The Oliní Group (Spanish: Grupo Oliní, K₃k₅o, K2ol, Kso) is a fossiliferous geological group of the VMM, VSM and the eastern flanks of the Central and western flanks of the Eastern Ranges of the Colombian Andes. The regional group stretches from north to south across approximately 700 kilometres (430 mi) and dates to the Late Cretaceous period; Coniacian, Santonian and Campanian epochs, and has a maximum thickness of 287 metres (942 ft). Fossils of Eonatator coellensis have been found in the unit, near Coello, Tolima.

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Oliní Group
Stratigraphic range: Coniacian-Campanian ~87–75 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Type	Geological group
Sub-units	See text
Underlies	Córdoba Fm., La Tabla Fm.
Overlies	Güagüaquí Group  Loma Gorda Formation
Thickness	up to 287 m (942 ft)
Lithology
Primary	Radiolarite, siltstone, chert, mudstone
Other	Sandstone, limestone, conglomerate
Location
Coordinates	3°44′12.6″N 75°27′55.5″W
Region	VMM, VSM and Central, Eastern Ranges, Andes
Country	Colombia
Extent	~700 km (430 mi)
Type section
Named for	Quebrada Oliní
Named by	Peters
Location	Chaparral, Tolima
Year defined	1954
Coordinates	3°44′12.6″N 75°27′55.5″W
Approximate paleocoordinates	1.5°N 54.5°W / 1.5; -54.5
Region	Cundinamarca, Boyacá, Huila, Santander, Tolima
Country	Colombia
Paleogeography of Northern South America 90 Ma, by Ron Blakey

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The group was named in 1954 by Peters, and redefined by De Porta in 1965.^[1] The group was named after Quebrada Oliní in Chaparral, Tolima.^[2]

The Oliní Group is a geological group usually described as a whole due to the problematic lateral continuity,^[3] although in other cases the individual formations forming the group are used. Earlier names used were Lower Chert member, Upper Sandstone Member and Upper Chert member.^[4] According to Acosta and Ulloa (2002), the group is subdivided into, from bottom to top:

Fossils of the mosasaur Eonatator coellensis were found near Coello, Tolima in the Oliní Group.^[10][11]

The Oliní Group conformably^[12] overlies the Loma Gorda Formation of the Güagüaquí Group and is overlain by the Cimarrona Formation in the VMM, the Córdoba Formation in the Guaduas Syncline and the La Tabla Formation near Tocaima and in Huila and Tolima.^[8] The age has been estimated on the basis of ammonites to be ranging from Coniacian to Campanian. Stratigraphically, the lower part of the formation is time equivalent with the upper part of the Chipaque Formation and the Conejo Formation,^[13] while the upper portion correlates with the La Luna Formation and Guadalupe Group.^[14] The Oliní Group was deposited in a relative high sea level environment in an outer platform setting,^[15] following a sequence boundary, forming the base of the unit. The radiolarites of the Upper Lydite Formation represent a maximum flooding surface.^[16]

Type locality of the Oliní Group in Tolima

Northern- and southernmost outcrops of the Oliní Group
Type locality

The type locality of the Oliní Group is Quebrada Oliní in Chaparral, Tolima. The group is furthermore found over a large stretch in the eastern Central and western Eastern Ranges of Colombia, bordering the Magdalena River on both sides. The group crops out to the northwest of Vélez in the hanging wall of the El Minero Fault,^[17] around Caparrapí,^[18] in the footwall of the El Cámbulo Fault between Útica and Guaduas and in the Bituima Synclinal,^[19] where it is cross-cut by the Vianí Fault and occurs in the hanging wall of the Alto del Trigo Fault,^[20] in the heavily faulted banks of the Magdalena River surrounding Guataquí and northwest of Coello and in the Eastern Ranges cross-cut by the Sumapaz River northeast of Ricaurte,^[21] in the hangingwall of the Salcedo Fault to the west of Apulo,^[22] on both sides of the Cucuana River near Ortega,^[23] in both the hangingwall and footwall of the El Páramo Fault east and south of Carmen de Apicalá and in the hangingwall of the Prado Fault,^[24] the hangingwall of the Quinini Fault west and south of Icononzo,^[25] the footwall of the La Pava Fault east and southeast of Chaparral,^[26] in the footwall and hangingwall of the Altamizal Fault east of Dolores, east and west of the Prado Reservoir near Prado,^[27] in the footwall and hangingwall of the Chusma Fault, west of Aipe,^[28] east of Alpujarra,^[29] in the footwall of the Baché Fault in Palermo,^[30] offset by the Picarní and San Andrés Faults,^[31] north of Yaguará,^[32] east of La Plata, Huila,^[33] and the southernmost exposure is found in Naranjal, where the group is emplaced by the Altamira Fault.^[34]

Geology of the Eastern Hills

Geology of the Ocetá Páramo

Geology of the Altiplano Cundiboyacense