Magnetostratigraphy and relative paleointensity study of a late Quaternary lacustrine sediment sequence from Southwest China and its chronological significance

Abstract

Long and continuous lacustrine sedimentary sequences from southwest (SW) China is an excellent material for research on the evolution of the Indian summer monsoon (ISM). However, well-dated research spanning periods exceeding 50 ka in the late Quaternary remains scarce because of the limited dating range of the 14C method. Therefore, we collected a 33.9-m long lacustrine sedimentary core (PT2) from SW China for a chronology study in the late Quaternary using geomagnetic excursion (GE) and relative paleointensity (RPI) correlation. This study will improve our understanding of the dynamics and evolutionary rules of the ISM. Detailed rock magnetic analyses showed that single domain- and vortex-state magnetite (and/or maghemite) dominated the magnetic properties in moderate and strong magnetic intervals. Moderate variations in concentration-dependent (SIRM, ARM) and grain size-dependent (ARM/SIRM) parameters satisfied the criteria for RPI research. Consequently, we present the magnetostratigraphy and RPI record of the PT2 lacustrine sedimentary core based on stepwise alternating field demagnetization. Five GEs were identified by at least three continuous reversed inclinations. Using the radiocarbon dating results as constraints, we identified the Hilina Pali, Mono Lake, and Laschamp excursions. By proxy correlation with the adjacent sedimentary core, an age tie of 140.07 ka was obtained. Subsequently, four RPI lows matched the NRM/ARM troughs in the adjacent HQ2002 drill core according to their synchronous changes. Based on the age ties above, post-Blake and Blake excursions were identified. Accordingly, three RPI lows were correlated with troughs in the global target curve PISO-1500 between 60 and 100 ka. Using AMS 14C dates, proxy-matched ties, magnetic excursions, and RPI correlation ties as constraints, we established an age-depth model of the PT2 lacustrine sequence since ∼184 ka.