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Depositional evolution of La Parra kasrtic lake (Iberian Chain, Spain) during the last 1,600 years: Climate and human impact implications! ! ! ! Fernando Barreiro-Lostres! Trabajo Fin de Máster! Máster de Iniciación a la Investigación en Geología Curso 2011-2012 “Lakes are dynamic response systems collecting complex signatures of the landscape (vegetation, carbon, pollen, dust, ash, soil erosion, floods, seasons) and aquatic systems (water source, composition, balance, temperature, chemistry, isotopes, carbon, precipitates, biotic and abiotic processes). These signatures integrate climate parameters of temperature, precipitation, wind, seasonality, climate extremes, and variability” "#$%%&!#$'()*! 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Depositional evolution of La Parra kasrtic lake (Iberian Chain, Spain) during the last 1,600 years: Climate and human impact implications ABSTRACT Lake La Parra (39º 50.948’, 1º 52’, 1014 m) is a small, relatively deep (Zmax = 17.5 m), freshwater monomictic lake with a circular morphology and a diameter of 116 m It is part of a karstic lake complex of seven lakes located in the Iberian Range (Cuenca, East of Spain), and it has been developed in a sinkhole that intercepted the main regional aquifer. The sedimentary record of the deepest part of the lake, analysed using sedimentological, microscopic, geochemical and physical techniques is mainly constituted by clastic carbonated sediments, characterized by a high variability of sedimentary facies, which is controlled mainly by changes in the detritic input. At same time, these fluctuations reflect a wide hydrological variability along the last 1600 years. The chronological model for the sediment sequence is based on 7 AMS 14C dates. The depositional history of Lake La Parra comprises five stages: (i) The onset of lacustrine sedimentation around 300 cal. yr AD; (ii) a shallow to deep lake during the Dark Ages (500 - 900 cal. yr AD); (iii) lower lake levels with increase in detritic input, coincident with the Medieval Climate Anomaly; (iv) a period of generally higher lake levels with development of frequent meromixis but with some low lake level phases during the Little Ice Age (1400 - 1850 cal. yr. AD); and (v) a slight increase of lake levels on recent times (1900-nowadays), preceded by an initial period of lower levels during the late 19th century. The main human impact in the lake and the watershed environment is related to changes in the land uses during the Middle Ages due to agriculture and transhumation that increased sediment delivery to the lake, and more recently the use of groundwater from regional aquifer for agricultural purposes. The paleohydrological-paleoclimate reconstructions of Lake La Parra are coherent with other paleoclimate archives of the Iberian Peninsula showing a more arid MCA and more humid LIA in the western Mediterranean. These new finding also support the hypothesis of an east-west climate see-saw in the Mediterranean region since 900 AD. Key-words: Late Holocene, sedimentary facies, geochemistry, Iberian Peninsula, karstic lake, lacustrine depositional environments, palaeohydrology, sedimentary facies, X-Ray Fluorescence. RESUMEN La laguna de La Parra (39º 50.948’, 1º 52’, 1014 m) es un lago pequeño relativamente profundo (Zmax = 17.5 m) de agua dulce, monomíctico y con morfología circular (116 m diámetro). Forma parte de un complejo kárstico constituido por siete lagos situado en la Cordillera Ibérica (Cuenca, este de España), originado en una dolina que interceptó el acuífero regional. El registro sedimentario de la zona más profunda del lago se ha estudiado mediante técnicas sedimentológicas, microscópicas, geoquímicas y físicas. Está constituido principalmente por sedimentos clásticos carbonatados, caracterizados por una gran variabilidad de facies sedimentarias que están controladas por cambios en la entrada de detríticos al sistema. Al mismo tiempo, estas fluctuaciones reflejan una amplia variabilidad hidrológica durante los últimos 1600 años. El modelo cronológico de la secuencia sedimentaria se basa en 7 dataciones de 14C AMS. La historia sedimentaria de la laguna de La Parra comprende 5 etapas: (i) el comienzo de la sedimentación lacustre hacia el año 300 DC; (ii) un lago somero que aumenta progresivamente su nivel durante la Baja Edad Media (500 – 900 DC); (iii) niveles del lago bajos, con aumento en los aportes detríticos coincidiendo con la Anomalía Climática Medieval (ACM); (iv) un periodo con predominio de niveles altos del lago, pero algún episodo de niveles bajos, con desarrollo de meromixis frecuente durante la Pequeña Edad del Hielo (PEH, 1400 . 1850 DC) y (v) un ligero aumento de los niveles del lago en Fernando Barreiro-Lostres tiempos recientes (1900 - actualidad), precedido por un periodo inicial de bajo nivel de agua a finales del siglo XIX. La principal afección antrópica en el lago y su entorno está relacionada con cambios en el uso de la tierra durante la Edad Media debido a la agricultura y la transhumancia, lo que implicó un aumento en los aportes detríticos al lago; y más recientemente, con la extracción de aguas subterráneas del acuífero regional mediante pozos agrícolas. Las fluctuaciones paleohidrológicas y paleoambientales de la laguna de La Parra son coherentes con otros registros paleoclimáticos de la Península Ibérica, mostrando una fase más árida durante la ACM y más húmeda durante la PEH en el Mediterráneo occidental. Este nuevo aporte refuerza la hipótesis de un comportamiento antitético esteoeste del clima en la region mediterránea desde el 900 DC. Palabras clave: Holoceno tardío, facies sedimentarias, geoquímica, Península Ibérica, lago kárstico, ambientes de sedimentación lacustre, paleohidrología, facies sedimentarias, Fluorescencia de Rayos X. Depositional evolution of La Parra kasrtic lake (Iberian Chain, Spain) during the last 1,600 years: Climate and human impact implications 1 Introduction The discovery during the last decades of periods of past rapid changes within the climate system (Mann, 2007) has demonstrated the high frequency variability of Earth's climate and the occurrence of variations from annual to millennial timescales. This variability is known to result from both internal and external factors, the latter associated with both natural and anthropogenic influences (Mann, 2007; Hegerl et al., 2011, Crowley, 2000). A number of natural processes besides the Earth-orbital changes as oscillations of the coupled atmosphere-ocean-ice sheet system, solar activity changes, volcanic greenhouse-gases emission, tectonics and relative location of continents and even meteoritic impacts control the climate system (Alley et al., 1997; Mann, 2007). Over past two millennia, the main boundary conditions of the climate system (orography, orbital parameters and the spatial extent of continental ice sheets) have not changed significantly, so this time interval provides an appropriate context for estimating the envelope of natural climate variability. Although these variations have been smaller than those from past glacial - interglacial periods, they have deeply affected human societies, forcing people to develop subsistence strategies to overcome changing conditions. Since Neolithic times, environmental change has been a determinant factor in civilizations’ fate and even in historical times, climate has greatly affected humankind (Turney et al., 2006). On the other hand, changes in human activities affect back climate's evolution at hemispheric scales, particularly since the industrial revolution (Houghton, 2001; Mann, 2007). Instrumental records are too short to fully record the variability of the climate system. Quaternary palaeoclimatic archives often record more variability than typically observed instrumentally during this century, providing estimates of the past atmospheric composition, temperature, precipitation, vegetation, extension of glaciers, and past ocean circulation (Duplessy, 2005). Lacustrine records are an excellent high-resolution sedimentary archive of regional abrupt changes in climate (Batist and Chapron, 2008), including regional variations in hydrology (precipitation/evaporation ratios, flood events, changes in river input), climate-controlled weathering and sediment transport processes, human impact and even seismic activity on the lake catchment. A number of Holocene climatic reconstructions in the Mediterranean have been performed using lacustrine multiproxies (isotopes, pollen, geochemistry, sedimentology) (e.g. Roberts et al., 2011). In the Iberian Peninsula, lakes occur in a large variety of geographic, climatic and ecologic settings. There are lakes in mountains originated by glacial activity (Enol, Sanabria); karstic lakes that owe their origin to exokarstic activity (Taravilla, Somolinos) or to dissolution of evaporites or carbonates: (Banyoles, Moncortes, Zoñar, Estanya); and ephemeral saline lakes in the Ebro, Duero and Tajo River Basin originated by combination of erosion and karstic processes (Bujaraloz salt lakes) (González-Sampériz et al., 2008). The most significant Late Holocene climatic abrupt changes described in these sequences are the Ibero-Roman Humid Period, the Medieval Climate Anomaly and the Little Ice Age ((Moreno et al. 2009);(Morellón et al. 2009); (Martín-Puertas et al. 2009); (Corella et al. 2010); (Valero-Garcés and Moreno 2011); (Currás et al. 2012)). In this work, high-resolution sedimentological, mineralogical and geochemical studies carried out on short gravity cores and long piston cores from La Parra Lake, a small karstic lake in the Iberian Range (central Spain) provide a detailed record of main depositional and hydrological changes during the last 1.600 cal. years in this region of the Iberian Range. The relatively high area/depth ratio of the lake basin amplifies the record of the local hydroclimatic variability, which is expected to be affected by climate and the wellknown human impact in the area (grazing, crops, and fires) since Medieval times. The sedimentary facies and geochemical data together with a robust chronological model, provided by AMS radiocarbon dating techniques, have allowed disentangling the changing environmental conditions surrounding the lake and its watershed and the complex interplay between climate and human activities since the end of the Roman Period. Fernando Barreiro-Lostres 2 Regional setting Study site In the Iberian Peninsula there are large carbonate-dominated regions where endo and exo-karstic processes have been very active during the Quaternary. As a consequence, a number of lake basins have developed, mainly in tufa-dammed valleys and dolines. Particularly, in the Iberian Range, thick dolomitic Jurassic and Middle and Upper Cretaceous dolomitic formations have been affected by intense karstic processes (Alonso, 1986; Gutiérrez and Valverde, 1994; Carmona and Bitzer, 2001; Peña and Lozano, 2004) originating small funnel-shaped depressions, relatively deep that sometimes intercept the surrounding aquifers, developing karstic lakes (Valero-Garcés and Moreno 2011). Fig. 1: A - Location of the study area and geological scheme of the Iberian Range. B - Detailed geological map of the surroundings of La Parra lake (see legend at the right-top side (based on Ramírez del Pozo et al., 1973) and national topographical map (IGN, 2002). C - La Parra lake’s bathymetry and location of studied core. La Parra lake is located on the western branch of the Iberian Range (Central - Eastern Spain). It belongs to the karstic lake complex of Cañada del Hoyo (Fig. 1), formed on Upper Cretaceous limestones and dolostones (Cenomanian-Turonian) but affecting as well Late Jurassic materials as Weald and Utrillas facies, composed of massive beds up to 2 m thick, lying sub-horizontally above Middle/Upper-Cenomanian green marls (correlated with Margas de Chera Formation, Segura et al., 1988). The origin of this complex is probably structural, following the NE-SW trace of the known Guadazaón polje, which follows the orientation of the Valdemoro fault (Eraso et al. 1979). Geomorphology The Guadazaón polje is one of the main morphological features on the study area, characterized as an open, elongated NE-SW trending depression (Fig. 2). The polje is developed on a slightly deformed surface that corresponds to the Pliocene Main Erosion Depositional evolution of La Parra kasrtic lake (Iberian Chain, Spain) during the last 1,600 years: Climate and human impact implications 3 Surface of the Iberian Chain (which presents a faint inclination towards the SE of 1%), affecting carbonatic Cenomanian-Turonian formations and more clastic (Weald and Utrillas) Cretaceous formations (Gutiérrez and Valverde, 1994). The Utrillas Formation constitutes the base level of the polje. From a climatic point of view, this polje can be classified as a Mediterranean-type, but considering its evolution and morphology (progressive trend to subdivision), Peña et al. (1989) define it as an Iberian-type polje. Fig. 2: Aerial orthophotograph of the study site showing the Guadazaón polje and the location of the karstic doline system in both margins. Only western margin present dolines with water. In the Late Quaternary, the polje was captured by the actual fluvial system (Gutiérrez y Valverde, 1994). The Guadazaón River has deposited silts and red clays with angular cuarzitic and carbonatic pebbles on the bottom of the polje. Along the scarps, small alluvial fans occur, as well as tufa deposits associated to springs in the contact between Upper Cretaceous limestones-dolostones and the sandy Utrillas formation. Near Cañada del Hoyo village and over the Main Erosion Surface a complex doline system developed. Although they are located on both margins of the Guadazaón polje, only some dolines situated on the right margin are flooded. One of these dolines is the lake La Parra. Related to their origin, some authors defend their genesis by dissolution processes facilitating by the diaclase net surrounding the dolines and their progressive widening (Alonso, 1986). Other authors as Eraso et al., 1979 explain their genesis by structural factors, particularly the occurrence of Jurassic and Cretaceous folds and fractures, responsible for the collapse of unkarstificable pre-Cenomanian materials (Utrillas and Weald facies) and dissolution of carbonatic deposits (Jurassic and Cenomanian limestones and dolostones) along preferential directions. More recently, Carmona and Bitzer (2001) argued that the regional NW-SE syncline affecting the Cretaceous has been a main factor in the development of these sinkholes by collapse as consequence of karstic dissolution. Fernando Barreiro-Lostres 4 Climate and vegetation The Iberian Peninsula climate is influenced by both subtropical and the mid-latitude climatic dynamics. La Parra lake is located in a Mediterranean climatic context modulated by continental influences with sharp daily and seasonal temperature fluctuations. The mean annual precipitation in the study area is 542 mm, and the mean annual evapotranspiration has been estimated as 237 mm (Thornthwaite method; Custodio y Llamas, 1996; Escuder et al., 2009). The mean annual temperature is 14,6 ºC, ranging from 4 ºC (January) to 23 ºC (July) (Cuenca Meteorological Station, 12 Km NW of the lake). July is the driest month and October the wettest, with mean rainfall of 15,7 and 59,4 mm, respectively. Fig. 3: A – Mean annual precipitation (mm), evapotranspiration (mm) and temperature (ºC) data of the study area. B - Mean monthly precipitation (mm), evapotranspiration (mm) and temperature (ºC) data. Data is derived from the Cuenca meteorological station, 12 Km NW of the lake, for the complete 1956-2011 period. In figure 3A, a direct relation between precipitation and evapotranspiration is shown, with a lineal decrease from 1956 until 2011, ranging from 600 to 490 mm (P) and from 300 to 200 mm (ETP). This may be indicative of the synergetic response of the vegetation and the amount of rain. An increase of the mean annual temperature from about 11 ºC in 1956 B) A) Depositional evolution of La Parra kasrtic lake (Iberian Chain, Spain) during the last 1,600 years: Climate and human impact implications 11 max. length) characterized by black, massive fine-grained (facies 1.1B) and medium (facies 1.2) silts, with abundant OM. Sediments are transported as suspended load to distal areas and away from the influence of coarse terrigenous particles input. Lake basin topography, water depth and distance to shore appear to be the main factors controlling the distribution of present-day surface sediments in the lake. The distance to shore obviously controls grain-size, showing a decreasing trend towards the distal areas (Fig. 9). Organic matter content decreases towards the transitional area and it is a mixture of terrestrial, submerged macrophytes and algal material. Around the N shore of the lake, an important factor contributing to the input of sediments to the lake is the block-falling processes along the steep scarp of the sinkhole, formed by dolostones and limestones, which may develop mass-wasting processes. Chronological model To construct the age model of La Parra sequence, seven of the nine radiocarbon dates listed in Table I were used. Two radiocarbon dates were rejected because they are not coherent with the age model. The date Poz-37956 (307±26 cal. yr. BP) is too young for its stratigraphical location in the sequence, and this could be due to contamination with younger material; the date Poz-37960 (2033±85 cal. yr. BP) shows an age older than two dates from stratigraphically lower intervals, suggesting reworking processes. The age model has been constructed by lineal interpolation between the dates. Table I: Radiocarbon dates on La Parra core analysed at the Poznan Radiocarbon Laboratory, Poland (Poz- ) Calibrated age (2!) Drive Core Depth (cm) Laboratoy code 14C AMS age (BP) (cal. yr. BP) (cal. yr. AD) Material Calibration 1 66 Poz-37954 230±30 291±24 1659 ±27 Wood fragment INTCAL09 1 93 Poz-37955 390±35 468±43 1482 ±43 Wood fragment INTCAL09 2 145 Poz-37956 265±30 307±26 1644±26 Wood fragment INTCAL09 3 324 Poz-37957 1190±30 1117±64 834±64 Wood fragment INTCAL09 3 375 Poz-37958 1155±30 1097±54 854 ±54 Wood fragment INTCAL09 3 542.5 Poz-37960 1640±30 1548±66 403±66 Wood fragment INTCAL09 4 563 Poz-37960 1640±30 2033±85 -83±85 Wood fragment INTCAL09 5 624 Poz-37962 1700±30 1588±50 362 ±50 Wood fragment INTCAL09 5 675 Poz-37963 1740±30 1639±77 311 ±77 Wood fragment INTCAL09 Samples in italics were discarded (reversals or stratigraphically inconsistent) According with this chronological model, the sedimentary record spans from 1639±77 cal. yr. BP (coinciding with the end of the Humid Iberian-Roman Period) to present (Fig. 8). The occurrence of 137Cs in the upper centimetre demonstrates that the sequence contains the sediments deposited during the last decades. The average sedimentation rate is 0,40 cm/yr but there are some changes along the sequence. The base of the sequence displays the highest sedimentation rate (1,46 cm/yr, Unit III) during a relatively Fernando Barreiro-Lostres 12 short period (around a century). During most of the sequence, sedimentation rate is about 0,36 cm/yr (Unit II and almost all the Unit I), corresponding to deposition of fine facies. The top sequence composed mainly of silts displays even lower (0,15 cm/yr) sedimentation rates. Fig. 8: Age model of the sedimentary record of lake La Parra constructed by lineal interpolation of seven radiocarbon dates. Depositional evolution of La Parra kasrtic lake (Iberian Chain, Spain) during the last 1,600 years: Climate and human impact implications 13 Sedimentary Facies Analyses The identification and interpretation of the different facies of the sedimentary record integrates the sedimentological and microscopical observations with geochemical data. The 6.95 m long core PA10-1A-U from the deepest part (17,5 m) of lake La Parra is mainly composed of carbonatic clastic sediments with variable amounts of organic remains. Eleven sedimentary facies and sub-facies have been identified and distributed in two main groups: i) clastic and ii) finely laminated with endogenic carbonate (Table II). Table II: Description and interpretation of main sedimentary facies Lithology Facies Description Processes CLASTIC FACIES 1.1A Fine grey silts Dark grey and massive, in beds of 10-25 cm and diffuse contacts, with abundant diatoms and amorphous OM. Abundant carbonatic and quartz grains. 1.1B Fine black silts Massive, in isolated levels of 2-5 cm with net boundaries, with diatoms and amorphous OM. Abundant carbonatic and quartz grains. Distal, relatively deep environments, more frequent anoxic conditions 1.2 Medium brown silts Dark and light banded, in layers of 5- 20 cm with diffuse boundaries and macrophytes remains. Abundant carbonatic and angular quartz grains. Distal to transitional setting; strong alluvial influence; rapid oxidation-reduction changes 1.3A Coarse light silts Fining-upwards beds, 5-15 cm thick, with irregular basal boundaries. Disperse carbonatic cm-pebbles. Abundant mm-sized, OM fragments and presence of ostracods. Silts 1.3B Coarse dark silts Beds of 2-10 cm thick, with irregular basal boundaries. They present abundant mm-sized OM fragments. Turbidite - like processes, allochthonous material supply reaching the centre of the lake, moderate depth 2.1 Fine green sands Massive, isolated levels of 3-4 cm in a green silty matrix. Dominated by angular carbonatic and quartz grains. 2.2 Medium brown sands Massive, in levels of 2-10 cm with irregular boundaries with a silty finemedium matrix. Abundant alotriomorphous and altered carbonatic grains. Sands 2.3 Coarse brown sands A 10 cm thick, massive bed, with angular carbonatic pebbles and diatom fragments and irregular boundaries. . Littoral to transitional settings. High energy, relatively lower lake levels. 3.1 Fine brown gravels A 2 cm bed, massive, with irregular boundaries composed of carbonate pebbles and some invertebrate exoskeleton fragments. Gravels 3.2 Medium brown gravels A 30 cm thick bed, massive, with irregular boundaries. Pebbles are carbonatic, in a silty matrix. Strong alluvial influence in a littoral setting. High allochthonous clastic input, and high energy LAMINATED, ENDOGENIC CARBONATE FACIES Silts 4 Fine laminated silts Sets of 5 cm thick intervals with 1 mm thick white calcitic and dark OM-rich laminae with net and regular boundaries. Organic layer shows a high amount of diatoms and calcite layer is composed of homometric sub idiomorphous calcite grains. Distal, low energy, frequently anoxic bottom waters; carbonate bioproduction, deep lake Fernando Barreiro-Lostres 14 Clastic facies The following clastic facies have been identified (Fig. 10) ! (1) Silts: Intercalation between: ! (1.1A) Fine grey silts: Dark grey massive silts, in beds of 10-25 cm with diffuse contacts. They are composed of heterometric carbonatic grains of 4-20 !m,, amorphous organic matter (OM) remains, diatoms and quartz grains of up to 80 !m. ! (1.1B) Fine black silts: Black massive silts appear in isolated levels of 2-5 cm with net boundaries. They are composed by heterometric carbonatic grains of 4-12 !m with abundant amorphous OM, macrophytes fragments and homometric grains of quartz of up to 25 !m. ! (1.2) Medium brown silts: Weakly-banded silts formed by 2 cm thick dark and brown layers, appearing in beds of 5-20 cm with diffuse boundaries. They are form by homometric and irregular carbonatic grains of 10-20 !m, with homometric quartz grains of 20-50 !m, and macrophytes fragments. ! (1.3A) Coarse light silts: Brown beds, 5-15 cm thick, with fining-upwards textures and, irregular basal boundaries. They present disperse carbonatic grains of less than 2 mm, with abundant OM fragments. Microscopically, they are composed by heterometric carbonatic grains with two main distributions: i) fine, 4-10 !m and ii) coarse, less abundant, of 50-60 !m; also there are abundant remains of amorphous OM and some ostracods, and homometric sub-angular quartz grains of 50-100 !m. ! 1.3B) Coarse dark silts: Dark brown, 2-10 cm thick beds with irregular basal boundaries. They present abundant mm macrophyte fragments. Microscopically, they are composed by heterometric carbonatic grains with two main groups: i) fine, more abundant, average 10 !m and ii) coarse, sub-angular grains, of 50-70 !m; also there are abundant remains of macrophytes and amorphous OM and homometric quartz grains of 25-50 !m. Sedimentological features of facies 1.1A and 1.1B indicate low energy transport processes linked to deposition of fine particles near the centre of the lake, away from the influence of coarse terrigenous alluvial input and presumably with relative high lake levels. Bottom conditions would fluctuate between more oxic conditions (grey silts) and more reduced ones (black silts). The occurrence of abundant rounded, irregular calcite grains and abundant macrophyte fragments in Facies 1.2 suggests dominant traction transport processes. Alternation of brown and dark layers also implies relative rapid changes in oxidation/reduction conditions. Coarse silt facies (1.3A and 1.3B) present normal gradation and irregular basal boundaries, suggesting turbidite - like processes carrying allochthonous material to the centre of the lake. ! (2) Sands: ! (2.1) Fine green sands: Massive, isolated levels of 3-4 cm composed of a green silty matrix, and heterometric, angular carbonatic grains of 4-100 !m and quartz of 20-100 !m, with abundant amorphous OM and macrophytes remains. ! (2.2) Medium brown sands: Massive, in levels of 2-10 cm with irregular Depositional evolution of La Parra kasrtic lake (Iberian Chain, Spain) during the last 1,600 years: Climate and human impact implications 15 boundaries. They are composed of a fine-medium silty matrix and homometric alotriomorphous-altered carbonatic grains of 4-10 !m, with amorphous OM, macrophytes remains, invertebrate exoskeletons and heterometric angular quartz grains of 50-100 !m. ! (2.3) Coarse brown sands: Massive, with angular carbonatic pebbles of about 1 mm, and some up to 1 cm, in a level of 10 cm with very irregular boundaries. The matrix is composed by medium silt with heterometric angular, carbonatic grains, amorphous OM, diatoms remains and homometric angular quartz grains of 20-100 !m. Sand facies represents littoral to transitional deposition from relatively low energy (fine sands) to high (coarse sands). They represent alluvial input of watershed sediments and littoral erosion of previously deposited lake sediments transported to deeper areas of the lake. ! (3) Gravels: ! (3.1) Fine brown gravels: Massive, in only one bed, 2 cm thick with irregular boundaries. Pebbles are carbonatic in composition, heterometric (less than < 5 cm) and angular. The matrix is formed by fine silts, with heterometric carbonatic grains of 10-40 !m and homometric quartz grains up to 40 !m. Amorphous OM and diatoms remains are also present. ! (3.2) Medium brown gravels: Massive, in only one bed 30 cm thick, with very irregular boundaries. Pebbles are carbonatic, less than 5 cm long, in a silty matrix. Matrix is composed by heterometric alotriomorphous carbonatic grains of 4-25 !m. Diatoms, amorphous OM, invertebrate exoskeleton fragments and heterometric quartz grains of less than 100 !m are also present. Gravel facies imply very high-energy traction transport of allochthonous sediment originated in the watershed and transported by the small creek located at the SW of the lake and also reworking of sediments from shallow zones around the lake. Deposition of these facies in the centre of the lake suggests littoral environments dominated even these areas. Laminated, endogenic carbonate facies There is only one facies in this group (Fig. 10): ! (4) Fine laminated silts with endogenic carbonate: Constituted by 5 cm thick intervals composed of 1 mm thick white calcitic and dark OM laminae with net and regular boundaries. Calcite layers are composed by homometric subidiomorphous carbonatic grains with some amorphous OM and homometric angular quartz grain of up to 30 !m. Diatoms are very abundant in this facies, particularly in the organic laminae. The distinctive characteristic of facies 4 is the presence of laminations and the occurrence of endogenic calcite. It consists of couplets of light (white) and dark (black) laminae, similar to carbonate laminites found in many karstic lakes in Spain (Zoñar, Martín – Puertas et al., 2008; Arreo, Corella et al., 2010; Montcortès, Corella et al., 2010; La Cruz, Romero-Viana et al., 2008). The light laminae are composed of calcium carbonate Fernando Barreiro-Lostres 16 crystals formed in the epilimnion during algae blooms in summer and the dark ones consist mainly of organic-rich silts with some fine quartz clasts deposited during late summer and winter. Laminations in lacustrine deposits are frequently associated with a lower energy environment, less alluvial influence, and the existence of stratified waters, usually in deeper lake level stages (Brauer et al., 2004). Depositional evolution of La Parra kasrtic lake (Iberian Chain, Spain) during the last 1,600 years: Climate and human impact implications 17 Fig. 10: 1.1A) Fine grey silts - SEM image: homometric calcite and diatoms. 1.1B) Fine black silts - SEM image: altered crystals of dolomite, round quartz grains and diatoms.1.2) Medium brown silts - SEM image: rounded and irregular carbonatic grains.1.3A) Coarse light silts - SEM image: heterometric irregular dolomite grains. 1.3B) Coarse dark silts - SEM image with heterometric dolomite grains. 2.1) Fine green sands with the characteristic green matrix. 2.2) Medium brown sands showing some of the light carbonatic pebbles. 2.3) Coarse brown sands and finer silty facies.3.1) Fine brown gravels whit white carbonatic pebbles. 3.2) Medium brown gravels. 4) Fine laminated silts - SEM image: abundant diatoms and fine endogenic calcite crystals Fernando Barreiro-Lostres 18 Substrate The base of La Parra lacustrine sequence is the Cenomanian green marl formation. The substrate consists of gravels (Fig. 11) with a green matrix and some evidences of chemical alteration (corrosion, dissolution) of the heterometric and angular carbonatic pebbles (0,5-5 cm). The matrix is formed by homometric angular carbonatic grains of 50- 70 !m and quartz of 80-100 !m. Litostratigraphic Units. The sedimentological and geochemical analyses (see text below) allowed to distinguish three main lithoestratigraphic units (units I to III, Fig. 12) corresponding to the lacustrine record. The base of the sequence (Unit IV) is composed of Cenomanian green marls, with evidences of karstic alteration (dissolution and brechification textures). Unit III is formed by a coarsening upward sequence, showing medium brown silts (facies 1.2) in the bottom and an alternation between coarse dark silts (facies 1.3B) and fine green sands (facies 2.1) towards the top. Unit II presents a fining upward sequence, which starts with fine and medium brown sands (facies 2.2), followed by an alternation between coarse black silts (facies 1.3B) and medium brown silts (facies 1.2) distributed in layers from 5 to 20 cm thick. Unit I is composed of three fining upward sequences: i) the lower, Fig. 11: Photograph showing the base of the sequence: altered green Cenomanian marls. Fig. 12: Sedimentary sequence for PA10-1A-U core, including: sedimentary units and sections, core CCD image, sedimentological profile and grain evolution of main sequences. Sif: fine silts; Sim; medium silts, Sic, coarse silts; Savf: very fin sands; Saf: fine sands; Sam: medium sands; Sac: coarse sands; Gf: fine gravels; Gm: medium gravels. Depositional evolution of La Parra kasrtic lake (Iberian Chain, Spain) during the last 1,600 years: Climate and human impact implications 19 formed by a 30 cm interval of medium brown gravels (facies 3.2), followed by alternating coarse black silts (facies 1.3B) and medium brown silts (facies 1.2) in layers of 10-15 cm thick; ii) the intermediate sequence is the most variable in facies; it starts with a fining upward 40 cm thick subsequence, from coarse brown sands (facies 2.3) to fine laminated silts (facies 4), and continues with an alternation of coarse dark silts (facies 1.3B) and fine laminated silts (facies 4) -with presence of facies 1.3A and 1.2-; towards the top, coarse black silts (facies 1.3B) and medium brown silts (facies 1.2) with facies 4 occurs; iii) the upper sequence is formed by two fining upward subsequences: the lower one, 20 cm thick, is composed by fine brown gravels (facies 3.1), coarse light an dark silts (facies 1.3A and 1.3B) and medium brown silts (facies 1.2), and the upper subsequence, 95 cm thick, starts with medium brown sands (facies 2.2), continues with alternating facies 1.3B and1.2, and finishes with fine grey silts (facies 1.1A). Mineralogy The sediments of lake La Parra are mainly composed of three mineral types (Fig. 13): carbonates, the most important contributors (91,4 %), with dolomite, calcite, magnesiancalcite and aragonite; clay minerals (5,1 %) represented by illite and clinochlore; and other silicates (3,5 %), mainly quartz and microcline. The mineralogy is dominated by dolomite, which is coherent with the carbonated steep scarps (basically dolostones) surrounding the lake's basin and the watershed. Fig. 13: Left: Average distribution of different minerals measured by X-ray diffraction (XRD) for the sedimentary record of Lake La Parra in percentages. Right: Percentages of the mineralogical species grouped by families. In Fig. 14 the mineralogical composition of Lake La Parra sediments are represented versus the composite depth. Mineralogical composition does not show large changes through the sequence. Nevertheless based on mineral dominance and the occurrence of some minor mineral phases, the three sedimentological units show some differences. Unit III is characterized by high values of dolomite, illite and quartz, decreasing towards the top, and the presence of aragonite, calcite and Mg-rich calcite in some intervals.. Unit II and the bottom of Unit I are characterized as well by high values of dolomite, illite and quartz. These minerals experiment a slight decrease at the beginning of Unit I, coinciding with the deposition of gravels. During Unit II, Illite and clinochlore present high values, coherent with the abundance in fine-grained facies. The middle of Unit I is characterized by the highest values in calcite, and the occurrence of Mg-calcite and aragonite. Aragonite occurs in two intervals at the onset of deposition of laminated facies and just after them. During deposition of laminated facies, clinochlore and illite are more abundant. The top of Unit I is characterized by higher calcite and illite contents and the decrease of dolomite. Fernando Barreiro-Lostres 20 One of the clear features of the mineralogical composition of La Parra sequence is that silicate fraction (quartz, clay minerals, microcline) distribution presents a similar pattern as dolomite. That is a clear indication of the clastic nature of dolomite in La Parra Lake. This assessment is supported by the fact that well-formed, euhedral dolomite crystals have not been identified, either on sediment frotis or SEM images in any facies. The illite and clinochlore are more abundant in fine-grained facies. Calcite has an opposite pattern compared to dolomite, showing significant peaks in Unit III and in the middle of Unit I. The peak of Unit III and the peaks of Unit I coincide with the presence of aragonite (580, 240 and 120 cm respectively), and they are related to laminated facies. Mg-calcite, occurs at the transition between Unit III and II and in the middle of unit I, and it seems associated to shallowing – upwards trends from silts to sands. It is interesting to notice that Mg-Ca peaks always occur prior to aragonite peaks, suggesting that carbonate phase succession could be related to increase salinity as shown in other carbonate lakes (Morellón et al., 2009). Fig. 14: Mineralogical profiles measured by X-ray diffraction (XRD) for the composite sequence of Lake La Parra in percentages versus depth. Lithological units are indicated by the left panel. Geochemistry XRF analyses allow high-resolution reconstructions of past global and climate changes in marine sediments (Richter et al. 2006) and in lakes (Moreno et al., 2008; Saez et al., 2009). It has been found that the relationships between the intensity of the XRF signal between different elements vary over time with changes in lake dynamics, which is ultimately driven, by changes in climate or in the lake environment or the watershed (Kylander et al., 2011). Several examples of karstic lakes in Spain have been recently Depositional evolution of La Parra kasrtic lake (Iberian Chain, Spain) during the last 1,600 years: Climate and human impact implications 27 of Sr/Ti, Ca/Ti, TIC and TOC, single out a period from 1400 to 1700 cal. yr. AD with the highest lake levels and frequent anoxia in the bottom. During this period - chronologically coinciding with the Little Ice Age (LIA, 1300-1850) - the absence of high-Mg calcite in the mineral phases suggest less mineralized waters. Development of laminated facies, longer periods of meromixis and higher lake levels have been described as well in the nearby Lake La Cruz (Julià et al., 1998) during this period. Two periods of relatively lower lake levels during this stage have been identified. A short dry period in the XVth century (1450-1400 AD) is suggested by the presence of coarser sandy facies and high values in Ca/Ti and Sr/Ti ratios. Later on, coarse clastic facies are deposited around 1700 cal. yr. AD (facies 3.1 and 2.3), coinciding with high values of Sr/Ti, Ca/Ti, Pb/Ti, Cu/Ti and Zn/Ti, suggesting an increase in clastic inputs and relatively lower lake levels, probably due to a new agricultural period. Fig. 17: The five main stages of the depositional history and environmental evolution of Lake La Parra during the last 1600 cal. Yr AD. Fernando Barreiro-Lostres 28 Stage V: Slight increase of lake levels on recent times, from 1850 to 2010 cal. yr. AD The dominance of massive fine silts in the upper part of Unit I indicates a slight increase of water table levels on recent times, after 1900 AD, coinciding with a decrease in Al/Ti and Si/Ti ratios. Contrary, Pb/Ti, Cu/Ti and Zn/Ti show increasing values, maybe indicating a major human impact in the basin due to agricultural practices during the last century. The absence of fine laminated facies and the high values of Mn/Ti, suggest the dominance of oxic bottom conditions. Climate and Human Impact in Las Torcas Complex during the last 1600 years Climatic changes are expected to amplify the hydrological variability in the Mediterranean region, where climate, water availability and human activities have been strongly interdependent. The paleohydrological fluctuations and the evolution of the sedimentary environments in La Parra provides an excellent case study of such variability, because the sedimentary record of Lake La Parra is the longest and more accurately dated record of Las Torcas Complex, spanning the last 1600 cal. yr. BP. Other available paleohydrological reconstructions in this lake complex from La Cruz Lake and Lagunillo del Tejo sedimentary records, see figures 18 and 19 (Julià et al., 1998; Romero-Viana et al., 2010; López-Blanco et al., 2011), have also identified several climatic fluctuations during the last millennia, particularly the Medieval Climatic Anomaly (MCA) and the Little Ice Age (LIA), showing rapid successions between wet and dry periods. Episode I: The onset of lacustrine sedimentation during the end of the Iberian-Roman Humid Period (IRHP), 300 to 500 cal. yr AD, with a rapid increase in water table levels and development of anoxia. The rise in water level would have coincided with an increase in regional humidity, which have been observed as well in nearby lacustrine records (Lake El Tejo, unpublished data) and in other examples from the NE Spain as the lakes Estanya (Morellón et al., 2009) and Moncortés (Corella et al., 2010) in the Pre-Pyrenean zone, or in the salt lakes of La Playa and La Salineta in the Ebro’s Basin (González-Sampériz et al., 2008). Interestingly, this increase in humidity occurred at the end of the IRHP a wet period in the west Mediterranean region, and not at the beginning as in southern Spain (Zoñar Lake, Martín – Puertas et al., 2008). Local hydrogeological factors or a regional variability in moisture availability in Iberian Peninsula during the IRHP could explain this N-S variability. Episode II: Rise of water levels during the Dark Ages (DA, 500 to 900 cal. yr AD), and lowering of lake levels with increase in detritic input during the Medieval Climate Anomaly (MCA), from 900 to 1400 cal. yr AD Deposition of homogenous, fine sediments suggests higher lake levels during the first part of the medieval period (Dark Ages). Higher clastic input during this period occurred not only in La Parra, but also in La Cruz Lake (Julià et al., 1998). Higher clastic input could be related to the strong human impact associated to the frequent wars between the Muslims and the Christians (Reconquest) and the emergence of the livestock breeding (“Mesta”) lands with frequent burning practises to clear vegetation to increase grassland for pastures (Julià et al., 1998). The presence of coarse facies during this period is indicative of lowered lake levels, as occurs in Lagunillo del Tejo, where periods (López- Blanco et al., 2011) of slightly lower lake levels around 1150 and 1250 AD, and particularly low levels around AD 1400 have been identified. Episode III: High lake levels and development of meromictic conditions during the Little Ice Age (LIA), from 1400 to 1800 cal. yr. AD. This period is characterised by generally higher lake levels and lower salinity waters in Depositional evolution of La Parra kasrtic lake (Iberian Chain, Spain) during the last 1,600 years: Climate and human impact implications 29 all the Torcas (Lagunillo del Tejo, La Cruz, La Parra). Deposition of laminated facies in La Parra is indicative of higher lake levels and likely a reflection of higher effective moisture. However, some anthropogenic effects may have played a significant role. The development of anoxic conditions in La Cruz with consequent deposition of laminated facies with endogenic calcite have been explained by changing farming practices (Julià et al., 1998), with the full development of nomadic livestock breeding or transhumance (“Mesta”). A sparse vegetation cover would favour the rise of the water level in the lake, due to the decrease of plant evapotranspiration. Historical sources (Klein, 1994) indicate that seasonal transhumance or “Mesta” was widespread all over the Cuenca territory during the XVIth century, reaching a maximum from 1500 to 1550 AD, when more than 3 million head of cattle were recorded. Higher lake levels in Lake La Parra contrast with the low lake levels of Lagunillo del Tejo around 1550-1600 AD (López-Blanco et al., 2011). Based on the macrofossil data and historical record, these authors considered that the sixteenth century was locally very dry. The different hydrology and bathymetry of La Parra (17 m water depth) and El Lagunillo del Tejo (7 m water depth) could be responsible for different sensitivities to hydrological changes. The relatively shallow depth of El Lagunillo de El Tejo could have amplified the environmental changes during the LIA. The 1760-1800 period coincident with the Malda anomaly (Barriendos y Llasat, 2003) is characterized by major climatic fluctuations, with rapid succession of droughts and floods (Romero-Viana et al., 2010). Nevertheless, from the middle of the eighteenth century, both lakes recorded successively lower lake levels, coinciding with important droughts in both northern and southern Spain around 1750 AD (López-Blanco et al., 2011). The end of the LIA is characterized in La Parra as a period of relatively lower lake levels with deposition of coarser facies. Episode IV: Relatively high lake levels from 1800 to 2010 cal. yr. AD. During this period, the lake level is generally high, with some minor episodes of lower levels, coincident with the drought at the beginning of the 20th century (López-Blanco et al., 2011). Later, fine facies and depositional sub-environments are similar to the presentday distribution. Clastic input from the watershed is relatively high, and carbonate production is restricted to the epiliminion and the littoral areas. Up to the mid 20th century, a demographic increase occurs, with increased agricultural pressure in the watershed, and even the use of some terraces in the Lagunillo del Tejo basin at the beginning of the twentieth century (López-Blanco et al., 2011). Increase in some heavy metals in La Parra sequence, could be related to higher anthropogenic pressure during the late 19th and mid 20th centuries. Fernando Barreiro-Lostres 30 Fig. 18: Compilation of the macrocharcoal record and lake-level reconstruction from Lagunillo del Tejo (first right sub-panel, López-Blanco et al., 2011), synthetic pollen and charcoal records from Lake La Cruz (second right sub-panel, Julià et al., 1998) and principal socio-economic and climatic changes; compared with the stratigraphic profile of Lake La Parra, the periods of higher water levels, and the main geochemical indicators Depositional evolution of La Parra kasrtic lake (Iberian Chain, Spain) during the last 1,600 years: Climate and human impact implications 31 Climate and paleohydrology in the Iberian Peninsula The number of extant lakes in Spain is relatively small, compared with other countries, but they occur in a variety of geographic, climatic and ecologic settings (Valero-Garcés and Moreno, 2011). The dominance of semi-arid conditions at present day in a large part of the Iberian Peninsula makes this region very sensitive to hydrological and climatic variations. The intense water management during its long history of human occupation highlights the decisive role of hydrological resources. A number of studies in lakes have been carried out in the Iberian Peninsula to provide reconstructions of past climatic changes to understand the climate mechanisms and the hydrological impacts, as summarised in Moreno et al. (2011). Fig. 19: Location of other lacustrine records used for comparison: in the North of Spain, Moncortés and Estanya; Centre of the Peninsula, Somolinos, La Cruz and Lagunillo del Tejo; and in the South of Spain, Zoñar lake. Two Pre-Pyrenean Spanish lake records (Northern Spain, Fig. 19), Moncortès and Estanya show good correlation with main climatic changes reconstructed for the last 1600 years in Lake La Parra. In Moncortès lake, (Corella et al., 2010) warmer temperatures and arid conditions have been suggested during the MCA (1000-1300 AD), coinciding with a period of high clastic input; while the LIA (1330-1840 AD) marks an episode of lower clastic input (low magnetic susceptibility) occurred during wetter climatic conditions and likely decrease anthropic pressure in the watershed. At nearby brackish karstic Estanya lake, shallower water levels and saline conditions predominated during medieval times (870-1300 AD), and generally higher lake levels and more diluted waters during the LIA (1300-1900 AD), althought this period shows a complex pattern of wet and arid intervals (Morellón et al., 2009). Maximum lake levels occurred during the nineteenth century, and declined during the twentieth century. Inside Las Torcas Lake Complex (Middle-East Spain, Fig. 19), La Cruz lake record (Julià et al., 1998) shows lower lake levels during the ninth-eleventh centuries (Medieval Fernando Barreiro-Lostres 32 ages), indicative of drier conditions. Later, the development of meromictic conditions during the LIA is related to synergetic effects of colder temperatures and higher lake levels, suggesting wetter conditions. This pattern is similar to La Parra Lake. In Central Spain, between Tajo and Duero basins (Fig. 19), higher water levels have been also reported at Somolinos tufa lake (Currás et al., 2012), during the Late Roman Period, as suggested by the disappearance of benthic diatoms and a reduction in molluscs populations. Later, the marked increase in the proportion of facultative planktonic and benthic diatoms provides strong evidence for lake shallowing, suggesting a decline in lake levels after 370 AD, coinciding with the drop of water levels in Lake La Parra between 400-500 AD. In southern Spain, sedimentological data from Zoñar lake (Fig. 19, Martín-Puertas et al., 2008) presents a varved interval deposited during the Iberian-Roman ages (550 BCAD 350), with similarities with the short fine-laminated interval showed in La Parra record around 350-400 AD, although it includes an arid interval during the Roman Imperial Epoch (190 BC-AD 150). Then, from 300 BC to 600 AD, includes the most humid conditions of the last three millennia in southern Spain. Later, the record indicates arid conditions synchronous with the MCA and two humid periods between 1200 and 1400 AD and around 1600 AD during the LIA, consistent with La Parra record interpretation. Regional implications The paleohydrological and paleoenvironmental fluctuations reconstructed from Lake La Parra are coherent with other lacustrine records of the Iberian Peninsula (Fig. 20) showing overall agreement since 900 AD, giving confidence that they reflect common climatic forcing. In general, Iberian lakes show lower water levels and higher salinities during the 11th to 13th centuries, synchronous with the MCA. On the other hand, during the LIA (15th to 19th centuries) more humid conditions and higher lake levels have been reconstructed. This pattern is confirmed by other lake, marine and tree-rings records from Iberia and Morocco (Moreno et al., 2011) In contrast, some lakes of the eastern Mediterranean show an opposite pattern of wet MCA and dry LIA (Roberts et al., 2012) (Fig. 20), reflecting an anti-phase relationship in precipitation and atmospheric pressure with the western Mediterranean. Then, Lake La Parra provides additional paleolimnological evidence for an east-west climate see-saw pattern in the Mediterranean for the MCA and the LIA, enforcing the hypothesis of an east-west climate anti-phase in this region since 900 AD. Depositional evolution of La Parra kasrtic lake (Iberian Chain, Spain) during the last 1,600 years: Climate and human impact implications 33 . Fig. 20: Centennial trends in proxy climate records (Roberts et al., 2012) compared with the main geochemical proxies of Lake La Parra record. High water levels are represented in blue. First right subpanel - Western Mediterranean: Moncortés magnetic susceptibility, Estanya PCA axis 2 and Moroccan tree ring data. Second right subpanel – Eastern Mediterranean: !18O for Nar and Van lakes and Levantine marine cores Fernando Barreiro-Lostres 34 Conclusions The sedimentary record of Lake La Parra constitutes the longest (6,93 m, last 1600 years) and more accurately dated record (nine radiocarbon AMS samples) of Las Torcas Lake Complex. The sedimentary and hydrologic reconstruction based on sedimentological, geochemical and mineralogical analysis has allowed identification of four main lithostratigraphical units and five main paleohydrologic episodes during the Late Holocene. Four main depositional sub-environments have been described based on the spatial distribution of sedimentary facies in Lake La Parra: (i) the littoral platform; (ii) the talus area; (iii) the offshore transitional area; and (iv) the offshore distal area. The distribution of these sub-environments is controlled strongly by lake bathymetry that today exerts a key influence on the depositional conditions. The sedimentary sequence of Lake La Parra is mainly constituted by clastic carbonated sediments and it is characterized by a high variability of sedimentary facies, mainly controlled by changes in the detritic input and hydrological variability along the last 1600 years. The onset of lacustrine sedimentation around 250 yr AD demonstrates a rise of the water levels that changed the hydrogeology of the basin from a “dry” to a “flooded” torca. The dominance of fine clastic homogeneous sedimentation before the 8th century (Dark Ages) suggests a period of relatively high lake levels. Deposition of relatively coarser clastic facies during the late Middle Ages is interpreted as a decrease in lake levels synchronous to the Medieval Climate Anomaly (900-1400 AD) and the impact of increased human activities in the region to increase grassland for pastures with the emergence of “Mesta”, the livestock breeding transhumance. The deposition of fine silts and the presence of fine-laminated facies, which reflect a trend to more frequent anoxia in the bottom of the lake, are coherent with higher lake levels during the Little Ice Age (1400- 1800 AD). More recently, a slight lowering of water levels is indicated by deposition of coarser facies around 1900 AD. Deposition during the last century is dominated by fine silts facies. The increase of detrital input in Lake La Parra during the Middle Ages is in agreement with the effect of socio-economic transformations and climate change observed in nearby Lagunillo del Tejo (López-Blanco et al., 2011) and Lake La Cruz (Julià et al., 1998). The main socio-economic land use changes were the woodland clearance to increase grassland for pastures during the 16th century. However, the geographical situation and climate conditions limited the land management either during past and present to forest exploitation, pastures and small areas of cereals and subsistence agriculture, without excessive modification of the natural environment (Romero-Viana et al., 2010). Although the lakes and watersheds are protected, currently, the local karstic aquifer feeding the lake complex is being exploited for irrigation. The paleohydrological and paleoenvironmental fluctuations of Lake La Parra can be correlated with other lacustrine records of the Iberian Peninsula. The main climate and hydrological episodes recorded in La Parra are coherent with available Iberian records. Especially relevant are: i) the synchronicity of the Iberian-Roman Humid Period (300-500 AD) with the presence of fine-laminated sediments, indicating a wetter episode with high lake-levels of regional significance although with large regional variability, ii) the occurrence of shallower lake levels during a drier phase corresponding with the Medieval Climatic Anomaly; and iii) the development of laminated facies with endogenic carbonates from 1450 to 1650 AD, coincident with the Little Ice Age and suggestive of higher lake Depositional evolution of La Parra kasrtic lake (Iberian Chain, Spain) during the last 1,600 years: Climate and human impact implications 35 levels although with a large climate and hydrological variability. 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