A review on Late Scythian to Middle Anisian Ammonoids from the Alam Formation in Nakhlak area, Central Iran

Introduction: the up to 1298 m thick, mainly turbiditic, siliciclastic alam formationconsists of conspicuous carbonatic alternations at the lower part, and predominantly of asequence of marine turbidities with frequent volcanic components at the middle and upperparts, deposited on a forearc side of an active margin in a continental shelf to slope setting.aim: the study and review of ammonoids collected from the alam formation andtheir paleobiogeographical relationships with other areas.material and method: in the present study many ammonoids were collected andsystematic studied from different levels of the alam formation and theirpaleobiogeographical distributions and relationships surveyed.results: ammonoids collected from different levels of the alam formation indicate alate scythian to middle anisian age for the formation. the recognized ammonoids belong to35 genera and 31 species, including epacrochordiceras sp., procladiscites sp.,pseudosageceras sp., sturia sp., acrochordiceras aff. hyatti meek, propthyhitoides decipiens,paragoceras mediterrangeum, kazahstanites dolnapensis, isculitoides seyedemamii,dagnoceras nopscanum, columbits ventroangusts, subcolumbites perrinismithi, prenkites cf.malsorensis, stacheites undatus, albanites triadic us, tirolites cassianus, metadognocerasamiidi, eophylites davoudzadehi, leiophyllites stoecklini, l. aff. pitamaha, hollandites tozeri,norites gondola, nicomedites cf. toulai, hungarites cf. proponticus, stenopapnocerastransiens, ussurites arthaberi, semibeyrichites ruttneri, aghdarbandites ismidicus,paraceratites aff. binodosus, parapinacoceras cf. damesi, ptychites aff. pauli, gymnitesreligiouscus, g. palmai, g. asseretoi and monophyllites kieperti .conclusion: the mentioned ammonoids belong to a single bio-province at southernmargin of turan continent and have common faunas with the nazarkardeh formation inaghdarband area (ne iran). the paleobiogeographical relationships of triassic ammonoids ofthe nakhlak group with other areas show the existence of a certain province in the southernmargin of eurasia from the eastern most to western most portion of paleothetys ocean. thisdistribution shows the bio-district distinction of eurasia (in the north) from gondwana (in thesouth) and also shows the boundary between eurasia (at north) and gondwana (at south) innorthern iran.