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The geological history of the Istria 'Depression', Romanian Black Sea shelf; tectonic controls on second-/third-order sequence architecture

David R. D. Boote
The geological history of the Istria 'Depression', Romanian Black Sea shelf; tectonic controls on second-/third-order sequence architecture (in Petroleum geology of the Black Sea, M. D. Simmons (editor), G. C. Tari (editor) and A. I. Okay (editor))
Special Publication - Geological Society of London (October 2017) 464 (1): 169-209


The Istria 'Depression' or sub-basin of offshore Romania lies at the intersection of the trans-European Tornquist-Teisseyre 'Zone' and the Black Sea back-arc basin, just outboard of the East Carpathian orogenic welt. Its Late Mesozoic-Cenozoic succession records an extraordinary polyphase history of subsidence and sedimentation, interrupted by several quite spectacular second-/third-order erosional unconformities, reflecting the interplay between these tectonic domains. The unconformities divide the succession into a number of stratigraphic sequences.The sub-basin first developed as a transtensional rift in the Triassic-Early Jurassic, evolving into a narrow oceanized trough in the later Jurassic. This was tilted west during the Early Cretaceous, and the residual Late Jurassic topography was filled and buried by a west-facing clastic-evaporite wedge. Following Late Aptian-Albian(?) rifting, post-rift subsidence and spreading in the Western Black Sea imposed a strong easterly tilt, encouraging the partial evacuation of its Early Cretaceous sedimentary fill by gravity-driven mass wastage. The incised valley topography was subsequently infilled and buried during the later Cretaceous and Early Cenozoic. During the mid-Late Cenozoic, the Black Sea Basin experienced intermittent periods of partial to complete isolation from the world ocean and significant base-level drawdown. The first major sea-level fall occurred in the Eocene when the Istria 'Depression' was deeply incised, to be healed by Oligocene shales during the subsequent rise. Yet another period of drawdown and exposure occurred in the mid-Miocene, with extensive shelf-margin mass wastage and erosion, followed by re-flooding and deposition of a transgressive backstepping sequence in the middle-late Miocene. Messinian drawdown in the Mediterranean caused a further period of isolation and falling base level. The shelf margin was again exposed, and experienced widespread mass wastage and slumping. Rising sea level eroded the earlier slumped sequence and the margin was healed by a lowstand prograding wedge in the late Miocene-early Pliocene. This was followed by shelf sedimentation in the Plio-Pleistocene periodically interrupted by canyon-incision events, testifying to continued climatically or tectonically imposed base-level fluctuations.Several direct and indirect tectonic factors were responsible for valley/canyon incision within the Istria Depression and erosion of the Romanian Black Sea shelf margin. These include: (1) the local structural framework; (2) direct tectonic uplift and tilting; and (3) more indirect tectonically imposed isolation encouraging significant base-level falls.

ISSN: 0305-8719
Serial Title: Special Publication - Geological Society of London
Serial Volume: 464
Serial Issue: 1
Title: The geological history of the Istria 'Depression', Romanian Black Sea shelf; tectonic controls on second-/third-order sequence architecture
Title: Petroleum geology of the Black Sea
Author(s): Boote, David R. D.
Author(s): Simmons, M. D.editor
Author(s): Tari, G. C.editor
Author(s): Okay, A. I.editor
Affiliation: 12 Elsynge Road, London, United Kingdom
Pages: 169-209
Published: 20171009
Text Language: English
Publisher: Geological Society of London, London, United Kingdom
References: 129
Accession Number: 2017-087929
Categories: StratigraphyStructural geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., sketch map
N44°00'00" - N45°00'00", E28°30'00" - E29°30'00"
Source Note: Online First
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data from The Geological Society, London, London, United Kingdom
Update Code: 201746
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