--> ABSTRACT: Comparison of Tarim and Central Asian FSU Basins, II: Differences in Hydrocarbon Systems and Possible Explanations, by Shangyou Nie and Christoph Heubeck; #91019 (1996)

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Comparison of Tarim and Central Asian FSU Basins, II: Differences in Hydrocarbon Systems and Possible Explanations

Shangyou Nie and Christoph Heubeck

If the Tertiary crustal shortening and indentation in the Pamirs is restored palinspastically, it would be evident that the Central Asian basins in the FSU (including Amu Darya, Tajik, Fergana, and Syr Darya) in the west and the Tarim basin in the east probably shared many similarities in their geological history after becoming part of the Eurasia continent in the Late Paleozoic. For example, both areas contain significant amounts of coal-bearing Jurassic sequences, and a marine connection no doubt existed between the two during the maximum marine transgression period Late Cretaceous and Early Tertiary. A direct comparison is more difficult for the Paleozoic sequences because in the Central Asia basins, they are either buried too deeply or highly metamorphosed in the outc ops.

It is interesting to note that these basins exhibit vast differences in the age and type of source and reservoir rocks. For the Tarim basin, most of the source rocks are Paleozoic (Ordovician and Carboniferous) and marine in nature, whereas in the Central Asian basins, the dominant source rocks are Jurassic and younger and include both marine and non-marine sequences. Similarly for reservoir rocks, most of the hydrocarbons found in the Tarim basin is from the Paleozoic (such as Devonian and Carboniferous clastics/carbonates), whereas in Amu Darya and Fergana basins, the reservoir rocks are dominated by Jurassic carbonates and Paleogene clastics respectively.

This presentation will highlight these differences and address the probable causes mainly from the view points of tectonics and paleogeography. We conclude that the dominant effect is the Early Tertiary India-Asia collision, which caused significant differences in the distribution and thickness of the post-collisional clastic sediments, which in turn resulted in different maturation and migration history. This collisional event also allowed the formation of structural traps in these basins. Additional causes include 1) Jurassic - Cretaceous amalgamation between the Kohistan arc to the northern Pamirs in the west and that between Qiangtang and Tarim in the east, with the former limiting the normal marine sedimentation only in the Central Asian basins, 2) extent of Cretaceous and Early ertiary seals of siltstone and gypsum beds, and 3) effects of eustatic sea level change and its differential influences on these basins.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California