Fossil Sites and Paleopedology Abstract
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AN OVERVIEW OF THE TERRESTRIAL EARLY TERTIARY OF SOUTHERN NORTH AMERICA- FOSSIL SITES AND PALEOPEDOLOGY JUDITH A. SCHIEBOUT DEPARTMENT OF GEOLOGY LOUISIANA STATE UNIVERSITY ABSTRACT would have suggested. Evidently, neither Increasingly detailed stratigraphic work the slow-to-open North Atlantic nor the in intermontane basins from Montana to long distances were insurmountable bar Texas has revealed significant differences riers to many mammals before the end of between northern and southern early Ter the early Eocene. The Cretaceous interior tiary terrestrial faunas of western North seaway split North America and served as America. Paleontological data from south a barrier to migration between west and ern California, Mexico, New Mexico, and east Texas. The effects of this separation west Texas allows analysis of the effects of may have lingered throughout the Pale topography and climate on southern faunal ocene. distribution. Endemism in the Paleocene and Eocene of southern California and the INTRODUCTION Paleocene of west Texas can be attributed in part to geographic isolation. Observed Several recent developments make this differences between northern and south a good time to look both backwards and ern faunas are tied to climatic differences, forwards at the terrestrial Paleocene and which are traceable from locality to locali Eocene of southern North America. Are ty using paleopedology. For example, Pa vision of terrestrial Cenozoic chronology edited by M.O. Woodburne is in prepara leocene fluvial mudstones in west Texas and New Mexico show prominent red and tion and should be published within 1979 or 1980 (Woodburne, 1978, pers. comm.). black banding. Red layers are rich in soil Although many aspects of this summing up formed calcite nodules. Red color-banding of available data on Cenozoic chronology and nodules are not widespread in north will be highly controversial, it should serve ern localities until the early Eocene, indi as a reference point for decades, as tts cating a northward spread of warm, vari predecessor by Wood et al. (1941) did. A able climate. Migrations of animals, trig great deal of new stratigraphie data has gered by such climatic changes, may be become available recently. Detailed strati responsible for abrupt faunal changes m graphic studies such as those of Gingerich the northern intermontane basins. (1976) are making possible a much greater Early Tertiary fossil vertebrate sites are precision in examining past evol~bonary scarce east of the Big Bend region of Texas and paleoecologic events. New datmg and now but within a decade lignite strip min fossil-collecting techniques and changes m ing in east Texas, Louisiana, and Arkan the legal status of pre-Pleistocene fossils sas will be producing outcrops. The best also provide an increasingly detailed back hope for fmding extensive early Terltary ground against which attempts can be terrestrial faunas in eastern North Amen made to correlate paleontological data on ca lies in the Gulf Coast. animal distributions with information on The early Tertiary Gulf Coast may have small scale environmental changes, ~vail served as a source for new forms migrat able from studies of depositional environ ing to the west and north. The Paleocene ments and paleopedology. and early Eocene faunas of the southeast ern U. S. can be expected to have strong ADVANCES IN European affinities, and the late Eocene to TERRESTRIAL PALEONTOLOGY have close ties to western North Amenca. Screen washing for microvertebrat: The Paleocene faunas of west Texas show f~s sils (Hibbard, 1949; McKenna, 1962) IS m less resemblance to those of France, which creasing the value of vertebrate fossils as were similar in latitude, than the high de stratigraphic tools. It greatly mcrease~ gree of similarity of early Eocene animals sample sizes and recovers rare matena of Europe and western North Amenca 75 76 Tulane Studies in Geology and Paleontology Vol. 15 from sediments essentially barren to sur migration route (see summary of Berg face hunting and quarrying. For example, gren et al., 1978). a screen washing of approximately one ton Both problems and opportunities arise of sediment from a single Paleocene site in from changes in the legal status of verte west Texas yielded 19 genera (Schiebout, brate fossils and from extensive mining 1974), three times the total previously and other disturbances that will affect known from the whole formation (Wilson, early Tertiary terrestrial deposits more 1967). New techniques of sorting fossils and more frequently in the future. A de from concentrate (screen wash residue), bate is underway between federal officials such as the heavy liquid method reported and the paleontological community regard by Murray and Lezak (1977), will make ing the applicability of such legislation as this technique more and more useful. the Antiquities Act of 1906, the National New dating techniques and increasing Environmental Protection Act, and the application of old ones are producing a Moss-Bennett Bill to those paleontological more reliable framework for reconstruc materials not associated with anthropologi tion of early Tertiary events. For example, cal or archaeological material. The Nation radiometric dating of volcanic rocks in al Heritage Act of 1972 specifically includes tercalated with vertebrate-bearing sedi paleontological materials for protection, ments is producing better resolution of the and new legislation specifically aimed at age of many classic sites. A magnetic re providing salvage procedure for such fos versal scale for the terrestrial early Terti sils can be expected in a few years (Me ary is also being developed (Berggren et Kinney, 1978, pers. comm.). Marshall (1976) al., 1978; Lindsay et al. , 1978). provided a review of the legal status of pa Widespread acceptance of the idea of leontology in the U.S. at that time. plate tectonics has revolutionized paleo At present, regulation often means that geography and spurred interaction of pa scientists and conscientious amateurs are leocologists in testing reconstruction of excluded from areas where vandals and continental positions and latitudes. The re ill-trained amateurs continue to roam at cent work of Dawson et al. (1976) and West will. As the historical, scientific, and aes et al. (1977) in the Eureka Sound Forma thetic values of vertebrate fossils are grad tion of Ellesmere Island is an example of ually communicated to the bureaucracy "continental drift" providing incentive for responsible for regulating antiquities, bet investigation of a new and unusual area ter cooperation between government agen for vertebrate fossils. Drift theory and pa cies and scientists should develop. As pale leobotanical evidence had led McKenna ontologic remains come to be regarded as (1972a, 1972b, 1972c, 1975) to consider an a natural resource, they can no longer be early Tertiary North Atlantic migration blithely ignored by miners and land devel route for terrestrial animals between North opers. Availability of funds for survey and America and Europe. Dawson et al. (1976) salvage, long a boon to archeologists, is reported a small Eocene fauna of verte beginning to extend to paleontologists. An brates which supports the idea that a example is the Bureau of Land Manage warm temperate climate extended to 80° ment-sponsored survey in 1977 by the north latitude. A symposium entitled "Cen University of New Mexico and Louisiana ozoic History in and around the northern State University of 41/2 million acres of land Atlantic and Arctic Oceans" at the 1978 in the San Juan Basin (Kues et al. , 1977). Geological Society of America Annual Cretaceous and early Tertiary paleonto Meeting drew workers interested in recon logic resources threatened by coal strip structing early Tertiary conditions in this mining were the specific target of the region from a wide variety of disciplines. study (Fig. 2). Opportunities for employ The early Eocene (Wasatchian) mammali ment for paleontologists, particularly ver an faunas of North America show at last tebrate paleontologists, with governmental 50o/o generic similarity to those of Europe; agencies and industry are likely to increase such similarity is not repeated again and in the future and museums can expect drops to 10o/o in the Bridgerian (Dawson et large, sometimes overwhelming, increases al. , 1976), suggesting that this marks the in specimens recovered in salvage work. severance of the North America-to-Europe A concurrent flood of new data on the No. 3 Terrestrial Early Tertiary 77 7• Figure 1. Index Map to Paleontological and Paleopedological Localities. Paleocene: 1, G?ler Format~on locahty; 5, San Diego County; 6, Punta Prieta; 9, San Juan Basin ; 14, Big Be nd NatiOnal Park; 16, Caddo Parish. Eocene: 2 & 3 Ventura Basin· 4 Carlsbad· 5, ~an Diego; 7, Guanajuato; 8, Parras and La Popa B~sins; 9 San Ju;n Basin ; 10: Galisteo Formation locality; 11, Baca Formation locality; 12, Vieja; 13, Agua Fria; 14, Big Bend Nationa l Park; 15, Laredo; 17, Clark County; 18, Little Stave Creek; 19, Twiggs County. early Tertiary of North American can also well-known rock units and the names re be expected. main a link to western history. The redefi A fossil "gold rush" in the last quarter of nition now in progress should bring use of the 19th century set the stage fo r modern these terms more into line with modern work on the terrestrial early Tertiary of stratigraphic practice. From oldest to North America. Deposits that are still con youngest, the Paleocene is divided into the sidered the best terrestrial fossil-bearing following Land Mammal Ages: Puercan, Paleocene and Eocene sites in the world Torrejonian, and Tiffanian. The Eocene is were discovered in the Ame rican west, divided into the Wasatchian, Bridgerian, a nd fo ssils stream ed back from Wyoming, Uintan and Duchesnean. Some specialists Colorado, and New Mexico, to eastern consider the Clarkforkian wholly Eocene museum s. The Cope-Marsh feud raged, and others partly Paleocene and partly leaving a legacy of over-split early Tertiary Eocene.