Antonio Rodríguez-Ramírez

Recent coastal evolution of the Doñana National Park (SW Spain)

Abstract Since the last Holocene sea level rise, about 6900 BP, a series of depositional littoral landforms has been generated at the outlet of the Guadalquivir River, with progradation along the predominant longshore drift (towards the east). The first coastal progradation occurred between 6900 and 4500 BP. The Donana and (perhaps) La Algaida spits, both associated with the oldest and highest marshland in the Donana National Park, are assumed to have been developed at an early stage. Originally, the Guadalquivir estuary was wider and deeper than now, and its environment was mainly marine. The oldest littoral formations have been dated as ca. 4735 BP. They show erosional events, and indicate the breaking-up of earlier spit-barriers to form inlets. The marine environment became increasingly dominant, with heavy erosion of cliffs and a retreating coastline. This period was followed by another sedimentary cycle (4200-2600 BP) that surrounded the earlier eroded barriers. The size of the estuary decreased due to the increasing marsh deposits, and a fluvial environment was born. About 2600 years ago, progradation gave way to a new period of intense erosion. The resulting morphology of littoral strands and erosional surfaces permitted the return to a marine environment. The shoreline again retreated. From 2300 BP, coastal progradation has prevailed, with an erosional interruption at 1000 BP. The present-day outlet of the Guadalquivir is an estuarine delta of inactive marshland (the Donana National Park), the dominant environment is fluvial.

Late Holocene evolution of the southwestern Doñana National Park (Guadalquivir Estuary, SW Spain): a multivariate approach

Four phases are distinguished in the Late Holocene evolution of the southwestern Donana National Park (SW Spain), based on a multidisciplinary analysis of the sediments present in drill cores. In the oldest phase (>2400–2500 cal. yr BP), a coastal lagoon (the Roman Lacus Ligustinus) was recognized in the central part of this area, partly closed by the Donana spit and limited by fluvial levees. The following phase (∼2400–2200 cal. yr BP) is characterized by high-energy events, which caused the breakthrough of the Donana spit and the creation of new littoral strands in the inner areas. In the third phase (∼2200–2050 cal. yr BP), this new outlet was closed, coinciding with the progradation of the Donana spit. The last phase (∼2050 cal. yr BP–Recent) comprises three periods: (a) an unstable period (∼2050–1950 cal. yr BP), with the deposit of cheniers over the previous levees; (b) an infilling period, with a diminution of the marine influence; and (c) the appearance of temporary ponds between the emerged levees and cheniers.

Analysis of the recent storm record in the southwestern Spanish coast: implications for littoral management.

This work compares the geomorphologic evolution of the Huelva coast (SW Spain), some climatic-oceanographic data of the Cádiz Gulf and the recent storm record of this zone, covering the last 4 decades (1956-1996). An interesting correlation was found between the southwestern wind periodicity, the number of storm periods and the beach ridges observed in the main spits (El Rompido and Doñana). The spectral analysis of the wind time series permits to establish two most probable levels of periodicity: 6 and 9-10 years. Both periods coincide with the storm record and the creation of new beach ridges after a high-energy period. Beach damage, another storm-induced effect, was analysed by deducing different implications for the future management of tourist localities.

Impact of late-Holocene aridification trend, climate variability and geodynamic control on the environment from a coastal area in SW Spain

A detailed pollen analysis has been carried out on two sediment cores taken from a marsh area located in the Doñana National Park, southwestern Spain. The studied sedimentary sequences contain a similar late Holocene record of vegetation and climate and show a progressive aridification trend since at least 5000 cal. yr BP, through a decrease in forest cover in this area. Long-term vegetation changes shown here (semi-desert expansion and Mediterranean forest decline) paralleled declining summer insolation. Decreasing summer insolation most likely impacted negatively on tree growing season as well as on winter precipitation in the area. Superimposed on the long-term aridification trend were multi-centennial scale periods characterized by forest reductions or increases in arid and halophytic plants that can be interpreted as produced by enhanced droughts and/or by local geodynamic processes. These are centered at ca. 4000, 3000–2500, and 1000 cal. yr BP, coinciding in timing and duration with well-known dry events in the western Mediterranean and other areas but could have also been generated by local sedimentary or geodynamic processes such as a marine transgression in a subsidence context and extreme wave events (EWEs). The alternation of persistent North Atlantic Oscillation modes probably played an important role in controlling these relatively humid–arid cycles.

Population age structure techniques and ostracods: Applications in coastal hydrodynamics and paleoenvironmental analysis

Abstract Ostracods are microcrustaceans that grow by moulting (eight to nine instars in most cases) and, consequently, studies of its populations need the application of some special techniques. The population age structure techniques [Whatley, in: Ostracoda in the Earth Sciences, 1988, pp. 245–256] are a simple statistical method to estimate paleoenvironmental conditions in fossil/Recent populations of ostracods. For its application, it is necessary to determine the percentages of each instar present in the samples studied, in order to analyze the different types of population age structure histograms and their (paleo-)environmental interpretations. Some potential applications are the (paleo-)energy levels or the sedimentation rates. In this paper, these special techniques are applied to Recent populations of the ostracod Pontocythere elongata collected in littoral sediments of southwestern Spain. In this area, the relative percentages of this species and the adult percentages are closely related with depth and consequently this species was used as a bathymetrical tracer in shallow Neogene areas of the Guadalquivir Basin. In addition, a first three-step multivariate analysis permits the definition of three groups, closely related to the theoretical models proposed by Whatley: (a) Group 1 structure or biocoenosis, present either in Recent low- to medium-energy environments located in erosional coastal stretches and Neogene fair-weather conditions; (b) Group 2 structure or high-energy thanatocoenosis, observed either in Recent river mouths with groynes and Neogene storm and post-storm conditions; and (c) Group 3 structure or low-energy thanatocoenosis, characteristic of Recent, progradational coastal areas and present in the Recent–Neogene deeper areas analyzed in this paper (30–40 m depth). This separation is mainly controlled by intrinsic factors (i.e. the natural growth of this species), whereas the extrinsic factors (i.e. the hydrodynamic levels) are only a minor cause of the distribution of this species in the area studied.

Sedimentary Characteristics of the Holocene Tsunamigenic Deposits in the Coastal Systems of the Cadiz Gulf (Spain)

Juan A. Morales1, Jose M. Gutierrez Mas2, Jose Borrego1 and Antonio Rodriguez-Ramirez3 1Departamento de Geologia. Facultad de Ciencias Experimentales. Universidad de Huelva. Campus Universitario del Carmen, s/n. 21007 Huelva. 2Departamento de Ciencias de la Tierra. Facultad de Ciencias del Mar y Ambientales. Universidad de Cadiz. Campus Universitario Rio San Pedro, s/n. Puerto Real (Cadiz). 3Departamento de Geodinamica y Paleontologia. Facultad de Ciencias Experimentales. Universidad de Huelva. Campus Universitario del Carmen, s/n. 21007 Huelva. Spain

The use of clay minerals and microfossils in palaeoenvironmental reconstructions: The Holocene littoral strand of Las Nuevas (Donana National Park) SW Spain

Abstract Three steps have been established during the Holocene formation of the bar-built estuary of Las Nuevas (Doñana National Park, Spain), on the basis of the clay mineralogy variations and the palaeontological record. The first step is characterized by the presence of ostracodes and homogeneous quantities of clay minerals (17−20% illite, 25−29% smectites), values of smectite (0.64− 0.70) and illite (0.60−0.70) crystallinity indexes, and the ratio of AlVI/(FeVI + MgVI) in illite (0.46− 0.47). This zone is interpreted as a very shallow lagoon with euryhaline conditions. The presence of roots, the progressive disappearance of foraminifers and an increase in the smectite content (up to 35%) define the second step. A salt-marsh environment with low-energy hydrodynamic conditions is deduced for this zone. The third step is characterized by an increase in illite content (up to 35%), and a decrease of the smectite content (up to 21%). The smectite crystallinity index decreased to 0.38, whereas the illite ratio AlVI/(FeVI + MgVI) decreased to 0.36. In this zone, the ostracode assemblage contains numerous juvenile stages of coastal species coinciding with lumachelle accumulations of the estuarine bivalves, abundant foraminifers and the presence of charophytes. This zone represents a strong marine input, probably caused by storms.

The Guadalquivir Estuary: Spits and Marshes

The estuary of the Guadalquivir River is the largest in the Gulf of Cadiz, covering an area of some 185,000 ha. From a geological standpoint, the estuary represents the culmination of the marine filling of the Cenozoic Guadalquivir Basin. The present-day configuration of the estuary is the result of the post-glacial transgression of the Atlantic Ocean, starting ca. 15,000 years, that developed during the latest Pleistocene-Holocene up until some 5,500 years ago, when the level of the sea stabilised. The lower Guadalquivir valley was transformed into a wide estuary as the interfluves turned into pronounced headlands. Marine and fluvial dynamics, dependent upon climate and tectonics, thus shaped the present landscape, which features extensive dune systems, marshes and spits, as well as erosion of the headlands (cliff formation).

Beaches of Huelva

The Huelva Coast forms the littoral sector of the SW Iberian Peninsula which extends from the mouth of the Guadiana River, on the border with Portugal, to the mouth of the Guadalquivir River. From a physiographic point of view, the Huelva Coast can be considered a linear, low and sandy coast formed by long beaches, although it could be divided in different sectors according to its topographic configuration and distribution of sedimentary environments.