Biostratigraphy and palaeogeographic implications of Ordovician and Silurian chitinozoa from the High Zagros Mountains, Northern Persian Gulf, Iran

Abstract

A siliciclastic succession is exposed at the Faraghan mountain, northern Persian Gulf, southeastern Iran. A detailed, high-resolution palynological analysis was performed on the Zardkuh, Seyahou, Dargaz, and Sarchahan formations to verify the exact age and palaeogeographic position of the High Zagros Mountains. Two hundred surface samples from this succession were collected and analysed. Most samples yielded abundant and well-preserved chitinozoans, acritarchs, scolecodonts, and cryptospores. Fifty-three chitinozoan species (21 genera) were identified that permitted to establish the

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

“…In the present study, E. brevi s (Plate 8, figure 25) occurred in the samples MG-MHP 212 to MG-MHP 214 of the Lashkarak Formation and was recorded for the first time from the Alborz Mountains (Figure 4 and Table 2). According to the literature, E. brevis has up to now been recorded from the Floian, Algerian Sahara (Paris 1990), Anti-Atlas, Morocco (Elaouad-Debbaj 1984, 1986), Libya (Paris 1990), France and Portugal (Rauscher 1968; Paris 1981), Pakistan (Tongiorgi et al 1994); early Darriwilan, Turkey (Paris et al 2007); late Early Ordovician (Floian)–early Middle Ordovician (Dapingian) of the Suri and Molle formations, north-western Argentina (Achab et al 2006); late Tremadocian–middle Floian, Colombia (Rubinstein et al 2019); Floian–Dapingian, Libya (Abuhmida and Wellman 2017); Early Ordovician (Floian), South China (Chen et al 2009; Liang et al 2018); late Early Ordovician (Floian), Turkey (Paris et al 2007); late Early Ordovician (Floian), Upper Shale Member of the Zardkuh Formation in the High Zagros Mountains (Ghavidel-Syooki 2021, 2023); Early Ordovician (Floian), peri-Gondwanan, southern Europe and northern Africa (Gutiérrez-Marco et al 2013); and Middle Ordovician (lower Darriwilian), Portugal (Vaz 2014). In the present material, Eremochitina brevis was associated with Cyathochitina campanulaeformis (Eisenack 1931) and Velatachitina veligera (Poumot 1968).…”

“…Among the associated taxa, C. campanulaeformis is long-ranging, through the Early Ordovician–Early Silurian (Paris 1990; Butcher 2009), whereas V. veligera is a diagnostic taxon in the Floian or Middle Ordovician (Al-Hajri 1995; Rubinstein et al 2019). Velatachitina veligera has until now been recorded from the Middle Floian of Europe (Paris 1981); late Tremadocian–middle Floian, Colombia (Rubinstein et al 2019); Floian or early Middle Ordovician (Dapingian), the Arabian Peninsula (Al-Hajri 1995); late Floian (stage slice Fl3 and time slice 2c), the Upper Shale Member of the Zardkuh Formation, southern Iran (Ghavidel-Syooki 2021, 2023). Furthermore, some specific peri-Gondwana acritarch taxa, such as C. bohemicum , C. almohadillum , Striatotheca mutua and Dactylofusa velifera var .…”

“…In the present study, D. ornensis (Plate 7, figure 15) occurred in the samples MG-MHP 215 to MG-MHP 216 of the Lashkarak Formation and was recorded for the first time in the Alborz Mountains (Figure 4 and Table 2) . Desmochitina ornensis has been recorded in numerous localities, including the lowermost part of the Pissot and Postolonnec formations of France (Paris 1981); the lower part of the Caceres Group (base of the Brejo Fundeiro Formation), central Portugal (Young 1988); Algerian Sahara and Libya subsurface materials (Paris 1981); the lower part of the Edjeleh Formation, Illizi Basin, and the Kasbah Leguiné Formation, north-western Libya (Paris 1990); Middle Ordovician (Dapingian) in peri-Gondwanan southern Europe and northern Africa (Gutiérrez-Marco et al 2013); Middle Ordovician (lower Darriwilian), Portugal (Vaz 2014); and Middle Ordovician (Dapingian) of the Upper Shale Member of the Zardkuh Formation, south-eastern Iran (Ghavidel-Syooki 2021, 2023).…”

“…In the present material, B. henryi (Plate 6, figures 12, 16) was included in the samples MG-MHP 217 to MG-MHP 218 of the Lashkarak Formation (Figure 4 and Table 2). This taxon is an excellent index fossil for the Dapingian Stage in the North Gondwana Domain and was recorded from numerous localities, including the Dapingian type section (Dawan Formation), Yichang area, China (Chen et al 2009); early Middle Ordovician (Dapingian), Argentina (Rubinstein et al 2019); Middle Ordovician Dapingian Stage in southern Europe and northern Africa (Gutiérrez-Marco et al 2013); and Middle Ordovician (Dapingian) of the Upper Shale Member of the Zardkuh Formation, the High Zagros Mountains, southern Iran (Ghavidel-Syooki 2023). Furthermore, distinct Middle Ordovician peri-Gondwana acritarch taxa such as Arkonia virgata were present in this biozone, confirming the early Middle Ordovician age for this interval of the Lashkarak Formation.…”

“…In the present study, S. formosa (Plate 7, figure 18; Plate 8, figures 1–24) appeared with high frequency in the samples MG-MHP 225 to MG-MHP 226 of the Lashkarak Formation (Table 2). This taxon has been recorded from numerous localities, including Middle Ordovician, the Hope Shales (Darriwilian), England (Jenkins 1967), Florida, USA (Andress et al 1969), and France (Paris 1981, 1990); middle–late Darriwilian, Hanadir Shale Member of the Qasim Formation, the Arabian Peninsula (McClure 1988; Al-Hajri 1995; Le Hérissé et al 2007), Turkey (Paris et al 2007), Libya (Combaz and Poumot 1962; Abuhmida and Wellman 2017), and the Upper Shale Member of the Zardkuh Formation in the High Zagros Mountains, southern Iran (Ghavidel-Syooki et al 2011b; Ghavidel-Syooki 2021, 2023). The co-existing chitinozoan taxa of this biozone are Lagenochitina megaesthonica (Liang et al 2022) and Conochitina chydaea (Jenkins 1967).…”