A Detail Study of the Genus Vallatisporites as a Lower Carboniferous Stratigraphic and Paleogeographic Indicator

Abstract

ABSTRACT The genus Vallatisporites Hacquebard emend. Sullivan 1964b is studied in detail due to it's biostratigraphical and paleogeographical significance in the Carboniferous strata on a global scale. This cosmopolitan genus is widely used in chronostratigraphy and many of its species are used as a zonal fossils in different zonal schemes. The common occurrence of the majority of the species belonging to this genus in the Carboniferous strata recorded in two boreholes in Iraq (Akkas-1 and Kh5/1), demanded detail study. Samples from borehole Akkas–1 which represented Lower Carboniferous (Late Visean–Early Namurian) age were critical to this study because they contained most of the Vallatisporites index species, especially the distinctive indemic, index species V.agadesi for the Visean / Namurian age in the North Africa and Middle East (including Iraq). The present study provided an additional existence of the most zonal Vallatisporites spp. in the world, the ranges of some key forms of Vallatisporites in Iraq, neighboring areas and North Africa are different from those observed elsewhere which reflect that Iraq, adjacent areas and North Africa belong to the same phytogeographical province during the carboniferous period. In addition to that we take in to consideration the recent differentiation between V. pusilletes and V. hystricosus by the Vallatisporites Group and we consider all the Vallatisporites pusilletis recorded in the two boreholes studied as V. hystricosus. The botanical affinities of the genus Vallatisporites is Pteridophytes (Lycopsids).