Lower Ordovician (late Tremadocian?- Floian) palynomorphs from the Llanos Basin, Colombia: Biostratigraphic and paleogeographic significance

Abstract

Four core and fifteen cutting samples of well RH-2 from the Ordovician of the Llanos Basin, Colombia, were palynologically analyzed. They yielded mostly diverse and well-preserved marine palynomorph assemblages, dominated by acritarchs. Forty-six acritarch taxa and two chitinozoan species were identified. Palynological assemblages indicate an Early Ordovician, maximum Floian age, for the upper core samples and a late Tremadocian?- Floian? age for the lower cutting samples. Based on a thorough revision of the updated stratigraphic ranges of the taxa, and especially on the First Appearance Datums (FADs) of selected acritarch taxa such as Arbusculidium filamentosum, Arkonia, Barakella, Aureotesta clathrata simplex, Coryphidium bohemicum and Frankea, the age of the four upper core samples could be constrained to the middle to late Floian and the 15 cutting samples most probably to the late Tremadocian or early to middle Floian. The recognized chitinozoan taxa, Eremochitina brevis and Velatachitina veligera, support the interpreted ages. The presence of taxa such as Arbusculidium, Arkonia, Aureotesta clathrata simplex, Coryphidium, Dactylofusa velifera var. brevis, Frankea and Striatotheca confirm affinities with the Perigondwana Province. Eisenackidium orientalis which first appears outside the Early to Middle Ordovician basins of Argentina, could become a useful species for correlations among Eastern Gondwana Ordovician basins. The genus Frankea, considered as a biostratigraphic and paleogeographic component of the Perigondwana Province, is recorded for the first time in Eastern Gondwana, and its occurrence could represent one of the oldest worldwide records of the genus. The palynological results constitute a step towards the establishment of a biostratigraphic framework for the Ordovician of Colombia.