Presentations for National and Southeastern Sections of Geological Society of America Meeting, March, 2000
Summit 2000 Meeting, GSA, Reno, Nevada
The role of paleobotanical and geological data in biogeographical studies of groups with limited fossil records: an example using Asteraceae.
The Asteraceae (Sunflower family) is one of the largest families of flowering plants (25-30,000 species) and has a worldwide distribution. Very few macrofossils representing Asteraceae have been reported and the family's fossil history has been based mainly on palynological data. Despite the lack of strong, direct, fossil evidence, trends in fossil flowers, the distribution of the closest families related to Asteraceae, and tectonic histories have been utilized to estimate a Middle to Late Eocene age for the family. This age estimate has been supported by studies using sequence data for Asteraceae as a "molecular clock". One of the most interesting aspects of the family's history is the sudden appearance of Asteraceae pollen in the Oligocene of South America, North America, Europe, and India. Ancestral area analyses, which utilize Camin-Sokal parsimony methods to determine losses and gains of areas on cladograms (Bremer, 1992), have suggested that Asteraceae had an ancestral area consisting of the Pacific and South America. Africa and Eurasia are not considered part of the ancestral area for the family. Fossil data (Graham, 1995) indicates that the family appeared later in the south Pacific. Furthermore, ancestral area analyses of tribal level phylogenies for the family strongly suggest that Africa played a key role in the early evolution of the family. Based on these results, biogeographical data from other groups, origin and position of anomalously thick oceanic crust, and Oligocene sea levels, it appears that Asteraceae may have radiated from South America to Africa.
A JACKSONIAN MOLLUSCAN FAUNA FROM CENTRAL GEORGIA: CLAIBORNIAN RELICTS OR JACKSONIAN NEWCOMERS?
DEVORE, Melanie, Dept. Biological and Environmental Sciences, Georgia College and State University, Milledgeville, GA 31061, email@example.com; FREILE, Deborah, Dept. of Geology, Berry College, Mount Berry, GA; PARMLEY, Dennis, Dept. Biological & Environmental Sciences, Georgia College & State University, Milledgeville, GA 31061
The middle section of the Riggins Mill member of the Clinchfield Formation (Barnwell Group) is a poorly sorted, pebbly, argillaceous, highly fossiliferous, high silica content limestone. Numerous vertebrate remains have been collected from exposures in a kaolin mine near Gordon, Wilkinson County, Georgia. Ray dental plates, shark teeth, and bony fish remains, are abundant. Rarer vertebrate fossils from the locality include snake vertebra and diagnostic remains of large mammals. Molluscs are the dominant element of the invertebrate fauna. The Gordon site includes in situ oyster bioherms and a molluscan fauna including Ostrea georgiana, Periarchus, Plicatula, and Chlamys. Other elements of the fauna include a high percentage of bryozoans, as well as some gastropods, and corals. The presence of a well-preserved molluscan fauna at the Gordon locality is significant because of the key role molluscs play in Claibornian-Jacksonian boundary problems. Molluscs from the Barnwell Group appear to have more of an affinity to the molluscan faunas from sand deposits of Claibornian age than to those of the Jacksonian age (Huddlestun and Hetrick, 1985). Documentation of mollusca from the Gordon site, along with studies of the depositional environment, may provide insights to whether there are true morphological distinctions between the mollusca from the Gordon site and Claibornian molluscan assemblages or if the same fauna continued to flourish through the Eocene of Georgia.
DEPOSITIONAL ENVIRONMENT, LITHOLOGY AND TAPHONOMY OF AN EOCENE MARGINAL MARINE SECTION IN CENTRAL GEORGIA AND ITS MODERN ANALOGUE.
GARNER, Elizabeth, P., and FREILE, Deborah, Dept. of Geology, Berry College, Mount Berry, GA 30149, firstname.lastname@example.org; DEVORE, Melanie L., Dept. of Biological and Environmental Sciences, Georgia College and State University, Milledgeville, GA 30162
The Clinchfield Formation (Barnwell Group) was deposited during the Jacksonian transgression. A stratigraphic section from a quarry near Gordon, GA is compared to a core from the Holocene coastal plain from a tidal creek near Little St. Simons, GA. A detailed depositional environment is constructed for the Eocene section. Lithological characteristics and faunal assemblages are also described. A taphonomic analysis is also undertaken for both the ancient and the modern. Preliminary results from the Eocene section indicate a well preserved assemblage of phosphatized vertebrate hard parts (sharks teeth, ray dental plates and assorted vertebrate bone fragments) with a strong detrital angular component of a molluscan assemblage, primarily oysters (some in situ), and bryozoans. A very minor coral component is also present. Total assemblage components were measured using 25 cm squared quadrats and bulk random sediment sampling. To date the >2mm fraction consists primarily of molluscan (oyster) fragments [85.4% +/- 4.2%; range 79.7-89.8%]; bryozoan fragments [8.4% +/- 2.3% range 6.7%-11.7%]; shark teeth [2.8% +/- 1.9% range 1.0% -5.4%]; ray dental plates [1.5% +/- 0.9% range 0.7%-2.7%] and assorted bone fragments [2.0% +/- 2.4% range 0.0%-5.4%]. A very interesting aspect of the Eocene unit is its poorly sorted angular to sub-angular pebble and gravel quartz component which can comprise as much as 43.4% +/- 9.2% (range 32.1%-54.5%) of the >2mm fraction. This is good supporting evidence that the shoreline, at this time, was very proximal to the clastic provinance centers. Our results further support the idea that the coastal region during the Jacksonian was a marginal marine environment comprised of low lying and marshy areas. This is supported not only by the distribution and nature of components in the sediment, but also by the presence of vertebrate fossils such as large mammals and snake vertebra.
Presentation for AMERICAN SOCIETY OF PLANT TAXONOMISTS, August 2000
DEVORE, MELANIE L. Department of Biological and Environmental Sciences, Georgia College and State University, Milledgeville, GA 31061. - Tectonism and its impact on the biogeography of SouthAmerica.
Biogeographical patterns observed in floras are the result of a number of historical factors. Biogeographers have viewed tectonic events assignificant historical factors influencing patterns of species richness, endemism, and biotic history based on phylogenetic analyses. In many cases, biogeographers consider tectonic events in the context of major plate movements resulting in continental separation, convergence and generalized orogenic events. Other phenomena associated with major plate movements, as well as motions of smaller "microplates", have also had a considerable impact on theevolution of major groups and development of biota. In particular, plant evolution and floras of South America have been stronglyinfluenced by tectonic events on several scales. Microplate movements have played a significant role in the continental evolution of both the northern and southern margins of the continent. Hot spots and their associated aseismic ridges have also influenced the development of floras on both the eastern and western margins of South America. Finally, recent studies have indicated that the main Andean deformation consisted of a series of events starting in the Jurassic(Andes of Columbia-Ecuador) and continuing into the present. These events have resulted in segmenting the 9000 km mountain range intoseven sections. Each section has a distinct orogenic history of its own. The potential impact of these events on biota was examined using both distribution data and phylogenies of selected angiosperm groups. Although we think of the evolution of older groups being influenced by tectonics, younger families (e.g. Asteraceae and Calyceraceae) also have histories tied with tectonic events.
BOTANICAL SOCIETY OF AMERICA, AUGUST 2000
FREILE, DEBORAH* AND MELANIE DEVORE. Geology, Berry College, Mt. Berry, GA 30149, Department of Biological and Environmental Sciences, Georgia College and State University, Milledgeville, GA31061-0490. - Utility of petrographic thin section analysis of fossil plant material and associated sediments in taphonomicstudies: An example from the Oligocene of Texas.
Petrographic thin sections of the late Oligocene Catahoula Formation in Huntsville, TX show well preserved plant fragments including some with clear indications of permineralization. The plant fragments show primarily a reddish-brown low grade thermal maturation. Authigenic feldspar crystals, some within the organic fragments, are clearly visible. Other cements include chert and quartz. The highly variable lithology of the samples indicates the potential of a multiple provenance rock. Some grains are clearly volcanic in origin (including clear examples of volcanic glass clasts), others are clearly detrital (principally subrounded quartz and chert grains), while a few other quartz grains show the characteristic undulose extinction patterns of metamorphic quartz. The rock samples are either finely parallel laminated, very fine to fine grained, angular to subangular, and moderately sorted OR wavy laminated, fine to medium grained, subangular to subrounded, and moderately to well sorted. Accessory minerals include feldspars-exhibiting good twinning, altered micas, zeolites and nascent stage glauconitic globules. Some specimens show cementation by opal and clays; probably related to the diagenesis of volcanic ashes into silica and smectite. The Catahoula Fm. has been described as a primarily terrigenous, fluvial, deltaic, marginal unit. The presence of glauconite is an indication of shelf (60-550m depth) marine environments and/or a transgressive episode. The late Oligocene was a time of transgression after a period of lowest (-200 to -350 m relative to present) sea level. The rapid rise of sea level at the end of the Oligocene, increased erosion and sedimentation to the shelf, and catastrophic flooding events may all have contributed to the unusual circumstances in which glauconite is preserved as authigenic crystals within quartz grains and cements within the plant fragments. This contradicts previous descriptions suggesting that the fine laminations present in some members of the formation represent a terrestrial, oxbow lake, fluvial environment.