Outlines of the Siberian Platform sequence stratigraphy in the Lower and lower Middle Cambrian (Lena-Aidan area)

Abstract

The development of Cambrian reefal complexes on the inherited pre-Cambrian uplifts determined a subdivision of the Siberian Platform basin into three facies belts: western saliferous basin, eastern open shelf, and transitional reefal belt. Facies shifts which affected all belts emphasised the sequence and parasequence boundaries. The study of the stratotype area of the Russian Lower Cambrian stages (middle courses of the Aidan and Lena rivers) allowed us to distinguish four (third-order?) sequences spanning the Tommotian-lower Mayan interval. The sequence boundaries, except for the base of the Nemakit-Daldynian Stage, are restricted to intrazonal levels rather than to the boundaries between stages and even between zones. Such a relationship between biostratigraphic and sequential boundaries excludes significant chronostratigraphic hiatuses in the Siberian Early Cambrian time scale. This fact together with high fossil content, and good magnetostratigraphic, chemostratigraphic (C and Sr isotopes), and radiometric data show that stable cratons located at low latitudes keep a better record of events serving the chronostratigraphic basis. A special attention should be paid to the fact of the absence of a pronounced correlation between biostratigraphic and sequential events.