Abstract
Preliminary palynological analysis of a Holocene peat bog from Apakara-tepui (Chimanta Massif, Venezuelan Guaya- na).- This paper reports the preliminary palynological results, at a millennial scale, of a Holocene peat bog sequence, since around 8.0 cal kyr BP to the present, obtained in the summit of the Apakara-tepui (2170 m elevation), in the Chimanta massif, located in the neotropical Venezuelan Guayana. The early Holocene was characterized by a vege- tation different to the present, in which trees and shrubs dominated and Myrica (Myricaceae) was the main element of the gallery forests around a permanent water body, as indicated by the continuous presence of Isoetes (Isoetaceae) in high percentages. Around the middle Holocene (5.3 cal kyr BP), a shift towards more herbaceous and non-flooded communities occurred, and the present day vegetation established. This has been interpreted as a shift from warmer and wetter climates to cooler and drier conditions. The first phase, from 8.0 to 5.3 cal kyr BP, falls within a warming phase widely documented worldwide, known as the Holocene Thermal Maximum. The millennial trends shown here will be refined with further studies at centennial to decadal time scales. These results support the hypothesis that the best sites to detect paleoenvironmental changes in the summits of the tabular Guayana mountains are close to altitudinal ecotones.
Highlights
Peat bogs in the summits of the table mountains from the neotropical Guayana Highlands (Fig. 1) have been considered a priori excellent locations to record late Pleistocene and Holocene paleoecological and paleoenvironmental changes, due to its pristine nature, which excludes human interference (Rull, 2007a; 2010)
Localities situated within the grasslands and far from this ecotone, as for example the other Chimantá sites, would be less useful to record paleoenvironmental changes (Rull, 2005a)
This paper reports a preliminary palynological study in the Apakará-tepui (Chimantá massif), which is close to the mentioned grasslandshrubland altitudinal ecotone, at an elevation similar to the Churí-tepui, where a conspicuous vegetation shift was recorded during the late
Summary
Peat bogs in the summits of the table mountains (tepuis) from the neotropical Guayana Highlands (Fig. 1) have been considered a priori excellent locations to record late Pleistocene and Holocene paleoecological and paleoenvironmental changes, due to its pristine nature, which excludes human interference (Rull, 2007a; 2010). Whereas most records from the summits of the Chimantá massif (Akopán-tepui, Amurí-tepui and Toronó-tepui) have shown heterogeneous patterns of change likely due to the dominance of local micro- and meso-climatic processes over general paleoclimatic trends (Rull, 2005a), other sequences (Churí-tepui and Guaiquinima massif) suggested vegetation shifts linked to temperature and moisture variations of potential regional extent (Rull, 2004; 2005b). The better suited sites to document paleoecological shifts associated to climate changes were considered to be close to key altitudinal ecotones, and the highest mountaintops (Rull, 2005a). Localities situated within the grasslands and far from this ecotone, as for example the other Chimantá sites, would be less useful to record paleoenvironmental changes (Rull, 2005a). A study in one of the highest Chimantá mountaintops (Eruoda-tepui) showed remarkable vegetation constancy during the Holocene; ecotonal localities seem to be the preferred tepuian sites for paleoecological reconstruction (Nogué et al, 2009a)
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