Algal diversity during the onset of the Late Paleozoic Ice Age in low-latitude basins of the Western Palaeotethys

A study of calcareous algae from the late Viséan to Serpukhovian interval in basins from the western margin of Palaeotethys (basins located currently in Western Europe and Northern Africa) shows varied responses in terms of palaeoecological diversity, specimen abundance, genus richness and taxonomic distinctness for the low-latitude basins. Algal associations are more similar in cratonic areas, although many local diversity peaks correspond to ecological/environmental factors. Terranes with Laurussian affinities contain the most unusual abundances and seem to be the most affected by palaeogeographic reorganization and local tectonics. Algae from the palaeo-equatorial zone show more dramatic changes than those in the southerly tropics. The varied results suggest that it is not suitable to extrapolate a particular diversity result from a single region to global conditions, since many factors have influenced the regional assemblages. The main taxonomic turnover of most fossil groups occurred from the uppermost Serpukhovian, linked to a severe cooling phase inferred by δ18O data from brachiopods. It coincides with the post-glacial phase C1 defined in eastern Australian basins. Most ecological changes occurred from the early Serpukhovian, predating the glacial phase C1 and coinciding with the Main Eustatic Signal. Far-field proxies used to define the onset of icehouse intervals in the LPIA are inconsistent and are located several million years before the main biota changes. This questions the definition of the onset of sustained icehouse glaciation at different levels of the low palaeolatitude Viséan, without the resulting modifications in the warm-water biota.Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasInstituto de Geociencias (IGEO)TRUEpu

Diagenetic and Biological Overprints in Geochemical Signatures of the Gigantoproductus Tertiary Layer (Brachiopoda): Assessing the Paleoclimatic Interpretation

Variations in the geochemical signatures of fossil brachiopod shells may be due to diagenesis and/or biological processes (i.e., ‘vital effects’). It is critical to characterise them in order to identify reliable shell areas suitable for paleoclimate studies. This investigation contributes to an in-depth understanding of geochemical variations in Gigantoproductus sp. shells (SW Spain, Serpukhovian age), throwing light onto the Late Paleozoic Ice Age interpretation. Microstructural, crystallographic, cathodoluminescence and geochemical (minor and trace elements, δ18O, δ13C, and strontium isotopes) characterisations have been performed on the tertiary layer of the ventral valve, to assess the preservation state. Poorly preserved areas exhibit microstructural and geochemical changes such as recrystallisation, fracturing and higher Mn and Fe enrichment. Moreover, these areas have a higher dispersion of ⁸⁶Sr, ⁸⁷Sr, δ18O and δ13C than well-preserved areas. Three structural regions have been identified in well-preserved areas of the ventral valve by differences in valve curvature and thickness, such as the umbonal and thick and thin regions. These regions have different proportions of Mg, S, Na, δ18O, and δ13C, which are interpreted as ‘vital effects’ and probably related to growth-rate differences during shell growth. The Gigantoproductus tertiary layer seems the most suitable for paleoclimate studies, because it retains the original microstructure and geochemical composition

Geodivulgar: Geología y Sociedad 2018

Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasFALSEsubmitte

GEODIVULGAR: Geología y Sociedad

Fac. de Ciencias GeológicasFALSEsubmitte

Geodivulgar: Geología y Sociedad

Con el lema “Geología para todos” el proyecto Geodivulgar: Geología y Sociedad apuesta por la divulgación de la Geología a todo tipo de público, incidiendo en la importancia de realizar simultáneamente una acción de integración social entre estudiantes y profesores de centros universitarios, de enseñanza infantil, primaria, de educación especial y un acercamiento con público con diversidad funcional

Gigantoproductid shell spiral and microstructure of tertiary layer: evaluation as taxonomical characters

Brachiopodtaxonomyisbasedondescriptionsofshellmorphologyandkeycharacters, but diagenesis generally modifies orerases some of them, hindering brachiopod identification. Brachiopods that are taxonomically related usually present shells with similar appearance but can differ in size (i.e., Rhynchonellata). Some aspects of morphology¿ for example the angular measurement of the curvature of the shell or details of shell microstructure¿ could aid taxonomic identification. Gigantoproductids, which lack a robust taxonomy, have the largest shells among brachiopods and are ideal for this kind of study because of theirgigantic size and morphological variability. Furthermore, they have a great abundance and worldwide distribution during the mid-Carboniferous. More than 700 samples have been collected from Sierra Morena (Spain), Montagne Noire (France) and Adarouch (Morocco) identifying up to six gigantoproductid genera: Globosoproductus, Semiplanus, Kansuella?, Latiproductus, Gigantoproductus andDatangia. Microstructural features from 170thin sectionsbelonging togigantoproductid ventral valves have been studied, and six crystal morphologies have been distinguished within the tertiary layer: subhorizontal, imbricated, crenulated, acicular, short and long columnar morphologies. Moreover, 23 complete shells from all genera have been selected to investigate shell size and curvature. Results from this study emphasise that shell size, curvature and crystal shape are taxa-related. Finally, a remarkable morphological change in the gigantoproductid populations from the western Palaeo-Tethys occurred during the Viséan¿Serpukhovian, from thin-shelled genera with subhorizontal morphology (Viséan) to thick-shelled genera with a tertiary layer consisting of long columnar crystals (Serpukhovian). This study proves that microstructure, maximum thickness and shell spiral characterisation are robust characters when applied to gigantoproductid taxonomy, but also have great potential in other brachiopod groups.Financial support through the Spanish Ministerio de Economía y Competitividad (research projects CGL2012-30922BTE and CGL2016-78738-P) and the Complutense University Research Group (910231) is gratefully acknowledged. J.R.M.-C. acknowledges financial support through an FPI-MINECO grant. This article is a contribution to the Spanish Working Group IGCP 596(UNESCO).Wethanktheanonymousreviewersandtheeditor for theircorrections and suggestions, which improved anearlier version of this manuscript

Gigantoproductid shell spiral and microstructure of tertiary layer: evaluation as taxonomical characters

Brachiopod taxonomy is based on descriptions of shell morphology and key characters, but diagenesis generally modifies or erases some of them, hindering brachiopod identification. Brachiopods that are taxonomically related usually present shells with similar appearance but can differ in size (i.e., Rhynchonellata). Some aspects of morphology – for example the angular measurement of the curvature of the shell or details of shell microstructure – could aid taxonomic identification. Gigantoproductids, which lack a robust taxonomy, have the largest shells among brachiopods and are ideal for this kind of study because of their gigantic size and morphological variability. Furthermore, they have a great abundance and worldwide distribution during the mid-Carboniferous. More than 700 samples have been collected from Sierra Morena (Spain), Montagne Noire (France) and Adarouch (Morocco) identifying up to six gigantoproductid genera: Globosoproductus, Semiplanus, Kansuella?, Latiproductus, Gigantoproductus and Datangia. Microstructural features from 170 thin sections belonging to gigantoproductid ventral valves have been studied, and six crystal morphologies have been distinguished within the tertiary layer: subhorizontal, imbricated, crenulated, acicular, short and long columnar morphologies. Moreover, 23 complete shells from all genera have been selected to investigate shell size and curvature. Results from this study emphasise that shell size, curvature and crystal shape are taxa-related. Finally, a remarkable morphological change in the gigantoproductid populations from the western Palaeo-Tethys occurred during the Viséan–Serpukhovian, from thin-shelled genera with subhorizontal morphology (Viséan) to thick-shelled genera with a tertiary layer consisting of long columnar crystals (Serpukhovian). This study proves that microstructure, maximum thickness and shell spiral characterisation are robust characters when applied to gigantoproductid taxonomy, but also have great potential in other brachiopod groups

GEODIVULGAR: Geología y Sociedad

Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasFALSEsubmitte

Geodivulgar: Geología y Sociedad

Depto. de Geodinámica, Estratigrafía y PaleontologíaDepto. de Química InorgánicaDepto. de Didáctica de las Ciencias Experimentales , Sociales y MatemáticasFac. de Ciencias GeológicasFac. de Ciencias QuímicasFac. de EducaciónFALSEsubmitte