Cerbatana Gravels and Clays (Miocene of Colombia)

Where: Huila, Colombia (3.3° N, 75.2° W: paleocoordinates 2.6° N, 72.4° W)

• coordinate based on nearby landmark

• local area-level geographic resolution

When: Honda Group, Middle Miocene (16.0 - 11.6 Ma)

• Cerbatana Gravels and Clays

Environment/lithology: fluvial; lithified conglomerate and lithified claystone

• "The strata between the top of the El Libano Sands and Clays and the base of the Monkey Unit are included in the Cerbatana Gravels and Clays. This unit is composed of massive, torrentially bedded conglomerates with current-bedded sandstone and siltstone lenses. The richly fossiliferous San Nicolas clays exposed in the El Dinde and San Nicolas areas (map 2) are the largest of the silt and mudstone lenses and are part of the upper half of this unit. The basal part of the unit is composed predominantly of coarse sands and pebble conglomerates. Upward into the middle of the unit bedding becomes more torrential and the sandstones are replaced by pebble and granule conglomerates with scattered sandstone lenses. Iii the upper part, the beds become progressively more conglomeratic and torrential-bedding becomes extreme. Sandstones nevertheless persist (pl. 37, a) . The mudstone and siltstone Lenses vary greatly in thickness and lateral extent. Twenty-five or thirty lenses are present but only five are large enough to express on the geologic map.

•They occur sporadically through the section and show no definite evidence of gradational change. However, at the base of each of the five mapped lenses there is a basal concretionary sandstone.

•The conglomerates (pl. 37, a, b) are light-brown to brick-red. The darker colors usually correlate with larger detrital materials and are most abundant near the top of the unit. Individual beds vary from less than 1 meter to more than 10 meters in thickness. Most of the conglomerates in the basal part of the unit are pebble gravels, the fragments becoming progressively larger toward the top of the section, until in the beds immediately below the Monkey Unit the conglomerates are composed of large-cobble gravels. These gravels and conglomerates form prominent cliffs throughout the area and produce the headlands of many of the drainage patterns in the region. Sandstones in the Cerbatana unit are lenticular. Most of the lenses measure a few meters across (pi. 37, a), but a few can be traced for more than a kilometer. These larger masses show extensive cross-bedding of both diagonal and convex type, and are coarse- to fine-grained. Subangular to subrounded quartz makes up about 80 per cent of the mineral composition; feldspar, hornblende, micas, and metallic minerals are accessories. The sands are firmly packed but contain little or no calcareous cement. Near the base of the lenses, pebbles become more abundant and are usually oriented along the bedding planes. Finally, at the base, the sandstones grade into pebble gravels. Conversely, the upper parts of most of these strata contain thin silt and mudstone lenses and some have a concretionary upper surface (pl. 37, c; pl. 38 o,6). The interbedded clays and siltstones of the Cerbatana Gravels are more or less alike in color and mineral content. Beds vary from 10 or 15 centimeters up to about 2 meters in thickness. Rounded quartz grains make up 70 or 80 per cent of the identifiable mineral fraction. Amphiboles and metallic minerals account for the remaining determinable percentages. These sediments are relatively well indurated but weather quickly to form extensive badlands. Thin sandy beds are usually present in the siltstones. Thickness and lateral extent of the five mapped clay lenses are quite variable (fig. 2, secs. F-J). The richly fossiliferous San Nicolas Clays compose the thickest and most extensive lens within the Cerbatana unit. For the most part these clays are much like the other siltstone and mudstone lenses in the gravels. The lower part of the clays is sandy and rests upon a sandstone displaying large rounded concretions (pl. 37, c). The upper levels are progressively more silty and grade into clay near the top. The upper limit is marked by a massive, cross-bedded buff sandstone. Silt and clay beds in the San Nicolas Clays average about 25 centimeters in thickness." Description lithology taken from Fields (1959)

Size class: macrofossils

Collected by Fields

Primary reference: P. Bondesio and R. Pascual. 1977. Restos de Lepidosirenidae (Osteichthyes, Dipnoi) del Grupo Honda (Mioceno Tardío) de Colombia. Sus denotaciones paleoambientales. Asociación Geológica Argentina 17(1):34-43 [A. Cardenas /L. Mora-Rojas]more details

Purpose of describing collection: taxonomic analysis

PaleoDB collection 186805: authorized by Andrés Cardenas, entered by Laura Mora-Rojas on 04.07.2017

Creative Commons license: CC BY (attribution)

Taxonomic list

Osteichthyes
 Ceratodontiformes - Lepidosirenidae
Lepidosiren sp. Fitzinger 1837 Australian lungfish
UCMP 39645