The interactions between the solid earth and the atmosphere
and oceans are presently only understood in outline and represent a
major field for scientific exploration in the 21st Century. Exploring
the relationships between mountain building and climate change has been
highlighted as a primary objective for IODP.
In particular, the growth of the Himalaya and Tibet and their effects on
the climate of South Asia are recognized as the prime example of climate-tectonic
interactions in the recent geologic past. Moreover, they have been the subject
of several ODP and IODP proposals for
drilling the Indus and Bengal Fans. Together these fans record most of
the Cenozoic erosion in Asia and must be accounted for if the relationships
between climate, tectonics and erosion are to be quantified. Because of their
different drainage basins, each fan contains a different record of erosion
and climate change, each of which must be deciphered if the behavior of the
entire system is to be understood. By bringing together a core community of
both marine and land-based earth, ocean, and atmospheric scientists and identifying
the key scientific objectives, we aim subsequently to propose to IODP a coherent
drilling strategy for scientific exploration in the region. In this way we
will demonstrate why both Indus and Bengal Fan need to addressed and specify
key areas for deep riser and riserless sampling. The two fan proposals are
currently often viewed as competitive with one another, while after the workshop
we hope that IODP will view the resultant revised and new proposals as being
different requests of a single unified community, similar to drilling proposals
for work on the East Pacific Rise and Mid Atlantic Ridge are to the ridge
Department of Geology and Geophysics
MS#22, Woods Hole Oceanographic Institution
Woods Hole, MA 02543,
Cooperative Institute for Research in Environmental Science
Department of Geological Sciences,
University of Colorado
Boulder, CO 80309-0399
Apart from changes in ocean circulation
precipitated by closure of “gateways”, the building of mountain ranges
appears to have the largest influence on global and regional climate.
The Himalaya and Tibet represent the most dramatic example of mountain
building in the recent geologic past, and no topographic feature perturbs
the atmosphere as much as the Tibetan Plateau. Although much of the
exhumation history that once was recorded onshore has subsequently been
eroded, many aspects of the growth of the orogen have been recorded offshore
in the submarine fans of the Indian Ocean. In fact, the Bengal
and Indus constitute the largest sedimentary masses on the planet. The
sediments of these bodies also preserve information on changes in continental
weathering that can be correlated with independent records of oceanographic
evolution, global climate and orogenic exhumation in order to quantify
the relationships between tectonics, erosion and climate. The Integrated
Ocean Drilling Program (IODP) has the opportunity to provide simultaneously
constraints on the understanding of orogenesis in this region and the
impact of mountain building on the climate system.
With the development of both high terrain
and the Asian monsoon during Cenozoic time, a comprehensive study
of sediment deposited in the Indian Ocean Fans offers the opportunity
to quantify the growth of the Himalaya and Tibetan Plateau, as well as
to examine changing rates of erosion and weathering regimes onshore.
Key objectives include testing the hypothesis of a positive link between
Tibetan elevation and monsoon strength (Harrison et al., 1992; Molnar
et al., 1993), as well to the link between Himalaya weathering and long-term
global cooling since the Eocene (Raymo and Ruddiman, 1992). Because the
Indus and Bengal Fans have quite different drainage basins, study of both
is required for a comprehensive understanding of evolving regional erosion.
In addition, the sediments of the smaller Nicobar and Irrawaddy Fans
should provide important information of the nature of erosion in their
drainage basins, which may interact with the Bengal system.
Understanding the Indian Ocean fans was
highlighted by the COMPLEX meeting as being a key objective to future
attempts to examine the links between tectonic and climatic evolution.
At the moment there are several independent proposals active within the
IODP system that propose drilling of the Indus and Bengal Fans, yet how
each relates to the others is not well justified and understood by the
image of the Ganges-Brahmaputra delta in flood during the monsoon.
This fan is largely fed by material from the Himalayas, rather
north of the suture as in the Indus system.
Nature of the Marine Clastic Record
Two widely different processes affect the
composition, facies, and thickness of sedimentary units deposited
in marine settings. Clearly deep seated geodynamic processes create
high terrain that in turn is eroded, but climate profoundly affects
both rates of erosion and the weathering of sediment that winnows it
en route to ocean basins. The basins surrounding the Himalaya provide
particularly good sites for studying the relationship between tectonics
and climate in the generation of sedimentary sequences, because (a) the
rivers of the area drain the world’s highest terrain, (b) the sediment
records the history of the world's most spectacular continental collision
zone, and (c) the current arid climate punctuated by heavy rains during
the Asian monsoon should be more erosive than a more equable climate.
With the development of both the high terrain and the Asian monsoon during
Cenozoic time, a comprehensive study of sediment deposited in the Indus
and Bengal fans offers the opportunity to quantify the growth of the Himalaya
and Tibet, to determine the temporal evolution of the Asian monsoon, and
to isolate the effects of mountain building and climate change on sedimentation.
The early Cenozoic collision of India with
Eurasia and the consequent growth of the Himalaya and Tibetan Plateau
have created the most dramatic relief on earth and, not surprisingly,
a large fraction of the terrigenous sediment eroded of this terrain now
lies on the ocean floor surrounding this region. Thus, the Indus and
Bengal fans should record both erosion of the world's highest terrain
as it grew and the development of one of the earth's most dramatic climatic
phenomena, the Asian monsoon. The two fans, however, cannot be considered
as mirror images of one another. While the Bengal Fan principally drains
the High Himalaya (France-Lanord et al., 1993), the greatest source of
the Indus sediment is the Karakoram Mountains and the Indus Suture (Clift
et al., 2001). Thus although the Bengal Fan represents the bulk of the
erosional detritus shed by the orogen (~80%), the Indus provides a complementary
record of the more internal zones of the orogen.
Existing full drilling proposals aim to
drill the entire thickness of the Indus Fan using a two phase riser
and non-riser approach (595). Proposal 552 intends to drill parts
of the Bengal Fan to provide the Paleogene and early Miocene record
for the eastern Himalaya. In addition, a recent planning letter proposed
a multi-leg program of drilling on the Bengal Fan in order to fully understand
its construction and significant in the light of orogenic and climatic
reflection profile from the proximal Indus Fan showing the channel-levee
that form the bulk of the fan systems and that must be mapped and
then drilled during any IODP campain in the region.
This workshop aims to bring the core community
of those working in the field of climate-tectonic interactions in South
Asia together in order to formulate a list of scientific priorities
and then to pick appropriate drill sites in the fan systems to address
those priorities. We envisage input from both marine geoscientists and
those working on land in the foreland basins and the ranges themselves,
in order to generate the scientific consensus needed to support a multi-leg
The start of IODP is the ideal time to start
such a scientific initiative, because not only are the issues at the
cutting edge of the science at the moment, but for the first time the
possibility of riser drilling allows the deep penetration of these sediment
bodies that were largely beyond the capabilities of the JOIDES Resolution.
The fans further provide a natural arena for building on the stated intention
of IODP to work more closely with the petroleum industry, since the
proximal fan areas are regions of hydrocarbon production and exploration.
Involvement of the industry in the planning stages is crucial, especially
given the potential reservoir of site survey materials that might be
released and which are required for the deep riser work.
Drilling the Indian Ocean fans should provide
the sedimentary record needed to date the emergence of the Himalaya
and Tibet and quantify the rates and location of erosion within this
system. The proposed drilling will generate a record of erosion and
weathering styles within the continental drainage basin that can be
directly correlated to existing monsoon records from the Arabian Sea,
Loess Plateau and Indian foreland basin (e.g., Prell, Niitsuma et al.,
1989). A study of the clastic record using provenance studies augmented
by radiometric dating techniques should reveal the history of erosion
of the Himalaya. In addition, drilling will allow study of the patterns
of erosion using isotopic finger-printing techniques, and the variations
in clay mineralogy that are linked to changes in the weathering regime,
which in turn is likely to be affected by climate. These types of record
are not readily obtained in the exposed sediments of the foreland basin
in the western Himalaya, which are of continental facies. Although paleomagnetic
dating of the Late Miocene-Recent foreland is good (e.g. Badgley and Tauxe,
1990), older sediments are dated only locally by benthic foraminifers found
in sporadic marine intercalations, and mammal or plant material (e.g.,
Bossart and Ottiger, 1989). Although we propose to drill marine sediment,
of course, we do not envision doing so ignorant of what is exposed on
land. Yet, because of the record on land is incomplete, the marine record
holds the vital clues. Drilling will allow the relationship between oceanic
upwelling and monsoonal development in the Indian Ocean to be related
to the Late Miocene–Recent evolution of the western Himalaya and Karakoram.
Space shuttle image of the
Irrawaddy delta. The Irrawaddy and its neighbor the Salween
are often overlooked when considering the Indian Ocean fan
represent important and different components of the Asian
The meeting is open to all with an interest
in the future of the IODP in the Indian Ocean. We envisage a core group
of key scientists who have recently been active in studying the tectonic
evolution of Tibet and the Himalaya, the sedimentary history of the foreland
basins, the growth of the delta systems, the paleoceanography of the Asian
marginal seas, as well as the marine geology and geophysics of the Arabian
Sea and Bay of Bengal. Involvement from scientists based in the countries
around the Indian Ocean is crucial and strongly encouraged via our link
to IOMACS. We also encourage participation by representatives from
the oil companies active in the area. We aim to build on what they already
know of the seismic stratigraphy and age structure of the fans.
Badgley, C. and Tauxe, L., 1990. Paleomagnetic stratigraphy
and time in sediments; studies in alluvial Siwalik rocks of Pakistan.
Journal of Geology, 98: 457-477.
Bossart, P., and Ottiger, R., 1989. Rocks of the Murree Formation
of Northern Pakistan: Indicators of a descending foreland basin of late
Paleocene to middle Eocene age. Eclogae Geologicae Helveticae
Clift, P.D., Shimizu, N., Layne, G., Gaedicke, C., Schlüter,
H.U., Clark, M. and Amjad, S., 2001. Development of the Indus Fan and
its significance for the erosional history of the western Himalaya and
Karakoram. Geological Society of America Bulletin, 113,
France-Lanord, C., Derry, L. and Michard, A., 1993. Evolution
of the Himalaya since Miocene time: isotopic and sedimentological evidence
from the Bengal Fan. In Treloar, P.J. and Searle, M.P. (Eds.) Himalayan
Tectonics, Geol. Soc. spec. publ., 74: 603–622.
Harrison, T.M., Copeland, P., Kidd, W.S.F., and Yin, A., 1992.
Raising Tibet. Science, 255:1663–1670.
Molnar, P., England, P., and Martinod, J., 1993. Mantle dynamics,
the uplift of the Tibetan Plateau, and the Indian monsoon. Reviews
of Geophysics, 31:357–396.
Prell, W.L, Murray, D.W., Clemens, S.C., and Anderson, D.M.,
1992. Evolution and variability of the Indian Ocean Summer Monsoon:
evidence from the western Arabian Sea drilling program. In Duncan,
R.A., Rea, D.K., Kidd, R.B., von Rad, U., and Weissel, J.K. (Eds.,)
Synthesis of results from scientific drilling in the Indian Ocean.
AGU monograph, 70: 447–469.
Raymo, M.E. and Ruddiman, W.F., 1992. Tectonic forcing of the
late Cenozoic climate. Nature, 359:117–122.
Integrated Ocean Drilling Program
Ocean Drilling Program
ODP Site Survey databank
Joint Oceanographic Institutions
Arabian Sea Links
Download the existing IODP proposal for the Indus Fan and Murray Ridge
and the recent site survey addendum.
Download the existing IODP Bengal Fan proposal
and a drilling summary
Page is maintained by
Department of Geology and Geophysics
MS#22, Woods Hole Oceanographic Institution
Woods Hole, MA 02543, USA
Last up-dated 29th August 2003
See details of the related JOI/USSAC workshop on "Continent-Ocean Interactions
in the East Asian Marginal Seas".