Evolution of Kaolinite Accumulation in the Phanerozoic

Abstract

Kaolin weathering profiles (WP) were formed during the continental hiatuses when the relief was flattened under warm humid conditions. In the Phanerozoic, most favorable were prolonged hiatuses (with weak tectonic movements) that promoted the formation, preservation, and burial of eluvial and other correlated formations. Such periods were marked by active crust formation identified by V.P. Petrov as early as in 1967. They can be manifested repeatedly within positive structures, such as the Voronezh anteclise. Its WPs correlate rather well with the coeval rocks in other structures of the East European Platform (EEP). However, they lack such complete sections with the WP age specified as in the Voronezh anteclise. Therefore, the Voronezh section with the specified WP levels can serve as a reference section for the EEP and, possibly, for other regions in the world on the whole. A historical–mineralogical analysis concerning the chronological formation of kaolinite clay deposits in the Phanerozoic revealed that that the kaolin WPs were thin and almost lacked deposits in the pre-Middle Devonian. They started to appear as primary and secondary kaolins in the Frasnian, but did not become widespread. In the Carboniferous period, WPs served as the sources of material for the refractory and high-melting clay deposits at the margins of coal basins with abundant vegetation. The main primary and secondary kaolin deposits were formed in the Late Triassic–Early Jurassic and Early Cretaceous. In North America, the accumulation of secondary kaolins was maximal during the Late Cretaceous and Tertiary. In the Cenozoic, the scale of kaolinite accumulation reduced considerably, as compared to the Mesozoic, giving way to the formation of bauxite concentrated in the lateritic sheet of tropical countries. During that time, over 80% of all bauxites in the Earth’s history were accumulated. Kaolin rocks in the form of eluvium, secondary kaolins, and kaolinite clays were formed mainly within the lower areas of peneplains and on alluvial plains. The obtained results showed that the evolution of kaolinite accumulation, represented mainly by primary kaolins, had an interrupted-directional trend due to the geocratic stages of the Earth’s development, increase of land areas, and flattening of elevated regions. The kaolinite deposits began to form in the Late Devonian, which was facilitated by the development of plant life on land, reached the maximum in the Mesozoic during the continental hiatuses, and slowed down in the Cenozoic. The slowdown was due to the intensification of weathering with the formation of final products of hydrolysis represented by alumina and iron oxides. Vast areas were marked by the formation of laterites instead of kaolinite accumulation in the lowered areas of peneplains and alluvial plains.