STRATIGRAPHIC AND CORRELATIVE SIGNIFICANCE OF TERRIGENOUS COMPONENTS OF SEDIMENTARY ROCKS

Abstract

The widely applied method of stratigraphic division of sediments and their correlation on the base of terrigenous components developed by 11ling, Baturin and others, was based on the fact that the composition of the sedimentary terrigenous components depends upon the petrographic composition of the distributive province rocks. The author, using terrigenous components for stratigraphic purposes, has based his method of the influence of the ancient crusts of weathering upon their composition. Under the ancient kaolin-type weathering conditions the mineralogy of forming sediments was very uniform: among rock-building minerals prevailed quartz, kaolin, partly hydromicas. Among accessories the following stable minerals prevailed: ilmenite, leucoxene, chromite, zircon, rutile, disthen, staurolite, tourmaline, cassiterite, and also less widely spread minerals such as sillimanite, anatase, brucite, corundum, xenotime, columbite, monazite, topaz, spinel, andalusite, diamond, gold, platinum, osmiridium. Unstable under the ancient kaolin weathering conditions were: garnets, pyroxenes, amphiboles, epidote, magnetite, apatite, sphene, serpentine, olivine, titano-magnetite. Their contents in the deposits, formed at the expense of the kaolin crust of weathering, were as a rule insignificant. From the above it is clear that the ancient weathering could have affected the mineralogical composition of accessory minerals of deposits, even much stronger than the petrographical composition of the distributive province. In the course of geological times the total balance of stable accessory minerals, able to undergo repeated weathering and erosion, has the tendency to grow in spite of their dilution in sediments during certain epochs. The author tried to give a stratigraphic division of the Mesozoic and Cenozoic deposits in the South Urals from terrigenous components. This method can find a wide application. In the future it will be advisable to combine the above mentioned method with the method of Illing and Baturin and others, taking into account the petrographic influence of the rocks of the distributive province. — Auth. English Summ.