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2009 Portland GSA Annual Meeting (18-21 October 2009)

Paper No. 11
Presentation Time: 10:30 AM

LATE DEVONIAN CONODONTS AND ASSOCIATED ISOTOPE GEOCHEMISTRY FROM NORTHWESTERN THAILAND


SAVAGE, Norman M., Geological Sciences, University of Oregon, 1272 University of Oregon, Eugene, OR 97403, RACKI, Grzegorz, Institute of Paleobiology, Polish Academy of Sciences, Twarda St. 51/55, Warsaw, PL 00-818, Poland, LUTAT, Petra, Palaeontological Research and Education Centre, Mahasarakham University, Mahasarakham 44150, Mahasarakham, 44150, Thailand and SARDSUD, Apsorn, Bureau of Fossil Research and Geological Museum, Department of Mineral Resources, Rama VI Rd., Ratchathewee, Bangkok, 10400, Thailand, nmsavage@uoregon.edu

An eleven-meter vertical section near the town of Mae Sariang, northwestern Thailand, has yielded conodont faunas of late Frasnian to late Famennian age. The section appears to include the Lower and Upper Kellwasser, Enkeberg, and the lower part of the Hangenberg events, as indicated by the conodonts and delta 13C isotope excursions. The faunas are mostly cosmopolitan but include several new species. The delta 18O isotope data are unreliable because of diagenetic overprint.

The 80 conodont faunas suggest the presence of the Late rhenana, linguiformis, triangularis, crepida, rhomboidea, marginifera, trachytera, postera, expansa, and praesulcata zones. The delta 13C pattern closely resembles the global carbon isotope pattern of Buggisch and Joachimski (2006). In the linguiformis Zone the delta 13C isotope data have values less than 0.9 but there are major positive spikes to between 3.0 and 4.0 during the Late rhenana and Early triangularis zones. In the succeeding samples the 13C values fluctuate with a general trend down to about 2.1 but with a positive spike to 3.1 in the Middle marginifera Zone and an increase to approximately 2.8 during what is thought to be the lower and middle praesulcata zones near the top of the section.

The Late Devonian Mae Sariang conodonts studied here are mostly cosmopolitan. The Mae Sariang section includes the global Lower and Upper Kellwasser, Enkeberg, and Hangenberg extinction events recorded in Europe, N. America, China, and elsewhere. The Late Devonian conodont zonation scheme used by many workers elsewhere is fully applicable in Thailand. The extinction event affects the d13C composition of seawater and the atmosphere, possibly because of changed ocean mixing, burial of d12carbon in sediments, anoxia, and sea level changes related to temperature fluctuations. There is some evidence that volcanic episodes may trigger these other changes and thus be a major part of global extinction events

Session No. 159

T84. Volcanism, Impacts, Mass Extinctions, and Global Environmental Change III
Tuesday, 20 October 2009: 8:00 AM-12:00 PM
Portland Ballroom 253 (Oregon Convention Center)
Geological Society of America Abstracts with Programs. Vol. 41, No. 7, p.419
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