ABSTRACT Spore assemblages are described from three cored intervals in the Silurian sequence in borehole Hawiyah-151 from central Saudi Arabia. Those from the oldest cored interval are correlated with the Imperfectotriletes spp.- Laevolancis divellomedia spore Assemblage Biozone [ divellomedia Interval Biozone (α Subzone)], suggesting a Rhuddanian (possibly early Aeronian) age. The older samples from the middle cored interval are correlated with the Imperfectotriletes spp.- Laevolancis divellomedia spore Assemblage Biozone [ divellomedia Interval Biozone (β Subzone)], suggesting a late Aeronian-early Telychian age, but the younger samples from this interval are correlated with the chulus-nanus spore Assemblage Biozone, suggesting a late Telychian-early Homerian age. Samples from the youngest cored interval are correlated with the brevicosta-verrucatus spore Assemblage Biozone, suggesting an early (but not earliest) Homerian-?earliest Gorstian age. Palynofacies analysis indicates that the deposits of the oldest and middle cored interval accumulated in a nearshore marine environment, but those of the youngest cored interval were deposited during a nearshore marine to non-marine regressive sequence. In the middle cored interval, the abundance of chitinozoans coupled with the paucity of acritarchs is intriguing. The sequence of Silurian spore assemblages in Saudi Arabia is clearly different to that reported in Laurentia, Avalonia and probably also Baltica. In Saudi Arabia, trilete spores and ornamented hilate cryptospores appear to make their inception earlier, and envelope-enclosed cryptospores persist in relative abundance for longer.

ABSTRACT Diverse and well-preserved acritarchs have been recovered from Qalibah Formation of Llandovery-Ludlow age, from well Kahf-1 drilled in northwestern Saudi Arabia. One new genus and 8 new species are described and illustrated: Baltisphaeridium qusaibaense sp. nov., Dictyotidium callum sp. nov., Duvernaysphaera siderea sp. nov., Eupoikilofusa tenua sp. nov., Geron ludlovensis sp. nov., Membranites minutus gen. et sp. nov., Muraticavea irregularis sp. nov., Proteolobus cylindrus sp. nov., and Veryhachium ? owensii sp. nov. Two new combinations are proposed: Eupoikilofusa punctalirella comb. nov. and Eupoikilofusa rhikne comb. nov. Ludlow age acritarchs were encountered from the uppermost Sharawra Member. Unlike in the reference sections, the palynofacies and lithofacies of the Sharawra Member indicate an offshore environment. The presence of fresh-water algae with marine palynomorphs in the upper Sharawra Member indicates a fresh-water influx into the marine system.