Venado Formation

Venado Formation Stratigraphic range: Mid-Late Floian ~475–470 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Type	Geological formation
Unit of
Underlies
Overlies	Basement
Thickness	up to 670 m (2,200 ft)
Lithology
Primary	Shale
Other	Siltstone, sandstone, pyrite
Location
Coordinates	3°13′21.3″N 74°52′01.4″W / 3.222583°N 74.867056°W / 3.222583; -74.867056Coordinates: 3°13′21.3″N 74°52′01.4″W / 3.222583°N 74.867056°W / 3.222583; -74.867056
Region	Eastern Ranges, Andes
Country	Colombia
Type section
Named for
Named by	et al.
Location	Baraya
Year defined	1997
Coordinates	3°13′21.3″N 74°52′01.4″W / 3.222583°N 74.867056°W / 3.222583; -74.867056
Region	Huila
Country	Colombia
Thickness at type section	670 m (2,200 ft)

The Venado Formation (Spanish: Formación Venado, Oir) is a geological formation of the , in the Eastern Ranges of the Colombian Andes, cropping out along the in northern Huila. The sequence of pyrite containing dark grey micaceous shales interbedded with siltstones and sandstones dates to the Ordovician period; Middle to Late Floian epoch, and has a maximum thickness of 670 metres (2,200 ft) in the type section.

The unit is one of the few Early Paleozoic fossiliferous formations of Colombia; many graptolites of the genus Phyllograptus have been found in the Venado Formation. The graptolites are mostly found in the silty beds and indicative of a fair weather environment on a siliciclastic shallow marine platform at the northern edge of Gondwana. The shallow sea where the Venado Formation was deposited ranged into the deeper cold Iapetus and Rheic Oceans, separating the South American continent of the time from Laurentia, Avalonia and Baltica.

Etymology[]

The formation was first described by et al. in 1997 and named after the , a left tributary of the Cabrera River.^[1][2]

Description[]

The Venado Formation is one of few Ordovician formations outcropping in Colombia. The formation, part of the ,^[3] crops out on both banks of the Venado River in El Totumo, a vereda of the municipality Baraya in the department of Huila.^[4] The thickness of the Venado Formation proper at its type section is 670 metres (2,200 ft), put in faulted contact with an overlying 30 metres (98 ft) thin unit and an underlying 50 metres (160 ft) sequence.^[1] The series is unconformably overlain by the Jurassic .^[1][5] The Venado Formation has been correlated to the contemporaneous of the Central Ranges in Tarqui.^[6][7]

Lithologies[]

The Venado Formation comprises laminated dark grey micaceous shales, with intercalating siltstone levels and very fine sandstone beds. Calcareous concretions up to 1 metre (3.3 ft) in diameter are present. The shales frequently contain aggregates of pyrite. The formation is heavily folded and in a faulted contact with the Cretaceous Caballos Formation,^[3] at time of definition of the Venado Formation considered part of the Villeta Group.^[8]

Depositional environment[]

The Venado Formation was deposited in a shallow marine environment, on a siliciclastic platform with persistent normal wave action with repetitive storm wave activity.^[9] Anoxic conditions of the shallow sea probably led to the deposition of pyrite. The siltstone layers contain fragmented fossils of graptolites and are probably indicative of a fair weather environment and the coarser sediments resulted from episodic and rhythmic storms.^[10]

Paleogeography[]

During the Ordovician, the present-day area of northwestern South America was located in the southern temperate region. The cold^[11] Iapetus Ocean to the north of the South American terrane separated the landmass from Laurentia, most of present-day North America. The Rheic Ocean separated South America from the paleocontinents Baltica and Avalonia, that today is part of northeastern North America and northwestern Europe. North of the emerged continent of Gondwana, a shallow sea existed, bordering the Guyana and Brazilian Shields comprising the oldest crustal parts of the current South American continent.^[11] During this time in the Ordovician, Gondwana was experiencing an orogeny; the Famatinian orogeny, when the Iapetus Plate was subducting beneath Gondwana.^[12]

Fossil content[]

Fossiliferous formations of the Early Paleozoic are rare in Colombia. Apart from the Venado Formation, El Hígado Formation of the Central Ranges also in Huila, has provided fossils dating to the Ordovician, the Cambrian of the in Meta contains fossils of the trilobite Paradoxides,^[13] and the westernmost Ordovician unit in Colombia, in the Central Ranges of eastern Antioquia that provided four species of Didymograptus.^[14]

The formation has provided many fossils of graptolites; the most frequently occurring genus is Phyllograptus.^[15] Additionally, Villarroel et al. (1997) reported having found Lingulella sp. and Didymograptus cf. D. artus in the formation.^[5][9] The latter graptolite genus fossils have been assigned rather to by Gutiérrez Marco in 2006.^[16]

Regional correlations[]

Stratigraphy of the Llanos Basin and surrounding provinces

Ma	Age	Paleomap	Regional events			proximal Llanos	distal Llanos			Environments	Maximum thickness	Petroleum geology	Notes
0.01	Holocene		Holocene volcanism Seismic activity	alluvium								Overburden
1	Pleistocene		Pleistocene volcanism Andean orogeny 3 Glaciations		Soatá Sabana					Alluvial to fluvial (Guayabo)	550 m (1,800 ft) (Guayabo)		[17][18][19][20]
2.6	Pliocene		Pliocene volcanism Andean orogeny 3 GABI		Subachoque
5.3	Messinian		Andean orogeny 3 Foreland		Marichuela				Honda				[19][21]
13.5	Langhian		Regional flooding		hiatus					Lacustrine (León)	400 m (1,300 ft) (León)	Seal	[20][22]
16.2	Burdigalian		Miocene inundations Andean orogeny 2							Proximal fluvio-deltaic (C1)	850 m (2,790 ft) (Carbonera)	Reservoir	[21][20]
17.3										Distal lacustrine-deltaic (C2)		Seal
19										Proximal fluvio-deltaic (C3)		Reservoir
21	Early Miocene		Pebas wetlands						Barzalosa	Distal fluvio-deltaic (C4)		Seal
23	Late Oligocene		Andean orogeny 1 Foredeep							Proximal fluvio-deltaic (C5)		Reservoir	[18][21]
25										Distal fluvio-lacustrine (C6)		Seal
28	Early Oligocene									Proximal deltaic-marine (C7)		Reservoir	[18][21][23]
32	Oligo-Eocene				Usme		onlap			Marine-deltaic (C8)		Seal Source	[23]
35	Late Eocene									Coastal (Mirador)	240 m (790 ft) (Mirador)	Reservoir	[20][24]
40	Middle Eocene				Regadera				hiatus
45
50	Early Eocene									Deltaic (Los Cuervos)	260 m (850 ft) (Los Cuervos)	Seal Source	[20][24]
55	Late Paleocene		PETM 2000 ppm CO2		Bogotá
60	Early Paleocene		SALMA	Barco	Guaduas					Fluvial (Barco)	225 m (738 ft) (Barco)	Reservoir	[17][18][21][20][25]
65	Maastrichtian		KT extinction		Guadalupe					Deltaic-fluvial (Guadalupe)	750 m (2,460 ft) (Guadalupe)	Reservoir	[17][20]
72	Campanian		End of rifting										[20][26]
83	Santonian							Villeta/Güagüaquí
86	Coniacian
89	Turonian		Cenomanian-Turonian anoxic event		Chipaque	Gachetá	hiatus			Restricted marine (all)	500 m (1,600 ft) (Gachetá)	Source	[17][20][27]
93	Cenomanian		Rift 2
100	Albian				Une	Une		Caballos		Deltaic (Une)	500 m (1,600 ft) (Une)	Reservoir	[21][27]
113	Aptian				Fómeque					Open marine (Fómeque)	800 m (2,600 ft) (Fómeque)	Source (Fóm)	[18][20][28]
125	Barremian		High biodiversity		Paja					Shallow to open marine (Paja)	940 m (3,080 ft) (Paja)	Reservoir	[17]
129	Hauterivian		Rift 1		Las Juntas	hiatus				Deltaic (Las Juntas)	910 m (2,990 ft) (Las Juntas)	Reservoir (LJun)	[17]
133	Valanginian				Macanal Rosablanca					Restricted marine (Macanal)	2,935 m (9,629 ft) (Macanal)	Source (Mac)	[18][29]
140	Berriasian			Girón
145	Tithonian		Break-up of Pangea		Arcabuco					Alluvial, fluvial (Buenavista)	110 m (360 ft) (Buenavista)	"Jurassic"	[21][30]
150	Early-Mid Jurassic		Passive margin 2	La Quinta	Noreán	hiatus				Coastal tuff (La Quinta)	100 m (330 ft) (La Quinta)		[31]
201	Late Triassic												[21]
235	Early Triassic		Pangea		hiatus							"Paleozoic"
250	Permian
300	Late Carboniferous		Famatinian orogeny						()				[32]
340	Early Carboniferous		Fossil fish Romer's gap		Cuche (355-385)	()				Deltaic, estuarine (Cuche)	900 m (3,000 ft) (Cuche)
360	Late Devonian		Passive margin 1	Río Cachirí (360-419)					()	Alluvial-fluvial-reef (Farallones)	2,400 m (7,900 ft) (Farallones)		[29][33][34][35][36]
390	Early Devonian		High biodiversity	Floresta (387-400)						Shallow marine (Floresta)	600 m (2,000 ft) (Floresta)
410	Late Silurian
425	Early Silurian			hiatus
440	Late Ordovician		Rich fauna in Bolivia	(450-490)		()
470	Early Ordovician		First fossils		(>470±22)	()		()	() Venado (470-475)				[37][38][39]
488	Late Cambrian		Regional intrusions	(490-515)	()	()		(490-590)	()				[40][41]
515	Early Cambrian		Cambrian explosion										[39][42]
542	Ediacaran		Break-up of Rodinia		pre-Quetame		post-Parguaza		()	Yellow: allochthonous basement (Chibcha Terrane) Green: autochthonous basement (Río Negro-Juruena Province)		Basement	[43][44]
600	Neoproterozoic		Cariri Velhos orogeny	(600-1400)				pre-Guaviare					[40]
800			Snowball Earth										[45]
1000	Mesoproterozoic		Sunsás orogeny			(1000)			(1030-1100)				[46][47][48][49]
1300						pre-Ariarí	(1300-1400)		(1180-1550)				[50]
1400				pre-Bucaramanga									[51]
1600	Paleoproterozoic						(1500-1700)		pre-Garzón				[52]
1800							(1800)						[50][52]
1950							pre-Mitú						[50]
2200			Columbia
2530	Archean												[50]
3100			Kenorland
Sources

Legend

• group
• important formation
• fossiliferous formation
• minor formation
• (age in Ma)
• proximal Llanos (Medina)^{[note 1]}
• distal Llanos (Saltarin 1A well)^{[note 2]}

See also[]

• List of fossiliferous stratigraphic units in Colombia
• Geology of the Eastern Hills
• Geology of the Altiplano Cundiboyacense
• Iscayachi Formation, contemporaneous fossiliferous formation of Bolivia
• Pircancha Formation, contemporaneous fossiliferous formation of Bolivia
• San Lorenzo Formation, contemporaneous fossiliferous formation of Bolivia
• San Juan Formation, contemporaneous fossiliferous formation of Argentina
• Great Ordovician biodiversification event

Notes[]

References[]

Bibliography[]

• Borrero, C.; G.N. Sarmiento; C. Gómez González, and J.C. Gutiérrez Marco. 2007. Los Conodontos de la Formación El Hígado y su contribución al conocimiento del metamorfismo y la paleogeografía del Ordovícico en la Cordillera Central Colombiana. Boletín de Geología 29. 39–46. Accessed 2019-03-07.
• Chernicoff, Carlos J.; Eduardo O. Zappettini; João O.S. Santos; Shelley Allchurch, and Neal J. McNaughton. 2010. The southern segment of the Famatinian magmatic arc, La Pampa Province, Argentina. Gondwana Research 17. 662–675. Accessed 2019-03-07.
• González, Humberto. 2001. Mapa Geológico del Departamento de Antioquia - 1:400,000 - Memoria explicativa, 1–120. INGEOMINAS.
• Moreno Sánchez, Mario; Arley de Jesus Gómez Cruz, and Hardany Castillo González. 2008. Graptolitos del Ordovícico y geología de los afloramientos del Río Venado (norte del Departamento del Huila). Boletín de Geología 30. 9–19. Accessed 2019-03-07.
• Toro Toro, Luz Mary; Mario Moreno Sánchez, and Arley Gómez Cruz. 2014. Metagabro del Ariarí, plutonismo MORB, Cordillera Oriental de Colombia. Boletín de Geología 36. _. Accessed 2019-03-07.
• , C.; C. Macia S., and J. . 1997. Formación Venado, nueva unidad litoestratigráfica del Ordovícico colombiano. 22. 41–49. Accessed 2019-03-07.

Maps[]

• Acosta, Jorge; Pablo Caro; Jaime Fuquen, and José Osorno. 2002. Plancha 303 - Colombia - 1:100,000, 1. INGEOMINAS.

External links[]

• (in Spanish) Hallados en Colombia fósiles de hace 488 millones de años