Document Type : Original Research Paper


Research Institute of Earth Science, Tehran, Iran


The Mobarak Formation with 347.5 m, thickness is well exposed  in Valyabad section , at the Karaj - Chalus road . The lower contact with underlying  Laloon Formation is disconformable ,whereas stratigraphic relation to the overlying Dozdeband formation is transitional. According to the lithological  character, the studied section can be  subdivided into  rock units . The lower part of the fm. consist of dark- gray to black limestone as well as marly limestone, while upper part consist mainly of sandy limestone with interbeds of marlstone.  According to the microfossil investigation 14 genius and species have been recognized which leads 2 conodont biozones . The both conodont biozones correspond to the international standard conodont  biozonation which suggest an Early Tournisian to Middle Visean time interval . in addition , a Namurian age is suggested for deposites of informal Dozdeband formation , based on foraminifers . Received conodont bizones are as :
Neopriniodus peracutus - Polygnathus longiposticus Assemblage- Zone
Hibbardella roundya - Gnathodus girtyi Assemblage- Zone
More over , 5 Holotorian species as well as 6 genuse ,72 species  Foraminifers in form of 5 biozone have been distinguished. These biozones are as :
Eotuberitina retligener - Endothyra spirilloformis Assemblage-  Zone
Archaediscus permodiscus - Archaediscus(Paraarchaediscus)mixtus Assemblage-  Zone
Endostaffella parva - Brunsina pulchera Assemblage-  Zone
Tuberitina bulbacea - Kammaena sp. Barren  Interval  Zone
Lipinella notata - Archaediscus planoarchaediscus Assemblage-  Zone
The studied foraminifers support  the given age . Conodonts the Color Alteration Index(CAI) correspond 190 to 300 C which indicate dry gas stage or empty of any hydrocarbon.


Assereto , R., 1963- The Paleozoic Formation in central Elborz (Iran) poilimnery not RIV. Paleont. Strata, N.64, pp.542.
Bozorgnia, F., 1973- Paleozoic Foraminiferals biostratigraphy of cenral and east Alborz mountains , Iran (NATIONAL IRANIAN OIL COMPANY) .N.o.4
Epstein, A. G., Epstein, J. B. A. & Harris, 1977- Conodont color alteration ind. to organic metamorphism, us, Geol. Suerv.
Rhodes, T. F, Austin. L. R , Druce. E. C., 1969- British Avonian (Carboniferous) Conodont faunas and their value in local and intercontinental correlation, bulletin of the british museum (Natural history Geology) London.
Loblich, A. R. J & Tappan, H., 1988- Foraminiferal Genera and their classification ,VAN NOSTRAND REINHOLD COMPANY , NEW YORK.
VACHARD, D. & TAHIRI, A., 1991- Foraminiferes , Algues et Pseudo - algues du Viseen du la region d,Oulmes (Maroc) . Geologie Mediterraneenne.Tome XVIII,No.1-2.
 Metcalfe, I., 1978- Conodont zonation and correlation of the Dinantian and Early Namurian strata of the Craven Lowlands of northern England.20p.