Late Alpine tectonics and Neotectonics
International Conference - May 2001
Padala graben is situated in
the western part of the Rila Mountain, in the best accessible part of the
mountain. The rocks of the graben and the adjacent horsts are exposed along
the asphalt road leading to the Rila Monastery. The graben is filled in
by Tertiary sedimentary rocks (Padala Formation; Zagorchev et al.,
The Padala Formation consists mostly of coarse polymictic breccia and conglomerate. The rock fragments that build up the rock come from the close surrounding, and are mostly amphibolite-facies metamorphic rocks of the Precambrian Rhodopian Supergroup (biotite schist, gneiss, migmatite, granite-gneiss, amphibolite, and occasional marble), aplite, pegmatite, diorite (Strouma diorite formation of pre-Ordovician age), quartz. The dimensions of the pebbles vary from millimetric to metric ones, the largest boulders being of the order of 1 - 1.5 m. The largest blocks reach up to several tens of cubic metres.
The matrix is sandy, and the degree of cementation is high. However, the rocks in some beds are only slightly cemented and have a loose appearance. Interbeds of sandstones with coalefied plant debris and scarce pebbles are also recorded as well as coal lenses associated with shales. Spores and pollen determined by Chernjavska (2000) indicate an Early Oligocene age.
The thickness of the Padala Formation in the type section is about 120 - 150 m. The maximum exposed thickness of the formation has been evaluated by Moskovski to more than 280 m, and may even exceed 350 - 450 m. The initial pre-erosional thickness may have reached 1000 - 1500 m if taking into account the vertical amplitude along the normal faults and the supposed erosion along the river Rilska.
Many of the above-cited facts have been known since the first travels of Ami Boue in 1844, and the coal occurrences have been reported by Bonchev in 1912 and Konyarov in1932. All field studies since that time gave descriptions of the Palaeogene East of the town of Rila, and made different correlations with other Palaeogene outcrops in the region. However, Shipkova (1999) and Shipkova and Ivanov (1999, 2000) have declared that the rocks described are not of a sedimentary origin at all, and represent "autoclastic breccia formed at the expence of amphibolite facies metamorphics during movements along a Djerman detachment fault in greenschist-facies conditions". Although the absurdity of this statement is obvious to the majority of Bulgarian geologists, the "descriptions" of the "autoclastic breccias" and the "Djerman detachment fault" have been multiplied in several papers in support of the fashionable ideas about exhumation of Tertiary metamorphic core complexes along Early Neogene detachments (Dinter, Royden, 1993).
Detailed structural studies during the last 20 years have shown that tectonic breccias are widespread in the Rila Mountain, too. They are present along normal faults and wrench faults (Figure) of different relative age (e.g., Moskovski, 1983; Zagorchev et al., 1999). The faults belong to several sets, and are usually steep (60 - 90o) although some of them dip between 30 and 60o. Along some of the faults the movements pre-dated, and along others, were coeval to the sedimentation within the Padala graben. A number of faults post-dated the sedimentation, and formed the modern Padala graben as a post-sedimentation structure. In most of the cases observed, tectonic breccias may be easily recognized and discriminated from the sedimentary breccias.
The position of the Palaeogene deposits in the Padala graben indicates the presence of a wider continental (fluvial - lacustrine) sedimentation basin in the area. The Padala Formation with its composition of coarse pebbles originating from the adjacent basement rocks of the Rila horst points at a close proximity to the source area for that basin.
The so-called "Djerman detachment" may be regarded as an example of a scientific hoax based on false observations and/or fabricated data. Together with similar fabricated data, it may easily compromise even a sound scientific hypothesis.
Figure. Simplified geological map of the Padala graben (Zagorchev et al., 1999)
Field work in the Palaeogene rocks of the Padala Formation will be performed during the field trip of the international conference, together with a visit to Rila Monastery - one of the most outstanding monuments of the Bulgarian past. The programme of the field trip includes also other important localities of Palaeogene and Neogene grabens, active faults, etc.