An NSF/ICDP Workshop on
Scientific Drilling on Lakes Malawi and Tanganyika

October 10-16, 1999
Club Makakola, on the southwestern lakeshore of Lake Malawi

Workshop Report
EXECUTIVE SUMMARY


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Introduction

       During the week of October 10, 1999, a group of 47 scientists, engineers, local institutional representatives, and funding agency administrators met at Club Makakola, Malawi, on the shore of Lake Malawi, to review the prospects for scientific drilling on Lakes Malawi and Tanganyika. The meeting was opened by the Hon. Harry Thomson, Minister for Natural Resources and Environmental Affairs of Malawi, and was followed by an open discussion of the natural resources of Lake Malawi. Participants included representatives from Malawi, Tanzania, the United States, and 8 other nations in Africa and Europe. Support for the workshop was provided by the U.S. National Science Foundation (Paleoclimate, Continental Dynamics, and Geology and Paleontology programs), and from the International Continental Scientific Drilling Program. Major topics considered during the meeting included reviews of the major scientific themes to be addressed through drilling, roles of local institutions, engineering and logistical concerns, and the funding environments within likely target funding agencies.

Workshop Agenda

       Many of the workshop discussions were centered around the current proposal submitted to the ICDP and NSF for the GLAD800 drilling rig, a lightweight coring system designed for sampling lake basins to a total drilling depth of 800-1200 meters. Administrative, financial and engineering infrastructure of the GLAD800 concept were considered during this opening session.Following brief summaries of the existing science programs, several speakers presented science reviews in the areas of crustal structure and rift basin evolution, paleoclimatology, environmental background to human origins, paleoecology and evolutionary biology, and geochronology and paleomagnetic studies in lacustrine basins. Several breakout sessions provided the opportunity for international groups to consider key questions to be addressed during scientific drilling. Summary white papers on the four main scientific themes are presented following this summary. A 1-day field trip to the Lake Malawi port facility and shipyard at Monkey Bay, the container port at Chipoka, and to the Limnological Field Station at Senga Bay provided participants with a sense of local infrastructure around the lakeshore.

Plenary Sessions


       Following the science reviews, there were several plenary discussions covering the following topics: Roles for Local Institutions, Reviews of Seismic Reflection Site Survey Data, Engineering and Logistical Issues, and Funding Conditions within Target Funding Agencies.

Roles for Local Institutions

       Developing opportunities for capacity building within the geosciences community in East Africa is a high priority objective of the local institutions that were represented at the workshop. The drilling program should develop a plan for expanding educational opportunities at various levels, including training of graduate students at local universities and abroad, and enhancing professional growth of the present staff of professionals in University and government positions. In addition to training, it is important for the project to explore opportunities for improving the equipment and instrumentation infrastructure at Universities and within government-supported laboratories.

       In addition to capacity building, a top priority for local governments is to expand the understanding of the regional geology of Lakes Malawi and Tanganyika. In order for countries such as Malawi and Tanzania to best manage their natural resources, it is critical to improve the state of knowledge of the subsurface structure, stratigraphy and lithofacies variability of the lakes of the western branch of the rift valley.

Reviews of Seismic Site Survey Data

       Considerable amounts of seismic reflection data of different type and vintage have been acquired on Lakes Malawi and Tanganyika. In the mid-1980's Project PROBE acquired about 4500 km of 24-fold seismic reflection data on the two lakes, in reconnaissance grids with line spacing s of 8-16 km. These data show that the lakes are each underlain with upward of 5-6 km of syn-rift lacustrine sediment. In the case of Lake Malawi, which has the greatest concentration of data, it appears that the sedimentary section thins from a maximum of 5-6 km in the northern part of the rift valley to a few hundred m thickness at the southernmost part of the lake. Since 1992, several medium-resolution single-channel seismic surveys have been undertaken over selected areas on both lakes. These seismic images provide information on the seismic stratigraphy of the lakes to 1-2 km sub-bottom, at a vertical resolution of 1-2 m. These data reveal the complex facies geometries evidently inherent on such tropical lakes, and reveal that several unconformities exist in the stratigraphic section. In the case of Lake Malawi, shallow unconformities produced by dramatic drops in lake level are observed in water depths of more than 500 m, suggesting that it will be necessary to drill in water depths >500 m in order to obtain a continuous stratigraphic record in that lake.

Engineering, logistics, and drilling strategies

       Several engineering presentations covered the proposed GLAD 800 lake drilling rig, Ocean Drilling Project- type drilling tools, and deployment of this equipment on a modular barge system with dynamic positioning. The GLAD 800 concept was originally proposed for small-medium lakes, but is also adaptable for large lake drilling, including extending the drill string to 1200 m from 800 m, through use of a narrower-diameter drill string. Thus the GLAD rig appears to be adequate for subsurface sampling to depths of several hundred meters in both Malawi and Tanganyika. ODP drilling/sampling tools, including the Advanced Piston Corers, are effectively off-the-shelf technology and are easily fit to the GLAD rig.

       Adapting local vessels for drilling operations is probably the most economical means of providing a drilling platform for a single drilling operation. However it was demonstrated that over the lifespan of several large lake projects it may be cost effective to acquire a modular (@C-Float@) barge system to serve as a drilling platform on successive lake drilling projects. Options for positioning the drilling platform included an anchor mooring system, dynamic positioning system, or hybrid system involving a combination of dynamic positioning and anchoring technologies. Whereas anchoring/mooring systems are simple and robust, they are slow to deploy and require a large anchor-handling tug for mooring deployment. Dynamic Positioning Systems involve large up-front costs and require careful maintenance and oversight during operations, but offer the greatest flexibility and rapid deployment capability. Given the rapidly changing sea states on the lakes, this may be the most advisable choice of positioning technology, according to the engineering team present at the workshop.

       Several strategies were discussed for initial drilling, which will likely be proposed first for Lake Malawi, on account of its favorable infrastructure and thorough site survey geophysical data sets already in-hand. Since distances across Lake Malawi are significant, it is likely that 2 support vessels will be required for servicing the drilling platform. Additionally, drilling operations will likely be carried out on a 24 hour per day, 7 day per week basis during the favorable weather window (December-March). It is unlikely that the GLAD drilling rig will be able to operate in sea states greater than 1-2 m, therefore it will be necessary to factor in weather delays when developing drilling operation time lines.

Reviews of funding environments at NSF and ICDP

       Several presentations considered the state of funding of the Earth System History Program at the U.S. National Science Foundation, and at the International Continental Scientific Drilling Program. These presentations placed the proposed scientific effort into a realistic fiscal framework.The ICDP will fund up to 1/3 of total operational costs for any given drilling program, with the balance of the funds to be derived from national science agencies. In addition, ICDP is able to provide additional funding for ancillary tasks such as downhole geophysical logging. It is expected that the total drilling budget for a 4-site project will be in the vicinity of $2M, USD.

Excursions to scientific staging sites

       October 14, we ran an excursion to the potential engineering staging sites at Monkey Bay, Chipoka, and to the Lake Malawi Biodiversity Project lakeside facility at Senga Bay, a possible site for core handling and conducting preliminary whole-core analyses. All three sites were observed to be highly suitable. In Monkey Bay, local engineers provided a tour of the local shipyard with its machine ships, slipway, two main piers, and dry-dock facility . Three possible support vessels were in port in Monkey Bay, and seen by the participating scientists. These vessels included the S/V Timba (Dept. of Surveys), the R/V Usipa (Lake Malawi Biodiversity Project) and the R/V Ndunduma (Dept. of Fisheries). In addition, two other vessels were inspected as possible drilling platforms: the barge Viphya (52 m), and the container ship Katundu (~70 m), operated by Malawi Lake Services. The initial impression of the engineer from Seacore Ltd., was that the barge Viphya, with modifications, would be an adequate drilling platform for Lake Malawi.

Recommendations

Thematic Science Summaries

       The following pages contain four separate thematic summaries covering areas of Paleoclimate Studies, Basin Evolution Studies,Evolutionary Biology, and Environmental Background to Human Origins

Paleoclimate Studies

       The large lakes of the East African Rift Valley are unique among the large lakes of the world in terms of their sensitivity to climate change and their long, continuous, high-resolution records of past climate change in the tropics. The paleoclimate group identified three main questions to be addressed by deep drilling in Lake Malawi:

Elaboration:

GeoChronology:


We are confident that the suite of geochronometers available in Lake Malawi sediments will provide sufficient control to develop a rigorous age-depth model. Magnetostratigraphic and low-field-susceptibility measurements will provide the backbone of our geochronological work. These techniques have been applied successfully in other ancient lakes (i.e. Lake Baikal). This record will be calibrated using a series of horizons dated by a range of independent techniques. Reliable radiocarbon chronologies using woody material and charcoal exist for the last 20 ka. We anticipate that this approach will provide age control to 40 ka. In addition, there are a series of carbonate-rich horizons deposited during periods of evaporative concentration of lake waters. These have the potential to be dated by uranium series techniques (isochron method, e.g. Bischoff and Fitzpatrick, 1991), developing chronologies for the last 400 ka. Finally , the numerous volcanic ash layers present, particularly in the northern basin, provide opportunities for Ar-Ar dating. This should be possible for sediments older than 25 ka given the abundance of crystalline material in some of the young ash layers in the northern basin. In addition, trace element fingerprinting of these ash layers will provide a means of developing stratigraphic linkages among cores

References

Basin Evolution Studies

       Lakes Malawi and Tanganyika are among the largest Aclosed@ sedimentary systems on earth, and hence are ideal sites for evaluating processes of basin evolution. Their stratigraphic record contains a rich history of interplay between surface, near-surface, and crustal processes ranging from climatic forcing of sediment loadings (e.g. Soreghan et al., 1999) to deep-crustal control of extensional deformation and associated vertical movements that impact regional climate. There are three main sets of questions to be considered under the framework of Basin Evolution: Chronology and Active Tectonics, Lithofacies Calibration, and Thermal Structure.

I. Chronology and Active Tectonics

       Using dated drill cores, extensive seismic reflection grids (e.g. Rosendahl, 1987; Scholz, 1995), and information on footwall uplift and denudation and catchment evolution (e.g. van der Beek et al.,1998), we can generate well-constrained models of sediment mass and flux rates unavailable from other sedimentary systems. In order to accurately study tropical paleoclimate history and evolutionary biological records on a time scale of 10-1000 kyr it is necessary to determine the morphotectonic boundary conditions for the rift basins. Additionally, a well-constrained basin chronostratigraphy will allow us to assess with high temporal precision the evolution of linked fault systems (e.g. Anders and Schlische, 1994) within the basin at different scales in space and time

The main question:- What are the rates of fundamental basin-forming and basin-filling processes (e.g. subsidence, heat flow, extension, margin uplift, sediment supply, lake level change, sediment compaction) in continental rifts and how episodic or continuous are these processes? In order answer this question, we set the following goals:

GOALS

TOOLS

A stratigraphic test of the major part of sedimentary section (through the Pliocene) in these lakes is the highest priority for local institutions, and will provide the principal basis for renewed capacity-building in the East African regional geoscience community.

II. Lithofacies calibration, Sedimentology and Sedimentary Geochemistry

       The first-order indicator of environmental change in the Lake Malawi and Lake Tanganyika rift basins is sediment lithology (texture and composition) (Soreghan and Cohen, 1996; Soreghan et al., 1999; Wells et al, 1999). High-amplitude and high-frequency shifts in lake water levels exert extreme forcing on sediment character (Scholz and Rosendahl, 1988; Scholz et al., 1990); this is accomplished through changes in base level, sediment supply, catchment area conditions, and limnological and biotic boundary conditions. Rapid facies variations, both laterally and vertically are the paradigm in these basins.

The main question:- What are the principal controls on the deposition of the main sedimentary facies in tropical rift basins, what are the first-order characteristics of these lithofacies, and how do they accumulate in space and time?

Deriving the three-dimensional variability of depositional facies in rift basins is fundamental for extracting paleoclimate and deformational histories. This 3-D geometry is well-established from existing seismic reflections data. However the seismic facies framework must be calibrated using continuous sediment cores, and down-hole geophysical data.

Principal goals are to :

III. Thermal Structure of the Rift Basin


The main question:-
What is the nature of heat flow across the Lake Malawi rift basin, and how has the thermal history impacted the evolution of extensional faults in the rift basin.

       In this project, we propose to use new heat flow observations obtained from the drill holes in Lake Malawi to critically evaluate models for the structural development of rift faults. Although there is a large volume of scientific literature on continental rifting, substantial gaps still remain in our understanding of how continental rifts form and evolve structurally. In particular, little is known about fault growth during the earliest stages of rifting, in part because fault growth is directly linked to the thermal and mechanical structure of the lithosphere (Cowie, 1998; Jackson and Blenkinsop, 1997; Hayward and Ebinger, 1996; Ebinger et al., 1999; Scholz and Contreras, 1998), for which we have few constraints. Heat flow observations provide a first?order constraint on the thermal structure of the lithosphere, and without such constraints it is not easy to assess the mechanical state of the lithosphere at the time of rifting.

       While heat flow measurements have been made in other areas of East Africa, they either come from unrifted parts of the East African Plateau (Nyblade et al., 1990, Nyblade, 1997), or else from regions of the Kenya rift where the crustal thermal regime has been hydrologically disturbed (Whieldon et al., 1997). Marine type heat flow measurements were made several decades ago in Lakes Malawi, Tanganyika, and Kivu (Von Herzen and Vacquier, 1967; Degens et al., 1971; Degens et al., 1973), but the uncertainties associated with these measurements are so large (>50%) that the data provide only weak constraints the thermal structure of the rifted lithosphere. Nonetheless, they suggest that crustal temperatures beneath the rift are elevated, while most fault models assume that the crust is cold and brittle (Cowie, 1998; Jackson and Blenkinsop, 1997; Hayward and Ebinger, 1996; Ebinger et al., 1999; Scholz and Contreras, 1998). The proposed drill holes in Lake Malawi would afford us an opportunity to make high quality conventional heat flow determinations that would indicate to what extent the rifted crust is thermally modified.

       Heat flow observations can be made in the drill holes by logging temperatures several times after drilling is complete. From the multiple measurements, the disturbance to the thermal field around the drill hole can be determined and an estimate of the equilibrium temperature s can thus be obtained. In addition to temperature measurements in the drill holes, core samples will be needed to measure thermal conductivities.

References


Evolution of Biodiversity and Ecology in Ancient Lakes: Biological Objectives of deep drilling in Lakes Malawi and Tanganyika


The Biological Significance of Lakes Malawi And Tanganyika

Lakes Malawi and Tanganyika are aquatic island systems of elevated endemic biodiversity, unparalleled for their potential to test hypotheses of comparative evolution on large scales. The sedimentary record of these lakes offers us the opportunity to resolve both evolutionary and ecological changes in their biota at time scales of decades, over hundreds of thousands to millions of years

Despite their long histories and geological similarities, the patterns of diversity and genetic differentiation of the biota differ dramatically between Lakes Malawi and Tanganyika . Both lakes were colonized by cichlid fishes, thiarid gastropods and ostracode crustaceans , but these exemplar taxa currently have contrasting aspects in the two lakes. Approximately 1000 fish species are estimated to have evolved within the cradle of Lake Malawi, which is approximately 10% of all freshwater fish species in the world. Despite their astonishing multitude, these species encompass a rather modest degree of molecular genetic and morphological change (Kornfield, 1978; Moran et al., 1994; Parker and Kornfield , 1997). The fishes in Tanganyika are genetically and morphologically much more diverse than those in Malawi (Sturmbauer and Meyer, 1992, 1993)., yet total only 300 species (which is still more than all the species in the 10s of thousands of North American lakes combined ). In Lake Tanganyika, about 240 out of 250 species of prosobranch gastropods and ostracode crustaceans are unique to that lake, and like the cichlid fish, form numerous distinct, divergent lineages (Michel, 1994; Park and Downing, in press). The living prosobranch gastropod fauna of Lake Malawi has undergone only limited differentiation and few if any endemic ostracodes are reported from this lake (Martens, 1994; Michel,1994)

Understanding the history of the Malawi and Tanganyika radiations, their similarities and differences, represents an extraordinary opportunity for evolutionary biology. In these lakes we have a unique opportunity to investigate the dynamics of evolutionary and ecological change. Patterns of speciation, the origin of major morphological evolution, and the origin of major reorganizations in community structure can all be investigated in a comparative setting in these two lakes, in the context of high resolution, long stratigraphic records. Paleoenvironmental, tectonic and climatic reconstructions obtained from other components of this drilling program will provide the context for interpreting those dynamics.

Major Questions to be Addressed in Evolutionary Biology And PaleoEcology

For our purposes of evolutionary studies the most promising groups of fossil organisms are the gastropod molluscs and ostracode crustaceans. In addition to their preservation potential these animals are small (easily obtained in cores), can be identified to species level as fossils, and provide interesting targets for evolutionary studies.

Constraints on Drilling Targets


As we have alluded to above, not all lacustrine organisms are going to be equally amenable to study in this project. Our best hopes for evolutionary records clearly lie with small, benthic, shelled invertebrates. These organisms are completely restricted to the oxic zones of the two lakes today, and will not be found therefore in deep water sediments, except during periods of significant lake level decline. This assertion is based on considerable coring experience of the authors in Holocene and Late Pleistocene sediments and the observation that deep water transport of dead shell material, while a real phenomenon on steep slopes, is unlikely to be important in the types of locations where we will drill (flat, away from rocky highs). For this reason we strongly advocate that at least some cores in each lakes be taken from relatively shallow, sublittoral sites, or sites that have likely been at such depths over geologic time. We recognize that these areas may not be ideal for other purposes, such as the highest resolution paleoclimate studies. Nevertheless, the added information such shallow sites will provide us for evolutionary ecology studies makes the additional effort of obtaining such records well worthwhile. This justification is further strengthened when one considers the potential of these same, shallow-lake organisms for providing paleoclimatic proxies such as carbonate, growth banding (for bivalves), trace elements and stable isotope records, all of which are unobtainable in deep water.

Our experience suggests that large structural platforms or perhaps distal deltaic environments are the best sites for collecting the types of records we require, with paleowater depths of 0-100m. Clearly depth will change over time, but the lakes seem to return to similar spillway elevations repeatedly, so modern depth ranges are probably realistic guides for locations of abundant fossils in cores.

Our prior experience in the large lake coring in these types of environments suggests that decadal-scale resolution is quite feasible. Bioturbation exists in these water depths, but is relatively unimportant (2-3cm mixing depths) for the likely sampling spacing we would employ. Depositional hiatuses during lake low stands are a greater concern for our records, but these hiatal intervals in the shallow site records would be dovetailed with records from deeper basinal sites, so we can expect a reasonably complete record at the millenial scale considering the lakes in their entirety.

References


Impact of Lake Malawi/Tanganyika Drilling on Issues of Human Origins
A Prospectus


Abstract

Paleoclimate research focusing on Africa has made a rich contribution to the development of hypotheses regarding human evolutionary history.

Two examples: The turnover pulse hypothesis (advanced by E. Vrba, 1980-1995) and the variability selection hypothesis (advanced by R. Potts, 1996-1998) were developed as a direct result of the past two decades of research on global paleoclimates and environmental change in ancient African lake basins.

Turnover pulse means that species origins and extinctions, including episodes involving hominids, were initiated by dramatic climatic change (aridity and cooling) in Africa during the late Pliocene and again in the Pleistocene. Variability selection draws attention to the oscillation evidenced in global and regional sedimentary records. According to this body of evidence, environmental fluctuation caused inconsistencies in the adaptive settings of early humans and thus had a formative impact on the origin of toolmaking, brain enlargement, and other advances in human adaptability.

So far, these ideas have mainly been tested by looking at evidence of environmental change in terrestrial sediments (e.g., the Turkana and Olorgesailie basins) and deep-sea cores. Terrestrial records, however, have many gaps due to erosional unconformities, while the marine record is rather far removed from the places where hominids lived.

Recovery of high-resolution cores from Lakes Malawi and Tanganyika would provide an unparalleled record of environmental change relevant to the time and place of early human origin and the evolutionary history of our own species. An international contingent of geologists, paleontologists, and archeologists are ready to dedicate themselves to comparing the records from these African lakes to those of past lakes and associated settings inhabited by hominids.

Cores drilled from Lakes Malawi and Tanganyika will offer a body of evidence directly pertinent to the fact that human adaptations have evolved in association with African lakes for over 4.4 million years. This body of evidence signifies an opportunity that is otherwise unavailable for testing the link between human evolution and change in climate and the biota.

Potential Case Studies