Tertiary

Abstract: Physical geography of South America quaternary tectonics of South America quaternary volcanism in South America characteristics of the quaternary volcanic zones quaternary of the alluvial basins structure and quaternary stratigraphy quaternary of the alluvial basins aeolian features - paleoclimate quaternary of the South American Highlands - Highlands of the Brazilian Shield quaternary of the South American Highlands - case studies in Southeast Brazil Campos de Jordao and Serra de Itatiaia quaternary of the South American Highlands the Northern and Southern Highlands the glaciers and glacial landforms of South America late Cenozoic glacial history of the Andes - late Miocene-Middle Pleistocene, the late quaternary (isotope stages 7-3), the last glaciation maximum (isotope stage 2), the late-glacial and holocene quaternary gravel formations of southern South America quaternary palaeolakes of the arid regions of South America quaternary geocryogenic features of South America and the Falkland Islands (Islas Malvinas) quaternary of the South American coasts quaternary palnological studies in South America - pre-quaternary-late-quaternary, the last glaciation palaeoecology of the late-glacial and holocene intervals the quaternary of South America - overview and implications.

Abstract: This chapter sets out to give a historical overview of the African rain forest from its origins, towards the end of the Cretaceous period. The areas around the Gulf of Guinea, in particular from Ivory Coast to Nigeria and especially Cameroon, Gabon and Congo, appear to have been already occupied at this time by wet tropical forest formations mainly composed of Angiosperms which were then becoming established. In the course of the Tertiary period the combined effect of the equator being situated further north than now and the development of the Antarctic ice cap favoured the development of wet tropical conditions over a large part of North Africa which in turn led to the extension of tropical forest to various sites on the shores of the Tethys Sea. There were probably at this time common taxa and similar vegetation patterns stretching from the Gulf of Guinea to the Tethys Sea.Towards the end of the Tertiary, the equator reached its present position and the northern hemisphere ice caps appeared, and these phenomena resulted in the disappearance of the forest formations spread across the north of Africa, and the concentration of these formations near the equatorial zone around the Gulf of Guinea and in the Congo–Zaire basin. From 800 000 years ago onwards the marked glacial variations at middle and high latitudes in both hemispheres, with a periodicity of about 100 000 years determined by the orbital variations of the earth around the sun, lowered temperatures in equatorial areas and brought arid climates at times of maximum glacial extension. The most arid periods resulted in the fragmentation of the forest cover, and the forest biotopes and their biodiversity were preserved in a series of refugia. The lowering of temperatures also resulted in the extension of montane flora to low altitudes, with migration of montane flora and fauna between main mountain ranges. These compounded phenomena of isolation and migration, probably involving genie exchange, must have resulted in numerous speciation phenomena. Subsequently, such montane flora or fauna became isolated on mountain areas during periods of maximum warming, in the last instance in the course of the Holocene, when a vast forest cover became re-established from Guinea westwards, and to the East as far as the Lake Victoria area. The phases of maximum fragmentation, which appear to have been connected with only the coldest periods – in the last instance during the second part of isotopic stages 6 (from c. 160 to 130 000 years) and 2 (from c. 24 to 12000 years BP) – relate to less than 10% of the last 800 000 years, and the phases of maximum forest extension would likewise appear to be less than 10% of the period. The remaining 80–90% of the time relates to ‘intermediate situations’ which varied from period to period, and these intermediate extension situations seem to have been the norm over the larger part of the Quaternary, rather than the present situation which is closer to a situation of maximum extension.

Abstract: The temperate deciduous forest of North America is more diverse than the deciduous forest of western Europe. This difference has traditionally been explained by greater survival in North America of deciduous species during the Quaternary. More recent investigations have shown, however, that late-Tertiary forests of Europe had already become dominated by conifers, with deciduous angiosperms a minor component. During the Quaternary, coniferous species and genera were lost from the European flora, leaving a few species and genera of angiosperms as the dominant trees. Cold, dry, continental climate during the glaciations caused the extinction of conifers; deciduous trees apparently survived these climatic conditions in pockets of favorable habitat in the eastern Mediterranean region. In eastern North America, in contrast, temperate deciduous forests are quite similar to the forests that were present in the late Tertiary. During the Quaternary, relatively few extinctions occurred, although deciduous angiosperms were displaced from the Appalachian mountains, surviving in small populations in the lower Mississippi valley or on the southern coastal plain. Coniferous forests dominated by spruce grew in the Great Plains, and forests dominated by pine grew on the southern part of the Atlantic coastal plain. At the opening of the Holocene, and presumably at the beginning of all the previous interglacials, tree distributions changed dramatically as temperate species rapidly extended their ranges northward. Range boundaries have continued to change throughout the Holocene, as expansions and contractions of range have occurred as the result of climatic change. Quaternary climatic history caused dramatic changes in the forests of both areas, indicating that modern species distributions can no longer be considered relicts of Tertiary distributions. Throughout the Quaternary, species ranges have changed in response to changes in regional climate; many forest communities are of recent origin, having received their present complements of tree species within the last 5,000 years. Forest communities in Eastern North America and in Western Europe as well have been invaded repeatedly during the Holocene by forest species expanding from refuges far to the south. Temperate deciduous forest grows over a wide area of eastern North America. The forest is rich in numbers of species, especially the mixed mesophytic forest communities of the southern Appalachians. These forests were traditionally compared with forests of the Tertiary Period (Reid, 1935; Braun, 1947, 1950; Campbell, 1982), when the so-called Arcto-Tertiary geoflora was supposed to have been widespread throughout the northern hemisphere (Chaney, 1944). Reid (1935) and Chaney (1944) believed that severe climate during the Quaternary Period eliminated the Arcto-Tertiary geoflora entirely from many regions, such as western North America, while in others, such as western Europe, extinctions eliminated all but a few species and genera. The modern deciduous forests were thus seen as remnants of an originally widespread, uniform vegetation. The geoflora concept has been challenged recently by Wolfe (1978, 1979) who argued that a uniform broad-leaved forest never existed. His analysis of the paleobotanical data shows that Tertiary floras were diverse, with evergreen gymnosperms such as Sequoia dominant in some regions, and evergreen angiosperms present elsewhere. He argued that a number of major climatic changes occurred during the Tertiary, especially during the Oligocene; these changes led to local changes in abundances of various components of the Tertiary flora. Thus changes of climate caused local adaptations rather than migrations of intact plant communities from one latitude to another as Chaney hypothesized (Wolfe, 1979). Before the end of the Tertiary Period, the forests of western United States were already dominated by conifers. A similar change had also occurred in Europe, where Pliocene floras contained many genera and species of conifers (Wolfe, 1979). Sequoia was the dominant tree in some regions (Traverse, 1982). Mixed coniferous-deciduous forest in Europe during the Pliocene is a new interpretation of forest history that stands in marked contrast to the traditional view. The traditional view held that deciduous forest persisted in Europe into the early Quaternary Period, when increasing se1 This work was supported by the National Science Foundation. 2 Department of Ecology and Behavioral Biology, University of Minnesota, Minneapolis, Minnesota 55455. ANN. MISSOURI BOT. GARD. 70:550-563. 1983. This content downloaded from 157.55.39.181 on Thu, 29 Sep 2016 05:51:40 UTC All use subject to http://about.jstor.org/terms 1983] DAVIS-QUATERNARY HISTORY 551 verity of climate caused extinctions of many angiosperm trees (Tralau, 1973; Campbell, 1982). In contrast, Wolfe emphasized that coniferous species and genera were the important losses from the European flora during the Quaternary. The Taxodiaceae, for example, once so important in the Black Sea region, were eliminated entirely (Traverse, 1982). The angiospermous genera that remain today represent differential survival of one component of what had been mixed coniferous-deciduous forest (Wolfe, 1979). Wolfe pointed out that Europe today has the type of climatic regime that elsewhere in the world supports mixed coniferous forest; the dominance of deciduous species in the region today is therefore anomalous. Eastern North America, in contrast, has a climatic regime typical of deciduous forest regions. Today it supports forests dominated by deciduous angiosperms, just as it did during the late Tertiary (Wolfe, 1979). The Quaternary pollen record adds a useful perspective to these differing views of the origin of the European deciduous forest and the relationship of deciduous forests in eastern North America and Europe. First, the Quaternary record shows that dramatic changes in the geographical ranges of forest species occurred during the Quaternary. We can no longer speak of Tertiary forest "remaining" in a region throughout the Quaternary, because many tree species were repeatedly displaced during the Quaternary from the geographical region where they now occur. For this reason, modern geographical ranges cannot be used to identify the locations of "relict" Tertiary forests. Second, the response of temperate forest trees to Quaternary climatic change was individualistic, supporting Wolfe's contention that Tertiaryfloras would not have migrated as units in response to climatic events. Third, the extinctions that occurred during the Quaternary, especially the differential extinctions of conifers and deciduous angiosperms document that the differential severity of Quaternary climate affectedforests differently in Europe and North America. These three factors contributed to the makeup of the modem temperate forest floras of North America and Europe. In considering how Quaternary climate changed Pliocene floras into modem floras, the two phases of Quaternary climate, glacial climates and interglacial climates, are important. The two phases appear to have had quite different effects. -Glacial phases, i.e., times when ice sheets were more extensive than at present, comprised about 90 percent of the time during the Quaternary period. During these long, cold intervals, temperate species survived in small populations that were susceptible to extinction. The severity of the climate, both in terms of average temperature, continentality, and drought; the extent of geographical displacement of plant species; the sizes of populations; and the community composition of forests in refuge areas; all had an effect on the probability of extinction for individual species. Interglacial intervals comprised a much smaller proportion (about 10 percent) of the Quaternary period. They were characterized by climates similar to those of today, which in Europe and eastern North America seem to bear a general resemblance to late-Tertiary climate. Each interglacial was short, lasting only 10,000 to 1 5,000 years, and began and ended with a sudden, major climatic change (Emiliani, 1972; Broecker & Van Donk, 1970). The interglacials, although favorable for survival and population expansion of temperate forest trees both in Europe and eastern North America, were times of vegetational instability. During interglacials the geographical distributions of temperate species shifted many hundreds of kilometers, and the composition of forest comunities changed rapidly. GEOLOGICAL EVIDENCE OF EVENTS DURING THE QUATERNARY PERIOD The exploration of the deep sea by geologists in the last twenty years has led to a new understanding of Quaternary events, revolutionizing our thinking about the time scale of glaciation. Many marine cores include sediment extending through the entire Quaternary Period. Previously, four major glaciations were recognized within the Quaternary. We now know that there were 18 or 20 glaciations during the last 2 million years, the time interval now assigned to the Quaternary. Each of these glacial cycles lasted about 100,000 years (Hays et al., 1969). Figure 1 shows oxygen-isotope paleoclimatic records for the last 800,000 years. The climatic events are well dated: the last interglacial (the earliest part of stage 5) started 125,000 years ago, lasted about 15,000 years, and ended with a sharp decline in temperature that initiated the last glaciation. Warm conditions returned, followed by a cold period, then a short warm interval. Seventy thousand years ago a long cold interval (stages 2-4) began, which culminated in the glacial maximum 18,000 to 20,000 years ago (Broecker & Van Donk, 1970). This content downloaded from 157.55.39.181 on Thu, 29 Sep 2016 05:51:40 UTC All use subject to http://about.jstor.org/terms 552 ANNALS OF THE MISSOURI BOTANICAL GARDEN [VOL. 70

Abstract: In early 1975, Chevron Overseas Petroleum Inc. commenced what became a major petroleum exploration effort in previously unexplored interior Sudan. With the cooperation of the Sudanese government, Chevron has acquired a vast amount of geological and geophysical data during the past 12 years. These data include extensive aeromagnetic and gravity surveys, 36,040 mi (58,000 km) of seismic data, and 86 wells. This information has defined several large rift basins now recognized as a major part of the Central African rift system. The sedimentary basins of interior Sudan are characterized by thick nonmarine clastic sequences of Jurassic(?)-Cretaceous and Tertiary age. Over 45,000 ft (13,716 m) of sediment was deposited in the deepest trough and extensive basinal areas are underlain by more than 20,000 ft (6,096 m) of sedimentary rocks. The depositional sequences include thick lacustrine shales and claystones, floodplain claystones, and lacustrine, fluvial, and alluvial sandstones and conglomerates. Those lacustrine claystones deposited in a suboxic environment provide good oil-prone source rocks. Reservoir sandstones have been found in a wide variety of nonmarine sandstone facies. The extensional tectonism that formed these basins began in the Jurassic(?)-Early Cretaceous. Movement along major fault trends continued intermittently into the Miocene. This deformation resulted in a complex structural history that led to the formation of several deep fault-bounded troughs, major interbasinal highs, and complex basin flanks. This tectonism has created a wide variety of structures, many of which have become effective hydrocarbon traps. During the past eight years, several important oil discoveries have been made. Significant accumulations have been delineated in the Heglig and Unity areas, where estimated recoverable reserves are 250-300 million bbl of oil.