About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

CSPG Bulletin

Abstract


Bulletin of Canadian Petroleum Geology
Vol. 42 (1994), No. 3. (September), Pages 352-364

Structure and Petroleum Potential of the Dagestan Thrust Belt, Northeastern Caucasus, Russia

Konstantin O. Sobornov

ABSTRACT

Exploration boreholes and seismic reflection data in the foothills zone of the northeastern Caucasus obtained during the last decade reveal considerable differences between the surface and subsurface structures of the area. The new data suggest that this zone may be viewed as a buried thrust belt. The allochthonous assemblage of the belt is formed mainly by stacked north-verging thrust sheets made up mostly of Mesozoic carbonates and sandstones bounded at the top and bottom by conjugate detachment surfaces. The thrust sheets are interpreted to be inserted into the clastic section of the Terek-Caspian foredeep along the base of Oligocene - Early Miocene mudstones. The blind subsurface thrusts have been active since the Late Miocene. Strata above and below the allochthonous unit are characterized by independent styles of deformation. The mildly deformed foredeep clastics create a hinterland-facing monocline that is passively uplifted by underthrusting. These rocks mask the subsurface structures. Tectonic wedging in the Dagestan thrust belt was facilitated by the mechanical weakness of the overpressured mudstones of the Maykop Formation (Oligocene - Lower Miocene) which prevented transmission of the compressional stress across it. The interpreted geometry of the thrust belt front implies a shortening ranging from 20 to 50 km.

This interpretation of the regional structure suggests a petroleum exploration play consisting of structural traps within the buried antiformal stacks. Regionally, oil- and gas-bearing Upper Cretaceous and Upper Jurassic carbonate rocks involved in thrust sheets and sealed by Maykop mudstones are considered primary prospecting targets.

RESUME

Des forages d'exploration et des donnees de reflection sismique provenant de la zone des contreforts des monts Caucase du nord-est obtenus durant la derniere decennie, revelent des differences considerables entre les structures de surface et de subsurface de la region. Ces nouvelles donnees suggerent que cette zone peut etre envisagee comme une ceinture de chevauchement ensevelie. L'assemblage allochtone de la ceinture est constitue surtout de nappes de charriage empilees, situees a la limite nord et composees surtout de roches carbonatees et de gres mesozoiques limites au haut et au bas par des surfaces de decollement de meme direction. Les nappes de charriage sont interpretees comme etant inserees dans la coupe clastique de l'avant-fosse Terek-caspienne le long de la base des pelites de l'Oligocene - Miocene inferieur. Les chevauchements de la subsurface sans affleurements ont ete actifs depuis le Miocene superieur. Les strates au-dessus et en-dessous de l'unite allochtone sont caracterisees par des styles de deformation independants. Les sediments clastiques legerement deformes de l'avant-fosse creent un monoclinal faisant face a l'arriere-pays et passivement souleve par sous-charriage. Ces roches cachent les structures de la subsurface. L'insertion tectonique dans la ceinture de chevauchement Dagestan fut facilitee par la faiblesse mecanique des pelites en surpression de la formation Maykop (Oligocene - Miocene inferieur) qui empecha la propagation de l'effort de compression a travers cette derniere. L'interpretation de la geometrie du front de la ceinture de chevauchement laisse supposer un raccourcissement allant de 20 a 50 Km.

Cette interpretation de la structure regionale suggere une region d'exploration petroliere qui consiste en pieges structuraux au sein des empilements de structures anticlinales ensevelies. A l'echelle regionale, les roches carbonatees du Cretace superieur et du Jurassique superieur renfermant du petrole et du gaz, impliquees dans les nappes de charriage et scellees par les pelites de la formation Maykop, sont considerees comme des cibles d'exploration primaires.

Traduit par Marc Charest.


Pay-Per-View Purchase Options

The article is available through a document delivery service. Explain these Purchase Options.

Protected Document: $10
Internal PDF Document: $14
Open PDF Document: $24