Parángula Formation
Geologic formation in Venezuela
From Wikipedia, the free encyclopedia
The Parángula Formation is a lithostratigraphic unit in the states of Barinas and Portuguesa[2] in Venezuela. It was deposited from the Oligocene to the Miocene.[3][1]
| Parángula Formation | |
|---|---|
| Stratigraphic range: | |
Holotype of Barinasuchus arveloi, recovered from the Parángula Formation | |
| Type | Geological formation |
| Underlies | Río Yuca Formation |
| Overlies | El Mene Formation |
| Thickness | 550–1,600 m[1] |
| Lithology | |
| Primary | Sandstone |
| Other | Shales, claystones |
| Location | |
| Approximate paleocoordinates | 9.3°N 66.1°W |
| Region | Barina, Portuguesa |
| Country | Venezuela |
| Type section | |
| Named for | Quebrada Parángula |
| Named by | Mackenzie, 1937 |
.svg)  Parángula Formation (Venezuela) | |
Research history
The Parángula Formation was first published about by A. N. Mackenzie in 1937, who used the name in reference to a series of sandstones, conglomerates, and mottled clays from the Parángula ravine.[4] In 1946, a further description of the formation's geology was published by R. A. Liddle.[5] In 1960, a thorough description of the stratigraphy of the Parángula Formation was published by G. R. Pierce. Pierce attempted to emend the name of the formation, renaming it to the Parángulo Formation,[6] though this was unsuccessful.[1]
Description
Stratigraphy
The lowermost layers of the Parángula Formation, those overlying the "El Mene" Formation, were deposited in the Oligocene epoch,[1] whereas the uppermost layers, those underlying the Río Yuca Formation, were deposited in the Miocene.[1][2] The surface layers of the Parángula Formation consist predominantly of coarse lenticular conglomerates, fine-grained sandstones deposited in massive layers, limonites, and mudstones, which may be red, reddish-brown, brown, or purple in colour. The layer immediately below the surface is similar but lacks conglomerates. Below that is a layer of basal sandstone, with certain elements, such as the presence of small amounts of glauconite, which suggest influence from marine sediments. Upper layers show a gradual increase in sand deposition, a likely result of debris accumulated from the uplifting of the Andes.[1]
Depositional environment
The uppermost strata of the Parángula Formation were likely deposited in a brackish environment.[1] Certain portions of the upper Parángula Formation, such as the Tucupido River site[2] (sometimes interpreted as part of the overlying Río Yuca Formation[1]) show signs of fluvial (river) deposition.[2] The Lexico Estratigrafico de Venezuela suggests that the depositional environment of the upper Parángula Formation was partly marine and may have sported mangrove swamps.[1]
Fossils
The Parángula Formation preserves a number of microfossils, many suggested to have been reworked from middle Eocene strata.[1] Fragmentary remains from small mammals, turtles, and caimans have been reported from the upper strata.[1][2] Two named taxa from different localities are found in the Parángula Formation, both from the upper Miocene.[2] One is a ground sloth, Pseudoprepotherium venezualanum, recovered on the banks of the Tucupido River in Portuguesa;[1][2] the other is a species of very large sebecid crocodyliform, Barinasuchus arveloi,[2] whose type specimen was recovered near a tributary of the Rio Masporro River during the construction of a road, and which was largely destroyed in the process.[7]