Portland Group (geology)

Portland Group
Stratigraphic range: Tithonian PreꞒ Ꞓ O S D C P T J K Pg N ↓
Cliffs of the Portland Stone Formation on the western side of Portland Bill
Type	Group
Sub-units	Portland Stone Formation, Portland Sand Formation
Underlies	Purbeck Group
Overlies	Kimmeridge Clay Formation
Thickness	up to 75 metres (250 ft)
Lithology
Primary	Limestone, sandstone
Other	Mudstone, micrite
Location
Region	England
Country	UK
Extent	Dorset
Type section
Named for	Isle of Portland

The Portland Group (defining the Portlandian) is a Late Jurassic (Tithonian) lithostratigraphic group (a sequence of rock strata) in South East England.^[1] The name is derived from the Isle of Portland in Dorset where the strata are exposed and have been extensively worked. Rocks of this age have in the past been called the Portlandian stage by geologists, which corresponds with the late Tithonian stage of the internationally used geological timescale.