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Cor Langereis

Utrecht University, Earth Sciences, Faculty Member

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Paleomagnetist
Address: Paleomagnetic Laboratory
Fort Hoofddijk
Dept. Earth Sciences
Utrecht University

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Papers by Cor Langereis

The top of the Olduvai Subchron in a high-resolution magnetostratigraphy from the West Turkana core WTK13, hominin sites and Paleolakes Drilling Project (HSPDP

by Mark J. Sier and Cor Langereis

One of the major challenges in understanding the evolution of our own species is identifying the ... more One of the major challenges in understanding the evolution of our own species is identifying the role climate change has played in the evolution of hominin species. To clarify the influence of climate, we need long and continuous high-resolution paleoclimate records, preferably obtained from homininbearing sediments, that are well-dated by tephro-and magnetostratigraphy and other methods. This is hindered, however, by the fact that fossil-bearing outcrop sediments are often discontinuous, and subject to weathering, which may lead to oxidation and remagnetization. To obtain fresh, unweathered sediments, the Hominin Sites and Paleolakes Drilling Project (HSPDP) collected a~216-meter core (WTK13) in 2013 from Early Pleistocene Paleolake Lorenyang deposits in the western Turkana Basin (Kenya). Here, we present the magnetostratigraphy of the WTK13 core, providing a first age model for upcoming HSPDP paleoclimate and paleoenvrionmental studies on the core sediments. Rock magnetic analyses reveal the presence of iron sulfides carrying the remanent magnetizations. To recover polarity orientation from the near-equatorial WTK13 core drilled at 5 N, we developed and successfully applied two independent drill-core reorientation methods taking advantage of (1) the sedimentary fabric as expressed in the Anisotropy of Magnetic Susceptibility (AMS) and (2) the occurrence of a viscous component oriented in the present day field. The reoriented directions reveal a normal to reversed polarity reversal identified as the top of the Olduvai Subchron. From this excellent record, we find no evidence for the 'Vrica Subchron' previously reported in the area. We suggest that outcrop-based interpretations supporting the presence of the Vrica Subchron have been affected by the oxidation of iron sulfides initially present in the sediments -as evident in the core record-and by subsequent remagnetization. We discuss the implications of the observed geomagnetic record for human evolution studies.

Discovery of Holocene millennial climate cycles in the Asian continental interior: Has the sun been governing the continental climate?

Global and Planetary Change, 2013

We conducted a high-resolution study of a unique Holocene sequence of wind-blown sediments and bu... more We conducted a high-resolution study of a unique Holocene sequence of wind-blown sediments and buried soils in Southern Siberia, far from marine environment influences. This was accomplished in order to assess the difference between North Atlantic marine and in-land climate variations. Relative wind strength was determined by grain size analyses of different stratigraphic units. Petromagnetic measurements were performed to provide a proxy for the relative extent of pedogenesis. An age model for the sections was built using the radiocarbon dating method. The windy periods are associated with the absence of soil formation and relatively low values of frequency dependence of magnetic susceptibility (FD), which appeared to be a valuable quantitative marker of pedogenic activity. These events correspond to colder intervals which registered reduced solar modulation and sun spot number. Events, where wind strength was lower, are characterized by soil formation with high FD values. Spectral analysis of our results demonstrates periodic changes of 1500, 1000 and 500 years of relatively warm and cold intervals during the Holocene of Siberia. We presume that the 1000 and 500 year climatic cycles are driven by increased solar insolation reaching the Earth surface and amplified by other still controversial mechanisms. The 1500 year cycle associated with the North Atlantic circulation appears only in the Late Holocene. Three time periods -8400-9300 years BP, 3600-5100 years BP, and the last~250 years BPcorrespond to both the highest sun spot number and the most developed soil horizons in the studied sections.

Reconstructing the geometry of central Anatolia during the late cretaceous: Large-scale cenozoic rotations and deformation between the Pontides and Taurides

Earth and Planetary Science Letters, 2012

The Central Anatolian Crystalline Complex (CACC) exposes metamorphic, ophiolitic and igneous rock... more The Central Anatolian Crystalline Complex (CACC) exposes metamorphic, ophiolitic and igneous rocks that were formed and deformed during closure of the Neotethyan ocean. The CACC is located in central Turkey, between the Pontides in the north and the Taurides in the south, separated by major fault zones. Composite plutons intruded the meta-sedimentary and ophiolitic units between $ 95 and 75 Ma, and form linear magmatic belts ( $ 100 km long) along the western and northern margins of the CACC. Exhumation of the metamorphic and igneous complex was finalized by the Paleocene time. In this study, we paleomagnetically study fifteen plutons spanning the entire non-deformed upper Cretaceous granitoid belt to test whether the initial configuration of the CACC was modified by vertical axis rotations after its exhumation. Our results show three internally coherent domains with significantly different vertical-axis rotations: (1) in the north-east, the Akdag-Yozgat block (AYB) records $ 151 clockwise rotation, (2) in the north-west, the Kırs -ehir-Kırıkkale block (KKB) shows $ 6-91 counterclockwise rotation and (3) in the south-west, the Agacören-Avanos block (AAB) shows 28-351 counterclockwise rotation. We propose that these rotations were accommodated by two transpressional fault zones: in the south, the existing Savcılı Thrust Zone between the AYB and KKB and in the north, the newly introduced Delice-Kozaklı Fault Zone between the KKB and AAB. The restored configuration of the CACC suggests that the three blocks were largely aligned in a $ NNE orientation at an early stage of their history. Consequently, since the late Cretaceous the shape of the CACC was affected by large scale deformation, resulting in its modern triangular geometry. This deformation phase is best explained as a result of collision of the CACC with the Pontides.

Structural evidence for strike-slip deformation in the ˙ Izmir–Balıkesir transfer zone and consequences for late Cenozoic evolution of western Anatolia (Turkey)

Journal of Geodynamics, 2013

Theİzmir-Balıkesir transfer zone (İBTZ) is a recently recognized strike-slip dominated shear zone... more Theİzmir-Balıkesir transfer zone (İBTZ) is a recently recognized strike-slip dominated shear zone that accommodates the differential deformation between the Cycladic and Menderes core complexes within the Aegean Extensional System. Here, we present new structural and kinematic data obtained from field observations and 1/25,000 scale mapping of Miocene to Recent units within theİBTZ aroundİzmir Bay. The results point out that theİBTZ is a transtensional brittle shear zone that affects the pre-Neogene basement rock units, the early-middle Miocene volcano-sedimentary units and the Plio-Quaternary continental units.

Archaeomagnetic study of five mounds from Upper Mesopotamia between 2500 and 700 BCE: Further evidence for an extremely strong geomagnetic field ca. 3000 years ago

Earth and Planetary Science Letters, 2012

The distribution of archaeomagnetic data in eastern Europe and the Near and Middle East shows a r... more The distribution of archaeomagnetic data in eastern Europe and the Near and Middle East shows a remarkable gap in Turkey. This study presents the first archaeomagnetic results from five different mounds in southeast Turkey, the northern part of Mesopotamia. The rock magnetic experiments indicate that in the majority of the samples the dominant magnetic carrier is magnetite, which is stable to heating to temperatures of 700 1C. In general, the demagnetization diagrams are single component and all five sets display well-defined characteristic magnetizations and clustered directions. For the period between 2500 and 700 BCE, the declinations are between 3501 and 201 while inclinations are in the range of 49-641. The directional results are compared with the global geomagnetic field models (CALS7k.2, ARCH3k_cst.1 and CALS3k.4) and the data from the archaeomagnetic database GEOMA-GIA50v2. The results are coherent with both the data and the models except for two nearcontemporaneous sets dating $ 2000 BCE, which are offset to the east by more than 201 with respect to CALS7k.2. Archaeointensity measurements were made using the microwave and conventional thermal Thellier methods applied to five sets of samples (four furnaces and a mud-brick wall). These yielded comparable and intriguing results. While those from the furnaces are slightly higher than the CALS7k.2 model and in agreement with the GEOMAGIA50v2 and the Middle East data, the results from the mud-brick wall suggest a high intensity of 100.8 mT (17.7 Â 10 22 Am 2 ) at $ 1000 BCE. This result is in excellent agreement with recent claims of extremely high intensity measured in other regions of the Middle East for this time period though less consistent with these being associated with extremely short-lived events. Finally, we discuss our new and other recently published archaeointensity results in terms of geomagnetic intensity versus climate.

Palaeomagnetism of Archaean rocks of the Onverwacht Group, Barberton Greenstone Belt (southern Africa): Evidence for a stable and potentially reversing geomagnetic field at ca. 3.5 Ga

Earth and Planetary Science Letters, 2011

Palaeomagnetic results from Upper Triassic red-beds and CAMP lavas of the Argana Basin, Morocco

Geological Society, London, Special Publications, 2011

Geomagnetic secular variation and the statistics of palaeomagnetic directions

Geophysical Journal International, 2011

In this study, we examine the role of palaeosecular variation (PSV) in the use of statistics for ... more In this study, we examine the role of palaeosecular variation (PSV) in the use of statistics for palaeomagnetic studies, and we provide new reliability criteria for palaeomagnetic poles or directions. We first conclude that Fisher statistics should not be applied to average palaeomagnetic directions but to virtual geomagnetic pole (VGP) distributions instead.

Pervasive Palaeogene remagnetization of the central Taurides fold-and-thrust belt (southern Turkey) and implications for rotations in the Isparta Angle

Geophysical Journal International, 2011

Magnetostratigraphy and radio-isotope dating of upper Miocene–lower Pliocene sedimentary successions of the Black Sea Basin (Taman Peninsula, Russia)

Palaeo3, 2011

We present a new chronology for the upper Miocene to Pliocene deposits of the Black Sea basin bas... more We present a new chronology for the upper Miocene to Pliocene deposits of the Black Sea basin based on highresolution magnetostratigraphic data coupled with 40 Ar/ 39 Ar dating from the 475 m long Zheleznyi Rog section on the Taman Peninsula (Russia). This section comprises the stratigraphic interval of the Khersonian to Kimmerian regional stages of the Eastern Paratethys. Our magnetostratigraphic record is based on biogenic and early-diagenetic greigite components and yields a magnetostratigraphic sequence of 8 polarity zones. A volcaniclastic ash layer at the upper part of the Khersonian is radio-isotopically dated at 8.69 ± 0.18 Ma. The age of the Khersonian-Meotian transition arrives at 8.6 or 8.2 Ma, which is significantly younger than earlier estimates. The new age has important consequences for the Hipparion-datum in the Eastern Paratethys, and implies that all Vallesian fossil sites are younger than 11.2 Ma. The Meotian stage has a total duration of 2.2 to maximum 2.6 Myr, and is marked by multiple erosional events. The end of the Paratethys Sea is dated at 5.5 Ma, when the Black Sea becomes isolated from the Caspian Sea, the Dacian basin and the Mediterranean.

Magnetostratigraphy – concepts, definitions, and applications

Newsletters on Stratigraphy, 2010

The most characteristic feature of the Earth's magnetic field is that it reverses polarity at irr... more The most characteristic feature of the Earth's magnetic field is that it reverses polarity at irregular intervals, producing a 'bar code' of alternating normal (north directed) and reverse (south directed) polarity chrons with characteristic durations. Magnetostratigraphy refers to the application of the well-known principles of stratigraphy to the pattern of polarity reversals registered in a rock succession by means of natural magnetic acquisition processes. This requires that the rock faithfully recorded the ancient magnetic field at the time of its formation, a prerequisite that must be verified in the laboratory by means of palaeomagnetic and rock magnetic techniques. A sequence of intervals of alternatively normal or reverse polarity characterized by irregular (non-periodic) duration constitutes a distinctive pattern functional for correlations. Over the last 35 Myr, polarity intervals show a mean duration of ~300,000 years, but large variations occur from 20,000 yr to several Myr and even up to tens of Myr. By correlating the polarity reversal pattern retrieved in a rock succession to a reference geomagnetic polarity time scale (GPTS), calibrated by radioisotopic methods and/or orbital tuning, the age of the rock succession can be derived. Magnetostratigraphy and correlation to the GPTS constitute a standard dating tool in Earth sciences, applicable to a wide variety of sedimentary (but also volcanic) rock types formed under different environmental conditions (continental, lacustrine, marine). It is therefore the stratigraphic tool of choice to perform correlations between continental and marine realms. Finally, we emphasise that magnetostratigraphy, as any other stratigraphic tool, works at best when integrated with other dating tools, as illustrated by the case studies discussed in this paper.

New late Paleozoic paleopoles from the Donbas Foldbelt (Ukraine): Implications for the Pangea A vs. B controversy

Earth and Planetary Science Letters, 2011

a b s t r a c t Editor: M.L. Delaney Keywords: paleomagnetism plate reconstructions Pangea Eurasi... more

Late Cretaceous to Paleocene oroclinal bending in the central Pontides (Turkey)

Tectonics, 2010

The Turkish Pontide fold-and-thrust belt formed since the Paleozoic and is an important element i... more The Turkish Pontide fold-and-thrust belt formed since the Paleozoic and is an important element in the Africa-Eurasia convergence and the resulting closure of the Neo-Tethys ocean. It has a peculiar arc-shaped geometry in its central part, along the Black Sea coast, which may have resulted from oroclinal bending. We have determined the vertical-axis rotation history of this area using paleomagnetism on Cretaceous to Eocene rocks from 47 sites and critically analyzed previously published data. We applied the same reliability criteria to all data. Our results show that late Cretaceous sites have clockwise and counterclockwise rotations perpendicular to the structural trend in the central Pontides. In the eastern Pontides, they show only local rotations. Paleocene to Eocene rocks in the central and eastern Pontides show no rotation. We conclude that the central Pontide northward arc-shaped geometry results from oroclinal bending in latest Cretaceous to earliest Paleocene times. The timing and scale of geological processes that occurred in the region make it likely that orocline formation resulted from Neo-Tethys closure between the Pontides and the metamorphic promontory of the Anatolide-Tauride Block. Earlier studies on the southerly located Çankırı Basin reveal that clockwise and counterclockwise rotations occurred in Eocene-Oligocene times. This implies that the entire region underwent continuous deformation from late Cretaceous to Eocene, caused by convergence of the Pontides and the Anatolide-Tauride Block, with a southward moving deformation front. Deformation was first localized in the northern part of the central Pontides until the Paleocene, resulting in oroclinal bending, and from at least Eocene times it shifted toward the Çankırı Basin region.

Jurassic–Cretaceous low paleolatitudes from the circum-Black Sea region (Crimea and Pontides) due to True Polar Wander

Earth and Planetary Science Letters, 2010

The intensity of the geomagnetic field in the late-Archaean: new measurements and an analysis of the updated IAGA palaeointensity database

Earth, Planets and Space, 2009

We firstly present the results of a detailed palaeointensity study performed on 54 samples from 9... more We firstly present the results of a detailed palaeointensity study performed on 54 samples from 9 volcanic units of late Archaean age (2724-2772 Ma) from the Pilbara Craton, Western Australia. These results were severely affected by magnetomineralogical alteration occurring during the laboratory heating process necessitating the application of a correction procedure. The correction allowed results from three lavas to pass strict selection criteria but we deem that only one of these exhibits sufficient internal consistency to be considered moderately reliable. It yields a virtual dipole moment of 47±6 ZAm 2 which is 60% of the present-day value. We combine this determination with a filtered dataset from the updated IAGA (International Association of Geomagnetism and Aeronomy) palaeointensity database, PINT08. Directional secular variation has recently been shown to have changed fundamentally since the Archaean, probably as a consequence of inner core growth since that time. However, here we argue that it is still unclear whether this evolution was accompanied by a single long timescale change in average poloidal field intensity. While the distribution of Precambrian palaeointensity determinations as a whole is significantly lower than that for the last 300 Myr, we show that this finding largely reflects data from the Proterozoic aeon. The distribution of more ancient measurements from the late Archaean-earliest Proterozoic is indistinguishable from that of the last 300 Myr which might suggest that a 'Proterozoic dipole low' period existed between two periods of higher field intensity. Were this pattern of long-term geomagnetic intensity variation to be supported by the addition of new data in the future, then it could indicate a related three-stage evolution in core dynamics, namely: vigorous thermal convection caused by high core-mantle heat flux early in the Earth's history, weaker thermal convection later as the heat flux fell, and finally, strong compositional convection since the inner core nucleated.

A comparison of detailed equatorial red bed records of secular variation during the Permo-Carboniferous Reversed Superchron

Geophysical Journal International, 2009

Detailed secular variation records during a superchron may provide information on the behaviour o... more Detailed secular variation records during a superchron may provide information on the behaviour of the geodynamo during periods that the field does not reverse. The Permian red beds in Dôme de Barrot (southern France)-deposited during the Permo-Carboniferous Reversed Superchron (PCRS, 317-265 Ma) -were previously argued to accurately record palaeosecular variation (PSV). This result is particularly valuable because the red beds were deposited near the palaeo-equator and therefore, according to one model of secular variation, determine the contribution of the even (symmetric) spherical harmonics of the field.

The influence of sea-level changes on tropical coastal lowlands; the Pleistocene Coropina Formation, Suriname

Sedimentary Geology, 2009

The Pleistocene Coropina Formation largely constitutes the Old Coastal Plain of Suriname. It is e... more The Pleistocene Coropina Formation largely constitutes the Old Coastal Plain of Suriname. It is exposed fully only in open-pit bauxite mines in the central coastal plain as part of the unconsolidated overburden of Paleocene-Eocene bauxites. This study deals with the stratigraphy, sedimentology and chronology of this formation, and is based on a study in the recently closed Lelydorp-III bauxite mine operated by N.V. BHP Billiton Maatschappij Suriname. The Coropina Formation consists of the Para and Lelydorp Members. We present a detailed lithological subdivision of these members. In the Para Member, four units are discerned which are grouped in two transgressive cycles, both ranging upward from terrestrial towards chenier and coastal mudflat deposits reflecting glacio-eustatic sea-level changes. The sandy sediments represent fluviatile and beach-bar (chenier) deposits, and were supplied by rivers from the Precambrian basement and to a lesser extent by westward longshore coastal drift. Clays, largely derived from the Amazon River and transported alongshore over the shelf, were deposited in extensive coastal mudflats. The Lelydorp Member, also comprising four units, represents a depositional system that is closely comparable to the recent Suriname coastal setting, i.e., a lateral and vertical alternation of mudflat and chenier deposits formed over a period characterised by more or less constant sea level. Palaeomagnetic data indicate a dominantly reversed magnetic polarity in the Para Member, whereas the Lelydorp Member shows a normal magnetic polarity with a minor reversed polarity overprint. The reversed polarities of the Para Member exclude a Brunhes Chron (0.78-0.0 Ma) age, and thus assign it to the Matuyama Chron (2.58-0.78 Ma). This implies that the Coropina Formation is much older than hitherto assumed, and that one or more (long-term) hiatuses are not recognizable in the lithological succession.

Geomagnetic secular variation in the Cretaceous Normal Superchron and in the Jurassic

Physics of the Earth and Planetary Interiors, 2008

It is now widely thought that geomagnetic polarity reversals occur spontaneously as a result of n... more It is now widely thought that geomagnetic polarity reversals occur spontaneously as a result of normal dynamo action rather than being externally triggered. If this is the case, then it may well be that periods of time in which the geomagnetic reversal frequency was dramatically different were characterised by different styles of secular variation. Two such periods were the Cretaceous Normal Superchron (CNS: 84-125 Ma) when the field was dominantly of a single polarity for 40 Myr and the Jurassic period when reversals occurred at an average rate of as much as 4.6 Myr -1 . Here, we analyse a database of new and published palaeomagnetic directions from lavas emplaced during these periods in order to obtain first-order descriptions of the palaeosecular variation (PSV) during these times. We then compare these records with one another and with that produced for the period 0-5 Ma (with average reversal frequency of 4.0 Myr -1 ). Our results are more equivocal than those obtained in a previous similar study [McFadden, P.L., Merrill, R.T., McElhinny, M.W., Lee, S.H., 1991. Reversals of the Earths magnetic-field and temporal variations of the dynamo families. Journal of Geophysical [3923][3924][3925][3926][3927][3928][3929][3930][3931][3932][3933]. We demonstrate that this is probably a result of the previous study being affected by an artefact of their correction for within-site scatter. The usefulness of our Jurassic record is severely limited by the restricted palaeolatitudinal span of the available data. However, our record for the CNS is sufficient to allow us to conclude that it was likely that secular variation then was different from that in the 0-5 Ma period. This supports the hypothesis of a link between PSV and reversal frequency and therefore endorses PSV analysis as a first-order tool for determining geomagnetic stability in the past.

Evidence for a very-long-term trend in geomagnetic secular variation

Nature Geoscience, 2008

The Earth's inner core is believed to inhibit rapid fluctuations in the geomagnetic field from de... more The Earth's inner core is believed to inhibit rapid fluctuations in the geomagnetic field from developing into full polarity reversals 1,2 . Consequently, during the Precambrian, the smaller size of the inner core might suggest that polarity reversals could occur more readily. It is therefore surprising that there are indications that reversals were rare during this period 3,4 . Here we use new and existing palaeomagnetic data from three continents to examine the stability of the Earth's magnetic field from 2.82 to 2.45 billion years ago. We show that, on average, geomagnetic secular variation (the field variations produced by normal geodynamo action) during the late Archaean and early Proterozoic was different from that of the past 200 million years; specifically, the apparent variability of the geomagnetic pole as viewed at low and mid-latitudes was reduced relative to the past 200 million years. According to both dynamo simulations 4 and more recent palaeomagnetic field observations 5 , the observed pattern of secular variation suggests a lower frequency of polarity reversals 2.5 billion years ago. This may imply that the geodynamo is becoming progressively less stable over long timescales, consistent with some numerical simulations 6,7 , possibly as a result of changing outer-core geometry that has accompanied inner-core growth.

Timing and distribution of tectonic rotations in the northeastern Tibetan Plateau

Geological Society of America, Special Paper, 2008

We report paleomagnetic data from the northeastern margin of the Tibetan Plateau to help understa... more We report paleomagnetic data from the northeastern margin of the Tibetan Plateau to help understand the timing and distribution of deformation (i.e., vertical-axis rotations ) during the India-Asia collision. Paleomagnetic results throughout Xining Basin strata, recently dated using magnetostratigraphy to between 52 and 17 Ma, show that some 25° of clockwise rotation with respect to the stable Eurasian continent occurred at ca. 41 Ma. In view of a regional compilation of existing paleomagnetic data from the northeastern Tibetan Plateau, these results suggest that this region experienced clockwise rotations in the regional Paleocene-Miocene basin system, including rotation in the Xining Basin, ca. 41 Ma, thus establishing the existence of widespread deformation at this time. During a mid-Miocene phase, between 17 and 11 Ma, clockwise rotations were restricted to the Miocene-Quaternary basin system, implying that the Laji Shan thrust belt, which separates the two basin systems, was active during this time interval.

The top of the Olduvai Subchron in a high-resolution magnetostratigraphy from the West Turkana core WTK13, hominin sites and Paleolakes Drilling Project (HSPDP

by Mark J. Sier and Cor Langereis

One of the major challenges in understanding the evolution of our own species is identifying the ... more One of the major challenges in understanding the evolution of our own species is identifying the role climate change has played in the evolution of hominin species. To clarify the influence of climate, we need long and continuous high-resolution paleoclimate records, preferably obtained from homininbearing sediments, that are well-dated by tephro-and magnetostratigraphy and other methods. This is hindered, however, by the fact that fossil-bearing outcrop sediments are often discontinuous, and subject to weathering, which may lead to oxidation and remagnetization. To obtain fresh, unweathered sediments, the Hominin Sites and Paleolakes Drilling Project (HSPDP) collected a~216-meter core (WTK13) in 2013 from Early Pleistocene Paleolake Lorenyang deposits in the western Turkana Basin (Kenya). Here, we present the magnetostratigraphy of the WTK13 core, providing a first age model for upcoming HSPDP paleoclimate and paleoenvrionmental studies on the core sediments. Rock magnetic analyses reveal the presence of iron sulfides carrying the remanent magnetizations. To recover polarity orientation from the near-equatorial WTK13 core drilled at 5 N, we developed and successfully applied two independent drill-core reorientation methods taking advantage of (1) the sedimentary fabric as expressed in the Anisotropy of Magnetic Susceptibility (AMS) and (2) the occurrence of a viscous component oriented in the present day field. The reoriented directions reveal a normal to reversed polarity reversal identified as the top of the Olduvai Subchron. From this excellent record, we find no evidence for the 'Vrica Subchron' previously reported in the area. We suggest that outcrop-based interpretations supporting the presence of the Vrica Subchron have been affected by the oxidation of iron sulfides initially present in the sediments -as evident in the core record-and by subsequent remagnetization. We discuss the implications of the observed geomagnetic record for human evolution studies.

Discovery of Holocene millennial climate cycles in the Asian continental interior: Has the sun been governing the continental climate?

Global and Planetary Change, 2013

We conducted a high-resolution study of a unique Holocene sequence of wind-blown sediments and bu... more We conducted a high-resolution study of a unique Holocene sequence of wind-blown sediments and buried soils in Southern Siberia, far from marine environment influences. This was accomplished in order to assess the difference between North Atlantic marine and in-land climate variations. Relative wind strength was determined by grain size analyses of different stratigraphic units. Petromagnetic measurements were performed to provide a proxy for the relative extent of pedogenesis. An age model for the sections was built using the radiocarbon dating method. The windy periods are associated with the absence of soil formation and relatively low values of frequency dependence of magnetic susceptibility (FD), which appeared to be a valuable quantitative marker of pedogenic activity. These events correspond to colder intervals which registered reduced solar modulation and sun spot number. Events, where wind strength was lower, are characterized by soil formation with high FD values. Spectral analysis of our results demonstrates periodic changes of 1500, 1000 and 500 years of relatively warm and cold intervals during the Holocene of Siberia. We presume that the 1000 and 500 year climatic cycles are driven by increased solar insolation reaching the Earth surface and amplified by other still controversial mechanisms. The 1500 year cycle associated with the North Atlantic circulation appears only in the Late Holocene. Three time periods -8400-9300 years BP, 3600-5100 years BP, and the last~250 years BPcorrespond to both the highest sun spot number and the most developed soil horizons in the studied sections.

Reconstructing the geometry of central Anatolia during the late cretaceous: Large-scale cenozoic rotations and deformation between the Pontides and Taurides

Earth and Planetary Science Letters, 2012

The Central Anatolian Crystalline Complex (CACC) exposes metamorphic, ophiolitic and igneous rock... more The Central Anatolian Crystalline Complex (CACC) exposes metamorphic, ophiolitic and igneous rocks that were formed and deformed during closure of the Neotethyan ocean. The CACC is located in central Turkey, between the Pontides in the north and the Taurides in the south, separated by major fault zones. Composite plutons intruded the meta-sedimentary and ophiolitic units between $ 95 and 75 Ma, and form linear magmatic belts ( $ 100 km long) along the western and northern margins of the CACC. Exhumation of the metamorphic and igneous complex was finalized by the Paleocene time. In this study, we paleomagnetically study fifteen plutons spanning the entire non-deformed upper Cretaceous granitoid belt to test whether the initial configuration of the CACC was modified by vertical axis rotations after its exhumation. Our results show three internally coherent domains with significantly different vertical-axis rotations: (1) in the north-east, the Akdag-Yozgat block (AYB) records $ 151 clockwise rotation, (2) in the north-west, the Kırs -ehir-Kırıkkale block (KKB) shows $ 6-91 counterclockwise rotation and (3) in the south-west, the Agacören-Avanos block (AAB) shows 28-351 counterclockwise rotation. We propose that these rotations were accommodated by two transpressional fault zones: in the south, the existing Savcılı Thrust Zone between the AYB and KKB and in the north, the newly introduced Delice-Kozaklı Fault Zone between the KKB and AAB. The restored configuration of the CACC suggests that the three blocks were largely aligned in a $ NNE orientation at an early stage of their history. Consequently, since the late Cretaceous the shape of the CACC was affected by large scale deformation, resulting in its modern triangular geometry. This deformation phase is best explained as a result of collision of the CACC with the Pontides.

Structural evidence for strike-slip deformation in the ˙ Izmir–Balıkesir transfer zone and consequences for late Cenozoic evolution of western Anatolia (Turkey)

Journal of Geodynamics, 2013

Theİzmir-Balıkesir transfer zone (İBTZ) is a recently recognized strike-slip dominated shear zone... more Theİzmir-Balıkesir transfer zone (İBTZ) is a recently recognized strike-slip dominated shear zone that accommodates the differential deformation between the Cycladic and Menderes core complexes within the Aegean Extensional System. Here, we present new structural and kinematic data obtained from field observations and 1/25,000 scale mapping of Miocene to Recent units within theİBTZ aroundİzmir Bay. The results point out that theİBTZ is a transtensional brittle shear zone that affects the pre-Neogene basement rock units, the early-middle Miocene volcano-sedimentary units and the Plio-Quaternary continental units.

Archaeomagnetic study of five mounds from Upper Mesopotamia between 2500 and 700 BCE: Further evidence for an extremely strong geomagnetic field ca. 3000 years ago

Earth and Planetary Science Letters, 2012

The distribution of archaeomagnetic data in eastern Europe and the Near and Middle East shows a r... more The distribution of archaeomagnetic data in eastern Europe and the Near and Middle East shows a remarkable gap in Turkey. This study presents the first archaeomagnetic results from five different mounds in southeast Turkey, the northern part of Mesopotamia. The rock magnetic experiments indicate that in the majority of the samples the dominant magnetic carrier is magnetite, which is stable to heating to temperatures of 700 1C. In general, the demagnetization diagrams are single component and all five sets display well-defined characteristic magnetizations and clustered directions. For the period between 2500 and 700 BCE, the declinations are between 3501 and 201 while inclinations are in the range of 49-641. The directional results are compared with the global geomagnetic field models (CALS7k.2, ARCH3k_cst.1 and CALS3k.4) and the data from the archaeomagnetic database GEOMA-GIA50v2. The results are coherent with both the data and the models except for two nearcontemporaneous sets dating $ 2000 BCE, which are offset to the east by more than 201 with respect to CALS7k.2. Archaeointensity measurements were made using the microwave and conventional thermal Thellier methods applied to five sets of samples (four furnaces and a mud-brick wall). These yielded comparable and intriguing results. While those from the furnaces are slightly higher than the CALS7k.2 model and in agreement with the GEOMAGIA50v2 and the Middle East data, the results from the mud-brick wall suggest a high intensity of 100.8 mT (17.7 Â 10 22 Am 2 ) at $ 1000 BCE. This result is in excellent agreement with recent claims of extremely high intensity measured in other regions of the Middle East for this time period though less consistent with these being associated with extremely short-lived events. Finally, we discuss our new and other recently published archaeointensity results in terms of geomagnetic intensity versus climate.

Palaeomagnetism of Archaean rocks of the Onverwacht Group, Barberton Greenstone Belt (southern Africa): Evidence for a stable and potentially reversing geomagnetic field at ca. 3.5 Ga

Earth and Planetary Science Letters, 2011

Palaeomagnetic results from Upper Triassic red-beds and CAMP lavas of the Argana Basin, Morocco

Geological Society, London, Special Publications, 2011

Geomagnetic secular variation and the statistics of palaeomagnetic directions

Geophysical Journal International, 2011

In this study, we examine the role of palaeosecular variation (PSV) in the use of statistics for ... more In this study, we examine the role of palaeosecular variation (PSV) in the use of statistics for palaeomagnetic studies, and we provide new reliability criteria for palaeomagnetic poles or directions. We first conclude that Fisher statistics should not be applied to average palaeomagnetic directions but to virtual geomagnetic pole (VGP) distributions instead.

Pervasive Palaeogene remagnetization of the central Taurides fold-and-thrust belt (southern Turkey) and implications for rotations in the Isparta Angle

Geophysical Journal International, 2011

Magnetostratigraphy and radio-isotope dating of upper Miocene–lower Pliocene sedimentary successions of the Black Sea Basin (Taman Peninsula, Russia)

Palaeo3, 2011

We present a new chronology for the upper Miocene to Pliocene deposits of the Black Sea basin bas... more We present a new chronology for the upper Miocene to Pliocene deposits of the Black Sea basin based on highresolution magnetostratigraphic data coupled with 40 Ar/ 39 Ar dating from the 475 m long Zheleznyi Rog section on the Taman Peninsula (Russia). This section comprises the stratigraphic interval of the Khersonian to Kimmerian regional stages of the Eastern Paratethys. Our magnetostratigraphic record is based on biogenic and early-diagenetic greigite components and yields a magnetostratigraphic sequence of 8 polarity zones. A volcaniclastic ash layer at the upper part of the Khersonian is radio-isotopically dated at 8.69 ± 0.18 Ma. The age of the Khersonian-Meotian transition arrives at 8.6 or 8.2 Ma, which is significantly younger than earlier estimates. The new age has important consequences for the Hipparion-datum in the Eastern Paratethys, and implies that all Vallesian fossil sites are younger than 11.2 Ma. The Meotian stage has a total duration of 2.2 to maximum 2.6 Myr, and is marked by multiple erosional events. The end of the Paratethys Sea is dated at 5.5 Ma, when the Black Sea becomes isolated from the Caspian Sea, the Dacian basin and the Mediterranean.

Magnetostratigraphy – concepts, definitions, and applications

Newsletters on Stratigraphy, 2010

The most characteristic feature of the Earth's magnetic field is that it reverses polarity at irr... more The most characteristic feature of the Earth's magnetic field is that it reverses polarity at irregular intervals, producing a 'bar code' of alternating normal (north directed) and reverse (south directed) polarity chrons with characteristic durations. Magnetostratigraphy refers to the application of the well-known principles of stratigraphy to the pattern of polarity reversals registered in a rock succession by means of natural magnetic acquisition processes. This requires that the rock faithfully recorded the ancient magnetic field at the time of its formation, a prerequisite that must be verified in the laboratory by means of palaeomagnetic and rock magnetic techniques. A sequence of intervals of alternatively normal or reverse polarity characterized by irregular (non-periodic) duration constitutes a distinctive pattern functional for correlations. Over the last 35 Myr, polarity intervals show a mean duration of ~300,000 years, but large variations occur from 20,000 yr to several Myr and even up to tens of Myr. By correlating the polarity reversal pattern retrieved in a rock succession to a reference geomagnetic polarity time scale (GPTS), calibrated by radioisotopic methods and/or orbital tuning, the age of the rock succession can be derived. Magnetostratigraphy and correlation to the GPTS constitute a standard dating tool in Earth sciences, applicable to a wide variety of sedimentary (but also volcanic) rock types formed under different environmental conditions (continental, lacustrine, marine). It is therefore the stratigraphic tool of choice to perform correlations between continental and marine realms. Finally, we emphasise that magnetostratigraphy, as any other stratigraphic tool, works at best when integrated with other dating tools, as illustrated by the case studies discussed in this paper.

New late Paleozoic paleopoles from the Donbas Foldbelt (Ukraine): Implications for the Pangea A vs. B controversy

Earth and Planetary Science Letters, 2011

a b s t r a c t Editor: M.L. Delaney Keywords: paleomagnetism plate reconstructions Pangea Eurasi... more

Late Cretaceous to Paleocene oroclinal bending in the central Pontides (Turkey)

Tectonics, 2010

The Turkish Pontide fold-and-thrust belt formed since the Paleozoic and is an important element i... more The Turkish Pontide fold-and-thrust belt formed since the Paleozoic and is an important element in the Africa-Eurasia convergence and the resulting closure of the Neo-Tethys ocean. It has a peculiar arc-shaped geometry in its central part, along the Black Sea coast, which may have resulted from oroclinal bending. We have determined the vertical-axis rotation history of this area using paleomagnetism on Cretaceous to Eocene rocks from 47 sites and critically analyzed previously published data. We applied the same reliability criteria to all data. Our results show that late Cretaceous sites have clockwise and counterclockwise rotations perpendicular to the structural trend in the central Pontides. In the eastern Pontides, they show only local rotations. Paleocene to Eocene rocks in the central and eastern Pontides show no rotation. We conclude that the central Pontide northward arc-shaped geometry results from oroclinal bending in latest Cretaceous to earliest Paleocene times. The timing and scale of geological processes that occurred in the region make it likely that orocline formation resulted from Neo-Tethys closure between the Pontides and the metamorphic promontory of the Anatolide-Tauride Block. Earlier studies on the southerly located Çankırı Basin reveal that clockwise and counterclockwise rotations occurred in Eocene-Oligocene times. This implies that the entire region underwent continuous deformation from late Cretaceous to Eocene, caused by convergence of the Pontides and the Anatolide-Tauride Block, with a southward moving deformation front. Deformation was first localized in the northern part of the central Pontides until the Paleocene, resulting in oroclinal bending, and from at least Eocene times it shifted toward the Çankırı Basin region.

Jurassic–Cretaceous low paleolatitudes from the circum-Black Sea region (Crimea and Pontides) due to True Polar Wander

Earth and Planetary Science Letters, 2010

The intensity of the geomagnetic field in the late-Archaean: new measurements and an analysis of the updated IAGA palaeointensity database

Earth, Planets and Space, 2009

We firstly present the results of a detailed palaeointensity study performed on 54 samples from 9... more We firstly present the results of a detailed palaeointensity study performed on 54 samples from 9 volcanic units of late Archaean age (2724-2772 Ma) from the Pilbara Craton, Western Australia. These results were severely affected by magnetomineralogical alteration occurring during the laboratory heating process necessitating the application of a correction procedure. The correction allowed results from three lavas to pass strict selection criteria but we deem that only one of these exhibits sufficient internal consistency to be considered moderately reliable. It yields a virtual dipole moment of 47±6 ZAm 2 which is 60% of the present-day value. We combine this determination with a filtered dataset from the updated IAGA (International Association of Geomagnetism and Aeronomy) palaeointensity database, PINT08. Directional secular variation has recently been shown to have changed fundamentally since the Archaean, probably as a consequence of inner core growth since that time. However, here we argue that it is still unclear whether this evolution was accompanied by a single long timescale change in average poloidal field intensity. While the distribution of Precambrian palaeointensity determinations as a whole is significantly lower than that for the last 300 Myr, we show that this finding largely reflects data from the Proterozoic aeon. The distribution of more ancient measurements from the late Archaean-earliest Proterozoic is indistinguishable from that of the last 300 Myr which might suggest that a 'Proterozoic dipole low' period existed between two periods of higher field intensity. Were this pattern of long-term geomagnetic intensity variation to be supported by the addition of new data in the future, then it could indicate a related three-stage evolution in core dynamics, namely: vigorous thermal convection caused by high core-mantle heat flux early in the Earth's history, weaker thermal convection later as the heat flux fell, and finally, strong compositional convection since the inner core nucleated.

A comparison of detailed equatorial red bed records of secular variation during the Permo-Carboniferous Reversed Superchron

Geophysical Journal International, 2009

Detailed secular variation records during a superchron may provide information on the behaviour o... more Detailed secular variation records during a superchron may provide information on the behaviour of the geodynamo during periods that the field does not reverse. The Permian red beds in Dôme de Barrot (southern France)-deposited during the Permo-Carboniferous Reversed Superchron (PCRS, 317-265 Ma) -were previously argued to accurately record palaeosecular variation (PSV). This result is particularly valuable because the red beds were deposited near the palaeo-equator and therefore, according to one model of secular variation, determine the contribution of the even (symmetric) spherical harmonics of the field.

The influence of sea-level changes on tropical coastal lowlands; the Pleistocene Coropina Formation, Suriname

Sedimentary Geology, 2009

The Pleistocene Coropina Formation largely constitutes the Old Coastal Plain of Suriname. It is e... more The Pleistocene Coropina Formation largely constitutes the Old Coastal Plain of Suriname. It is exposed fully only in open-pit bauxite mines in the central coastal plain as part of the unconsolidated overburden of Paleocene-Eocene bauxites. This study deals with the stratigraphy, sedimentology and chronology of this formation, and is based on a study in the recently closed Lelydorp-III bauxite mine operated by N.V. BHP Billiton Maatschappij Suriname. The Coropina Formation consists of the Para and Lelydorp Members. We present a detailed lithological subdivision of these members. In the Para Member, four units are discerned which are grouped in two transgressive cycles, both ranging upward from terrestrial towards chenier and coastal mudflat deposits reflecting glacio-eustatic sea-level changes. The sandy sediments represent fluviatile and beach-bar (chenier) deposits, and were supplied by rivers from the Precambrian basement and to a lesser extent by westward longshore coastal drift. Clays, largely derived from the Amazon River and transported alongshore over the shelf, were deposited in extensive coastal mudflats. The Lelydorp Member, also comprising four units, represents a depositional system that is closely comparable to the recent Suriname coastal setting, i.e., a lateral and vertical alternation of mudflat and chenier deposits formed over a period characterised by more or less constant sea level. Palaeomagnetic data indicate a dominantly reversed magnetic polarity in the Para Member, whereas the Lelydorp Member shows a normal magnetic polarity with a minor reversed polarity overprint. The reversed polarities of the Para Member exclude a Brunhes Chron (0.78-0.0 Ma) age, and thus assign it to the Matuyama Chron (2.58-0.78 Ma). This implies that the Coropina Formation is much older than hitherto assumed, and that one or more (long-term) hiatuses are not recognizable in the lithological succession.

Geomagnetic secular variation in the Cretaceous Normal Superchron and in the Jurassic

Physics of the Earth and Planetary Interiors, 2008

It is now widely thought that geomagnetic polarity reversals occur spontaneously as a result of n... more It is now widely thought that geomagnetic polarity reversals occur spontaneously as a result of normal dynamo action rather than being externally triggered. If this is the case, then it may well be that periods of time in which the geomagnetic reversal frequency was dramatically different were characterised by different styles of secular variation. Two such periods were the Cretaceous Normal Superchron (CNS: 84-125 Ma) when the field was dominantly of a single polarity for 40 Myr and the Jurassic period when reversals occurred at an average rate of as much as 4.6 Myr -1 . Here, we analyse a database of new and published palaeomagnetic directions from lavas emplaced during these periods in order to obtain first-order descriptions of the palaeosecular variation (PSV) during these times. We then compare these records with one another and with that produced for the period 0-5 Ma (with average reversal frequency of 4.0 Myr -1 ). Our results are more equivocal than those obtained in a previous similar study [McFadden, P.L., Merrill, R.T., McElhinny, M.W., Lee, S.H., 1991. Reversals of the Earths magnetic-field and temporal variations of the dynamo families. Journal of Geophysical [3923][3924][3925][3926][3927][3928][3929][3930][3931][3932][3933]. We demonstrate that this is probably a result of the previous study being affected by an artefact of their correction for within-site scatter. The usefulness of our Jurassic record is severely limited by the restricted palaeolatitudinal span of the available data. However, our record for the CNS is sufficient to allow us to conclude that it was likely that secular variation then was different from that in the 0-5 Ma period. This supports the hypothesis of a link between PSV and reversal frequency and therefore endorses PSV analysis as a first-order tool for determining geomagnetic stability in the past.

Evidence for a very-long-term trend in geomagnetic secular variation

Nature Geoscience, 2008

The Earth's inner core is believed to inhibit rapid fluctuations in the geomagnetic field from de... more The Earth's inner core is believed to inhibit rapid fluctuations in the geomagnetic field from developing into full polarity reversals 1,2 . Consequently, during the Precambrian, the smaller size of the inner core might suggest that polarity reversals could occur more readily. It is therefore surprising that there are indications that reversals were rare during this period 3,4 . Here we use new and existing palaeomagnetic data from three continents to examine the stability of the Earth's magnetic field from 2.82 to 2.45 billion years ago. We show that, on average, geomagnetic secular variation (the field variations produced by normal geodynamo action) during the late Archaean and early Proterozoic was different from that of the past 200 million years; specifically, the apparent variability of the geomagnetic pole as viewed at low and mid-latitudes was reduced relative to the past 200 million years. According to both dynamo simulations 4 and more recent palaeomagnetic field observations 5 , the observed pattern of secular variation suggests a lower frequency of polarity reversals 2.5 billion years ago. This may imply that the geodynamo is becoming progressively less stable over long timescales, consistent with some numerical simulations 6,7 , possibly as a result of changing outer-core geometry that has accompanied inner-core growth.

Timing and distribution of tectonic rotations in the northeastern Tibetan Plateau

Geological Society of America, Special Paper, 2008

We report paleomagnetic data from the northeastern margin of the Tibetan Plateau to help understa... more We report paleomagnetic data from the northeastern margin of the Tibetan Plateau to help understand the timing and distribution of deformation (i.e., vertical-axis rotations ) during the India-Asia collision. Paleomagnetic results throughout Xining Basin strata, recently dated using magnetostratigraphy to between 52 and 17 Ma, show that some 25° of clockwise rotation with respect to the stable Eurasian continent occurred at ca. 41 Ma. In view of a regional compilation of existing paleomagnetic data from the northeastern Tibetan Plateau, these results suggest that this region experienced clockwise rotations in the regional Paleocene-Miocene basin system, including rotation in the Xining Basin, ca. 41 Ma, thus establishing the existence of widespread deformation at this time. During a mid-Miocene phase, between 17 and 11 Ma, clockwise rotations were restricted to the Miocene-Quaternary basin system, implying that the Laji Shan thrust belt, which separates the two basin systems, was active during this time interval.