Early Silurian (Llandovery) graptolites from central Saudi Arabia: First documented record of Telychian faunas from the Arabian Peninsula

Abstract

ABSTRACTGraptolites from three shallow core holes penetrating lower Silurian strata in central Saudi Arabia identify rocks of mid Aeronian and early Telychian age. The graptolites comprise Campograptus undulatus?, C. lobiferus?, Lituigraptus convolutus, Metaclimacograptus bohemicus, Neolagarograptus rickardsi, Normalograptus? aff. scalaris, cf. Paradiversograptuscapillaris,Petalolithusminor,P.praecursor,P.ovatoelongatus?, Pristiograptus regularis sl, Pseudorthograptus insectiformis, Pseudoretiolites perlatus? and Torquigraptus? decipiens, which identify the mid Aeronian convolutus Biozone, and Monograptus bjerreskovae, Monograptus ex gr. marri, Paradiversograptus runcinatus?, Petalolithus cf. altissimus, Pristiograptus renaudi, Stimulograptus becki and S. halli?, which indicate the early Telychian guerichi Biozone. The graptolite faunas are generally of low diversity, with most levels yielding between one and three species, occasionally rising to as many as seven species. The palaeogeography of the depositional basin, coupled with the low diversity and the abundance of Pristiograptus and Normalograptus species, suggests a marine-shelf setting. This is also indicated by the common occurrence of benthic shelly fossils, including articulated bivalves and gastropods. In general, the graptolite faunas are of much lower diversity than contemporaneous marine assemblages from the British Isles or the Czech Republic, and probably represent a graptolite biotope of “cratonic invaders.” Graptolites are very well preserved, displaying detail of fusellar banding (growth increments) and perhaps ultrastructure.