Early Brunhes Chron Research Articles

Characterization of Lower and Middle Pleistocene tephra beds in the southern plains of western Canada

Wellsch Valley tephra, near Swift Current, southwestern Saskatchewan, and Galt Island tephra, near Medicine Hat, southeastern Alberta, have been referenced in the literature since the 1970s, but little is available on their physical and chemical attributes — necessary information if they are to be recognized elsewhere. This study seeks to remedy this situation. Both have a calc-alkaline rhyolitic composition with hornblende, biotite, plagioclase, pyroxene, and Fe–Ti oxides being dominant. They have a similar composition but are not the same. Wellsch Valley tephra has a glass fission-track age of 0.75 ± 0.05 Ma, a reversed magnetic polarity, and was deposited at the close of the Matuyama Chron. Galt Island tephra has an age of 0.49 ± 0.05 Ma, a normal magnetic polarity, and was deposited during the early Brunhes Chron. Rich fossil vertebrate faunas occur in sediments close to them. Major- and trace-element concentrations in their glass shards indicate a source in the Cascade Range of the Pacific Northwest, USA, but differences in trace-element ratios suggest they are not consanguineous.

Magnetostratigraphic dating of the hominin occupation of Bailong Cave, central China

Intermontane basins in the southern piedmont of the Qinling Mountains are important sources of information on hominin occupation and settlement, and provide an excellent opportunity to study early human evolution and behavioral adaptation. Here, we present the results of a detailed magnetostratigraphic investigation of the sedimentary sequence of hominin-bearing Bailong Cave in Yunxi Basin, central China. Correlation to the geomagnetic polarity time scale was achieved using previously published biostratigraphy, 26Al/10Be burial dating, and coupled electron spin resonance (ESR) and U-series dating. The Bailong Cave hominin-bearing layer is dated to the early Brunhes Chron, close to the Matuyama-Brunhes geomagnetic reversal at 0.78 Ma. Our findings, coupled with other records, indicate the flourishing of early humans in mainland East Asia during the Mid-Pleistocene climate transition (MPT). This suggests that early humans were adapted to diverse and variable environments over a broad latitudinal range during the MPT, from temperate northern China to subtropical southern China.

Magnetostratigraphic study of the Melka Kunture archaeological site (Ethiopia) and its chronological implications

A magnetostratigraphy is established for the Melka Kunture archaeological site of Ethiopia, whose chronological setting needed improvement. The magnetostratigraphy is constructed from four distinct stratigraphic sections, Garba-IV (5 sites), Gombore-I (21 sites), Gombore-II (8 sites), and Simbiro (13 sites). Natural remanent magnetizations (NRM) were measured and analyzed over a total of 214 specimens to isolate the characteristic components of magnetization and determine magnetic polarities. Two magnetization components were isolated in every sample analyzed: (i) a low-temperature (low coercivity) secondary normal component and (ii) a high-temperature characteristic component of normal or reversed polarity and allows to identify five magnetozones (N1–R1–N2–R2–N3). Rock magnetic analysis attests that the magnetization is carried by magnetite or titanomagnetite within the range of pseudo-single domain grain sizes. Anisotropy of magnetic susceptibility (AMS) supports a sedimentary origin of the magnetic remanence. Based on recent 40Ar/39Ar geochronological dating of the site, faunal constraints and a magnetostratigraphic pattern, the sequence is correlated to the time between the early Matuyama chron (<1.80 Ma) and early Brunhes chron (∼0.709 Ma) of the geomagnetic polarity time scale (GPTS). Completing recent 40Ar/39Ar age series, the magnetostratigraphy study presented here allows computation of interpolated ages for various faunal and artifact findings at Melka Kunture and similar fossiliferous deposits in the region.

Magnetostratigraphy of the Qiliting section (SE China) and its implication for geochronology of the red soil sequences in southern China

SUMMARY The red soil sequences in southern and southeastern China provide important terrestrial archives of palaeoclimate and palaeoenvironment and are important sources of Palaeolithic settlements and, therefore, early human occupation. Here we present detailed palaeomagnetic investigation coupled with mineral magnetic and petrographic analyses of a red soil sequence at Qiliting, southeastern China. The sediments contain both strongly magnetic minerals (such as maghemite and magnetite) and weakly magnetic minerals (such as haematite and possibly goethite). Maghemite and haematite were identified as the main carriers of the natural remnant magnetisations. Only haematite dominates the characteristic remnant magnetisations. Palaeomagnetic findings suggest that the Qiliting sedimentary sequence recorded the early Brunhes Chron and the late Matuyama Chron, including the Jaramillo Subchron. Our finding, coupled with previously published magnetostratigraphy, establishes that the red soil sequences in southern China began to accumulate no later than the Jaramillo age (i.e. ∼1.0 Ma). It is further suggested that the capabilities of recording magnetic polarity stratigraphy in Chinese red soil sequences are variable between areas because of different climate regimes.

Magnetochronology of the Feiliang Paleolithic site in the Nihewan Basin and implications for early human adaptability to high northern latitudes in East Asia

We present a new magnetostratigraphic dating of the Feiliang Paleolithic site in the Nihewan Basin, northern China. Partially‐oxidized magnetite and hematite were identified as the main carriers for the characteristic remanent magnetizations of the fluvio‐lacustrine sediments. Paleomagnetic results suggest that the sequence recorded the very early Brunhes chron and the upper Matuyama chron, including the Jaramillo subchron. The Feiliang artifact layer was determined to be within the pre‐Jaramillo Matuyama chron, with an estimated age of ca. 1.2 Ma. Our finding, coupled with previously published magnetochronology, strongly indicates a prominent early human flourishing in the high northern latitudes of East Asia during or just prior to the Mid‐Pleistocene climate transition.

Paleomagnetism of the Datong monogenetic volcanoes in China: paleodirection and paleointensity during the middle to early Brunhes Chron

Abstract Paleomagnetic measurements were conducted on Datong volcanic rocks from China, which are thought to have formed in the mid to early Brunhes Chron. Meaningful site-mean paleodirections were obtained from 21 sites which are considered to represent 17 independent cooling units. They give a mean VGP (virtual geomagnetic pole) position of (76.5°N, 7.9°E) with A95=7.7° (N=17), which is statistically distinct from geographic north. This dataset also yields an ASD (angular standard deviation) of 17.2° around the mean VGP position. Because the paleodirections form two clusters, the samples may record the paleomagnetic field during two different short periods and therefore may not average out paleosecular variation. Paleointensity measurements were conducted using three different methods. The DHT and LTD-DHT Shaw methods, the Thellier method, and the microwave Thellier method were applied to 119, 29 and 73 specimens respectively, and they give 66, 16 and 12 successful results (success rates are 55, 55 and 16%). From the LTD-DHT Shaw dataset, eight acceptable site-mean paleointensities are obtained. They give an average VDM (virtual dipole moment) of 3.79±1.94x 1022 A m2. This is 56% lower than the average VDM of 5.91±1.74x 1022 A m2 (N=14) calculated from the selected Thellier data from the latest paleointensity database using the same criteria. One possible reason for this difference might be systematic overestimations of paleointensities by the Thellier method on volcanic rocks.

Paleomagnetic dates of hominid remains from Yuanmou, China, and other Asian sites.

Two hominid upper central incisors found in the Yuanmou Basin in southwest China in 1965 have affinities with Homo erectus fossils from Zhoukoudian, but exhibit primitive features. The Yuanmou hominid remains are alleged to be coeval with or older than African specimens dated at about 1.8 m.y.a. Recent age refinements of geomagnetic short reversal events and excursions permit assigning the Yuanmou hominid-bearing bed to the early Brunhes chron (about 0.7 m.y.a.). Magnetochronological assessments confirm that the Lantian calotte which has been dated to about 1.2 m.y.a., is the oldest reliable evidence for the emergence of Homo in eastern Asia as well as China, and that hominid fossils from Sangiran and Mojokerto, Java, do not exceed 1.1 Ma in age. These results refute the view that the genus Homo migrated into eastern Asia in the late Pliocene or the earliest Pleistocene.

Lithostratigraphy and depositional history of the Late Cenozoic hominid-bearing successions in the Yuanmou Basin, southwest China

Late Cenozoic strata bearing hominids and hominoids are distributed in the Yuanmou Basin, Yunnan, southwest China. Incisors of Homo erectus discovered in these strata in 1965 reportedly show primitive features known in Africa (Hu, Acta geologica sinica 1 (1973, p. 65). However, recent paleomagnetic study has revealed that the age of the hominid correlates to the early Brunhes chron (Hyodo et al., Journal of human evolution (2001), submitted). The lithostratigraphy of the successions that yield many mammalian fossils including those of the hominid, and the record of Equus is re-examined. The successions are divided in ascending order into the Longchuan, Shagou, Gantang (newly proposed Yangliuchun and Daipojing Members) and Yuanmou (newly proposed Dainawu and Niujianbao Members) Formations, based on different lithology and sedimentary facies. The newly proposed depositional systems of the formations are in ascending order, alluvial fan, ephemeral braided river, sandy braided river, ephemeral gravelly braided river and alluvial fan systems. The change in facies and paleocurrents revealed in the successions suggest that the basin was initiated as a syncline basin at ca 3.5 Ma and was completed as an asymmetric half graben by active movement of the eastern marginal fault in the early Middle Pleistocene.

Paleomagnetic evidence for multiple Late Pliocene - Early Pleistocene glaciations in the Klondike area, Yukon Territory

The Late Pliocene - Early Pleistocene terraces of the Klondike area provide a conformal record of sedimentation which marks the transition from preglacial to glacial conditions, and is one of the most complete records of glaciation and interglaciation in the northern Cordillera. Preglacial sedimentation is recorded in the Lower White Channel gravel that contains a reverse-normal polarity sequence. A re-aggradation of the nonglaciated valleys of the goldfields in response to Late Pliocene cooling is recorded by the Upper White Channel gravel, which is characterized by a dominant normal polarity with a lower reversal likely associated with the first ice-wedge casts. Klondike gravel interfingers with Upper White Channel and is normally magnetized, indicating an equivalent magnetostratigraphic unit. This glaciofluvial gravel provides evidence of extra-basinal clasts, marking a major reorganization of drainage associated with the first advance of the Cordilleran Ice Sheet in western Yukon Territory correlated with the Gauss chron (&gt;2.58 Ma). An intermediate terrace in Klondike valley is overlain by 8 m of fluvial and glaciofluvial gravel named the Midnight Dome gravel. This gravel is mantled by 15 m of loess and hillslope deposits, named the Midnight Dome loess, which preserve at least three interglacial pollen assemblages, and a reverse-normal-reverse-normal polarity sequence assigned to the late Matuyama chron, including Jaramillo subchron (1.07-0.99 Ma), and early Brunhes chron (&lt;0.78 Ma). The oldest glaciations here, based on the preferred interpretation, extend well into the Pliocene (&gt;2.58 Ma) making these among the oldest glacial sediments in North America.

Magnetostratigraphy of Plio-Pleistocene sediments in a 1700-m core from Osaka Bay, southwestern Japan and short geomagnetic events in the middle Matuyama and early Brunhes chrons

A magnetic polarity stratigraphy spanning more than the past 3.2 Myr was determined for a long 1545 m continuous sedimentary sequence of marine, fluvial, and lacustrine deposits from the Osaka Basin, southwestern Japan. Additionally two short geomagnetic reversal events were identified: a short event at about 0.69 Ma lasting for about 7 kyr in the early Brunhes chron around the lower boundary of a marine clay deposited during a period of eustatic high sea level during the marine oxygen isotope stage 17; and another short Matuyama event (1.60–1.58 Ma) correlated with Stage 54 event, and the early stage of the Sangiran Excursion. Accumulation rate was 0.3–0.4 mm/yr from 3 to 2 Ma, and then increased by about 50% with a rate of 0.51 mm/yr during the Olduvai subchron. High values of >0.59 mm/yr were maintained from the Upper Olduvai boundary to the Brunhes–Matuyama boundary (from 1.77 to 0.78 Ma), with a peak at 0.74 mm/yr during the Jaramillo subchron. These changes in accumulation rate probably reflect the history of tectonic subsidence of the drilling site. The magnetic polarity stratigraphy provides a chronological framework for sedimentological, paleoenvironmental, tephrochronological, and tectonic studies of the Osaka Basin.

Magnetic stratigraphy of the Siwalik group, Bhittani, Marwat and Khasor ranges, northwestern Pakistan and the timing of neocene tectonics of the Trans Indus

Nine stratigraphic sections in the Siwalik Group, three from the Bhittani Range, five from the Marwat Range, and one from the Khasor Range, were measured and sampled for magnetostratigraphic studies. Progressive alternating field and partial thermal demagnetization of samples indicated the presence of two components of magnetization. These are a secondary component of low coercivity, which can be removed by alternating field demagnetization in fields up to 40 mT and/or temperatures to 400°6, and a stable primary component of magnetization which has blocking temperatures above 450°C. Therefore all samples were subjected to blanket demagnetization at 450°C and 500°C, and some to temperatures up to 600°C. Positive fold tests from the Bhittani and Marwat ranges indicate the successful isolation of a prefolding characteristic direction of magnetization. A magnetic polarity reversal sequence for each of the sampled sections is determined and correlated to the magnetic polarity time scale utilizing a fission track date and fauna from the sequences which have previously been shown correlated to the magnetic polarity time scale. This correlation shows that the Siwalik Group in the area of study ranges in age from the late Gilbert chron to the early Brunhes chron (about 0.5 m.y. B.P.). Deposition of the thick sandstone units of the Siwalik Group in the Marwat Range began at least by Gauss chron time. The correlation of observed magnetic polarity stratigraphy, of the Khassor Range, with the standard magnetic polarity time scale shows that the Siwalik Group of this area ranges in age from the early Gauss chron (about 3.2 Ma) to the Brunhes chron. The region of this study began to subside prior to 4 Ma and subsided at a rate of from 60 to 100 cm per 1000 years. The tectonism of the region began within the last 1 m.y. and may well be synchronous with folding in the Pabi Hill anticline on the other limb of the syntaxis near Jelum. This orogeny is therefore one of the world's youngest and is undoubtedly still in progress.