Incompleteness of the geological record in Middle-Upper Pleistocene key sections of the Northern Caspian Lowland

Abstract

Pleistocene key sections of the Northern Caspian Lowland are characterized by the incompleteness of the geological record, which is presented in depositional breaks, their duration, causes, and types. Depositional breaks occurred in all periods of the Middle and the Late Pleistocene and occupied various time intervals, usually quite continuous – from ∼180 ka (Cherny Yar) to 100–110 ka (Alexandrov Gay, Gorky Erik, Kopanovka, Enotaevka), rarely shorter – about 15–40 ka (Seroglazovka, Mergenevo). Period of accumulation in these sections is small (3.5–44 ka) and covers only 1.2–9% (average 3–4%) for presented deposits and less than 10% from all chronological record. The total chronological assessment of the geological record incompleteness in all studied sections estimated as more than 90%. In all studied sections accumulation rates for Holocene, Upper Khvalynian, Lower Khvalynian, Upper Khazarian, Chernoyarian, and Lower Khazarian are lower than the average for this region. Incompleteness is usually characterized by erosion of river waters of the Volga and Ural system, but more often by abrasion of the Khvalynian and the Khazarian transgressive waters. Another cause of incompleteness of the geological record is long continuous periods without significant deposition. This is often observed in subaerial conditions in the vast watershed area.