| The plate tectonic setting of Indonesia is complex, and catastrophic geologic events have likely been plentiful. Event deposits induced by those catastrophic events have been widely preserved in sediments of the land and seabed. The deep-sea basin in this region is mainly documented by pelagic and himipelagic sedimentation. So the sedimentation rate of the deep-sea basin is relatively low. Thus, it can be served as an ideal situation to the long-term research on sedimentary events.Based on existing research, this paper is done to systematically analyze the sedimentary sequences of the core IR-GC1from abyssal sediments off Indonesia, recognize the sedimentary events recorded in the sediments, and discuss their trigger mechanism.Through comprehensive analysis, results obtained as follow:The sediment is mainly composed of clayey silt and clay-silt-containing sandy mud. The lithology, grain size and element geochemistry in the vertical direction changes significantly, suggesting that the sedimentary environment have occurred mutation.The age model for core IR-GC1was established mainly by oxygen isotope stratigraphy. Additional age markers, such as the last appearance datum (LAD) of pink-pigmented Globigerinoides ruber (127ka BP) and the occurrence of Younger Dryas cooling event (12.68-11.59ka BP), were also used for age control. Hence, the base of core IR-GC1was determined to ca.136ka. The average sedimentation rate was1.23cm/ka. Four period of relatively rapid deposition, respectively, occurred in90.1-82.Oka,75.0-70.9ka,54.8-50.4ka, and20.0-11.6ka. A sedimentary hiatus occurred in118-109ka, which is related to the erosion by turbidity current.Using the mutation of particle size characteristics as the main indicator, seven deep-sea turbidite layers can be clearly identified, corresponding to seven deposition events occurred in130-128ka,107-105ka,100-98ka,87-86ka,53-50ka,41-37ka, and 29-20ka respectively. The total thickness of the turbidite layers up to28cm, which is about30%of the core length. Deep-sea turbidite deposition is characterized by coarse grain size, poor sorting, wide kurtosis, bimodal frequency curve, and deposition mutation. In addition, particle size classification is also an important feature of deep-sea turbidite deposition, which can be used as an indicator to identify the turbidite layer.Three volcanic ash layers were identified from core IR-GC1. They were dominated by glass shards with minor mineral crystals, such as plagioclase, biotite, and hornblende. According to the morphology and major element compositions of the representative glass shards, we suggest that ash layer A is correlated to the youngest Toba Tuff (YTT,80-76ka). Layer B is thought to be a basal part of layer A and could be the result of reworking of the sediments by slumping, bottom currents, or bioturbation. Ash layer C bear different geochemistry characteristics of layers A and B suggesting it was not originated from Toba but recorded another eruption event of high-silica rhyolite in the region. In addition, SiO2/A12O3and K2O/A12O3ratio can be used as a marker for acid volcanic ash deposition events.Over the past136ka, turbidite deposition events occurred frequently in deep-sea off Indonesia. The possible trigger mechanism including tsunamis, earthquakes, volcanic eruptions and sea-level change. |
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