Writers : Mousavinia,Abdolmajid;Vilmson,Markoos;Seyd Emami,Kazem;Ariaee,Aliasghar
Refference : 11th Symposium Of Geological Society Of Iran - Mashhad, Ferdowsi University
Publishing Year : 1386

Abstract :

Five species of the Mortoniceratinae Spath, 1925, are described from the Albian-Cenomanian Atamir Formation from three localities in the Koppeh Dagh Mountains, north of Mashad, NE Iran (Gharehsu, Padegane Ghods and Zawin). The Atamir Formation at Zawin consists of metre-scale intercalations of dark-grey, fine-silty and partly glauconite-bearing shales and fine- to medium-grained glauconitic, quartzrich sandstone beds of inner to mid-shelf origin. Ammonites, bivalves and gastropods are the commonest fossils of the formation. In the upper part of the succession exposed at Zawin, fossiliferous and upwardfining sandstone beds occur, overlain by a conspicuous, 50-70 m thick sequence of shale. From the upper part of the last, fine-grained sandstone bed below the thick shale interval, the described ammonites were
collected.
The fauna consists of Mortoniceras (Mortoniceras) inflatum (J. Sowerby, 1818), Mortoniceras (Mortoniceras) pricei (Spath, 1922), Mortoniceras (Mortoniceras) fissicostatum Spath, 1932, Mortoniceras (Deiradoceras) bipunctatum Spath, 1933, and Mortoniceras (Deiradoceras) cunningtoni Spath, 1933. All taxa are recorded for the first time from Iran. The ammonite assemblage indicates the lower part of the Callihoplites auritus Subzone of the M. inflatum Zone of the “middle” Upper Albian (cf. Amedro, 1992). It stems from a slightly condensed horizon at the base of a major transgressive interval (the abundance of ammonites suggests initial condensation). From a sequence stratigraphic viewpoint, this ammonite-rich sandstone bed is related to the initial period of a major transgressive development culminating in an overlying interval of thick (deeper marine) shales.

Subject List : Ammonite, stratigraphy