engleski

Olenikan (Early Triassic) fossil assemblage from eastern Julian Alps (Slovenia)

New palaeontological and sedimentological data from the Lower Tri as sic strata of the east ern Julian Alps in Slovenia are pre sented., They are un usual for the Early Tri as sic of the Alps in rep re sent ing a rel a tively deeper, un re stricted ma rine (mid-ramp) set ting. There are two ba sic microfacies types in the sec tion in ves ti gated (types A and B), which are or ga nized as cou plets with coarse- grained tempestitic de pos its (microfacies A), over lain by lam i nated or bioturbated lime mudstones and/or marls (microfacies B), fre quently con tain ing ammonoids. This pat tern is in ter preted as storm de po si tion with oc ca sional win now ing of bot tom sed i ments and the for ma tion of coarse-grained skel e tal de pos its (lags), fol lowed by the slow set tling of sus pended par ti cles, when the storm waned, in ad di tion to back ground de po si tion. Dom i nantly lime mud de po si tion and the pres ence of ammonoids in di cate de po si tion on a dis tal deeper ramp with an un re stricted con nec tion to the open sea. In tense re - work ing of bot tom skel e tal-rich sed i ment and ac cu mu la tion of storm lags sug gest de po si tion above the storm wave base, pos si bly in a wide low-en ergy mid-ramp en vi ron ment. Fau nas from such set tings have been re ported rel a tively rarely from the Early Tri as sic of the Alps. The macrofauna con tains ammonoids, bi valves and gas tro - pods, whereas the micro fauna is rep re sented by foraminifer tests and cono dont el e ments ; rare fish re mains also oc cur. In the foraminifer as sem blages, spe cies of Ammodiscus, Hoyenella, Glomospirella dom i nated, cor re spond ing to the wide spread “Glomospira-Glomospirella” foraminifer com mu nity, with some miliolids and nodosariids. The cono dont fauna is char ac ter ized by Triassospathodus hungaricus (Kozur and Mostler), in di cat ing an early Spathian (Olenekian) age. The fos sil as sem blage high lights the wide dis tri bu tion of Early Tri as sic taxa in the Tethys and fa cil i tates its world wide cor re la tion. Its rel a tively low di ver sity by com par i son with shal low ma rine set tings is in ter preted as an evo lu tion ary prox i mal-dis tal trend in the wake of the end-Perm ian mass ex tinc tion. Rediversification first oc curred in nearshore set tings and ex panded into deeper/dis tal ma rine en vi ron ments through geo log i cal time.

Olenekian ; Early Triassic ; foraminifers ; bivaves ; gastropods ; conodonts ; sedimentology ; Julian Alps ; Slovenia

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