The Tremp Formation (Spanish: Formación de Tremp, Catalan: Formació de Tremp), alternatively described as Tremp Group (Spanish: Grupo Tremp), is a geological formation in the comarca Pallars Jussà, Lleida, Spain. The formation is restricted to the (Catalan: Conca de Tremp), a piggyback foreland basin in the Catalonian Pre-Pyrenees. The formation dates to the Maastrichtian to Thanetian, thus the formation includes the Cretaceous-Paleogene boundary that has been well studied in the area, using paleomagnetism and carbon and oxygen isotopes. The formation comprises several lithologies, from sandstone, conglomerates and shales to marls, siltstones, limestones and lignite and gypsum beds and ranges between 250 and 800 metres (820 and 2,620 ft) in thickness. The Tremp Formation was deposited in