Northwest Kamchatka Area
|Cape Konglomeratoviy||Yelistratov Peninsula||Cape Valizhgen||NE Russia Map|
Geology and Paleontology of Northwest Kamchatka
Terrigenous deposits of the Mameta Formation overlying eroded Lower Cretaceous beds constitute the lowermost part of the Upper Cretaceous section in Northwest Kamchatka. The sandstones in the lower strata of the Mameta Formation contain Neogastroplites remains (Neogastroplites aff. americanus Reeside et Weymouth, etc.) indicating a Late Albian age for these beds (Vereshchagin, 1977). Within the formation overlying beds contain the remains of Cenomanian molluscs (see panel middle right). The upper strata of the Mameta Formation have yielded Inoceramus pennatulus Perg., I. scalprum Boehm., I. nipponicus Nagao et Matsumoto, etc. and correspond to the regional zone I. nipponicus - I. scalprum at the top of the Cenomanian section of Northwest Kamchatka (Pergament, 1978). Thus, the age of the Mameta Formation is determined as Late Albian - Cenomanian (see panel middle right).
According to V.P.Pokhialaynen and G.P.Terekhova (Decisions...,1982) the I. nipponicus zone corresponds not only to the Late Cenomanian but also to the Early Turonian and, hence, the upper part of the Mameta Formation may include the Lower Turonian deposits as well. The total thickness of the formation is about 1200 m.
The Mameta Formation is overlain (possibly unconformably) by the marine deposits of the Pel-El Formation. Pergament (1978) points out an occasional angular disconformity between these formations. The lower part of the Pel-El Formation is not paleontologically characterized but is placed between the uppermost Cenomanian zone I. nipponicus - I. scalprum and the early Turonian zone I. lamarcki. Pergament (1978) assumes these strata correspond to the earliest Turonian Inoceramus labiatus zone (see panel middle right). The superadjacent rocks of the Pel-El Formation have exhibited numerous fossil Turonian and Coniacian inoceramids and ammonites (Pergament, 1961, 1978). Therefore, the entire formation is considered to be of Turonian (possibly, excluding lowermost Turonian) - Coniacian age. The thickness of the formation is about 1100 m.
The Valizhgen Formation, 500 to 600 m thick, consists of terrigenous and coal-bearing deposits of continental origin featuring plant fossils and disconformably overlies Aptian - Albian and even older rocks. These deposits are known in the vicinity of the Konglomeratoviy and Valizhgen Capes. According to Pergament's observations, continental deposits of the Valizhgen Formation are laterally replaced by the marine rocks of the Pel-El Formation north of latitude 62°N.
According to another point of view (Ivanov, Pokhialainen, 1973) the basal conglomerates of the Mameta Formation (rather than of the Pel-El Formation) are laterally continuous with the lowermost conglomerates of the Valizhgen Formation. Thus, the deposits of the Valizhgen Formation "...by the time of formation correspond to the marine sediments of the Mameta and Penzhina formations (Late Albian - Coniacian)" (Ivanov, Pokhialainen, 1973, p. 85). According to V.P. Pokhialainen the Penzhina Formation includes rocks assigned to the upper strata of the Mameta Formation and the Pel-El Formation (see panel bottom right).
Thus, there are two opinions on the correlation of the deposits containing the flora of the Valizhgen Formation with marine strata and therefore on the age of these plant-bearing beds (see panel bottom right). Since no marine mollusc fossils were found in the Valizhgen formation, paleobotanical evidence is critical for distinguishing between these divergent views.
Stratigraphy of Upper Albian and Upper Cretaceous sediments in Northwestern Kamchatka according to Pergament (1978) with supplements.
The Pel-El and Valizhgen formations are conformably overlain by the Bystrinskaya Formation (see panel top right). Its lower subformation, as thick as 430 m, contains in the lower strata remains of Inoceramus undulatoplicatus Roemer, I. naumanni Yok., and higher up - I. lingua lingua Goldf., I. patootensis sokolovi Perg., I. transpacificus Peg. etc., arguing for a Santonian and, possibly, Early Campanian age for these deposits (Pergament, 1978; Ivanov, Pokhialainen, 1973). The upper parts of the Lower Bystrinskaya Subformation have yielded the ammonites Bostrychoceras cf. polyplocum (Roemer), indicating, according to Pokhialainen (1984), a Campanian rather than Santonian age for this part of the section. The Upper Bystrinskaya Subformation, whose thickness is about 265 m, contains plant-bearing beds. Foraminifera recovered from the upper part of this subformation are evidence for a likely Campanian age for these strata (Vassilenko, 1985). The total thickness of the Bystrinskaya Formation amounts to about 700 m.
The Bystrinskaya Formation is concordantly overlain by the 520 to 630 m thick Vesselovskaya Formation (see panel top right). Its lower and upper subformations have a poor paleontological characterization. The middle subformation allied to the beds with I. balticus contains marine bivalve remains of Campanian - Maastrichtian age (Pergament, 1978). The Upper Cretaceous section in Northwest Kamchatka terminates in the Pillalvayam Formation of Maastrichtian age conformably overlying the Vesselovskaya Formation.
Thus, the plant-bearing deposits of the Upper Bystrinskaya Subformation are concordantly superadjacent on the strata with Inoceramus lingua - I. transpacificus - I. patootenis (Santonian - ? Early Campanian) and are overlapped by paleontologically poorly characterized rocks. The latter are overlain by the beds with Inoceramus balticus of Campanian - Maastrichtian age (see panel top right) and dated as Campanian (most probably, Early Campanian).