Palygorskite-rich mudstone interbedded with gypsum occurs in the Neogene Baiyanghe Formation in the Yangtaiwatan basin, northwest China, but the genesis of palygorskite in the mudstone is unclear. The objective of the present study was to clarify the manner by which the palygorskite evolved by analyzing the mineralogical and geochemical characteristics of the mudstone. The mineralogical composition of bulk-rock mudstone consisted of clay minerals, quartz, feldspar, dolomite, calcite, and gypsum. Palygorskite is dominant in the clay fraction together with illite and accessory chlorite and kaolinite. The interwoven rod-like palygorskite aggregates and delicate palygorskite particles indicated an authigenic origin. The bulk rock of palygorskite-rich mudstone was rich in the trace elements Cs, U, B, Li, Sb, Bi, and As, which, together with REE, all showed very positive correlation with major element oxides Al 2 O 3 , Fe 2 O 3 , MgO, K 2 O, and TiO 2 of the mudstone, indicating that the REE and trace elements occurred mainly in the clay minerals. The detrital illite, chlorite, and kaolinite were the main original host of the REE and enriched trace elements. Statistical analyses showed that the authigenic palygorskite had strong affinity to such elements compared to the detrital clay minerals. In addition, the chondrite-normalized REE of the bulk mudstone showed essentially the same pattern irrespective of the proportions of detrital illite, kaolinite, chlorite, and authigenic palygorskite present in the samples. Thus, the conclusion reached was that palygorskite was generated from the dissolution of detrital clay minerals. The REE and enriched trace elements in authigenic palygorskite were inherited from the detrital clay minerals.

中文翻译：

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洋台滩盆地新近系白洋河组坡缕石的成因及富集微量元素和稀土元素的赋存

洋台洼滩盆地新近系白洋河组发育富含坡缕石与石膏互层的泥岩，但泥岩中坡缕石的成因尚不清楚。本研究的目的是通过分析泥岩的矿物学和地球化学特征来阐明坡缕石的演化方式。块状泥岩的矿物组成为粘土矿物、石英、长石、白云石、方解石和石膏。坡缕石与伊利石和副绿泥石和高岭石一起在粘土组分中占主导地位。交织的棒状坡缕石聚集体和精致的坡缕石颗粒表明自生起源。富坡缕石泥岩块体富含微量元素Cs、U、B、Li、Sb、Bi、As，与稀土元素一起，均与泥岩的主要元素氧化物Al 2 O 3 、Fe 2 O 3 、MgO、K 2 O、TiO 2 呈极正相关，说明稀土元素和微量元素主要存在于粘土矿物中。碎屑伊利石、绿泥石和高岭石是稀土元素和富集微量元素的主要原始宿主。统计分析表明，与碎屑粘土矿物相比，自生坡缕石对这些元素具有很强的亲和力。此外，无论样品中碎屑伊利石、高岭石、绿泥石和自生坡缕石的比例如何，块状泥岩的球粒陨石归一化 REE 显示出基本相同的模式。因此，得出的结论是坡缕石是由碎屑粘土矿物的溶解产生的。