Mid-Cretaceous marine microfossils preserved in fossil tree resin
Résumé
It has been postulated that, because of its terrestrial origin, amber could not have preserved marine organisms. However, investigation of Upper Albian/Lower Cenomanian amber from south-western France showed that this assumption is wrong. Several highly fossiliferous samples provided the first known amber-preserved marine microfossils. A plethora of marine diatoms has been discovered. More than fifteen different morphospecies have been found corresponding to twelve different genera. A lot of oxea of demosponges, a tetraxone and a microsclere of demonsponges have been found associated with this diatom flora. Two specimens of radiolarians, a foraminifer and a spine of a larval sea urchin complete the assemblage of marine microfossils found in the mid-Cretaceous amber of south-western France. Mixed coastal forests dominated by conifers of the Araucariaceae family, growing at the eastern rim of the young Atlantic Ocean, were the amber source. The peculiar resin pieces containing the marine inclusions solidified on the forest floor and not on the trees, as evidenced by numerous syninclusions of litter and soil dwelling arthropods and microorganisms. The occurrence of marine organisms in the resin suggests that the amber forest must have been temporarily influenced by the nearby sea. The coastal resinous Araucaria forests of New Caledonia can possibly be considered as a modern equivalent of the French Mid-Cretaceous amber forests. The nearby sea influences the resiniferous forest as the mid-Cretaceous amber forest of south-western France should have been influenced by the Atlantic Ocean. In these peculiar conditions, shells and remnants of marine organisms can easily be introduced by wind, spray or high tide from the beach or the sea into the abundant resin flows of these forests. Investigation of other ambers for marine inclusions might become relevant for dating of ambers.