Search

Most studies on the geomorphological evolution of the Holocene from the Ebro depression (NE Spain) are focused on the period up to the Roman Epoch (218 BC–476 AD) while some references to medieval (476 AD–15th century) deposits are also occasionally dated. This paper focuses on the establishment of aggradation units on the valley bottoms and slopes of the Ebro depression after 1400 BP, their origin, comparison with other areas, and relationship with global paleoenvironmental changes. These units were produced after the incision phase that marked the end of the large Holocene accumulation (unit H1) around 1400 BP (at the end of the Late Roman Epoch). Morphosedimentary records enable us to establish three aggradation units during the last 1400 years: unit H2 (ca. 1400–650 cal BP); unit H3 – with two H3A subunits (ca. 650–500 cal BP) and H3B (ca. 500–320 cal BP); and the H4 unit (after 320 cal BP). These units are organized following five types of aggradation/incision arrangements with differing complexities. There are also connections among these units and two slope stages in the region. Finally, the genetic relationships between these units and global paleoenvironmental changes are shown (LALIA, MCA, and LIA) and related to anthropic activity. This contribution is the first detailed and systematic approach to the study of morphosedimentary units and sedimentary arrangements during the Recent Holocene in the Mediterranean area. [ABSTRACT FROM AUTHOR]

Sedimentological evidence for an abrupt dry spell in south-eastern Spain during the middle Holocene, from c. 4906 to 4384 cal. yr BP, is presented. This phase was determined primarily from halite beds deposited between muddy slimes in a lagoon system of Puerto de Mazarrón (Murcia province) with a peak phase from c. 4550 to 4400 cal. yr BP. A multi-core, multi-proxy study of 20 geotechnical drills was made in the lagoon basin to identify the main sedimentary episodes and depositional environments. The results suggest that this halite bed, more than 80 cm thick, was conditioned by climate change and was accompanied by a generalized drying-out of the basin. Halite precipitation was linked with palaeoecological changes, including forest and mesophyte depletions and increasing cover and diversity of xerophytic plant species. Archaeological evidence indicates a demise of the population at this period probably due to resource exhaustion. An overall picture of the biostratigraphy and palaeoclimates of the region is given in a broader geographical context. [ABSTRACT FROM AUTHOR]

Three contrasting sedimentary environments on the continental shelf off the Guadiana River (northern Gulf of Cadiz) were integrated in a chronological framework and analysed in terms of sedimentology and benthic foraminiferal assemblages to understand the Holocene paleoenvironmental evolution. The analysed environments differ in terms of their depositional regimes and benthic foraminiferal assemblages. However, a dominant fluvial origin of the sand fraction was observed in all three environments. Holocene sedimentary processes were mainly controlled by natural (sea level changes and climate variations) and human-induced processes (e.g. deforestation, agriculture) along four evolutionary stages. The three older stages were mainly influenced by natural processes, such as sea level variations and fluvial inputs, whereas the most recent stage reflects a combination of climatic- and human-induced processes. A deepening of sedimentary environments related to a period of rapid sea level rise, strongly influenced by river discharges occurred from c. 11,500 to c. 10,000 cal. yr BP. A reduction in sediment export to the shelf, as a result of the continuous and rapid sea level rise and enhanced estuary infilling reflects the second stage, from c. 10,000 to c. 5000 cal. yr BP. The beginning of the third stage, from c. 5000 to c. 1500–1000 cal. yr BP, is marked by a sea-level slowdown and the relatively stable climate and environmental conditions. The fourth stage, from c. 1500–1000 cal. yr BP to Recent times, reflects the intensification of human-induced processes and climatic variability in the Guadiana River basin. This stage also reflects modern depositional conditions, with the formation of a proximal prodeltaic wedge and a distal muddy body. [ABSTRACT FROM AUTHOR]

The late Holocene in the central Ebro Depression is characterized by a number of morphodynamic stages that affected hillslopes and channels. Climate fluctuations and human activities together caused severe erosion and floods, resulting in alternating stages of accumulation and incision in the valley floors. Seven accumulation levels (N6-N0) correlated with Ebro River fluvial terraces have been identified in the secondary fluvial network of the central Ebro Depression. The main accumulation level (N3) corresponds to a long period of increased hillslope erosion and sedimentation in the valleys, from the Neolithic to the late Roman periods. The accumulation levels are evident throughout the valleys and extend to the valley mouths, where many connect with alluvial fans. The study of several sedimentological profiles, 14C AMS dating, and many archaeological remnants, have enabled detailed assessment of sedimentation characteristics in the alluvial fans and the relationship thereof to the presence of human settlements. Four sedimentation stages have been identified: (i) pre-Bronze Age (> 3800 years BP), (ii) Bronze Age/Iron Age (3800-2500 years BP), (iii) Roman/post-Roman period (2500-1500 years BP), and, (iv) the early Middle Ages, mainly during the Visigothic period (sixth century). The sedimentation dynamics of the alluvial fans are related to: (i) climate variability, (ii) human activities in the watershed, and (iii) the meandering character of the Ebro River, which has lateral displacements that change the local base level of tributaries and fans. Level N3 in the valley floors corresponds to stages i-iii of the alluvial fans, which are mostly related to human-induced transformation of characteristics of the secondary basins, coinciding with enhanced erosion under favorable (warm and humid) climatic conditions. In contrast, the Medieval stage, which corresponds to level N2 in the valleys, was caused by floods during a period of high climatic variability. [ABSTRACT FROM AUTHOR]

Eight sites distributed over a distance of some 400 km of the Cantabrian coast (northern Spain) provided 153 wood, 50 fruit and over 350 leaf remains belonging to the area's Holocene forests. The high taxonomic precision with which these macroremains were identified (in many cases at the species level), plus the accurate information available regarding the original growth locations of these plants, provide new geobotanical insights into the history of northern Spain's Atlantic forests. Radiocarbon dating of the wood samples showed the collected material to have lived between 8550 and 800 cal. BP. Analysis of the macroremains showed the deciduous mixed forests of the Holocene to contain a majority of Quercus robur and Corylus avellana, accompanied by Acer pseudoplatanus, Ulmus minor, Castanea sp., and hygro-thermophilous taxa (Arbutus, Laurus and Vitis vinifera). The remains of hygrophilous communities, dominated by Salix atrocinerea, Alnus glutinosa and Fraxinus sp., show these to have expanded during the Holocene. The absence of conifer macroremains is interpreted as reflecting the disappearance of Würmian conifer populations at the beginning of the Holocene. The different taxa (eg, Ilex spp. and V. vinifera) that survived the last glaciation in the refugia offered by Spain's northern coast persisted in the same areas during the Holocene. A leaf sample of Ulmus minor dating to 3950 ± 120 cal. BP reveals for the first time the natural occurrence of this species on the northern coast of Spain. [ABSTRACT FROM AUTHOR]

A high-resolution, 5300-yr record of pollen and lithogenic elements (K, Ca, Ti, Rb, Sr, Y, Zr) from an ombrotrophic peat bog located in northwest Spain, reveals that the variations in the fluxes of lithogenic elements supplied to the bog by atmospheric deposition were coupled to the evolution of the vegetation of the area. A strong negative correlation exists between the percentage of tree pollen and the concentration of lithogenic elements. For example, the correlation between total tree pollen and Sr concentrations is -0.94. The main phases of decline of the deciduous forest occurred during known cultural periods (late Neolithic, the Metal Ages, the Roman Period, the Middle Ages and the Industrial period) suggesting a close link between human activities (fires and forest clearances), changes in the vegetation and soil erosion. The flux of lithogenic elements seems to have increased before a significant variation in pollen is detected, which may indicate that changes in soil erosion are reflected earlier than the changes in vegetation in the bog record. Variations in the composition of the deposited dust reflect impacts that occurred at different spatial scales, with local sources dominant in the late Neolithic, the Metal Ages and the Middle Ages, whilst regional sources are more important in the Roman period and the Industrial Revolution. During the prehistoric period, arboreal pollen percentages recovered to their former levels, suggesting that woodland regenerated following a disturbance phase, but for the last 1400 years no significant recovery took place until afforestation with pines was introduced 200 years ago. While this must be the result of continuous clearances to convert forest into arable land, a cumulative effect on soil degradation must also be implied. [ABSTRACT FROM AUTHOR]

A Holocene palaeoecological sequence from Villaverde, south-central Spain, is presented. The pollen stratigraphy is used to infer past vegetation changes within a catchment area that represents the boundary between semi-arid, plateau and mountain vegetation. From c. 9700–7530 cal. yr BP, Pinus is dominant, probably as a result of a combination of a relatively dry climate and natural fire disturbance. From c. 7530–5900 cal. yr BP, moderate invasion by Quercus appears to be a migrational response following increased moisture and temperature, but in part shaped by competitive adjustments. From c. 5900–5000 cal. yr BP, the pine forests are replaced by deciduous-Quercus forests with an important contribution from Corylus, Betula, Fraxinus and Alnus. Mediterranean-type forests spread from c. 5000 to 1920 cal. yr BP coincident with expansions of Artemisia, Juniperus and other xerophytes. From c. 1920–1160 cal. yr BP, Pinus becomes dominant after a disturbance-mediated invasion of the oak forests. Human impact upon the regional landscape was negligible during the Neolithic, and limited in the Bronze and Iron Ages. Local deforestation and the expansion of agropastoral activities occur after c. 1600 cal. yr BP. [ABSTRACT FROM AUTHOR]

Palaeolimnological data (diatoms, ostracods, foraminifera, molluscs, aquatic pollen and lithology) 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 oscillations culminate in maximum lake levels from c. 6960–6680 cal. BP (c. 6070–5830 BP), indicating enhanced early- to mid-Holocene humidity and a mid-Holocene humidity maximum. Prolonged shallowing thereafter reflects in part increased aridity in the later Holocene. Lake desiccation followed by a c. 800-yr phase (zone 2) of major limnological change commencing at c. 8000 cal. BP (c. 7200 BP), and a number 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 uncertain; there is some evidence it may apply predominantly to the westerly (Atlantic) Peninsula, with 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 on c. 8.1–8.2 cal. BP. Other correlations made 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 decadal- to century-scale climatic variability throughout the Holocene. [ABSTRACT FROM AUTHOR]

Pollen analysis from a 14.1 m core recovered from a valley mire at Espinosa de Cerrato (Palencia, Spain), suggests that Pinus woodland has dominated this area of the Northern Meseta throughout almost the entire Holocene, in contrast to many other locations in Iberia where early-Holocene conifer woodland was progressively replaced by deciduous taxa. This unique pattern of vegetation development is attributable to a combination of continental climate, edaphic conditions of these Mesetas, and perhaps fire. These data suggest that vegetation in this area has been remarkably stable over an extended timescale and that arguments concerning Pinus communities not being native in the region are unfounded. Anthropogenic impact can be detected at c. 4500 [sup 14C] yr BP, affecting evergreen Quercus woodlands, and between c. 3000 and 2000 [sup 14]C yr BP affecting Pinus woodlands. The pine forests were replaced by plant communities resembling the present-day landscape (shrubs and cereals) from c. 1500 [sup 14]C yr BP. [ABSTRACT FROM AUTHOR]

A radiocarbon-dated peat core from Ojos del Tremedal, Montes Universales, Spain, provides insights into the dynamics of high montane forest communities in Central Iberia from the Lateglacial to the late Holocene. The Lateglacial landscape was characterized by grassland dominated by Gramineae, Cyperaceae and Artemisia, together with Juniperus, which was invaded from c. 9600 cal. BP by Betula and Pinus as climate conditions improved. Given the reduced role that Betula plays currently in the region, its presence throughout most of the Holocene suggests that the area experienced more mesic conditions until c. 2500 cal. BP. Distinct signs of human interference in the vegetation are apparent from c. 3500 cal. BP. [ABSTRACT FROM AUTHOR]

New pollen-analytical data from the Navarrés peatbog (Valencia, eastern Spain) show a synchronous Late-Quaternary fluctuation of P. pinaster- (cluster pine) and Quercus- (oak) dominated assemblages. During glacial times, P. pinaster survived in refugia together with other trees such as Corylus, Fraxinus Quercus, and a number of Mediterranean shrubs such as Arbutus, Erica arborea, Olea, Phyllirea, Pistacia terebinthus, Myrtus communis and Viburnum tinus. These nuclei of vegetation expanded around c. 30 000–27 000 BP invading areas formerly occupied by pine forests. P. pinaster retreated considerably during the last glacial maximum and the Younger Dryas event, but not as much as Quercus. During c. 10 000–6000 BP, a local pine forest resisted possible oak and P. pinaster invasion. Around 6000 BP, P. pinaster was involved in a post-fire change towards oak-dominated vegetation. This work supports the contention that P. pinaster is native to the Iberian Peninsula and that well-developed P. pinaster forests, particularly if mixed with oaks, are a natural feature of the landscape. The data presented here disagree with the floristic-phytosociological assumption that considers that the forest patches of P. pinaster and other Mediterranean species of pines are incidental and mainly derived from afforestation. [ABSTRACT FROM AUTHOR]

Analyses of pollen, non-pollen microfossils and carbonaceous particles from a valley mire in the Lozoya Valley in the Sierra de Guadarrama, which forms part of the Spanish Central System, are presented. The sedimentary sequence, which covers the last 8500 years, provides one of the oldest records in the central sector of this mountain chain. The core displays evidence of well developed Pinus sylvestris forests coupled with the presence of taxa such as Castanea or Olea in the early Holocene, highlighting the value of near-tree-line montane enclaves in the reconstruction of vegetation dynamics. The results show that the Lozoya Valley was an important refugial area for thermophilous taxa and that taxa like Olea and Castanea were present in pre-Roman times in this part of the Central System. In contrast to other areas of Spain and elsewhere in Europe where Quercus replaces Pinus in the early Holocene, evidence is presented of a natural pine belt in the Iberian continental montane system throughout the Holocene. The first signs of human impact are recorded in the pollen record at about 3740 BP, but major deforestation of the montane forests belts in the Sierra de Guadarrama is not visible until c. 1000 BP. This date is similar to dates for maximum human pressure in other Iberian environments and appears to be synchronous with a flourishing socioculture in Spain. [ABSTRACT FROM AUTHOR]