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The Permian marks the transition between the end of the accretion of the supercontinent Pangea and the beginning of its dislocation. In the Eastern Pangea intertropical domain (i.e. the present-day Western Europe), the late-Paleozoic (i.e. uppermost Carboniferous–Permian) history remains poorly constrained due to the lack of precise radiometric data. This is particularly true for Permian basins from the southern part of the French Massif Central, making it difficult to determine correlations between basins and therefore robust timings and constraints on the environmental and climate events described in these basins, and to compare them with the larger-scale settings. This article focuses on the Saint-Affrique Basin, via an integrated petrological, geochemical and geochronological study of eight of the volcanic-ash levels interbedded in the sedimentary succession. It highlights the existence of two different groups of felsic volcaniclastic rocks. The first group, located at the base of the basin and attributed to the Stephanian continental stage, is related to a late-orogenic volcanic setting and corresponds to calc-alkaline trachy-andesitic tuffites that could not be dated due to the lack of volcanic zircon. The second group, located towards the top of the succession, is composed of calc-alkaline dacitic ash beds and tuffites yielding Kungurian ages, i.e. late early Permian (Cisuralian, $283.5\pm 0.6$ to $273.01\pm 0.14~\mathrm{Ma}$), and are attributed to a post-orogenic deposition setting. These ages show that the sedimentary filling of the basin is younger than hitherto expected (i.e. Artinskian, $290.1\pm 0.26$ to $283.5\pm 0.6~\mathrm{Ma}$). The elemental geochemistry, the presence of inherited detrital zircons and the Hf signatures of the volcanic ones indicate the involvement of an old (Proterozoic and older) basement in the magma genesis; this crustal contribution becomes more prominent towards the top of the sedimentary succession.

Clay mineral and stable isotope (C, O) data are reported from the upper Sinemurian (Lower Jurassic) of the Cardigan Bay Basin (Llanbedr–Mochras Farm borehole, northwestern Wales) and the Paris Basin (Montcornet borehole, northern France) to highlight the prevailing environmental and climatic conditions. In both basins, located at similar palaeolatitudes of 30–35 ∘ N, the clay mineral assemblages comprise chlorite, illite, illite–smectite mixed layers (R1 I-S), smectite, and kaolinite in various proportions. Because the influence of burial diagenesis and authigenesis is negligible in both boreholes, the clay minerals are interpreted to be derived from the erosion of the Caledonian and Variscan massifs, including their basement and pedogenic cover. In the Cardigan Bay Basin, the variations in the proportions of smectite and kaolinite are inversely related to each other through the entire upper Sinemurian. As in the succeeding Pliensbachian, the upper Sinemurian stratigraphic distribution reveals an alternation of kaolinite-rich intervals reflecting strong hydrolysing conditions and smectite-rich intervals indicating a semi-arid climate. Kaolinite is particularly abundant in the upper part of the obtusum zone and in the oxynotum zone, suggesting more intense hydrolysing conditions likely coeval with warm conditions responsible for an acceleration of the hydrological cycle. In the north of the Paris Basin, the succession is less continuous compared to the Cardigan Bay Basin site, as the oxynotum zone and the upper raricostatum zone are either absent or highly condensed. The clay assemblages are dominantly composed of illite and kaolinite without significant stratigraphic trends, but a smectite-rich interval identified in the obtusum zone is interpreted as a consequence of the emersion of the London–Brabant Massif following a lowering of sea level. Following a slight negative carbon isotope excursion at the obtusum–oxynotum zone transition, a long-term decrease in δ13Corg from the late oxynotum –early raricostatum zones is recorded in the two sites and may precede or partly include the negative carbon isotope excursion of the Sinemurian–Pliensbachian Boundary Event, which is recognised in most basins worldwide and interpreted to signify a late pulse of the Central Atlantic Magmatic Province volcanism. [ABSTRACT FROM AUTHOR]

High resolution clay mineral and stable isotope (C, O) data are reported from the upper Sinemurian (Lower Jurassic) of the Cardigan Bay Basin (Llanbedr [Mochras Farm] borehole, northwest Wales) and the Paris Basin (Montcornet borehole, northern France) to highlight the prevailing environmental and climatic conditions. In both basins, located at similar palaeolatitudes of 30-35° N, the clay mineral assemblages comprise chlorite, illite, illite-smectite mixed-layers (R1 I-S), smectite and kaolinite in various proportions. Because the influence of burial diagenesis and authigenesis is negligible in both boreholes, the clay minerals are interpreted to be derived from the erosion of the Caledonian and Variscan massifs, including their basement and pedogenic cover. In the Cardigan Bay Basin, the variations in the proportions of smectite and kaolinite are inversely related to each other over the entire upper Sinemurian succession. As in the Pliensbachian, the stratigraphical distribution reveals an alternation of kaolinite-rich intervals reflecting strong hydrolysing conditions, and smectite-rich intervals indicating a semi-arid climate. Kaolinite is particularly abundant in the upper part of the obtusum Zone and in the oxynotum Zone, suggesting more intense hydrolysing conditions likely coeval with warm conditions responsible for an acceleration of the hydrological cycle. This interval is also marked by a negative excursion of δ13Ccarb and δ18Ocarb, which may confirm a warmer palaeoclimate, although these excursions may be exaggerated or overprinted by the carbonate diagenesis. In the north of the Paris Basin, the stratigraphical succession is much thinner compared to the Cardigan Bay Basin site, and the oxynotum Zone is either absent or highly condensed. The clay assemblages are dominantly composed of illite and kaolinite without significant stratigraphical trends, but a smectite-rich interval identified in the obtusum Zone is interpreted as a consequence of the emersion of the London-Brabant Massif following a lowering of sea-level. A long-term decrease of δ13Corg from the late oxynotum/early raricostatum zones is also recorded in the two sites and may precede or partly include the negative carbon-isotope excursion of the Sinemurian/Pliensbachian Boundary Event, recognised in most basins worldwide, and interpreted as a late pulse of the Central Atlantic Magmatic Province volcanism. [ABSTRACT FROM AUTHOR]

The lacustrine-to-palustrine Pastos Grandes Laguna (Bolivia) is located in a volcanic caldera fed by active hot springs, with a carbonate crust extending over 40 km2. An integrated approach based on geology and hydrochemistry was used to characterize La Salsa, one of its hydrothermal systems, composed of a flat mound with a hydrothermal discharge. The mound is composed of carbonate–diatom aggregates, forming muds that accumulate and undergo slight swelling. The discharge area along the hydrothermal pathway exhibits several facies and microfabrics, with considerable biological activity and microbialite development. Both the downstream evolution of carbonate and silica content in sediments and the distribution of microbialites can be linked to changes in biotic-abiotic processes occurring along the pathway. The spatial distribution of microbialites and their morphologies are related to hydrodynamic conditions, the nature of the substrate on which they grow and, to a lesser extent, to the accommodation space available. The evolution of the physicochemical properties of the water and biological activity mainly impact mineral precipitation but also affect microbialite morphologies and microstructures. This atypical Si- and Ca-rich hydrothermal system therefore provides insights into the diversity of environmental, chemical, and biotic factors controlling mineralization, which also responds to independent thermodynamic controls. [ABSTRACT FROM AUTHOR]