Conodont biostratigraphy of late Devonian deposits in the Shirband section (Damghan, NE Iran)
- PDF / 16,646,763 Bytes
- 15 Pages / 595.276 x 790.866 pts Page_size
- 62 Downloads / 213 Views
ORIGINAL PAPER
Conodont biostratigraphy of late Devonian deposits in the Shirband section (Damghan, NE Iran) Bahareh Valizadeh Kakhki & Seyed Mahmood Hosseini-Nezhad & Mohammad Vahidinia
Received: 24 February 2014 / Accepted: 29 October 2014 # Saudi Society for Geosciences 2014
Abstract The Upper Devonian deposits are relatively thick and developed in eastern Alborz. These deposits are located in Shirband area which is attributed to Geirud Formation. Shirband Upper Devonian deposits are situated by a discontinuity with the same gradient on Mila Formation and also under Mobarak Formation. The thin limestone, shaly limestone, and shale layers of the Geirud Formation are gradually followed by thin limestone and shale layers of the Mobarak Formation. Study of conodont fossils in this section probably indicates continuity deposits between the Geirud and Mobarak Formations. On the basis of studying conodonts, seven standard biozones were determined with the Famennian age (arranged from oldest to youngest): 1—triangularis to linguiformis zone, 2—crepida zone, 3—rhomboidea zone, 4—trachytera to marginifera zone, 5—postera zone, 6— postera to expansa zone, and 7—praesulcata to sulcata zone. Keywords Biostratigraphy . Biozonation . Conodont . Geirud . Shirband section . Damghan
Introduction There was only a shallow marginal sea in the east and northeast of Iran at the Early and Middle Devonian, so the central
B. Valizadeh Kakhki (*) Ferdowsi University of Mashhad, International Campus, Mashhad, Iran e-mail: [email protected] S. M. Hosseini-Nezhad School of Earth Sciences, Damghan University, Damghan, Iran M. Vahidinia Department of Geology, Faculty of Sciences, Ferdowsi University of Mashhad, Mashhad, Iran
Alborz deposits are attributed to Upper Devonian (which are located on Ordovician or older rocks by erosional unconformity) (Hashemi and Tabe 2009). This unit, composed of detrital deposits (including conglomerate, sandstone, and shale) and fossiliferous limestone, was firstly named by Assereto (1963) as Geirud Formation. This name was applied for the thick succession of limestones and lime shales located between Mila Formation (Cambrian) and Dorud Formation’s red sandstone layers (Permian). This formation was initially divided to four parts (from oldest to youngest: A, B, C, and D), but part D was not visible in type section. In later revisions, members C, D, and a part of member B (Mobarak Formation) were omitted from the Geirud Formation. Conodonts are valuable fossils from the Paleozoic era and Triassic period. These are widely studied globally and many of them are proposed as index fossils. Considering the importance of conodonts for age determination of Cambrian to Triassic deposits, biozonation and biostratigraphy of Devonian deposits in Damghan area (Shirband section) was studied based on conodonts.
The Shirband section The study area is located on the east Alborz zone, in Semnan province at 25 km northeast of Damghan City. The Shirband section is situated in the Semnan quadrangle map of the geological
Data Loading...
