Late Triassic dasycladacean alga from northeastern Oregon: significance of first reported occurrence in western North America

Abstract

An Upper Triassic metaspondyle dasycladacean alga,Diplopora oregonensisn. sp., is described from the Hurwal Formation, southern Wallowa Mountains, northeastern Oregon. It occurs in the accreted Wallowa terrane, which is interpreted as far-travelled relative to the craton of North America. The fossil alga is found in limestone clasts within a limestone–chert–volcanic clast conglomerate of the Hurwal Formation. The new species is related toDiploplora borzaiBystricky, known from the Upper Triassic of the Carpathian Mountains and Sicily, but is distinguished by very small branches and a distinct segmentation of the thalli.Diplopora oregonensisis the first Triassic dasycladacean alga known from the United States, and perhaps from all of North America. The absence of calcareous green algae from rocks of cratonal North America, as well as from most Triassic displaced terranes of the eastern and western Pacific, is in stark contrast to counterparts in the former Tethys region of central Europe, where dasycladacean algae were abundant and contributed significantly to the sediment. This paucity of algae may be related to differences in environment, but more likely is linked to the paleogeographic situation and dispersal abilities of the algae. The similarity of the Oregon dasyclads to species in western Europe, coupled with the lack of dasyclad algae in any other part of North America, is evidence in support of a far-travelled nature for the Wallowa terrane.