| Popis: |
Sedimentological investigations of the lower Bakhtiari Formation in central Iraq proved that this formation represents typical post-orogenic molasse sedimentation. It originated by the rapid erosion of lifted Zagros Mountains and deposition of the complex of fluviatile and lacustrine sediments in foothill troughs. Textures and structures of the sediments, their thickness and other properties are comparable to other molasse sediments of various geosynclines. General palaeocurrent direction in central Iraq was from northeast to southwest. This is in accordance with the palaeogeological situation and with the trend of decreasing thickness of the formation. Some structures, also typical for turbidites, as flute casts and convolutions, were observed in the formation. Sandstones are represented by lithic greywackes, unstable clastic constituents of which consist mostly of limestone grains. There is some evidence supporting C ummins ' (1962) theory of secondary graywacke origin. Fluviatile origin of the sediments was proved by the lack of palaeontologic marine evidence, by the current bedding pattern as well as by the grain-size distribution of the deposits. The classic model of fluviatile sedimentation can be applied also on the lower Bakhtiari Formation. Coarser sediments were deposited in broad and rapidly shifting bed-load channels, whereas the finer deposits are the products of sedimentation on flood plains and in backswamps. |
