Magnetostratigraphic Data Research Articles

Magnetostratigraphic dating of the uplifted atoll of Maré: Geodynamics of the Loyalty Ridge, SW Pacific

The Loyalty Islands (SW Pacific) are uplifted as they are progressively affected by the lithospheric flexure of the Australian plate, before its subduction under the New Hebrides Arc. These geodynamic changes are constrained by magnetostratigraphically dating two sections from Maré Island, where mineral extractions coupled with rock‐magnetic experiments suggest that the magnetic remanence is mostly carried by a mixture of single‐domain to multidomain magnetite/maghemite. With the help of faunal determinations and radiometric dating, the sequences of polarity reversals, correlated to the geomagnetic polarity timescale, range from the top of Chron C4n (late Miocene) to the top of the Gauss Chron (late Pliocene). This new chronostratigraphy refines the timing of two distinctive carbonate units (rhodolith platform/coral reefs) separated by a hardground whose transition is known to coincide approximately with a regional event around the Miocene/Pliocene boundary. The magnetostratigraphic dating indicates that the hardground represents about a 1.9 m.y. hiatus and suggests variable sedimentation rates ranging from 4.7 to 65.4 m/m.y. during the atoll construction. The lithospheric bulge seems to have influenced the evolution of Maré Island some 3.1 m.y. ago, leading to a diachronous emersion of the northeast and southwest rim of the atoll with a mean uplift rate of the order of 4 cm/kyr.

Chronostratigraphic framework for the Thanetian and lower Ypresian deposits of southern England

Abstract Magnetostratigraphic and palynomorph data are used to assess the timing and nature of the late Paleocene-earliest Eocene depositioanl sequences of SE England. Ormesby Clay Formation mudstones in east Norfolk are the oldest upper Paleocene deposits (C26r) of southern England. The base of the type Thanet Sand Formation (= start of the Thanetian Stage) is c. 0.65 million years younger (C26n). A subaerial erosion surface separates the Thanet-Ormesby package from the Lambeth Group sediments. The duration of the hiatus (>0.5 million years) separating the two units can be calculated from the magnetostratigraphic data; C25n is missing from the stratigraphic record across almost all of southern England. However, the Upnor Formation in central London contains a record of C25n. A hiatus of c. 0.4 million years separates the late Paleocene Lambeth Group from the early Eocene Harwich Formation. The Lambeth Group, Harwich Formation and lower London Clay Formation were all deposited during C24r. The start of Chron C24n.3n is positioned at the base of Division B of the London Clay Formation.

First quantitative test of alluvial stratigraphic models: Southern Rio Grande rift, New Mexico

Since 1978 the results of computational architectural models have been widely used to aid interpretation of ancient alluvial successions: here we present the first quantitative test of such models. We parameterize variables from field and magnetostratigraphic data collected from the well-exposed Pliocene-Pleistocene Camp Rice and Palomas Formations of the Rio Grande rift in south-central New Mexico. Computational runs establish that the LAB (Leeder, Allen, and Bridge) model correctly predicts the gross architectural patterns of ancestral axial Rio Grande half grabens and full grabens. Convergence of tectonic subsidence rate and mean sedimentation rate over the studied interval suggests that the dynamic basis of the models is correct; i.e., it is the tectonic “drawdown” of axially supplied sediment that controls the net preservation potential of alluvial successions.

Late Cretaceous basalts from Rosemary Bank, Northern Rockall Trough

Abstract A borehole drilled on the top of Rosemary Bank (Rockall Trough, NE Atlantic), recovered 16.72m of basalts and volcaniclastic sediments beneath a 1.53m thick limestone with basalt clasts, biostratigraphically dated as late Maastrichtian. Magnetostratigraphic data, constrained by the biostratigraphy, indicate extrusion of Rosemary Bank basalts took place during magnetochron C31R (71–69 Ma), or possibly earlier. This provides definite proof of pre-Tertiary volcanism in the Rockall Trough, and indicates that the onset of activity in the North Atlantic Igneous Province took place at least 7 Ma earlier than the postulated arrival of the Icelandic plume at 62 Ma. Geochemical and isotopic data suggest there was an enriched component to the magmatic source. Present data cannot resolve whether the Rosemary Bank basalts are an early manifestation of the Icelandic plume, whether they were associated with a different plume, or whether they were derived from enriched upper mantle without a significant thermal anomaly.

Biostratigraphic and magnetostratigraphic intercalibration of latest Cretaceous and Paleocene depositional sequences from the deep-water Basque basin, western Pyrenees, Spain

Latest Cretaceous (Late Maastrichtian) and Paleocene depositional sequences from the deep-water Basque basin have been calibrated with published [1,2] and newly acquired magnetostratigraphic data. Sequences mostly consist of hemipelagic marls and limestones, and their relative ages are well constrained with planktic foraminifera. They accumulated during a phase of tectonic tranquillity and reduced clastic input into the basin, and therefore they can be attributed to eustatic sea-level changes with reasonable confidence. On the basis of the planktic foraminifera zonation, a good match has been observed previously between the depositional sequences of the Basque basin and specific sea-level cycles of the 1988 version of the Exxon Global Cycle Chart (GCC) [3]. Here, a new attempt at correlation using their respective magnetostratigraphic data has failed to confirm such a match. The disagreements observed may indicate that, for the studied interval, (1) the current planktic foraminifera biostratigraphy lacks the necessary level of resolution to ensure synchrony between sequences of different basins, and/or (2) the magnetostratigraphy of the GCC needs to be revised. Whatever the case, the new findings lend support for some criticism on the use of the GCC for interregional correlations.

Revised age calibration points for the geomagnetic polarity time scale

Two of the seven Cenozoic age calibration points in the widely used Cande and Kent's geomagnetic polarity time scale have recently been revised. The rest of the five calibration points are revised here based on recently available radioisotopic dates and magnetostratigraphic data. Ages of the magnetic reversals are recalculated using the revised calibration points. Differences between the present time scale and Cande and Kent's revised time scale are generally less than 0.3 m.y., the largest (up to 1.3 m.y.) being in the early Miocene.

Phases of compression during the evolution of the Pannonian Basin and its bearing on hydrocarbon exploration

Progress in understanding the structural evolution of the Pannonian Basin is reported. This has been driven by the application of seismic stratigraphy constrained by magnetostratigraphic data and the recent release of a great amount of hydrocarbon exploration data. This has led to a redefinition and better understanding of the syn-rift period and style of rifting. In addition, a complex structural evolution history during the post-rift phase has been recognized. Two compressive events are defined: one in the early stage and another in the late stage of evolution. The importance of these findings for hydrocarbon exploration includes an improved knowledge of the timing of trap formations and a possible explanation for remarkably variable reservoir pressures in pools of the Great Hungarian Plain.

Magnetostratigraphic Correlation and Dating of the Early to Middle Miocene Stratigraphy Within the Suez Rift: ABSTRACT

Magnetostratigraphic Correlation and Dating of the Early to Middle Miocene Stratigraphy Within the Suez Rift: ABSTRACT

Magnetostratigraphic dating of the middle Miocene climate change in the continental deposits of the Aragonian type area in the Calatayud-Teruel basin (Central Spain)

The exceptionally dense mammalian faunal record of the Aragonian type area in Central Spain shows that an important climate change towards a cooler and more humid climate is recorded during the Neogene Mammal Zone MN 5 [1]. The magnetostratigraphic results from mammal-bearing middle Miocene continental sections in the Aragonian type area indicate that the onset of this climate change, at the MN 4/MN 5 boundary, occurs in the reversed chron C5ACr and has an age of 14.1 Ma, according to the geomagnetic polarity timescale (GPTS) of Cande and Kent [2]. This age is consistent with the age estimate of 14.1–14.05 Ma for the main increase in δ 18O in the marine record [3]. These independent obserbations of time-equivalent cooling in both continental and marine records confirm and accurately date a global cooling event in the middle Miocene. The age of 14.1 Ma for the MN 4/MN 5 boundary is significantly younger than previously recorded in continental timescales [4,5]. This results in a longer duration, by approximately 3 Myr, of the MN 4 zone, which is consistent with the many important faunal changes occurring in MN 4. Furthermore, the MN 5/MN 6 boundary occurs in chron C5ACn (13.8–13.9 Ma) and the MN 6/MN 7–8 boundary in the interval C5Ar.1n-C5Ar.3r (12.7–13.0 Ma).

Miocene stable isotopic stratigraphy and magnetostratigraphy of Buff Bay, Jamaica

Previously reported biostratigraphic relationships from middle-upper Miocene sections exposed near Buff Bay, Jamaica (18°N, tropical bioprovince), differ from the subtropical North Atlantic (Sites 563 and 558). Time scales for this interval rely on correlations established at these subtropical sites, and the differences with the tropical section have implications to global correlations. Planktonic foraminiferal Zones N13 and N15 are thick at Buff Bay but are virtually absent at Sites 563 and 558; nannofossil Zone NN9 is associated with Zone N15 and uppermost Zone N14 at Buff Bay but is associated with Zone N16 at the other sites. Magnetostratigraphic data presented here further complicate the interpretation: Zone NN9 is associated with a thick normal magnetozone at Sites 563 and 558; at Buff Bay, it is associated with a thick reversed magnetozone. Although a secondary magnetization at Buff Bay makes it difficult to identify confidently Miocene normal magnetozones, the thick reversed magnetozone most likely represents the paleomagnetic field and correlates with Chron C5r. The magnetobiostratigraphic relationships require either diachrony of taxa or two mutually exclusive hiatuses in Jamaica and the North Atlantic. We address this problem by analyzing benthic foraminiferal δ 18 O and δ 13 C from the Buff Bay section. These isotopic data allow us to evaluate three hypotheses that reconcile the magneto-, bio-, and isotopic stratigraphic data and conclude that the first and last occurrences of five taxa were diachronous by ∼0.3-0.5 m.y. between tropical and subtropical locations. This requires revised age estimates for late middle to early late Miocene biostratigraphic datum levels. We suggest that the ranges of several taxa are useful for endemic tropical or subtropical zonations, but correlations between the low and midlatitudes were affected by an increase in latitudinal thermal gradients during the late middle Miocene. However, we admit that further studies are needed before this issue is resolved.

Stratigraphie intégrée du Toarcien stratotypique (coupes de Thouars et Airvault, Deux-Sèvres, France)

Multidisciplinary stratigraphic study of Toarcian Stage in its stratotype area (mainly the Airvault quarry referencesection) yields new chronostratigraphic and paleoenvironnemental results. Correlations between biostratigraphic (Ammonites. Foraminifera, Ostracods, Nannofossils, Palynomorphs) and magnetostratigraphic data improve the chronostratigraphic resolution of the Toarcian: some lacunae are established on the Bifrons and Insigne Ammonite zones. Organic carbon contents are low: between 0.1 to 1.9%. The origin of organic matter is mixed (both continental and marine); mainly continental at the base of the Airvault section (mid Toarcian) and more marine within the Upper Toarcian. Geochemical results (trace elements and stable isotopes) reflect the evolution in marine environment and can provide elements to suggest a warming at the Pseudoradiosa-Aalensis Zones boundary. A sequence stratigraphic interpretation is suggested for the Airvault section.

Magnetostratigraphic dating of an Upper Miocene shallow-marine and continental sedimentary succession in northeastern Morocco

A high-resolution magnetostratigraphy has been developed for an Upper Miocene shallow-marine carbonate complex, equivalent basinal marls, diatomites, and lime mudstones, and an overlying succession of marine to continental carbonate and siliciclastic sedimentary rocks in the Melilla Basin, northeastern Morocco. Units of the carbonate complex, from bottom to top, contain a bryozoan/red algal ramp, bioclastic platform, fringing-reef complex and a unit referred to as the Terminal Carbonate Complex (TCC) [1]. Lithologies from these units contain at least three components of magnetic remanence: (1) a low unblocking temperature component that is likely carried by a viscous remanent magnetization, (2) a low-coercivity, intermediate unblocking temperature component that is probably carried by magnetite or magnetite and maghemite, and (3) a high unblocking temperature component that is probably carried by hematite. Lithologies are typically dominated by the low-coercivity component and single-domain to pseudo-single-domain grain behavior. Rock-magnetic studies suggest biogenic magnetite may contribute to the magnetic remanence of the low-coercivity component. The Melilla Basin magnetostratigraphy, independently corroborated with new 40 Ar 39 Ar dating of volcanic ashes and foraminifer biostratigraphy, has been correlated to the recently developed geomagnetic polarity time scale of Shackleton et al. [2]. This correlation suggests deposition of the bioclastic platform began approximately at the Tortonian/Messinian boundary, which is defined as the base of chron 3Ar [3], and continued into chron 3An.2n. The fringing-reefs span an interval that begins in chron 3An.2n until just above the base of chron 3r (lower Gilbert). The overlying TCC and mixed carbonate and siliciclastic succession correlate to within chron 3r. The new magnetostratigraphy is not without minor ambiguities, possibly due to either remagnetization within the TCC or the presence of a short-duration normal subchron in the lower portion of chron 3r. Results of this study have important implications for correlating between Late Miocene shallow-marine carbonate sections and basinal sections within the Mediterranean Basin, for improving the understanding of the history of the Messinian Salinity Crisis, and for deciphering the roles of eustacy, tectonics, and regional processes in the development of shallow-marine carbonate sequences in the Mediterranean region.

Age Assignment of the Lycoptera ‐ bearing Bed

Abstract In the Yanliao area, the occurrence of the Nestoria ‐ Keratestheria fauna and the Eoparacypris‐ Luanpingella ‐ Darwinula assemblage in the Dabeigou Formation s.s., a Rb‐Sr isochron age of 145.2 Ma for the Baiqi Formation and a complete stratigraphie sequence—all this proves that the Lycoptera‐ bearing bed overlies the Upper Jurassic. The Jehol fauna comprises the primitive Trigonioidids fauna, Eosestheria fauna, Lycoptera fauna et al., and their own laws of evolution expound that they belong to Cretaceous faunas. The associations of Eosestheria with Yanjiestheria, Lycoptera with Eosestheria, and Kuntulunia with Yanjiestheria as well as the occurrence of early angiosperms and sporo ‐ pollen in the Fuxin Formation and its equivalents also demonstrate that the Lycoptera‐ bearing bed should be assigned to the Cretaceous. The confirmation of the existence of Aucellina in the Jixi Group and the correlation of Trigonioidids and Cypridids with those in the equivalent strata of Japan and Western Europe have also been verified by corresponding marine strata. According to the magnetostratigraphic data from Zhejiang and Songliao, it has been preliminarily ascertained that M0 between the mixed polarity zone in the lower part and the normal polarity zone in the middle part of the Cretaceous is located in the upper member of the Huangjian Formation of the Jiande Group and the top member of the Denglouku Formation of the same group, and the isotopic age data of the Jehol and Jiande Groups show that the approximate geologic age of the Lycoptera bed is 135‐122 M a. These prove that the Lycoptera bed should be assigned to the Cretaceous.

Magnetostratigraphy of the Mayerling section (Austria) and Erenkolu Mezarlik (Turkey) section: Improvement of the Carnian (late Triassic) magnetic polarity time scale

We present a magnetostratigraphic study of two Carnian (late Triassic) pelagic limestone sections from the Northern Calcareous Alps (Mayerling section) and southwestern Turkey (Erenkolu Mezarlik section). Biostratigraphic control is based on conodont zonation for the Mayerling section, and both on conodonts and ammonoids for the Erenkolu Mezarlik section. In both sections, the characteristic magnetization is essentially carried by a mineral of the magnetite family. Eight magnetic intervals are obtained from the Mayerling section and fourteen from Erenkolu Mezarlik. When these results are compared to the Carnian magnetostratigraphic sequence obtained from the Bolücektasi Tepe section, satisfactory correlations are observed and a composite Carnian magnetic polarity time scale containing 24 intervals can be proposed by combining all these results. The lower part of the upper Carnian is however missing (Tuvalian 1 zone and lower part of the Tuvalian 2 zone). No clear correlation is observed between our composite sequence and the other published magnetostratigraphic data of Carnian age. The satisfactory correlation observed between the Mayerling and the Bolücektasi Tepe sections indicates that both sections were deposited in the northern hemisphere, thus providing constraints on the origin of the Antalya nappes.

Magnetostratigraphic Data From Late Quaternary Sediments From the Yermak Plateau, Arctic Ocean: Evidence For Four Geomagnetic Polarity Events Within the Last 170 Ka of the Brunhes Chron

SUMMARY Palaeomagnetic investigations of two sediment cores recovered from RV Polarstern near the eastern slope of the Yermak Plateau (sites PS 1533 and PS 2212) reveal convincing evidence for four polarity events of the Earth's magnetic field during the last 170 Ka. A comprehensive rock magnetic study of the sediments proved that fine-grained magnetite is the principal carrier of the remanent magnetization. No changes in magneto-mineralogy across the polarity transitions in the sediments investigated were found. Calcareous nannofossil biostratigraphy, AMS-14C (accelerated mass spectrometry) and oxygen isotope data, and 10Be and 230Th stratigraphies yielded age ranges of 24–29 Ka for the Mono Lake event, 34–43 Ka for the Laschamp event, 72–86 Ka for the Norwegian-Greenland Sea event and 118–128 Ka for the Blake event. Two reverse polarity samples at the base of core PS 2212–3 KAL are interpreted as the termination of the Biwa I event (171-181 Ka). the events exhibit full inversion of inclination in both cores. the data suggest that the transition process of the Earth's magnetic field during such polarity events requires some 1 Ka.

Land mammal biostratigraphy and magnetostratigraphy of the Etadunna Formation (late Oligocene) of South Australia

ABSTRACT Field work recently completed in the Lake Eyre Basin, South Australia, has resulted in the development of a land mammal (marsupial) biostratigraphy of the Etadunna Formation. Whereas traditional interpretations of the age of this sequence suggest it is about 15 m.y. old, new information indicates that the Etadunna likely is 24–26 m.y. old. In either case, it appears possible to document a four-fold fossil mammal zonation of this rock unit at lakes Palankarinna, Kanunka, Pitikanta, and Ngapakaldi, in a composite section of strata that spans at least 30 m. Magnetostratigraphic data for the same succession are generally consistent with the correlation of the Etadunna Formation sites at Lake Palankarinna with of those at lakes Kanunka, Pitikanta, and Ngapakaldi to the north, as based on paleontological information. The magnetic polarity zonation of these Etadunna Formation strata is consistent with a correlation to the world magnetic polarity time scale at about 24–26 m.y. This is the first fine-scal...

Neogene sequences in the Pannonian basin, Hungary

The rifting in the extensional Pannonian basin occurred in the Middle Miocene, the subbasins within the Pannonian system formed under the control of expansional tectonics during this time. Sequence stratigraphic analysis on well logs revealed a single third-order synrift sedimentary sequence developed due to tectonically enhanced eustatic sea-level change in shallow-marine environments. The Pannonian basin became an isolated lake by its postrift phase during the Middle-Late Miocene boundary. The first postrift sequence formed under peculiar conditions, when the basin lost its marine connections and simultaneously a considerable differential subsidence began. The large volume of freshwater input supplied by rivers and the rapid subsidence of the basement caused the basin to be a deep freshwater lake. The lacustrine postrift infill was studied by sequence stratigraphy using seismic reflection, well log and magnetostratigraphic data. Numerous unconformities can be revealed which represent relative lake-level fluctuations of different magnitudes. The water level and volume of the large inland lake was very sensitive to different effects, the most important ones are lake-water budget, sediment influx and differential subsidence of the basement. The style of extension and sedimentation show differences with respect to passive continental margins that are reflected in the sedimentary architecture. A significant third-order water-level change has been discovered in the eastern part of the Pannonian basin, while the western side did not experience such a great change in lake level. This fact gives credit to the view of different interplay of lake-level-influencing effects in different areas of the basin. This major third-order lake-level change has been age dated using magnetostratigraphy and a very close match was found with the age of the Mediterranean salinity crisis. The Pannonian basin offers the possibility to study the infilling style and stratigraphic evolution of an inland rifted basin. Detailed sequence analysis allows the recording of the apparent sea/lake-level motion which can be compared to those observed in the surrounding seas. Further tectono-stratigraphic evaluations of the Pannonian basin may reveal hidden facts on the nature of lake-level fluctuations and contribute new data to the discipline of sequence stratigraphy.

New data from Hadar (Ethiopia) support orbitally tuned time scale to 3.3 MA

Support for the astronomically calibrated geomagnetic polarity time scale is provided by new 40Ar/39Ar dating and magnetostratigraphic data from the Hadar Formation, Ethiopia. Three tuffs and a basalt flow at Hadar span the Mammoth subchron of the Gauss chron, and range in age from 3.18±0.01 to 3.40 ±0.03 Ma. Interpolation of sediment accumulation rates in two magnetostratigraphic sections yields an estimated age range of 3.30±0.02 to 3.21±0.01 Ma for the Mammoth subchron, closely coinciding with orbitally based predictions of 3.33 to 3.22 Ma rather than with previous estimates of 3.15 to 3.05 Ma.

Origin and Evolution of Turkish blocks during the Late Triassic from magnetostratigraphic data

A palaeomagnetic and magnetostratigraphic study has been carried out on lower Carnian and Norian rocks (Late Triassic) from four different sections of two different units of the Upper Antalya Nappes in the Taurus region of southwestern Turkey, the Bakirli Dag unit and the Kaymaz Dag unit. The origin of these nappes is uncertain and under debate. This study provides well defined directions of probable primary origin and good magnetostratigraphic correlations between the different sections, which allows us to propose a palaeogeographic interpretation. The Bakirli Dag unit of the Upper Antalya Nappes were located at a palaeolatitude of 6.9°N ± 1.5° during the early Carnian and at 10.2°N ± 1.0° during the latest Carnian-middle Norian. This slight northward movement is accompanied by a large clockwise rotation (29.5° ± 6.7°) which may correspond to an important breakup-phase of the north African margin during middle-late Carnian time. The palaeo­magnetic results from the Kavur Tepe section of the Kaymaz Dag unit, previously considered to belong also to the Upper Antalya Nappes, show a palaeolatitude of 17.4°S ± 1.1° during Norian time. This result surprisingly indicates that this unit was located in the vicinity of the northern Indian margin during the Late Triassic.

Paleomagnetically derived folding rates, southern Pyrenees, Spain

Well-dated syntectonic unconformities with the Spanish Pyrenees allow characterization of sedimentation and deformation within an orogenic foreland. The Spanish Pyrenees are composed of a south-vergent thrust belt and foreland basin in which folds developed both parallel and perpendicular to tectonic transport. Unconformity geometries and magnetostratigraphic data from synorogenic strata provide a precise temporal framework for the quantitative analysis of the Mediano anticline, the largest of the transverse folds. Folding began in the early Eocene and ended by ∼42 Ma at which time an anticline 20 km long and ∼5 km in wavelength had been produced. Angular and progressive unconformities within syntectonic sedimentary units preserve the history of fold development. Fold growth resulted from west-ward salt movement driven by prograding sediments and was characterized by 2-3 m.y. intervals of slow continuous limb tilting, 2.2°-4.2°/m.y., preserved as progressive unconformities within syntectonic strata. Because the emplacement of the Cotiella-Montsec thrust sheet was episodic, intervals of slow fold growth were punctuated by intervals lasting