The effects of astronomically forced climate change on hemipelagic carbonate sedimentation in a tectonically active setting: the Albian Mioño Formation in Castro Urdiales (Cantabria, N Spain)

Our understanding of the stratigraphic expression of astronomically driven climate-change cycles in the Milankovitch frequency band has improved significantly in recent decades. However, several aspects have been little studied to date, such as the nature of the climatically regulated environmental processes that ultimately control cyclic sedimentation. Similarly, relatively little is known about the expression of Milankovitch cycles in successions accumulated in tectonically active basins. In order to fill this knowledge gap, the Albian hemipelagic deposits of the Miono Formation exposed in Castro Urdiales (Basque-Cantabrian Basin) are studied herein. These deposits were accumulated during a rifting phase with strong tectonic activity. The sedimentological, petrographic and cyclostratigraphic analysis demonstrates that, despite the synsedimentary tectonic instabilities and some diagenetic overprinting, the hemipelagic carbonate alternation was astronomically forced 110.68-110.47 Ma. Seasonality fluctuations driven by precession cycles caused periodic (20 ky) variations in the rate of carbonate productivity (abundance of pelagic calcareous plankton and micrite exported from adjacent shallow-water areas) and/or siliceous dilution (terrestrially derived siliciclastic sediment supply and siliceous particle production by sponges). These variations resulted in the formation of marly limestone beds when annual seasonality was low (i.e., boreal summer at aphelion, winter at perihelion) and the accumulation of marlstones when seasonality increased (i.e., boreal summer at perihelion, winter at aphelion). The incidence of these processes increased and decreased in line with seasonality modulation by short-eccentricity cycles of 100 ky. In conclusion, this study shows that Milankovitch cycles can be reliably recorded in hemipelagic successions accumulated in tectonically active settings if sediment gravity flows or other disturbances do not affect autochthonous sedimentation.Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. Research funded by the MCIN/AEI project PID2019-105670GB-I00/AEI/10.13039/501100011033 of the Spanish Government and by the Consolidated Research Group IT160222 of the Basque Government

Análisis de la enseñanza de los procesos geológicos externos en la educación secundaria obligatoria del País Vasco

Los expertos han constatado una pérdida de interés hacia la geología de la población en general que podría estar relacionada con su exclusión progresiva en el currículo básico en la educación obligatoria. Sin embargo, es necesario que el alumnado que finaliza la Educación Secundaria Obligatoria (ESO) adquiera una correcta alfabetización en Ciencias de la Tierra, en la que entender los procesos geológicos externos y su acción en el relieve es un contenido clave. Este estudio ha evaluado qué procesos geológicos externos se enseñan en la ESO de la Comunidad Autónoma del País Vasco, mediante el análisis de los libros de texto más utilizados y la realización de cuestionarios al profesorado. Ambas fuentes revelan que el estado actual de su enseñanza muestra deficiencias y necesita mejoras, tales como dedicarle el tiempo y espacio que le corresponde o mejorar la calidad de los textos empleados.Analysis of teaching external geological processes in the compulsory secondary school of the Autonomous Community of the Basque Country Abstract: Experts have noted that the interest of the general population in geology has decreased. This seems to be related to an exclusion of geology from compulsory education curriculum. However, it is mandatory that the students who complete compulsory secondary school acquire a correct literacy in Earth Sciences, in which understanding external geological processes and their action on the relief is a key content. Our study has evaluated which external geological processes are taught in the compulsory secondary school of the Autonomous Community of the Basque Country. To this end, the most commonly used textbooks were analyzed and teachers were asked to fill out questionnaires. Both sources reveal that the current teaching of this unit shows deficiencies and, consequently, needs improvement in both the quality of the texts used and in the time and space devoted to this unit

El eóceno de la cuenca de Pamplona: estratigrafía, facies y evolución paleogeográfica. (The Eocene of the Pamplona basin: stratigraphy, facies and paleogeographic evolution)

This project has focused on the Early and Middle Eocene sediments of the Pamplona Basin, an area which had seldom been previously studied. However, the Eocene Pamplona Basin has turned out to be of considerable interest, first because it is one of the few areas in the pyrenean domain that allows for the reconstruction of a complete shallow- to deep-water transect (i.e., from the Northiberian Platform to the Southpyrenean Trough), and also because of its strategic position between the Central Southpyrenean Zone and the Basque-Cantabrian Region. In addition to an improvement of existing geological maps, this study has produced the following results: (a) new lithostratigraphic and sequence stratigraphic schemes of succession, (b) the biostratigraphic age dating of the different units of both schemes, (c) a better understanding of the sedimentological and tectonic processes which control the development of the succession, and (d) the determination of the paleogeographic evolution. @@ Three main stratigraphic units have been defined, all of the them bounded by important sedimentological breaks (RSBE, RSiY, RSiL and RSiB). Unit 1 (early-middle Ypresian) represents a stage of gentle regression and incipient tectonic activity. Unit 2 (late Ypresian/middle Lutetian-I) records the enhancement of the regression and the amplification of the tectonic activity, with important right lateral movements along the Pamplona fault zone. Unit 3 (middle Lutetian-II/early Bartonian) has a transgressive trend developed during a period of attenuated tectonism. Units 1 to 3 are parts of two 2ndorder transgressive-regressive facies cycles (CTR-1 and 2). Thus, Units 1 and 2 form the regressive hemicycle of CTR-1, the former representing a depositional regression, the latter a forced one. Unit 3, on the other hand, represents the transgressive hemicycle of CTR-2 (the Upper Maastrichtian-Paleocene transgressive hemicycle of CTR-1 and the latest Eocene regressive hemicycle of CTR-2 have not been studied in this Thesis). The genesis of both CTRs was determined by changes in the second-order tectonic subsidence rate. Thus, the regressive hemicycle of CTR-1 (Units 1 and 2) record the tectonic uplift of the shallow-water domain, a process probably linked to the initial development of a forebulge in the western part of the southpyrenean foreland basin. Likewise, the transgressive hemicycle of the CTR-2 (Unit 3) was driven either by the disappearance of the forebulge or by its southwards migration. Climate was an additional control of the sedimentation during the studied interval, the earliest Eocene climatic maximum being particularly important. @@ Thirteen depositional sequences (SD-E1 to SD-E13) have also been recognised. Their genesis responds to 3rd-order relative changes of sea level that, at least in certain cases, were undoubtedly caused by tectonics. Internal organisation of these depositional sequences varies depending on their position within the CTRs, probably due to the interference of the 2nd-order subsidence curve. Highorder sequence stratigraphic units and a variety of event deposits have finally been identified. The most interesting examples of the latter are carbonate megabeds redeposited within the deep-water deposits, that represent important tectonic tilting episodes of the platform domain. The temporal restriction of such megabeds to the late Ypresian/middle Lutetian-I reinforces the strong tectonic activity deducted for this particular interval. @@ The CTRs of the Pamplona Basin and some of their depositional sequences seem to occur in other pyrenean zones. Also, the major sedimentary breaks of the Pamplona Basin can be correlated with specific discontinuities of other euro-atlantic zones, and seem to be contemporaneous with periods of readjustment of lithospheric plates. Such coincidences suggest that the main controls of the tectonosedimentary evolution of the Eocene Pamplona Basin were the interactions in both the north-Atlantic ridge and the Iberian-European plate boundar

Climate and biota of the early Paleogene: recent advances and new perspectives

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Correlation of the Thanetian-Ilerdian turnover of larger foraminifera and the Paleocene-Eocene thermal maximum: confirming evidence from the Campo area (Pyrenees, Spain)

It has long been known that a major larger foraminifera turnover (LFT) occurred at the boundary between the Thanetian and Ilerdian stages, but its possible correlation with the Paleocene-Eocene thermal maximum (PETM) was unsuspected until the work of Baceta (1996), and has been controversial ever since. After summarizing the history of this controversy, we present information from three new sections that conclusively resolve the issue, all of them placed less than 2 km to the east of the classical Campo section in the southern Pyrenees. In these three sections, an up to 7 meter-thick intercalation of continental deposits rich in pedogenic carbonate nodules is sandwiched between uppermost Thanetian and lowermost Ilerdian shallow marine carbonates. The d13C composition of 42 pedogenic nodules collected from two of these sections (San Martín and La Cinglera) ranges between –11.4 and -14.3‰ and averages –12.9‰, values that conclusively represent the PETM and for the first time are recorded in sections where the LFT is clearly represented. Further, a high-resolution lithological correlation between Campo and the three new sections across the P-E interval unquestionably demonstrates that the lowermost marine beds with autochthonous specimens of Alveolina vredenburgi (a tell-tale of the LFT) are laterally interfingered –and are therefore coeval- with the nodule-bearing PETM continental deposits. On the basis of the new evidence, the temporal coincidence of the PETM and the LFT can no longer be doubted