Holocene evolution of two ponds on the Devès Plateau in the French Massif Central

Abstract

The siliceous sub-fossil content (diatoms, chrysophyte cysts, sponges and phytoliths) of two cores was studied to determine the evolution and environmental changes that have occurred since the formation of two fenland lakes, Lac de Collanges and Lac de Freycenet, on the Devès Plateau, Massif Central, France. Cluster analyses determined eight siliceous zones, whereas a detrended correspondence analysis showed similar changes occurring in both sites, and principal component analysis identified four major shifts occurring over time at both sites, corresponding to the establishment of the fenland, the development of a pond and changes in the terrestrial environment. Four classic pollen zones previously determined for the French Massif Central were recorded in the core. The Boreal and beginning of the Old Atlantic period (9445-9250 cal bp) are marked by the development of the fenland, a decrease in pine trees and loss of grassland. The siliceous component was dominated by chrysophyte cysts indicating a cooler and lower trophic level. The Atlantic period (8365-7852 cal bp) saw maximum expansion of the fenland and the first occurrence and dominance of Aulacoseira perglabra (Østrup) Haworth, indicating higher water levels as a result of climate change. Increasing numbers of sponge spicules and the decrease in A. perglabra showed a shift to dryer conditions. During this phase, greater and more frequent droughts occurred in Collanges compared with Freycenet, most likely due to its smaller drainage basin. With the Subboreal, around 5000 cal bp, a change in conditions occurred: A. lacustris (Grunow) Krammer became the most important centric diatom and phytoliths became an important component. Pine trees increased and total herb and grasses became more important. The increase in total herb and grass pollen, along with the major increase in phytoliths, indicated an increase in human agro-pastoral activity within the area. The Subatlantic saw a decrease in water levels with periods of desiccation. A cyclic pattern of wet and dry phases was documented by a diatom increase in regularly moist and mostly moist subaerial environments. Including counts of phytoliths, sponges and chrysophyte cysts with diatoms allows better interpretation of the changes occurring over time within the area and permitted determination of the arrival of human agro-pastoral activity. The other three groups, namely phytoliths, sponges and cysts, were particularly useful when certain samples contained very few or were totally devoid of diatoms.

The Late Quaternary flora, vegetation and landscape of the Massif Central (France) under climatic and anthropogenic constrains

“…In this context lots of geomorphological, palynological, diatomological, macrofossil, as well as palaeoecological studies were performed since the late 1990s by the research group of Hervé Cubizolle at the University of Saint-Etienne (France), thanks to the interdisciplinary environmental PIREN-Program ("Programme Interdisciplinaire de Recherches sur l'Environnement") of the French National Research Centre (CNRS), which since 2001 became the "Zone Atelier Loire". This research was also supported by the Regional Directorate of Cultural Affairs (DRAC), the AGES program ("Ancient Geomorphological Evo-lutionS of the Loire"), and the "Etablissement Public Loire" (Argant and Cubizolle, 2005;Cubizolle, 2005;Cubizolle et al, 2005Cubizolle et al, , 2012Cubizolle et al, , 2013Cubizolle et al, , 2014Cubizolle et al, , 2015Cubizolle et al, , 2016Serieyssol et al, 2011Serieyssol et al, , 2012Dendievel et al, 2015Dendievel et al, , 2019Dendievel et al, , 2020Fassion et al, 2015;Dendievel, 2017). In addition, substantial palaeoecological studies concerned the formerly neglected areas, such as the Morvan Mountains (Jouffroy-Bapicot, 2010; Jouffroy- Bapicot et al, 2008Bapicot et al, , 2013.…”

From natural to cultural mires during the last 15 ka years: An integrated approach comparing 14C ages on basal peat layers with geomorphological, palaeoecological and archaeological data (Eastern Massif Central, France)

“…95 %) (Reimer et al, 2013;Stuiver and Reimer, 1993). On some sites, the best interval for peat initiation was calculated by integrated Lithological and Palaeoecological Syntheses (LPS) implying a detailed pollen, macrofossil, diatoms, geomorphological and radiocarbon study at: La Narce du B eage (Dendievel et al, 2019), La Sauvetat, Le P echay, and Marais de Limagne (Beaulieu et al, 1984); Ribains, Collanges, Freycenet, and La Gimberte (Serieyssol et al, 2012;Tourman, 2007). Information was also obtained from textual archives (ARCH) for very recent mires (75e15 years cal.…”

6700 years of diatom changes related to land use and climatic fluctuations in the Lake Aydat catchment (Auvergne, France): Coupling with cyanobacteria akinetes, pollen and non-pollen palynomorphs data

“…The earliest diatom studies were the study of Frère Héribaud with the study of diatomite deposits and travertines in many areas of the Massif Central (1883,1902,1903,1908). Some other studies were done in fenlands (Cubizolle et al, 2005;Serieyssol et al, 2012) and peat bogs (Gandouin et al, 2016). In lakes, diatom studies have pertained mainly to Lake Pavin.…”