Linking sedimentation rates and large-scale architecture for facies prediction in nonmarine basins (Paleogene, Almazán Basin, Spain)

This paper focuses on the relationships between the large-scale stratigraphic architecture of the Almazán basin infill and the sedimentation rates (SR) calculated for precise time intervals. Our aim is to improve the understanding of the timing and causes of the architectural changes, their significance in terms of accommodation space and sediment supply, and their relationship with climate and tectonics. The study area includes the Gómara fluvial fan, the main sediment transfer system of the Almazán basin during Paleogene times. Its large-scale architecture shifted through time between a stacking pattern of low density ribbon-like and high density sheet-like channel fills. Laterally to the fluvial system, mudstone and evaporitic mudstone units represented evaporitic mudflats which passed laterally into palustrine/lacustrine limestone units interpreted as lakes and ponds. Stacked calcretes occurred in distal alluvial and distal floodplain settings. A magnetostratigraphy encompassing 2600 meters guided by available fossil mammal biochronology has provided a temporal framework that spans the complete Paleogene infill of the basin, from Late Lutetian to Late Oligocene, filling a gap in the Cenozoic chronostratigraphy of Spanish basins. This permits to constrain the kinematics of the structures both in the basin and in its margins, and to provide the timing for the depositional sequences. These data, combined with a magnetostratigraphic map, where magnetic reversals were traced through the Gómara monocline, allow a detailed analysis of the SR variability across the fluvial system and its adjacent depositional environments. The results show that high sedimentation rates (around 30-40 cm/kyr) are related to fluvial environments with low density ribbon-shaped channels, while low SR (around or below 10 cm/kyr) are related to high density sheet-like channels. Laterally, mud dominated environments with high SR (15-20 cm/kyr) grade into palustrine/lacustrine carbonated environments with low SR (around 9 cm/ky). The lowest SR (about 3 cm/kyr) are related to the development of stacked calcrete profiles in distal floodplain and in the connection of distal alluvial and palustrine/lacustrine units

Eocene-Oligocene magnetostratigraphy from the central part of the SE margin of the Ebro Basin

Previous magnetostratigraphic studies focused in the Eocene successions of the eastern Ebro Basin have provided some absolute age for the basin infill. These results were based on some biostratigraphic constraints wich have been recently challenged. Our new results from the approximately 3000 m thick Montserrat and Maians-Rubió magnetostratigraphic sections have been integrated into the both marine and continental biochronology data, providing a more independent chronology. The resulting absolute chronology of the Montserrat-Rubió composite section represents about 10 My, covering the Lutetian to Rupelian (approximately 40.7 to 30.5 Ma). This leads to the re-evaluation of the age of the La Salut Fm. (Lutetian to Bartonian) and the Montserrat conglomerates (Bartonian to Priabonian). The last marine regression in the central part of the SE margin of the Ebro Basin yields an approximate age of about 36.0 Ma (Priabonian)

Updated Iberian archeomagnetic catalogue: new full vector paleosecular variation curve for the last three millennia

In this work, we present 16 directional and 27 intensity high‐quality values from Iberia. Moreover, we have updated the Iberian archeomagnetic catalogue published more than 10 years ago with a considerable increase in the database. This has led to a notable improvement of both temporal and spatial data distribution. A full vector paleosecular variation curve from 1000 BC to 1900 AD has been developed using high‐quality data within a radius of 900 km from Madrid. A hierarchical bootstrap method has been followed for the computation of the curves. The most remarkable feature of the new curves is a notable intensity maximum of about 80 μT around 600 BC, which has not been previously reported for the Iberian Peninsula. We have also analyzed the evolution of the paleofield in Europe for the last three thousand years and conclude that the high maximum intensity values observed around 600 BC in the Iberian Peninsula could respond to the same feature as the Levantine Iron Age Anomaly, after travelling westward through Europe

Long-term vegetation dynamics of a tropical megadelta: Mid-Holocene palaeoecology of the Orinoco Delta (NE Venezuela)

© 2019 Elsevier Ltd Coastal wetlands have been proposed as highly threatened by the ongoing and future climatic change, including projected sea-level changes as an additional forcing factor compared to more inland locations. The limited knowledge generated to date in this topic has been primarily focused on those areas attaining a high population density, and rarely deals with long-term (>50 years) dynamics. Here we present the first Holocene palaeoecological study carried in the Orinoco Delta, in NE Venezuela. The record presented here contains sediments from the last 6200 years and is located in a river-shore swamp dominated by the palm Mauritia flexuosa. Current human occupation is almost restricted to small settlements of the Warao indigenous culture, closely related to the use of M. flexuosa and other palm species present in the zone. The results show the occurrence of three well-distinguished palynological zones: (i) from 6200 to 5200 cal yr BP, characterised by mixed rainforest and other taxa related to salinity (coastal-like), low (negative) values of magnetic susceptibility and magnetic grain size, absence of transported clays, and the highest macrocharcoal particles abundance; (ii) from 5200 to 2950 cal yr BP, marked by a replacement of the mangrove-like vegetation by a more inland mixed-swamp forest community with low levels of charcoal, and (iii) from 2950 cal yr BP to present-day, characterised by the establishment of the current vegetation community, dominated by M. flexuosa, and an increasing trend in the charcoal curve since the last 700 years. A combination of regional (climatic changes) and local (sediment ontogeny) has been proposed as the key drivers influencing the vegetation succession recorded. The stabilisation of the sea-level that occurred during the mid-Holocene would have favoured the transgression of the coastal line, with the migration of the coastal-like vegetation seawards. Synchronous to this event, a trend towards drier conditions has been reported in the close Cariaco record, that could have also influenced the vegetation replacement. Between 3800 and 2800 years ago, the increased ENSO variability registered in Cariaco may have played a key role in the expansion of the Mauritia palm community. It is suggested that in our location, the potential inhabiting human populations were differently influenced by these environmental changes. First, the disappearance of the coastal resources could have favoured land abandonment, whereas the increase in the abundance of the palm might be influential for the arrival of other inland cultures that were previously used to manage Mauritia. This sequence shows the importance of the ecosystem services for the location inhabitants, highlighting the abandonment of the mid-Holocene culture coeval with the disappearance of its ecosystem. These results also provide information about the sensitivity and resilience in facing external stressors of both humans and vegetation, and will be valuable tools for managing the future of this ecosystem

Rapid Intensity Decrease During the Second Half of the First Millennium BCE in Central Asia and Global Implications

Recent paleomagnetic studies have shown that important short-lived intensity fluctuations occurred during the first millennium BCE. However, the knowledge of the spatial and temporal extension of these features is still limited by the scarce availability of robust data. In this study we focus on the study of the intensity decrease that took place in Central Asia during the second half of the 1st millennium BCE after the high intensities that characterized the Levantine Iron Age Anomaly. Since previous archeointensities available for this period and region were obtained without accomplishing modern standards of quality, we present here new archeointensities that are derived from classical Thellier and Thellier experiments, including partial thermoremanent magnetization (pTRM) checks, thermoremanent magnetization (TRM) anisotropy and cooling rate corrections at the specimen level. The new 51 archeointensities, together with previous archeointensities, have been used to present a new local paleosecular variation curve for Central Asia. The results confirm the existence of an important geomagnetic field intensity decrease in South Uzbekistan from the 4th century BCE to the end of the 1st century BCE associated with rates of changes up to −15 μT/century. A critical analysis of the archeointensity global database indicates that this feature was present at continental scale, from Western Europe to Central Asia. However, this trend is not identified in other regions such as Japan or Mexico. Finally, the comparison with the dipole moment derived from recent global geomagnetic field reconstructions suggests a strong influence of non-dipolar sources upon this continental intensity feature.Financial support was given by the Spanish Ministry of Science and Innovation thorough the projects CERAC (HAR2016-75133-C3-1-P), CONCERAC (HAR2016-75133-C3-3-P), SPYKE (CGL2017-87015-P), SÚMATE (PID2020-113316GB-I00) and PULSES 5.K (PID2020-117105RB-I00). R. Bonilla-Alba thanks the FPI fellowship (PRE2018-085949) associated with the SPYKE project. This study has been also funded by the Ramón y Cajal program (contracts of M. Gómez-Paccard and V. Martínez-Ferreras, refs. RYC-2013-14405 and RYC-2014-15789). The authors wish to acknowledge the professional support of the CSIC Interdisciplinary Thematic Platform Open Heritage: Research and Society (PTI-PAIS). E. Beamud thanks the Geomodels Research Institute (UB) and the Grup de Geodinàmica i Anàlisi de Conques-2017SGR596 (Generalitat de Catalunya). A. Palencia-Ortas thanks the PTA contract of the Spanish Ministry of Science and Innovation

Rapid Intensity Decrease During the Second Half of the First Millennium BCE in Central Asia and Global Implications

Recent paleomagnetic studies have shown that important short-lived intensity fluctuations occurred during the first millennium BCE. However, the knowledge of the spatial and temporal extension of these features is still limited by the scarce availability of robust data. In this study we focus on the study of the intensity decrease that took place in Central Asia during the second half of the 1st millennium BCE after the high intensities that characterized the Levantine Iron Age Anomaly. Since previous archeointensities available for this period and region were obtained without accomplishing modern standards of quality, we present here new archeointensities that are derived from classical Thellier and Thellier experiments, including partial thermoremanent magnetization (pTRM) checks, thermoremanent magnetization (TRM) anisotropy and cooling rate corrections at the specimen level. The new 51 archeointensities, together with previous archeointensities, have been used to present a new local paleosecular variation curve for Central Asia. The results confirm the existence of an important geomagnetic field intensity decrease in South Uzbekistan from the 4th century BCE to the end of the 1st century BCE associated with rates of changes up to −15 μT/century. A critical analysis of the archeointensity global database indicates that this feature was present at continental scale, from Western Europe to Central Asia. However, this trend is not identified in other regions such as Japan or Mexico. Finally, the comparison with the dipole moment derived from recent global geomagnetic field reconstructions suggests a strong influence of non-dipolar sources upon this continental intensity feature

Rapid Intensity Decrease During the Second Half of the First Millennium BCE in Central Asia and Global Implications

Recent paleomagnetic studies have shown that important short-lived intensity fluctuations occurred during the first millennium BCE. However, the knowledge of the spatial and temporal extension of these features is still limited by the scarce availability of robust data. In this study we focus on the study of the intensity decrease that took place in Central Asia during the second half of the 1st millennium BCE after the high intensities that characterized the Levantine Iron Age Anomaly. Since previous archeointensities available for this period and region were obtained without accomplishing modern standards of quality, we present here new archeointensities that are derived from classical Thellier and Thellier experiments, including partial thermoremanent magnetization (pTRM) checks, thermoremanent magnetization (TRM) anisotropy and cooling rate corrections at the specimen level. The new 51 archeointensities, together with previous archeointensities, have been used to present a new local paleosecular variation curve for Central Asia. The results confirm the existence of an important geomagnetic field intensity decrease in South Uzbekistan from the 4th century BCE to the end of the 1st century BCE associated with rates of changes up to -15 mu T/century. A critical analysis of the archeointensity global database indicates that this feature was present at continental scale, from Western Europe to Central Asia. However, this trend is not identified in other regions such as Japan or Mexico. Finally, the comparison with the dipole moment derived from recent global geomagnetic field reconstructions suggests a strong influence of non-dipolar sources upon this continental intensity feature

A catalogue of Spanish archaeomagnetic data

International audienceA total of 58 new archaeomagnetic directions has been determined from archaeological structures in Spain. Together with five previous results they allow the compilation of the first archaeomagnetic catalogue for Spain, which includes 63 directions with ages ranging between the 2nd century BC and the 20th century AD. Characteristic remanence directions have been obtained from stepwise thermal and alternating field demagnetization. The hierarchical structure has been respected in the calculation of the mean site directions. Rock magnetic experiments reveal that the main magnetic carrier is magnetite or titanomagnetite with different titanium contents. The age estimate of the studied structures is generally well justified by archaeological constraints. For six structures the proposed date is also supported by physical methods. The data are in close agreement with the French secular variation (SV) curve. This catalogue represents the first step in the construction of a SV curve for the Iberian Peninsula, which will be of much use in archaeomagnetic dating and in modelling of the Earth's magnetic field in Western Europe

Preliminary archeointensity results from well-dated ceramics from ancient Bactria (Uzbekistán, Central Asia).

Improving geomagnetic field reconstructions clearly poses a high-priority challenge in Earth Sciences today. A better characterization of the variation of the geomagnetic field strength at centennial to millennial time scales is particularly crucial to disentangle the long-term evolution of the Earth´s dipole moment, a global characteristic of our planet. Here we present new high-quality archeointensities for Central Asia, a vast and rather poorly known region in terms of geomagnetic field intensity fluctuations. These new data are obtained from the study of 26 pottery fragments from Termez, a great urban and Buddhist religious center in ancient Bactria (south Uzbekistan) during the Kushan period. The samples have been collected in several sectors related to different stages of the occupation as demonstrated by 14C analysis: 1) two sectors in the alluvial plain (AC2 and AC1), dated to the Greco-Bactrian (from the 3rd to the 1st centuries BC) and the nomadic Yuezhi (≈1st century AD) periods respectively; 2) sector RC at the Tchingiz Tepe fortress, dated to the Kushan and Kushano-Sassanian periods (from the 2nd to the 4th centuries AD). The classical Thellier method including regular partial thermoremanent magnetization (pTRM) checks and TRM anisotropy and cooling rate corrections has been used for archeointensity determination. The new data obtained shed new light on the past fluctuation of geomagnetic field strength in Central Asia. In addition, a critical revision of archeointensity data from Central Asia is presented. Selected high-quality archeointensities are finally compared with regional and global geomagnetic field reconstructions.Peer Reviewe

TRM anisotropy correction: An essential requirement to assess past geomagnetic field strength from ancient potteries. Evidence from new archeointensity data from NW Argentina

Trabajo presentado en la International Conference on Rock Magnetism, celebrada en Utrech (Países Bajos) del 10 al 14 de julio de 2017Improving geomagnetic field reconstructions clearly poses a high-priority challenge in Earth Sciences today. A better characterization of the variation of the geomagnetic field strength at centennial to millennial time scales in the southern hemisphere is particularly crucial to disentangle the long-term evolution of the Earth's dipole moment, a global characteristic of our planet. Here we present new high-quality archeointensities obtained from the study of four collections of well-dated pottery fragments from La Puna (Northwest Argentina). The classical Thellier method including regular partial thermoremanent magnetization (pTRM) checks and TRM anisotropy and cooling rate corrections has been used for archeointensity determination. The new data obtained shed new light on the past fluctuation of geomagnetic field strength in South America, a rather poorly known region in terms of geomagnetic field intensity fluctuations. In addition, the results confirm that TRM anisotropy corrections are an essential requirement when studying past geomagnetic field strength from the archeomagnetic study of pottery fragments. Future geomagnetic field reconstructions do well to have the TRM anisotropy requirement in mind when trying to unravel geomagnetic field variations from pottery-based archeointensity data, both at regional or global scales.Peer reviewe