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Research about Spain

Source-linked reports with geographic coverage including Spain.

At least 55 records · Page 3Linked to original sources
USGS2005

Seed storage conditions change the germination pattern of clonal growth plants in Mediterranean salt marshes

The effect of salinity level and extended exposure to different salinity and flooding conditions on germination patterns of three salt‐marsh clonal growth plants ( Juncus subulatus , Scirpus litoralis , and S. maritimus ) was studied. Seed exposure to extended flooding and saline conditions significantly affected the outcome of the germination process in a different, though predictable, way for each species, after favorable conditions for germination were restored. Tolerance of the germination process was related to the average salinity level measured during the growth/germination season at sites where established individuals of each species dominated the species cover. No relationship was found between salinity tolerance of the germination process and seed response to extended exposure to flooding and salinity conditions. The salinity response was significantly related to the conditions prevailing in the habitats of the respective species during the unfavorable (nongrowth/nongermination) season. Our results indicate that changes in salinity and hydrology while seeds are dormant affect the outcome of the seed‐bank response, even when conditions at germination are identical. Because these environmental‐history‐dependent responses differentially affect seed germination, seedling density, and probably sexual recruitment in the studied and related species, these influences should be considered for wetland restoration and management.

Doñana National Park↗
USGS2003

The impact of grazing on plant fractal architecture and fitness of a mediterranean shrub (Anthyllis cytisoides L.)

1. We examined natural grazing by livestock (sheep and goats) on Albaida Anthyllis cytisoides L. with the aim of determining whether variation in the allometric relationships between plant parts provides a sensitive indicator of the impact of grazing. 2. The intra-individual variation in translatory symmetry with scale and increased complexity of fractal structures reflect environmental disturbance under heavy grazing pressure and lack of grazing. 3. Fitness consequences of grazing were also investigated. Grazing promotes growth and adult survival, and a drop in seed production as a consequence of consumption. In spite of that, total inclusive fitness (population rate of change) tends to increase with grazing. 4. Moderate grazing, while promoting growth, also enhances stability of vegetative structures. The favourable effect of moderate levels of herbivory on A. cytisoides is reflected in the homeostatic maintenance of its translatory symmetry and in the increased complexity of its fractal structures.

Almería↗
USGS2003

Quantitative characterization of the regressive ecological succession by fractal analysis of plant spatial patterns

We studied the effect of grazing on the degree of regression of successional vegetation dynamic in a semi-arid Mediterranean matorral. We quantified the spatial distribution patterns of the vegetation by fractal analyses, using the fractal information dimension and spatial autocorrelation measured by detrended fluctuation analyses (DFA). It is the first time that fractal analysis of plant spatial patterns has been used to characterize the regressive ecological succession. Plant spatial patterns were compared over a long-term grazing gradient (low, medium and heavy grazing pressure) and on ungrazed sites for two different plant communities: A middle dense matorral of Chamaerops and Periploca at Sabinar-Romeral and a middle dense matorral of Chamaerops, Rhamnus and Ulex at Requena-Montano. The two communities differed also in the microclimatic characteristics (sea oriented at the Sabinar-Romeral site and inland oriented at the Requena-Montano site). The information fractal dimension increased as we moved from a middle dense matorral to discontinuous and scattered matorral and, finally to the late regressive succession, at Stipa steppe stage. At this stage a drastic change in the fractal dimension revealed a change in the vegetation structure, accurately indicating end successional vegetation stages. Long-term correlation analysis (DFA) revealed that an increase in grazing pressure leads to unpredictability (randomness) in species distributions, a reduction in diversity, and an increase in cover of the regressive successional species, e.g. Stipa tenacissima L. These comparisons provide a quantitative characterization of the successional dynamic of plant spatial patterns in response to grazing perturbation gradient. ?? 2002 Elsevier Science B.V. All rights reserved.

Cabo de Gata Natural Park↗
USGS2003

Geology and geochemistry of the Reocín zinc-lead deposit, Basque-Cantabrian Basin, Northern Spain

The Reocín Zn-Pb deposit , 30 km southwest of Santander, Spain , occurs within Lower Cretaceous dolomitized Urgonian limestones on the southern flank of the Santillana syncline. The Reocín deposit is one of the largest known strata-bound, carbonate-hosted, zinc - lead deposits in Europe. The total metal endowment of the deposit , including past production and remaining reserves, is 62 Mt of ore grading 8.7 percent Zn and 1.0 percent Pb. The epigenetic mineralization consists of sphalerite and galena, with lesser marcasite and trace pyrite with dolomite as gangue. Microprobe analyses of different generations of dolomite revealed nonstoichiometric compositions with various amounts of iron (up to 14 mol % of FeCO 3 ). Replacement of host dolomite, open-space filling of fractures, and cementation of breccias derived from dissolution collapse are the principal types of ore occurrence. Detailed cross-section mapping indicates a stratigraphic and structural control on the deposit . A stratiform morphology is present in the western part of the orebody (Capa Sur), whereas mineralization in the eastern part is highly discordant but strata bound (Barrendera). Stratigraphic studies demonstrate that synsedimentary tectonic activity, related to the rifting of the North Atlantic (Bay of Biscay), was responsible for variation in sedimentation, presence of unconformities (including paleokarsts), local platform emergence and dolomitization along the N60 fault trend. In the Reocín area, two stages of dolomitization are recognized. The first stage is a pervasive dolomitization of the limestone country rocks that was controlled by faulting and locally affected the upper part of the Aptian and the complete Albian sequence. The second dolomitization event occurred after erosion and was controlled by karstic cavities. This later dolomitization was accompanied by ore deposition and, locally, filling of dolomite sands and clastic sediments in karstic cavities. The circulation of hydrothermal fluids responsible for sulfide deposition and the infilling of karst cavities were broadly contemporaneous, indicating a post-Albian age. Vitrinite reflectance data are consistent with previously measured fluid inclusion temperatures and indicate temperatures of ore deposition that were less than 100°C. Carbon and oxygen isotopic data from samples of regional limestone, host-rock dolostone and ore-stage dolomite suggest an early hydrothermal alteration of limestone to dolostone. This initial dolomitization was followed by a second period of dolomite formation produced by the mixing of basinal metal-rich fluids with local modified seawater. Both dolomitization events occurred under similar conditions from fluids exhibiting characteristics of basinal brines. The δ 34 S values of sulfides are between -1.8 and +8.5 per mil, which is consistent with thermochemical sulfate reduction involving organic matter as the main source of reduced sulfur. Galena lead isotope compositions are among the most radiogenic values reported for Zn-Pb occurrences in Europe, and they are distinct from values reported for galena from other Basque - Cantabrian deposits. This suggests that a significant part of the lead was scavenged from the local underlying Asturian sediments. The stratigraphic and structural setting, timing of epigenetic mineralization, mineralogy, and isotopic geochemistry of sulfide and gangue minerals of the Reocín deposit are consistent with the features of most of Mississippi Valley-type ore deposits.

northern Spain↗
USGS2003

Research observation: Hydrolyzable and condensed tannins in plants of northwest Spain forests

Tannins are secondary metabolites that may influence feeding by mammals on plants . We analyzed hydrolyzable and condensed tannins in 30 plant species consumed by livestock and deer, as a preliminary attempt to study their possible implications on browsing and grazing in forest ecosystems. Heathers ( Ericaceae ) and plants of the Rose ( Rosaceae ) family had tannins , while forbs, grasses and shrubs other than the heathers did not show astringency properties. We found the highest tannin content of all the species in Rubus sp., with the highest value around 180 mg TAE/g dry weight in spring. Potentilla erecta , Alnus glutinosa and Quercus robur were next with 57 to 44 mg TAE/g dw. Total tannins in heathers ranged from 22 to 36 mg TAE/g dw. Levels of condensed tannins were higher than hydrolyzable for most of the species. Only Betula alba , Calluna vulgaris , Pteridium aquilinum and Vaccinium myrtillus had 100% hydrolyzable tannins . Tannin content of the species changed seasonally with highest values during the growing season, corresponding to late winter or early spring, depending on the species.

northwest Spain↗
USGS2001

Lead poisoning in the globally threatened marbled teal and white‐headed duck in Spain

Marbled teal ( Marmaronetta angustirostris ) and white‐headed duck ( Oxyura leucocephala ) are the two European ducks threatened with global extinction. We investigated lead (Pb) poisoning in stifftails ( Oxyura spp., n = 83) and marbled teal ( n = 80) shot or found dead or moribund in Spanish wetlands via gizzard examination and liver, bone, and blood Pb analysis. Ingested Pb shot was present in 32% of shot stifftails and 70 and 43% of dead or moribund stifftails and marbled teal, respectively. Lead‐shot ingestion was more frequent in Valencia (eastern Spain), where Pb‐shot densities were higher and grit scarcer. Selection of larger grit similar in size to Pb shot may explain the higher rate of Pb‐shot ingestion observed in stifftails. Ingested shot was found more frequently in juvenile stifftails than in adults. Lead bone concentrations were higher in ducklings <9 d old than in fully grown teal and were also higher in adult than in juvenile teal. Our results show the need for a ban of Pb shot for waterfowl hunting in Spain and the cleanup of spent shot at major wetlands.

Environmental Toxicology and Chemistry↗
USGS1996

Paleoslope, sea-level and climate controls on Upper Miocene platform evolution, Las Negras area, southeastern Spain

Carbonate platforms in the Las Negras area (southeastern Spain) evolved from onlapping ramps to fringing reef complexes later draped by cyclic shallow marine strata. Although sea-level history and paleoclimate had an effect on platform evolution, substrate topography played a dominant role. The strata are divided into five depositional sequences of Tortonian and Messinian age. From base to top these depositional sequences are labeled as DS1 A (newly dated at 8.5±0.1 Ma) mostly consisting of coarse-grained carbonates and volcanic detritus; DS1Β consisting of fining upward carbonate cycles; DS2 mostly consisting of reef megabreccia clasts and fine-grained carbonates; DS3 mostly consisting of reef and forereef carbonates and some volcanic detritus; and TCC (Terminal Carbonate Complex) dominated by oolitic cyclic carbonates. Ramp strata of DS1A and DS1Β mostly onlap against volcanic basement. DS1A and lower DS1B strata have characteristics that are consistent with deposition in cool water, probably resulting from a temperate climate and possibly coinciding with upwelling. DS1Β strata consist of fining-upward cycles of red algal packstone-grainstone and fine grained wackestone-packstone that suggest repeated variations of water depth from 40-100 m to greater than 100 m. Beds of both facies lap out against basement without any indication of facies change at or approaching the point of onlap. Although sediments likely were generated upslope above the point of onlap in shallow marine water, paleoslope was too steep for those sediments to accumulate permanently. Therefore, deposits of DS1Β represent a type of carbonate ramp in which sediment production was in water depths of approximately 40-100 m or more and any sediments generated in shallower water upslope positions were bypassed downslope until areas of low basement paleoslope were reached. Importantly, the onlap in this type of ramp is not necessarily tracking baselevel. The fining-upward character of DS 1Β cycles may result from an overall high or rising sea level punctuated by higher frequency fluctuations, lower sedimentation rates related to a more temperate climate, or bypass into the distal toe-of-slope setting. The sediments that accumulated during DS 1Β filled in significant basement topography and created a more gently sloping substrate on which later deposits could accumulate. Unlike DS 1A and most of DS 1B, the last phase of DS 1 B, DS2, and DS3 contain significant amounts of chlorozoan facies indicating a shift toward a more subtropical to tropical climate. Normal marine platform deposits of DS2 essentially draped the gentle paleotopography created by DS 1Β deposition, but megabreccias composed mostly of reef clasts indicate instability in upslope areas due to steep paleoslopes and relative sea-level falls. During deposition of the Porites-dominated fringing reef strata of DS3, sea level was at a position near the tops of relatively flat hills created by earlier deposition. Reef aggradation, progradation and downstepping in DS3 created steep forereef slope topography. These reefal platforms were preserved only on substrates of relatively low paleoslope, where earlier deposits had filled in the steep substrate topography. In contrast, steep-sided volcanic hills in the area were sites where DS3 and DS2-equivalent reefs may have been formed but were bypassed downslope because of the steep paleoslope. Finally, during deposition of latest Miocene strata (TCC), sea level was at a position that allowed for accumulation of shallow-water carbonate cycles, but these cycles were only preserved on areas where the substrate, created either by earlier deposition or erosion, was relatively flat.

Las Negras area, southeastern Spain↗
USGS1994

Dating of the Basal Aurignacian Sandwich at Abric Romanı́ (Catalunya, Spain) by Radiocarbon and Uranium-Series

Abric Romaní, a rock shelter located near Barcelona, Spain, contains a charcoal-bearing basal Aurignacian occupation level sandwiched between beds of moss-generated carbonate. The Aurignacian culture is the oldest artefact industry in Europe with which anatomically modern human remains have been associated. Radiocarbon analysis of charcoal fragments by accelerator mass spectrometry (AMS) dates the basal Aurignacian to about 37 ± 2 ka bp. U-series analyses by alpha spectrometry (AS) and mass spectrometry (MS) date the enclosing carbonate to 43 ± 1 ka bp. These results confirm the great antiquity of the Aurignacian in northern Spain and support the similar AMS dates from El Castillo and l'Arbreda caves. They also show that radiocarbon dates are significantly younger than U-series at 40 ka bp, as predicted by theory.

Catalunya↗
USGS1993

Mediterranean undercurrent sandy contourites, Gulf of Cadiz, Spain

The Pliocene—Quaternary pattern of contourite deposits on the eastern Gulf of Cadiz continental slope results from an interaction between linear diapiric ridges that are perpendicular to slope contours and the Mediterranean undercurrent that has flowed northwestward parallel to the slope contours and down valleys between the ridges since the late Miocene opening of the Strait of Gibraltar. Coincident with the northwestward decrease in undercurrent speeds from the Strait there is the following northwestward gradation of sediment facies associations: (1) upper slope facies, (2) sand dune facies on the upstream mid-slope terrace, (3) large mud wave facies on the lower slope, (4) sediment drift facies banked against the diapiric ridges, and (5) valley facies between the ridges. The southeastern sediment drift facies closest to Gibraltar contains medium-fine sand beds interbedded with mud. The adjacent valley floor facies is composed of gravelly, shelly coarse to medium sand lags and large sand dunes on the valley margins. Compared to this, the northwestern drift contains coarse silt interbeds and the adjacent valley floors exhibit small to medium sand dunes of fine sand. Further northwestward, sediment drift grades to biogenous silt near the Faro Drift at the Portuguese border. Because of the complex pattern of contour-parallel and valley-perpendicular flow paths of the Mediterranean undercurrent, the larger-scale bedforms and coarser-grained sediment of valley facies trend perpendicular to the smaller-scale bedforms and finer-grained contourite deposits of adjacent sediment drift facies. The bottom-current deposits of valleys and the contourites of the Cadiz slope intervalley areas are distinct from turbidite systems. The valley sequences are not aggradational like turbidite channel—levee complexes, but typically exhibit bedrock walls against ridges, extensive scour and fill into adjacent contourites, transverse bedform fields and bioclastic lag deposits. Both valley and contourite deposits exhibit reverse graded bedding and sharp upper bed contacts in coarse-grained layers, low deposition rates, and a regional pattern of bedform zones, textural variation, and compositional gradation. The surface sandy contourite layer of 0.2–1.2 m thickness that covers the Gulf of Cadiz slope has formed during the present Holocene high sea level because high sea level results in maximum water depth over the Gibraltar sill and full development of the Mediterranean undercurrent. The late Pleistocene age of the mud underlying the surface sand sheet correlates with the age of the last sea-level lowstand and apparent weak Mediterranean undercurrent development. Thus, the cyclic deposition of sand or mud layers and contourite or drape sequences appear to be related to late Pliocene and Quaternary sea-level changes and Mediterranean water circulation patterns. Since its Pliocene origin, the contourite sequence has had low deposition rates of < 5 cm/1000y on the upper slope and < 13 cm/1000y in the middle slope sediment drift.

Gulf of Cadiz↗
USGS1991

Radiometric dating of quaternary deposits and the hominid mandible of Lake Banyolas, Spain

We report results of U-series analyses of the travertine matrix surrounding the Banyolas mandible that indicate an age of 45??4 ka bp. The mandible, an archaic hominid fossil generally deemed of mid-Pleistocene age, was recovered from a travertine matrix in 1887. Similar analyses on 21 travertine samples from quarries near the discovery site yield coherent U-series dates in correct stratigraphic order, ranging from 44 ka bp to 117 ka bp. Isotopic composition of these samples and the mandible matrix show no evidence of open system behaviour. Coherent isotopic results from adjacent quarries support the validity of the date on the mandible travertine, and we conclude the mandible is much younger than previously believed. ?? 1991.

Catalonia↗
USGS1990

Pliocene-Pleistocene growth of the Rio Ebro margin, northeast Spain: A prograding-slope model

Pliocene-Pleistocene marine deposits overlying Messinian evaporites off northeast Spain are composed of five distinct seismic facies. These facies are interpreted to represent deposition in five adjacent settings: distal (isolated) basin, basin plain, base of slope,slope, and shelf. Contrary to previous studies, a submarine-fan style of deposition is not evident. Distal-basin deposits are characterized by thin, wavy, parallel beds draping the sea floor. Basin-plain deposits are similar but also have flat-lying beds and some low-relief channels. Base-of-slope deposits are dominated by stacked, overlapping, elongate channel/levee deposits that have concave-upward bases and convex-upward tops. Slope sequences are thick accumulations of overbank deposits laterally interrupted by large upward-climbing canyon fill. The shelf component is composed of overlapping and stacked delta lobes. The composite sediment body is a prograded, upward-shallowing, offlap sequence initiated and controlled by the influx of terrigenous sediment from the Rio Ebro during the Pleistocene. This style of deposition is common in the rock record, and our model may be more appropriate as a modern analogue for some rocks than are conventional shelf-canyon-fan models of margin sedimentation.

Ebro River, Gulf of Valencia, Mediterranean Sea↗
USGS1989

Abrupt Mousterian/Aurignacian boundary at c. 40 ka bp: Accelerator 14C dates from l'Arbreda Cave (Catalunya, Spain)

The cultural transition from Mousterian to Aurignacian is abrupt at l'Arbreda Cave and occurs within a homogeneous sedimentary unit with no visible lithologic changes. Fragments of milligram-size charcoal were collected immediately above and below the cultural boundary for radiocarbon dating by accelerator. Four charcoal fragments from the lowest basal Aurignacian level yielded dates of 37·7 ± 1·0, 37·7 ± 1·0, 39·9 ± 1·2, and 38·7 ± 1·2 ka bp (average 38·5 ± 1·0 ka bp). These ages are similar to three dates from the same cultural horizon at El Castillo Cave in Cantabria and both sets of dates are significantly older than the earliest reported for the Aurignacian in the Aquitaine and in other parts of Central and Western Europe. The dates are in accord with similarly early dates for Aurignacian in Bulgaria and suggest that appearance of Aurignacian peoples is synchronous across Europe. Three fragments from the uppermost Mousterian level yielded dates of 39·4 ± 1·4, 34·1 ± 0·75, and 41·4 ± 1·6 ka bp. Discounting the spurious 34·1 ka bp result, these dates are slightly older (average 40·4 ± 1·4 ka bp) but overlap with counting error the basal Aurignacian dates. The data show that the transition from Mousterian to Aurignacian was chronologically abrupt at this location. These results strongly support the replacement hypothesis.

l'Arbreda Cave↗
USGS1988

Uranium-series dating of the Mousterian occupation at Abric Romani, Spain

The precise evolutionary position of the Neanderthal people continues to be a major uncertainty in human evolution. Their origin and their relationship to anatomically modern people are unclear and are clouded by poor chronology. Lithic artefacts of the Mousterian type, found throughout Europe and the Mediterranean Basin, are believed to be the tool kit of the Neanderthals, but dates within Mousterian-bearing deposits are extremely rare. We report here on 20 high-quality uranium-series dates from Mousterian beds at Abric Romani, a rock shelter near Barcelona, Spain. The dates range from 39 to 60 kyr before present ( BP ) in an orderly stratigraphic succession and provide precise chronological control on an important Mousterian archaeological site.

Nature↗
USGS1987

Mapping contact metamorphic aureoles in Extremadura, Spain, using Landsat thematic mapper images

In the Extremadura region of western Spain, Ag, Pb, Zn, and Sn deposits occur in the pieces of late Hercynian granitic plutons and near the pluton contacts in late Proterozoic slate and metagraywacke that have been regionally metamorphosed to the green schist facies. The plutons generally are well exposed and have distinctive geomorphological expression and vegetation; poor exposures of the metasedimentary host rocks and extensive cultivation, however, make delineation of the contact aureoles difficult. Landsat Thematic Mapper (TM) images have been used to distinguish soil developed on the contact metamorphic rocks from soil formed on the stratigraphically equivalent slate-metagraywacke sequence. The mineral constituents of these soils are similar, except that muscovite is more common in the contact metamorphic soil; carbonaceous material is common in both soils. Contact metamorphic soil have lower reflectance, especially in the 1.6-micrometers wavelength region (TM 5), and weaker Al-OH, Mg-OH, and Fe 3+ absorption features than do spectra of the slate-metagraywacke soil. The low-reflectance and subdued absorption features exhibited by the contact metamorphic soil spectra are attributed to the high absorption coefficient f the carbonaceous material caused by heating during emplacement of the granitic plutons. These spectral differences are evident in a TM 4/3, 4/5, 3/1 color-composite image. Initially, this image was used to outline the contact aureoles, but digital classification of the TM data was necessary for generating internally consistent maps of the distribution of the exposed contact metamorphic soil. In an August 1984, TM scene of the Caceras area, the plowed, vegetation-free fields were identified by their low TM 4/3 values. Then, ranges of TM 4/5 and 3/1 values were determine for selected plower fields within and outside the contact aureoles; TM 5 produced results similar to TM 4/5. Field evaluation, supported by X-ray diffraction and petrographic studies, confirmed the presence of more extensive aureoles than shown in published geologic maps; few misclassified areas were noted. Additional plowed fields consisting of exposed contact metamorphic soil were mapped digitally in an August 1985 TM scene. Subsequently, this approach was used to map two 1-km-wide linear zones of contact metamorphosed rock and oil in the San Nicolas-Sn-W Mine area, which is located approximated 125 km southeast of the Caceras study area. Exposures of granite in the San Nicolas area are limited to a few unaltered granitic dikes in the mine and a small exposure of unaltered pegmatite-bearing granite in a quarry about 1.5 km west of the mine. The present of coarsely crystalline biotite and beryl in the granite in the quarry and of contact metamorphosed slate up to 2.5 km from the nearest granite exposure suggest that only the apical part of a pluton is exposed in the quarry and that a larger, shallowly buried body is probably present. These results indicate that potential application of TM image analysis to mineral exploration in lithologically similar areas that are cultivated in spite of poor rock exposures.

Extremadura↗
USGS1984

Reevaluation of the systematic position of Scenella

Specimens originally illustrated from Lower Cambrian rocks of the Sierra Morena in Badajoz and Sevilla Provinces, southwestern Spain are supplemented by new material from another locality and are described as Scenella morenensis n. sp. Although Scenella was originally considered to be a patelliform gastropod, for three decades now the genus has been classified as a monoplacophoran. The type species of Scenella, S. reticulata Billings, does not show any paired muscles scars, nor does this new species; such scars are indicative of the Monoplacophora. This new species of Scenella does exhibit features which suggest assignment to the chondrophorine coelenterates. If so, Scenella cannot represent the ancestral form of mollusk.

Sierra Morena in Badajoz and Sevilla Provinces, so↗
USGS1983

Rb-Sr, Sm-Nd, K-Ca, O, and H isotopic study of Cretaceous-Tertiary boundary sediments, Caravaca, Spain: evidence for an oceanic impact site

Isotopic ratios and trace element abundances were measured on samples of Ir-enriched clay at the Cretaceous-Tertiary boundary, and in carbonate and marl from 5 cm below and 3 cm above the boundary. Samples were leached with acetic acid to remove carbonate, and with hydrochloric acid. Leachates and residues were measured. The Sr, Nd, O and H isotopic compositions of the boundary clay residues are distinct from those of the stratigraphically neighboring materials. The data indicate that most of the clay material was derived from a terrestrial source with relatively low 87 Sr/ 86 Sr and high 143 Nd/ 144 Nd ratios. The δ 18 O data suggest that the detritus has been modified by submarine weathering. K-Ca and Rb-Sr systematics, as well as O isotope ratios of K-feldspar spherules within the boundary clay, suggest that they are predominantly authigenic and may have formed after the time of deposition. However, Sm-Nd and Rb-Sr isotopic data indicate that the spherules contain relict material that provides information on the nature of the original detritus. The isotopic evidence for foreign terrestrial detritus in the boundary clay, the low rare earth element concentrations and high Ni concentration, support the hypothesis of a terminal Cretaceous asteroidal impact that produced a global layer of fallout. The data are most easily explained if the impact site was on oceanic crust rather than continental crust, and if a substantial fraction of the fallout was derived from relatively deep within the lithosphere (>3 km). This would probably require a single large impactor.

Caravaca↗
USGS1980

Evolution of the continental margin of southern Spain and the Alboran Sea

Seismic reflection profiles and magnetic intensity measurements were collected across the southern continental margin of Spain and the Alboran basin between Spain and Africa. Correlation of the distinct seismic stratigraphy observed in the profiles to stratigraphic information obtained from cores at Deep Sea Drilling Project site 121 allows effective dating of tectonic events. The Alboran Sea basin occupies a zone of motion between the African and Iberian lithospheric plates that probably began to form by extension in late Miocene time (Tortonian). At the end of Miocene time (end of Messinian) profiles show that an angular unconformity was cut, and then the strata were block faulted before subsequent deposition. The erosion of the unconformity probably resulted from lowering of Mediterranean sea level by evaporation when the previous channel between the Mediterranean and Atlantic was closed. Continued extension probably caused the block faulting and, eventually the opening of the present channel to the Atlantic through the Strait of Gibraltar and the reflooding of the Mediterranean. Minor tectonic movements at the end of Calabrian time (early Pleistocene) apparently resulted in minor faulting, extensive transgression in southeastern Spain, and major changes in the sedimentary environment of the Alboran basin. Active faulting observed at five locations on seismic profiles seems to form a NNE zone of transcurrent movement across the Alboran Sea. This inferred fault trend is coincident with some bathymetric, magnetic and seismicity trends and colinear with active faults that have been mapped on-shore in Morocco and Spain. The faults were probably caused by stresses related to plate movements, and their direction was modified by inherited fractures in the lithosphere that floors the Alboran Sea.

Alboran Sea↗