the structural characteristics of I/S could have more microscopic environmental significance.更多还原