Late Cenozoic seismic stratigraphy of the Andaman Forearc Basin, Indian Ocean

Abstract

Interpretation of new multichannel seismic reflection data from the Andaman Forearc Basin (AFB) in the northern Indian Ocean is presented here. The highquality multichannel seismic data from the Andaman Forearc region enable us to examine the seismic characters and to demarcate seismic sequences bounded by distinct unconformities. Ages of marked seismic horizons have been calibrated with available litholog data from nearby industry boreholes. Seismic interpretation of new data shows that the AFB is filled with * 4.5-s-two way travel time (TWT) thick Neogene to Recent sediments. The entire basin assemblage exhibits two distinct major sequences pertaining to the Neogene and Quaternary times. A large part of the basin is filled with intermittent mass transport deposits (MTD). We infer that the episodic uplift of the Invisible Bank, protuberance of the outerarc and regular deformation through reactivation of preexisting normal faults since the Pleistocene could be attributed as causal mechanisms for the MTDs. Strong bottom simulating reflectors are identified in the Late Miocene and younger sediments of the outerarc and AFB at a depth of * 0.6 s TWT and correspond to the presence of gas hydrates in this region. Our interpretations have significant implications for geodynamic as well as resource exploration in the AFB.

Structural complexity in the boundary of forearc basin – accretionary wedge in the northwesternmost Sunda active margin

“…The WAF remains a prominent morphologic feature to the north of the ASC and probably was one of the primary active structures prior to the initiation of spreading in the Andaman Sea (Cochran, 2010). The northern segment of this fault zone may extent from the Gulf of Martaban in the north (Cochran, 2010;Curray, 2005;Goli and Pandey, 2014;Pandey et al, 2017) to offshore Nicobar Island (Pandey et al, 2017). However, the southern boundary of this northern segment should be observed in high resolution bathymetry data.…”

“…Recently acquired seismic reflection data in the Andaman Sea also support this mechanism for the EMF by showing a large subsiding basin to the east of the EMF (Moeremans and Singh, 2015). However, re-observation on the data set reveal that anticlinal structures are prominence in the area of the EMF (Goli and Pandey, 2014;Moeremans and Singh, 2015;Pandey et al, 2017), suggesting that vertical fault in the slope of the EMF seems to be unlikely. These folded sediments in the EMF zone may coeval to the younger sedimentary successions observed in Andaman Island (Allen et al, 2007;Roy and Banerjee, 2016).…”

“…anticlinal structures and landward-vergence thrusts are prominent in the DFZ (Goli and Pandey, 2014;Pandey et al, 2017). However, the width of DFZ decreased toward south with the occurrence of steeper thrust with the deformed strata.…”

“…The WAF is traceable on the bathymetry as a linear feature extent farther south to offshore Nicobar and even to northern Sumatra (Figure 1). A surface fault break had been proposed in the area around Nicobar Island by some author (Pandey et al, 2017) although there is no high resolution bathymetry to support that. However, relocation of the hypocenters of events between the 2004 and 2005 Sumatran earthquakes show activity only in the segment of WAF from the spreading center to the Nicobar Island (Cochran, 2010).…”

Methane gas flares in the forearc basin of the Andaman-Nicobar subduction zone

“…Our primary focus in the Andaman basin is on the forearc region encompassing accretionary prism sediments, a forearc high, and a forearc basin. This region spans roughly 50 km east-west and extends ∼900 km north-south, stretching from the southern extremities of the Irrawaddy Delta to the northern reaches of Sumatra (Pandey et al, 2017). The forearc basin (Figure 1B), situated to the north of Nicobar Island, contains 3-5 km thick sedimentary layers, primarily shaped by the interplay of tectonic forces and sediment deposition over roughly 60 million years (Dickinson and Seely, 1979;Moeremans and Singh, 2015).…”