STRUCTURAL GEOLOGY OF MOGHAN BASIN NORTHWEST IRAN

Moghan sedimentary basin with 8-10km Cenozoic clastic sediments is located at the northwest corner of Iran, west of Caspian Sea and south of the Kura Basin of the country of Azerbaijan. Paleocene to Quaternary continental and marine sediments of the basin is composed of alternation of tuffaceous sandstones, conglomerates, shales, silty marls and clay beds. There are a major and few minor volcanic flows within the sequence. Sedimentary sequence thickness is decreased from 10km to a few hundred meters at the north reaching to the buried Cretaceous paleohigh and eroded out or never deposited at the south on the highlands of Lesser Caucasus-Talesh Range. They overlay thin bedded marine Cretaceous shale and limestone beds with angular unconformity. Thickness variation of the Cenozoic formations of the basin and their grain size distribution show that tectonically active southern mountain range was the feeding source of the rapidly subsiding Moghan Basin. Multiple unconformities and lava flows show the basin was tectonically active during deposition and the major folding started in Pliocene and created E-W trending folds.

In this study detail collected field data used to construct seven structural N-S cross sections (40-80km) perpendicular to the structures trend. Analysis of the sections shows three different types of anticlines: A- Gigantic anticlines with broad wave length, moderate dips and exposed Cretaceous core at the uplifted and mountainous regions of the basin at the south (en-echelon Molouk, Gozalan, Menjow, Emarat and Salavat anticlines). B- Narrower, long, steeply dipping, faulted anticlines with Cenozoic exposures at the center of the basin (Towlir, Germi, Ojaghgeshlagh, Ghir dareh, Takdagh, Sheikhlan, Koramalu, Digdash, Ortadagh, Khomarlu, and Qara Su anticlines). C- Minor anticlines at the north or between the main anticlines. Most of the anticlines are asymmetric with steeper north limb. Type B and C anticlines are detached on top of Cretaceous beds or upper levels, and underlying Cretaceous and older layers subducted under the southern volcano-sedimentary horizons and plutonics of Lesser Caucasus-Talesh range. Restoration of the cross sections shows about ten kilometers shortening of the basin in N-S direction accommodated in 6-8 parallel E-W trending anticlines and synclines in between.