OTTO, S.C., E. IWANIW, A.C.ALEXANDER and C. DARLINGTON, Robertson Research International Limited, Llandudno, North Wales, UK
Abstract: Post-Cimmerian (Jurassic) Petroleum Systems of the Central Paratethys Region
The end-Triassic Cimmerian Orogeny was the result of the collision of a number of blocks of Gondwanan affinity with the southern margin of Eurasia, and led to the closure of the Palaeo-Tethys Ocean.The effects of this orogenic event are widespread and are recorded in sedimentary basins throughout Central Asia. In basins close to the orogen, pre-Jurassic rocks are deformed and are typically considered to be economic basement; basins lying further from the orogenic front have active Palaeozoic petroleum systems.
In the Central Paratethys
area, illustrated in Figure 1, Post-Cimmerian extensional basins contain
sequences of continental shales and coals that form source rock units of
varying importance, stretching from the Caspian Sea to western China. These
source rocks reached initial maturity from mid Cretaceous (Amu-Dar'ya)
to Miocene (Tarim) and generated hydrocarbons that migrated into coeval
sandstones (e.g. North Ustyurt,Turfan) and overlying Upper Jurassic sandstones
(Turgay) and carbonates (Amu-Dar'ya, Afghan-Tajik).Variations in the timing
of source rock maturity are dependent on heat flow and subsequent sedimentation;
a function of the varying tectonic histories of the area. There is a marked
difference in Jurassic tectonics either side of the Talasso-Fergana Fault
,
being broadly extensional to the west and compressional to the east. Considerable
variation also exists in the effects of the end-Jurassic collision of the
Lhasa Block and there are significant local and regional differences in
uplift, deformation and subsidence histories in the Oligocene-Recent following
the collision of the India Block.
Post-Cimmerian Petroleum Systems
Basins in the Central Paratethys
area can be divided into a number of groups on the basis of the Mesozoic
tectonic regime
, the strength of the Tertiary compressional overprint and
the thickness of Cretaceous to Tertiary overburden; the influence of these
parameters on the presence of both Jurassic source rock intervals and Jurassic-Jurassic
petroleum systems can then be analysed (Table 1).
Jurassic rocks are also play elements in other petroleum systems: for example, Jurassic source rocks feed hydrocarbons into younger Cretaceous and Tertiary reservoirs in all basins with mature proven Jurassic source rocks, and Jurassic reservoirs host hydrocarbons generated by both older (Precaspian Basin) and younger (Rioni Basin) source rocks.
It is estimated that Jurassic reservoirs host over 6 billion bbl and over 100 Tcf generated from Jurassic source rocks.
Figure 1. Location map of the basins in the study.
Table 1. Parameters influencing the presence of Jurassic-Jurassic petroleum systems in basins in Central Paratethys.
AAPG Search and Discovery Article #90923@1999 International Conference and Exhibition, Birmingham, England