The geology of Antigua and Barbuda is part of the Lesser Antilles volcanicisland arc. Both islands are the above water limestone "caps" of now inactive volcanoes. The two islands are the surface features of the undersea Barbuda Bank and have karstlimestone landscapes.[1]
Barbuda is primarily flat and formed from coral reefs. The Middle Miocene Highlands Formation has limestones which are the oldest rocks on the island, rising 120 feet above sea level. The Beazer Formation and the Codrington Formation are both from the Pleistocene and include reef and lagoon related rocks.[2]
On Antigua, the south of the island is mainly calc-alkaline volcanic rock such as dacite and quartz basalt or andesite, along with limestone lenses, agglomerate and tuff formed during the Oligocene.[4] Generally andesite dominated volcanism across the island gave way to limestone and chert formation.[5]
^Brasier, M. D.; Mather, J. D. (1975). "The stratigraphy of Barbuda, West Indies | Geological Magazine | Cambridge Core". Geological Magazine. 112 (3): 271. doi:10.1017/S0016756800047026. S2CID130933554.
^Donovan, Stephen (6 July 2017). "The geology of islands". depositsmag.com. Deposits Magazine. Retrieved 13 October 2019.
^Donovan, Stephen K.; Jackson, Trevor A.; Harper, David A.T.; Portell, Roger W.; Renema, Willem (2014). "The Upper Oligocene of Antigua: the volcanic to limestone transition in a limestone Caribbee". Geology Today. 30 (4): 151–158. Bibcode:2014GeolT..30..151D. doi:10.1111/gto.12061. S2CID140649360.