The clay mineralogy and chemical composition of the white veins, red matrix and both Fe- and Mn-bearing nodules occurring in a laterite profile in Hubei, south China were investigated using X-ray diffraction, scanning electron microscopy equipped with an energy-dispersive spectrometer, and high-resolution transmission electron microscopy. The results show that the mineral components of the red matrix are mainly quartz, kaolinite, halloysite, goethite and minor illite, whereas the white net-like veins contain mostly quartz, kaolinite, halloysite, and illite. In the net-like horizon, the chemical index of alteration (CIA, the ratio of Al2O3/(Al2O3+CaO+K2O+Na2O)) and the TiO2/Al2O3 ratio are 89.8% and 0.021 for the white vein and 90.7% and 0.025 for the red matrix, respectively. Both white-vein and red-matrix components have similar TiO2/Al2O3 ratios, and are similar to the ratio 0.027 of the unaltered bedrock. The similarity in TiO2/Al2O3 values indicates that all three portions of the laterite soil share the same origin. Also, although the white-vein and red-matrix components differ in Fe2O3 abundance, the similar CIA values do imply similar degrees of alteration. The Fe-bearing and Mn-bearing nodules were produced by the local accumulation of Fe2O3 and MnO, respectively. Halloysite in the weathering profile occurs in two different morphologies, tubular and platy crystals. Tubular halloysite occurs both in the red matrix and the Fe-bearing nodule whereas platy halloysite occurs only in the white vein and Mn-bearing nodule assemblages. Crystallization of small tubular halloysite from Si and Al concretions in the red matrix is observed, indicating that the morphology of these crystals in the weathering environment is mainly controlled by Fe3+ cations, whereas platy halloysite may be derived from the hydration of kaolinite.

Agnostid trilobites are relatively abundant and taxonomically diverse in outer shelf facies of the Yangtze Platform and Jiangnan Transitional Belt regions of the South China Plate. Nine Arenig and Llanvirn species, representing at least five genera or subgenera in the Agnostidae, Diplagnostidae and Metagnostidae, are treated in a taxonomic review of the South Chinese Agnostida, based on new material from the Dawan and Kuniutan formations of W Hubei and the Zitai and Jiuxi formations of N Hunan. The new genus Han is established to incorporate the globally youngest known diplagnostid species. The new species Han solo, Geragnostus (Geragnostus) balanolobus and G. (G.) waldorfstatleri are established. G. carinatus is recognised as being based on inaccurately interpreted material, and is only tentatively retained within Geragnostus. Three further taxa represented by poorly preserved material are left in open nomenclature. The geographic distributions of different agnostid species across the South China Plate, and the endemicity to the palaeoplate displayed by all Arenig–Llanvirn South Chinese species, suggest that these agnostids at least were either benthic or epibenthic.