First record of Early Devonian (Lochkovian) flora from the Santa Rosa Formation - Alarache, Southern Bolivia

Abstract

New information on plants and palynomorphs from Angosto de Alarache, South Bolivia, is presented. The plant remains appear at the base of the section. Dichotomizing sterile forms are assigned to Hostinella sp. and scarce stems terminated in spherical structures are interpreted as indetermined sporangia. The palynological association 1 recovered from this level contains abundant phytodebris, trilete spores, few cryptospores, algae, very poorly preserved chitinozoans, and other elements (fungi, ?lichens). Trilete spores assignable to Apiculiretusispora sp., Punctatisporites sp. and Retusotriletes sp., are obtained from the maceration of some isolated sporangia. The dichotomous branching of the stems and the trilete spores recovered from the isolated sporangia support its tracheophyte affinity. The palynological assemblage 2, obtained three metres above, contains abundant phytodebris and more diverse palynomorphs. Two new species (Retusotriletes albarinii n. sp., Acinosporites macgregorii n. sp.) are described. Based on the presence of the trilete spores Dictyotriletes emsiensis (ALLEN) MCGREGOR, Retusotriletes maculatus MCGREGOR and CAMFIELD, Apiculiretusispora plicata (ALLEN) STREEL and the absence, mainly of Verrucosisporites polygonalis LANNINGER and Urochitina loboi VOLKHEIMER et al., we propose a Lochkovian age but restricted up to the Late not latest Lochkovian, and the correlation with the lower part of the Emsiensis Zone of the Amazon Basin and the MN Zone of Western Europe. The abundance of fragmented stems of varied size and parallel to bedding planes, along with the isolated sporangia in the plant assemblage suggests a short distance transportation under low energy conditions, probably from marginal palaeoenvironments to low energy marine settings.