Jurassic deep-water fans in the Neo-Tethys Ocean: The Kashafrud Formation of the Kopet-Dagh Basin, Iran

The Middle Jurassic Kashafrud Formation of northeast Iran was deposited in the Kopet-Dagh Basin, linked to the Neo-Tethys Ocean. The 2 km thick succession commences with fluvio-marine boulder conglomerates that occupy bedrock valleys, but the bulk of the formation comprises a deep-water succession of interbedded sandstone and mudstone packages with trace fossils and sparse ammonites. Neogene collisional events deformed the strata to create the Kopet-Dagh mountains. The deep-water succession represents channel-lobe systems and associated levees and overbank areas on slope to basin-floor fans. Northward paleoflow suggests that rivers drained uplands along the Paleo-Tethys Suture zone, forming fan deltas on a narrow shelf, with associated sediment transport to deeper water. Coarse sands, extrabasinal pebbles, and plant fragments are present throughout the formation, and a thick boulder conglomerate unit lies within the turbidite succession. These observations suggest proximity to terrestrial sources throughout deposition. Sandstone packages are mainly less than 10 m thick (maximum 84 m), and numerous lensoid packages of thick-bedded sandstone tens of meters thick and up to 200 m wide represent submarine channel fills. Thick-bedded lenses and sheets show a relatively narrow range of paleoflow direction and represent major submarine conduits, whereas the more varied paleoflow direction of thin-bedded packages suggests that many were deposited on levees. The presence in the Kashafrud Formation of potential source rocks in the form of organic-rich mudstones and abundant plant fragments suggests that the formation may have contributed to hydrocarbon fields within overlying formations. Sandstone sheets and channel fills could form local reservoirs. (C) 2006 Elsevier B.V. All rights reserved.