Volume 32, Nº 3 (2024)

The publication presents the results of geochemical, isotopic-geochemical (Sm–Nd) and isotopic-geochronological (U–Th–Pb) studies of terrigenous rocks of the Middle Riphean (?) Nadarov formation and the Upper Riphean (?) Nortui formation of the northwestern part of the Argun continental massif. Features of the material composition of the deposits indicate the presence of formations of various silicia acidity in the source area. According to Sm–Nd data, sedimentary rocks of the Nadarov and Nortui formations are characterized by negative values å_Nd(t) = –6.6…–3.5 at Early Proterozoic values of Nd model age (t_Nd(DM) = 2.0–1.8 Ga). According to U–Th–Pb dating of grains of detrital zircon, it was defined that the lower age limit of accumulation of terrigenous deposits of the Nadarov and Nortui formations falls at the Late Riphean (~775 and ~ 744 Ma, respectively). The main provenances area for them were Late Riphean igneous rocks with the participation of Early Proterozoic rocks, extended in the structure of the Argun massif.

The first results of U–Th–Pb isotope dating of detrital zircons (dZr) from the Chenka sandstones of the Cimmerides of the Mountainous Crimea are presented. Carboniferous–Triassic dZr dominate among dZr from Chenka sandstones. Analysis of previously obtained sets of dZr ages from the different-age and lithology formations of Cimmerides of the Mountainous Crimea has revealed the certain regularities in the change in time of the provenance signal and, accordingly, of the sources, the erosion products of which compose the studied formations. A comparison of the obtained of U–Pb ages of dZr from Chenka sandstones with similar data for sandstones from the Upper Triassic–Jurassic formations has shown that the provenance signals of the Chenka sandstones and Upper Triassic–Lower Jurassic flysсh strata are different, but the provenance signals of the Chenka sandstones and Middle–Upper Jurassic coarse clastic strata are similar. Detrital zircons from the Chenka sandstones are characterized by the parameters of the distribution of Th/U values intermediate between those from sandstones of flysch strata and from sandstones of coarse-grained strata. In general, the obtained isotope-geochronological and geochemical data and some features of the internal structure of dZr from the Chenka sandstones can be used as a strong argument in favor of interpretation of Chenka sandstones as an independent stratigraphic unit with an age not older than the Middle Jurassic. The similarity of the characteristics of dZr from sandstones of the Chenka sandstones with those of Middle–Upper Jurassic coarse clastic sequences casts doubt on the correlations of the Chenka sandstones with a number of lithologically similar units of the southwestern regions of the Mountainous Crimea, specified as Early Jurassic in age based on faunal finds.

The additional arguments regarding Cretaceous evolution of angiosperms are provided which further develop the evolutionary ideas of S.V. Meyen. The quantity, diversity and geographical distribution of angiosperms, which first appeared at the beginning of the Cretaceous (in Berriasian), had been increasing significantly starting from the end of the Albian. This could be due to the fact that for the first time in the Cretaceous history of the Earth, a hot and humid equatorial belt appeared in the Albian and acted as a “generator of suprageneric taxa” of higher plants. The speed of the angiosperm macroevolution had increased dramatically due to the development of this belt, while the fluctuations in the Late Cretaceous climate “launched the equatorial pump at full capacity.” The anatomy of the Triassic bennettitalean microsporangium Leguminanthus indicates that this group of gymnosperms possessed a morphological structure, which could have led to the formation of a closed (with closed margins) seed organ similar to the carpel of angiosperms, probably by means of a large evolutionarily significant saltation – gamoheterotopic transformation of female bennettite fruitifications to the anatomy of male ones. The presence of wide and probably flattened petioles and rachis in the Triassic bennettitalean Pterophyllum leaves confirms indirectly the validity of the assumption that angiosperm leaves could have evolved from those of bennettitaleans by means of phyllodization (flattening and enlargement of the leaf petiole).