Chronological Relationship of Pliocene Deposits in Fluviatile Plains between the Prut and Southern Bug Rivers

Abstract

Deposits of three Pliocene fluviatile plains between the Prut and South Bug rivers were studied in order to reconsider their disputed age determinations and chronological relations. Different ages of these deposits have been established, and their correlation with the Eastern Paratethys stratigraphie scale and magnetochronologic and stratigraphie scales of West European continental deposits have been established. The oldest deposits of the Stol' nicheny Formation are dated as the early Kimmerian (magnetic Chron 5). On a continental scale, they are close to the boundary between the Turolian and Ruscinian. The Kuchurgan Gravel is dated as the terminal early and mid­ dle Kimmerian (middle part of the Gilbert Chron) and also as the terminal early Ruscinian (MN zone 14). The Kar- boliya Beds correspond to the late Kimmerian (the end of Gilbert Chron) and to the late Ruscinian (MN zone 15). Neogene continental deposits are widespread in the area between the Prut, Dniestr, and South Bug rivers. Their formation was initiated at the end of the middle Sarmatian. At that time, the sea regressed from the Galician Bay far to the south and left a wide depression covered with marine sandy and clayey deposits of the middle Sarmatian. As the marine basin regressed the original fluviatile plain gradually progressed to the south. In the middle Pontian, this plain covered the entire territory of Moldova and southwestern Ukraine. Its deposits were composed of cyclic gravel, sandy, and clayey sediments of fluviatile, lacustrine, and deltaic origin. This continental sequence is subdivided into two major parts: the Miocene (Balta Formation) and Pliocene. Deposits of older fluviatile plains, containing Carpathian pebbles (jaspers, silified argillites, and others) and alluvium from the higher terraces of the Prut, Dniester, and Danube rivers are referred to the Pliocene (Khubka, 1981; Bukatchuk et ai, 1983). Deposits of Pliocene fluviatile plains are preserved on the most elevated watershed areas. Only in the south of the Prut region are they submerged below the sea level. There are three fields of old fluviatile deposit occurrences (Fig. 1). These are areas between the South Bug and Dniester rivers (Kuchurgan Gravel), between the Dniester and Prut rivers (Stol'nicheny sequence), and between the Prut, Danube, and Yalpug rivers, where deposits bear mammals of the Molda­ vian Roussellion (Bilinkis, 1987). The latter have been