Abstract In Mexico, Ordovician sedimentary rocks are exposed in the states of Baja California, Sonora, Chihuahua and Oaxaca, comprising approximately 30 stratigraphic successions ranging from Lower to Upper Ordovician. The ages of the sequences have been established primarily by utilizing conodonts and graptolites, which have also allowed us to differentiate between platform and oceanic basin environments. The State of Sonora has the most complete Ordovician stratigraphic sequences, ranging from Tremadocian to Hirnantian. The deposits in Baja California are Floian in age, while the sequences of Chihuahua range from Sandbian to Katian, and the deposits in Oaxaca are Tremadocian. The Ordovician deposits of northern Mexico (Baja California, Sonora, and Chihuahua) present a palaeogeographic relationship to the North American craton, mainly owing to faunal interspecific affinities, while the southern deposits (Oaxaca) are controversial owing to the high degree of endemism of the faunas; however, they show affinity with Gondwana, Baltica and Avalonia, with a possible insular origin. The biotic assemblages of the Ordovician of Mexico include a variety of taxa, including algae, poriferans, corals, bryozoans, brachiopods, molluscs, trilobites, echinoderms, graptolites and conodonts as predominant elements. Despite many years of field studies in Mexican Ordovician localities, biostratigraphic correlations are as yet insufficient and incomplete or are based on limited interpretations. Thus, the Ordovician biostratigraphic data from Mexico compiled in the present paper have great potential and significant value. The advancement in the knowledge of the Ordovician biostratigraphy of Mexico will contribute to a major understanding of the relationships with the Ordovician System to a continental scale. Future advances will come mainly through increasing the amount and quality of data as well as improving biocorrelations among the Ordovician sequences of Mexico.

Abstract The Ordovician of North and West Africa comprises three main transgressive–regressive sequences understood as ‘second-order’ cycles of 10–15 myr duration. Tide- to wave-dominated shallow-marine clastic successions, preserving incidental bryozoan carbonates to the north, include fluvial deposits over the most proximal southern stretches of the platform. The boundary with Cambrian strata remains unclear but the latter are progressively less represented to the south in the undifferentiated ‘Cambro-Ordovician’. To the north, graptolites, brachiopods and trilobites combined with palynomorphs provide a robust biostratigraphic frame. Maximum flooding intervals occurred in the early to middle Tremadocian, middle Darriwilian and middle to late Katian. Two events interfered with an overall long-term transgressive trend. The ‘intra-Arenig’ (late Floian?) tectonic event highlighted palaeohighs coinciding with Paleoproterozoic basements. Gondwanan drainage basins were reorganized, which had an impact on sediment sourcing and distribution of detrital material (e.g. zircons) feeding the pre-Variscan Europe. The second event is the end-Ordovician glaciation. The domain supported the greatest part of the Hirnantian glaciers and may also have preserved pre-Hirnantian glacial archives. It is not until the very latest Ordovician that offshore conditions developed far inland; it is however suspected that this inundation benefited from a transient postglacial isostatic flexure.

Abstract The stratigraphic overview presented in this chapter substantially updates and revises the last major review of the Ordovician rocks of Australia and New Zealand published 40 years ago. In the western two-thirds of the present-day continent of Australia, Ordovician sedimentary rocks are restricted to intracratonic basins. The Canning Basin (Western Australia) and Amadeus Basin (central Australia) contain the best known Lower and Middle Ordovician shallow marine successions. The eastern third of the continent, known as the Tasmanides, comprises multiple orogens (i.e. Delamerian, Lachlan, New England, Thomson, Mossman) that formed along the convergent East Gondwana Margin. As a result, volcanic and intrusive rocks are much more common in these orogens than in the intracratonic basins. Their deep-water depositional environments span 31 graptolite biozones. Slope and basinal siliceous sedimentary rocks are constrained by a newly defined set of 12 conodont biozones, complementing the conodont biostratigraphic scheme refined for shallow-water environments from the basal boundary of the Ordovician to the latest Katian. In some places, these conodont biozones are integrated with radiometric ages from tuff interbeds (e.g. Canning Basin). Ordovician graptolitic strata in the Buller Terrane of New Zealand share palaeogeographic links with those in the Bendigo Zone of the western Lachlan Orogen.

Abstract Two remarkable events in the history of life on the Earth occur during the Ordovician Period (486.9–443.1 Ma). The first is an exceptionally rapid and sustained radiation of marine life known as the ‘Great Ordovician Biodiversification Event’ (GOBE), and the second is a catastrophic Late Ordovician mass extinction (LOME). Understanding the duration, rate and magnitude of these events requires an increasingly precise global correlation framework. In this chapter we review the major subdivisions of the Ordovician System, their Global Stratotype Section and Points, and the chronostratigraphic levels that define their bases. We also present a detailed set of correlation charts that illustrate the relationships between most of the regional graptolite, conodont and chitinozoan successions across the world.

Abstract The lower Paleozoic succession of central Europe exposed in the Bohemian Massif is a classic area of geology with a long-standing tradition of research dating back to the eighteenth century. The Ordovician rocks form parts of sections in several units that sit on the Cadomian basement. These sedimentary and volcano-sedimentary fills of partial depressions in the basement are relics of the system of rift basins in the Gondwanan margin reflecting the rifting of the Rheic Ocean. The Ordovician sections are related to the subsidence period during the extensional regime accompanied by volcanism. They are underlain by Neoproterozoic or Cambrian rocks and continue up usually without breaks. After closure of the Rheic Ocean owing to the Gondwana–Laurussia collision, the Ordovician successions were incorporated into the Variscan Orogen belt and preserved in denudation relics such as the Bohemian Massif and its units. Ordovician strata with Gondwanan shelf affinities can be traced along the Variscans from Spain to central Europe, and are reflected in the regional stratigraphic scale based mainly on the succession in the Prague Basin. The Ordovician fill of this accumulation centre, together with relics of another preserved in the Schwarzburg Anticline, represents the main exposures in the Bohemian Massif. The individual features of the Ordovician successions, such as facies developments, fossil associations and volcanism, make them model areas both for understanding the palaeogeographic and geotectonic evolution of the peri-Gondwanan margin and a stratigraphic standard for a cool-water regime.

Abstract The Ordovician documented in southeastern Europe reflects different sedimentary environments, from shallow water to basin, belonging to diverse palaeogeographical domains. Some of these geological sectors and their palaeontological content have been well described for a long time such as the Carnic Alps, which represent one of the most continuous Paleozoic sequences in the world. For some other areas, the quality of the data is variable and the knowledge is less detailed, sometimes with lithostratigraphic units still to be formalized, which also reflects the fragmentary nature of the outcrops. The Ordovician stratigraphy of southeastern Europe with its diverse successions has been revised herein and integrated with new data in an attempt to develop a global scenario for this critical time interval in the evolution of life.

Detailed mapping and reevaluation of biostratigraphic data provide new insights into the regional stratigraphic significance of the Ordovician Comus Formation at its type locality at Iron Point, Edna Mountain, Humboldt County, Nevada. Mapping of the internal stratigraphy of the Comus Formation yielded six new subunits and a previously unrecognized formation that is potentially correlative to the Middle Ordovician Eureka Quartzite. The age designation of the Comus Formation was reexamined, using the most current understanding of Ordovician graptolite biostratigraphy. The species of graptolites found in the Comus strata at Iron Point are Late Ordovician, in contrast to the Middle Ordovician age assignment in previous studies. Structural analyses using the new detailed mapping revealed six deformational events at Iron Point. The first fold set, F 1 , is west-vergent and likely correlative to mid-Pennsylvanian folds observed nearby at Edna Mountain. The second fold set, F 2 , records north–south contraction and is likely correlative to Early Permian folds observed at Edna Mountain. The King fault is a normal fault that strikes north and dips east. It truncates the F 1 and F 2 fold sets and has not been active since the Early Permian. The Silver Coin thrust strikes east, places the Ordovician Vinini Formation over the Comus Formation, truncates the King fault, and is not affected by the F 1 and F 2 fold sets. Timing of the Silver Coin thrust is unknown, but it is likely post-Early Permian based on crosscutting relationships. The West fault strikes southeast and dips southwest. It truncates the Silver Coin thrust on the west, and the fault surface records several phases of motion. Finally, Iron Point is bounded on the east side by the Pumpernickel fault, a normal fault that strikes north and dips east. The movement on this structure is likely related to Miocene to Recent Basin and Range faulting. Several key findings resulted from this detailed study of the Ordovician rocks at Iron Point. (1) Based on detailed mapping of the internal stratigraphy of the Comus Formation at Iron Point, it is here interpreted to be correlative with the autochthonous Late Ordovician Hanson Creek Formation rather than the well-known “Comus Formation” that hosts Carlin-style gold mineralization in the Osgood Mountains to the north. (2) The Comus Formation at Iron Point is autochthonous, and the Roberts Mountains thrust is not present at Iron Point, either at the surface or in the subsurface. (3) The stratigraphic mismatch between Iron Point and Edna Mountain requires a fault with significant lateral offset between the two areas; its current expression could be the West fault. (4) West- and southwest-vergent structures at Iron Point and Edna Mountain are rotated counterclockwise relative to northwest-vergent structures at Carlin Canyon and elsewhere in northern Nevada. This relationship is consistent with large-scale sinistral slip along the continental margin to the west.

Abstract The extensive, predominantly siliciclastic deposits of the Upper Ordovician of the Tafilalt have long been the subject of scientific investigation. In the past 25 years, intensified collecting for commercial purposes has resulted in the discovery of several exceptionally-preserved faunas (Konservat-Lagerstätten) in the Tafilalt region, preserving a range of non-biomineralized and soft-bodied organisms. The preservation of these fossils in the coarse clastic sediments of the Tafilalt is surprising, and in the case of soft-bodied organisms, remarkably similar to the preservational mode of typical Ediacaran biotas. These relatively recent discoveries have increased the scientific significance of the Tafilalt Biota, providing an unparalleled insight into the composition and temporal evolution of the shallow, open-marine ecosystems and their denizens during the later stages of the Great Ordovician Biodiversification Event. At least nine different phyla, in addition to several soft-bodied problematica are represented in the Tafilalt. While the highly diverse and remarkably well-preserved echinoderm and euarthropod faunas are most emblematic for the Tafilalt Biota, further studies have revealed a relatively high diversity of molluscs and brachiopods. Among soft-bodied fossils, the problematic paropsonemid eldonids are iconic for the Tafilalt and stand out both through their abundance, and their wide temporal and geographical range throughout the area.

ABSTRACT The very first scientific paper by Eduard Suess (1831–1914) treats the graptolites of Bohemia in the present-day Czech Republic (in the Upper Proterozoic to Middle Devonian “Barrandian” extending between Prague and Plzeň). This paper is accompanied by superb drawings of his observations in which Suess took great care not to insert himself between Nature as he perceived it in the framework of the knowledge of his day and his readers. His only limitation was the one imposed by the size of his study objects. His technological means did not allow him to see what we today consider the “right” picture. Nevertheless, we can see what he saw and interpret it through a modern lens of understanding. In his drawings, Suess exercised what the great German geologist Hans Cloos later called “the art of leaving out.” This meant that in the drawings, the parts not relevant to the discussion are left only in outline, whereas parts he wished to highlight are brought to the fore by careful shading. Even the parts left only in outline are not schematic, however; instead they are careful reconstructions true to Nature as much as the material and his technological aids allowed. This characteristic of Suess’ illustrations is seen also in his later field sketches concerning stratigraphy and structural geology and in his depiction of the large tectonic features of our globe representing a window into his manner of thinking.