Sediment Cores from the Kalya platform, slope and horst:
long-time span paleolimnology and paleoclimate records
High resolution and
Students: Derrick Zilifi and Meagan Eagle
Mentor: Dr. Kiram Lezzar
Introduction
The large lakes of the East African rift valley are underlain with thick sedimentary sequences containing
significant paleoclimate and paleolimnological records (Pilskaln & Johnson, 1991). Lake Tanganyika is the
largest (32,600 km2 ), deepest (1470 m) and oldest (>12 Ma) of the East African Rift Lakes (Cohen et al,
1993), so potentially contains very long time-scale, high-resolution sediment records. Previous studies of
sediment cores from Lake Tanganyika correlate changes in sedimentation with shifting limnological and
climatic regimes over the broad region of equatorial Southern Africa where Lake Tanganyika is situated
(Cohen et al, 1997; Tiercelin et al, 1992). Preliminary analysis of the stratigraphy, organic and inorganic
carbon (OC and IC) of four cores obtained from the platform, slope and horst of Kalya in the southern
basin of Lake Tanganyika (Fig 1, Henderson & Gans, Nyanza Project Annual Report 2000) offers a new
site for high-resolution continuous sediment records in Lake Tanganyika.
Selection of the study area
The Kalya Horst is a structural high that separate two subsiding half-grabens at the northern tip of the
Southern Lake Tanganyika Rift Basin. This horst is a northwest trending ridge bounded by NNW trending
border faults with opposite dip. The basinal bedrock lithology consists of Precambrian pre-rift lacustrine
sedimentary rocks. Previous studies have collected deep multichannel lines (Rosendahl, 1987), but no
studies have yet examined in detail that horst’s sediments. The location of the Kalya Horst is ideal for
obtaining long, continuous sequences because it is a structural high, located 20 km from shore and removed
from the effects of terrestrial sediment input. The oxicline for the southern basin currently fluctuates
between 130 m in the dry season and 100 m in the rainy season, leaving the horst core sites in perpetually
anoxic conditions, perfect for the preservation of organic matter. Four cores were collected from the Kalya
region in a transect across the platform (LT00-01 at 128 m water depth), slope (LT00-02 at 309 m) and the
horst (LT00-03 at 608 m and LT00-04 at 578 m).
Methodology
Four gravity cores (from 115 to 172 cm in length) were collected using a crane and winch from aboard the
M/V Maman Benita on a 6 –days Nyanza Project cruise during July 2000. The cores were brought to the
Nyanza Project research facilities at TAFIRI (Kigoma, Tanzania) and stored vertically prior to opening to
preserve stratigraphy. Stratigraphic columns were drawn immediately after the core was opened and colors
and structures were described, and then photographed for future analysis. The sediments in the cores were
analyzed under a microscope (10x64) to refine facies descriptions, including the dominant mineralogy,
grain size, and microfossil content. The cores were subsampled every 5 cm (cores LT00-02 and LT00-03)
or every 10 cm (cores LT00-01 and LT00-04) for total organic carbon (OC) and inorganic carbon (IC). OC
and IC were determined using loss on ignition (LOI) methods with a muffle furnace. OC is found by firing
the sample to 550 C and applying the following equation:
(Pre-fired sample weight – 550 Fired sample weight) x 100 x *ROC = % OC
Beginning sample weight
(550 Fired sample weight – 925 Fired sample weight) x 100 x *RIC = % IC
Beginning sample weight
* The correction factors applied to these equations, ROC and RIC, are based on the percent carbon in the
organic matter and the percent carbon in the carbonate fraction. Using CH2 O as typical organic matter, ROC
Figure 1
Burundi
Kigoma
Tanzania
D.R.
Congo
Study Site
Zambia
29.92
30.00
30.08
AH
M
1500m
E
AL
900m
30.17
U
O
M
Lugonesi
River
900m
N
900m
S
N
LI
E
K2
K3
y
ck
RE
HO
S
Y
Sibwesa
Village
ND
LT00-01 WD 128m
SA
Ro
6.50
K1
Cultivation
Cultivation
Kalya
Village
K4
K5
K6
Lufubu
River
0m
Msofwe
River
Kisinsa
River Swamp
90
Mpanga
River
900m
6.42
s
ion ain
ns unt
xte Mo
n E le
t
er ha
en
uth Ma
pm
ar
So e
h
c
t
ne
of p Es 200m
el i
1
0m
ee
or
90
St
Sh
900m
IN
TA
6.42
90
Central
Lake
Tanganyika
6.50
0m
LT 00-02 WD 309m
6.58
6.67
6.58
6.67
LT00-04 WD 578m
N
LT00-03 WD 608m
1 2 34 5
km
6.75
29.92
30.00
30.08
6.75
30.17
is 0.40; and using CaCO3 as a typical carbonate, RIC is 0.12 (G. Ellis & C.A. Scholz., personal
communications). The species used for correction factors are “typical” species, used in the absence of
known organic matter and carbonate species for the LT00 cores.
Results
Detailed stratigraphic analysis on cores LT00-01, LT00-02, LT00-03 and LT00-04 provides a highresolution sediment record. Major facies were identified and correlated between each core for paleoenvironment interpretations, and correlated with OC and IC plots for each core. All descriptions work upcore (Fig. 2 & 3).
LT00-01 (128m water depth, and 115 cm length) has four main lithological facies (Fig. 4).
The layered clay of Facies 1 (105-115 cm) has 0.25 cm thick light and dark olive gray clay layers with low
OC and IC (4.17% and 0.29%) compared to the slope and horst cores, as expected due to oxic conditions
(Fig. 3).
The fecal pellet clay of Facies 2 (73-105 cm) is dominated by alternating layers of fecal pellet rich clays in
sharp contact with light gray massive clay layers 1-3 cm thick. Massive clay layers on the shallow platform
represent density current deposits and indicate that the sedimentation on the platform is active today.
Facies 3 (46-73 cm) is a diatom-rich clay, with yellow-gray diatom rich layers alternating with gray layers
every centimeter. OC and IC remain steady for facies 2 and 3 (5.25% and 0.33%).
Facies 4 (0-46 cm) is a layered clay that contains alternating layers of fecal pellet and massive clays,
similar to facies 2. A sand lens at 23-30 cm embedded in a clay unit most likely represents slumping on the
platform and is accompanied by a decrease in OC and IC (4.88% and 0.28%) due to terrestrial dilution.
LT00-02 has three lithological facies (Fig. 5).
The gray silt of Facies 1 (156-172 cm) is a silty diatomaceous dark olive gray unit with a few diatom ooze
laminations. OC (6.31%) is reduced from the laminated unit up-core (6.78%). Lake productivity during the
deposition of this unit may be lower than the above units, or increased autochthonous sedimentation may be
diluting OC.
Facies 2 (46-156 cm) is a flocculated clay that alternates between yellow-gray flocculated diatom-rich and
dark gray clay laminated bundles.
Facies 3 (0-46 cm) is a diatom-rich flocculated clay with yellow-gray flocculated layers larger than the
previous unit, dominating the clay rich bundles. This facies change is possibly a result of a recent increase
in lake productivity. The flocculated units are cohesive and large (1-5 cm across) and full of benthic
diatoms (Michelo, V. Nyanza Project Annual Report 2000). These flocculated units may aggregate while
the diatoms are alive and then the entire unit is transported away from the platform. Turbidity and
dissolved inorganic carbon are high in the southern basin from 300-700 m, which may indicate the presence
of particulate rich currents within the water column (Adams & Charles, Nyanza Project Report 2000).
LT00-02 is laminated over 91% of the core length, with light and dark laminae making up a 1 mm thick
couplets, providing a sediment record with seasonal resolution. OC levels are reduced compared to Scholz
et al. (Kavala Island Ridge, in review at Paleo3) Core T97-52V’s 10-12% OC at comparable water depths
(LT00-02 at 309 m and T97-52V at 393 m). The OC and IC graphs (Fig 5) display an interesting cylicity
with evenly spaced peaks throughout the core length. This variation may be due to periodic changes in lake
conditions.
LT00-03 (608 m, 170 cm) (Fig. 6).
The basal clay of Facies 1 (109-170 cm) contains alternating laminated layers of yellow-gray diatomaceous
ooze with a dark gray clay rich in terrestrial plant fragments. Stephanodiscus dominates the diatom rich
laminated layers and Aulacoseira, in lesser abundance, dominates the gray layers (for complete discussion
of diatom assemblages in core LT00-02 and LT00-03, refer Michelo, V. (Nyanza Project Annual, Report
2000). OC and IC fluctuate throughout facies 1, with the average values for OC high (7.92%). IC (0.33%)
fluctuates synchronously with the OC.
Facies 2 (88-109 cm) gray clay is non-laminated with small (0.1-0.5 mm) flocculated clay particles and
Stephanodiscus appears in low abundance.
The banded clay of Facies 3 (59-88 cm) is also non-laminated with several prominent dark brown and light
gray clay bundles.
Figure 2: Correlations between LT00 Cores based on facies relationships.
LT00-01
LT00-02
128m water depth
0 cm
309m water depth
0 cm
Layered
Diatom
Clay
Diatomrich
Flocculated
Clay
LT00-04
LT00-03
Fecal Pellet
Clay
608m water depth
578m water depth
0 cm
Flocculated
Clay
Layered
Diatom
Clay
Laminated
Diatomaceous
Ooze
Gray Clay
Laminated
Clay
115 cm
0 cm
Laminated
Diatomaceous
Ooze
Layerd
Clay
Gray Clay
Banded Clay
LT-02 139.5cm (wood fragment)
2845+/-48 C-14 yr.
LT-02 139.6 (bulk organic)
3303+/-40 C-14 yr
Basal Clay
Gray Clay
Gray
Silt
117 cm
172 cm
LT-03 108.75 (bulk organic)
9280+/-55 C-14 yr
Basal Clay
170cm
Figure 3
LT00 Cores % TOC
(LOI corrected)
%TOC
0%
5%
10%
0
20
40
Length
60
80
100
120
140
160
LT00-01
LT00-02
LT00-03
LT00-04
15%
Figure 4
LT00-01
S 6°30.756'
E 30°1.062'
128 m
%IC & % OC
LOI corrected
0%
5%
10%
15%
0
Facies 4 (0-46 cm) contains
alternating layers of fecal pellet rich
clays in sharp contact with massive
clays. Laminations occur in several
of the clay units.
20
Sand lens at 23-30 cm is embedded in
a clay unit.
Length
40
Facies 3 (46-73 cm) is a laminated
clay unit, with yellow-gray diatom
ooze laminations alternating with
gray clay.
60
Facies 2 (73-105 cm) has alternating
layers of fecal pellet rich clays in
sharp contact with light gray massive
clay layers 1-3 cm thick.
80
Facies 1 (105-115 cm) is layered
(0.25 cm thick) with alternating light
and dark olive gray clay.
100
120
TOC%
Carbonate
The laminated clay of Facies 4 (50-59 cm) is a dark gray and medium gray clay unit that grades into Facies
5 (37-50 cm), a massive gray clay unit with sparse terrestrial plant fragments. OC (6.5%) and IC (0.28%)
remain steady throughout facies 2, 3, 4 and 5, and are reduced from the OC and IC levels in the laminated
units, indicating a less productive lake regime. The laminated diatom ooze of Facies 6 (0-37 cm) resumes
distinct laminations between yellow-gray diatom rich ooze and dark gray clay bundles, and is has increased
levels of OC (9.33%) and IC (0.42%).
LT00-04 (578 m, 117 cm) has three dominant facies (Fig. 7). The basal clay of Facies 1 (64-117 cm)
contains alternating light and dark gray bundles of laminated gray diatom ooze and dark gray clay.
Stephanodiscus again dominates the diatom-rich laminations. Dark gray bundles within the laminated units
signal terrigenous input during the deposition of the diatom ooze. Similar to LT00-03, OC (9.32%) and IC
(0.42%) increase in the laminated units. Facies 2 (50-64 cm) is a medium gray, faintly laminated, clay.
Facies 3 (0-50 cm) is a laminated diatom ooze with yellow-gray 100% diatom rich laminae alternating with
brownish black and light medium gray laminae couplets. OC and IC (6.75% and 0.36%) remain stable
throughout facies 2 and 3.
Discussion
Lake Tanganyika is currently in a productive, well-stratified, high lake stand and under the current
sediment regime organic-rich, laminated units are deposited on the slope and horst. We interpreted the
down-core laminated, OC-rich units (Laminated Diatom Ooze and Flocculated Clay) to represent highly
productive lake conditions with excellent preservation of organic material in the anoxic bottom waters.
During cold, dry climates associated with lower lake stands, sedimentation is dominated by clay facies
(Basal Clay and Gray Clay) seen in the horst cores. Lake level curves (Fig. 6 & 7) use changing
sedimentation conditions on the horst as a proxy for lake level changes.
The tops of the two horst cores can be correlated through stratigraphy and geochemistry. Both have
Laminated Diatom Ooze in the top units and show similar enrichments in OC and IC. Below this correlated
unit in LT00-03 are a series of massive and layered clays, covering 72 cm, while LT00-04 only has a 14 cm
thick clay unit. The basal clays of both cores are well laminated, diatom ooze and clay, and appear to be
the same layer. This suggests a lower sedimentation rate in the top unit of LT00-03 compared to LT00-04,
but the Gray Clay units of LT00-03 probably had higher sedimentation rates than LT00-04. LT00-03 is
down slope from LT00-04, so when the location of the LT00-03 is subsiding, sedimentation rates increase.
The observed differences in sedimentation rates on the horst may be attributed to neotectonic readjustments
of intra-horst faults and a reduced subsidence of the horst arm.
Following previous studies, lake level reconstructions based on stratigraphy and organic matter is possible
(Pilskaln et al, 1991). The horst and slope cores contain high levels of organic matter (OC) (slope average
6.89%, max 9.71%; and horst average 7.80%, max 11.82%) compared to values published for the northern
Bujumbura sub-basin (average 4.3% and maximum 12.0%) (Tiercelin et al, 1992), and slightly reduced
from the nearby Kavala Island Ridge (average 10-12% and maximum 14 %) (Scholz et al., in review).
LT00-02 is continuously laminated for the entire length of the core, so using published sedimentation rates
from similar environments of 1mm/yr in Lake Tanganyika, the core covers 1700 years. The similarity of
flocculated units throughout the core suggests that productivity has remained high for this time span.
Similar paleoproductivity analysis can be done on the horst cores. The Basal Clay and Laminated Diatom
Ooze of LT00-03 and LT00-04 represents highly productive regimes similar to today’s conditions, and
three thick massive Gray Clay units represent low lake stands when the lake was not as productive.
Preliminary lake level reconstructions from LT00-03 and LT00-04 show slight reductions in productivity
(decreased OC) during low lake stands (Fig. 6 and 7).
Using Scholz et al (in review) sedimentation rates of 0.1 mm/yr (from the Kavala Island Ridge, a similar
environment to the Kalya Horst but deeper) LT00-03 may span 17,000 years of sedimentation. With these
sedimentation rates, low lake stands dominated from 3,700 to 5,000 yr BP and 8,800 to 10,900 yr B.P.
These last dates may coincide with the low lake stands of the Younger Dryas recorded in nearby Lakes
Natron and Magadi at 10,000 to 11,000 yr BP (Roberts et al, 1993).
Figure 5
LT00-02
S 6°33.154'
E 29°58.306'
309 m
% IC & % OC
LOI corrected
0%
5%
10%
15%
0
1
Facies 3 (0-46 cm) has thick
yellow-gray diatom-rich
flocculated clay layers.
2
20
40
3
60
4
Facies 2 (46-156 cm) alterna es
betw en yellow-gray flocculated
diatom-rich layers and dark gray
clay laminated layers. The
flocculated units are cohesive and
large (1-5 cm across) and full of
benthic diatoms
5
Length
80
100
6
7
120
8
139.5cm (wood fragment)
2845+/-48 C-14 yr.
139.6 (bulk organic)
3303+/-40 C-14 yr
140
9
160
10
TOC%
Carbonate
Facies 1 (156-172 cm) is a silty
diatomaceous dark olive gray unit
with a few diatom ooze
laminations.
Figure 6
LT00-03
S 6°41.165'
E 29°51.663'
608 m
% IC & % OC
LOI corrected
0%
5%
10%
0
15%
Lake Level
(Present = +)
-
20
0
+
Facies 6 (0-37 cm) is a brownish
black clay with distinct yellow-gray
diatom rich laminae and dark gray
laminae containing terrigenous plant
material
Facies 5 (37-50 cm) is a massive
gray clay unit with sparse terrestrial
plant fragments grading into Facies 4
(50-59 cm) dark and medium gray
laminated clay.
40
60
Facies 3 (59-88 cm) is a medium
dark gray massive clay.
Dark gray clay (69 cm)
Yellow gray clay (77 cm)
80
Length
- Dark brown clay (87 cm).
- Facies 2 (88-109 cm) is dominated
by a non-laminated, dark gray clay.
There are small (0.1-0.5 mm)
floculated clay particles and
Stephanodiscus appears in low
abundance.
-108.75 cm (bulk organic)
9280+/-55 C-14 yr
100
120
Silty diatomaceous layer at 125 cm
shows a reduced TOC.
Facies 1 (109-170 cm) has mm-scale
laminated yellow-gray diatomaceous
ooze alternating with a dark gray
clay rich in terrestrial plant
fragments. Stephanodiscus diatoms
dominate the yellow-gray
laminations and Aulocaseria , in
lesser abundance, dominates the gray
laminations
140
160
TOC%
Carbonate
Figure 7
% IC & % OC
LOI corrected
0%
LT00-04
S 6°40.750'
E 29°416'
578 m
10%
0
Facies 3 (0-50 cm) has three distinct
laminations. The yellow-gray 100% diatom
ooze laminations alternate with brownish
black and light medium gray laminations.
20
40
Length
Facies 2 (50-64 cm) is a medium gray
faintly laminated clay.
60
80
Facies 1 (64-117 cm) contains alternating
layer of light and dark gr y lamin ted
clay and yellow-gray diatom-rich ooze
laminated with dark gray laminated clay.
Stephanodiscus dominates the diatom-rich
laminations.
100
120
TOC%
Carbonate
Conclusion
Analysis of the Kalya cores shows that sediments in the slope and horst region are rich in OC and IC and
preserve seasonal signals at varying resolutions, thus providing an excellent opportunity for
paleolimnological and paleoclimate reconstructions. LT00-02 is continuously laminated with seasonal
varves for nearly the entire length of the core, while LT00-03 and LT00-04 have very fine laminations that
can provide long-scale annual resolution records. The differing resolution of slope and horst cores offers
an exciting opportunity to correlate between the longer time range of the horst and the high-resolution slope
cores.
Recent Research Progress as of February 2001
AMS 14 C dates on wood fragment and bulk organic from cores LT 00-02 and LT 00-03 have been recently
provided (January 2001) by the AMS Laboratory at the University of Arizona.
LT-02 139.5cm (wood fragment) 2845+/-48 C-14 yr.
LT-02 139.6 (bulk organic) 3303+/-40 C-14 yr
LT-03 108.75 (bulk organic) 9280+/-55 C-14 yr
These dates will be included and discussed in a paper we are working on (February 2001) with Luc Andre,
Damien Cardinal, Andy Cohen, Geoffrey Ellis and Kiram Lezzar.
Further Research
An intensive coring expedition to the Kalya Horst would add exciting and important paleolimnological and
paleoclimate records for the East African Lakes region. Complete analysis of organic matter and carbonate
species, isotope analysis, more C14 dating, fine grain size analysis, and further investigation of diatom
assemblages are necessary to constrain the age of the core and provide sedimentation rates for the Kalya
region in central Lake Tanganyika.
Acknowledgements
Our mentor, Dr. Kiram Lezzar, provided endless support and encouragement throughout the entire project.
He guided us through an exciting analysis of all cores collected. David Knox was a great help with
technical details and Kamina Chororoka provided the hamna shida attitude. We thank the AMS Laboratory
at the University of Arizona for the 14 C dating. The crew of the M/V Maman Benita provided a wonderful
coring team in the windy Southern Basin of Lake Tanganyika. Above all we would like to thank the
Nyanza Project for the opportunity to study Lake Tanganyika.
References
Cohen, A.S., Soreghan. M. & Scholz, C.A. (1993) Estimating the age of rift lake basin. Geology, V. 36 (3): 544-577.
Cohen, A.S., Lezzar., K.E. Tiercelin, J. -J. and M. Soreghan (1997) New Palaeogeographic reconstructions of Lake Tanganyika:
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Ellis, G. & Scholz, C.A. (Personal Communications). RSMAS, University of Miami, FL and Lacustrine Rift Basin Program,
Department of Earth Sciences, Syracuse University, NY.
Pilskaln, C.H. & Johnson, T.C. (1991) "Seasonal Signals in Lake Malawi Sediments," Limnology & Oceanography, V. 36 (3):544577.
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Africa from lake-level changes,” Nature V. 366, Nov 1993.
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Africa, over the past 100 kYr,” for Special Issue of Paleolimnology —Keynote papers from LENNOU, 2nd Congress on Limnogeology
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Middle Pleistocene--Modern Deposits of the Tanganyika Trough, East African Rift System," Elf Aquitaine Production (BCREDP 16).