J. Martín-Chivelet

Determination of sea surface temperatures using oxygen isotope ratios from Phorcus lineatus (Da Costa, 1778) in northern Spain: Implications for paleoclimate and archaeological studies

Changes in oxygen isotope ratios from shell carbonates are mainly dependent on sea surface temperature, which enables the estimation of temperatures during periods of shell growth and helps to determine the season of the year when the mollusk died. The marine topshell Phorcus lineatus (Da Costa, 1778) is commonly found in Holocene archaeological deposits of Atlantic Europe and is one of the most abundant subsistence resources utilized during the Mesolithic in northern Spain. Before applying isotopic techniques to ancient samples, calibration of the past isotopic data and its variability must be performed through the study of modern specimens to test their potential as paleoclimate proxy and their suitability for determining the collection season. Although previous studies performed in the region highlighted the existing relationship between sea surface temperatures and isotopic signatures, no systematic works have been done so far. In this paper, calibration of modern P. lineatus shells from northern Spain was carried out using δ18O analysis. The results showed (1) the existence of a robust inverse correlation between instrumental temperatures (Tmeas) and δ18Oshell (R2u2009>u20090.9), accompanied by the lack of significant dependence from δ18Owater variations (R2u2009=u20090.06); (2) the existence of conditions of (or close to) isotopic equilibrium during the formation of the aragonite in the P. lineatus shells; and (3) that using mean annual δ18Owater values, past temperatures could be calculated with a maximum uncertainty of ±3°C. Moreover, results suggested that P. lineatus generally grew without substantial slow/cessation throughout the year, reflecting the four annual seasons. Therefore, our study not only confirms the potential of oxygen isotope analysis on P. lineatus for paleoclimate reconstruction and archaeological studies highlighted in previous studies but also shows for the first time that the aragonite of those shells grew under conditions of isotopic equilibrium, opening new avenues for future research.

Mg/Ca ratios measured by laser induced breakdown spectroscopy (LIBS): a new approach to decipher environmental conditions

The potential application of Mg/Ca ratios in top shells of the mollusc species Phorcus lineatus (Da Costa, 1778) obtained by Laser Induced Breakdown Spectroscopy (LIBS) has been evaluated as an environmental proxy to reconstruct paleotemperatures and season of capture of molluscs for the first time. All samples were collected from the Cantabrian Sea (Spain). The results were compared with instrumental sea surface temperatures (SSTs) and with a known reliable proxy as the oxygen isotope ratio (δ18Oshell) which is mainly dependent on the SST, obtained from the same shells. Measurements were taken in two different biominerals of the shell (aragonite and calcite) resulting in a correlation between Mg/Ca ratios and SSTs of R2 = 0.43 and 0.44, respectively. Mg/Ca ratios were also studied through a long sequence on three shells collected in autumn 2012. The results show variations in Mg/Ca ratios related to seasonal changes in the SST throughout the year and a good correlation between Mg/Ca ratios and δ18Oshell in two shells (R2 = 0.70 and 0.65, respectively).

Mid-depth calcareous contourites in the latest Cretaceous of Caravaca (Subbetic Zone, SE Spain). Origin and palaeohydrological significance

Abstract Deep marine carbonates of Late Campanian to Early Maastrichtian age that crop out in the Subbetic Zone near Caravaca (SE Spain) contain a thick succession of dm-scale levels of calcareous contourites, alternating with fine-grained pelagites/hemipelagites. These contourites, characterised by an abundance and variety of traction structures, internal erosive surfaces and inverse and normal grading at various scales, were interpreted as having been deposited under the influence of relatively deep ocean currents. Based on these contourites, a new facies model is proposed. The subsurface currents that generated the contourites of Caravaca were probably related to the broad circumglobal, equatorial current system, the strongest oceanic feature of Cretaceous times. These deposits were formed in the mid-depth (200–600 m), hemipelagic environments at the ancient southern margin of Iberia. This palaeogeographic setting was susceptible to the effects of these currents because of its position close to the narrowest oceanic passage, through which the broad equatorial current system flowed in the westernmost area of the Tethys Seaway. Regional uplift, related to the onset of convergence between Iberia and Africa, probably favoured the generation of the contourites during the Late Campanian to the Early Maastrichtian.

Quantitative analysis of accommodation patterns in carbonate platforms: an example from the mid-Cretaceous of SE Spain

Abstract For sequence stratigraphic analysis of extensive carbonate platforms (hundreds of kilometres wide) developed in greenhouse climates on broad, passive margins, less emphasis should be placed on large-scale seismic geometries, and more attention paid to sequence stratigraphic correlation of stratigraphic sections based usually on isolated outcrops. To this end, quantitative analysis of accommodation emerges as a simple, useful tool, that allows detailed architectural reconstructions, regional chronostratigraphical correlation and systems tract interpretation. In this paper, a quantitative analysis of accommodation was applied to the wide platforms that developed in the southern passive continental margin of Iberia during the mid-Cretaceous (late Albian to early middle Cenomanian interval). This analysis was based on several integrated techniques including: (1) construction of total accommodation curves with the aid of backstripping techniques for calculating decompacted sedimentary accumulation through time, (2) mathematical analysis of these curves and characterisation of second- and third-order accommodation patterns, and (3) analysis of parasequence stacking patterns in peritidal cyclic successions by means of Fischer plots. By applying these techniques to eight individual sections logged at the decimetre scale in outcrops of the External Zones of the Betic orogenic belt, it was possible to characterise the second- and third-order accommodation signal for this interval in the basin. The second-order curve defines a long-term sigmoidal pattern of nearly six million years, with low rates of accommodation generation in the first and the last part of the interval, and high rates in the mid-interval. The third-order signal defines six accommodation events of one million years average duration, which controlled the development of six successive depositional sequences and their systems tracts. On the basis of this new sequence stratigraphic framework, a high-resolution, 2-D platform transect, showing the spatial distribution of facies, was erected and analysed. The results notably complete previous qualitative sequence stratigraphic data on the platform and contribute to a better understanding of the nature of systems tracts and their boundaries in response to overlapping of second- and third-order accommodation patterns.

Long-term hydrological changes in northern Iberia (4.9–0.9 ky BP) from speleothem Mg/Ca ratios and cave monitoring (Ojo Guareña Karst Complex, Spain)

An absolute-dated stalagmite from Kaite Cave (Ojo Guareña Karst Complex, N Spain) provides a nearly continuous, high-resolution record of a proxy of regional precipitation patterns through the 4.9–0.9xa0ka BP interval. This record is based on the Mg/Ca ratio of the calcite and its variation through the stalagmite stratigraphy, which is interpreted to be primarily driven by changes in precipitation amount. The calibration of the proxy is supported by the present-day monitoring carried out in the cave for the last 10xa0years, which reveals a robust inverse relationship between the inter-annual/inter-decadal variability of rainfall and the Mg concentration of dripwaters and precipitating speleothems. The record of paleoprecipitation, based on 2400xa0Mg/Ca measurements, shows strong variability at inter-annual to inter-decadal scales, and more subtle but significant changes at secular to millennial scales. This long-term paleohydrological evolution outlines five successive intervals with consistent trends, which are bounded by abrupt shifts in the regional precipitation. These shifts took place at 4.65, 4.2, 2.6, and 1.3xa0ka BP. Significantly, the intervals of maximum precipitation of the whole record (around 4.9–4.65, 2.6–2.45, and 1.3–1.1xa0ka BP) can be related with episodes of minimum solar activity and correlated with cold climatic events elsewhere.

Variations in Trace Elements of Drip Waters in Kaite Cave (N Spain): Significance in Terms of Present and Past Processes in the Karst System

Drip-water chemistry in karstic caves can vary at seasonal to inter-annual scales in response to climatic factors such as temperature, rainfall, and seasonality, which determine changes in the hydrological and hydrochemical processes of the percolating waters in their paths from the atmosphere to the cave. In this paper the characterization of stalagmite forming drip-waters based on long-term (years) time-series data is presented as a key task for understanding the geochemical behavior of a specific system, the Kaite Cave (N Spain). The work focuses on the relationships between rainfall, drip rates, drip-water calcium concentration, and drip-water trace elements amount (e.g., Mg and Sr); as indicators of hydrologic processes defining the karst system and controlling speleothem growth and composition patterns.

Trace Elements in Speleothems as Indicators of Past Climate and Karst Hydrochemistry: A Case Study from Kaite Cave (N Spain)

A stalagmite that grew during the Holocene (between 4.9 and 0.9 ka BP) in Kaite Cave (Ojo Guarena Karst Complex, Burgos, N Spain) has been analyzed by Laser-Induced Breakdown Spectroscopy (LIBS) with the aim of reconstructing secular variations in the hydrochemistry of the karst system, in turn related to changes in the environment outside the cave. LIBS analyses yield significant changes in Mg/Ca and Sr/Ca intensity ratios through the stalagmite, which reveal consistent trends and patterns at decadal to centennial scales. The origin of the observed changes in Mg/Ca and Sr/Ca ratios is discussed in the framework of the cave system and the regional climatic variability, particularly the changes in precipitation.

New challenges for Journal of Iberian Geology

The issue you now hold in your hands represents the beginning of a new era for the Journal of Iberian Geology, a step forward in a trajectory that was initiated 47 years ago, when the first issue of the journal—back then, titled Cuadernos de Geologia Iberica—was released with the aim of disseminating the growing knowledge on the regional geology of the Iberian Peninsula and surrounding areas. With the new century (year 2000) a fundamental orientation of the journal began, including a change of names to Journal of Iberian Geology. Further, the journal became an international research forum, supported by the Complutense University of Madrid (Spain) and the Spanish Research Council (CSIC).

Palaeoenvironmental Changes and C-Isotope Stratigraphy in the Alarcón Formation Stratotype (Upper Cenomanian-Lower Coniacian), Iberian Ranges, Spain

This study analyses the sedimentary facies, palaeosols, and δ13C stratigraphy of the Alarcon Formation in its stratotype in the Iberian Ranges (Spain). The aim is to characterize the palaeoenvironmental changes that occurred in the shallow-marine carbonate environments of central Iberia during the late Cenomanian to early Coniacian. These changes, recorded in seven transgressive–regressive cycles, are interpreted in the framework of regional sea-level variations, local subsidence, and climate. The possible influence of supraregional changes, such as those related to Oceanic Anoxic Event 2 (OAE2), on the sedimentary succession of the Alarcon Formation is also analysed and discussed.