Magnetostratigraphy

Climate variability is driven by a complex interplay of global-scale processes and our understanding of them depends on sufficient temporal resolution of the geologic records and their precise inter-regional correlation, which in most cases cannot be btained with biostratigraphic methods alone. Chemostratigraphic correlation based on bulk sediment carbon isotopes is increasingly used to facilitate high-resolution correlation over large distances, but complications arise from a multitude of possible influences from local differences in biological, diagenetic and physico-chemical factors on individual δ13C records that can mask the global signal. To better assess the global versus local contribution in a δ13C record it is necessary to compare numerous isotopic records on a global scale. As a contribution to this objective, this paper reviews bulk sediment δ13Ccarb records from the Late Cretaceous in order to identify differences and similarities in secular δ13C trends that help establish a global reference δ13C record for this period. The study presents a global-scale comparison of twenty δ13C records from sections representing various palaeo-latitudes in both hemispheres and different oceanic settings from the Boreal, Tethys, Western Interior, Indian Ocean and Pacific Ocean, and with various diagenetic overprinting. The isotopic patterns are correlated based on independent dating with biostratigraphic and paleomagnetic data and reveal good agreement of the major isotope events despite offsets in absolute δ13C values and variation in amplitude between the sites. These differences reflect the varying local influences e.g. from depositional settings, bottom water age and diagenetic history, whereas the concordant patterns in δ13C shifts might represent δ13C fluctuations in the global seawater dissolved inorganic carbon. The latter is modulated by variations in organic matter burial relative to re-mineralization, in the global-scale formation of authigenic carbonate, and in partitioning of carbon between organic carbon and carbonate sinks. These variations are mainly controlled by changes in climate and eustasy. Additionally, some globally synchronous shifts in the bulk δ13Ccarb records could result from parallel variation in the contribution of authigenic carbonate to the sediment. Formation of these cements through biologically mediated early diagenetic processes is related to availability of oxygen and organic material and, thus, can be globally synchronized by fluctuations in eustasy, atmospheric and oceanic oxygen levels or in large-scale oceanic circulation. Because the influence of early diagenetic cements on the bulk δ13Ccarb signal can, but need not be synchronized, chemostratigraphy should not be used as a stand-alone method for trans-continental correlation, and especially minor isotopic shifts have to be interpreted with utmost care. Nevertheless, the observed consistency of the δ13C correlations confirms global scale applicability of bulk sediment δ13C chemostratigraphy for the Late Cretaceous, including sediments that underwent lithification and burial diagenesis such as the sediments from the Himalayan and Alpine sections. Limitations arise from increased uncertainties (1) in sediments with very low carbonate content, (2) from larger δ13C variability in sediments from very shallow marine environments, (3) from unrecognized hiatuses or strong changes in sedimentation rates, and (4) in sections with short stratigraphic coverage or with few biostratigraphic marker horizons.

The combination of chemostratigraphy with biostratigraphy and magnetostratigraphy substantially increases the precision and temporal resolution of inter-regional correlations and helps overcome problems that arise from differences in biostratigraphic schemes, facies or provincialism of key fossils. By using an iterative approach to stepwise increase precision of the correlations, isochroneity of first and last occurrences of marker species versus chemostratigraphy is tested, which helps to improve biostratigraphic zonations, to assess zonal boundary ages and to identify useful criteria for defining Late Cretaceous stage boundaries, many of which are still not formally defined. The presented correlations indicate a consistent position for most planktic foraminifer zonal boundaries relative to corresponding isotope shifts during the mid-Cretaceous sea-level high, whereas diachroneity appears to be more pronounced during the Late Campanian and Maastrichtian global sea-level fall. A similar pattern is observed for trans-continental consistency in the δ13C shifts. Graphic correlation of isotopic shifts, magnetostratigraphic and biostratigraphic events among the compared sections is used to detect hiatuses or relative changes sediment accumulation rates and visualizes consistency or offsets of individual biostratigraphic markers relative to chemo- and magnetostratigraphy. Finally, an attempt of a global average δ13C stack is presented for the Turonian through Maastrichtian.

A 13-million-year continuous record of Oligocene climate from the equatorial Pacific reveals a pronounced “heartbeat” in the global carbon cycle and periodicity of glaciations. This heartbeat consists of 405,000-, 127,000-, and 96,000-year eccentricity cycles and 1.2-million-year obliquity cycles in periodically recurring glacial and carbon cycle events. That climate system response to intricate orbital variations suggests a fundamental interaction of the carbon cycle, solar forcing, and glacial events. Box modeling shows that the interaction of the carbon cycle and solar forcing modulates deep ocean acidity as well as the production and burial of global biomass. The pronounced 405,000-year eccentricity cycle is amplified by the long residence time of carbon in the oceans.

At the coast of the río de la Plata in the Buenos
Aires city lies a classic paleontological site, known as “toscas del Río de La Plata” or simple as “las toscas”. It has
been studied for over 120 years and, although it has been widely spread, today is only possible to observe it
during low tide. For this reason, most of the available materials are those collected during the first half of the
XXth century, and that so far have only been incorporated into scarce taxonomic reviews. Among the fossils
collected in “las toscas” highlights Glyptodon munizi Ameghino, Neosclerocalyptus pseudornatus Ameghino,
Mesotherium cristatum Serrés, Arctotherium angustidens Gervais y Ameghino and Theriodictis platensis
(Mercerat); all are exclusive species from the Ensenadan Stage (early to -middle Pleistocene). The sediments of
“las toscas” were deposited during times of normal polarity, more precisely during the “Jaramillo” event (Chron
C1r1n, ca. de 1 Ma). Faunistic evidences (e.g. Tolypeutes, Catagonus) allow to interpret “las toscas” as an open
environment with dry conditions and probably colder than the present.

A well-preserved 11.8-million-years-old lower face attributed to the seminal taxon Dryopithecus fontani (Primates, Hominidae) from the Catalan site ACM/C3-Ae of the Hostalets de Pierola area (Vallès-Penedès Basin, Catalonia, NE Spain) is described. The new data indicate that D. fontani is distinct at the genus level from Late Miocene European taxa previously attributed to Dryopithecus, which are here reassigned to Hispanopithecus. The new facial specimen also suggests that D. fontani and the Middle Miocene Pierolapithecus catalaunicus are not synonymous. Anatomical and morphometric analyses further indicate that the new specimen shows a combination of lower facial features—hitherto unknown in Miocene hominoids—that resembles the facial pattern of Gorilla, thus providing the first nondental evidence of gorilla-like lower facial morphology in the fossil record. Considering the current evidence, the gorilla-like facial pattern of D. fontani is inferred to be derived relative to previously known stem hominids, and might indicate that this taxon is either an early member of the Homininae or, alternatively, a stem hominid convergent with the lower facial pattern of Gorilla. The biogeographic implications of both alternatives are discussed. This new finding in the Hostalets de Pierola section reinforces the importance of this area for understanding the elusive question of the Middle Miocene origin and early radiation of great apes. Am J Phys Anthropol, 2009. © 2009 Wiley-Liss, Inc.

This paper presents first a discussion on the status of the subdivisions of the European Neogene mammal chronology and second, it synthesizes all available magnetostratigraphic data from Europe to provide chronological framework for mammal localities, mammalian events and mammalian biochronologic units of the European Neogene.Because of the lack of their rock equivalents, the subdivisions of the European Neogene, based on mammals, have not attained the stage status in terms of reliability, except the Vallesian and Turolian. Therefore they are designated as the European Land Mammal Ages (ELMA).Magnetostratigraphic data on mammal-bearing deposits in Europe is still scarce in time and space; consequently, it is not yet possible to correlate accurately all ELMA and MN zones with the geomagnetic polarity time-scale (GPTS). Nevertheless, several studies dealing with mammal localities (and their deposits) around the Oligocene/Miocene boundary, in the middle and late Miocene provide reliable correlations of some ELMA and MN zone boundaries. Thus, the calibration of the Oligocene/Miocene boundary at the base of Chron C6Cn.2n is in agreement with its age in marine deposits. The well-known Hipparion Datum (Astaracian/Vallesian boundary) is now dated as about 10.8 Ma, occurring slightly above the base of Chron C5n.2n.This paper also reviews magnetostratigraphic correlations of some late Miocene and Pliocene mammal localities in the Paratethys area. Taking into account the chronological assessments in other parts of Europe for some key mammalian events, new correlations with the GPTS have been proposed for these localities. Thus some new ages are suggested for the late Miocene and Pliocene Paratethys stages.

The thick red mudstone unit that crops out at Laguna Umayo (Puno department, southern Peru), here referred as LURMU, has yielded in different levels a fossil assemblage with plants and vertebrates (including mammals). On the basis of charophytes, the unit was initially assigned to the Vilquechico Formation (Maastrichtian-Danian), of regional extension, and the dinosaurian structure of egg fragments was interpreted as consistent with that age. Revision of the regional stratigraphy leads to reassignment of this unit to the Lower Muñani Formation (Early Tertiary). Mammals from the LU-3 and Chulpas levels present affinities with forms from the Upper Paleocene of South America (Patagonia, Brazil). A bunodont marsupial, Chulpasia, is evidence for chronologic proximity to a transantarctic interchange with Australia at the end of the Paleocene. Furthermore, magnetostratigraphy of the LURMU reveals a single reverse polarity zone of 300 m thickness. Because of the new stratigraphic and paleomammalogic data, this long reverse polarity zone is likely correlative to Chron 26r (early Late Paleocene) or Chron 24r (latest Paleocene–earliest Eocene), or, less likely, to Chron 29r (latest Cretaceous–earliest Paleocene). The arguments previously invoked in favor of a Cretaceous age (charophytes, dinosaurian eggs) are critically evaluated, and correlation to Chron 24r is favored.L’épaisse unité de pélites rouges de Laguna Umayo (département de Puno, Sud Pérou), désignée ici par l’acronyme LURMU, qui a livré en différents niveaux des assemblages fossiles à végétaux et vertébrés (dont mammifères), a été d’abord attribuée à la Formation régionale Vilquechico (Maastrichtien-Danien) sur la base de charophytes. La structure dinosaurienne de fragments d’œufs fut aussi produite à l’appui de cette acception d’âge. La révision de la stratigraphie régionale conduit à réattribuer ces terrains à la Formation Muñani inférieure (Tertiaire inférieur). Les mammifères décrits des niveaux LU-3 et Chulpas ont des affinités avec des formes connues du Paléocène supérieur d’Amérique du Sud (Patagonie, Brésil). Un marsupial bunodonte, Chulpasia, témoigne de la proximité chronologique d’un échange transantarctique, fini-Paléocène, avec l’Australie. D’autre part, l’étude du paléomagnétisme de la LURMU montre une polarité inverse continue. Vu les nouvelles données stratigraphiques et paléomammalogiques, cette longue section magnétostratigraphique inverse correspond vraisemblablement aux chrons 26r (partie inférieure du Paléocène supérieur) ou 24r (Paléocène terminal—Eocène basal), ou, moins favorablement, au Chron 29r (Crétacé terminal—Paléocène basal). Les arguments précédemment allégués pour l’âge crétacé (charophytes et œufs dinosauriens) sont envisagés de façon critique.La espesa unidad de pelitas rojas de Laguna Umayo (departamento de Puno, Sur del Perú), aquí referida como LURMU, ha proporcionado en distintos niveles asociaciones fósiles con vegetales y vertebrados (incluyendo mamíferos). En base a carófitas, fue inicialmente atribuida a la Formación Vilquechico (Maastrichtiano-Daniano), de extensión regional, y se ha invocado la estructura dinosauriana de fragmentos de huevos para sustentar esta edad. La revisión de la estratigrafía regional conduce a reatribuir esta unidad estratigráfica a la Formación Muñani inferior (Terciario inferior). Los mamíferos descritos en los niveles LU-3 y Chulpas presentan afinidades con formas conocidas del Paleoceno superior de Sudamérica (Patagonia, Brasil). Un marsupial bunodonto, Chulpasia, atestigua la proximidad cronológica de un intercambio transantárctico con Australia a fines del Paleoceno. Por otra parte, la magnetoestratigrafía de la LURMU indica una polaridad inversa continua. Dado los nuevos datos estratigráficos y paleomamalógicos, esta larga sección magnetoestratigráfica inversa corresponde más probablemente a los crones 26r (parte inferior del Paleoceno superior) o 24r (Paleoceno terminal - Eoceno basal), o, menos favorablemente, al Cron 29r (Cretácico terminal—Paleoceno basal). Los argumentos anteriormente invocados en favor de una edad cretácica (carófitas, huevos dinosaurianos) se evaluan de manera crítica.

We present here an integrated magnetic stratigraphy by attempting magnetic polarity, rock magnetism and magnetic fabric analysis along with lithostratigraphy over a Late Paleocene-Eocene marine to continental transition recorded in the Subathu and Dagshai formations exposed along the Koshaliya River near Kalka (H.P). The study based on total 168 oriented block samples collected from 261 m thick measured section reports several breaks in the polarity pattern coinciding with rock magnetic and magnetic fabric anomalies along with occurrence of erosional, bioturbation and non depositional (pedogenic) surfaces. Ambiguity in the degree of completeness of the polarity pattern resulted in intricate matching of the geomagnetic polarity time scale (GPTS) and tentative ages are produced by iterative matching taking into account the erosional/non-depositional surfaces, demanding further data from laterally correlative sections. A sharp turnover in the magnetic mineral composition from ferrimagnetic (anoxic) to antiferromagnetic (oxic) at ~27 m below the lithological contact of Subathu (marine) and Dagshai (continental) formations suggest a time period of >500 Ka of shore face migration/continentality, critically available for biotic adaptability to new depositional environments in this basin. The magnetic stratigraphy further indicates two 'high energy' events noted at: a) ~39.8 Ma (relative ages) with paleoflow reversal followed by high sediment flux and b) at ~39.15 Ma with unaltered paleoflow and rate of sedimentation. We infer the former as response of orogenically forced regression and the later depicting a major climatic shift demanding further investigations. The coincidence of prominent erosional/non depositional surfaces with magnetic stratigraphy anomalies envisages the scope for detailed sequence stratigraphic attempt in the Subathu basin that otherwise is represented by complexly folded and faulted strata in the Himalayan foreland basin.

This article is concerned with nannofossil study of Tithonian-Berriasian sediments of Eastern Crimea. The NJT 16, NJT 17a, NJT 17b, NKT, and NK 1 nannofossil zones were determined. The occurrence of Nannoconus kamptneri minor, one of the potential marker-types of the Tithonian-Berriasian boundary (the base of the NKT Zone) of the Tethyan sequence in the Feodosiyan section is assigned here to the Pseudosubplanites grandis ammonite Subzone and the magnetic Chron M18n. The base of the NKT Zone is closer to the Grandis Subzone base than to the base of the Jacobi Subzone. Contradictions in the interpretation of magnetic chrons obtained by the present authors (Arkadiev et al. 2018) and by Bakhmutov et al. (2018) might be caused by mistakes admitted in the latter work on the compiled section.

ABSTRACT
The study area is located at 56 km nearly NW of  PyinOoLwin, Shan State (North). It lies between latitude 22  ံ30 'N and 22  ံ35' N and longitude 96  ံ25 'E and 96  ံ 30 'E in one inch topographic map  of  93 B/6. The major units of the study area are the ChaungMagyi Group (late Precambrian), the Pangyun Formation (Cambrian ) and the Plateau limestone (Permian ) and Naunkangyi  Group ( Ordovician ).
Lithologically in the study area, metasediments and sedimentary rocks of Naungkangyi Limestone and the Pangyun Formation of sandstone were exposed.
In the study area, especially Pangye, and Mokhso areas are related to N-S trending mineralization zone. In it Ni-Co mineralization is significant and hosted by N-S trending  sandstone. The most significant alteration in these areas aresilicification and oxidation.
The mineralization of the study area is  very interesting for nickel and cobalt  in the silicified porous sandstone of  Pangyun Formation.
Mineralization nature is mainly of stratabound type occurring  in the  porous  sandstone  of  Pangyun Formation .
By the study of geochemical analysis , economic elements such as nickel and  cobalt are important  and lead, zinc and  gold are also significant.
Therefore, in the study area anomalous  nickel and cobalt values are found in the sandstone of the  Pangyun Formation, and this will serve as a guide for regional  geochemical exploration . It will be the first-time discovery of the of sediment-hosted Ni-Co mineralization in Myanmar.

New bio-magnetostratigraphic data have been acquired from the Burdigalian part of the Moria section in the Umbria–Marche Apennine (Central Italy). The investigated sedimentary sequence is 55 meters thick and comprises the transition between the Bisciaro and the Schlier formations (Auctorum), composed of five meters of indurated marly limestones, followed by about 40 meters of blue marly clays capped by 10 m of alternating clays and calcareous layers. According to existing literature, the sequence contains the so-called “Piero della Francesca Level” (Auctorum), a few-centimeters-thick biotite-rich level. The sequence has been sampled for paleomagnetic and calcareous plankton analyses. Four magnetic polarity zones have been documented in the middle and upper part of the section. The calcareous plankton content shows different degrees of preservation, from poor to good for calcareous nannofossils and poor to medium for planktonic foramini - fers. Several useful biohorizons have been observed and chronologically constrained through calibration to the magnetostratigraphic data.
The studied section ranges from the top of Chron C5Dr.1n to Chron C5Cn.2r, covering the time interval from 17.7 to 16.4 Ma (according to the ATNTS04) almost continuously, with a small hiatus of at least 34 ka at the C5Dn/C5Cr transition. The integration of our results with those from previous studies of the same section and comparisons with data from other Mediterranean and North Atlantic sequences allows to evaluate the synchrony of the observed biohorizons with other parts of the Mediterranean and the Atlantic Ocean during a still relatively poorly known time interval.

We present an updated time frame for the 30 m thick late Miocene sedimentary Trachilos section from the island of Crete that contains the potentially oldest hominin footprints. The section is characterized by normal magnetic polarity. New and published foraminifera biostratigraphy results suggest an age of the section within the Mediterranean biozone MMi13d, younger than ~ 6.4 Ma. Calcareous nannoplankton data from sediments exposed near Trachilos and belonging to the same sub-basin indicate deposition during calcareous nannofossil biozone CN9bB, between 6.023 and 6.727 Ma. By integrating the magneto-and biostratigraphic data we correlate the Trachilos section with normal polarity Chron C3An.1n, between 6.272 and 6.023 Ma. Using cyclostratigraphic data based on magnetic susceptibility, we constrain the Trachilos footprints age at ~ 6.05 Ma, roughly 0.35 Ma older than previously thought. Some uncertainty remains related to an inaccessible interval of ~ 8 m section and the possibility that the normal polarity might represent the slightly older Chron C3An.2n. Sediment accumulation rate and biostratigraphic arguments, however, stand against these points and favor a deposition during Chron C3An.1n.