|Exploring for Oil and Gas Traps|
|Series||Treatise in Petroleum Geology|
|Part||Predicting the occurrence of oil and gas traps|
|Author||Robert L. Fleisher, H. Richard Lane|
Biogeography is the study of patterns of the spatial distribution of organisms and their changes with time.
Major paleogeographic and climatic shifts through the Phanerozoic have produced frequent changes in biogeographic patterns of plant and animal distribution. The resulting biogeographic arrays can be used in two ways:
- To constrain paleogeographic reconstructions
- To interpret the nature of climatic change
Paleogeographic reconstructions based on geologic or geophysical evidence can be tested using patterns in the distribution of organisms. Analyzing the biogeographic patterns of fossils provides a basis for the proposal of new, and the evaluation of existing, paleogeographic reconstructions.
Examples of paleogeography
The occurrence of Lower Triassic reptiles and amphibians of the Lystrosaurus fauna in Antarctica, southern Africa, and India is strong confirmation that the Early Triassic Gondwana reconstruction, which placed Antarctica in contact with southern Africa and India, must be correct. Terrestrial vertebrates require dry-land connections to complete such a pervasive migration.
Australia's eventual separation from Gondwana to become an island continent about 43 Ma is also reflected in biogeographic patterns. The fossils and living marsupials of Australia are significantly different from those elsewhere because they evolved in isolation.
The distribution of benthic marine organisms can help us constrain latitudinal sea-surface temperature gradients and quantitative paleoclimate models.
Examples of climate
The total paleolatitudinal range of ancient reefs has been used as a guide to rate of change of sea-surface temperature with paleolatitude. This is based on a broad analogy with the distribution of modern reef corals. Because of the Late Ordovician Gondwana glaciation, the lower Silurian reefs are asymmetrically distributed. They did not reach as far south as 30°S paleolatitude but extended north of 30°N, reflecting the existence of a colder south polar region in the Early Silurian. This conclusion is also supported by the development of a cold-water Clarkeia brachiopod province in the early Silurian of Gondwana which is supplanted at lower latitudes by other faunal provinces.
Published interpretations of interior Australian surface temperatures during the Permian, reaching values as high as 50°C323.15 K
581.67 °R, cannot be reconciled with the existence of terrestrial vertebrates in the same area because such temperatures would have been lethal. A reassessment of this quantitative model is needed.
Problems such as the following can adversely affect biogeographic interpretations:
- Inconsistent taxonomic identifications by practitioners, impairing the validity of the basic data
- Difficulty in distinguishing local differences in the composition of fossil communities from those produced by geographic separation
- Development of accreted terranes, which may tectonically juxtapose contrasting biogeographic entities that were not naturally contiguous
- Stratigraphic and geographic distribution of fossils
- Temporal and environmental distribution of microfossils
- Taphonomy and provenance
- Colbert, E., 1972, Antarctic fossils and the reconstruction of Gondwanaland: Natural History, v. 12, p. 67–72.
- Jardine, N., and D. McKenzie, 1972, Continental drift and the dispersal and evolution of organisms: Nature, v. 235, p. 20–25, DOI: 10.1038/235020a0.
- Copper, P., and O. Brunton, 1990, A global review of Silurian reefs: The Palaeontological Association, London, Special Papers in Palaeontology 44, p. 225–259.
- Cocks, L., 1972, The origin of the Silurian Clarkeia shelly fauna of South America, and its extension to West Africa: Palaeontology, vol. 15, p. 623–630.