Journal of Geophysical Research – Solid Earth
Supporting Information for
Penultimate Predecessors of the 2004 Indian Ocean tsunami in Sumatra: Stratigraphic,
Archeological and Historical Evidence
Kerry Sieh,1* Patrick Daly,1,2 E. Edwards McKinnon,3 Jessica E. Pilarczyk,1,4,5 Hong-Wei
Chiang,1 Benjamin Horton,1,4,5 Charles M. Rubin,1 Chuan-Chou Shen,6 Nazli Ismail,7
Christopher H. Vane,8 and R. Michael Feener9
1
Earth Observatory of Singapore, Nanyang Technological University, 50 Nanyang
Avenue, Singapore 639798
2
University Scholars Programme, National University of Singapore, University Town, 18
College Avenue East, Singapore 138593
3
Institute of Southeast Asian Studies, Nalanda-Srivijaya Project, Archaeology Unit, Heng
Mui Keng Terrace, Singapore 119614
4
Institute of Marine and Coastal Science, Rutgers University, New Brunswick, NJ
08901, USA
5
Institute of Earth, Ocean, and Atmospheric Sciences, Rutgers University, New
Brunswick, NJ 08901, USA
6
Department of Geosciences, National Taiwan University, No. 1, Sec. 4, Roosevelt Rd.,
Taipei 10617, Taiwan, Republic of China
7
Department of Physics/Geophysics, Faculty of Mathematic and Natural Sciences, Syiah
Kuala University, Jalan Syech Abdurrauf, Darussalam - Banda Aceh 23111,
Indonesia
8
British Geological Survey, Centre for Environmental Geochemistry, Keyworth,
Nottingham, NG12 5GG, UK
9
Asia Research Institute, National University of Singapore, Singapore
*Corresponding author: sieh@ntu.edu.sg
Contents of this file
Text S1 to S30
Figures S1.1 to S4.2
Tables S2.1 to S5.7
Additional Supporting Information (Files uploaded separately)
Figure S1.6
1
Introduction
We investigated two seacliff exposures (Lhok Cut and Lubhok Bay Beach) along
the Lamreh Peninsula (Figure 1). At the Lhok Cut site, we found archeological deposits
capped by a tsunami deposit that arrived from the sea. At the Lubhok Bay Beach site, we
found two tsunami deposits within a small alluvial fan. This Supporting Information
comprises observations and analyses that help substantiate our claims in the paper.
1.
Images
1.1 Lhok Cut site
Figure S1.1. Overhead view of the lime-plaster floor and one of the postholes that
pierces it in the seacliff exposure.
2
Figure S1.2. Photographs of the mapped Lhok Cut seacliff exposure. The lower photo
shows nearly the entire mapped exposure, for comparison with Figure 4 in the main text.
The upper photo is a close up of the cobbly destruction layer that overlies the lime-plaster
floor in the seacliff exposure. The large cobbles are Porites sp. coral.
3
A
B
Figure S1.3. Overhead views of the lime-plaster floor in the square and rectangular
excavations into the earthen mound (Fig. 3). Note the window into the underlying stone
foundation in the lower left of the square excavation. Small Porites sp. boulder resting on
the lime-plaster floor in the middle of the lower photo may have been emplaced by a
tsunami. Width of both excavations is about a meter.
4
Description of units exposed in excavation of the earthen mound
EM 1: Uppermost (about 0.10 m thick) rich soil layer, high organic content and heavily
bioturbated. Contains a mix of stone fragments, shells, a few residual ceramic sherds and
modern debris. Contemporary ground surface is in an area of current human activity.
EM 2: Underlying the modern ground surface (about 0.50 m thick) is a brown, friable
sandy soil that has a poorly sorted matrix with fragments of charcoal, animal bone,
earthenware and stoneware ceramics, and fragments of iron. Abundant stones (ranging up
to 0.5 m in diameter) that are smooth and well-rounded. Although poorly articulated, it
seems likely that the stones were part of a structure. It is clear from the composition of
the matrix that this layer was a cultural construction.
EM 3: Loosely compacted brown sandy soil (about 0.20 m thick) with coarse sand and
about 20% small limestone fragments and occasional large rounded stones. Cultural
material both includes both earthenware and stoneware ceramics, animal bone fragments,
metal, and glass fragments. It is clear from the composition of the matrix that the layer
was a cultural construction, although lacking any indication of structure. Midden
material may be the fill for the structure.
EM 4: Loosely compacted greyish-brown sandy soil (about 0.45m thick). The color of
the soil lightens downward through the unit. Limited fragments of ceramics and larger
stones (mostly concentrated in the southeast corner of the trench) and numerous shell
fragments are present within the unit. The matrix is poorly sorted and contains ~20%
small limestone flakes.
EM 5: Highly compacted very fine white lime-plaster deposit with less than 15% small
limestone fragments. No cultural material was found in the unit. We interpret this unit as
a deliberate and constructed deposit, likely serving as a floor or foundation for a
structure. No evidence for post-holes in the area exposed.
EM 6: Layer of limestone and coral blocks packed with coarse lime powder directly
underlying the lime-plaster deposit. No cultural inclusions are present. The excavation
stopped at this layer, but this may well not be the bottom of the sequence. See Figure
S1.4 for photograph of pristine coral cobble from this unit, which was used to date
construction precisely (see Supporting Information, Section 5).
5
Figure S1.4. Uneroded and unweathered large cobble of coral within the openframework stony foundation of the lime-plaster floor beneath the earthen mound. Since
the cobble was plucked alive from the sea just before incorporation into the foundation,
the AD 1366±3.3 U-Th age of the coral dates precisely the construction of the structure.
The long-axis of the cobble is about 20 cm.
1.2 Lubhok Bay Beach site
Figure S1.5. Photograph of a WWII Japanese bunker about 40 m northwest of Lubhok
Bay Beach site exposure (Figure 5). The abandoned track leading to the bunker appears
on the western side of the map. The rounded-boulder foundation of the bunker (black
arrows) fills an excavation dug into pre-bunker alluvium. The dark organic horizon
(white arrows) was the surface of the alluvial fan at the time of construction. The postbunker alluvium thins southward along the seacliff and does not appear in the excavation
that shows the ancient tsunami deposits. View is southward.
6
Figure S1.6. Large annotated photomosaic of the seacliff exposure at the Lubhok Bay
Beach site. See PDF file.
7
2.
Grain-size analysis
2.1 Methods
We conducted grain-size analysis using a Beckman
Coulter laser particle-size analyzer (measures grain sizes
between 0 and 2000 μm) on all bulk sediment samples (~5
cm3) from the Lhok Cut and Lubhok Bay sites (Tables and
Figures S2.1and S2.2, respectively). Prior to analysis, we
removed organics with a solution of 20% hydrogen peroxide,
then rinsed the samples with distilled water and treated them
with sodium hexametaphosphate for 24 hours to disperse
clays (Donato et al., 2009). Grain size values for all samples
are according to the Wentworth-Phi Scale, and descriptions
follow those of Blott and Pye (2001). Mean (average particle
size), mode (dominant particle size), and standard deviation
(degree of sorting) appear in the tables and figures. We also
calculated dominant grain sizes for the 10th (d10), 50th (d50)
and 90th (d90) percentiles, because reporting a range of d
values illustrates well the skewness (non-Gaussian
distribution) of a sediment distribution curve (e.g., fine or
coarse tail) (Blott and Pye, 2001).
2.2 Results
Lhok Cut site
We analyzed samples from the upper four units at the
Lhok Cut seacliff (Table S2.1 and Figure 4).
LC 1: The thin soil that caps the sequence has a matrix of
very poorly sorted (SD = 2.817ɸ) very coarse silt (mean =
4.718ɸ).
LC 2: LC 2 is a man-made earthen ridge. The matrix is a
very poorly-sorted (SD = 3.512ɸ) very fine silt (mean =
3.112ɸ).
LC 3: The matrix of the unit overlying the tsunami deposit is
a very poorly-sorted (SD = 3.430ɸ) very fine silt (mean =
8.413ɸ).
LC 4: The fine-grained matrix of the tsunami deposit
consists of a very poorly-sorted (SD = 2.193 ɸ) clay (mean =
10.330ɸ).
Table S2.1. Grain size data for the Lhok Cut site, including
mean, mode, standard deviation (SD), and d10, d50 and d90
values. Descriptions are based on the mean grain size and
interpreted using the Wentworth-Phi Scale and Blott and Pye
(2001).
8
Figure S2.1. Grain size data
from four stratigraphic layers
above the lime-plaster floor at
the Lhok Cut site.
Sample
localities appear on Figure S1.2.
SD = standard deviation
(sorting).
Lubhok Bay Beach site
We subdivide the strata at the Lubhok Bay Beach seacliff exposure into seven
units (Figure and Table S2.2).
LB 1: Modern sandy soil. No grain size data.
LB 2: Sampled at 47.2 cm below the modern surface, overlies LB 3 with a gradational
contact that has been heavily bioturbated. The matrix of this 15-cm thick bed is similar
9
in grain size (medium silt; mean = 6.834ɸ)
and sorting (SD = 3.318ɸ) to the matrix of
LB 4.
LB 3: LB 3 outcrops discontinuously about
62.5 cm below the surface. Its matrix is a
very poorly sorted (SD = 3.143 – 3.321ɸ)
coarse silt with large coral clasts.
LB 4: Overlying LB 5 is a ~40-cm thick
bed (LB 4), the matrix of which ranges from
a very poorly sorted (SD = 3.143 to 3.053ɸ)
very fine silt (mean = 8.471ɸ to 6.905ɸ) at
its base to a very poorly-sorted (SD =
3.254ɸ) medium silt (mean = 6.396ɸ) at the
top.
LB 5: Lining much of the channel cut into
LB 6 is a ~15-cm thick, black soil (LB 5b)
that shows minor grading from very fine silt
at the base (mean = 7.018ɸ) to clay silt at the
top (mean = 9.72ɸ). Filling the channel is
LB 5a, a framework-supported deposit with
a sparse very poorly sorted (SD = 3.934ɸ)
fine silt (SD = 6.911ɸ) matrix. The bulk of
the stratum comprises abundant coral pebble
clasts.
LB 6: A gradational contact separates LB 7
from LB 6. LB 6 is a 30-cm thick deposit
characterized by a poorly sorted (SD =
1.528ɸ) clay (mean = 10.880ɸ).
LB 7: An analysis of a sample 167.5 cm
below the modern surface shows that the
matrix of LB 7 is a poorly-sorted (SD =
1.769ɸ) medium sand (mean = 1.622ɸ).
Table S2.2. Grain-size data for the Lubhok
Bay Beach site, including lithologic field
descriptions,
mean,
mode,
standard
deviation (SD), and d10, d50 and d90
values. Descriptions are based on the mean
grain size and interpreted using the
Wentworth-Phi Scale and Blott and Pye
(2001).
10
Figure S2.2. Grain size data from eleven sampling intervals within the seven
stratigraphic layers at the Lubhok Bay Beach site. Sample localities are shown in Figure
S1.6. SD = standard deviation (sorting).
11
3.
Foraminiferal analysis
3.1 Methods
We examined four samples from the Lhok Cut site for foraminiferal taxa to
constrain both their ecological provenance and their taphonomy (i.e. surface weathering).
The latter provides information on residence time and transport history. We dried each 510 cm3 sample at approximately 25°C before sieving to recover specimens >63 µm. We
then examined the sample for foraminiferal content using a binocular microscope.
Seven taxa from the taxonomy of Loeblich and Tappan (1987) exist within the
samples. We categorized individual foraminifers using the same taphonomic criteria
defined by Pilarczyk et al. (2011). Pristine specimens are termed “unaltered.” Specimens
with rounded edges are termed “abraded” and those that are pitted are termed “corroded.”
We collected 11 samples from the Lubhok Bay Beach exposure and enumerated the total
number of species and recorded the presence/absence of benthic and planktic species.
3.2 Results
Foraminifera are present in all examined units of both seacliff exposures, but in
varying concentrations. The units of the Lhok Cut site contained higher abundances of
foraminifera than the Lubhok Bay Beach site.
Lhok Cut site
The tsunami deposit at the Lhok Cut site contains very high concentrations of
foraminifera (1160 per 10 cm3). Other layers contain far lower concentrations (40 to 70
foraminifera/10 cm3).
Samples from LC 1 (LBS-11-1 0-5 cm), LC 2 (40-50 cm) and LC 3 (85-95 cm)
contained low abundances of foraminifera (4 to 7 individuals/cm3), and these were
predominantly abraded/corroded. This implies prolonged subaerial exposure (Table and
Figure S3.1). Individuals found in these intervals are likely to have been deposited by
wind.
The sample from the tsunami deposit (LC 4, sample LBS 115-125 cm),
contained a high concentration (1160/cm3) of foraminifera, of which, 44% of these
individuals were taphonomically altered. Fragmented and abraded/corroded specimens
accounted for 31% and 25%, respectively. Subtidal (Amphistegina lobifera, A. lessonii,
Cibicides refulgens, Elphidium craticulatum, Palaeonummulites venosus,) and intertidal
(Ammonia parkinsoniana, Asterorotalia pulchella) species predominated. All but one
species found inhabit shallow (0 - 10 m) depths. However, one species (P. venosus),
which constituted 14% of the assemblage has previously been found to occupy depths
>20 m in Indonesian waters (Cleary and Renema, 2007). The relatively high abundance
of unaltered P. venosus strongly supports a tsunamigenic source for the deposit.
12
Core ID
Unit No.
LBS -11-1
LC 1
LBS -11-1
LC 2
LBS -11-1
LC 3
LBS -11-1
LC 4
0-5
40-50
85-95
115-125
Species ecology
40
50
70
1160
-
Ammonia parkinsoniana
40
0
0
190
intertidal (brackish); <10 m
Amphistegina lessonii
0
0
0
110
subtidal; <10 m depth
Amphistegina lobifera
0
30
20
310
subtidal; <10 m depth
Asterorotalia pulchella
0
0
0
40
intertidal (brackish); <10 m
Depth below surface (cm)
Specimens per 10 cm
3
Taxonomy:
Cibicides refulgens
0
0
20
130
subtidal
Elphidium craticulatum
0
20
30
220
subtidal; 1-30 m depth
Palaeonummulites venosus
0
0
0
160
subtidal; >20 m depth
Taphonomy:
Unaltered
10
0
20
510
-
Fragmented
0
0
10
360
-
Abraded/corroded
30
50
40
290
-
Table S3.1. Foraminiferal data (taxa and taphonomy) for four samples obtained from the
Lhok Cut site.
13
Figure S3.1. Dominant foraminiferal
species and taphonomic characters
from the Lhok Cut exposure.
14
Lubhok Bay Beach site
Total foraminifera abundances are low and do not differentiate between tsunami and nontsunami sediment (Table S3.2). Benthics appear in all seven units, whereas planktics are
present only in LB 3, the upper tsunami deposit.
Depth below
surface (cm)
Unit No.
Benthic sp.
present?
Planktic sp.
present?
Total specimens
per 10 cm3
47.5
62.5
68.5
74.5
87.5
105.5
112.5
123.0
126.0
137.5
167.5
LB 2
LB 2/3
LB 3
LB 4
LB 4
LB 4
LB 5a
LB 5b
LB 5b
LB 6
LB 7
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
no
no
yes
no
no
no
no
no
no
no
no
6
7
6
4
6
2
2
2
4
3
6
Table S3.2. Foraminiferal data for eleven samples obtained from the Lubhok Bay Beach
site.
15
4.
Geochemical analysis
4.1 Methods
The utility of δ13C as a tracer in fluvial and marine sediments is based upon
whether plants use atmospheric CO2 (terrestrial plants), dissolved CO2 or bicarbonate
(HCO3) (aquatic plants and organisms) to fix carbon during photosynthesis. Ultimately,
terrestrial organic matter is depleted in 13C compared to marine organic matter. Thus
marine particulate and dissolved organic matter typically yield δ13C values of between 18 to -23‰, whereas freshwater particulate and dissolved organic matter show more
negative δ13C values in the range of -26 to -32‰ (Deines, 1980). In theory the main
source(s) of marine and terrestrial of organic matter supplied to estuarine, coastal and
marine sediments can be readily determined (Kemp et al., 2010). However, in practice a
number of physical processes such as tidal mixing, grain-size sorting, seasonality of river
discharge, organic matter residence time and biological decay processes including
bioturbation by invertebrates, fungal and bacterial decay as well as overprinting of the
natural carbon signature by anthropogenic pollution may hinder such distinctions (Abril
et al., 2002; Middelburg & Herman, 2007; Vane et al., 2010).
Rock Eval Pyrolysis has been used to track organic carbon sources and
transformations in mangrove peats and paleaolake sediments (Copard et al., 2006; Jacob
et al., 2004; Marchand et al., 2008). The two most important parameters for
paleoenvironmental reconstructions are thermo-vaporized free hydrocarbons (oil)
expressed in mg/HC/g rock (S1) and hydrocarbons released from cracking of bound
organic matter (polymers or kerogen) expressed in mg/HC/g rock (S2). The basic
interpretive premise applied to the Rock Eval data is that marine/coastal sediments
contain lower amounts of thermally labile organic matter (S1 and S2) than terrestrial or
riverine sediments. We do not use a third Rock Eval parameter, the hydrogen index (HI =
[100 × S2]/TOC) because of very low value, ranging from just 5 up to 98 (typical HI
values range from 100 to 600).
Stable Carbon Isotope (δ13C) and C/N
For measurement of δ13C and TOC, four sediment samples from the Lhok Cut
seacliff exposure and eleven from Lubhok Bay were treated with 5% HCl for 18 hours,
washed with deionised water, dried in an oven at 40ºC overnight and milled to a fine
powder using a pestel and mortar. Plant samples were treated with 5% HCl for 2-3 hours
washed with deionised water, dried in an oven at 40ºC overnight and milled to a fine
powder using a freezer mill.13C/12C analyses were performed on sediment samples by
combustion in a Costech Elemental Analyser coupled on-line to an Optima dual-inlet
mass spectrometer. δ13C values were calculated to the VPDB scale using a within-run
laboratory standard (cellulose, Sigma Chemical prod. no. C-6413) calibrated against
NBS-19 and NBS-22. TOC values were analysed on the same instrument. Replicate
analysis indicated a precision of <0.1‰ (1 SD) for δ13C and TOC% (wt/wt)
measurements.
Rock Eval Pyrolysis
Pyrolysis was performed on approximately 60 mg of powdered sediment (dry/wt)
using a Rock-Eval 6 analyser (Vinci Technologies) in standard configuration (pyrolysis
and oxidation as a serial process). Briefly samples were heated from 300ºC (hold 3 min)
16
to 650ºC (hold 3 min) at 25ºC/min in an inert atmosphere of N2. The residual carbon was
then oxidized at 300ºC to 850ºC at 20ºC/min (hold 5 min). Hydrocarbons (HC) released
during the two stage pyrolysis were measured using a flame ionization detector (FID).
The CO and CO2 released during thermal cracking of the bound organic matter (OM) was
monitored using an IR cell. The performance of the instrument was checked every 10
samples against the accepted values of Institut Français du Pétrole (IFP) standard (IFP
160 000, S/N1 5-081840).
4.2 Results
Lhok Cut site
Sediments from Lhok Cut seacliff exposure show δ13C values in the range of-24.3
to -23.8 which suggests little variation in organic matter source through the section
(Table S4.1; Figure S4.1). In general marine organic matter yield δ13C of -18 to -23‰
whereas terrestrial organic matter show more negative δ13C values in the range of -26 to 32‰. Thus the values obtained here lie between the two suggesting possibly mixed
source(s). TOC values increased from <0.9 % (125 to 40 cm) up to 2.4 % (2.5cm) which
perhaps, gives credence to the notion that the uppermost interval (0-5 cm) has either a
different source of organic matter or that has undergone less diagnetic alteration than the
lower intervals. Similarly, the simultaneous rise in HI from <50 to >100 mg/HCgTOC
and S2 parameter (concentration of bound hydrocarbons) suggest a change in organic
matter source.
Depth below
surface (cm)
2.5
45.0
90.0
120.0
Unit No.
LC 1
LC 2
LC 3
LC 4
S1
(mg/g)
S2
(mg/g)
TOC
(%)
HI
δ13C
0.17
0.02
0.02
0.02
2.81
0.34
0.21
0.37
2.38
0.76
0.39
0.89
118
38
56
39
-20.2
-24.1
-25.2
-24.9
Table S4.1. Geochemical data for the Lhok Cut site.
17
Figure S4.1. Geochemical data for the Lhok Cut site.
Lubhok Bay Beach site
From the base of the Lubhok Bay Beach seacliff exposure (170 cm to 135 cm
depth; LB 7 and lower portion of LB 6) the δ13C down values range from -23.2 to -21.6‰
and show very low TOC values ranging from 0.1 to 0.4%. In contrast the overlying
sediment interval (128 to 121 cm depth; includes LB 5b channel soil) shows less negative
δ13C values (-19.5 to -18‰) and maximal TOC values of 0.78% (wt/wt) (Figure and
Table S4.2 S4.2). The increase in TOC between is in complete agreement with the visual
observation of a palaeo-soil. There isn’t a parallel shift to more negative δ13C values of >
-26‰ that would usually be associated with soils comprised in part of partially
decomposed C3 plant biomass and humic C3 terrestrial organic matter is not shown. One
plausible explanation for the more positive δ13C values (~ 19‰) could be that the soil
(catchment) was dominated by either C4 or CAM plants. Between 115 to 110 cm depth
(LB 5a lower tsunami deposit) the δ13C is -20.7‰ and TOC is 0.3 %. The three sediment
intervals between 108 up to 71 cm depth (LB 4) show rather invariant δ13C values of ~22‰ and TOC values ranging from 0.2 to 0.5 %. The shift back to marine sourced
organic matter is then reflected at 70 to 67 cm core depth (LB 3 upper coral rubble) by a
δ13C of -19.2‰. The upper two intervals from -65 to 45 cm depth (LB 2 and the diffuse
contact with LB 3) represent a transition to very high δ13C values but slightly greater
TOC values than the underlying coral rubble.
The δ13C values from the seacliff exposure suggest a marine origin for all layers
(marine organic matter δ13C values range -18 to -24‰). Our interpretations are in part
supported by analysis of a single sample of known marine origin (UBK-B-4 Trench)
which gave somewhat similar negative δ13C value of -23.9‰ and TOC of 0.3 %.
18
The S1 and S2 profiles deviate to low values similar to that of the marine endmembers at -170 to -165 cm (LB 7), -125 to -110 cm (includes LB 5) and between 77 to
60 cm (includes LB 3; Table S4.2; Figure S4.2). This suggests that these sediment
intervals have received some marine organic matter.
Depth below
surface (cm)
Unit No.
47.5
62.5
68.5
74.5
87.5
105.5
112.5
123.0
126.0
137.5
167.5
LB 2
LB 2/3
LB 3
LB 4
LB 4
LB 4
LB 5
LB 5
LB 5
LB 6
LB 7
S1
(mg/g)
S2
(mg/g)
TOC
(%)
HI
δ13C
0.07
0.02
0.01
0.02
0.03
0.04
0.01
0.01
0.01
0.04
0.01
0.47
0.2
0.17
0.16
0.28
0.42
0.07
0.04
0.08
0.25
0.04
0.48
0.23
0.21
0.20
0.34
0.51
0.26
0.78
0.33
0.36
0.10
98
87
81
80
82
82
27
5
24
69
40
-14.1
-18.6
-19.2
-22.6
-22.3
-22.7
-20.7
-18.9
-19.5
-21.6
-23.2
Table S4.2. Geochemical data for Lubhok Bay Beach site.
19
Figure S4.2. Stable carbon isotope (δ13C), total organic carbon (TOC), free and bound
hydrocarbon concentration and hydrogen index for the Lubhok Bay Beach site.
20
5.
Geochronological analyses
This section contains all the documentation of dates that appear in the paper. The
first section contains radiocarbon analyses. The second contains Uranium-Thorium
analyses. In each section, the analyses for the Lhok Cut site appear first and the analyses
for Lubhok Bay appear second.
The Lubhok Bay data include radiocarbon and U-Th analyses conducted on
materials from Fort Lubhok, about 200 hundred meters southeast along the coast from the
seacliff exposure that we mapped (Figure 7). For lack of space, we do not discuss these
dates in the paper, but present them here, so that they will be available to future
researchers.
We did not find suitable materials to date the man-made earthen ridge or mound
at the Lhok Cut site (Figures 2, 3 and 4). Nor were we able to find materials within the
uppermost, cobbly unit at the Lubhok Bay Beach seacliff exposure (Figures 7 and 8),
which we suspect to have resulted from accelerated erosion after construction of the dirt
road above the site. We suspect that these layers and landforms are contemporaneous
with the construction of the two forts on Lamreh peninsula, the Fort of the Widows above
Lhok Cut and Fort Lubhok on Lubhok Bay (Figure 2).
Edwards McKinnon [2009] argues that these forts and several other stone
structures between the peninsula and Banda Aceh were constructed in the early decades
of the Aceh sultanate, specifically in the middle of the 16th century. If so, then their
construction dates would provide a minimum age for the tsunami deposits within our
exposures.
5.1 Radiocarbon analysis
5.1.1
Methods
All radiocarbon samples were analyzed by Beta Analytic Inc, Miami, Florida,
using accelerator mass spectrometry.
5.1.2
Results
Lhok Cut site
Sample Material:
number Pre(LAMBS1- treatment
)
21
tooth:
collagen
extraction:
with alkali
20
charred
material:
acid/alkali/aci
d
Measured
Age (BP)
590 +/- 30
640 +/- 40
13C/12C Convention 2 Sigma
(‰)
al
Calibration
Age (BP) (Common
Era)
-19.8
680 +/- 30 1270-1310
and 13601390
-21.6
700 +/- 40
1260-1310
and 13601390
21
19
18
17
16
13
12
11
8
6
bone
collagen:
collagen
extraction with
alkali
bone
collagen:
collagen
extraction with
alkali
bone
collagen:
collagen
extraction with
alkali
bone
collagen:
collagen
extraction with
alkali
bone
collagen:
collagen
extraction with
alkali
bone
collagen:
collagen
extraction with
alkali
bone
collagen:
collagen
extraction with
alkali
tooth:
collagen
extraction:
with alkali
bone
collagen:
collagen
extraction with
alkali
590 +/- 30
-16.8
720 +/- 30
1260-1300
610 +/- 30
-14.6
780 +/- 30
1210-1280
520 +/- 30
-9.0
780 +/- 30
1210-1280
700 +/- 30
-19.1
800 +/- 30
1200-1270
590 +/- 40
-19.4
680 +/- 40
1270-1320
and 13501390
460 +/- 40
-9.4
720 +/- 40
1240-1300
and 13701380
600 +/- 40
-20.1
680 +/- 40
1270-1320
and
1350-1390
410 +/- 40
-7.3
700 +/- 40
1260-1310
and 13601390
640 +/- 40
-18.8
740 +/- 40
1220-1300
22
3
bone
320 +/- 40
-9.3
580 +/- 40 1300-1430
collagen:
collagen
extraction with
alkali
2
bone
440 +/- 40
-13.8
620 +/- 40 1280-1410
collagen:
collagen
extraction with
alkali
Table S5.1. Radiocarbon analyses for the Lhok Cut seacliff exposure, which appear in
Figure 4.
Lubhok Bay Beach site
Sample
Material:
number
Pre-treatment
(LMR 10-B-)
Measured
Age (BP)
13C/12C
(‰)
Conventional
Age (BP)
AM6a
organic sediment:
acid washes
810 +/- 30
-17.9
930 +/- 30
2 Sigma
Calibration
(Common
Era)
1030-1170
7a
charred material:
acid/alkali/acid
1050 +/- 40
-24.6
1060 +/- 40
890-1030
6b
charred material:
acid/alkali/acid
800 +/- 40
-25.6
790 +/-40
1170-1280
6a
charred material:
acid/alkali/acid
980 +/- 40
-24.3
990 +/- 40
980-1160
4b2
charred material:
acid/alkali/acid
510 +/- 40
-23.1
540 +/- 40
1310-1360
and 13901440
Table S5.2. Radiocarbon analyses for the Lubhok Bay Beach site, which appear in the
map of the Lubhok Bay Beach seacliff exposure (Figure 6).
23
Kuta (Fort) Lubhok
The loose lime mortar used in construction of Fort Lubhok contains abundant
angular, small pebbly clasts of charcoal. This charcoal likely derives from wood fires
used to create the lime mortar from nearby deposits of limestone. Hence its age should
be the age of the wood used to fuel the fires. Since it would have been easier to cut
younger rather than older trees, it could well be that the radiocarbon ages of the charcoal
are within a decade or so of the date of construction of the fort.
Table S5.3 displays three dates from charcoal within the mortar of the main wall
of the fort. All three come from a location near the base of the wall and within ten or so
centimeters from its seaward face.
Note that two of the analyses (LK13-A1-A and G) yielded date ranges that
suggest construction of the fort between 1490 and 1650 CE, consistent with construction
within the first century and a half of the Aceh sultanate. The third sample (LK13-A1-B)
yielded an age within the younger ranges of 1640-1670 and 1780-1800 (The third range
for this analysis – 1940-1950 – is of course not plausible). We suggest that the two earlier
age ranges bracket the date of construction of the fort. The one younger date could well
reflect repair of the loose lime mortar at a later date, something that was common for
structures held together with weak lime mortar.
Sample
number
(LK13-)
Material:
Pre-treatment
Measured
Age (BP)
A1-A
charred material:
acid/alkali/acid
300 +/- 30
A1-B
charred material:
acid/alkali/acid
170 +/- 30
A1-G
charred material:
acid/alkali/acid
300 +/- 30
13C/12C Conventional 2 Sigma
(‰)
Age (BP)
Calibration
(Common
Era)
-20.5
370 +/- 30
1450-1530
and 15401630
-20.8
240 +/- 30
1640-1670,
1780-1800
and 19401950
-24.7
300 +/- 30
1490-1600
and 16101650
Table S5.3. Radiocarbon analyses of charcoal from the lime mortar of Fort Lubhok.
24
5.2 U-Th analysis
5.2.1
Methods
All coral fossil samples were selected for U-Th chemistry (Shen et al., 2003) and
isotopic measurements on a multi-collector inductively coupled 4 plasma mass
spectrometer (MC-ICP-MS), Thermo Electron Neptune, at the HISPEC Laboratory,
Department of Geosciences, National Taiwan University (Shen et al., 2012) and at the
Earth Observatory of Singapore, Nanyang Technological University. A gravimetricallycalibrated triple-spike, 229Th-233U-236U, isotope dilution method (Cheng et al., 2013) was
employed to correct mass bias and determine uranium concentration. U-Th isotopic
compositions and concentrations and dates are listed in the tables that follow. All
measured isotopic uncertainties and date errors given are two standard deviations unless
otherwise noted.
5.2.2
Results
Table S5.4. Analysis of pristine coral cobble from the foundation beneath the lime
plaster floor of the earthen mound at Lhok Cut.
Table S5.5. Analyses of large-corallite corals from Fort Lubhok (Figure 2) and a
Goniastrea retiformis from the Lubhok Bay Beach seacliff exposure.
25
Table S5.6. U-Th analyses
of Porites sp. samples from
the Lubhok Bay Beach Site.
Two of the samples yielded
isochron ages, whereas the
other yielded an age based
upon averaging of several
analyses.
26
5.2.3 Initial Thorium assumptions
Both uncorrected and corrected ages appear in Table S5.6. Corrected age reflects
removal of the contribution of non-radiogenic 230Th (also called detrital 230Th) by
assuming an initial 230Th/232Th ratio. The higher the Th concentration, the larger the
correction. For instance, the corrected ages of coral samples with 5-14 ppb Th in our
corals can easily cause the corrected age to be more than one decade younger, even if the
initial 230Th/232Th ratio deviated by just 1 ppm from what we got from the isochron (that
is, 8.6 ppm in Table S5.7). The isochron technique undoubtedly helps to constrain the
initial 230Th/232Th ratio, but assumes a simplified two-end-member model, which we
know might not always be valid. Thus the isochron calculation may not yield an accurate
initial Th value. Thus, ages one to two decades older than the expected age of AD
1393±2 may well be the result of incorrectly modeled corrections.
[Th]
Corrected age (AD) by different initial 230Th/232Th value
8.6 ppm
9.6 ppm
Uncorrected age
(AD)
10.6 ppm
5 ppb
1353 ± 16.3
1365 ± 16.3
1377 ± 16.3
1247 ± 9.2
9 ppb
1325 ± 33.0
1353 ± 32.8
1380 ± 32.8
1089 ± 12.9
14 ppb
1333 ± 52.9
1377 ± 52.9
1422 ± 52.9
951 ± 20.1
Table S5.7. Comparison of corrected ages of coral samples with different assumptions
of Thorium concentrations, via application of different initial 232Th/232Th ratios.
27
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