From crystalberry@hotmail.com Sun May 7 16:39:58 2000 Date: Mon, 01 May 2000 20:51:22 PDT From: Nancy Shieh To: vespirus@socrates.berkeley.edu Subject: paris basin final paper Brian Speers: sec.120 Paris Basin during the Eocene The Paris Basin, which surrounds present day Paris, is an important and interesting geological area. Through fossil finds, scientists have been able to reconstruct what that specific area of the globe was like during the Eocene Epoch, also known as the "Dawn of Recent Life." The Eocene, ranging from 36.6 million years ago to 57.9 million years ago, lies directly in the center of the Paleogene, the first half of the Tertiary Period. The Eocene is split into four ages: the Ypresian, Lutetian, Bartonian, and Priabonian Ages: the Ypresian Age being the earliest of the four. Scientists conclude from the fossil evidences that the Paris Basin during the early Eocene consisted of a wet river forest surrounded by a semi-deciduous forest or deciduous woodland, which was affected by dry periods in the year. This time was an acme of tropicality and angiosperm-dominated closed forests. In Northern Europe, diverse flora, taxonomically and perhaps vegetationally most similar to those now in tropical Southeast Asia existed. Much later in the Eocene, the climate began to dry, causing a change in the flora and fauna inhabiting the Paris Basin ecosystem. The Paris Basin was mostly lowlands, bordered by mountains on the southeast coastal area as well. In the later Eocene, the trees began to die as the climate warmed, leading to the appearance of grasslands. These grasses and small shrubs needed periodic burning to survive. At this time, the climate warmed as a result of tectonic movement and volcanic activity. The volcanic ashes that was sprayed into the atmosphere formed a layer that trapped the heat from the sun's radiation and prevented it from dissipating to outer space. As a result of the warmer climates and therefore greater frequency of fires, the selection of plant life that would survive these conditions led to the dominance of grasslands. Many fossils have been found in the Paris Basin that have been dated to this epoch. Most of them are examples of fossiliferous amber; amber that contains preserved specimens of life from that time. The flora of the area has been extensively researched through the discoveries of amber with individual or clusters of pollen grains, or lignified twigs, bulbs and galls. Other fossils include bones, teeth, feathers, hair and skin. Many teeth have been found with strange marking on them, which was to found to have occurred when they were ingested by the crocodiles of the time. In many locations fossils tend to be disturbed, so it is more difficult to determine where the organism actually lived or died. However, it seems that in the Paris Basin, most of the small plant and animal remains were only locally moved, so the fossil record can still be quite accurate. However, many of the large trees that were fossilized were rolled, so their exact location cannot be determined. The fossil record is very detailed in showing us the diversity of the flora and fauna of the Paris Basin during the Eocene. From the layers of strata corresponding to the earliest Eocene ages, the Ypresian in particular, we can clearly see the many types of species sharing this environment. Plants with angiosperm-like pollen, as seen in the fossiliferous amber, dominated the plant life in the early Eocene. These plants were mainly dicotyledons. Monocotyledons, such as the palms, and gymnosperms were also present, but the most common plant species found was an amber-producing tree related to the Aulacoxylon sparnacense. Middle to late Paleocene, there was a great range of sizes of angiosperm diasporas. There were more of the species with diasporas suited to dispersal by small animals. A hypothesis was developed, in which there is a co-evolutionary radiation relationship of large biotically dispersed angiosperms and the number of species of fruit and seed eating mammals. During the early Eocene, insects were abundant in this area, as the fossil specimens show. Over fifteen thousand different insect-containing amber samples have been collected, and from those over three hundred different insect species have been identified. Most of these are hexapods, mites, spiders, and pseudoscorpions. An increase in number of insect families throughout the Paleocene, as in moths and butterflies in middle Eocene, is the reason for the success in the pollination mechanism of angiosperms. Amphibians and reptiles have also been found, although amphibians are rare. The amphibians that have been classified are dominated by urodeles, and a species of Koaliella is known to have been present. The presence of amphibians confirms the hypothesis that freshwater played an important role in sustaining the environment. The twenty-two species of reptiles also found help to establish the idea that the palaeoclimate was warm and wet during the early Eocene. Twenty-four species of mammals belonging to twenty families have also been discovered in fossils from the early Eocene. In the later Eocene, hoofed animals such as sheep, goat, camels, pigs, cows, and deer took over as the trees gave way to grass in the drying climate. In the rise of the mammals, initially rather small and similar looking, specialized anterior dentitions implies selection and processing of small food items- fruits, seeds, and small prey. In west North America and Europe, a shift towards increasingly open savanna-like vegetation, (plants of lower stature) led to a concurrent trend among mammalian herbivores with increased body size. Larger forms don't have dental specialization, because they needed vegetation resources, and there was a large variety available. In addition, more open vegetation due to increased seasonality created opportunities for many lineages to develop features of open-country bulk feeders, which in turn maintained suitable conditions for weedy plants, particularly herbaceous angiosperms - coevolution. As a result of major biotic interchange between north America and Europe, homogenization of mammalian faunas in the northern hemisphere occurred. For example, ungulates, artiodactla and perissodactyla (oddtoed) appeared at the northern hemisphere at the beginning of the Eocene, major radiation accompanied by the trend toward larger body size. Geology: Paris Basin In the Paris Basin, silica-filled profiles are 2-3 meters thick. There are two distinct types of material, one called "massive type" (that maintains the primary structures of the sedimentary material) and a "nodulas type" that is a lumpy texture characteristic, with intermittent differentiating appearances along the rock body, and contains pedological structures (material for the scientific study of soils). Examining the geochemistry and mechanism of the formation of these silifications help with reconstruction of the paleoenvironmental conditions surrounding their development. The study of the Paris Basin geology is based upon observation and samples from the site for laboratory study. There is evidence of marine withdrawal at the end of the Upper Cretaceous in the South Paris Basin. The climate was warm and humid until the end of Paleocene. The withdrawal of the seas from Cretaceous to Eocene accounts for the kalolinite-rich deep weathered profiles. Leaching was the main weathering process. We are sure of this weathering process from evidence of the mixture of materials from different startigraphic horizons resulting in varying deposits (flint breccia to flint gravel, clay deposits and lacrustrine limestone). The silcrete (silicified geologic material) distribution reflects the occurrences of the paleosurface. In the Southern Paris Basin, silcretes are mainly residual and crop out in a scattered fashion, to allow construction of the paleolandscapes. The distribution of the silicious material in many regions of Western Europe corresponds to the relatively stable continental area of Southern border of the North Sea Basin during the Tertiary. It is the stability that led to the development of these silcretes. During the Eocene period, tectonic activity occurred, and climate changed to a pronounced dry season. This is shown by evidence of the thick gypsum deposits in the center of the basin. Lack of vegetative cover gave rise to significant erosion. In the middle Eocene, it became more arid and there was evaporation and diminishing of downstream drainage. Methods of study include mineralogical analyses and thin section preparation. In mineralogical analysis, samples were finely grounded in an agate mortar. This powder was "packed into Al holders against a rough paper sheet to achieve random orientation of particles for X-ray diffraction (XRD) analysis" (Thiry, 3). Data were recorded and qualitatively assessed. In thin section preparation, micromorphological studies used polarising microscopes, electron microprobes and wavelength-dispersive spectrometers. Conclusion By linking together the data obtained from geological studies and piecing this together with historical remains of ancient life (fossils), scientists are able to piece together a good idea of the area's paleoenvironmental conditions, landscape developments and ancient fauna, and give us a look at the Earth's gradual change from the past. Bibliography Behresmeyer, Anna K. et al. "Terrestrial Ecosystems Through Time: Evolutionary Paleoecology of Terrestrial Plants and Animals." The University of Chicago Press, Chiago and London, 1992 Nel, Andre. et al. " Un Gisement Sparnacien Exceptionel e Plante, Arthropodes et Vertebres: le Quesnoy." Sciences de la Terre et des Planetes. Vol 329 n. 1 July 15, 1999 Pomerol, Charles. Les Sables de L Eocene Sperieur Des Bassins de Paris it de Bwxelles Imprimene Nationale: Paris, 1965 Thiry, Medaer, Simon-Coinccon, Regine. "Tertiary Paleoweatherings and Silcretes in the Southern Paris Basin." Catena. (1996) Vol.26 p1-26 ________________________________________________________________________ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com