APPLICATIONS OF FUSULINID CYCLICITY MODEL IN BIOSTRATIGRAPHY, CORRELATION, AND INTERPRETATION OF UNCONFORMITIES

For biozone definition in the Donets Basin we use fusulinid acme-zones controlled by long-term relative sea level changes documented in a continuous Pennsylvanian silisiclastic succession by cyclic reoccurrence of three main fusulinid assemblages: (1) Hemifusulina, (2) Beedeina, (3) Fusulinella. A proposed fusulinid distributional model is also recognized in carbonate succession in the Moscow Basin and allows very precise correlation of strata with different lithology. In the Donets Basin limestones M₇-M₁₀¹ corresponds to one full fusulinid cycle. M₇-M₈ are transgressive limestones and belong to zone Hemifusulina subrhomboides – H. vozhgalica– Beedeina elshanica vaskensis, which is coeval to the latest Kashirian H. vozhgalica zone of Smedva Fm of the Moscow Basin represented by dolomites. M₉ – M₁₀¹ are regressive limestones and characterized by increased fusulinid diversity. Two zones are recognized Putrella donetziana (M₉) and Kamaina rossoshanica (M₁₀), which are respectively coeval to Podoloskain Putrella brazhnikovae zone (Vaskino Fm) and to Fusulinella colaniae - Beedeina ulitinensis zone (Ulitino Fm) of the Moscow Basin.

Although sedimentation during a full fusulinid cycle was interrupted several times both in transgressive and regressive parts documented in unconformities, we recognize a steady paleoecological change in shallow water of vast area of the eastern margin of Pangea from slightly colder, low salinity, high nutrient in the beginning of each cycle to warmer, higher salinity, low nutrient to the end of each cycle. This allows hypothesizing that duration of glacial-interglacial cycle was coeval to a one fusulinid cycle (600,000 – 1,000,000 y).

The intermediate unconformities within transgressive and regressive parts of a cycle are interpreted as an isostatic response of the individual basins to the melting and accumulation of alpine glaciers. Comparative analysis of unconformities in the Donets and Moscow basins reveals its greater number in the latter that may indicate an impact of other smaller glaciers situated further from the equatorial mountain belt, in the northern regions of Pangea.