SCOLECODONTS/BIOSTRATIGRAPHY

The lower paleozoic sequence is well exposed in kuh-e saluk, 2 km, north of ghelli village. In ascending stratigraphic order this sequence has been divided into mila (519 m), lashkarak (250 m), ghelli(1140 m) and niur (160 m) formations. The age relationship of each rock unit, has been determined based on acritarches, chitinozoans and scolecodont microfossils. Therefore 200 surface samples were selected from the lashkarak, ghelli and niur formations. A total of 31 species were encountered from the lower paleozoic rock units of studied area. The encountered scolecodont species have been arranged in 3 ascending local stratigraphic zones. Zone 1-2 occurs in the ghelli formation, indicating the middle and late ordovician age. Zone 3 cryptospores. But no attention was paid on occurs in the niur formation and suggest the early silurian age (llandovery) base on acritarch biozones, among the encountered families of scolecodonts, two families of polychaetaspidae and paulinitidaehave more genera and species rather than other families. Moreover, the scolecodont genera and species of silurian sediments (member 1 of niur fm.)Have more diversity than the ordovician strata. (lashkarak and ghelli formations). This may be related to cold condition in ordovician and warm in the silurian.

The encountered critical scolecodonts species in this study are:

Kettnerites fjaelensis, kettnerites versabilis, kettnerites microdentatus, kettnerites sp., polychaetaspis latus, polychaetaspis warkae, polychaetaspis varsoviensis, protarabellies staufferi, kalloprion triangularis, mochtyella sp. Xanioprion sp., tetraprion sp.

The above mentioned scolecodont genera and species compared with those of contemporaneous strata from Sweden, Poland, Estonia, Italy and United States of America. This comparison reveals broad similarity with the above mentioned countries. Therefore the scolecodonts can be applied as a useful tool for biostratigraphy, paleoecology and paleogeography purposes.