Indonesia Conference Directory

Events in Southeast Asia Surrounding the Brunhes-Matuyama Reversal Jason Herrin1,2,a), Brian Jicha3, Brad Singer3, Marcus Phua4, Kyle Bradley4,1 1Earth Observatory of Singapore, Nanyang Technological University, 50 Nanyang Ave, Block N2-01a-15, Singapore, 639798 2Facility for Analysis Characterisation Testing and Simulation, Nanyang Technological University, 50 Nanyang Ave, Block N2-01a-15, Singapore, 639798 3Department of Geoscience, University of Wisconsin-Madison, 1215 W Dayton St, Madison, WI, 53706 4Asian School of the Environment, Nanyang Technological University, 50 Nanyang Ave, Block N2-01c, Singapore, 639798 a)Corresponding author: jsherrin@ntu.edu.sg Geomagnetic reversals are among the most enigmatic of recurring events in the geologic record. The short duration of reversals with respect to geologic time makes deciphering the precise sequence of events relating to reversals challenging. High-precision geochronology is an important tool for studying these events. Accurate and precise ages are critical for regional or global correlation of events recorded in sediments and lavas. The Brunhes-Matuyama reversal The Brunhes-Matuyama (B-M) reversal is the most recent full reversal of the Earth-s magnetic field and is thus the most accessible in the geologic record. The final full reversal of the Earth-s magnetic field at 772 ka was the culmination of a series of field irregularities lasting 22,000 years [1]. It is the only reversal for which modern geochronologic methods have sufficient precision to discriminate between events within the timespan of the reversal and relevant precursor events. Like all reversals, its causes and effects remain poorly understood. Study of events surrounding this reversal is pursued across multiple disciplines, as it coincides with the Early-Middle Pleistocene transition, a profound shift in global climate dynamics linked to changes in Earth-s orbital motions [2,3]. Minor extinctions [4], multiple asteroid impacts [5,6], a surge in solar and cosmic radiation, several major volcanic eruptions, and some localized hominid transition periods [7,8] are also broadly coincident with the B-M reversal. In this presentation, we will explore events recorded in the geologic record of southeast Asia that occurred in the run-up to reversal, during what appears to have been an eventful period of geologic time. Volcanic eruptions The importance of volcanic eruptions to the study of reversal processes is twofold. Firstly, explosive eruptions can generate widespread tephra, providing finite, datable stratigraphic markers. Secondly, thermoremanent magnetization preserved in lava flows and welded tuffs can lock in timestamped “snapshot” recordings of the orientation and intensity of the magnetic field at the moment of eruption, without the convolution effects commonly seen in the sedimentary record. These empirical data guide modeling of geodynamo activity and reversal processes. Gaseous decay product dating sche