Paper No. 6
Presentation Time: 9:35 AM
LETHALLY HOT TEMPERATURES DURING THE EARLY TRIASSIC GREENHOUSE
WIGNALL, Paul B., School of Earth and Environment, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, United Kingdom, SUN, Yadong, State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences (Wuhan), 388 Lumo Road, Wuhan, 430074, China and JOACHIMSKI, Michael M., Institute of Geology and Mineralogy, University of Erlangen, Schlossgarten 5, Erlangen, 91054, p.wignall@see.leeds.ac.uk
It is proposed that the Early Triassic world suffered some of the hottest ever climates with profound consequences for plant and animal life. Evidence comes from near sea-surface temperature (NSST) records derived from conodont phosphate apatite and fossil distributions at this time. Our oxygen isotope record comes from equatorial Tethyan conodonts from South China, especially the pelagic genus
Neospathodus estimated to have lived at water depths of 70 m. Following a rapid temperature rise across the Permo-Triassic boundary, Early Triassic NSSTs never dropped below 32
°C whilst the late Griesbachian and late Smithian stages saw peak values. Analysis of surface-dwelling conodont genera from the latest Smithian suggests SSTs reached exceptional values of 40°C. Annual SSTs in excess of 32°C are lethal for many organisms and temperatures >35°C will cause wholesale changes in ecosystem structure. Many aspects of Early Triassic paleoecology support these high temperatures.Tetrapods are excluded from equatorial latitudes during peak temperature intervals. Amphibians, a group that normally thrives in equatorial warmth, were entirely absent from the Early Triassic tropics but instead successfully radiated at higher latitudes. Similarly marine reptiles make their appearance at high latitudes at this time time but are absent from low latitudes.
Extreme warmth exerts a strong selection pressure for small organisms and a “Lilliput effect” has long been known in diverse Early Triassic groups.
Photosynthetic algae struggle to survive as temperatures rise above 32°C whilst cyanobacterial photosynthesis continues unabated even at temperatures >40°C. Biomarker evidence indicators a switch to cyanobacterial-dominated plankton populations at the start of the Triassic.
Terrestrial plant productivity was severely curtailed in the Early Triassic and re-establishment of peat formation only began in the later Triassic at higher latitudes.
