Сходство и различие состава среднеюрских и нижнеплиоценовых отложений на северо-западном берегу Байкала: Оценка вклада обломочного материала Приморского хребта в аллювий средней части долины Пра-Манзурки

Abstract

A comparative analysis is performed between compositions of pebbles and sandy filler of a pebble package that finalizes a section of the Lower Pliocene Buguldeyka alluvium horizon in the middle part of the Pra-Manzurka valley and those of pebbles and sandy cement of the Middle Jurassic conglomerates of the Nizhniy Koty sub-formation from outcrops of the Angara-Koty depression in the southeastern part of the Irkutsk coal basin. A partial similarity in major oxide and trace element contents in trachydacites and rhyolites of pebbles from Pliocene and Jurassic deposits is defined. From the difference in major oxide and trace element contents of the sand filler of the lower and upper layers of the pebble package of the Pra-Manzurka valley, the difference in their sources is inferred. It is proposed that the convergence between the composition of the sandy filler of the lower layers of the Pliocene pebble package and those of the trachydacite-rhyolite pebbles from this and of the sand cement of the Middle Jurassic conglomerates may reflect the erosion of the clastic material of the Middle Jurassic conglomerates and its removal into the middle part of the Pra-Manzurka valley in the initial phase of the uplift of the Primorsky Range. Occurrence of a Th/Co anomaly in the lower layers of the pebble unit, not typical for Jurassic conglomerates, indicates the formation of the pebbles from another source of clastic material.