EPEIRIC SEAS: A CONTINENTAL EXTENSION OF SHELF BIOTAS
1. Overview 1.1. Controls 1.2. Temporal Distribution 1.3. Geographic Distribution 1.4. Sedimentology 1.5. Climatic Impact 2. The Environment of Epeiric Seaways 3. Origin and Evolution of the Epicontinental Sea Biota 3.1. Nature of the Epicontinental Fossil Record 3.2. Measuring Biodiversity in Epicontinental Seas 3.3. The Endemism Question 3.4. Precambrian 3.5. Paleozoic 3.5.1. Cambrian 3.5.2. Ordovician–Permian 3.6. Mesoand Cenozoic 3.6.1. Triassic–Cretaceous 3.6.2. Paleocene–Recent 3.7. Mass Extinctions Glossary Bibliography Biographical Sketch
Stratigraphy and Paleobiology of the Upper Cretaceous-Lower Paleogene Sediments from the Trans-Saharan Seaway in Mali
An epicontinental sea bisected West Africa periodically from the Late Cretaceous to the early Eocene, in dramatic contrast to the current Sahara Desert that dominates the same region today. Known as the Trans-Saharan Seaway, this warm and shallow ocean was a manifestation of globally elevated sea level associated with the rapid break-up of the supercontinent Gondwana in the late Mesozoic. Although it varied in size through time, the Trans-Saharan Seaway is estimated to have covered as much as 3000 km2 of the African continent and was approximately 50 m deep. The edges of the sea were defined in part by the high topography of the Precambrian cratons and mobile belts of West Africa. Over its approximately 50 million year episodic existence, through six major periods of transgression and regression, the Trans-Saharan Seaway left behind extensive nearshore marine sedimentary strata with abundant fossils. The waters that yielded these deposits supported and preserved the remains of numerous vertebrate, invertebrate, plant, and microbial species that are now extinct. These species document a regional picture of ancient tropical life that spanned two major Earth events: the Cretaceous-Paleogene (K-Pg) boundary and the Paleocene-Eocene Thermal Maximum (PETM). Whereas extensive epeiric seas flooded the interior portions of most continents during these intervals, the emerging multicontinental narrative has often overlooked the Trans-Saharan Seaway, in part because fundamental research, including the naming of geological formations and the primary description and analysis of fossil species, remained to be done. We provide such synthesis here based on two decades of fieldwork and analyses of sedimentary deposits in the Republic of Mali. Northern parts of the Republic of Mali today include some of the farthest inland reaches of the ancient sea. 
 
We bring together and expand on our prior geological and paleontological publications and provide new information on ancient sedimentary rocks and fossils that document paleoequatorial life of the past. Ours is the first formal description of and nomenclature for the Upper Cretaceous and lower Paleogene geological formations of this region and we tie these names to regional correlations over multiple modern territorial boundaries. The ancient seaway left intriguing and previously unclassified phosphate deposits that, quite possibly, represent the most extensive vertebrate macrofossil bone beds known from anywhere on Earth. These bone beds, and the paper shales and carbonates associated with them, have preserved a diverse assemblage of fossils, including a variety of new species of invertebrates and vertebrates, rare mammals, and trace fossils. The shallow marine waters included a wide range of paleoenvironments from delta systems, to hypersaline embayments, protected lagoons, and carbonate shoals. 
 
Our overarching goal has been to collect vertebrate fossils tied to a K-Pg stratigraphic section in Africa. We provide such a section and, consistent with prior ideas, indicate that there is a gap in sedimentation in Malian rocks in the earliest Paleocene, an unconformity also proposed elsewhere in West Africa. Our phylogenetic analyses of several vertebrate clades across the K-Pg boundary have clarified clade-by-clade species-level survivorship and range extensions for multiple taxa. Few macrofossil species from the Trans-Saharan Seaway show conspicuous change at either the K-Pg boundary or the PETM based on current evidence, although results are very preliminary. Building on our earlier report of the first record of rock-boring bivalves from the Paleocene of West Africa, we further describe here a Cretaceous and Paleogene mollusk fauna dominated by taxa characteristic of the modern tropics. Among the newly discovered fossil osteichthyans, large body size characterizes both the pycnodonts and a new freshwater Eocene catfish species, one of the largest fossil catfishes found in Africa. Our new paleoecological and faunal reconstructions show an evergreen, broadleaf forest that included some of the oldest mangroves known. The ancient Malian ecosystem had numerous apex predators including Crocodyliformes, Serpentes, and Amiidae, some of which were among the largest species in their clades. The Trans-Saharan Seaway exhibited intermittent isolation from major seas. This environmental variable may have created aquatic centers of endemism, stimulating selection for gigantism as previously observed for species on terrestrial islands.
Mississippian Sedimentation and Oil Fields in Southeastern Saskatchewan
Marked facies changes occur in the Mission Canyon and lower part of the Charles formation (Mississippian) in southeastern Saskatchewan. Northeastward from the basinal area, four successive environments of deposition with characteristic rock types and fossils may be mapped as follows. 1. Basin: dark brown-gray argillaceous limestone containing scattered white crinoid columnals, black bituminous shale partings, and brownish gray chert. 2. Open marine shelf: cream-white fossiliferous-fragmental and chalky limestones containing crinoids, bryozoans, brachiopods, and zaphrentid corals. 3. Barrier bank: cream-white precipitated limestones including pisolitic, oolitic, pseudo-oolitic, and lithographic types. Fossils include abundant algae and few scattered gastropods. 4. Lagoon: cream-white chalky argillaceous limestone containing ostracods, earthy to sucrosic secondary dolomite and anhydrite. Evaporitic (primary?) dolomites occur in the upper Charles as a result of basin-wide evaporitic conditions. These typically dense (cryptocrystalline) and non-porous dolomites are closely associated with anhydrite. Factors which control porosity in the limestones include sorting of fossil debris or precipitated calcareous grains, submarine erosion and re-deposition of partially lithified calcareous muds, solution, dolomitization (?), fractures, compaction, and infilling of pores by calcite, anhydrite, or chert. Stratigraphic trap oil accumulations occur where permeable units of the Mission Canyon and Charles are truncated and overlain by pre-middle Jurassic redbeds. Factors affecting oil accumulation include the presence of the following. a. Permeable reservoir beds at or near the unconformity. b. Anhydrite filling pores where the permeable reservoir beds are truncated by the pre-Jurassic erosion. c. Anhydrite beds conformably overlying and underlying the permeable units and thus form a roof and floor for the reservoir beds. d. Topography of the Mississippian erosion surface. Mississippian strata in the oil-producing area of southeastern Saskatchewan are characterized by the following. 1. Relatively steep dips (40-60 feet per mile) as compared with dips of 10-20 feet per mile in much of southwestern Saskatchewan. 2. Relatively rapid truncation (15-40 feet per mile) as compared with an average of approximately 5 feet per mile in southwestern Saskatchewan. 3. Relatively saline waters (50,000-150,000 parts per million of chloride ion content) as compared with 100-8,000 parts per million in southwestern Saskatchewan. In exploration for new trends or extensions of known producing areas, important consideration should be given to the distribution of permeable rock facies within individual stratigraphic units. In addition, it is possible to predict the location of topographically high trends as the various lithologic types are differentially resistant to erosion. For example, the precipitated barrier bank limestones End_Page 94------------------------------ are relatively resistant to weathering and form topographic ridges in the Nottingham field. The lower limit of oil accumulation within reservoir beds may be determined by the location of a spill point, in turn controlled by the downdip limit of lagoonal anhydrite floors.