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The Saluda Formation, a lithologically distinct but spatially variable unit, is mappable in the subsurface. Lithologic characters such as dolomitic and laminated finegrained carbonates, paucity of fossils and terriginous detritus, birdseye structures, and intraclasts distinguish the formation and aid in interpreting the depositional environment. Similarities of features for modern and ancient carbonate tidal-flats and those of the Saluda suggest a tidal-flat environment of origin for the formation. Lateral and vertical lithologic relationships with contiguous formations record spatially variable but time transgressive subenvironments of deposition for the tidal-flat complex and surrounding sea.

The Ordovician rocks of the Bail Hill area, Sanquhar, South Scotland : volcanism and sedimentation in the lapetus Ocean. by M. J .McMurtry. The Bail Hill area lies in the "Northern Belt" of the Southern Uplands and contains sedimentary and volcanic rocks of Llandeilo/Caradoc age. The sedimentary succession has been divided into four formations - the Glenflosh, Kiln, Spothfore and Guffock Formations. The Glenflosh and Guffock Formations are mainly arenaceous and were largely deposited by turbidity currents flowing to the southwest. They typically consist of Tae units. The fine-grained sandstones and siltstones of the Kiln Formation were also deposited by turbidity currents. Parallel-laminated units in the lower part of the formation represent "overbank" deposits, whilst lenticular- bedded units in the upper part are interpreted as channel- mouth deposits. Bouma sequences are not common in these lithologies. The Spothfore Formation consists of rudites deposited by a variety of sediment and fluid gravity flows close to a feeder system. The petrography of greywackes within the formations shows no significant variation across strike, in contrast to successions studied to the southwest. The provenance of detritus in the sediments is believed to be the north-westerly Laurentian continent with a significant but variable intrabasinal contribution of sedimentary and volcanic debris. A stratigraphic succession for the area is proposed, although graptolite evidence for the relative ages of the formations is equivocal. A new stratigraphic unit, the Bail Hill Volcanic Group, is proposed and the petrography and field relations of the subdivisions within this group are discussed. Field relations suggest that the Bail Hill volcano was a composite, central-type structure. Early basaltic lavas were succeeded by more differentiated lithologies and pyroclastic activity increased with time. The mineral and whole-rock chemistry indicates the Bail Hill Volcanic Group has differentiated along the sodic alkaline series (alkali basalt - hawaiite - mugearite - trachyte). Gabbroic and dioritic xenoliths in the extrusive rocks are believed to be fragments of a large sub-volcanic intrusive mass that underlay the Bail Hill volcano in Ordovician times. The volcanic pile as a whole has undergone metamorphism to zeolite facies grade. Higher grade assemblages in the xenoliths suggest that they were hydrothermally altered prior to incorporation in the extrusive rocks. It is concluded that the Bail Hill Volcanic Group represents the remnants of a seamount within the Iapetus Ocean, whilst the sedimentary rocks record the transition from the abyssal plain into a Lower Palaeozoic trench. Northwesterly subduction of the lapetus Ocean crust resulted in the accretion of the Bail Hill area on to the facing edge of the northwesterly Laurentian continent.

Dimeropygidae Hupé, 1953 is a family of highly vaulted and small trilobites from the paleotropics of the uppermost Cambrian through the Ordovician. Specimens are known from Laurentia, Baltica, Avalonia, Siberia, Australia, North China, and South China. Dimeropygids are difficult to recover because of their small size and vaulted, tuberculate, and often spiny exoskeletons. Thus, most of their diversity is known from secondarily silicified material which preserves remarkable amounts of detail on the sclerites. Such faunas, while often rare, are common in the Great Basin of the western USA. Trilobite research has been conducted in the Great Basin has been since the late 1800s. Recent high intensity sampling and collection of larger sample sized from silicified horizons has increased the known diversity of trilobites from Lower Early Ordovician. New collections from the Lower Ordovician are providing crucial new insight into the groups early evolutionary history (e.g., Adrain & Westrop, 2007, McAdams & Adrain, 2009, Adrain et al., 2014a). Skullrockicurus n. gen. is a new genus of dimeropygid trilobites including at least seven new species. Five of the new species are well known enough from silicified material to formally name: S. greeni (Garden City Formation, Idaho and House Formation, Utah), S. plummeri (House Formation, Utah), S. judyi (House Formation, Utah), S. massarellai (House Formation, Utah), and S. brocki (House Formation, Utah). Synapomorphies of the new genus include four pairs of tubercles on the glabella, a posteriorly bowed glabella, long preglabellar field, and semilunate pygidium with a corona of tubercles or spines at the fulcrum.

The purpose of this paper is to give a brief description of the stratigraphy of the Lower and Middle Ordovician formations of the St. Lawrence Lowlands together with a short summary of the historical geology of the time. The basis for the paper is the literature on the subject, as the author's personal investigation has been restricted to one summer's work in a small section of the Lowlands. For the purpose of this description, the limits of the area are first defined and the region is then subdivided into three parts. There follows a description of the Beekmantown formation in which the problem of the Potsdam and Nepean sandstones is discussed. Afterwards, the historical geology of the epoch is given in resume. The Chazy formations are in turn examined, and the historical geology of the period is supplied. The more complex problem of the Black River, Trenton, and Utica stratigraphy is then analyzed. Changes in facies and thicknesses of contemporaneous formations in different parts of the Lowlands are studied with particular reference to the work of Raymond, Kay, Okulitch, Clark, and Wilson. An attempt to correlate these formations is made, but, owing to the complexity of the problem and the small amount of information available on many areas, the picture is left incomplete. The historical geology of this third marine invasion covering the St. Lawrence Lowlands from Black River to Utica time, is reviewed. The bibliography does not pretend to be exhaustive. It contains works on the stratigraphy of the Lower and Middle Ordovician Period and some works dealing with the palaeontology have also been included as a useful complement to the stratigraphy. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The Hudson Bay Basin is the largest intracratonic basin in North America, but remains a frontier area for our knowledge of its stratigraphy and sedimentology and its hydrocarbon potential. Large domal reefs (up to 10 m thick and 500 m wide) in the Upper Ordovician Red Head Rapids Formation on Southampton Island developed on the margin of this shallow-marine evaporitic basin in which physical and chemical seawater parameters were distinct from the open ocean and in which a diverse community of reef-building and dwelling metazoans was unable to flourish. The main reef facies comprise boundstone and cementstone composed of various proportions of early-calcified sponge tissues, microbial encrusters, synsedimentary cement and small colonial metazoans. The accretionary mechanisms of the Red Head Rapids reefs were mainly the result of framebuilding by early-calcified sponges and small colonial corals and binding by calcimicrobial elements for the boundstone facies, and of massive aragonitic cement precipitation near the seafloor for the cementstone facies. These Upper Ordovician reefs, in which microbialites dominate but coexist with metazoans, were more widespread in the Early Ordovician immediately prior to the Middle to Late Ordovician expansion of skeletal-dominant reefs. The Upper Ordovician reefs on Southampton Island, porous and locally bitumen impregnated, underwent early marine, near-surface and progressive burial diagenesis; reducing its primary porosity but significantly increasing its secondary porosity. They represent one of the major untested petroleum play types identified in the Hudson Bay Basin.

N/A / Thesis / Master of Science (MS)

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