Quantitative analysis of Phanerozoic sedimentation

Abstract

This paper is the conclusion of many years of study of Phanerozoic sedimentation over the area of the present continents (without Antarctica). The compilation of the schematic lithological-paleogeographical maps for each section of the Phanerozoic systems (except the Quaternary) is taken as a basis for these studies; Ronov calculated areas of distribution and volumes of different groups of sedimentary and volcanogenic rocks within platforms and geosynclines, as well as changes in a mean rate of accumulation and intensity of volcanic activity. The volume of geosynclinal sediments of the whole of the Phanerozoic is 457 · 10 6 km 3. The volume of platformal sediments is 182 · 10 6 km 3. Our data confirm a periodic character in changes in the area, volume and rate of accumulation of sedimentary and volcanic deposits, concurrent with tectonic periodicity; the Hercynian and Alpine cycles being the most pronounced, the Caledonian weaker and the Salairian (Sardian) and Kimmerian cycles weaker still. The high rates of sedimentation and the high general intensity of volcanism are characteristic of the initial parts of tectonic cycles. The major transgressions and the peaks of carbonate accumulation fall in their middle parts. The high rates of sedimentation and the increase of clastic sediments corresponds to their final parts. Side by side with this cyclic character, our data reveal a certain time trend in the Phanerozoic changes under review. This is a general reduction of sea-covered area within the present continents and an increase of volume of sediments and of mean rates of subsidence. Since the changes within platforms and geosynclines have the same trend, they are obviously controlled by global processes. The global rhythm exists in spite of obviously uncoordinated movements of separate major blocks of the lithosphere, in particular of continental platforms. This is indicative of a global tendency predominating over regional ones.