Petrography and geochemical constrain on dolostones of the Shahbazan Formation in Lorestan (Iran)
Nemati, M.H.; Mohseni, H.; Memariani, M.; Yeganeh, B.; Janbaz, M.; Swennen, R. (2019). Petrography and geochemical constrain on dolostones of the Shahbazan Formation in Lorestan (Iran). Carbonates and Evaporites 34(1): 115-132. https://dx.doi.org/10.1007/s13146-018-0449-7
In: Carbonates and Evaporites. Springer: New York. ISSN 0891-2556; e-ISSN 1878-5212, more
|  |
| Author keywords |
Shahbazan Fm; Dolomite petrography; Geochemistry; Zagros basin; Iran |
| Authors | | Top |
- Nemati, M.H.
- Mohseni, H.
- Memariani, M.
|
- Yeganeh, B.
- Janbaz, M.
- Swennen, R., more
|
|
| Abstract |
The Shahbazan Formation (Fm.) was deposited in the Lorestan subzone of the Zagros Basin during middle to late Eocene, which presently is part of the Zagros fold and thrust belt. The Shahbazan Fm. consists of limestone and dolostone beds, which hosts some considerable hydrocarbon occurrences in the Zagros basin. In the present study, the reference Mamulan and Murani sections in the Lorestan province were studied. A total of 330 samples were collected. Petrographic examination of stained sections (alizarin red S and potassium ferricyanide) allowed differentiating five types of dolomites within the Shahbazan Fm. Within the Mamulan section, three distinct types where defined including dolomicrite (D1), associated by evaporites, peloides, intraclast, and algal laminites; dolomicrosparite (D2), with well-preserved algal laminites; and limpid dolosparite (D3) locally embedded within poikilotopic anhydrite. The Murani section comprises fabric-destructive dolosparite (D4), pore-filling dolomite (D5), as well as D1. Some fractures of the Shahbazan Fm. were occluded by evaporites and calcite spars in the Mamulan and Murani sections, respectively. The pore-filling (D5) dolomite displays a fine zonation pattern under CL, which may reflect successive growth stages during shallow to relatively burial diagenesis. According to microfacies analysis, seven microfacies including dolomudstone (F1), dolomitized bioclast-intraclast wackestone to packstone (F2), dolomitized lime mudstone (F3), interbedded laminated lime mudstone and evaporites (F4); dolomitized peloid packstone to wackestone (F5); dolomitized intraclast bioturbated wackestone (F6); bioclast miliolid wackestone to packstone (F7), as well as various anhydrites (e.g., nodular and laminated) were recognized which suggest intertidal-supratidal depositional setting for the Shahbazan Formation. ICP-MS analysis on some selected samples of the D1, revealed their chemical composition with an average for Fe of 1291 and 185ppm, for Na of 644 and 650ppm, for Sr of 125 and 185ppm, and a Mg/Ca ratio of 0.57 and 0.505, for Mn of 23ppm (only for Mamulan section) in the Mamulan and Murani sections, respectively. Relatively high Mg/Ca ratio suggests that these dolomites might be originated from salt waters. The Sr/Ca vs Mn suggests a relatively semi-closed diagenetic system. Variable Fe and Mn contents are probably due to reaction with meteoric water. |
|
