IDENTIFICATION OF CENTERS OF VOLCANIC ERUPTIONS FROM THE NUMBER OF SHEETS IN THE PLATEAU-BASALT SEQUENCES

Abstract

Correlation of more than 1700 specific layered sections of the volcanic sequence in terms of their rhythmic stratigraphy has led to identification of lithological and stratigraphic intervals corresponding to formations, subformations, individual members, and marker sheets. The basalt fields of each sequence interval are divided into zones within which the section consists of some arbitrarily chosen, fixed number of sheets. One selects the number of the constituent sheets to facilitate the attainment of the objective of the procedure, which is to identify the focal zones of eruptions and to depict the geological situation at the time of eruption is the form of a drawing, map or mechanism. The structural facies maps derived in this way indicate that the basalt area with the smallest numbers of sheets in the section almost always surround areas with the largest number of sheets. The way the areas with the greatest numbers of sheets lie within their immediate surroundings (i.e., other stratified basalt sequences) and the shapes of these areas in plan give an indication of the type of volcanic structures that were involved. An illustration of the method of reconstructing fissure and shield volcanic structures in the Tunguska basalt field is provided by the analysis of data on the titanium augite basalts of the Lower Ivakino Subformation of the Noril'sk region and the trachybasalts of the Yuryakh Formation in the Lake Khantay basin.