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 Research of Wout Krijgsman
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Paleomagnetic reconstructions in time and space Dating and time control are essential in all disciplines of the Earth Sciences, since they allow to correlate rock sequences from distant localities and different (marine and continental) realms. An accurate geological time scale (GTS) is crucial to understand rates of change of natural processes and thus to determine the underlying mechanisms that explain our observations. Biostratigraphy of different faunal and floral systems has been used to erect the relative geological age of sedimentary rocks and hence to perform correlations among them. Radioisotopic dating has become increasingly sophisticated and can now count on a wide variety of isotopic decay systems capable of providing numerical ages in sedimentary rocks formed under favourable environmental conditions. Magnetostratigraphy in particular is a world class expertise of our research group at Fort Hoofddijk. It is a standard tool in various fields of Earth sciences and refers to the dating of a rock sequence by using the unique reversal pattern of the Earth’s magnetic field. Magnetostratigraphy can be applied to a wide variety of rock types (volcanic, sedimentary) and in different kinds of environment (continental, lacustrine, marine). Crucial is that rocks faithfully record the ancient magnetic field at the time of their formation, an assumption that must be verified by paleomagnetic and rock magnetic techniques. The latest development in constructing magnetostratigraphic time scales comes from orbital tuning of the sediment record, the so called Astronomically calibrated Polarity Time Scale (APTS). This time scale has the inherent advantage of increasingly advancing our understanding of the climate system, because cyclostratigraphy and orbital tuning rely on deciphering environmental changes driven by climate change, which in turn is orbitally forced. The magnetostratigraphic dating tool also has a wide range of geodynamic applications, including quantification of accumulation rates and dating of tectonic structures. The directional data can also be used to determine vertical axis rotations and paleolatitudes, essential to understand large scale tectonic movements. It thus provides a solid framework for precise correlation of environmental records with tectonics and/or global climate variations in order to distinguish geodynamics from climate forcing. Dating the geological record A reliable chronologic framework is a ‘conditio sine qua non’ to unravel climatic from geodynamic forcing factors. During the last decades our research was focused on the Mediterranean domain where the sedimentary record is particularly sensitive to document astronomically induced changes in past climate. The sedimentary (Milankovitch) cyclicity of the Mediterranean successions underlies the construction of the astronomically calibrated time scale, that has now become the global standard for the Neogene. Recently, we also used this astrochronology to synchronize radiometric dating techniques (Fig. 1). Correlations to astronomically calibrated global climate records can now be established to determine the impact of climate variability on paleoenvironments, which will eventually discriminate the complementary tectonic component.  Fig. 1: Astronomical calibration of the Messinian Messadit section in the Melilla-Nador Basin of NE Morocco and 40Ar/39Ar ages of intercalated tephra (Kuiper et al., 2008). Recently, our research focus was extended into the Paratethys (former Black sea/Caspian sea region) domain. Geological time scales for the Paratethys region encompass mainly regional stages, which are all defined on the basis of characteristic faunal assemblages (mainly mollusks and ostracods) endemic to the Paratethys Sea. Correlations to the standard GTS are highly debated because radiometric age determinations are scarce and magnetostratigraphic studies are generally controversial. As a consequence, the ages of the Paratethyan stage boundaries can differ more than a million years in the various geological time scales, even for the Miocene. We already have provided high-resolution magnetostratigraphic studies on long and continuous sedimentary successions of the Carpathian foredeep of Romania that resulted in straightforward correlations to the APTS and a robust chronology for the Dacian Basin. We have furthermore shown that the magnetic signal of these sedimentary deposits was carried by two different populations of greigite; a biogenic component of primary origin generated by magnetotactic bacteria, and an authigenic component of secondary origin that formed by early diagenetic processes. In contrast to previous assumptions, we could prove that these greigite components provided reliable records of the ancient geomagnetic field variations. They can excellently be used for magnetostratigraphic dating if the proper demagnetization techniques we recently developed are applied. Main collaborators: Cor Langereis, Frits Hilgen, Klaudia Kuiper & Jan Wijbrans (VU), Marius Stoica (Bucharest) Research projects: Klaudia Kuiper, Iuliana Vasiliev, Silja Husing, Hemmo Abels, Liao Chang, Chris van Baak Key publications: Kuiper et al. (2008); Deenen et al. (2010); Husing et al. (2009), Hilgen et al. (2007); Krijgsman et al. (2010) The Messinian Salinity Crisis of the Mediterranean About 6 million years ago the Mediterranean Sea was transformed into a giant saline basin, one of the largest in the Earth’s history and surely the youngest one. This event, referred to as the Messinian Salinity Crisis (MSC), changed the chemistry of the ocean and had a permanent impact on both the terrestrial and marine ecosystems of the Mediterranean area. Its actual magnitude was not predictable or even imaginable from the relatively small and scattered outcrops of Upper Miocene gypsum and halite deposits of peri-Mediterranean areas, and became fully appreciated only at the beginning of the ‘70s, when Deep Sea Drilling Project (DSDP) cores recovered evaporite rocks from the M reflector, a seismic feature recognized below the deep Mediterranean basin floors since the pioneering seismic surveys of the ‘50s. It soon became clear that a salt layer varying in thickness from 1,500 m to more than 3,000 m for a total estimated volume of 1 million km3 had been laid down throughout the whole Mediterranean basin at the end of the Miocene. The DSDP drilling Leg 13 recovered gypsiferous strata in the upper few meters of the basinal sequences, but the full Messinian succession could not be drilled at that time. The first, fascinating and successful MSC scenario proposed in 1973 envisaged an almost desiccated deep Mediterranean basin (Fig. 2) with a dramatic 1,500 m evaporative drop of sea-level, the incision of deep canyons by rivers to adjust to the lowered base level and a final catastrophic flooding event when the connections with the Atlantic ocean were re-established at the base of the Pliocene, 5.33 Ma ago. In the 35 years since Leg 13 was completed, over 1,000 papers have been published on the Messinian Salinity Crisis. Outcrop studies based on the record of marginal basins clarified that this event occurred in a relatively short time window of ca. 600,000 years and that it was caused by the temporary reduction of the marine connections between the Mediterranean and the Atlantic Ocean.  Fig. 2: Present-day coast line of the Mediterranean Sea and extent of water-covered part after desiccation down to equilibrium level in western and eastern subbasin. Solid line denotes coast line at the time that mean salinity reaches the level at which gypsum precipitation starts (130g/l) (Meijer & Krijgsman, 2005). In spite of all this research activity, one fact remains: we have no complete calibration of the stratigraphy of the MSC record, because no scientific drilling has yet ventured into deepwater to drill through the thickest succession of the deep basin. In fact, of all the major stratigraphically propelled discoveries of modern geoscience, the MSC stands alone as being underpinned by an outrageously undersampled stratigraphic record. It is estimated that 95% of the total volume of the Messinian evaporites is now preserved in the deep basins, and our lack of knowledge of the deep basinal stratigraphy and facies association strongly limits our understanding of this dramatic event. For more than 30 years the Messinian Salinity Crisis has represented one of the most important and controversial topics of scientific debate, stimulating interdisciplinary research projects that aim to understand the multiple mechanisms involved in this event, from its timing, the inferred geographic upheavals, the relationships between external forcing and physical systems response, to the implications for the biological activity. Main collaborators: Frits Hilgen, Paul Meijer, Gert de Lange, Rachel Flecker (Bristol), Paco Sierro (Salamanca) Research projects: Iuliana Vasiliev, Chris van Baak, Walter Capella, EU-ITN MEDGATE Key publications: Meijer and Krijgsman, 2005; Hilgen et al., 2007; Krijgsman and Meijer, 2008; Govers et al., 2009; De Lange and Krijgsman, 2010 The Evolution of Paratethys: the lost sea of Eurasia Paratethys was a large epicontinental sea, stretching from Germany to China at the beginning of the Oligocene (~34 Myr ago), that progressively retreated by a complex combination of basin infill, glacio-eustatic sea-level lowering and tectonic uplift to its present-day remnants: Black Sea, Caspian Sea and Aral Lake. The influence of Paratethys on global change is still a great unknown, mainly through lack of relevant studies in this terra incognita, although model studies suggest a major effect of sea retreat on climate and environment. My aim here is to comprehend the causes of the extreme environmental changes that occurred in Central Eurasia. We will use high-resolution geochronology together with integrated stratigraphy and geochemical proxies (deuterium, strontium, neodymium) to unravel internal (geodynamics, tectonic uplift) from external (climate, glacio-eustatic sea-level change) forcing factors and to resolve the effects of Paratethys restriction (regional climate perturbations, biotic crises, aridification). A complex combination of geodynamic and climatic processes caused Paratethys to evolve from initially open oceanic settings into restricted marine settings and, ultimately, even into lacustrine environments. Associated with this transformation, the open marine fauna became increasingly replaced by highly endemic, fresh to brackish water biota. Modelling has shown that Paratethys sea retreat intensified the Asian monsoon system, shifting the central Asian climate from temperate to continental conditions. Until its demise Paratethys played a critical role as ‘thermostat’ for Eurasia, co-regulating the regional temperature and precipitation, while co-recording the changes in the continental climate system. It furthermore exerted a prime control on mammal migration out of Africa and Asia into Europe and strongly affected the radiation and evolution of endemic marine invertebrates. Paratethys influenced regional climate, ecosystems, and depositional settings, but also generated large amounts of natural resources (oil, gas, salt) that are of economic importance for the region today.  Fig. 3: Chronology for the different local and regional stages of the Paratethys allows detailed correlations to the GTS, the Mediterranean event stratigraphy during the Messinian Salinity Crisis (M1-M3) and to the oxygen isotope curves of the Atlantic margin of Morocco (Krijgsman et al., 2010). The evolution of Paratethys also had major consequences for neighbouring seas. Close to the final stages of its existence, Paratethys played a crucial role in the hydrology of the Mediterranean (Fig. 3). Timing and nature of water exchange between Paratethys and Mediterranean is a vital, but still poorly understood and highly controversial component of evaporite mechanisms in deep water systems. The land-locked configuration of the Paratethys makes it a unique natural laboratory to disentangle climatic and tectonic components of sedimentary successions during distinctive restriction events and to study the fundamental mechanisms of gateway evolution and basin restriction. Main collaborators: Marius Stoica (Bucharest), Liviu Matenco, Oleg Mandic (Vienna), Klaudia Kuiper (Amsterdam), Bettina Reichenbacher (München), Madelaine Böhme (Tübingen) Research projects: Iuliana Vasiliev, Marten ter Borgh, Liao Chang, Chris van Baak, Arjen Grothe, Maria Tulbure, Annique van der Boon, Yannick Lataster Key publications: Vasiliev et al., 2004; Vasiliev et al., 2007; De Leeuw et al., 2010; Mandic et al., 2010; Krijgsman et al., 2010 Paleomagnetic and rock magnetic investigations The ancient geomagnetic field can be reconstructed from its recording in rocks during the geological past. Almost every type of rock contains magnetic minerals, usually iron (hydr)oxydes or iron sulphides. During the formation of rocks, these magnetic minerals (or more accurately: their magnetic domains) statistically align with the then ambient field, and will subsequently be ‘locked in’, preserving the direction of the field as a natural remanent magnetization (NRM): the paleomagnetic signal. As a rule, the total NRM is composed of different components. Ideally, the primary NRM, i.e., originating from the time of rock formation, has been conserved, but often this original signal is contaminated with or even completely overprinted by remanence components acquired later in its geological history, e.g. through weathering, metamorphosis or tectonics. A parasitic component or partial overprint can be removed through ‘magnetic cleaning’ or demagnetization procedure. This implies that rock samples must be subjected to various methods to stepwise remove any unwanted or non-original magnetization component, either by increased temperatures or alternating magnetic fields. Such experiments are paleomagnetic routine lab procedure, aiming at retrieving the original acquired magnetization that has recorded the ancient geomagnetic field. Paleomagnetic data can be very useful for geodynamic reconstructions because they allow a quantitative estimation of both rotations around vertical axes and latitudinal tectonic transport. The fundamental concept in the use of paleomagnetism for plate tectonic studies is that the Earth’s magnetic field is, on the average, a geocentric axial dipole (GAD). The GAD hypothesis implies that a paleomagnetic pole indicates the position of the rotational axis with respect to the continent from which the paleomagnetic data were acquired. It allows us to calculate the geographic (paleo)latitude of any site from the measured inclination according to the equation: tan I = 2 tan , where I is the magnetic field inclination and is the geographic latitude at the point of measuring. A variety of paleomagnetic data from the Mediterranean and Paratethys region show a strong bias toward shallow inclinations. We can use the observation that in addition to the well known variation of magnetic inclination with latitude, the N-S elongation of directrional dispersion also varies, being most elongate at the equator and nearly symmetric at the poles. Assuming that inclination shallowing follows the relationship long known from experiment, we can invert the inclinations using a range of “flattening factors” to find the elongation/inclination pair consistent with a statistical model for the paleosecular variation. Application of the so-called “elongation/inclination” method to the extensive paleomagnetic data sets allows correction for dewatering and compaction. For any paleomagnetic signal to be reliable, the measured magnetic remanence must be a primary recording – created at the time when the rock itself was formed – of the ancient geomagnetic field, i.e. one that is stable over geological time, sometimes over billions of years. The Natural Remanent Magnetisation (NRM) carried by sediments is controlled by a suite of physical and chemical processes that act during and after deposition. Detrital iron oxides like magnetite and hematite can carry a reliable primary remanence, but early and late diagenetic processes can alter the primary magnetic mineral assemblage through dissolution, diffusion and (re)precipitation processes. This may lead to the formation of new magnetic minerals, and in oxygen-poor and/or organic-rich environments to magnetic iron sulphides, like pyrrhotite (Fe(1-x)S, x=0 to 0.2) or greigite (Fe3S4). Greigite can form authigenically any time after deposition – up to millions of years – if the necessary reactants are present. Therefore, greigite is often considered to be an unreliable magnetic carrier. In other cases, early greigite formation has been demonstrated, forming within within years or decades in a stagnant water column and as sedimentary greigite.  Fig. 4: Greigite-based magnetostratigraphy of the Bădislava valley. Three successive demagnetisation diagrams illustrate the transition from reversed to normal polarity via a sample recording the two antipodal directions. The directions of the LT components (blue arrows) are acquired later, opposite to the direction of the HT components (red arrows). The mean original inclination of the HT component is significantly lower than both the inclination (upon flattening) that fits the model (incEI = green line), and the most frequent inclination (red line) (Vasiliev et al., 2008). Our greigite-based magnetostratigraphies from the brackish to fresh water environments of the Paratethys domain in Romania and from the marine pelagic marls of Monte dei Corvi in Italy, straightforwardly correlate to the geomagnetic polarity time scale and support the formation and preservation of magnetofossil greigite in ancient sedimentary rocks (Fig. 4). Positive reversal tests, a positive fold test and the occurrence of inclination shallowing provided further evidence for an early acquisition of the NRM. We now aim to 1) develop advanced techniques to distinguish biogenic and authigenic greigite, crucial to recognizing the primary recording of the geomagnetic field and 2) to establish the relation between different greigite populations and paleoenvironmental conditions. In many recent freshwater and shallow marine sediments, fossil bacterial magnetic minerals are considered the main carrier of the magnetisation. Proof for this type of carrier in older sediments is still lacking, although we have observed putative magnetofossil greigite in Pliocene rocks of the Paratethys. Main collaborators: Mark Dekkers, Cor Langereis, Douwe van Hinsbergen, Miguel Garces (Barcelona), Lisa Tauxe (San Diego), Gillian Turner (Wellington) Research projects: Iuliana Vasiliev, Liao Chang Key publications: Krijgsman and Tauxe, 2004, Van Hinsbergen et al., 2008; Vasiliev et al., 2008; Hüsing et al., 2009, De Leeuw et al., 2012 The Middle Miocene climate change The Middle Miocene Climate Transition between 15-13.5 Ma, which followed the last Climate Optimum, marks a critical step in the evolution of Earth’s climate system towards its present ice-house state. This climate transition remains, however, little understood. The closure of the Mediterranean-Paratethys-Indian Ocean gateway may have played a crucial role by interrupting the global equatorial current system. Unfortunately, dating of the closure - being based on land-mammal evidence - is still poorly constrained. As a consequence, a causal connection between Middle Miocene cooling and the closure of the Mediterranean-Indian Ocean gateway has not been (dis)proven to date. Untangling the effect of tectonic closure and opening of marine gateways on regional and global climate has a long-lasting history. Such changes in palaeogeography have profound influence on surface and deep ocean circulation and consequently on both regional as well as global climate.  Fig. 5: Miocene climate variability and geodynamic evolution of the Mediterranean region The present-day Mediterranean Sea resulted from a sequence of closing such marine connections. The middle Miocene (19-14 Ma) closure of the gateway to the Indian Ocean had presumably the most profound climate implications because it interrupts a direct marine connection between Africa and Eurasia forcing ocean currents to pass south of Africa. The northward migration of the African-Arabian plate and collision with the Eurasian plate progressively disconnected the Proto-Mediterranean from the Indian Ocean during the Miocene (Fig. 5). The resulting closure of the Mediterranean-Indian Ocean gateway has been put forward to explain the dramatic climatic change that took place from Earth’s last major warm episode 17-15 Ma (the Mid-Miocene Climate Optimum) to the much colder ice house state and the development of a permanent East Antarctic ice cap as a consequence of circulation changes. The major climatic cooling step at 13.8 Ma, the Mi3b oxygen isotope event, gave rise to a much enlarged ice volume, but the age of this dramatic cooling step is in serious contrast with the available age constraints on the initial gateway closure at ~19 Ma. The latter age is mostly based on African-Eurasian mammal migration via the “Gomphotherium (elephant) Landbridge”. Several distinct waves of mammal migration and marine biogeographic evolution in the Proto-Mediterranean and Indo-West-Pacific region suggest intermittently short-lived marine connections - possibly related to sea-level rise during the Mid-Miocene Climate Optimum - until it was permanently closed at ~14 Ma. However, precise dating of any of these events is seriously hampered by the lack of well-dated mammal- or invertebrate-bearing sections. The Middle Miocene Badenian stage of the Paratethys marks the last period of significant connectivity between the Mediterranean and the Central Paratethys. The only postulated seaway was in the narrow area between the Alps and the Dinarids, which progressively closed during the lower Badenian by a combination of tectonic and glacio-eustatic processes. This resulted in the formation of massive salt deposits in the Central European Paratethys basins. Radiometric dating recently indicated that the onset of the Badenian Salinity Crisis in the Paratethys was primarily controlled by climatic changes and in particular by the Mi3 global cooling event which terminates the Middle Miocene Climatic Optimum. Main collaborators: Frits Hilgen, Elena Turco (Parma), Marius Stoica (Bucharest), Krzysztof Bukowski (Cracow), Klaudia Kuiper (Amsterdam); Research projects: Silja Hüsing, Maria Tulbure, Karin Sant Key publications: Abels et al., 2005; Hilgen et al., 2008; Hüsing et al., 2009; Hüsing et al., 2010; De Leeuw et al., 2010 Asian paleoclimate and environment The interplay between the Indo-Asia collision, uplift of the Tibetan Plateau, termination of the Indonesian Throughflow, and changes in Asian climate and environment belongs to the most significant and fascinating issues of tectonics and paleoclimate. According to prevailing hypothesis supported by some tectonic and climate models, the impact of the collision on climate is twofold: - (1) Globally, the orogenesis increases rock weathering and organic carbon burial which enhances consumption of atmospheric CO2 leading to Cenozoic global cooling. (2) Regionally, uplift of the Tibetan Plateau and the retreat of the Paratethys triggers dramatic aridification and cooling of continental Asia and the onset of the Asian monsoons. Recently, we provided evidence for regional aridification on the Tibetan Plateau, precisely dated at the Eocene-Oligocene Transition. This remarkable correlation demonstrated that global climate, and not only Tibetan uplift and Paratethys retreat, must be recognized as a major contributor to Asian palaeoenvironment. To find conclusive answers to questions such as the age of Indo-Asian collision, regional uplift, land-sea redistributions, and relations to global climatic change, the entire collision zone - from northernmost Tibet to the southern Himalayan margin - needs to be studied. A team lead by our former VIDI postdoc Guillaume Dupont-Nivet (now in Rennes) seeks specific answers within the sedimentary successions of northeastern (Xining basin) and northwestern (Tarim basin) Tibet (Fig. 6).  Fig. 6: Lithological column of the Shuiwan section showing lithology, bed colour, induration, sedimentary features, and arbitrarily labelled small-scale cycle numbers (Abels et al., 2001). The EU funded THROUGHFLOW project aims to obtain a greater understanding of key processes in the biotic response of coral reefs in SE Asia to long-term environmental changes resulting from closure of the Indonesian Throughflow during the Oligocene-Miocene transition (~25 Million years ago). This will establish important baseline data on which researchers can model the impact of predicted environmental change on present reef ecosystems. Our specific goal is to establish a detailed chronologic framework for the Oligocene-Miocene sedimentary successions on Kalimantan by the integration of a wide range of dating tools including biostratigraphy, magnetostratigraphy, and isotope (strontium) stratigraphy. A magnetostratigraphic time frame for the Oligocene-Miocene interval will be constructed by combining marginal shallow marine sequences to the basinal deep water successions that are exposed along several river incisions. Additionally, initial Sr-isotope dating in the region provides promising results for increasing the number of well-dated events, and can thus be used as controls on datum planes in magnetostratigraphy and biostratigraphy. Main collaborators: Guillaume Dupont-Nivet (Rennes), Willem Renema & Frank Wesselingh (Naturalis) Research projects: Roderic Bosboom, Hemmo Abels, Nathan Marshall, EU-ITN THROUGHFLOW Key publications: Dupont-Nivet et al., 2007, Bosboom et al., 2010; Abels et al., 2010 Mesozoic mass-extinction Cataclysmic impacts of celestial bolides are often favoured to explain mass extinctions, but the internal (volcanism, continental break-up) and external (atmospheric acidification, ozone breakdown) dynamics of the Earth likely play a far more important role. As a result, environmental stress initiates inhibition of photosynthesis and a decline in primary production, which in turn is believed to lead to widespread and collateral extinction of species. The Late Triassic mass extinction(s) provide an eminent case history of global turnover in the biosphere that is still not fully understood. Rather than focusing on catastrophic impacts, we will concentrate here on the geodynamic and environmental changes that occurred during this time span. It is a period when major biotic crises occurred repeatedly but also the time of a major plate tectonic event: the opening of the Atlantic Ocean. Despite the conflicting data for the late Triassic biotic crises there are several lines of evidence indicating mass extinctions in the marine and terrestrial realm throughout the Late Triassic with a series of major steps around the Carnian–Norian, Norian–Rhaetian boundaries, while the Rhaetian–Hettangian (Triassic/Jurassic) boundary event may have been the final strike. At present, stratigraphic resolution is inadequate to determine whether these extinctions occurred in a catastrophic or gradual fashion Catastrophism may be merely an artifact of inadequate sampling of accelerated but continuous biotic turnover. Therefore, the two major questions we will address are 1) are these extinctions best explained by a gradual process of deterioration or by (a series of) catastrophic events, 2) how do these turnovers in the biosphere of the terrestrial realm correlate, or couple, with those of the marine realm?  Fig. 7: Continental–marine T–J correlation. The two pulses of CAMP basalts (L.U. and I.U.) in the continental sections correlate to the initial isotope shift, spores spikes and the extinction events observed in the marine record of St. Audrie's Bay (UK) (Deenen et al., 2010). High-resolution palaeobiological studies focusing on the environmental changes that led to mass extinction in both the continental and marine domain require an accurate geological time frame to allow a detailed comparison of timing and duration of events in time and space. Evidently, it is essential that all data (palaeobotany, paleontology, geochemistry, geophysics, etc.) will be integrated together in a high-resolution astronomical time frame. This time scale will allow us to correlate our results directly with data from volcanology, geodynamics and other climate proxies (Fig. 7). In addition, the palaeobiological data will then provide conclusive answers about the character of the extinction process, the survivors, recovery and new originations. Main collaborators: Wolfram Kürschner (now Oslo), Michael Szurlies (Potsdam) Research projects: Martijn Deenen, Micha Ruhl, Silja Hüsing Key publications: Deenen et al., 2010; Ruhl et al., 2010; Hüsing et al., 2011; Deenen et al., 2011; Szurlies et al., 2012 |
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2013
Nature News
& Views: Bowen, G.J. (2007). When the world turned cold, Nature,
445,
607-608
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