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The Miocene-Pliocene sedimentary sequence in southwest Iran, a thick clastic wedge, is an excellent example of postorogenic sedimentation in the peripheral basin of a suture zone. The molasse records the rise of the Zagros Mountains, which formed as a result of the collision between the Arabian and Persian plates during the Miocene-Pliocene. The sequence is composed of two formations, the Agha Jari and Bakhtyari. Deposition of these units was preceded by deposition of the Mishan Formation, a shallow-marine limestone and marlstone deposit. The Mishan is conformably overlain by the Agha Jari, which consists of repetitious fining-upward fluvial cycles. The cycles comprise lithic sandstones (calclithites) and gypsum-veined marly mudstones. The unit is approximately 2,000 m th ck in the study area, but reaches thicknesses greater than 3,000 m in other areas. The Agha Jari is conformably overlain by the Bakhtyari, which consists of interbedded conglomerate, sandstone, and mudstone. The conglomerate beds are characterized by closely packed, well-rounded clasts of Cretaceous to Eocene limestone and chert which were derived from the Zagros Mountains on the northeast. The Bakhtyari clastic units probably represent deposition on an alluvial fan, whereas the finer grained Agha Jari clastic strata represent distal-fan or alluvial-plain deposition.
Previous workers have recorded the presence of an unconformity between the Agha Jari and Bakhtyari Formations, but no unconformity was found in the study area. The contact is gradational, with both formations composing a continuous, coarsening-upward sequence.
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