Regional Characterization of the Hirnantian Glacial Paleo-Physiography and Stratigraphic Architecture

The Late Ordovician marked one of Earth's most profound climatic transitions, culminating in the Hirnantian glaciation and the second-largest mass extinction in the Phanerozoic (Finlay et al., 2010). Glacial advance during this stage extended as far as ∼30°S (Trotter et al., 2008; Phol et al., 2016; Cocks & Torsvik, 2021), sculpting widespread erosional sequence boundaries observed across Gondwana (Le Heron, 2007; Le Heron et al., 2009). This includes the prominent Hirnantian unconformity, often placed near the extraordinarius graptolite zone (∼444–445 Ma) and linked to pronounced geochemical shifts (Sharland et al., 2001; Finlay et al., 2010). Hirnantian glaciogenic sandstones form important hydrocarbon-bearing rocks across North Africa and the Middle East (Clark-Lowes, 2005; Le Heron, 2007; Lang et al., 2012). Their deposition ceased abruptly during the persculptus Biozone, when greenhouse recovery reversed sea-level trends (Finlay et al., 2010). Glaciation length is debated, ranging from <0.5 Myr (Sharland et al., 2001) to >1 Myr (Brenchley et al., 1994; Ling et al., 2019), with postglacial rebound possibly occurring within 3000 years (Sutcliffe et al., 2000). The Hirnantian succession across Arabia and North Africa has been comprehensively described in literature (Bourahrouh et al., 2004; Ghavidel-Syooki et al., 2011; Girard et al., 2012a, 2012b, 2015; Hirst et al., 2002, 2019; Melvin, 2019; Tofaif et al., 2019). In the region south of our study area, the basal Hirnantian sandstone lies above a subglacial erosional surface marking the AP2/AP3 megasequence boundary (Sharland et al., 2001; Clark-Lowes, 2005).