Pleistocene plants from Zarzal Formation, middle valley of the Cauca River Basin, Colombia

Maria Alejandra Rojas-Granada,Juliana Guzmán,Arnol Cardozo-Rueda,Paula Andrea Sucerquia Rendon,Carlos Alberto Agudelo Henao

doi:10.4072/rbp.2021.2.03

Maria Alejandra Rojas-Granada, Juliana Guzmán + Show 3 more

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https://doi.org/10.4072/rbp.2021.2.03

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Abstract

We report macro and meso palaeobotanical records from the Zarzal Formation, in the Cauca River Depression, and the Quindío-Risaralda Basin between the Western and the Central Cordilleras of Colombia. The fossils correspond to leaves and seeds obtained from layers of mudstones, diatomites, and tuffaceous sandstones deposited in the inter-Andean valleys of Cauca and La Vieja rivers, separated by the Serranía Santa Bárbara ridge between the Valle del Cauca and Quindío departments. The sediments of the Pleistocene Zarzal Formation were deposited in a fluvial-lacustrine environment, with volcanic influence originated in the Central Cordillera to the east of the depositional area. The study here presented allowed the identification of thirteen morphotypes of leaf impressions grouped in six Angiosperm families: Poaceae?/Cyperaceae? and Araceae of the Monocots group, Melastomataceae, Fabaceae and Lauraceae belonging to the Eudicots group and one family of Lycopsida: Thelypteridaceae. On the other hand, very well-preserved silicified micro-seeds were grouped in eight morphotypes, belonging to the botanical groups Cyperaceae and Asteraceae. The fossils found allowed us to identify two types of plant associations that exhibit paleofloristic richness. In the Cauca River Basin, an autochthonous to parautocthonous plant association could correspond to a sub-Andean gallery forest, whilst in the La Vieja River Basin a parautocthonous plant association indicates a swamped floodplain. Keywords: paleoflora, leaves, seeds, Cauca River, La Vieja River, lacustrine deposit.

Highlights

In the intermountain valleys of the Cauca and La Vieja rivers sedimentary rocks of the Zarzal Formation (ZF) outcrop (Van Der Hammen & Hooghiemstra, 1997) (Figure 1)
Studies of Cenozoic fossil plants in the region of the middle valley of the Cauca River Basin are restricted to palynology of several units including Zarzal Formation (e.g. Van Der Hammen, 1958; Van Der Hammen & Hooghiemstra, 1997; Moreno-Sanchez, 2008; Suter et al, 2008; Bedoya & Giraldo, 2009; Neuwerth, 2012) and macrofossils from Miocene La Paila and La Pobreza Formations (Bedoya & Giraldo, 2009; Sanín et al, 2016) and Pliocene Mesa Formation (Botero, 2015)
Near the President landfill, San Pedro Municipality (Valle del Cauca), López et al, (2009) mentioned the presence of plant macrofossils in the area mapped by the Geological Service of Colombia (SGC) as La Paila Formation, and due to the diatom-bearing rocks associated, the authors considered the deposits of this area corresponding to the Zarzal Formation and not to La Paila Formation, but no paleontological study has been published of these fossil findings

Summary

Introduction

In the intermountain valleys of the Cauca and La Vieja rivers (central Andes of Colombia) sedimentary rocks of the Zarzal Formation (ZF) outcrop (Van Der Hammen & Hooghiemstra, 1997) (Figure 1). A detailed paleolimnological study characterizing and dating the paleolake implanted in the Cauca Basin during the Zarzal Formation deposition, was carried out by Jaramillo et al (2017), determining the taxonomy of diatom algae, and radiometric ages for tuffaceous sandstones. The results presented here constitute the first systematic classification of the fossil plant assemblages of the Zarzal Formation, through a descriptive systematic paleobotany, which help understanding some paleoecological relationships

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