NEW DATA ON LOWER CRETACEOUS (HAUTERVIAN- APTIAN) SEQUENCE STRATIGRAPHY WITHIN THE WESTERN GEORGIA REGION (CAUCASUS)

During Cretaceous, Georgia, a south-western part of the Caucasus, belonged to the active oceanic margin of the Tethys, with typical island-arc complexes. It is essential to note that all principal stratigraphical unconformities, which were recognized during the past century within Cretaceous deposits in Georgia (e.g., unconformities between Berriasian/Upper Jurassic, upper Barremian/lower Barremian, within lower Aptian, within upper Aptian, etc.), were interpreted as a result of Alpine orogenic pulses. The role of the phenomenon of eustasy was ignored. In the study area (adjacent regions of Imereti and Racha) of western Georgia within the Hauterivian-Aptian interval, five 3rd order sequences are revealed: upper Hauterivian-lowermost Barremian (H₂ -B₁¹), lower Barremian (B₁²-B₁³), uppermost lower Barremian-upper Barremian (B₁³-B₂), lower Aptian (A₁¹-A₁⁴) and middle-upper Aptian (A₂¹-A₃¹). Concerning the problem of causes of formation of the above-noted sequences and their boundaries, we can conclude that: (a) the lower boundary of the H₂ -B₁¹ sequence, which corresponds to mid-Hauterivian sea-level fluctuation, can be distinguished in this region, whereas in many other regions of the world there are insufficient data; (b) in the Mediterranean Tethys, the lower boundary of the B₁²-B₁³ sequence can be traced near the base of the S. nicklesi Zone (=K. compressissima Zone in Georgia), but we have insufficient data on how it is traced globally; (c) the lower boundary of the B₁³-B₂ sequence can be traced near the top of uppermost lower Barremian H. caillaudianus Zone in many regions, thus early/late Barremian regressive/transgessive successions were probably controlled by eustasy; (d) the lower boundary of the A₁¹-A₁⁴ sequence (fixed within D. tuarkyricus Zone) as well as the lower boundary of the next A₂¹-A₃¹ sequence (drawn at the base of middle Aptian E. subnodosocostatum Zone) can be traced in the Tethyan and Boreal regions within different geotectonic units and principal cause of this phenomenon most likely was the eustatic sea-level fluctuation; and (e) the boundary between the A₂¹-A₃¹ and A₃²-Al sequences, in the Tethyan and Boreal Europe/North America regions is drawn near the upper part of Clanseyesian and, as above, interpreted sea-level fluctuations at this boundary most likely of eustatic origin.