Cyclical environmental changes during the Pliocene in NE Spain: the Camp dels Ninots maar record (original) (raw)
Related papers
Seasonal sedimentation in the Pliocene Villarroya Lake (N Spain) inferred from pollen analysis
Sedimentary Geology, 2009
ABSTRACT High-resolution pollen analysis was performed on a short (8.7 cm thick) section with 94 varve couplets (made up of dark and light laminae) from a lacustrine facies of the Pliocene Villarroya Basin, Spain. The aim of the present study was (i) to verify the seasonality of the sedimentation and (ii) to determine if pollen data record the short-term climatic fluctuations related to variations in laminae thickness and colour. The samples displayed high pollen concentrations and very good taxonomic diversity. The composition of the pollen spectra indicated that the vegetation structure was closely linked to relief: (i) a regional open herbaceous vegetation, (ii) a local marshy and riparian environment, (iii) deciduous mixed forest at mid-altitudes, and (iv) coniferous mixed forest in the surrounding mountains at higher altitudes. In the 48 distinct couplets where the dark and light laminae have been separately sampled, the pollen content showed higher concentrations of early flowering trees in the dark ones, whereas late-flowering plants were more abundant in the light ones. Total pollen concentrations in the 48 couplets were higher in most of their dark layers. These results point to a seasonal layering. According to present-day flowering times, the dark laminae represent sedimentation in winter/spring and the light laminae sedimentation in late summer/autumn. The correlation between the AP (Arboreal Pollen)–NAP (Non-Arboreal Pollen) percentages and lamina thickness linked lamina thickness with the highest values of AP, indicating warmer periods. Variations in the ecological groups enabled us to differentiate eight pollen cycles related to short-term climatic fluctuations. These alternations seem to be more associated with seasonality in precipitation than with temperature oscillations and could be correlated with the NAO/ENSO-like and sunspot-like cycles.
Journal of Paleolimnology, 1997
A 27-m sequence of deposits from the Plio-Pleistocene Banyoles-Besalú lacustrine complex, at Tres Pins, N.-E. Spain, shows lithological, carbonate, pollen and spores, and ostracode-gastropod evidence of climatic and lake-level change. Upland pollen taxa from the lowermost zones 1, 3 and 5, show that the area was forested and indicate a progressive deterioration of the climate. Zone 2 (steppe vegetation) corresponds to a global glacial stage, with mild temperatures, if the comparison to modern analogues is valid. Only minor climate fluctuations occurred subsequently. Aquatic vegetation and micritic sediment facies show a pelagic environment during pollen zones 1 and 3 and a littoral one during pollen zone 5. A short-term lowering of the water level (sandy algal micrite and slightly brackish waters) occurred in zone 2, as a result of severe droughts. Subzone 2c records progressive recovery of the forest. The coarse lithology and the high carbonate content, however, continue to indicate shallow waters. The fluctuation marked by zone 4 (extensive marsh vegetation and spring waters) may be due to a lake-level decrease caused by karst activity, or by lower precipitation with only slight cooling, or more probably by a relative lake-level decrease caused by natural infilling. The sediment of pollen zone 4, a sandy algal micrite, indicates the development of a littoral bench at the core site. From pollen zone 4 to pollen zone 5 an evolution from lakeward to landward position occurred. In zone 2, droughts existed at least during the spring growing season, and probably also during the rest of the year. In subzone 2c, a shift to spring precipitation occurred. In contrast, during pollen zone 4, if there was a decrease in precipitation, it did not take place during the summer growing season.
Journal of Paleolimnology, 2011
During the middle and late Holocene, the Iberian Peninsula underwent large climatic and hydrologic changes, but the temporal resolution and regional distribution of available palaeoenvironmental records is still insufficient for a comprehensive assessment of the regional variability. The high sedimentation rate in karstic, meromictic Montcortès Lake (Catalan pre-Pyrenees) allows for a detailed reconstruction of the regional palaeoecology over the last 5,340 years using diatom analysis, aquatic pollen, sedimentological data, and historic documentary records. Results show marked fluctuations in diatom species assemblage composition, mainly between dominant Cyclotella taxa and small Fragilariales. We suggest that the conspicuous alternation between Cyclotella comta and C. cyclopuncta reflects changes in trophic state, while the succession of centric and pennate species most likely reflects changes in the hydrology of the lake. The diatom assemblages were used to identify six main phases: (1) high productivity and likely lower lake levels before 2350 BC, (2) lower lake levels and a strong arid phase between 2350 and 1850 BC, (3) lake level increase between 1850 and 850 BC, (4) relatively high lake level with fluctuating conditions during the Iberian and Roman Epochs (650 BC–350 AD), (5) lower lake levels, unfavourable conditions for diatom preservation, eutrophication and erosion triggered by increased human activities in the watershed during the Medieval Climate Anomaly (900–1300 AD), and (6) relatively higher lake levels during the LIA (1380–1850 AD) and afterwards. The combined study of diatoms, algae and pollen provides a detailed reconstruction of past climate, which refines understanding of regional environmental variability and interactions between climate and socio-economic conditions in the Pyrenees.
A multi-proxy record of Holocene climatic change in southwestern Spain: the Laguna de Medina, Cádiz
The Holocene, 2001
Palaeolimiinological data (diatoms, ostracods, foraminifera, molluscs, aquatic pollen and lithologyj) from a radiocarbon dated sediment core from a saline lake, the Laguna de Medina, provide the first complete record of Holocene lake-level change for southwest Spain for the last c. 9000 cal. years. The lake has always been relatively shallow but has exhibited marked fluctuations in salinity and water depth, especially in the earlier record when oscillationis ctUlminate in maxinmuim lake levels from c. 6960-6680 cal. BP (c. 6070-5830 BP), indicating enhanced earlyto mid-Holocene humidity and a mid-Holocene humidity maximuLm. Prolonged shallowing thereafter reflects in par-t increased aridity in the later Holocene. Lake desiccation followed by a c. 800-yr phase (zone 2) of major limnliological change commencing at c. 8000 cal. BP (c. 7200 BP), and a ntimber of other abrupt desiccation events, are also noteworthy. The mid-Holocene maximum is consistent with widespread evidence for high lake levels around 6000 BP, but the underlying climatic mechanisms are tincertaini; there is some evidence it may apply predomiainantly to the westerly (Atlantic) Peninsula, withi earlier maxima in the east. Phases of abrupt limnological change show affinities with African data; as in African lakes, the 'zone 2' phase appears to be a response to global change centred oni c. 8.1-8.2 cal. BP. Other correlations miiade are tenuous, due partly to the lack of preservation in the upper record of some of the proxies used. Other desiccation events currently appear to be of more local significance, reflecting high decadalto century-scale climatic variability throughout the Holocene. Lake-sediment records from hydrologically closed, saline lakes in semi-arid regions preserve a variety of biotic and abiotic remains from which regional changes in past climate (evaporation, precipitation or temperature) over time mav be inferred (Street-PetTott and Harrison, 1985). Data on lake-level change are particularly valuable since fluctuations in lake level can be related clearly to changes in the ratio of precipitation to evaporation (P:E), and the effect of changing salinity and brine composition with lake-level change on species composition. mineralogy and geochemistry offers a potentially wide variety of palaeoclimate pr-oxy indicators.
The Holocene, 2019
Lake Medina is a small, shallow and endorheic salt lake sensitive to climate variation in south-western Spain, close to Cádiz in western Andalusia. It is located in an evaporitic and karstic environment, and a saline lake affected by highly seasonal precipitation and evaporation. Geochemical and mineralogical data of core CO1313 combined with a robust age model show variation that contributes to the understanding of palaeoenvironmental and palaeoclimatic change. This study shows a pollen record that has been conducted on core CO1313, together with charcoal and non-pollen palynomorph analyses. The environmental and climatological history reconstruction of Lake Medina starts in early Holocene times (at 9.5 cal. ka BP) and shows intensified pasture and land use during middle-Holocene times as well as the 8.2 and 4.2 cal. ka BP abrupt climate events. Oxidation of plant remnants and resulting non-preservation at certain times reinforces the hypothesis of intense climate effects on vegeta...
The Holocene, 2020
Lake Medina is a small, shallow and endorheic salt lake sensitive to climate variation in south-western Spain, close to Cádiz in western Andalusia. It is located in an evaporitic and karstic environment, and a saline lake affected by highly seasonal precipitation and evaporation. Geochemical and mineralogical data of core CO1313 combined with a robust age model show variation that contributes to the understanding of palaeoenvironmental and palaeoclimatic change. This study shows a pollen record that has been conducted on core CO1313, together with charcoal and non-pollen palynomorph analyses. The environmental and climatological history reconstruction of Lake Medina starts in early Holocene times (at 9.5 cal. ka BP) and shows intensified pasture and land use during middle-Holocene times as well as the 8.2 and 4.2 cal. ka BP abrupt climate events. Oxidation of plant remnants and resulting nonpreservation at certain times reinforces the hypothesis of intense climate effects on vegetation during the 4.2 cal. ka BP climate event. Yet, oxidation of plant residues during other episodes shows other periods that were also affected by reduced precipitation. From around 2 cal. ka BP onwards, a recent trend towards aridification and enforced seasonality was detected.
Journal of Paleolimnology, 2016
Lakes with varved sediments are especially well suited for paleoecological study, from annual to even seasonal resolution. The interpretative power of such high-resolution paleoenvironmental reconstructions relies on the availability of modern analogs with the same temporal resolution. We studied seasonal pollen sedimentation in varved Lake Montcortès, Central Pyrenees (Spain), as a modern analog for high-resolution reconstruction of Late Holocene vegetation and landscape dynamics. Seasonal samples were obtained from sediment traps that were submerged near the maximum water depth for a two-year period (Fall 2013 to Fall 2015). Seasonal pollen sedimentation was compared with meteorological variables from a nearby weather station. Bulk pollen sedimentation, dominated by Pinus (pine) and Quercus (oak), followed a clear seasonal pattern that peaked during the spring/summer (SS), coinciding with maximum temperature and precipitation, minimum relative humidity and moderate winds from the SSE. Pollen sedimentation lags (PSL) were observed for most pollen types, as substantial amounts of pollen were found in the traps outside of their respective flowering seasons. Two pollen assemblages were clearly differentiated by their taxonomic composition, corresponding to spring/summer and fall-winter (FW). This pattern is consistent with existing interpretation of the sediment varves, specifically, that varves are formed by two-layer couplets that represent the same seasonality as pollen. We concluded that pollen sedimentation in Lake Montcortès exhibits a strong seasonal signal in the quantity of pollen, the taxonomic composition of the pollen, and relationships between the pollen and meteorological variables. Thus, varved sediments provide a potentially powerful tool for paleoecological reconstruction at seasonal resolution. This method could be used not only to identify paleoenvironmental trends, but also to identify annual layers and therefore date sediments, even in the absence of evident sediment laminations. A satisfactory explanation of PSL will require further studies that examine internal lake dynamics and pollen production/dispersal patterns.
CATENA, 2013
The Bardenas Reales Natural Park (western Ebro Basin, NE Spain) constitutes a fragile landscape where the prevailing semiarid climate and erodability of the bedrock have resulted in high sensitivity to erosion/sedimentation oscillations during the Holocene. In this paper, we present new chronologic, sedimentologic, paleomagnetic and environmental magnetic results from the oldest unit (Qah1) of a system of nested cut-and-fill alluvial sequences, which is 18 m thick and crops out extensively in the central part of the natural park at the Bardena Blanca Depression. Radiocarbon dating indicates that Early Holocene unit Qah1 is younger than 9.38-8.89 cal kyr BP and gives ages of 8.92-8.42 and 7.59-7.37 cal kyr BP in the middle and uppermost parts of the unit, respectively. Sedimentologic data indicate that distal alluvial sediments of unit Qah1 accumulated in sandy mud flats and ephemeral playa lakes under arid conditions. The coincidence of enhanced magnetite content with moderate to intense root bioturbation in the lowermost and likely also uppermost sediments of unit Qah1 suggests that magnetite formed authigenically in response to relatively wetter conditions at the beginning and end of this dry period. These results indicate that onset and cessation of alluvial aggradation mark the passing of a geomorphologic threshold, most likely plant cover in the watershed, during a progressive drying-wetting event. The radiocarbon-based age model of unit Qah1 indicates that alluvial aggradation under arid conditions began at 9.13 cal kyr BP and ended at 7.16 cal kyr BP. This period is strikingly centered at around the 8.2 kyr cold event but spans a longer time period, supporting the notion of a global climatic deterioration as the underlying cause for this event. Paleomagnetic directions do not clearly display the characteristic patterns recognized in paleosecular variation curves derived from other European lacustrine sediments and cannot be used to refine the radiocarbon-based age model for unit Qah1. Our results demonstrate a quick and strong response of alluvial systems to Early Holocene climate variability in fragile Mediterranean landscapes such as those at the semiarid Bardenas Reales Natural Park.
2014
A 52 m-long lacustrine sequence has been recovered from the basin of Bòbila-Ordis, near Banyoles (N-E Spain). The presence of Early Biharian rodent teeth (Early Pleistocene) and of a c. 9 ka-long palaeomagnetic reversal (Cobb-Mountain subchron) suggests an age centred on 1.2 Ma, making this sequence one of the very few well-dated terrestrial sequences of that age in Europe. The first 22.5 m (with an interglacial character) are very homogenous owing to sedimentation affected by underwater springs. In the middle part of the sequence, palynological analyses, supported by sediment visual description, ostracod and mollusc assemblages, allow the reconstruction of one glacial-interglacial cycle, with vegetation succession. A second incomplete climatic cycle is recorded in the top part, within a shallower lake. These brief interruptions in the two climatic cycles are possibly linked to lake bank collapse caused by Hippopotamus amphibius or faulting linked to karst. The succession is likely ...