ИСТИНА

Turonian-Coniacian Foraminifera and Radiolaria were analysed from Kamenny Brod (KB) section (Russian Platform, Ulyanovsk-Saratov depression). The stratigraphically most complete of the Turonian–Coniacian interval for this area was established. The benthic foraminifers (BF) Zones were established on the base of zonal scheme of Beniamovsky, 2008 with additions of new data for another area. BF assemblages are the most abundant, their distribution in the section have established 5 Zones. Middle—Upper Turonian, Lower-Middle Coniacian and Lower Santonian are present in KB section. Planktonic foraminifers (PF) are represented by two groups. The first group consists of trochospiral whiteinellids, archaeoglobigerinellids, rare dicarinellids and marginotruncanids. The second one is represented by biserial heterohelicids. Trochospiral PF have low taxonomic diversity, they are distributed very irregularly through section and do not allow to distinguish zonal divisions. At the same time, this section can be subdivided into 2 parts – first, corresponding to the Turonian, and second, corresponding to the Coniacian. Biserial heterohelicids are distributed through the section irregularly and demonstrate a low diversity of taxa (6 species). However, their joint distribution has allowed to establish 6 layers whose age is correlated with Cenomanian-Turonian, Turonian and Coniacian. Radiolarian assemblages are extremely poor, because the KB section is represented by carbonate rocks. However, in these assemblages, typical Santonian relatively boreal species, as well as relatively warm water Albian–Turonian species, are recorded. The PF/BF ratio within the foraminiferal assemblages indicates the predominance of shallow-water environments within the southern part of the Ulyanovsk-Saratov depression. According to this indicator, the incision can be clearly divided into two intervals. The content of PF reaches 50-60% in the Turonian and partially Lower Coniacian and generally fluctuates from 39 to 60%. In the upper part of the section, the content of PF is sharply reduced, not exceeding 10-20%, only in rare cases reaching 30%. The ratio of different morphological types of PF (trochospiral/biserial) is also variable. In the lower part of the section corresponding to the Turonian and Lower Coniacian the content of trochospiral PF is up from 40 to 100%.Biserial heterochelicids predominate above the section, their content stably stays within 60-70%. Such ratiosindicate an increase in transgression from the south throughout Turonian and early Coniacian.