|
Site Map / Index This page last modified: 7th January, 2008 ©Paul Markwick 2000-2008 |
|
| Return to List of Conference Abstracts |
|
Markwick, P.J., D.B. Rowley, A.M. Ziegler, M.Hulver, P.J.Valdes and B.W. Sellwood (1999) Late Cretaceous and Cenozoic global palaeogeographies: mapping the transition from a "hot-house" world to an "ice-house" world Proceedings. Early Paleogene warm climates and biosphere dynamics, Göteborg, Sweden Abstract A set of Late Cretaceous stage-level and Cenozoic sub-epoch level palaeogeographic maps have been constructed for 20 intervals representing the last 100 million years of Earth History. Maps include five levels of terrestrial elevation: 0m (shoreline); 200m, 1000m, 2000m, 3000m; two levels of bathymetry: -50m and -200m; together with terrestrial ice extent. These maps provide boundary conditions for GCM experiments and a backdrop for terrestrial palaeo-ecological, -climatological, and -biogeographical studies, which are essential for understanding the palaeoclimatic transition from the "Hot-house" world of the Mesozoic and early Cenozoic, to the "ice-house" world of the Recent. The method of constructing these maps follows that of the Paleogeographic Atlas Project as described in Ziegler et al. (1985) , in which the observed relationship between modern elevation and tectono-physiographic and environmental settings, are used to assign values to similar settings in the Geological Record. The geological data used is derived entirely from the published literature, utilizing the large lithological and reference databases of the Paleogeographic Atlas Project (Chicago), the databases of Markwick, and the libraries of the University of Chicago and University of Reading. The original maps were drawn at Chicago onto A3 basemaps (approximately 1:100,000,000) on which were printed reconstructed plate outlines (the plate reconstructions are those of Rowley, 1995, unpublished work), a simplified present coastline, and a modern five degree grid (all rotated to their appropriate past position). They were all subsequently redrawn at a scale of 1:45,000,000 (Mollweide) and 1:30,000,000 (Polar orthographic). Contours were then drawn. First the shoreline, which of all the levels of elevation is perhaps the least controversial. The mapping of the other topographic contours assumes the following: 1. that the modern relationship between elevation and tectonics is an acceptable assumption for reconstructing past topography--uniformitarianism; 2 that mountain belts are generally long-lived features. Additional information, including sedimentological and palaeobiogeographical evidence, was used where available. These maps were then digitized as ARC/INFO coverages using polar projections for areas poleward of about 50-60°, and the Mollweide projection for the tropical and equatorial regions. Consequently these maps may be considered to be precise at about 1:30,000,000, but it is not recommended that they be enlarged above this scale. The resulting maps provide the opportunity for better understanding not only the interaction between geography, topography and climate, but also the role of geography in delimiting past biogeographic and biodiversity patterns. They highlight the coincidence of orographic changes, with the known palaeoclimatic cooling of the Middle and Late Eocene--the uplift of the Transantarctic Mountains, Rocky Mountains, and those of central Asia, coincident with increasing isolation of the Antarctic continent. Changes in the distribution of major mid-latitude seaways are also suggestive of a link with at least regional climate changes. The presence of highland (Gamburtsev subglacial Mountains) in East Antarctica continues to be problematic, since their great height might be assumed to be the locus of ice accumulation, even during 'hot-house' intervals. However, Markwick and Rowley (1998) have shown that even were these mountains glaciated above 1500 or 2000m it would only accommodate an icesheet comparable to a eustatic sea-level change today of about 8 or 2m, respectively, which would probably not be resolvable on a global scale in the geological record. It is also interesting to note that the initiation of glaciation of Antarctica in the Middle Eocene coincides with the continent moving slightly off of the pole. Markwick, P.J., and Rowley, D.B., 1998, The geologic evidence for Triassic to Pleistocene glaciations: Implications for Eustacy, in Pindell, J.L., and Drake, C.L., eds., Paleogeographic evolution and non-glacial eustasy, northern South America. SEPM Special Publication No.58: Tulsa, SEPM, p. 17-43. Ziegler, A.M., Rowley, D.B., Lottes, A.L., Sahagian, D.L., Hulver, M.L., and Gierlowski, T.C., 1985, Paleogeographic interpretation: with an example from the Mid-Cretaceous: Annual Review of Earth and Planetary Sciences, v. 13, p. 385-425. |
|