Indus Fan
Report of the project:
The southern flank of the Murray Ridge exhibits multiple phases of uplift which tilted older channel-levee complexes of the Indus Fan. Sub-recent channel-levee complexes onlap the ridge flank.
Thinned continental crust underlies the northern Indus Fan. A NE-SW trending ridge, consisting of relict Mesozoic sediments above the acoustic basement, is draped by sediments of the rift and drift stage of the Indian Plate (Bild 1). Hemipelagic sequences became deposited during the northward drift of India that are overlain by post Middle Miocene channel-levee complexes of the Indus Fan. For the first time a sequence of seaward dipping reflectors (SDR) were recognized in seismic profiles beneath the outer Indus Fan (Bild 2). This sequence is interpreted as basalt flows extruded during the continental break-up and exhibiting the initial continent-ocean transition. Oman Abyssal Plain and Makran Wedge The 3000 m deep Oman Abyssal Plain belongs to the Arabian Plate. To the east the Oman Abyssal Plain narrows due to convergence of the Murray Ridge System with the Makran Accretionary Wedge. A distinct unconformity (M) unequivocally could be identified from the Strait of Hormuz to offshore eastern Pakistan. Two sedimentary megasequences are divided by this unconformity. The flat lying, turbiditic sequence M3 onlaps the M-unconformity. The lower sequence (M2) consists of channel-levee sediments of the Indus Fan. Sequence M2 is underlain by hemipelagic sediments and volcanoclastics (M1). In the Oman Abyssal Plain M1 overlies the oceanic basement of presumed Cretaceous age dipping northward below the Makran Accretionary Wedge (Bild 3a) and (Bild 3b). To the southeast the M-unconformity outcrops along the northern flank of the Murray Ridge. Isolated occurrences of the M-unconformity are also visible in the deeply subsided Dalrymple Through, which is part of the Murray Ridge System (Bild 3b). We conclude the M-unconformity developed in the frame of the uplift of the Makran-Zagros belt which in turn is due to changes in the movement vector of the Arabian Plate. Subsequently the Oman Abyssal Plain was filled with turbidites (conglomerates, sandstones and shales) of Pliocene to Present age shed from the Zagros-Makran belt and the Oman Mountains. In the Northeastern Dalrymple Trough sequence M3 is derived from the Murray Ridge and the Indian continental slope.
Conclusion
Sequences of dipping basement reflectors along the northern Murray Ridge and around 20°30' / 64°30' (Indus Fan) are interpreted as basalt flows indicating the ocean-continent transition during the initial continental break-up.
The Murray Ridge System is of continental origin and experienced stages of transpression and transtension, and a multi-phase volcanism from Paleocene to Upper Miocene/Pliocene. The Murray Ridge System borders the Indian and Arabian Plates and is active since the Paleogene. Recently the Murray Ridge System is in a trantensional, dextral strike-slip setting (Bild 4).
The Indus Fan is underlain by thinned continental crust in the area of investigation. Relict sedimentary ridges of Mesozoic(?) age are onlapped by hemipelagic drift sediments and channel-levee deposits of the Indus Fan.
Literature:
- Clift, P.D., Shimizu, N., Layne, G., Blusztajn, J., Gaedicke, C., Schlüter, H.U., Clark, M. & Amjad, S. (2001): Development of the Indus Fan and its significance for the erosional history of the western Himalaya and Karakoram. Geol. Soc. Amer. Bull., 113 (8), 1039-1051.
- Schlüter, H.U., A. Prexl, Ch. Gaedicke, H. Roeser, Ch. Reichert, H. Meyer & C. von Daniels (2002): The Makran accretionary wedge: sediment thickness and ages and the origin of mud volcanoes. Marine Geology, 185, 219-232.
- Gaedicke, C., Prexl, A., Schlüter, H.-U., Meyer, H., Roeser, H. & Clift, P. (2002): Seismic stratigraphy and correlation of major regional unconformities in the northern Arabian Sea. In: Clift, P.D., Kroon, D., Gaedicke, C. & Craig, J. (eds) The Tectonic and Climatic Evolution of the Arabian Sea Region. Geol. Soc. Lond. Spec. Publ., 195, 25-36.
- Gaedicke, C., Schlüter, H.-U., Roeser, H., Prexl, A., Schreckenberger, B., Reichert, C., Clift, P. & Amjad, S. (2002): Origin of the northern Indus Fan and Murray Ridge, Northern Arabian Sea: interpretation from seismic and magnetic imaging. Former title: Structure and Origin of the crust below the northern Indus Fan and Murray Ridge System, northern Arabian Sea. Tectonophysics, 355, 127-143.
