respectively) and were identified as Aso-4 shards. Two points had
abnormally low Na2O contents (both <3.50 wt.%), and one point
had an abnormally low SiO2 content (63.28 wt.%). As a cross-check
of this proposed correlation, tephra Aso-4 was sampled at
39.123162N, 140.987492E (Watanabe, 1991; Matsu'ura et al.,
2008). The shard chemistries of spike G3 and Aso-4 are similar,
and no other correlative of Aso-4 is found in the literature. Thus, we
consider them to be correlated.
Spike G4 (61.35e61.55 mbsf, early MIS 5) included 2263e2804
shards. It corresponds to the “pumice with sandy silt sized vitric ash
layer” of Aoike (2007). Its shards had low FeO* (total iron expressed
as FeO) (average 0.91 wt.%), low CaO (average 0.43 wt.%), high Na2O
(average 4.50 wt.%), and moderate K2O (average 2.98 wt.%) contents.
One point had an abnormally high K2O content (4.23 wt.%).
Spike G5 (75.40e75.60 mbsf, late MIS 6) included 1966e2055
shards. It roughly corresponds to the “silt sized pumiceous ash
layer” of Aoike (2007). Its shards had low K2O content (average
1.29 wt.%).
Spike G6 (97.26e97.36 mbsf, latest MIS 7) included 2636 shards.
It corresponds to the “lithic grain bearing sandy silt with glass and
ash layer” of Aoike (2007). Its shards had a wide range of K2O
contents, indicating contamination from various sources.
Spikes G7 and G8 (102.31e102.59 mbsf and
102.71e102.81 mbsf, late MIS 7) included 2740e2839 and 1786
shards, respectively. They correspond to the “silty clay with pumice
and glass shards” of Aoike (2007). Their shards were similar with
high FeO* (averages 2.70 and 2.71 wt.%, respectively), high CaO
(averages 2.75 and 2.80 wt.%, respectively), and very low K2O
contents (averages 0.84 and 0.85 wt.%, respectively). In spike G8,
two points had abnormal K2O contents (1.44 and 4.68 wt.%) and
one point had abnormally high SiO2 content (78.52 wt.%).
Spike G9 (108.91e109.51 mbsf, MIS 7) included 1591e2752
shards. It corresponds to the “coarse sand to granule sized pumice
layer,” about 50 cm thick, of Aoike (2007). The spike was stratigraphically
thicker than others and accompanied a spike in heavy
mineral (orthopyroxene) grains, indicating that it originated from a
nearby volcano. It had low K2O content (average 1.47 wt.%). One
point was abnormal with a moderate K2O content (2.50 wt.%).
Spike G10 (116.15e116.25 mbsf, MIS 7) included 2954 shards. It
corresponds to the “vitric clayey silt layer” of Aoike (2007). It had
moderate K2O content (average 2.71 wt.%).
Spike G11 (117.12e117.32 mbsf, MIS 7) included 1610e2153
shards. It corresponds to the “vitric clayey silt layer” of Aoike
(2007). It had low Al2O3 (average 11.54 wt.%) and very low K2O
contents (average 0.98 wt.%). Three points had abnormally high
K2O content (>2.42 wt.%).
Spike G12 (139.32e139.41 mbsf, MIS 7) included 2660 shards. It
corresponds to the “silty clay layer” of Aoike (2007) and had no
indication of an ash layer. It had very high Na2O (average 5.56 wt.%)
and K2O contents (average 6.11 wt.%), and one point had abnormally
low Na2O content (4.84 wt.%) and high K2O content
(6.74 wt.%).
Spike G13 (141.62e141.72 mbsf, MIS 7) included 1684 shards. It
corresponds to the “glass-bearing clayey silt layer” of Aoike (2007)
and had no indication of an ash layer. It had very high Na2O
(average 5.56 wt.%) and K2O contents (average 6.16 wt.%). Two
points had an abnormally low K2O content (both 1.55 wt.%).
Spike G14 (154.16e154.26 mbsf, MIS 7) included 2599 shards. It
corresponds to the “pumiceous ash” of Aoike (2007). It had moderate
K2O content (average 2.41 wt.%).
Spikes G15 and G16 (169.52e169.72 mbsf and
179.93e180.03 mbsf, MIS 8) included 2079e2907 and 1898 shards,
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