Downloaded from http://sp.lyellcollection.org/ by guest on October 2, 2021 Tectonic and climatic evolution of the Arabian Sea region: an introduction PETER D. CLIFT 1, DICK KROON 2, CHRISTOPH GAEDICKE 3 & JONATHAN CRAIG 4 1 Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA (e-mail: [email protected]) 2Institute of Earth Sciences, Free University Amsterdam, de Boelelaan 1085, 1081 HV Amsterdam, The Netherlands 3Bundesanstalt fiir Geowissenschafien und Rohstoffe (BGR), Stilleweg 2, D-30655 Hannover, Germany 4Lasmo plc, 101 Bishops Gate, London EC2M 3XH, UK The evolution of the global oceanic and atmo- The Arabian Sea is the natural laboratory to spheric circulation systems has been affected by study the interaction between orogenic growth and several forcing processes, with orbital variations regional climate change. Ocean Drilling Program being dominant on shorter geological time scales. (ODP) sampling of pelagic sediments on the Over longer periods of time (> 10 Ma) the tectonic Oman margin has revealed a detailed history of evolution of the solid Earth has been recognized monsoonal variability (Kroon et al. 1991; Prell et as the major control on the development of the al. 1992), most notably an intensification of the global climate system. Tectonic activity acts in monsoon at 8.5 Ma, as traced by the abundance of one of two different ways to influence regional Globigerina bulloides and other eutrophic species, and global climate. The earliest solid Earth- foraminifers associated with monsoon-induced climatic interaction recognized was the effect that coastal upwelling in the modern Arabian Sea. the opening and closure of oceanic gateways had Initially this result appeared to correlate well with on the circulation patterns in the global ocean. the start of extension on the Tibetan Plateau, an Major effects on regional and sometimes global event that was linked to a period of rapid plateau climate have been attributed to such changes, e.g. uplift. Consequently, Harrison et al. (1992) and closure of the Isthmus of Panama (Driscoll & Molnar et al. (1993) proposed a direct correlation Haug 1998). Since the late 1980s a second form between rapid Tibetan uplift at that time and a of climate-tectonic interaction has been recog- strong SW monsoon and increased rainfall. Mod- nized, involving the growth and erosion of oro- elling studies support a shift of increased precipi- genic belts. In this second category the Arabian tation from Indochina toward the Himalayas and a Sea region must be considered the global type strengthening of the Asian monsoon during late example. Tertiary time, separate from the strengthening at Growth of the Himalaya and associated Tibetan 8.5 Ma (Flutean et al. 1999). Plateau is now believed to have substantially More recently, fieldwork in Tibet has compli- altered Cenozoic climate. Raymo et al. (1988) cated our ideas about the timing of uplift, with suggested that chemical erosion of the uplifting some workers indicating at least southern Tibet orogen resulted in the draw-down of atmospheric reaching maximum elevation at c. 19Ma CO2, which was deposited as limestone, causing (Williams et al. 2001), whereas others suggest long-term global cooling, as a result of the reduc- rapid uplift of the northern plateau during Plio- tion in this important greenhouse gas. Orogenic cene time (Zheng et al. 2000). Work on the uplift is also believed to affect regional climate monsoon also continues to change our understand- and in particular development of the monsoon. ing of the climatic evolution of South Asia. Derry Summer heating of air above the Tibetan Plateau & France-Lanord (1997) proposed that the 8- is known to have induced a strengthening of the 7 Ma period in fact represented a weak monsoon, monsoon (Manabe & Terpstra, 1974), and so with greater regional aridity rather than the stan- tectonic uplift of the plateau has been linked to dard image of greater precipitation. Clearly much strengthening of the monsoon (Raymo & Ruddi- work remains in defining the timing of the SW man 1992; Molnar et al. 1993). monsoon and the timing of tectonism in Tibet. From: CLIFT, ED., KROON, D., GAEDICKE,C. & CRAIG, J. (eds) 2002. The Tectonic and Climatic Evolution of the Arabian Sea Region. Geological Society, London, Special Publications, 195, 1-5. 0305-8719/02/$15.00 © The Geological Society of London 2002. Downloaded from http://sp.lyellcollection.org/ by guest on October 2, 2021 2 P.D. CLIFT ETAL. Testing climate-tectonic models? Oman margin during most of Paleogene time. Chaubey et al. analyse marine magnetic anomaly Despite the current debate, the Arabian Sea has patterns, and conclude that not only was Paleo- several features that make it the best area globally gene spreading very asymmetric, with the Arabian to examine solid Earth-climatic interactions. The Sea accreting much faster than the Somali Basin, climatic signal is strong, especially with regard to but also India-Somali motion slowed rapidly after the monsoon, and the rates of sedimentation are 52 Ma. The evolution of the passive Indian margin often high, allowing detailed palaeoceanographic before collision with Asia is described by Sinew- records to be reconstructed. The Indus River has a ing et al. in a stratigraphic study of the southern large output, equivalent to that of the Mississippi Kirthar Fold Belt in Pakistan. Rift shoulder uplift River, and carries an erosional record of the high and erosion of Middle Jurassic limestones dates topography north of the High Himalaya, i.e. the the separation of India from East Africa. Subse- Karakoram and western Tibet, which are the quently, two phases of ophiolite emplacement are regions responsible for the monsoon. The modern recognized, in Late Cretaceous and Early Tertiary climate of arid conditions, punctuated by heavy time. Late Cretaceous (Campanian and Maastrich- seasonal rains, contributes to enhancing erosion, tian) submarine fans are interpreted to reflect the products of which can be found interbedded thermal uplift of India as a result of the Deccan with dateable fossiliferous sediments in the Indus Plume. Subsequently, Middle Eocene northerly- Fan. The western Himalaya and Karakoram have derived clastic sediments from the early Himalaya been the focus of much recent fieldwork, often constrain the age of collision in this region. The involving high-resolution radiometric dating of Kirthar Fold Belt is interpreted as an offshore basement units. This means that the thermal and equivalent of the Murray Ridge, which is under- tectonic development of these ranges can be lain by thinned continental crust. accurately correlated with the marine records. The slowing of India-Asia convergence after Indeed, the very fact that the Arabian Sea is 52 Ma described by Chaubey et al. is broadly in surrounded on three sides by land, often arid and accord with the evolving sedimentary character with good exposure, makes this an ideal area to within the Asian forearc basin revealed by Clift et attempt linked marine and land-based field experi- al. This study shows an influx of ophiolitic and ments. carbonate platform material from a deformed Much work remains to be done in understand- Indian margin into the Jurutze forearc basin no ing the tectonic and climatic evolution of the later than Ypresian time (>49 Ma). The subse- Arabian Sea area. Efforts are now under way to quent deposition of the alluvial Indus Group in expand our sampling on- and offshore so as to the Indus Suture in Ladakh has been linked by understand the temporal variations in climate, Clift to the earliest activity of a palaeo-Indus erosion and tectonism. Such efforts necessarily River, which flowed into a delta in the Katawaz require international collaboration between re- Basin of western Pakistan and Afghanistan by searchers within the region and elsewhere. Addi- Early Eocene time, and must have reached the tional marine geophysical surveys and deep Arabian Sea by Mid-Eocene time. Some of that scientific drilling are required in the Arabian Sea material has subsequently been accreted to the to construct the detailed records required to active margin of Asia. McCall shows that the quantify the nature of solid Earth-climatic cou- Makran Accretionary Complex contains large pling. None the less, much has been achieved by a volumes of Paleogene turbidites that were added series of cruises and field campaigns over the last to that margin, and may represent a palaeo-Indus 10 years, since the last major review of the region. Fan, in addition to the material still found in the It was the desire to bring together workers spread Arabian Sea. Clift et al. show that the Indus across many countries and disciplines that Group Basin was inverted no later than 14 Ma, prompted the special meeting of the Geological probably close to the time of tectonic uplift along Society, where much of the work published here the Murray Ridge (20 Ma), but that the Indus was presented. River has remained stationary in the suture since The development of the Arabian Sea before that time. India-Asia collision is reconstructed by three of Clift presents a sediment budget for the Indus the papers presented here. Royer et al. use a Fan that shows peak sedimentation rates in mid- compilation of marine geophysical data to demon- Miocene time accompanied by channel-levee strate that spreading in the Arabian Sea at 61- accumulation on the mid-fan, during a period of 46 Ma has been affected by a series of successive strong tectonic activity in the Karakoram, and ridge propagation events along the Carlsberg possibly linked to an early initiation of the SW Ridge, and that the Arabia-India plate boundary monsoon. Closer to the coast, Daley & Alam was located west of the Owen Ridge along the provide a review of the seismic stratigraphy of the Downloaded from http://sp.lyellcollection.org/ by guest on October 2, 2021 INTRODUCTION 3 offshore Indus Basin (Pakistan Shelf), highlighting Quaternary period and the SW monsoon was the existence of two distinct phases of canyon active during interglacial periods.