VOLUME 18 (2)/April 1988

The present complex structure of SE Strandza is a result of two superimposed deformation event : Late Cimmerian (?) thrusting and Subhercynian (?) folding.
   Two main Late Cimmerian (?) regional tectonic unit are divided: autochthon (Paleozoic granite, Triassic and Lower-Middle Jurassic sediments of Subbalkanide type) and allochthon (Strandža type Triassic). The allochthon consists of two subunits. The lower nappe is made up of the dominantly carbon ate rock of Malko Tarnovo, Kondolovo and Lipačka Formations (Middle – Upper Triassic) and the upper – of various metasediments and rare metavolcanics of Gramatikovo, Zaberska, Strȃvnica and Stoilovo Formations (Lower - Middle Triassic, possibly Paleozoic).
   The metamorphic zoning is inverted: greenschist facies in the upper nappe and local, very low-grade metamorphism in the lower nappe and the autochthon.
   The Late Cimmerian (?) phases of fold deformation in the autochthon and the lower nappe are similar: D₁ – recumbent folds; D₂ – upright folds; D₃ – kink-bands. The upper nappe shows different pattern: D₁ – intrafolial folds; D₂ – recumbent fold; D₃ – upright and N vergent folds of variable morphology; D₄ – upright open folds; D₅ – kink-zones. The intrafolial folds D₁ in the upper nappe are synchronous to greenschist metamorphism which took prior to the formali on of nappes, in other SPT conditions. D₂, D₃ and D₅ in the upper nappe are correlated with D₁, D₂ and D₃ in the lower nappe and the autochthon. They are probably synchronous to the thrusting and the associated very low-grade metamorphism.

V.M. Georgiev. Magnesian calcite and the problem of the origin of carbonates in the deep-sea Old Black Sea sediments. The Old Black Sea (Lower-Middle Holocene) deep-sea sediments in the Black Sea basin contain carbonate laminae with a fixed position in the section – in the base of the typical sapropelic muds. The areal distribution of these laminae covers the whole continental slope and rise. They are usually lacking in the sediments of the abyssal plain. XRD, SEM and EDS' studies show that the laminae comprise mainly authigenic carbonates – aragonite and magnesian calcite. Aragonite occurs as elongated rice-shaped monocrystals or as diverse aggregates of elongated crystal platelets. The magnesian calcite (6–14 mol % MgC0₃) forms aggregates of isometric grains with submicritic dimensions between the aragonite grains or individual laminae consisting of idiomorphic rhombohedral and/or skeleton crystals. Low-magnesian calcite is also found sometimes. Usually it is related to Hollocene coccoliths without traces of recrystallization. The laminae do not show traces of lithification. A hemogenic-synsedimentary genesis of the carbonate laminae is suggested; their mineral composition witnesses marine chemical composition of the initial solutions with a high Mg/Ca ratio