Abstract Outcrops of the Ordovician System in South Africa are extensive; they cover significant portions of the Northern, Western and Eastern Cape provinces as part of the Cape Fold Belt as well as the KwaZulu-Natal Province as supracrustal cover overlying the Natal sector of the Paleoproterozoic Namaqua-Natal metamorphic province. Within the Cape Fold Belt, Ordovician rocks of the Table Mountain Group (Piekenierskloof, Graafwater, Peninsula, Pakhuis and Cedarberg formations as well as the enigmatic Sardinia Bay Formation) outcrop extensively whilst pre-Cape rocks of the Kansa Group (Vaartwell, Uitvlug, Gezwinds Kraal and Schoongezigt formations) and Schoemanspoort Formation are present within the Kango Inlier encapsulated by the fold belt. The Natal Group (Durban and Mariannhill formations) is entirely located within KwaZulu-Natal. For the most part, these metasiliciclastic rocks are markedly unfossiliferous except for the world class fossil deposits of the Cedarberg Formation and important trace fossil sites in the Graafwater, Peninsula and Pakhuis formations. The lack of palaeontological material and other accurate geochronological proxies in these successions (as well as those of the Kansa and Natal groups and Schoemanspoort Formation) makes estimations of relative age constraints tenuous at best and difficult to correlate with global Ordovician chronostratigraphic frameworks. Regardless of the challenges faced in correlating these rocks within global frameworks, these rocks provide a unique low latitude glimpse into Earth surface processes and the feedback loops that ensued within the biological realm along the southern margin of Gondwana.

Abstract The late Ordovician glaciation in the Kingdom of Saudi Arabia is spectacularly represented in the rocks of the Sarah Formation, although relatively little has been published about this formation. This paper describes and discusses the Zarqa megafacies of the Sarah Formation, which crops out across a distance of 720 km in the NW of the Kingdom as a heavily deformed diamicton, representing an example of widespread subglacial deformation. At outcrop, this Zarqa megafacies consists of two major subfacies. Subfacies (M) consists of a deformed, pebble-bearing substrate of interstratified, argillaceous, very fine- to fine-grained sandstones and siltstones. It displays a glacio-tectonically derived internal stratigraphy consisting of two units. Unit (i) is a pebbly diamictite displaying recumbent folding and thrusting indicative of progressive simple shear and manifest in a number of glacio-tectonically stacked detachment sheets. Unit (i) is abruptly overlain by Unit (ii). This consists of a lower Unit (iia), which displays soft sediment folding, including common sheath folds, as well as dewatering phenomena, passing up gradationally into almost completely homogenized sandy siltstone of Unit (iib) with rare detached masses of contorted sandstone. Subfacies (M) represents subglacial deforming bed conditions that reflect variable, but overall upwardly increasing, pore fluid overpressure in the pre-glacial substrate as it was overridden by the advancing Hirnantian ice sheet. It has been identified in subsurface core material, displaying asymmetrical strain profiles that also indicate subglacial deforming bed conditions. Subfacies (N) is a heavily deformed, boulder-bearing subglacial tillite commonly expressed in a distinctive mounded landscape of irregular piles of debris up to 8 m high. Extremely poorly sorted, it contains outsize boulders of glaciogenically deformed Lower Paleozoic sediments and striated Precambrian crystalline rocks. This subfacies represents a subglacially uprooted substrate that was transported considerable distances by the overriding ice sheet. Aspects of the Zarqa megafacies have parallels in coeval glaciogenic rocks identified from across northern Gondwana and beyond. This megafacies is therefore considered to have considerable sequence stratigraphic significance, representing deformed lowstand substrate and subglacial deposits associated with the accumulation and advance(s) of the late Ordovician ice sheets.

Abstract Glaciogenic reservoirs host important hydrocarbon and groundwater resources across the globe. Their complexity and importance for exploration and palaeoclimate reconstruction have made glaciogenic successions popular subjects for study. In this paper we provide an overview of the palaeoclimatic and tectonic setting for Earth glaciation and a chronological account of glaciogenic deposits since c. 750 Ma, with particular emphasis on their reservoir potential and associated hydrocarbon systems. Hydrocarbon accumulations within glaciogenic reservoirs occur principally in Palaeozoic (Late Ordovician and Permo-Carboniferous) sandstones in South America, Australia, North Africa and the Middle East, with relatively minor occurrences of shallow gas hosted in Pleistocene deposits in the North Sea and Canada. Groundwater reserves occur within glaciogenic sandstones across the northern European lowland and in North America. The main glaciogenic environments range from subglacial to glacier front to proglacial and deglacial. Rapidly changing environments, hydrodynamic regimes and glacier-front and subglacial deformation often result in very complex glaciogenic sequences with significant challenges for reconstruction of their origin and resource importance, which this volume seeks to address.