César Viseras

Differential features of alluvial fans controlled by tectonic or eustatic accommodation space. Examples from the Betic Cordillera, Spain

Abstract The creation of accommodation space in subaerial sedimentary environments is closely linked to uplift the source area (along basin–margin faults) or to a rise in base level. Depending (amongst others) on the relative importance of these two factors, the margins of terrestrial sedimentary basins (where alluvial fans develop) produce aggradational, progradational or retrogradational stratigraphic architecture. We studied a total of 43 Quaternary alluvial fans in the Granada and Bajo Segura basins (Betic Cordillera, Spain). The analysis of their stratigraphic architecture and sedimentary facies has revealed the existence of three groups characterised by distinct stratal stacking patterns, which is the result of differences in eustasy and tectonics. The qualitative and quantitative analysis of these alluvial fans and their drainage basins has allowed us to define certain characteristic geomorphological patterns related, in each case, to the main mechanism operative in the creation of accommodation space. These patterns are described as follows. (1) Alluvial aggradation is the main result of high tectonic subsidence with the development of quite open, but small fans with a constant steep slope lacking incised channels and headward-eroding gullies. (2) In contrast, when the principal mechanism in creating accommodation space is low tectonic subsidence, progradation occurs and the fans are narrower and larger. Moreover, the slopes of such fans are less steep in relation to the drainage area than in the above case, being constant or even concave in longitudinal profile. They also have short, deep incised channels, culminating downfan in a depositional lobe. In inactive zones, long, deep headward-eroding gullies develop. (3) Areas of extremely low tectonic subsidence and base level rise produce very open fans in the sedimentary basin, although with a pronounced mountain embayment, which gives them a characteristic “mushroom” shape in plan view. In the latter case, retrogradation is the typical stratigraphic stacking pattern and the fans are quite extensive with respect to their drainage areas, usually showing a segmented longitudinal profile with a low gradient. The feeder channels do not surpass stream order 3, and various extremely long and shallow incised channels can appear. (4) Contrary to the case of fans developing under a regime of subsidence, when the accommodation is due to base level rise, the fan slopes bear no relation to the extent of the catchment basins. In such a case, the overall fan slope is strongly influenced by the extent of the mountain embayment because it determines the distributions of debris and sheet-flows over the alluvial surface.

Autopsy on a dead spreading center: The Phoenix Ridge, Drake Passage, Antarctica

New bathymetric and magnetic anomaly data from the Phoenix Ridge, Antarctica, show that extinction of all three remaining segments occurred at the time of magnetic chron C2A (3.3 ± 0.2 Ma), synchronous with a ridge-trench collision south of the Hero Fracture Zone. This implies that the ultimate cause of extinction was a change in plate boundary forces occasioned by this collision. Spreading rates slowed abruptly at the time of chron C4 (7.8 ± 0.3 Ma), probably as a result of extinction of the West Scotia Ridge, which would have led to an increase in slip rate and transpressional stress across the Shackleton Fracture Zone. Spectacular, high-relief ridges flanking the extinct spreading center, mapped for the first time using multibeam swath bathymetry, are interpreted as a consequence of a reduction in spreading rate, involving a temporary magma oversupply immediately prior to extinction.

Late Miocene stratigraphy and palaeogeographic evolution of the intramontane Guadix Basin (Central Betic Cordillera, Spain): implications for an Atlantic–Mediterranean connection

Abstract The Guadix Basin is an intramontane basin located in the central sector of the Betic Cordillera. Its Late Miocene stratigraphic record is divided into three depositional sequences limited by unconformities representing tectonic and/or eustatic events. Depositional sequence I (late Tortonian) is composed by two systems tracts. The lower marks the beginning of marine sedimentation in the basin, and comprises three retrograding lithological complexes or depositional systems (coastal, shallow platform and pelagic basin), and is interpreted as a transgressive systems tract. The upper systems tract consists of a shallow shelf prograding into a pelagic basin. This systems tract exhibits a typically regressive pattern and was deposited during high sea level, and is therefore interpreted as a highstand systems tract. Depositional sequence II (late Tortonian) is composed of both continental (alluvial cones) and shallow marine (Gilbert-type delta, shallow shelf, and reef) depositional systems. The deposits of this sequence record a significant fall in sea level and are interpreted as a lowstand systems tract. Depositional sequence III (late Turolian–Ventian or late Tortonian–Messinian) was formed of solely retrograding continental depositional systems (alluvial fan, lacustrine fan delta, mud flat, and lacustrine). With this sequence begins the continental sedimentation in Guadix Basin in an endorheic context. The palaeogeographic evolution of the Guadix Basin during the Late Miocene can thus be divided into three stages. The first corresponds to depositional sequence I and is characterised by the development of shallow marine environments on the basin margins and deep water deposits in its centre. During this stage the basin was connected to the west with the Atlantic Ocean via the Granada and Guadalquivir basins and toward the east with the Mediterranean Sea through the Almanzora and Campo Coy basins. In the second stage, represented by depositional sequence II, most of the basin was occupied by shallow marine environments. During this stage the connection with the Atlantic and Mediterranean was only open through the Guadalquivir and Campo Coy basins, respectively. Finally, the third and last stage, corresponding to depositional sequence III, is characterised by the development of continental environments throughout the basin. This stage records the definitive closing of the connections with the Atlantic Ocean and the Mediterranean Sea.

Controls on fan development — evidence from fan morphometry and sedimentology; Sierra Nevada, SE Spain

Abstract We have studied the morphology and the morphometric relations between alluvial fans and drainage basins in a bajada system including more than 20 coalescent fans developed since the Late Pleistocene as a result of the recent uplift of the Sierra Nevada (Betic Cordillera, Spain). Three allocycles of tectonic origin were recognised across which there is a clear evolution from debris flow to sheet flow dominated fans, in connection with a decrease in the volume of fines available in the source areas. The larger volume of accommodation space created by higher tectonic subsidence in the northern sector favoured vertical accumulation of sediment, with the appearance of less elongated fans. In the rest of the system, where subsidence is less, more elongated fans appear, with the development of incised channels and irregular distribution of sediment in depositional lobes. This involves the appearance of markedly asymmetric transverse profiles, as well as lengthy recurrence between the sedimentation events on particular sectors of the fans, where headward-eroding gullies develop. The lithology of the source area, where intensely fractured rocks are found, is responsible for an important sediment supply and a significant degree of clast sorting from the source area. Consequently, a weak longitudinal trend in particle size can be recognised, which influences the predominance of longitudinal constant-slope profiles and anomalous relations between both fan area and fan slope and their drainage areas. Recent intense tectonic activity has caused the appearance of abnormally low slopes in upper sectors of some catchments, where mass flows are trapped, and the fans present a subsequently higher proportion of sheet flows. Recent piracy phenomena can be recognised in some of the drainage basins, which indicate rejuvenation of the source area, in which case the fan presents a rapid increase in the proportion of mass flows with the development of a segmented longitudinal profile. Due to the recent nature of the processes, the morphometric relations in the fan fed by the basin affected by capture do not coincide with the other fans in the area.

Different phyllosilicates as supports for lipase immobilisation

The aim of this work was to determine the enzymatic activities resulting from the adsorption of Rhizomucor miehei lipase (RML) and Candida cylindracea lipase (CCL) onto three different phyllosilicates (sepiolite, palygorskite and montmorillonite), comparing the resultant activities with those obtained following similar immobilisation technique on a widely used resin (Duolite A-568). Due to the different adsorption mechanisms produced, different derivatives with higher hydrolytic activities can be obtained. Comparing the clays tested, the results showed that, in comparison with the laminar silicate (montmorillonite sample) and Duolite A-568 (spherical particles), fibrous materials (palygorskite and sepiolite) resulted in derivatives with higher hydrolytic activities in the hydrolysis of different ethyl esters. Moreover, according to the data obtained with the electrophoresis, the selectivity of immobilisation for RML in the case of fibrous silicates was optimal. As a conclusion, and according to the activities and selectivities measured, at least two out of the four studied materials (sepiolite and palygorskite) would be useful as supports for immobilisation for proteins of relatively low molecular weight (such as RML) for further use in biotransformations, while for C. cylindracea the immobilisation onto duolite rendered a derivative specially active in the hydrolysis of ethyl formiate (esterasic activity).

Long‐term Control Mechanisms of Stream Piracy Processes in Southeast Spain

The Guadix Basin developed as an endorheic depression during the Upper Miocene‐Upper Pleistocene. Its principal palaeogeographical characteristics are a large lake in the eastern sector, an axial fluvial system and two fluvial systems transverse to it in the western sector. The uplift of a central sector of the Betic Cordillera during the Upper Pleistocene affected the study area, causing northward tilting from the Internal Zone of the cordillera (Sierra Nevada and Sierra de Baza), step-faulting of the Plio-Pleistocene infill of the ancient basin (leaving more northern sectors in a lower topographical position), alteration of fluvial current profiles and displacement of the ancient Axial System to a position very close to the divide between the ancient endorheic Guadix Basin and the Guadalquivir Basin. This facilitated capture of the endorheic basin by the headward erosion of a tributary of the Guadalquivir River. The region then began to be rapidly eroded, as the new base level was now some 500 m lower than that of the ancient basin. The present drainage network is similar to that of the ancient endorheic basin as regards the location of the main streams and the distribution of drainage patterns and fluvial styles, although flow reversal is found in some stretches and a barbed drainage pattern appears locally. As a result of the inheritance of drainage from the ancient basin, fluvial superimposition is found in some stretches of the main streams.

Late Miocene–Pleistocene tectono-sedimentary evolution and subsidence history of the central Betic Cordillera (Spain): a case study in the Guadix intramontane basin

The Guadix Basin became established as an intramontane basin in the central sector of the Betic Cordillera at the beginning of Late Miocene time. Its geodynamic evolution starts with a unit of Tortonian marine sediments and is completed by a unit of Late Turolian-Pleistocene continental sedi- ments. In the two units, six depositional sequences have been differentiated whose boundaries, in most cases, coincide with tectonic events. Geohistorical diagrams show the results of quantitative analyses of subsidence in the northern sector of the basin and permit correlation of the main events with signif- icant changes in the history of subsidence and uplift. A period of strong subsidence occurred at the beginning of Tortonian time causing the formation of a marine basin 800 m deep. The mid- and end- Tortonian tectonic events involved periods of uplift leading to shallowing in the basin. After continen- talization at the end of the Tortonian, the basin was uplifted continuously from Late Turolian to Late Pleistocene times, finally accumulating sediments at a height of 1000 m.

Montmorillonite-chitosan-silver sulfadiazine nanocomposites for topical treatment of chronic skin lesions: in vitro biocompatibility, antibacterial efficacy and gap closure cell motility properties.

Silver compounds and especially silver sulfadiazine (AgSD) are reported as effective antimicrobial agents against almost all known bacteria, fungi and some viruses. However, AgSD has been shown to be cytotoxic toward fibroblasts and keratinocytes in vitro and consequently to retard wound healing in vivo. The aim of the present work was to evaluate the in vitro biocompatibility (cytotoxicity and proliferation), antimicrobial efficacy and cell motility gap closure (assay of wound closure) of MT/CS nanocomposites loaded with silver sulfadiazine (AgSD). It is envisioned to be administered as a powder or a dressing for cutaneous application in the treatment of skin ulcers. The loading of AgSD in MT/CS nanocomposites aimed at preventing the delay in wound healing, by decreasing the cytotoxicity of AgSD and maintaining its antimicrobial properties. Nanocomposites were prepared by using different amounts of MT (100-2000 mg) and 40 ml of a 1% (w/w) chitosan glutamate aqueous solution. The relative amounts of AgSD and chitosan in the systems were assessed by suitable analytic methods. The nanocomposite prepared using 100mg of MT was characterized for in vitro biocompatibility and proliferation and for wound healing using normal human dermal fibroblasts (NHDF). Antimicrobial properties were evaluated against four reference bacterial strains: Staphylococcus aureus, Streptococcus pyogenes, Escherichia coli, and Pseudomonas aeruginosa. AgSD loaded in the 100 MT/CS nanocomposite showed good in vitro biocompatibility and gap closure properties (fibroblasts) and maintained AgSD antimicrobial properties, especially against P. aeruginosa, that often complicates skin lesions.

A Mammalian Lost World in Southwest Europe during the Late Pliocene

Background Over the last decades, there has been an increasing interest on the chronology, distribution and mammal taxonomy (including hominins) related with the faunal turnovers that took place around the Pliocene-Pleistocene transition [ca. 1.8 mega-annum (Ma)] in Europe. However, these turnovers are not fully understood due to: the precarious nature of the periods fossil record; the “non-coexistence” in this record of many of the species involved; and the enormous geographical area encompassed. This palaeontological information gap can now be in part bridged with data from the Fonelas P-1 site (Granada, Spain), whose faunal composition and late Upper Pliocene date shed light on some of the problems concerning the timing and geography of the dispersals. Methodology/Principal Findings This rich fossil site yielded 32 species of mammals, among which autochthonous species of the European Upper Villafranchian coexist with canids (Canis), ovibovines (Praeovibos) and giraffids (Mitilanotherium) from Asia. Typical African species, such as the brown hyena (Hyaena brunnea) and the bush pig (Potamochoerus) are also present. Conclusions/Significance This assemblage is taxonomically and palaeobiogeographically unique, and suggests that fewer dispersal events than was previously thought (possibly only one close to 2.0 Ma) are responsible for the changes seen around 1.9–1.7 Ma ago in the fauna of the two continents.

Pharmaceutical grade phyllosilicate dispersions: the influence of shear history on floc structure.

The effect of mixing conditions on the flow curves of some clay-water dispersions was studied. Two Spanish fibrous phyllosilicates (sepiolite from Vicálvaro and palygorskite from Turón) and a commercial bentonite (Bentopharm Copyright, UK) were selected as model clays. The disperse systems were made up using a rotor-stator mixer working at two different mixing rates (1000 and 8000 rpm), for periods of 1 and 10 min. Rheological measurements were taken and the corresponding flow curves obtained immediately after interposition and then after a period of 24 h under low shear caused by a roller apparatus. Aqueous sepiolite dispersions showed the highest viscosity and were easily interposed, whereas palygorskite dispersions were more difficult to obtain, resulting in low to medium viscosity gels. Bentonite dispersions provided medium viscosity systems, which greatly increased their viscosity after the low shear treatment (as a result of swelling), whereas the viscosity of the fibrous clays stayed at approximately the same values or even decreased. A linear relation was found between mixing energy and apparent viscosity in the bentonite systems, while apparent viscosity in the sepiolite samples was related to mixing power, with minor influence of mixing times. All the systems studied had thixotropic behaviour, changing from clearly positive to even negative thixotropy in some palygorskite systems. Finally, we studied the effect of drastic pH changes on the system structure. Results showed that rheological properties were highly sensitive to pH in the fibrous dispersions, but less sensitive behaviour was found in the laminar clay systems.