Abstract
The study of the upper Lower to Middle Jurassic Badamu Formation in SE of central Iran represents the first report of Jurassic ooidal ironstone in Iran and exhibits a record of ferruginous radial ooid-dominated ironstone. The studies showed that this chamosite or ferric oxide-chamosite type ooidal ironstone is similar to Minette-type ironstones. A shoreface zone in an epeiric or epicontinental sea is proposed for formation and accumulation of the ferruginous ooids and the ooidal ironstone. Fe derived from lateritic weathering has been transported into the shoreface zone via a fluvial current during the synsedimentary formation of the ooidal ironstone. During the periods with moderate to lower-energy or weakly agitated and quiet environmental conditions, suspended ferruginous small radial ooids and Fe were increased in the lower shoreface subzone. Higher environmental energy resulted in the development of large concentric ooids and limited distribution of Fe in the upper shoreface subzone. Higher environmental energy also prevented the development of radial ooids and restricted Fe precipitation on carbonate ooids. Variations in environmental energy in the middle shoreface subzone were unfavorable for increasing ferruginous ooids and Fe in the environment. Although, short term periods with weakly agitated and quiet or moderate to lower-energy conditions could had been existed in the middle shoreface subzone but precipitation of Fe on a few small radial ooids was allowed. Environmental energy in the shoreface zone was the major factor controlling precipitation of Fe (especially suspended river Fe loads) on the ooids. However, precipitation of dissolved Fe could have been related to oxidizing conditions in the environment. Also, the probable presence of Fe oxidizing bacteria in the cortexes of the ferruginous small radial ooids indicates that bacteria could have possibly contributed to precipitation of Fe on the ooids in a calm environment.
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