The Late Cretaceous marine basin of platform Ukraine (morphometry, stages of development, lithology and stratigraphy of sedimentary formations)

Abstract

Formulation of the problem. The relevance of the research is related to the formation of a holistic view of the Late Cretaceous Sea basin of the study area: its boundaries, area, the existence of probable land areas, conditions of sediment accumulation and historical development. The purpose of the article. Based on the results of exploratory, structural-exploratory and parametric drilling conducted during the State Geological Survey on scales of 1:50,000, 1:100,000 and 1:200,000 and own field research, we supplemented the information on the geohistorical chronicle of the Late Cretaceous of the southwestern part of the SEE. Methods. The material for writing the article was the results of drilling more than 10,000 exploration, structural and parametric drilling wells conducted during the State Geological Survey at scales of 1:50,000, 1:100,000 and 1:200,000, which are stored in the State Information Geological Fund of Ukraine. Also, the results of own field research of 47 most complete open sections of the Upper Cretaceous of Platform Ukraine were taken into account and a significant literature on the geological structure of the studied area was processed. Research methods: facies and formation analysis, lithological, petrographic, paleontological, litho-biostratigraphic, geophysical, etc. At the final stage of the mapping of the Upper Cretaceous sediments of Platform Ukraine, the methodology of sedimentary basin monitoring and modeling of formation units was used with the help of the domestic software package "Geomapping" with further conversion to the ArcView grid format. Results. To find out the spatio-temporal distribution of the Upper Cretaceous deposits of the study area, their composition, stratigraphic position and parameters of the Late Cretaceous sea basin, we analyzed the materials of mapping, structural search, exploratory and parametric drilling over the past 50 years were analyzed, our own studies of open sections of the Upper Cretaceous were taken into account, and significant stock material on the geological structure of the studied area was also processed. The most informative wells were selected as reference wells. Their number varied from 1179 for Early-Middle Cenomanian deposits to 1103 for Turonian deposits. The maximum density of the studied sections of support wells was recorded for the territory of Volyn-Podillia and individual blocks of the Ukrainian Shield (USH) and is 23.1 wells per 1000 km2, the minimum - in the water areas of the Ukrainian part of the Black and Azov Seas - about eight per 1000 km2. The absence of Upper Cretaceous deposits on a significant territory of platform Ukraine was established. Early-Middle Cenomanian and Turonian deposits have the largest distribution area, and Maastrichtian deposits have the smallest. In our opinion, areas with continental conditions of existence in certain ages or during the entire Late Cretaceous period have been identified. This made it possible to calculate the areas of land areas and areas covered by the sea with the help of software, with a certain percentage of error (up to 10%). The area of the sea basin was up to 80% of the territory of platform Ukraine. In the historical development of the Late Cretaceous Sea basin of the study area, two stages are distinguished: early-Middle Cenomanian and late Cenomanian-Maastrichtian, which differed significantly from each other in terms of hydrological, hydrochemical, temperature regimes and the nature of sedimentation. The lithological characteristics of the deposits according to the modern stratigraphic division of the Upper Cretaceous rock complex are given.