DBPapers
DOI: 10.5593/SGEM2014/B11/S6.095

MODELING OF THE TRIASSIC AND JURASSIC RIFTING IN THE SOUTHERN PART OF CENTRAL NORTH BULGARIA – IMPLICATIONS FOR THE SOURCE ROCK MATURITY

N. Botoucharov
Wednesday 1 October 2014 by Libadmin2014

References: 14th International Multidisciplinary Scientific GeoConference SGEM 2014, www.sgem.org, SGEM2014 Conference Proceedings, ISBN 978-619-7105-07-0 / ISSN 1314-2704, June 19-25, 2014, Book 1, Vol. 1, 735-742 pp

ABSTRACT
The geodynamic evolution of the study area, restored from numerous well section data, demonstrates increased tectonic and basin subsidence during Late Permian-Early Triassic, Late Triassic and Early Jurassic rifting phases as well as after Mid-Cimmerian compression. There is a distinct trend for higher burial rates and depths of sediments from central southern part of the Moesian Platform to the south towards the Balkan orogenic system. Although, the extensional processes are very important for the tectonic subsidence the Late Jurassic-Early Cretaceous deposition of very thick sedimentary complex affected the overall basin subsidence to a greater extent. The main objective of modeling is to quantify the extension of the lithosphere for rift phases and their importance for the burial and thermal maturity of the source rocks. Modeling allowed the possibility of multiphase rifting and different extension of the crust (factor δ) and sub crust lithosphere (factor β). Comparing the computed lithospheric deformation with the actual tectonic history of the basin allows a relatively accurate assessment of the validity and limitations of the underlying models. The extensional phases during Late Permian-Early Triassic, Late Triassic and Early Jurassic are adopted, reflecting the complex history of the deposited sediments in the Mesozoic. Three models (A, B and C), which are close to the highest degree to the actual development of the study area, was drafted after a thorough analysis of the computer-generated curves and comparing them with the observed tectonic subsidence. Model B is the most plausible for the time of lithospheric extension during the Triassic and Jurassic. Quantitative indicators of lithospheric extension and the lack of widespread volcanism manifested probably a passive model with multiple rifts phases. The observed phases were not significant on its intensity and duration. The measured and calculated maturity parameters (%Ro, Tmax and PI) for Triassic and Lower-Middle Jurassic sediments vary from Early mature to Postmature stages. Significant subsidence and accumulation style during Early-Middle Jurassic and Late Jurassic-Early Cretaceous evolution, as well as the development of intensively blockfaulted structures seem to be the most important factors for the source rock maturity. The higher catagenetic transformation of these deposits in the study area, however, suggests that the significant hydrocarbon generation has already taken place. Based on the analysis of the obtained results it can be concluded that the thermal maturity trends of the Triassic and Jurassic sediments are determined by the Mesozoic geodynamic evolution of the study area with several rifting and compressional events.

Keywords:Central North Bulgaria, Moesian Platform, Triassic and Jurassic rifting, tectonic subsidence modeling, source rock maturity.