Magnetic stratigraphy constraints on the Matuyama–Brunhes boundary recorded in a loess section at the southern margin of Chinese Loess Plateau

Abstract

S U M M A R YAlthough the Matuyama-Brunhes boundary (MBB) in the Chinese Loess Plateau (CLP) is very important in reliably correlating Quaternary loess with other sediments in the world, particularly with marine and polar ice cores, its exact stratigraphic position remains controversial. Previous investigations usually placed the MBB between paleosol unit S8 and loess unit L8 in various locations. To better understand the spatial differences in the MBB position, a high-resolution paleomagnetic study was conducted in a loess section of the Lantian Basin at the southern margin of the CLP. The results show that the MBB is situated in the middle of the relatively weak paleosol unit S7, consistent with a recent report on the MBB based on a 10 Be study from the Xifeng and Luochuan loess sections of the central CLP. However, the regional anomalously low magnetic susceptibility in paleosols S7 and S8 indicates that it is more reliable to determine the paleoclimate boundaries between loess and paleosol horizons of this segment with median grain size. Then, the MBB in the Yushan section can be correlated with the bottom of paleosol S7, corresponding to the older part of interglacial marine isotope stage 19. This result temporally reconciles the striking discrepancy of the position of the MBB recorded in between loess and other typical sedimentary sequences, and further confirms that the stratigraphic position of the MBB could spatially vary to a certain extent due to regional sedimentary or paleoclimatic conditions in the marginal areas of the CLP. In the Yushan section, the high-frequency variations of paleomagnetic directions during a long period of ∼31 ka before the MBB, however, could not be attributed to a genuine response to the true geomagnetic behaviour. Moreover, the climate offset defined by the magnetic susceptibility and median grain size of the section can be preliminarily attributed to the regional geology and paleoenvironment background. A multiproxy-based stratigraphic division is considered very necessary when paleomagnetic and climatic boundaries are defined exactly in a specific area of the southern CLP.

Deepwater circulation variation in the South China Sea since the Last Glacial Maximum

“…Low‐field magnetic susceptibility ( k ), magnitude and the direction of the anisotropy of magnetic susceptibility (AMS), saturated isothermal remanent magnetization (SIRM), anhysteretic remanent magnetization (ARM), and characteristic remanent magnetization (ChRM) analyses were measured according to Wu et al . [].…”

“…Paleomagnetic samples were prepared using a standard 2 × 2 × 2 cm plastic cube at 2 to 4 cm intervals (total 100 samples) along a fiducial line that was drawn prior to sampling. Low-field magnetic susceptibility (k), magnitude and the direction of the anisotropy of magnetic susceptibility (AMS), saturated isothermal remanent magnetization (SIRM), anhysteretic remanent magnetization (ARM), and characteristic remanent magnetization (ChRM) analyses were measured according to Wu et al [2016].…”

Characteristics of the Matuyama‐Brunhes Magnetic Field Reversal Based on a Global Data Compilation

“…Paleomagnetic data that have been reported from deep-sea sediments, shallow-sea sediments, and lake sediments (including lacustrine deposits) are only considered during data compilation. We do not use paleomagnetic data reported from Loess deposits, because doubts have been raised about the ability of these sediments to record the magnetic field signal during reversals (Wang et al, 2014;Wu et al, 2016;Zhou et al, 2014).…”

“…Paleomagnetic data that have been reported from deep‐sea sediments, shallow‐sea sediments, and lake sediments (including lacustrine deposits) are only considered during data compilation. We do not use paleomagnetic data reported from Loess deposits, because doubts have been raised about the ability of these sediments to record the magnetic field signal during reversals (Wang et al., 2014; Wu et al., 2016; Zhou et al., 2014). Regarding RPI data, we accept bulk magnetic properties, magnetic susceptibility (MS), anhysteretic remanent magnetization (ARM), and isothermal remanent magnetization (IRM), as normalization factors.…”

Early–Middle Pleistocene Magnetostratigraphic and Rock Magnetic Records of the Dolynske Section (Lower Danube, Ukraine) and Their Application to the Correlation of Loess–Palaeosol Sequences in Eastern and South-Eastern Europe

“…Of the chronological approaches, magnetostratigraphic studies provide the key absolute time control for the loess-palaeosol deposits. The Matuyama-Brunhes boundary (MBB), the last geomagnetic field reversal, related to marine isotope stage (MIS) 19 and dated at ~780 ka [141,142] (or 773 ka according to recent data [143]), is one of the most frequently used time markers in the Quaternary stratigraphy [144][145][146][147][148][149][150][151][152]. The determination of the MBB allows for correlating even remote loess-palaesol sequences regardless of their lithostratigraphic subdivision.…”