Ice age at the Middle-Late Jurassic transition?

Details Ice age at the Middle-Late Jurassic transition? Ice age at the Middle-Late Jurassic transition?

Aug 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003e%26psl.213..205d&link_type=abstract

Earth and Planetary Science Letters, Volume 213, Issue 3-4, p. 205-220.

Computer Science

17

Scientific paper

A detailed record of sea surface temperatures in the Northern Hemisphere based on migration of marine invertebrate fauna (ammonites) and isotopic thermometry (δ18O values of shark tooth enamel) indicates a severe cooling at the Middle-Late Jurassic transition (MLJT), about 160 Ma ago. The magnitude of refrigeration (1-3°C for lower middle latitudes) and its coincidence in time with an abrupt global-scale fall of sea level documented through sequence stratigraphy are both suggestive of continental ice formation at this time. Ice sheets may have developed over the high-latitude mountainous regions of Far-East Russia. The drastic cooling just post-dated the Middle-Late Callovian widespread deposition of organic-rich marine sediments (e.g. northwestern Europe, Central Atlantic, and Arabian Peninsula). This thermal deterioration can thus be ascribed to a downdraw in atmospheric CO2 via enhanced organic carbon burial which acted as a negative feedback effect (i.e. the inverse greenhouse effect). The glacial episode of the MLJT climaxed in the Late Callovian, lasted about 2.6 Myr, and had a pronounced asymmetrical pattern composed of an abrupt (~0.8 Myr) temperature fall opposed to a long-term (~1.8 Myr), stepwise recovery. The glacial conditions at the MLJT reveal that atmospheric CO2 levels could have dropped temporarily to values lower than 500 ppmv during Mesozoic times.

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