Browsing by Author "López-Quirós, Adrián"
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- Holocene glaucony from the Guadiana shelf, Northern Gulf of Cadiz (SW Iberia): New genetic insights in a sequence stratigraphy contextPublication . López-Quirós, Adrián; Lobo, Francisco José; Mendes, Isabel; Nieto, FernandoGlaucony occurrences have been reported both from exposed transgressive and overlying highstand system tracts. However, its occurrences within highstand deposits are often invoked as the result of underlying condensed section reworking. Detailed textural, mineralogical and geochemical reports of glaucony grains in highstand deposits remain elusive. The northern Gulf of Cadiz shelf (SW Iberia) offers a unique opportunity to investigate late Holocene glaucony authigenesis in a well-documented time-stratigraphic context, where transgressive deposits are locally exposed on the seafloor and are laterally draped by highstand muddy deposits. In this study, glaucony grains extracted from a core retrieved from a highstand muddy depocenter off the Guadiana River were investigated by means of digital microscopy, X-ray diffraction (XRD), and electron microscopic methods (FESEM-EDX and TEM-HRTEM). To better constrain the glaucony origin (autochthonous vs. allochthonous) in highstand muddy deposits, glaucony grains from surficial samples—taken from exposed transgressive deposits—were also investigated. Glauconitization in the studied core can be largely attributed to the replacement of faecal pellets from c. ~4.2–1.0 cal. ka BP. Both XRD and TEM-HRTEM analyses indicate that glaucony consists mainly of an R1, with a minor presence of R0, smectite-rich (nontronite) glauconite-smectite mixed-layer silicate, made up of 35–75% glauconitic layers and 65–25% of interstratified smectite layers. At the mineral lattice level, minor individual 7Å layers (berthierine) were also identified by HRTEM. Shallow radial cracks at the pellet surface, along with globular and vermiform-like biomorphic to low packing density lamellar-flaky nanostructures, mineralogical properties, and K-poor content (average 0.4 atoms p.f.u.) indicate a scarcely mature glauconitization process, attesting to formation of the grains in situ (autochthonous). Glaucony grains from exposed transgressive deposits, i.e., in the tests of calcareous benthic foraminifera, do not share a genetic relationship with the grains investigated in the highstand deposits, thus supporting the autochthonous origin of glaucony within the highstand deposits. Our combined dataset provides evidence of a multiphase history for autochthonous glaucony formation in the Guadiana shelf, as its genesis is traced to both transgressive and highstand conditions. While eustatic sea-level changes favoured glaucony formation under transgressive conditions, factors such as protracted low sediment supply and the establishment of a strong nutrient-rich upwelling system in the study area promoted glaucony development during late Holocene highstand conditions.
- Origin and driving mechanisms of marine litter in the shelf-incised Motril, Carchuna, and Calahonda canyons (northern Alboran Sea)Publication . Cerrillo-Escoriza, Javier; Lobo, Francisco José; Puga-Bernabéu, Ángel; Rueda, José Luis; Bárcenas, Patricia; Sánchez-Guillamón, Olga; Serna Quintero, José Miguel; Pérez Gil, José Luis; Murillo, Yelvana; Caballero-Herrera, José Antonio; López-Quirós, Adrián; Mendes, Isabel; Pérez-Asensio, José NoelIntroduction and methodsMarine litter density, distribution and potential sources, and the impact on canyon seafloor habitats were investigated in the Motril, Carchuna and Calahonda canyons, located along the northern margin of the Alboran Sea. During the ALSSOMAR-S2S oceanographic survey carried out in 2019, canyon floor imagery was collected by a Remotely Operated Vehicle along 5 km in the Motril Canyon, 10 km in the Carchuna Canyon, and 3 km in Calahonda Canyon, together with 41 surficial sediment samples. Additionally, coastal uses, maritime traffic and fishing activity data were analyzed. A 50 m resolution multibeam bathymetry served as base map. ResultsIn the Motril and Calahonda canyons, the density of marine litter was low and the material was dispersed, very degraded and partially buried. In contrast, the Carchuna Canyon contained a greater amount and variety of litter. The Carchuna Canyon thalweg exhibited a density of marine litter up to 8.66 items center dot 100 m(-1), and litter hotspots with a density of up to 42 items center dot m(2) are found along the upper reaches of the canyon thalweg. DiscussionLow litter abundances found in the studied canyons most likely reflect low population densities and the absence of direct connections with streams in the nearby coasts. The high shelf incision of the Carchuna Canyon and its proximity to the coastline favor littoral sediment remobilization and capture as well as the formation of gravity flows that transport the marine litter along the thalweg toward the distal termination of the channel. Litter hotspots are favored by the canyon morphology and the occurrence of rocky outcrops. Most debris is of coastal origin and related to beach occupation and agricultural practices in the adjacent coastal plain. A third origin was represented by fishing gear in the study area. Fishing activity may be producing an impact through physical damage to the skeletons of the colonial scleractinians located in the walls of the Carchuna Canyon. In contrast, the Motril and Calahonda canyons can be considered passive systems that have mainly acted as depositional sinks in the recent past, as evidenced by buried marine litter.
- Western Mediterranean shelf-incised submarine canyons: multi-proxy evidence of Late Holocene natural and human-induced environmental changesPublication . López-Quirós, Adrián; Puga-Bernabéu, Ángel; José Lobo, Francisco; Ruíz-Caballero, Elvira; Cerrillo-Escoriza, Javier; Pérez-Asensio, José N.; Mendes, Isabel Maria de Paiva Pinto; Mena, Anxo; Puche-Polo, Natalia; Alberjón-Peñas, Tomás; Wacker, LukasSubmarine canyons play a critical role in continental margin sediment transport, functioning both as sediment traps and conduits. This study examines the depositional dynamics of the Motril, Carchuna, and Calahonda canyons in the northern Alboran Sea (western Mediterranean) to assess their role in Holocene sediment storage and transfer. Comprehensive sedimentological and elemental geochemical analyses reveal distinct sedimentation patterns driven by geomorphology, diverse transport mechanisms, and hydroclimatic variability. The Motril Canyon primarily functioned as a river-fed sediment trap, accumulating fine-grained terrigenous material from the Guadalfeo River. At the same time, the Carchuna Canyon was dominated by longshore drift and turbidity currents mobilizing coarse-grained sediments. In contrast, the Calahonda Canyon displays an intermediate behavior, influenced by alongshore drift and fluvial inputs. The Late Holocene sedimentary record from the Motril Canyon provides a high-resolution sedimentary archive of paleoenvironmental changes over the last similar to 2000 years Current Era, reflecting both climatic variability and human-induced landscape alterations. Four phases are identified based on the relationships between sediment physical and mineral-chemical characteristics: the Iberian Roman Humid Period (2600-1600 cal. yr Before Present), characterized by diminished terrigenous input despite increased late-phase humidity; the Dark Ages (1500-1000 cal. yr BP), marked by elevated sedimentation linked to soil erosion and intensified land use; the Medieval Climate Anomaly (1050-650 cal. yr BP), where persistent fine-grained deposition was driven largely by anthropogenic land degradation; and the Little Ice Age (650-150 cal. yr BP), which witnessed heightened sedimentation due to increased rainfall and river discharge. A decline in fluvial-derived material during the Industrial Period indicates a shift towards overall drier conditions, associated with changes in precipitation patterns and land use. These findings underscore the interplay between natural climatic fluctuations and human activities influencing western Mediterranean margin sedimentation. While the Motril Canyon does not serve as a direct conduit to deep waters, it nonetheless records the progressive aridification and anthropogenic impacts experienced in southern Iberia. Furthermore, the contrasting sediment dynamics observed in the Carchuna and Calahonda canyons highlight the inherent complexity of shelf-to-slope sediment transfer. This complexity underlines the necessity to consider human influences when interpreting Late Holocene paleoenvironmental records.