Отправлено: 09.11.12 06:43. Заголовок: Calcretes, fluviolacustrine sediments and subsidence patterns in Permo‐Triassic salt‐walled minibasi

Calcretes, fluviolacustrine sediments and subsidence patterns in Permo‐Triassic salt‐walled minibasins of the south Urals, Russiamore
by Andrew J Newell


Calcretes, fluviolacustrine sediments and subsidence patterns inPermo-Triassic salt-walled minibasins of the south Urals, Russia
ANDREW J. NEWELL*, MICHAEL J. BENTON. TIMOTHY KEARSEY GRAEMETAYLOR, RICHARD J. TWITCHETT§ and VALENTIN P. TVERDOKHLEBOV

British Geological Survey, Maclean Building, Wallingford OX10 8BB, UK
(E-mail: ajn@bgs.ac.uk)
School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK
British Geological Survey, Murchison House, West Mains Road, Edinburgh EH9 3LA, UK
School of Geography, Earth and Environmental Sciences, University of Plymouth, Plymouth,PL4 8AA, UK
Geology Institute of Saratov State University, Astrakhanskaya 83, 410075 Saratov, Russia
Associate Editor – Xavier Janson

Sedimentology 2012 pp.1659-1676

ABSTRACT
The south Uralian foreland basin forms part of the giant, yet sparselydocumented, PreCaspian salt tectonic province. The basin can potentiallyadd much to the understanding of fluviolacustrine sedimentation within salt-walled minibasins, where the literature has been highly reliant on only a fewexamples (such as the Paradox Basin of Utah). This paper describes the LatePermian terrestrial fill of the Kul’chumovo salt minibasin near Orenburg in thesouth Urals in which sediments were deposited in a range of channel,overbank and lacustrine environments. Palaeomagnetic stratigraphy showsthat, during the Late Permian, the basin had a relatively slow and uniformsubsidence pattern with widespread pedogenesis and calcrete development.Angular unconformities or halokinetic sequence boundaries cannot berecognized within the relatively fine-grained fill, and stratigraphic andspatial variations in facies are therefore critical to understanding thesubsidence history of the salt minibasin. Coarse-grained channel belts showevidence for lateral relocation within the minibasin while the development of a thick stack of calcrete hardpans indicates that opposing parts of theminibasin became largely inactive for prolonged periods (possibly in the orderof one million years). The regular vertical stacking of calcrete hardpans withinfloodplain mudstones provides further evidence that halokinetic minibasingrowth is inherently episodic and cyclical.
Keywords
Calcretes, fluviolacustrine, Permian, PreCaspian basin, salt mini- basin, salt tectonics, Urals.