An IODP Workshop for Drilling of the Indian Ocean Fan Systems


23-25th July 2003
University of Colorado
Boulder, Colorado, USA


Sponsored by JOI/USSSP
National Science Foundation and
IOMAC (Indian Ocean Marine Affairs Coooperation)



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indus delta
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Landsat image of the Indus Delta, Pakistan, source of the Indus Fan.




Summary

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 community.



Workshop Convenors


Peter Clift
Department of Geology and Geophysics
MS#22, Woods Hole Oceanographic Institution
Woods Hole, MA 02543,
USA


Peter Molnar
Cooperative Institute for Research in Environmental Science (CIRES)
Department of Geological Sciences,
University of Colorado
Boulder, CO 80309-0399
USA






Introduction

    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 IODP community.


Brahmaputra

Satellite image of the Ganges-Brahmaputra delta in flood during the monsoon.
This fan is largely fed by material from the Himalayas, rather than material
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 processes.


 levees

Seismic reflection profile from the proximal Indus Fan showing the channel-levee
complexes that form the bulk of the fan systems and that must be mapped and
then drilled during any IODP campain in the region.





Objectives


    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 drilling strategy.
    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.





Scientific Rationale

    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.



irrawaddy

Space shuttle image of the Irrawaddy delta. The Irrawaddy and its neighbor the Salween
are often overlooked when considering the Indian Ocean fan systems, but
 represent important and different components of the Asian erosion history.


Participants

    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.





References


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 82:133–165.

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, 1039–1051.

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.


Related links

Integrated Ocean Drilling Program

Ocean Drilling Program

ISAS Office

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 overview.




Page is maintained by

Peter Clift
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".