Paper No. 8
Presentation Time: 3:30 PM
WERE FOSSILS EXCEPTIONALLY PRESERVED IN UNUSUAL TIMES?
Exceptionally preserved fossil assemblages such as those of the Burgess Shale or Solnhofen Plattenkalk are commonly attributed to rapid burial or unusually anaerobic, saline, cold or arid local environments of preservation. Such mechanisms do not explain exceptional preservation of fish, insects, crustaceans and plants in the shallow marine to non-marine Grès á Voltzia (France and Germany), nor in coeval fish beds around the world, such as Bekkers Kraal (South Africa), Gosford (Australia), and Wapiti Lake (Canada). A global compilation with 4-m.-yr. temporal resolution of ages of thousands of localities with articulated fish, trilobites, crustaceans, insects, crinoids, or starfish, and with silicified and calcified wood, or cuticular preservation of fossil leaves shows 41 Phanerozoic modes, as follows (Ma in 2004 timescale): Lompoc (8), Clarkia (16), Chiavon (28), Florissant (34), Messel (49), Sheppey (54), Fur (64), Smoky Hill (84), Haqel (96), Laiyang (112), Liaoning (123), Purbeck (145), Solnhofen (150), La Voulte-sur-Rhône (163), Holzmaden (182), Bergamo (201), Coburg (217), Falang (228), Besano (237), Grès á Voltzia (245), Anaborano (251), Kupferschiefer (260), Tschekarda (271), Whitehill (284), Odernheim (300), Mazon Creek (309), Bear Gulch (324), Glencartholm (345), Cleveland (359), Canowindra (375), Achanarras (392), Hunsrück (407), Lesmahagow (428), Anticosti Island (440), Soom (448), Pencerrig (460), Portmadoc (478), Shineton (488), Mancetter (496), Burgess (508), and Chengjiang (520). Many were times of profound perturbations in the isotopic composition of carbon and sulfur, of mass extinctions, of era, period and stage boundaries, and of oceanic anoxic events. Many were times of elevated atmospheric carbon dioxide (from stomatal index), of increased rainfall and seasonality on land (from soil carbonate), and of global warming (from plant biogeography). Exceptional preservation was favored not only by local environments, but also by episodic global crises of atmospheric and aquatic dysaerobia. A steepened redoxocline in soils, lakes and oceans may have retarded aerobic decomposition and expanded opportunities for mass kills and permineralization. By burying carbon on unprecedented scales, mass kills may have saved the planet from runaway greenhouse heat sterilization.