Petrogenesis of Early Neogene Magmatism in the Northern Puna; Implications for Magma Genesis and Crustal Processes in the Central Andean Plateau

New compositional data and petrogenetic models are presentedfor pre-Upper Miocene volcanism in the northern Puna of Argentina(22°S–24°S). Two phases of volcanism producedsmall dome complexes of mainly silicic andesite to low-SiO₂rhyolite. The Upper Oligocene–Lower Miocene phase (UOLM,20–17 Ma), produced two distinct groups of rocks. TheUOLM-1 group is metaluminous and mainly andesitic, with isotopiccompositions like those of the recent arc (⁸⁷Sr/⁸⁶Sr_T     

INDUSTRIAL HERITAGE AND PLACE IDENTITY IN SPAIN: FROM MONUMENTS TO LANDSCAPES*

In Spain, the birth of interest in the nation's industrial heritage dates from the 1980s and occurred alongside the process of deindustrialization. Policies concerning derelict industrial sites have shifted gradually from destruction to preservation, rehabilitation, and enhancement, and industrial heritage enhancement projects are now widespread in the country. However, a clear mismatching has arisen between institutional and academic initiatives and local communities, which exhibit widespread disinterest in or even rejection of industrial remains. This problematic situation can be related to the utilization of industrial heritage as an economic resource without paying much attention to its connections with memory and identity. Also, the mismatching is due to a positivist approach to industrial heritage whereby the monument and the museum are prioritized. We argue that projects which consider industrial remains as part of cultural landscapes might shorten the gap between the institutional and economic side of industrial heritage and its identity‐building and popular facets.     

Limitations of sequence stratigraphic correlation between marine and continental deposits: a 3D experimental study of unconformity-bounded units

Experiments have been carried out in a model basin 16 × 1·2 × 0·9 m to address the effect of base‐level and discharge changes on actively growing alluvial‐shoreline wedges. Two distinct types of erosive surfaces were investigated: one produced by base‐level fluctuations in the coastal zone and the other by discharge and supply fluctuations in the upstream alluvial basin. In the first experiment, three similar base‐level cycles were simulated keeping sediment supply and basin tilting constant within each cycle, and changing discharge from one cycle to the next. In the second experiment, rises and falls of base level were instantaneous and discharge changes were in phase (high discharge linked to high water levels in the basin). In the third experiment, base level and discharge changed gradually, at different rates and they were out of phase, resembling a typical glacio‐eustatic cycle in which sea‐level rises and falls are linked to increased and decreased discharge, respectively. The resulting stratigraphy of the alluvial to deltaic sedimentary wedge was analysed in terms of the development of unconformities and the evolving depositional geometry. An intervening decoupled zone between parts of the model basin dominated by alluvial processes and that at the coastal zone is identified. Within this decoupled zone, unconformities in the alluvial succession tend to vanish basinward, and base‐level generated coastal unconformities disappear landward. The two types of unconformity can be generated at different times during a glacio‐eustatic cycle, and it is thus erroneous to correlate them, even though they may appear to form a continuous surface. Unconformities within the modelled stratigraphy do not constitute time lines nor do they consistently separate younger from older beds, as they require a significant time to form and they have thick sedimentary packages as depositional correlatives. The experiments also support a fourfold division of sequences, showing the development of a significant sedimentary package during base‐level falls.     

Temporal Evolution of Magmatism in the Northern Volcanic Zone of the Andes: The Geology and Petrology of Cayambe Volcanic Complex (Ecuador)

In the Northern Volcanic Zone of the Andes, the Cayambe VolcanicComplex consists of: (1) a basal, mostly effusive volcano, theViejo Cayambe, whose lavas (andesites and subordinate dacitesand rhyolites) are typically calc-alkaline; and (2) a younger,essentially dacitic, composite edifice, the Nevado Cayambe,characterized by lavas with adakitic signatures and explosiveeruptive styles. The construction of Viejo Cayambe began >1·1Myr ago and ended at 1·0 Ma. The young and still activeNevado Cayambe grew after a period of quiescence of about 0·6Myr, from 0·4 Ma to Holocene. Its complex history isdivided into at least three large construction phases (Angurealcone, Main Summit cone and Secondary Summit cone) and compriseslarge pyroclastic events, debris avalanches, as well as periodsof dome activity. Geochemical data indicate that fractionalcrystallization and crustal assimilation processes have a limitedrole in the genesis of each suite. On the contrary, field observations,and mineralogical and geochemical data show the increasing importanceof magma mixing during the evolution of the volcanic complex.The adakitic signature of Nevado Cayambe magmas is related topartial melting of a basaltic source, which could be the lowercrust or the subducted slab. However, reliable geophysical andgeochemical evidence indicates that the source of adakitic componentis the subducted slab. Thus, the Viejo Cayambe magmas are inferredto come from a mantle wedge source metasomatized by slab-derivedmelts (adakites), whereas the Nevado Cayambe magmas indicatea greater involvement of adakitic melts in their petrogenesis.This temporal evolution can be related to the presence of thesubducted Carnegie Ridge, modifying the geothermal gradientalong the Wadati–Benioff zone and favouring slab partialmelting. KEY WORDS: adakites; ⁴⁰Ar/³⁹Ar dating; Cayambe volcano; Ecuador; mantle metasomatism; Andes     

Late Quaternary deposition and facies model for karstic Lake Estanya (North-eastern Spain)

Lake Estanya is a small (19 ha), freshwater to brackish, monomictic lake formed by the coalescence of two karstic sinkholes with maximum water depths of 12 and 20 m, located in the Pre‐Pyrenean Ranges (North‐eastern Spain). The lake is hydrologically closed and the water balance is controlled mostly by groundwater input and evaporation. Three main modern depositional sub‐environments can be recognized as: (i) a carbonate‐producing ‘littoral platform’; (ii) a steep ‘talus’ dominated by reworking of littoral sediments and mass‐wasting processes; and (iii) an ‘offshore, distal area’, seasonally affected by anoxia with fine‐grained, clastic sediment deposition. A seismic survey identified up to 15 m thick sedimentary infill comprising: (i) a ‘basal unit’, seismically transparent and restricted to the depocentres of both sub‐basins; (ii) an ‘intermediate unit’ characterized by continuous high‐amplitude reflections; and (iii) an ‘upper unit’ with strong parallel reflectors. Several mass‐wasting deposits occur in both sub‐basins. Five sediment cores were analysed using sedimentological, microscopic, geochemical and physical techniques. The chronological model for the sediment sequence is based on 17 accelerator mass spectrometry ¹⁴C dates. Five depositional environments were characterized by their respective sedimentary facies associations. The depositional history of Lake Estanya during the last ca 21 kyr comprises five stages: (i) a brackish, shallow, calcite‐producing lake during full glacial times (21 to 17·3 kyr bp ); (ii) a saline, permanent, relatively deep lake during the late glacial (17·3 to 11·6 kyr bp ); (iii) an ephemeral, saline lake and saline mudflat complex during the transition to the Holocene (11·6 to 9·4 kyr bp ); (iv) a saline lake with gypsum‐rich, laminated facies and abundant microbial mats punctuated by periods of more frequent flooding episodes and clastic‐dominated deposition during the Holocene (9·4 to 0·8 kyr bp ); and (v) a deep, freshwater to brackish lake with high clastic input during the last 800 years. Climate‐driven hydrological fluctuations are the main internal control in the evolution of the lake during the last 21 kyr, affecting water salinity, lake‐level changes and water stratification. However, external factors, such as karstic processes, clastic input and the occurrence of mass‐flows, are also significant. The facies model defined for Lake Estanya is an essential tool for deciphering the main factors influencing lake deposition and to evaluate the most suitable proxies for lake level, climate and environmental reconstructions, and it is applicable to modern karstic lakes and to ancient lacustrine formations.     

Palynological data on major Holocene climatic events in NW Iberia

Three NW Iberia Cantabrian Mountain pollen records are presented. They reflect the main Holocene climatic shifts in the North Atlantic region as recorded in the isotopic data from Greenland ice, Irish speleothems and reconstructed sea surface temperatures. Two brief forest regression episodes reconstructed from pollen may be synchronous with GH-11.2 and GH-8.2 events. At mid-altitude, two woodland expansion phases (7000-6000 ¹⁴C yr BP and 4000-2500 ¹⁴C yr BP) are separated by a phase of heaths and peat deposits. Major woodland declines occurred during the Galician-Roman Period (which includes the Bronze Age, the Iron Age and the Roman occupation) and from the end of the Medieval Period. The pollen data, backed up by archaeological and historical sources, suggest climatic impact of the Iron Age Cold Period, but are indecisive concerning the Little Ice Age. However, the pollen records do not support any significant 'Neoglacial' period (4000-3000 ¹⁴C yr BP) influence on NW Iberia.     

Bed‐thickness and grain‐size trends in a small‐scale proglacial channel–levée system; the Carboniferous Jejenes Formation,Western Argentina: implications for turbidity current flow processes

Preserved in Quebrada de las Lajas, near San Juan, Argentina, is an ancient subaqueous proglacial sedimentary succession that includes a small‐scale (ca 50 m thick and ca 200 m wide) channel–levée system with excellent exposure of the channel axis and levée sediments. Coeval deposition of both the channel axis and the levées can be demonstrated clearly by lateral correlation of individual beds. The channel axis consists predominantly of a disorganized, pebble to boulder conglomerate with a poorly sorted matrix. The channel axis varies from 10 to 20 m wide and has a total amalgamated thickness of around 50 m. Beds fine gradationally away from the cobble–boulder conglomerates of the channel axis within a few metres, transitioning to well‐organized pebble to cobble conglomerates and sandstones of the channel margin. Within 60 m outboard of the channel axis in both directions, perpendicular to the trend of the channel axis, the mean grain size of the beds in the levées is silt to fine‐grained sand. Deposits in this channel–levée system are the product of both debris flows (channel axis) and co‐genetic turbidity currents (channel margins and levées). Bed thicknesses in the levées increase for up to 10 to 25 m away from the channel axis, beyond which bed thicknesses decrease with increasing distance. The positions of the bed thickness maxima define the levée crests, and the thinning beds constitute the outer levée slopes. From these relationships it is clear that the levée crest migrated both away from and toward the channel axis, and varied in height above the channel axis from 4 to 5 m (undecompacted), whereas the height of the levée crest relative to the distal levée varied from 4·5 to 10 m, indicating that the channel was at times super‐elevated relative to the distal levée. Bed thickness decay on the outside of the levée crest can be described quite well with a power‐law function (R² = 0·85), whereas the thickness decay from the levée crest toward the channel axis follows a linear function (R² = 0·78). Grain‐size changes are quite predictable from the channel margin outward, and follow logarithmic (R² = 0·77) or power‐law (R² = 0·72) decay curves, either of which fit the data quite well. This study demonstrates that, in at least this case: (i) levée thickness trends can be directly related to channel‐flow processes; (ii) individual bed thickness changes may control overall levée geometry; and (iii) levée and channel deposits can be coeval.     

Large‐scale architecture in non‐marine basins: the response to the interplay between accommodation space and sediment supply

Sedimentary successions of non‐marine basins can be considered in terms of accommodation space and sedimentary supply changes. Changes in accommodation space controlling the large‐scale architecture of non‐marine basins are different in areas with high and low sedimentary supplies. Uplift of intrabasinal monoclines and anticlines reduced the available accommodation space, resulting in changes in both the geometry of the depositional sequences and the large‐scale architecture of fluvial, mudflat and shallow carbonate lacustrine deposits. Main drainage fluvial systems record areas with a high sedimentary supply, while mudflats and shallow fluctuating lakes represent areas that received less sediment. Two end members in the large‐scale architecture of main drainage fluvial system in the Almazán Basin (Spain) are: (i) ribbon‐shaped channel fills with low interconnectivity which pass laterally into mudflats dominated by mudstones and evaporites and into palustrine and shallow carbonate lacustrine deposits (mainly in the A2 depositional sequence); and (ii) sheet‐like channel fills with high interconnectivity laterally correlated with stacked calcretes in the marginal mudflats (in the upper part of A3). Ribbon‐shaped channel fills formed in areas of high accommodation space and sheet‐like channel fills formed in areas of reduced accommodation space.