Depositional processes of reworked tephra from the Late Pleistocene Youngest Toba Tuff deposits in the Lenggong Valley, Malaysia

Abstract

Two fundamental issues for tephrostratigraphic work are the differentiation of primary from reworked tephra and the characterization of reworking mechanisms. We study the depositional processes of four deposits of Youngest Toba Tuff in the Lenggong valley, Malaysia. We focus on site stratigraphy, particle-size distributions, magnetic susceptibility and mineralogical associations. Reworked tephra display variable sedimentological characteristics including polymodal and unimodal, very fine to coarse-grained distributions, and variable concentrations of ash. Particle-size distributions from this study are similar to published analyses for primary deposits, demonstrating that particle size alone cannot distinguish primary from secondary tephra. The tephra sequences are associated with fluvial and colluvial deposition. Three facies are identified: flood flow, mudflow and slumping. The ash accumulated rapidly, over a period of a few days to months. In this valley the ideal site for paleoenvironmental reconstructions is Kampung Luat 3, where ash accumulated at least in two distinct phases. Despite the rapid accumulation, the Lenggong sites are not well-suited for paleoenvironmental studies of the YTT impact. The time lag between the primary deposition and the floods is unknown and the records could have been modified by site-specific characteristics. Such variables should be considered when proposing paleo-environmental reconstructions based on reworked tephra.

Regional stratigraphy and human occupation of the upper Susitna River basin, central Alaska Range

“…(Table ). Sediment sample 8 from the C2 A/Eb2‐horizon was analyzed at ×20–40 under a dissecting microscope and consists of 10–20% tephra and 80–90% sand, suggesting it is a reworked tephra deposit (Gatti et al, ). This contrasts with sediment samples 6, 7, and 9, which have ~1% small, weathered pumice fragments suggesting they were translocated from overlying tephra horizons.…”

The Application of Market Appeal-Robusticity Matrix: A Case Study of the Archaeological Heritage of Lenggong Valley, Perak, Malaysia

“…The assessment of cultural significance suggests that Bukit Sapi area has high historical, educational and scientific values, and has considerable aesthetic and social values. Its educational, historical and scientific values are significant to the catastrophic events, the Toba mega-colossal eruption dated by optically stimulated luminescence (OSL) to at least 70,000 years ago, had mingle its volcanic ash with the lithic artefacts recovered at AHLV especially at Kota Tampan and this mixture has suggested the 74,000-year date for the lithic workshop sites here (Gatti et al, 2013). The excavation work at Kota Tampan in 1987 proved to be a rare and thus significant in-situ workshop from the Palaeolithic period whose cause and date of abandonment are known (Zuraina, 1989).…”

Multi-proxy indicators in a Pontocaspian system: a depth transect of surface sediment in the SE Caspian Sea

“…Its presence nevertheless shows that the sampling site is within the catchment of one or more volcanic systems, and that therefore potential to apply tephrochronology in this area exists. Primary airfall deposits in a sedimentary sequence can be distinguished from background detrital material using absolute abundances, morphology and geochemical analyses of shards (Gatti et al, 2013).…”