The European land mammal age, a continental biostratigraphic zonation for the Cenozoic, as ammonites for the Mesozoic and conodonts for the Paleozoic, classification starts after this age, the Thanetian is correlative with the MP2 to 5 of the Mammal Paleogene zone of Europe. At this time in geologic history the climate was at an all-time high with estimated tropical temperatures of 34 °C (93 °F) and 2000 ppm atmospheric CO2.[1]
The formation is locally referred to and geologically known as tuff, although the lithology of the formation is glauconiticsandstone, deposited in a shallow marine environment at the southernmost edge of the North Sea Graben.
The thickness of the unit varies from 10 metres (33 ft) (near Garbecque) to around 20 metres (66 ft) (in Arques, Quiestède, and Aire-sur-la-Lys) and sometimes more (24 metres (79 ft) at Helfaut and 26 metres (85 ft) at Blendecques). The thickness of the tuff intersperses with the Sables d'Ostricourt, giving a total thickness of the Landenian section of 35 to 40 metres (115 to 131 ft).[2]