Search

The scientific literature describes two types of cheniers. These two types differ in the origin of the coarse sediments that constitute the ridge and the relative significance of the transversal and longitudinal wave transport. In both cases storm waves are described as the main factor responsible of the origin and development, and both final facies are characterized by ridges of coarse sediments above the finer sediments of a tidal flat. The Odiel–Tinto estuary is one of the most significant estuarine systems of the mesotidal Huelva Coast, on the northwestern portion of the Gulf of Cadiz, and Saltés Island is a part of the closure history of the estuarine system. Previous works on Saltés Island described the surficial disposition of sandy landforms as a classic ridge chain or a barrier-island succession; nevertheless an architectural scheme based on a vibracore study shows a disposition that accord to the typical chenier plain facies model. This disagreement was the basis for a controversy about the origin of the ridges. In this study historical nautical charts and aerial photographs document the evolution of the last of these cheniers during the past 200years. In contrast to the accepted models of chenier evolution, the cheniers of Saltés Island migrated on the tidal flat but did not evolve only during storms, indeed their development occurred mainly during high spring tides. The data presented in this paper are used as the basis for a new conceptual model of chenier generation and evolution. The model consists of a migration of sand bars in a similar way to the classic beach ridges, with the difference that in our case, the bars migrate over a tidal flat. From a local point of view this paper removes the controversy about the origin of the island's geomorphology, but from a global point of view this mechanism can explain certain chenier plains in estuarine mouths located in other coasts of the world. [ABSTRACT FROM AUTHOR]

Abstract: Rodríguez-Ramírez and Yáñez-Camacho (2008), Rodríguez-Vidal et al. (2009) and Rodríguez-Ramírez et al. (2009) have kept an ongoing discussion about the validity of radiocarbon ages in reconstructing Holocene palaeogeographical models in the Gulf of Cadiz. The discussion considered the validity and correctness of the ΔR value to be used in the area to calibrate radiocarbon ages of marine samples. These papers suggest that the ΔR value proposed by Lario (1996) and Dabrio et al. (1999, 2000) is erroneous, and consequently, that all the evolutionary models based on radiocarbon ages from marine samples that have been proposed in this area since 1996 must be revised. However, the papers commented here use erroneously the R, regional R and ΔR values. After reviewing the published data, it is apparent that the most reliable values of ΔR in the Gulf of Cadiz for middle-late Holocene samples range between ΔR =35±85yr and ΔR =95±15yr. This means that the values used in Lario (1996) and Dabrio et al. (1999, 2000) fall in this range, and also that the calibrated ages used by several authors adopting these values are fully reliable. Calibrations using ΔR values inside this range do not yield significant differences in terms of geological age owing to the magnitude of errors resulting from the methods employed. [ABSTRACT FROM AUTHOR]

Abstract: The application of the regional marine 14C reservoir effect (ΔR) to obtain an accurate calibration of conventional marine shell 14C dates requires prior research concerning the oceanographic conditions and the ΔR of that region. Rodríguez-Ramírez and Yánez-Camacho [A. Rodríguez-Ramírez, C.M. Yánez-Camacho, Formation of chenier plain of the Doñana marshland (SW Spain): Observations and geomorphic model, Marine Geology 254 (2008) 187–196] and afterwards A. Rodríguez-Ramírez, J.A. Morales, J. Borrego and E.G. San Miguel in a reply [A. Rodríguez-Ramírez, J.A. Morales, J. Borrego, E.G. San Miguel, Reply to the comment on “Formation of chenier plain of the Doñana marshland (SW Spain): Observations and geomorphic model” by A. Rodríguez-Ramírez and C.M. Yáñez-Camacho [Marine Geology 254 (2008) 187–196], Marine Geology 263 (2009) 123–125] to the comment by J. Rodríguez-Vidal, F. Ruiz and L.M. Cáceres on the paper mentioned above [J. Rodríguez-Vidal, F. Ruiz, L. M. Cáceres, Comment on “Formation of chenier plain of the Doñana marshland (SW Spain): Observations and geomorphic model” by A. Rodríguez-Ramírez, C.M. Yáñez-Camacho [Marine Geology 254 (2008) 187–196], Marine Geology 263 (2009) 120–122] use, in both cases, not only incorrect ΔR values for the calibration of 14C dates obtained from shell samples collected from the east coast of the Gulf of Cádiz, but they also confuse the ΔR concept with that of R(t), the 14C reservoir age. Because the misunderstanding of these concepts by these authors and, in the first case, also their failure to take into account the ΔR values obtained by us (and already published) from the east coast of Gulf of Cádiz, all the calibrated dates presented either in the first paper or in the reply cannot be accepted. Here I present a new calibrated dataset using accurate ΔR values and I recommend that the conclusions obtained by Rodríguez-Ramírez and their collaborators be revised, as J. Rodríguez-Vidal, F. Ruiz and L.M. Cáceres proposed in their comment. [Copyright &y& Elsevier]

Abstract: The Guadalquivir estuary is one of the most important in Europe. It is isolated from the sea by two important littoral spits (Doñana and La Algaida). Its sedimentary filling occurred as a result of deltaic contributions of the Guadalquivir River, giving rise to marshes primarily composed of mud deposits, among which a succession of sandy and shelly ridges can be found. The aim of this paper is to explain the genesis and evolution of these sandy and shelly ridges clarifying what types of ridges are found and their spatial distribution, identifying the processes responsible for their formation. These ridges extend in the form of long strands along the estuary, influencing its evolution during the Late Holocene. The geomorphologic and lithostratigraphic features of these ridges allow them to be defined as transgressive cheniers, regressive cheniers and laterally accreted ridges (spits), as components of the Guadalquivir estuary chenier plain complex. This chenier plain has the peculiarity of developing on a semi-enclosed shoreline, contrary to other chenier plains in the world, which develop on open coasts. In the Guadalquivir estuary the chenier plain formation is related to two relatively higher sea level (4200–2800 yr BP and 1400–1000 yr BP) during which high energy events occur (storms and tsunamis), that transgressed the large littoral spits. The Carrizosa (∼4000 yr BP) and Vetalengua (∼1400–1300 yr BP) spits have been formed across the inlet, and prograded landwards of the estuary. From here, several sequences of cheniers (mainly transgressive cheniers) associated with these events were formed. These cheniers form two groups: Las Nuevas (∼1100–1000 yr BP) and Marilópez (∼3000 yr BP), composed mainly of shells and shell fragments. These cheniers were constructed by waves which reworked the shells above estuarine levees, and led to their intense landward migration, thus explaining the peculiar, high inland position of the cheniers. [Copyright &y& Elsevier]

Abstract: It is paradoxical that work in question (Rodríguez-Ramírez and Yánez-Camacho, 2008) has started a debate in the scientific community about the values of the reservoir effect used in the 14C dates in the Gulf of Cádiz, since in their Comments Rodríguez-Vidal et al. (2009), Monges Soares (2010-this issue) and Lario et al. (2010-this issue), have not taken into account that these values are in reference to earlier studies (Morales et al., 2008). The new figures suggested by Rodríguez-Vidal et al. (2009) and Monges Soares (2010-this issue) for this part of the Gulf of Cadiz (Soares, 2008) had not been reported when the earlier papers were accepted and published. The values for the reservoir effect applied on the South Atlantic coast of the Iberian Peninsula need to be continually adjusted, due to the new contributions that have been made in recent years as a result of developments of the research being undertaken in this field. Without doubt, in the future, as further progress is made, the values will be even more finely tuned and the present ones will become obsolete, as our understanding of marine and estuarine dynamics in this sector over the last few thousand years is a topic which remains open to new interpretations. The new figures for the reservoir effect are an important contribution in determining more accurately the chronology of events in the Holocene, and they make it necessary to revise the previous studies on marine Holocene formations in the Gulf of Cadiz with 14C dates, owing to the errors that have occurred in this respect. For this reason the Comment should not be aimed at one paper alone, and instead this matter should be reviewed at a regional level. Those of us who are not specialists in the topic welcome these clarifications, which can help shed additional light on the chronological problems. [ABSTRACT FROM AUTHOR]