Disponible en ligne sur ScienceDirect www.sciencedirect.com Revue de micropaléontologie 60 (2017) 319–331 ARAMCO-CIMP special volume Middle Ordovician cryptospores from the Saq-Hanadir transitional beds in the QSIM-801 well, Saudi Arabia Marco Vecoli a,∗ , Charles H. Wellman b , Philippe Gerrienne c , Alain Le Hérissé d , Philippe Steemans c a Saudi Aramco, Geological Technical Services Division, Biostratigraphy Group, 31311 Dhahran, Saudi Arabia b Department of Animal & Plant Sciences, University of Sheffield, Alfred Denny Building, Western Bank, Sheffield S10 2TN, UK c Dépt. de Géologie, Unité de recherche PPP, Université de Liège, Campus du Sart Tilman, quartier Agora, allée du 6 Août, 14, Bât. B-18, 4000 Liège 1, Belgium d Université de Brest, CNRS UMR6538, Domaines Océaniques, Institut Universitaire Européen de la Mer, bâtiment G, 6, avenue le Gorgeu, 29238 Brest cedex 3, France Abstract The QSIM-801 well from Central Saudi Arabia contains beds transitional between the Sajir Member of the Saq Formation and the Hanadir Member of the Qasim Formation. Core samples from these beds yielded rich assemblages of well-preserved palynomorphs of low thermal maturity. They are dominated by marine forms (acritarchs, chitinozoans and scolecodonts) but also include relatively abundant and diverse terrestrial forms (cryptospores and dispersed phytodebris), especially in samples from the upper part of the Sajir Member. The cryptospore assemblage is taxonomically consistent with other Middle Ordovician assemblages previously reported from Saudi Arabia, and is concordant with the late Dapingian to early Darriwillian (Llanvirn) age of the Sajir-Hanadir transitional beds, as suggested by palynological evidence (i.e., presence of Siphonochitina formosa and Linochitina pissotensis chitinozoan zones in the basal Hanadir). It includes a variety of monads and permanent dyads and tetrads, which are often characterized by well-developed surface ornamentation such as microgranulation, as well as, in some instances, by thick walls displaying distinct layering. © 2017 Elsevier Masson SAS. All rights reserved. Keywords: Middle Ordovician; Cryptospores; Saudi Arabia; Terrestrialization 1. Introduction The Middle Ordovician Saq-Hanadir transitional beds pen- etrated by QSIM-801 well yield exceptionally preserved palynomorph assemblages dominated by marine forms but also containing allochthonous terrestrial elements. Le Hérissé et al. (this volume) describe the marine elements of the assemblage and this contribution focuses on the terrestrial elements. This paper is a further contribution to a series of reports documenting ∗ Corresponding author. E-mail addresses: marco.vecoli@aramco.com (M. Vecoli), c.wellman@sheffield.ac.uk (C.H. Wellman), p.gerrienne@ulg.ac.be (P. Gerrienne), alain.le.herisse@univ-brest.fr (A. Le Hérissé), p.steemans@ulg.ac.be (P. Steemans). Ordovician dispersed cryptospores from Saudi Arabia (Strother et al., 1996, 2015; Le Hérissé et al., 2007; Wellman et al., 2015). 2. Geological setting A cored section of QSIM-801 well penetrates a sequence of beds transitional between the Sajir Member of the Saq Formation and the Hanadir Member of the Qasim Formation (Fig. 1). The Hanadir Member is biostratigrapically well age-constrained by chitinozoans belonging to the formosa and pissotensis chitino- zoan zones of early to late Darriwilian age (Le Hérissé et al., this volume). The older Sajir Member is considered to span the Dapingian/Darriwilian boundary (Le Hérissé et al., 2007), but definitive age control is lacking. The sediments are entirely marine in origin. Details of the biostratigraphy and geology of these beds are provided in Le Hérissé et al. (this volume). http://dx.doi.org/10.1016/j.revmic.2017.06.003 0035-1598/© 2017 Elsevier Masson SAS. All rights reserved.