Microfossils of Turonian-Coniacian in the Kamenny Brod section (Russian Platform, Ulyanovsk-Saratov depression) − stratigraphic and palaeogeographic aspectsтезисы доклада
Дата последнего поиска статьи во внешних источниках: 28 февраля 2020 г.
Аннотация: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 ratioof 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.
This research was supported by the IGCP-609 Project and the RFBR: 18-05-00494, 18-05-00495, 18-05-00-501,18-05-00503 and was performed according to task 0135-2018-0036 (GIN RAS).