Reconstruction of a saline, lacustrine carbonate system (Priabonian, St-Chaptes Basin, SE France): Depositional models, paleogeographic and paleoclimatic implications (original) (raw)
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Sedimentology, 2022
Changes in sedimentary profiles and stratigraphic architecture over time in lake basins are shown to be relevant markers of climate changes in terrestrial palaeoenvironments. The stratigraphic architecture of the Priabonian (late Eocene)–early Rupelian (early Oligocene) Alès–Saint-Chaptes–Issirac saline lake system has been reconstructed from the sedimentological, biostratigraphic and magnetostratigraphic analysis of outcrops and well cores. As a function of the inflow–evaporation balance, three distinct depositional models have been proposed for the Priabonian Alès–Saint-Chaptes–Issirac lake system which is characterized by both fault-controlled and low-angle ramp-like margins: (i) freshwater to oligohaline lake; (ii) oligohaline to mesohaline closed-lake; and (iii) hypersaline, evaporitic closed-lake. Two major stages of lake spreading (middle Priabonian and late Priabonian–early Rupelian?) separated by two stages of significant lake closure represented by evaporite succession in the Alès Basin depocentre (middle to late Priabonian) have been evidenced. Regional tectonics and climate induced changes in inflow–evaporation balance of the lake and controlled the development of transgressive–regressive cycles with calcium-sulphate sedimentation during regression in the lake depocentre (Alès Basin) and during early transgression in lake margins (Saint-Chaptes and Issirac basins). The correlation between the palaeohydrological cycles inferred for the Alès–Saint-Chaptes–Issirac lake system and the regional climate changes of Priabonian stage, prior to the Eocene–Oligocene transition, strongly suggests that climate significantly impacted the nature of lacustrine depositional models and the depositional architecture of Palaeogene, syn-rift, saline lake basins from Western Europe.
BSGF - Earth Sciences Bulletin, 2022
The integrative analysis of a lacustrine carbonate succession from Butte Iouton hill (Vistrenque basin, SE France) brings new insights into depositional models and stacking patterns of oolitic saline lake margins and provides new details regarding the late Eocene paleogeography of southeast France. Depositional facies analysis and paleoenvironmental reconstructions allow reconstructing an oolitic lacustrine ramp model, displaying from the proximal to the distal areas: (1) shallow marginal saline lake domain with deposition of planar microbial laminites, and molluscan-ostracodal wackestone, (2) a more distal and open lacustrine environments with low to moderate energy characterized by the deposition of peloidal grainstones and (3) a domain of higher energy with accumulation of ooids mixed with peloids in the vicinity of the area of ooid production. Lake margin carbonate sedimentation dominantly occurred during stages of lake transgression while subaerial exposure surfaces developed during periods of negative inflowevaporation balance (forced regression). Carbon and oxygen isotopes together with vertical trends in salinity inferred from molluscan associations show that lake transgression does not result from increasingly positive freshwater-evaporation balance volume but from the combination of subsidence and outflow from neighbouring saline waterbodies. The Butte Iouton carbonate margin is part of a set of interconnected saline lakes, occupying continental basins from Languedoc and Rhodanian region during the Priabonian, with a siliciclastic-dominated sedimentation in the southern margin, sourced by erosion of Pyrenean reliefs, and a carbonate-dominated northern margin with significant oolitic sedimentation in high-energy nearshore area.
Holocene evolution of two ponds on the Devès Plateau in the French Massif Central
Diatom Research, 2012
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.
Archiv fur Hydrobiologie
With B figures, 3 tables in the text and 1 appendix .\bstract: AS a part of a rnultidisciplinary research prograrnrne in palaeoecology on the crater of Ribains (French Massif Central), pollen and diatonr analyses were undertaken. Results show rnajor chronological variability in both terrestrial and aigal comnrunities during the transition between the last interglacial (Eemian) and the last glacial (early Wûrm) periods. The end of the Eemian was marked by an expansion of Pirtus on the slopes of the lake and by a diatorrl cornmunity consisting of planktonic and eutrophic species indicating falling lake levels. Early Wtrm began with severe clirnatic degradation, characterized on the catchment by the sharp decline of the forest to the benefit of steppic species, and by the shallowing of the lake as indicated by the development of a larger littoral diatorn community and the dominance in the planktonic cor-nmunity by Aulacoseira subarctica. Subsequently warming-up occuned. as indicated by the developrnent of a Pirtus woodland and a retLrrn to higher lake-water levels as indicated by abundant densities of planktonic species. Another oscillation of the lake level torvards shallou'er depths rvas recorded by the development of aquatic macrophl'tes associated rvith a maximum developrnent of littoral diatoms. The last episode of the sequence presented here witnessed the expansion of thennophilous trees with the sin-rultaneous development in the lake of a planktonic and eutrophic diatorn assernblage characterizing hieher water levels and nutrient enrichment. On the whole, ' Authors' addresses: Environmental 0003-91 36 /sB/ 01 42-031 7 $ 6.s0 cr 1 998 E. Schweizerbart'sche Verlagsbuchhandlung, D-701 76 Stuttgart û) J @ q)
With B figures, 3 tables in the text and 1 appendix .\bstract: AS a part of a rnultidisciplinary research prograrnrne in palaeoecology on the crater of Ribains (French Massif Central), pollen and diatonr analyses were undertaken. Results show rnajor chronological variability in both terrestrial and aigal comnrunities during the transition between the last interglacial (Eemian) and the last glacial (early Wûrm) periods. The end of the Eemian was marked by an expansion of Pirtus on the slopes of the lake and by a diatorrl cornmunity consisting of planktonic and eutrophic species indicating falling lake levels. Early Wtrm began with severe clirnatic degradation, characterized on the catchment by the sharp decline of the forest to the benefit of steppic species, and by the shallowing of the lake as indicated by the development of a larger littoral diatorn community and the dominance in the planktonic cor-nmunity by Aulacoseira subarctica. Subsequently warming-up occuned. as indicated by the developrnent of a Pirtus woodland and a retLrrn to higher lake-water levels as indicated by abundant densities of planktonic species. Another oscillation of the lake level torvards shallou'er depths rvas recorded by the development of aquatic macrophl'tes associated rvith a maximum developrnent of littoral diatoms. The last episode of the sequence presented here witnessed the expansion of thennophilous trees with the sin-rultaneous development in the lake of a planktonic and eutrophic diatorn assernblage characterizing hieher water levels and nutrient enrichment. On the whole, ' Authors' addresses: Environmental 0003-91 36 /sB/ 01 42-031 7 $ 6.s0 cr 1 998 E. Schweizerbart'sche Verlagsbuchhandlung, D-701 76 Stuttgart û) J @ q)
Sedimentology, 2017
Chemostratigraphic studies on lacustrine sedimentary sequences provide essential insights on past cyclic climatic events, on their repetition and prediction through time. Diagenetic overprint of primary features often hinders the use of such studies for palaeoenvironmental reconstruction. Here the potential of integrated geochemical and petrographic methods is evaluated to record freshwater to saline oscillations within the ancient marginal lacustrine carbonates of the Miocene Ries Crater Lake (Germany). This area is critical because it represents the transition from shoreline to proximal domains of a hydrologically closed system, affected by recurrent emergent events, representing the boundaries of successive sedimentary cycles. Chemostratigraphy targets shifts related to subaerial exposure and/or climatic fluctuations. Methods combine facies changes with d 13 C-d 18 O chemostratigraphy from matrix carbonates across five closely spaced, temporally equivalent stratigraphic sections. Isotope composition of ostracod shells, gastropods and cements is provided for comparison. Cathodoluminescence and back-scatter electron microscopy were performed to discriminate primary (syn-)depositional, from secondary diagenetic features. Meteoric diagenesis is expressed by substantial early dissolution and dark blue luminescent sparry cements carrying negative d 13 C and d 18 O. Sedimentary cycles are not correlated by isotope chemostratigraphy. Both matrix d 13 C and d 18 O range from ca À7Á5 to +4Á0& and show clear positive covariance (R = 0Á97) whose nature differs from that of previous basin-oriented studies on the lake: negative values are here unconnected to original freshwater lacustrine conditions but reflect extensive meteoric diagenesis, while positive values probably represent primary saline lake water chemistry. Noisy geochemical curves relate to heterogeneities in (primary) porosity, resulting in selective carbonate diagenesis. This study exemplifies that ancient lacustrine carbonates, despite extensive meteoric weathering, are able to retain key information for both palaeoenvironmental reconstruction and the understanding of diagenetic processes in relation to those primary conditions. Also, it emphasizes the limitation of chemostratigraphy in fossil carbonates, and specifically in settings that are sensitive for the preservation of primary environmental signals, such as lake margins prone to meteoric diagenesis.
Cretaceous Research, 2012
The well-dated section of Cassis-La Bédoule in the South Provencal Basin (southern France) allows for a detailed reconstruction of palaeoenvironmental change during the latest Barremian and Early Aptian. For this study, phosphorus (P) and clay-mineral contents, stable-isotope ratios on carbonate (d 13 C carb) and organic matter (d 13 C org), and redox-sensitive trace elements (RSTE: V, U, As, Co, and Mo) have been measured in this historical stratotype. The base of the section consists of rudist limestone, which is attributed to the Urgonian platform. The presence of low P and RSTE content, and content of up to 30% kaolinite indicate deposition under oligotrophic and oxic conditions, and the presence of warm, humid climatic conditions on the adjacent continent. The top of the Urgonian succession is marked by a hardground with encrusted brachiopods and bivalves, which is interpreted as a drowning surface. The section continues with a succession of limestone and marl containing the first occurrence of planktonic foraminifera. This interval includes several laminated, organic-rich layers recording RSTE enrichments and high C org :P tot ratios. The deposition of these organic-rich layers was associated with oxygen-depleted conditions and a large positive excursion in d 13 C org. During this interval, a negative peak in the d 13 C carb record is observed, which dates as latest Barremian. This excursion is coeval with negative excursions elsewhere in Tethyan platform and basin settings and is explained by the increased input of light dissolved inorganic carbon by rivers and/or volcanic activity. In this interval, an increase in P content, owing to reworking of nearshore sediments during the transgression, is coupled with a decrease in kaolinite content, which tends to be deposited in more proximal areas. The overlying hemipelagic sediments of the Early Aptian Deshayesites oglanlensis and D. weissi zones indicate rather stable palaeoenvironmental conditions with low P content and stable d 13 C records. A change towards marl-dominated beds occurs close to the end of the D. weissi zone. These beds display a long decrease in their d 13 C carb and d 13 C org records, which lasted until the end of the Deshayesites deshayesi subzone (corresponding to C3 in Menegatti et al., 1998). This is followed by a positive shift during the Roloboceras hambrovi and Deshayesites grandis subzones, which corresponds in time to oceanic anoxic event (OAE) 1a interval. This positive shift is coeval with two increases in the P content. The marly interval equivalent to OAE 1a lacks organic-rich deposits and RSTE enrichments indicating that oxic conditions prevailed in this particular part of the Tethys ocean. The clay mineralogy is dominated by smectite, which is interpreted to reflect trapping of kaolinite on the surrounding platforms rather than indicating a drier climate.
Tertiary paleoweatherings and silcretes in the southern Paris Basin
CATENA, 1996
The southern border of the Paris Basin has undergone successive weathering events during the Tertiary. Fluviatile and lacustrine deposits are scattered, being mainly confined to several North-South trending grabens. These are generally devoid of fossils which would allow them to 0341-8 163/96/S IS.00 G 1996 Ekevier Science B.V. All rights reserved .s.w/ 0341.R162(95)00044-5 M. Thiry. R. Simon-Coinpn / Cutenn 26 (1996) l-26 gypsum deposits in the center of the basin. No remnants from Oligocene-Miocene times are preserved in the region studied. During Late Miocene. the disruption of these landscapes took place because a very low sea lcvci led to the renewal of erosion. As a result residual landforms with siliceous crusts now cap IIIC higher elevations.
BSGF - Earth Sciences Bulletin, 2024
Based on detailed sedimentological analyses of cores, interpretation of well logs and a set of geochemical measurements performed on lacustrine sedimentary rocks, the palaeoenvironmental evolution and the sedimentary architecture of the Paleogene continental Vistrenque Basin (SE France) have been reconstructed. The analysis of sedimentary archives revealed three main stages of basin infill evolution: (1) a deep-lake basin (Priabonian-earliest Rupelian) whose sedimentation was dominated by terrigenous gravity driven deposits during a period of high subsidence rate and strike-slip fault activity and under a prevailing humid climate; (2) an evaporative deep lake (early Rupelian) characterized by a drastic reduction in lake volume (forced-regression), terrigenous supplies and deposition of evaporites in disconnected sub-basins; (3) an overall long-term normal regressive stage (middle Rupelian to earliest Chattian) of lake infill characterized by an increase in terrigenous supplies and a vertical upward transition from deep-lake gravitydriven deposits to marginal lake and floodplain sedimentation. The onset of lake volume reduction and forced regression during the early Rupelian is associated with (1) the reworking of marginal lake carbonates into the deep lake areas, (2) the deposition of organic-rich sediments (TOC > 10%) coupled with sulphatereduction processes in the deepest areas of the lake, (3) an important decrease in terrigenous supplies and (4) a long-term increase in d18O of matrix-supported carbonates. This early Rupelian forced regression of the Vistrenque lacustrine system is interpreted to result from a regional decrease in precipitation in response to global cooling during the Eocene-Oligocene Transition (EOT). The final infill of the Vistrenque lake system (late Rupelian-early Chattian) and the onset of a floodplain occurred in more humid conditions during a stage of decreased activity of the Nîmes Fault, prior to or during an early stage of the Liguro-Provençal rifting.
Sedimentary Geology, 2013
Sedimentary successions of palustrine deposits from the Forez Graben recorded changes in depositional and hydrological conditions throughout the Middle to Late Miocene of France. Paleontological, mineralogical and geochemical data combined with mass-balance calculation allowed the identification of modern, diagenetic and eogenetic stages of authigenic precipitation within the sedimentary pile. Stratigraphic log contains six clay-and sand-rich sequences, some associated with freshwater ostracods. δ 13 C, δ 18 O values and Sr isotopic ratios of whole-rock samples and ostracods indicate that the Montrond-les-Bains upper sequence (8 to 175 mbs) is a continental lake system that recorded continental weather condition (15 to 25°C) during the upper Miocene time. Geochemical changes permit the estimation of variations of evaporation-inflow changes (E/I: 8 to 75% and δ 18 O rainfall − 6 to −8‰) associated with two sequences. δ 18 O and E/I progressive changes were related to runoff to colder climate conditions. Large E/I values in below 100 mbs are associated with the appearance of authigenic calcite and dolomite precipitation. Euhedral dolomite seems to be related to desiccation period that induced capillary pumping of water undersaturated with respect to calcite but saturated for dolomite. The lower part of the Middle Miocene sedimentary series (175 to 300 mbs) hosts continental deposits with scarce fossil, a larger proportion of dolomite and massive pyrite levels related to mixed eogenetic and diagenetic precipitation. Scarce preserved "eogenetic levels" with unrealistic E/I ratios suggest either δ 18 O values similar to the upper section but with temperature lower than 15°C, or a similar temperature but very low δ 18 O rainfall . Calculated δ 18 O H 2 O values have to be as low as −15‰. δ 18 O H 2 O values are similar to present-day melted snow. This stable isotope suggests episodes of regional warming melting surrounding snow, and able to mobilize as well as deposit thick sand levels. Eogenetic to diagenetic calcite, dolomite and pyrite precipitation involves S and Mg-fluid influxes associated with methanogenic process (eogenesis) mixed with recrystallized pyrite and dolomite with diagenetic fluid circulation.