Jurassic outcrop depositional sequence stratigraphy in western Bulgaria

Sloss (1963) and the group of EXXON used names of North American Indian tribes as Absaroka, Zuni for the nominqtion of the 1^st order sequence stratigraphic units. For their subdivisions they used Lower and Upper Absaroka, etc. and their subdivisions, in turn, were designated by number – 1, 1.3, etc. (Haq et aI., 1988). Latter, however, Hardenbol et aI. (1998) used another system. They gave to the sequence the index of the stage, where passed the lower sequence boundary – Toa 1, Toa 2, etc. for the Toarcian sequences, etc.
   For designation the sequences (Fig. 1) in the field, I used the name of the section and the number of the sequences above one reper – Lyalintsi - 1, Komshtitsa 2.1, etc., which nomination is expressed in the Fig. 2-4.
   The Bulgarian Lower and Middle Jurassic fauna, especially ammonites (Sapunov, 1976a, b, 1977 a, b), brachiopods, etc. possesses links with the Northwestern European (Boreal/Subboreal) bioprovince and the Upper Jurassic - with the Southwestern European (Tethyan/Submediterranean) bioprovince. That is why I correlate the two parts of the Bulgarian Jurassic sequence stratigraphic scheme with the relative western European sequence stratigraphic standards of Hardenbol et aI., (1998).
   The western Bulgarian Jurassic sediments are divided into two 1^st order sequences, called by Tchoumatchenco, Lakova (1994) – Lower and Upper Major Jurassic depositional sequences. Here I follow the manner of nomination of the sequences, used by Hardenbol et aI. (1998) – after their stratigraphical position. For the Lower Major Sequence I use the name Hettangian-Lower Callovian, and for the Upper Major Sequence-Middle Callovian-Berriasian Depositional Sequence. The Hettangian-Lower Callovian Sequence is subdivided, in its turn, into two 2^nd order sequences – Hettangian-Lower Toarcian sequence (coinciding more or less with the North American super cycles (Haq et aI., 1988) Upper Absaroka 2-4 (UAB 2-4) and Upper Toarcian-Lower Callovian sequence (coinciding partially with the super cycles Lower Zuni A 1-3 (LZA 1-3). Here will be described only the 1^st order sequences.