Sedimentary facies as indicators of Mesozoic palaeoclimate

Sedimentary facies alone provide equivocal, and qualitative, evidence about Mesozoic climates and climate changes. The most climatically informative sediments are laterites, evaporites and aeolianites. Tills would also be unequivocal where present. A range of other criteria (e.g. distributions of calcretes, gypcretes, vertisols, clay mineral species, storm deposits, glendonites and specific types of marine carbonates) provide supplementary evidence of climate, as does the distribution of wildfire-generated fusain. Sedimentary evidence must be integrated with other data. Coals, formerly considered to form in moist tropical climates, are now known to accumulate equally well in temperate mires. Oxygen isotopic data must also be critically evaluated in palaeotemperature studies, particularly because of possible diagenetic re-setting. Sedimentary rocks are the products of depositional and diagenetic averaging and seldom faithfully record the more subtle climate signals.