Abstract
This paper presents the quantitative and qualitative results obtained from palynofacies and geochemistry analyses carried out on a core covering approximately 8000 years of sedimentation of a pond of altitude located at the mining district of Ametista do Sul, southernmost Brazil. The main objective of this paper is to consider the paleoclimatic and paleoenvironmental significance of these analyses. The hydrological isolation renders this pond climatically sensitive to variations in pluviometric regime and this enabled infer rainfall events during the early Holocene, which was responsible for the beginning of the processes of water accumulation in the gossan and the sedimentation of the pond. Changes in the pattern of moisture over the time become the drier environment, resulting in the intermittent pattern of water depth that currently exists at the site. The fluctuations in water depth are inferred from the frequency of Botryococcus and other algae, which tend to decrease progressively toward the top where the autochthonous elements are replaced by parautochthonous and allochthonous elements. Pseudoschizaea, in turn, appears to act as a biological marker of these transitional intervals. The present results are of great importance for understanding the extent of climate change and its environmental impacts at regional and global levels.
Highlights
Lakes can be viewed as dynamic response systems that integrate environmental, climatic and tectonic forces into a continuous and high-resolution archive of local and region al changes (Gierlowski-Kordesch and Kelts 2000).Organic matter (OM) constitutes an important fraction of the lake sediments, providing important information for the interpretation of lacustrine paleo-environments, the history of climate change and the effects of regional and local anthropogenic actions
Corresponds to the lower portion of the core (65-95 cm) and shows a predominance of fragmented basalts with yellowish-gray color occurring as coarse gravel mixed with sand and claysilty mud; this latter material most likely originated in superjacent levels and percolated through the basalt
The study produced the following conclusions: 1 - the granulometric texture of the samples favors the preservation of organic compounds, the relatively low concentrations of total organic carbon (TOC) and total sulfur (TS) at the lower and middle portion of the section reflect an oxic setting in the pond due to a low to moderate sedimentation rate
Summary
Lakes can be viewed as dynamic response systems that integrate environmental, climatic and tectonic forces into a continuous and high-resolution archive of local and region al changes (Gierlowski-Kordesch and Kelts 2000).Organic matter (OM) constitutes an important fraction of the lake sediments, providing important information for the interpretation of lacustrine paleo-environments, the history of climate change and the effects of regional and local anthropogenic actions. Meaningful reconstructions of the paleoenvironmental and climatic history of lacustrine deposits have been achieved in the last twenty years via palynofacies analyses combined with other methods of investigation of the tropical and temperate sedimentary records in different regions of the world (Siffedine et al 1994, 1995, 1996, 1998, Noel et al 2001). In the Holocene Brazilian lacustrine sedimentary records, organic matter analyses were obtained from multiple parameters (total organic carbon, Rock Eval pyrolisis, C/N determination, organic petrography, radiocarbon dating) and have proven their utility for paleo-climatic and paleoenvironmental reconstructions (e.g., Sifedine et al 2001, 2003, Ledru et al 2001, 2002, Tturcq et al 2002, Jacob et al 2004, 2005, Boussafir et al 2012)
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