Middle Ordovician acritarchs and problematic organic-walled microfossils from the Saq-Hanadir transitional beds in the QSIM-801 well, Saudi Arabia

Abstract

Core samples from the QSIM-801 water well, drilled in central Saudi Arabia, cover a 93-foot interval spanning the transition between the Sajir Member of the Saq Formation, that consists mainly of sandstones of tidal sand flat environments, and the Hanadir Member of the Qasim Formation, characterized by argillaceous graptolitic mudstones, corresponding to a tidal delta front. The samples contain abundant, exceptionally well-preserved and diverse palynomorphs, which include cryptospores, acritarchs and chitinozoans, other problematic organic-walled microfossils as well as other organic particles such as cuticle-like fragments. The studied interval is biostratigraphically well constrained by the presence of chitinozoans of the formosa and pissotensis Zones of late-early to late Darriwilian age (Middle Ordovician) in the uppermost Saq Formation and Hanadir Member. The biostratigraphic age of the Sajir Member considered to span the Dapingian-Darriwilian boundary, is re-discussed based on the results herein. The uppermost part of the Sajir Member yielded the ichnofossil, Phycodes fusiforme. Acritarch assemblages from the Sajir Member of the Saq Formation are poorly diversified and dominated by sphaeromorphs. More diverse assemblages of acritarchs, associated with enigmatic forms, occur in the Hanadir Member of the Qasim Formation. The contact between the two formations and the transition between the palynomorph assemblages are sharp, suggesting a stratigraphic hiatus. A quantitative analysis allows us to discuss the paleoenvironmental changes and possibly climatic changes associated with an hypothesis of ice house conditions during this period. Among the diagnostic acritarch taxa observed are Frankea breviuscula, F. longiuscula, Baltisphaeridium ternatum, Dasydorus cirritus, Dicrodiacrodium ancoriforme, Poikilofusa ciliaris, Pterospermopsis colbathii and Uncinisphaera fusticula. These are associated with other typical forms known to range across the Lower-Middle Ordovician boundary, such as Aremoricanium rigaudae, Aureotesta clathrata, Barakella fortunata, B. rara, Baltisphaeridium klabavense, Glaucotesta latiramosa and Striatotheca spp. Galeate and peteinoid acritarchs are also well represented, as well as tiny forms of ultraplanctonic size. Three new species of acritarchs are proposed: Frankea longiuscula var. darriwilense var. nov, Micrhystridium regulum sp. nov, and Tyrannus proteus sp. nov. Repeated occurrences throughout the section of cryptospores, problematic microfossils such as organic filaments, cuticle-like tissues, striated and pigmented leiospheres frequently in clusters, are interpreted to reflect recurrent terrestrial and freshwater inputs in the depositional environment. Single-specimen, highresolution analyses using Confocal Laser Scanning Microscopy on the enigmatic form Tyrannus proteus sp. nov. show fluorescence emission spectra and microstructural properties significantly different from those of typical marine acritarchs from the same levels.

Peri-Gondwanan acritarchs and chitinozoans from the Lower–Middle Ordovician Lashkarak Formation in the Alborz Mountain Ranges, northern Iran: regional stratigraphical significance and palaeogeographical implications

“…This taxon has since been recorded from numerous localities, including the Sandbian, Libya (Deunff and Massa 1975); Ashgill, Portugal (Elaouad-Debbaj 1978); Upper Ordovician, south-eastern Turkey (Steemans et al 1996; Paris et al 2007); Caradoc-Ashgill, Québec, Canada (Martin 1980); Darriwilian–Sandbian, Ontario, Canada (Martin 1983); lower and middle Ashgill, Québec, Canada (Jacobson and Achab 1985); Middle Ordovician (Darriwilian–Sandbian), Götland, Sweden (Górka 1987); Ashgill, Morocco (Elaouad-Debbaj 1988); Ashgill, north-eastern Libya (Hill and Molyneux 1988); latest Ordovician, Czech Republic (Vavrdová 1988); Ashgill, Québec, Canada (Martin 1988); Darriwilian–Ashgill, Estonia (Uutela and Tynni 1991); late Ashgill (Hirnantian); Ashgill, north-eastern Missouri, USA (Wicander et al 1999); early Caradoc–late Ashgill, ‘northern’ Gondwana (Vecoli and Le Hérissé 2004); Ashgill, southern Oklahoma, USA (Playford and Wicander 2006); Hirnantian, southern Tunisia (Vecoli et al 2009); Katian–Hirnantian, southern Estonia (Delabroye et al 2011a); Hirnantian, Québec, Canada (Delabroye et al 2011b); Katian–Hirnantian, south-western Libya (Abuhmida 2013); Late Ordovician, Iran (Ghavidel-Syooki 1997, 2000, 2001, 2003, 2006, 2008, 2016, 2017a, 2017b); Hirnantian, the Zagros Mountains, Iran (Ghavidel-Syooki et al 2011b); Katian, the Alborz Mountains, northern Iran (Ghavidel-Syooki and Borji 2018), and Late Ordovician, Central Iran (Ghavidel-Syooki and Piri-Kangarshahi 2021). As a result, this acritarch assemblage zone suggests the latest Darriwilian age (stage slice Dw3 and time slice 4c) because both O. ternatum and O. quadrinatum begin their first appearance in the upper Darriwilian elsewhere, including Germany (Burmann 1970), France (Rauscher 1973), England (Booth 1979), the Arabian Peninsula (Le Hérissé et al 2017), Turkey (Paris et al 2007), and Iraq (Al-Ameri 2010). Among the associated acritarch taxa of this assemblage zone, O. insculptum is a common taxon in the Late Ordovician elsewhere; the presence of this species with the Middle Ordovician acritarch taxa suggests its first occurrence in the uppermost Darriwilian rather than the Late Ordovician.…”

“…This species was previously not recorded as older than Late Ordovician in Iran. Orthosphaeridium ternatum has so far been recorded from upper Darriwilian, Germany (Burmann 1970), France (Rauscher 1973), England (Booth 1979), the Arabian Peninsula (Le Hérissé et al 2017), Iraq (Al-Ameri 2010), North Gondwana Domain (Vecoli and Le Hérissé 2004); Middle Ordovician (Dapingian), Turkey (Paris et al 2007); and Upper Ordovician, Iran (Ghavidel-Syooki 2017b). Likewise, O. quadrinatum is restricted to upper Darriwilian elsewhere (Burmann 1970).…”

First Record of Cryptospores from the Late Ordovician–Early Silurian of Colombia: New Contribution to the Understanding of Plant Terrestrialization

“…In addition, the specimen assigned to Pterospermella franciniae by Le Hérissé et al . (2017, pl. 3, fig.…”

The Paleozoic formations of the Al Qassim Province in Saudi Arabia as potential sites for geotourism

“…4D). The Sajir Member had been reported to be of Early Ordovician age, based on comparison with similar facies in Jordan (Saudi Stratigraphic Committee, 2013), but recent studies by a team lead by Saudi Aramco paleontologists (Le Hérissé et al, 2017) suggest a Middle Ordovician (early Darriwilian) age for the upper part of the sandstone of the Sajir Member. The chitinizoan index species Siphonochitina formosa was found in the topmost Sajir Member, constraining the age to late-early Darriwilian.…”