Cretaceous resinous interval

Cornupalpatum burmanicum preserved in amber from Myanmar that was deposited during the Early Cretaceous.

The Cretaceous resinous interval (CREI) was a period of time where there was a high rate of resin production creating large deposits of amber. It occurred during the Cretaceous period for about 54 million years from the Barremian to the Campanian ages. The cause was a mix of both living and environmental factors. High temperatures from volcanic activity and increased Carbon dioxide (CO2) levels fueling large storms and wildfires caused ice to be absent from the poles and favored the growth of resin-producing forest at high latitudes.

While there is a preservation bias for amber deposits to be more preserved in the northern hemisphere, it is suspected that this was a global phenomenon. The overrepresentation of amber deposits in the northern Hemisphere compared to the southern Hemisphere makes amber deposits found in the southern hemisphere during this time valuable for reconstructing the palaeobiology and biodiversity of forest on Gondwana.

Cause

Map of annual temperature in Celsius during the Cretaceous period around 90 million years ago.

The cause of the Cretaceous resinous interval was complex involving both abiotic and biotic factors. It is still being studied to the extent each of these factors had in the cause of this time period and likely requires a multidisciplinary approach. The environment played a large role for during the Cretaceous period. The global average temperature during the Cretaceous was higher due to an increased volcanic activity and Carbon dioxide levels, causing ice to be absent on the poles. This allowed for the development of forests to occur at higher latitudes. Heavy rainfall also favored the development of forest at higher altitudes with higher rates of resin production. Increased rates of wildfires, storms, and hurricanes causing damage to trees increase the amount of resin too.

Biotic factors played a large role during this time too. The high temperatures and humidity during this time caused pathogenic activity. Damage to the plants cause by arthropod species were a major factor in the production of resin. Resin also produces insect-attracting compounds which may explain the large amount of bioinclusions.

History

Prostylotermes kamboja preserved in Cambay amber which was deposited in India during the Eocene epoch.

Evidence of amber deposits have been found as far back as the Carboniferous period, but it was scarce, only appearing in small quantities and, save from some Triassic amber deposits, has not yielded macroscopic bioinclusions. The Cretaceous resinous interval began roughly 125 million years ago during the Barremian age. It would last for another ~54 million years before ending in the Campanian stage around 72 million years ago. Amber after the interval during the Maastrichtian age were widely distributed across the world, but scarce, appearing in small amounts and rarely yielding any bioinclusions.