The Honda Group (Spanish: Grupo Honda, Tsh, Ngh) is a geological group of the Upper and Middle Magdalena Basins and the adjacent Central and Eastern Ranges of the Colombian Andes. The group, in older literature also defined as formation, is in its present-day type section in the Tatacoa Desert in the department of Huila subdivided into two main formations; La Victoria and Villavieja. The group was originally defined in and named after Honda, Tolima, but has been redefined based on the many fossil finds in the Tatacoa Desert, 250 kilometres (160 mi) to the south. In the original type section of its occurrence, the 3,255 metres (10,679 ft) thick group is subdivided into three formations, from old to young; Cambrás, San Antonio and Los Limones. The group dates to the Neogene period; in its broadest definition from the Late Oligocene to Late Miocene, and in the redefined type section restricted to the Laventan age of the South American Land Mammal Ages (SALMA), equivalent to the Middle Miocene Serravallian epoch. The Honda Group is a Konzentrat-Lagerstätte at the fossiliferous La Venta site in the department of Huila and eastern Tolima and hosts one of the richest formations containing Miocene fauna worldwide.
Etymology and definitions
The group was first defined by Hettner in 1892 in the area of the town after which it is named; Honda, Tolima. In 1942 and 1946, the group was defined as a formation by Royo and Gómez. The first author who used the name Honda for a group, was American zoologist who studied the La Venta fauna in detail, Ruben Arthur Stirton. Subdivisions of the group have been proposed by many different authors with high detail in the different beds. Names as "Monkey Beds", "Fish Beds" and "Unit above Fish Beds" have been colloquially used to designate certain stratigraphic units based on their fossil content. The most accepted definition of the group, formations and members was proposed by Villarroel et al. in 1996 to simplify the stratigraphy in a regional sense solving the excessive subdivision into 19 units by Guerrero et al. (1994).
Regional setting Today, the sediments of the Honda Group are exposed in the Middle (Valle Medio del Magdalena, VMM) and Upper Magdalena Valley (Valle Superior del Magdalena, VSM) in an intermontane valley between the Central Ranges in the west and the Eastern Ranges in the east. The valley in between the two major orogenic chains is filled by the Magdalena River, the longest river of Colombia. The Upper Magdalena Valley geologically is subdivided into the Neiva Sub-basin with the Girardot Sub-basin of the southernmost Middle Magdalena Valley to the north, divided by the Natagaima Arch. The Neiva Sub-basin is bound by the Chusma Fault in the west and to the east by the west-verging Garzón Fault. The Mulato-Getudo Fault possibly underlies the Honda Group south of the La Miel River. The Tatacoa Desert, where the type section of the Honda Group has been redefined is an unusually dry region in Colombia, caused by a mountain induced rain-shadow effect. In Middle Miocene times, the geography was more comparable to the present eastern foothills of the Andes. The tectonic history of the three mountain chains of Colombia, from west to east, the Western, Central and Eastern Ranges has been studied in detail. The Western and Central Ranges were the first to be exhumed in the Paleogene, with minor uplifts in the Eastern Ranges at this age. The onset of the regional uplift of the Eastern Ranges is dated around the Middle Miocene, with an increased rate of exhumation between 12 and 3 Ma. This caused a segmentation of the current Magdalena Basins and the Llanos Basin to the east, previously part of a larger foreland basin to the east of the Central Ranges. The León Formation in the Llanos Basin provides the first indication of the tectonic uplift of the Eastern Ranges, isolating the Llanos Basin from the Magdalena Valley.
Description
Stratigraphy The Honda Group unconformably overlies in parts the volcanic deposits of the Prado Member, Barzalosa Formation of the Payandé Group, and in other parts the Saldaña, and Santa Teresa Formations. The unit is overlain by the Neiva Formation of the Gigante Group. The presence of a hiatus between the Honda Group and the Barzalosa Formation has been suggested. The group is characterised by two main formations; the lower La Victoria Formation and upper Villavieja Formation. Previously, the La Dorada Formation has been named as a subdivision of the Honda Group, while other authors define that unit as a member. Other names for members and formations are Cerbatana Member, also published as Cervetana Member, named after Quebrada La Cerbatana, Las Mesitas Formation, El Líbano Formation, Baraya Volcanic Member, named after Baraya, and Cerro Colorado Red Bed Member. The Perico Member of the La Dorada Formation has been made equivalent to the La Victoria Formation, as well as the El Líbano Formation.
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