Tephra studies of Toba super-eruptions: implications for climate
change and human evolution
CHANG-HWA CHEN and tephra study team
Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan
The Toba Caldera is located in northern Sumatra, Indonesia.
The tectonic
regime of Sumatra area is the Indian-Australian Plate under the Southeast-Asian Plate
by the oblique low-angle subduction.
The Toba volcanism illustrates special
phenomenon of both island and continental arc (Rock et al., 1982). The Youngest
Toba Tuff (YTT) and Oldest Toba Tuff (OTT) eruptions in the Toba Caldera, ca. 75
Ka and 790 Ka, were considered as two of the largest known eruptions (Rose and
Chesner, 1987, Song et al., 2000; Lee et al., 2004; Chen et al., 2004). Thus, Toba
supereruptions can provide some natural criteria to testify the hypothesis of the
volcanic supereruption triggered the long-term climate change. However, the YTT
eruption has been postulated for as the trigger of the large-scale glaciation (Rampino
and Self, 1992), which occurred the last interglacial stage. On the contrary, the OTT
eruption happened with the transition from a glacial stage to an interglacial stage.
revealed an opposite effect.
It
Accordingly, the correlation of the supereruption with
any effect on Quaternary climate remains lots of unknown.
Volcanic ash is one of the best materials to preserve the Archaeological record,
and more then, the special characteristic of ash can be treated as the clue to infer the
age of archaeological stuffs. The Acheulian artifacts of the Paleolithic civilization
were wildly found with the tephra deposits in the Peninsular India. The locality of
the Peninsula India stands at the vital point of human migration from Africa to Asia
and Australia. Therefore, the study of human activities in the Peninsula India will
significantly improve the understanding of human evolution.
After numerous papers
for discussion, the tephra sources across Peninsular India with the Paleolithic tools
were definitely postulated as the Youngest Toba Tuff (YTT) eruption about 75 Ka
(Westgate et al., 1998).
However, it still leaves the impenetrable concerning from
the geological, dating, and archaeological viewpoints. When the tephrostratigrphy
and tephrochronlogy of tephra layers in the ODP 758 core in the India Ocean were
revised (Chen et al., 2004), it raised more contradictions in terms of the source
argument of tuff in the Peninsula India.
Based on recent results in the chemical and
isotopic compositions of volcanic tephra in Indian Ocean and the inland materials of
the Toba eruptions, the tephra sources in the Peninsula India can be clearly identified
from the OTT eruption with the special finger prints of the chemical compositions of
mineral crystal and isotopic values of glasses.
The tephra deposits in above place
can be considered as the synchronous event with the OTT eruption about 0.8 Ma,
instead of the former of the YTT eruption around 75 Ka. This discovery proved that
the human Acheulian civilization in the Peninsula India could be traced back at least
0.8 Ma. From the thickness and distribution of the OTT deposits in the Peninsula
India and Sumatra, there was a serious cataclysm in Sumatra and Peninsula India.
It
could be cogitated as the reason why Homo erectus eastward overcame the natural
barrier Movius’s line to Asia and southeastward floated over the biological Wallace’s
line to the Floors Island, Indonesia around 0.8 Ma.