Understanding the transformations of the climate system may help to predict and reduce the effects of global climate change. The geological record provides a unique archive that documents the long-term fluctuations of environmental variables, such as seasonal change. Here, we investigate how seasonal variation in seawater temperatures varied in the Mediterranean Sea during the early Pleistocene, approaching the Early-Middle Pleistocene Transition (EMPT) and the beginning of precession-driven Quaternary-style glacial-interglacial cycles. We performed whole-shell and sclerochemical stable isotope analyses (δ 18 O, δ 13 C) on bivalves, collected from

A B S T R A C TShells of brachiopods are excellent archives for environmental reconstructions in the recent and distant past as their microstructure and geochemistry respond to climate and environmental forcings. We studied the morphology and size of the basic structural unit, the secondary layer fibre, of the shells of several extant brachiopod taxa to derive a model correlating microstructural patterns to environmental conditions. Twenty-one adult specimens of six recent brachiopod species adapted to different environmental conditions, from Antarctica, to New Zealand, to the Mediterranean Sea, were chosen for microstructural analysis using SEM, TEM and EBSD. We conclude that: 1) there is no significant difference in the shape and size of the fibres between ventral and dorsal valves, 2) there is an ontogenetic trend in the shape and size of the fibres, as they become larger, wider, and flatter with increasing age. This indicates that the fibrous layer produced in the later stages of growth, which is recommended by the literature to be the best material for geochemical analyses, has a different morphostructure and probably a lower organic content than that produced earlier in life.In two species of the same genus living in seawater with different temperature and carbonate saturation state, a relationship emerged between the microstructure and environmental conditions. Fibres of the polar Liothyrella uva tend to be smaller, rounder and less convex than those of the temperate Liothyrella neozelanica, suggesting a relationship between microstructural size, shell organic matter content, ambient seawater temperature and calcite saturation state.

The Arda River marine succession (Italy) is an excellent site to apply an integrated approach to paleoenvironmental reconstructions, combining the results of sedimentology, body fossil paleontology, and ichnology to unravel the sedimentary evolution of a complex marine setting in the frame of early Pleistocene climate change and tectonic activity. The succession represents a subaqueous extension of a fluvial system, originated during phases of advance of fan deltas affected by high-density flows triggered by river floods, and overlain by continental conglomerates, indicating a relative sea level fall and the establishment of a continental environment. An overall regressive trend is observed through the section, from prodelta to delta front and intertidal settings. The hydrodynamic energy and the sedimentation rate are not constant through the section, but they are influenced by hyperpycnal flows, whose sediments were mainly supplied by an increase in Apennine uplift and erosion, especially after 1.80 Ma. The Arda section documents the same evolutionary history of coeval successions in the Paleo-Adriatic region, as well as the climatic changes of the early Pleistocene. The different approaches used complement quite well one another, giving strength and robustness to the obtained results.

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The Arda and Stirone marine successions (Italy) represent key sections for the early Pleistocene; they were deposited continuously within a frame of climate change, recording the Calabrian cooling as testified by the occurrence of the “northern guests,” such as the bivalve Arctica islandica. In addition, although the first occurrence of A. islandica in the Mediterranean Sea was used as the main criterion to mark the former Pliocene-Pleistocene boundary, the age of this bioevent was never well constrained. Here, we describe the Stirone depositional environment and constrain for the first time the section age using calcareous nannofossil and foraminifera biostratigraphy. We also correlate the Arda and Stirone sections using complementary biostratigraphic and magnetostratigraphic data. Our results indicate that A. islandica first occurred in both the successions slightly below the top of the CNPL7 biozone (dated at 1.71 Ma). Comparisons with other lower Pleistocene Mediterranean marine successions indicate that the stratigraphically lowest level where A. islandica first occurred in the Mediterranean Sea is in the Arda and Stirone sections; these environments satisfied the ecological requirements for the establishment and the proliferation of the species, which only subsequently (late Calabrian) has been retrieved in southern Italy and other areas of the Mediterranean Sea.

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Here, we provide the dataset associated with the research article “Mapping of recent brachiopod microstructure: A tool for environmental studies” [1]. We present original data relative to morphometric and statistical analyses performed on the basic shell structural units (the secondary layer fibres) of brachiopod shells belonging to six extant species adapted to different environmental conditions. Based on SEM micrographs of the secondary layer, fibres from ventral and dorsal valves, and from different shell positions, showing regular and symmetrical cross sectional outlines, were chosen for morphometric measurements using Adobe Photoshop CS6, Image-Pro Plus 6.0 and ImageJ. To work out the reliability of the measurements, the most significant parameters were tested for their probability density by distribution plots; for data visualization and dimension reduction, principal component analysis (PCA) was performed using R 3.3.0 [2] and independent-samples t-tests were performed using SPSS Statistics (IBM Version 22.0. Armonk, NY). Besides a quantitative analysis, a qualitative description of the shell microstructure is provided by detailed SEM imaging and EBSD measurements.