Tepui Peatlands: Age Record and Environmental Changes

Abstract

Peat deposits in tepui environment have been earlier described in the eastern part of the Venezuelan Guayana Highlands, focusing on peat dating and pollen analysis. The present study deals with the description, characterization, and dating of peat deposits on tepui and dome summits in the western Guayana Highlands, in contact with the Venezuelan Amazon Basin. No new peat data have been collected in these areas since our exploration missions in the early 1990s. This chapter focuses on the description of the sampling sites, the carbon-14 dating of selected peat layers, and the interpretation of the peat age record with respect to peat formation and environmental changes during the Holocene. Calibrated calendar ages stretch the initiation of peat accumulation back to ca 8400 calbp. Peat has been formed during the major part of the Holocene, but peat deposition was not constant. There are often important time gaps between consecutive dated peat layers, which are as large as 2000–4000 14C years. These gaps reflect depositional hiatuses that can result either from the interruption of peat accumulation because of climate change or from the truncation/removal of the peat cover through sliding. As a consequence, peat profiles are often polygenetic, resulting from more than one single accumulation phase. Ongoing (pseudo-)karstic activity provided periodically new depressions for water to concentrate and organic material to accumulate, so that peat inception was more diachronic than cyclic. There is a clear difference in the peat age–depth pattern before and after ca 4000 bp. The period around 4000 bp seems to be a time threshold in peat formation of broader significance in the regional context (Gran Sabana) as well as in the continental context (South America and Africa). Peat formation reflects a multiple environmental causality context, including climatic, vegetational, geodynamic, and hydrodynamic factors that induce variations in the peat cover. This makes it difficult to infer strict climatic changes at regional level and distinguish them from local-forcing causes, and calls for a multicriteria interpretation model to disentangle the history of the peat deposits in the Guayana Highlands.