Aptian (Lower Cretaceous) biostratigraphy and cephalopods from north central Tunisia

Thick Aptian deposits in north central Tunisia comprise hemipelagic lower Aptian, reflecting the sea-level rise of OAE 1a, and an upper Aptian shallow marine environment characterized by the establishment of a carbonate platform facies. Carbon stable isotope data permit recognition of the OAE 1a event in the Djebel Serdj section. Cephalopods are rare throughout these successions, but occurrences are sufficient to date the facies changes and the position of the OAE1a event. Ammonite genera include lower Aptian Deshayesites, Dufrenoyia, Pseudohaploceras, Toxoceratoides and ?Ancyloceras; and upper Aptian Zuercherella, Riedelites and Parahoplites. Correlation of carbon isotope data with those of other Tethyan sections is undertaken together with the integration of planktonic foraminiferal data.     

Gravity for Lithosphere Architecture Determination and Analysis: the Central Eastern Mediterranean case study

The Central-Eastern Mediterranean region is known to be a complex area due to the interaction of four tectonic plates, namely Arabia, Africa, Anatolia and Eurasia, and by the presence of an ancient oceanic crust in the Herodotus and Ionian Basins. The analysis of the available literature highlights that the distribution of the freely available geophysical data (i.e. seismic, gravity and magnetic observations) is quite disparate. In this framework, high-resolution global gravity field models, such as XGM2019e, mainly based (offshore) on satellite data, can be profitably used as a uniform dataset to study, in a coherent way, large regions. In the current work, we exploit the XGM2019e model, together with a set of a priori information, derived mainly from geophysical data retrieved from the literature, to study the structure of the crust in the Central-Eastern Mediterranean area. The study is organized in three different phases: in the first one, we enhanced the map of geological crustal provinces by means of an automatic Bayesian classification algorithm applied to the second radial derivatives of the gravitational potential. In the second phase, using as observation a grid of gravity anomalies, we applied a full three-dimensional inversion procedure (always based on a Bayesian paradigm) to estimate the mass density variations and the geometries of the main geological units in the whole study area. Finally, in the third phase, we performed a refined three-dimensional local inversion on the Cyprus area to improve the modelling of the shallowest layers. The main results of this study, carried out in the framework of the European Space Agency GIADA project, are freely available, upon request, at https://www.g-red.eu/geophysics/ .     

Seasonality of microzooplankton grazing in the northern Wadden Sea

A sequence of nine dilution experiments was conducted according to Landry and Hassett [Landry, M.R., Hassett, R.P., 1982. Estimating the grazing impact of marine microzooplankton. Mar. Biol. 67, 283–288] in the northern Wadden Sea from March until October 2004 to investigate the seasonality of microzooplankton grazing. From March until April, no grazing was observed. Microzooplankton grazing started in May (0.66 d^− 1) and increased until August (1.22 d^− 1). In October microzooplankton grazing was low again (0.17 d^− 1). Phytoplankton growth rates varied between 0 and 1.1 d^− 1. Since the reliability of dilution experiments is still frequently discussed in literature, we tested if our data obtained by dilution experiments reflected short-term in situ phytoplankton dynamics of the study site. We scaled experimental growth rates to water column irradiance, calculated short-term chlorophyll-a dynamics and compared the results to in situ measured chlorophyll-a concentrations. Calculated chlorophyll-a concentrations correlated significantly with in situ measured chlorophyll-a concentrations but slightly overestimated the in situ measured chlorophyll-a. This overestimation was in the range of phytoplankton assimilation reported for the Wadden Sea benthos. We will show that microzooplankton grazing had a large impact during the Phaeocystis bloom and during summer suggesting that a large proportion of phytoplankton biomass remained the pelagic food web. Microzooplankton grazing did not impact the diatom spring bloom and its demise.     

A new magnetostratigraphic framework for the Lower Miocene (Burdigalian/Ottnangian, Karpatian) in the North Alpine Foreland Basin

Oligocene–Miocene chronostratigraphic correlations within the Paratethys domain are still highly controversial. This study focuses on the late Early Miocene of the Swiss and S-German Molasse Basin (Late Burdigalian, Ottnangian–Karpatian). Previous studies have published different chronologies for this time interval that is represented by the biostratigraphically well constrained Upper Marine Molasse (OMM, lower and middle Ottnangian), Upper Brackish Molasse (OBM, Grimmelfingen and Kirchberg Formations, middle and upper Ottnangian to lower Karpatian, MN 4a–MN 4b) and Upper Freshwater Molasse (OSM, Karpatian–Badenian, MN 5). Here, we suggest a new chronostratigraphic framework, based on integrated magneto-litho-biostratigraphic studies on four sections and three boreholes. Our data indicate that the OBM comprises chrons 5D.1r and 5Dn (Grimmelfingen Fm), chron 5Cr (lower Kirchberg Fm) and the oldest part of chron 5Cn.3n (upper Kirchberg Fm). The OSM begins during chron 5Cn.3n, continues through 5Cn, and includes a long reversed segment that can be correlated to chron 5Br. The OMM-OSM transition was completed at 16.0 Ma in the Swiss Molasse Basin, while the OBM-OSM changeover ended at 16.6 Ma in the S-German Molasse Basin. As the lower Kirchberg Fm represents a facies of the Ottnangian, our data suggest that the Ottnangian–Karpatian boundary in the Molasse Basin is approximately at 16.8 Ma, close to the 5Cr–5Cn.3n magnetic reversal, and thus 0.4 Myr younger than the inferred age of 17.2 Ma used in recent Paratethys time scales. Notably, this would not be problematic for the Paratethys stratigraphy, because chron 5Cr is mainly represented by a sedimentation gap in the Central Paratethys. We also realise, however, that additional data is still required to definitely solve the age debate concerning this intriguing time interval in the North Alpine Foreland Basin. We dedicate this work to our dear friend and colleague Jean-Pierre Berger (8 July 1956–18 January 2012).     

Alternative conceptual models and the robustness of groundwater management scenarios in the multi-aquifer system of the Central Veneto Basin, Italy

A three-dimensional (3D) groundwater flow model of the deep multi-aquifer Quaternary deposits of the Po plain sedimentary basin, within a 3,300-km² area (Veneto, Italy), is developed, tested and applied to aid sustainable large-scale water-resources management. Integrated mathematical modelling proves significantly successful, owing to an unusual wealth of available geological, geophysical, and hydrologic data and to state-of-the-art numerical tools. Of particular interest is the evaluation of the influence of alternative conceptual models; that is, of reconstructed representations of the 3D geological model of the structure of the aquifers. The reference conceptual model is set up by means of extended geological sections and stratigraphic records, and is used to create a large, unstructured 3D finite element grid. By analyzing the effects on piezometric surfaces and on the overall water budget of geometrical perturbations from the reference structure, alternative geo-structural models, obtained by systematically shifting the pinch-out of the aquitards, are compared. Interestingly, the impacts of aquitard pinch-out prove far from negligible. The results suggest the critical importance of reliable geological models even for large, complex 3D models. The good practice of iteratively testing numerically the impact of surprises on the conceptual model, as more field information is collected, is thus supported.     

The making and unmaking of gendered crops in northern Ghana

In rural West Africa, the gendered division of labour extends to labelling certain crops as 'male' or 'female'. With the introduction of new varieties of crops and technologies, these constructions of gendered plants undergo a process of renegotiation at social intrafaces. This process of attaching meaning to new features in cultivation results in the remaking of gendered crops. These negotiations, in turn, have an effect on the construction of gender in specific ethnic and environmental settings, unlinking labour from its gendered connotations and, thus, unmaking the social meaning and creating room for manoeuvre. Based on fieldwork among the Dagomba and Kusasi people in northern Ghana, this study examines how gendered responsibilities and access to the cultivation of crops are linked and expressed in obligations related to the cultural ideal of a proper meal, in this case consisting of the food categories (male) staple and (female) soup, which serve as the blueprint for assigning crops to a specific gender.     

Ordovician K-bentonites in the upper-plate active margin of Western Gondwana, (Famatina Ranges): Stratigraphic and palaeogeographic significance

Numerous, thin-bedded, tabular pale-yellowish clay bands are interlayered with black shales in a biostratigraphically constrained Early Ordovician volcano-sedimentary succession at Famatina, western Argentina. This region was part of a fairly continuous upper-plate, convergent volcanic chain that fringed western Gondwana. Mineralogy on both clay and non-clay fractions, whole rock chemistry and field observations on these distinctive event-beds indicate that they originated as relatively coarse fallout tephras, altered first into bentonites and later, through burial metamorphism, into K-bentonites (metabentonites). These tephras were deposited as single crystals and glassy dust or pumiceous fragments in a restricted subtidal environment. The region of Famatina has previously been inferred as the source of abundant distal K-bentonites recorded in the adjacent lower-plate allochthonous Precordillera terrane. However, these K-bentonites within the proximal arc site were unknown and rather unexpected since they are generally better preserved like distal deposits, associated either with central vent plinian–ultraplinian eruptions or with accompanying co-ignimbrite ash clouds. Their chemistry and comparison with those K-bentonites in the Precordillera allow tracing an evolution from volcanic arcs into continental crust. K-bentonites described in this paper are much older than those recorded in the adjacent Precordillera terrane and seem to be associated with a first eruptive period along western Gondwana that has no counterpart in the Argentine Precordillera, suggesting a significant longitudinal separation between these two regions by the Early Ordovician.     

The distribution of mantle and atmospheric argon in oceanic basalt glasses

Argon analyses by both high-resolution stepheating and stepcrushing of MORB and Loihi basalt glasses were performed to separate pristine mantle-derived Ar and contaminating atmospheric Ar. In high-vesicularity glasses (> 0.8% vesicles), most of the mantle argon resides in vesicles, from which it is released by crushing or stepheating between 600 and 900 °C. By contrast, in low vesicularity glasses (< permil vesicularity), most mantle argon is dissolved in the glass matrix, as inferred from the correlation with neutron-induced, glass-dissolved argon isotopes (³⁹Ar, ³⁷Ar, ³⁸Ar from K, Ca, Cl). The distribution of mantle Ar between vesicles and glass matrix is well explained by melt-gas equilibrium partitioning at eruption according to Henry’s law, which is compatible with previously determined Henry constants of ∼(5-10) × 10⁻⁵ccSTP ⁴⁰Ar _mantle/g bar. Atmospheric Ar is heterogeneously distributed in all samples. Only a very minor part is dissolved in the glass matrix; a significant part correlates with vesicularity and is released by crushing, most probably from a rather small fraction of vesicles or microcracks that equilibrated with unfractionated air. Other carriers of atmospheric argon are pyroxene microlites and minor phases decomposing at intermediate temperatures that were probably contaminated upon eruption by fractionated atmospheric rare gases. Our high-resolution stepheating and stepcrushing analyses of low vesicularity samples with extraordinary high solar-like ²⁰Ne/²²Ne indicate successful discrimination of unfractionated air as a contamination source and suggest an upper mantle ⁴⁰Ar/³⁶Ar of 32,000 ± 4000 and a Hawaiian mantle plume source ⁴⁰Ar/³⁶Ar ratio close to 8000.