Basement tectonics and flexural subsidence along …geophysical data are some of the best utilized...

Geoscience Frontiers xxx (2016) 1e16

HOSTED BY Contents lists available at ScienceDirect

China University of Geosciences (Beijing)

Geoscience Frontiers

journal homepage: www.elsevier .com/locate/gsf

Research paper

Basement tectonics and flexural subsidence along western continentalmargin of India

D.K. Pandey*, Nisha Nair, Anju Pandey, G. SriramESSO-National Centre for Antarctic and Ocean Research, Goa, India

a r t i c l e i n f o

Article history:Received 18 June 2016Received in revised form3 October 2016Accepted 9 October 2016Available online xxxHandling Editor: S. Glorie

Keywords:Continental riftingSubsidenceMumbai Offshore BasinBackstrippingArabian SeaLaxmi Basin

* Corresponding author.E-mail address: [email protected] (D.K. Pandey).Peer-review under responsibility of China University

http://dx.doi.org/10.1016/j.gsf.2016.10.0061674-9871/� 2016, China University of Geosciences (BND license (http://creativecommons.org/licenses/by-n

Please cite this article in press as: Pandey, DGeoscience Frontiers (2016), http://dx.doi.or

a b s t r a c t

The Paleocene-recent post-rift subsidence history recorded in the Mumbai Offshore Basin off westerncontinental margin of India is examined. Results obtained through 2-D flexural backstripping modellingof new seismic data reveal considerable thermo-tectonic subsidence over last ca. 56 Myr. Reverse post-rift subsidence modelling with variable b stretching factor predicts residual topography of ca. 2000 m tothe west of Shelf Margin Basin and fails to restore late Paleocene horizon and the underlying igneousbasement to the sea level. This potentially implies that: (1) either the igneous basement formed duringthe late Cretaceous was emplaced under open marine environs; or (2) a laterally varying cumulativesubsidence occurred within Mumbai Offshore Basin (MOB) during ca. 68 to ca. 56 Ma. Pre-depositionaltopographic variations at ca. 56 Ma across the basin could be attributed to the extensional processes suchas varied lower crustal underplating along Western Continental Margin of India (WCMI). Investigationsabout basement tectonics after unroofing of sediments since late Paleocene from this region support atransitional and heavily stretched nature of crust with high to very high b factors. Computations of pastsediment accumulation rates show that the basin sedimentation peaked during late Miocene concur-rently with uplift of HimalayaneTibetan Plateau and intensification of Indian monsoon system. Resultsfrom basin subsidence modelling presented here may have significant implications for further studiesattempting to explore tectonoeclimatic interactions in Asia.

� 2016, China University of Geosciences (Beijing) and Peking University. Production and hosting byElsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/

licenses/by-nc-nd/4.0/).

1. Introduction

Passive continental margins such as the Western ContinentalMargin of India (WCMI) are typically defined as seismically quies-cent margins where adjoining oceanic and continental lithospheresare gelled together. Passive margins are often flanked by relativelyyoung and expanding ocean basins adjacent to their shelves (Whiteand McKenzie, 1989; Allen and Allen, 2006). The transition fromrifted margin to passive continental margin takes place at the rift todrift transition depending upon whether or not the sea-floorspreading stage was reached. Role of mantle plumes in shapingup of passive rifted margins has been widely debated for long time(McKenzie and Sclater, 1971;White andMcKenzie, 1989; Anderson,2001 and references therein). Plume-rift interactions can signifi-cantly modify the crustal geometry including ContinenteOcean

of Geosciences (Beijing).

eijing) and Peking University. Produc-nd/4.0/).

.K., et al., Basement tectonicsg/10.1016/j.gsf.2016.10.006

Transition (COT) (White and McKenzie, 1989; Kusznir et al., 1995;Watts, 2001). Therefore, identification of COT along passive mar-gins is often crucial due to anomalous nature of underlying crust.Knowledge about COT permits determination of the nature andextent of rifting along a margin. Further, passive margins usuallyexperience broad regional subsidence over a period of time. This isdue to lithospheric cooling following partial/complete attenuationof the continental lithosphere (White and McKenzie, 1989; Kuszniret al., 1995; Buck, 2001) and sediment accumulations. Therefore,the total subsidenceea function of the tectonic, eustatic sea leveland climatic changes over long periods (Watts, 2001; Allen andAllen, 2006) can be used to decipher extensional tectonics alonga margin. Precise knowledge about periodic sedimentation on amargin would provide key constraints about its evolutionaryjourney through time (Hopper and Buck, 1996). Post-rift sedimentthicknesses developed beneath the outer shelf and slope on suchmargins, may range from a few hundreds of meters to tens of ki-lometers (Clift et al., 2002). Marginal sedimentary basins are oftenimbibed with enormous resource potential. Deep penetratingseismic reflection, borehole information and other corroborative

ction and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-

and flexural subsidence along western continental margin of India,

Delta:1_given name

Delta:1_surname

Delta:1_given name

Delta:1_surname

http://creativecommons.org/licenses/by-nc-nd/4.0/


mailto:[email protected]

www.sciencedirect.com/science/journal/16749871

http://www.elsevier.com/locate/gsf

http://dx.doi.org/10.1016/j.gsf.2016.10.006




D.K. Pandey et al. / Geoscience Frontiers xxx (2016) 1e162

geophysical data are some of the best utilized tools to performbasin subsidence analyses to know more about periodic sedimen-tation and its effects on the extensional tectonics.

The central part of WCMI near Bombay High (Fig. 1) is geologi-cally referred as Mumbai Offshore Basin (MOB). This region, havingthick sediments and rich resource potential, is among leastexplored margins in terms of detailed 2-D flexural subsidence an-alyses. In the present study, we explore magnitude of total subsi-dence along WCMI through analyses of marine geophysical data(Fig. 1). Previous studies (e.g. Mohan, 1985; Agrawal and Rogers,1992; Whiting et al., 1994; Chand and Subrahmanyam, 2003)used 1-D backstripping analyses to reconstruct geohistory frombasin stratigraphy along WCMI. However, previous studies wereprimarily based upon scattered borehole data and used 1-D Airytype isostatic compensation (Watts, 2001). The Airy type (i.e. localisostasy) is known to have several limitations as it omits the flex-ural strength of the lithosphere. Resultantly it tends to work wellwith very low effective elastic thickness (i.e. Te z 0) which is notvalid in case of shorter wavelengths of loads on a margin (such asstructures in the range of ca. 10e25 km). Consequently, use of Airyrather than flexural backstripping tends to overestimate factors andmay deliver erroneous subsidence history (Kusznir et al., 1995;Roberts et al., 1998). The flexural approach on the other hand al-lows one to account for ‘sideways’ loads (Kusznir et al., 1995) andproduces much more reliable estimates for calculating basinsubsidence.

The primary objective of this study is to investigate subsidencehistory along WCMI using 2-D flexural backstripping approach(Kusznir et al., 1995; Roberts et al., 1998). In particular, we attempt

64˚

64˚

66˚ 68˚

68˚

14˚

16˚

18˚

20˚

22˚

−4000 −3000 −2000 −1000 0 1000m

28n

27n

26n

Gop-Basin

SaurashtraHigh

Kachchh-SaBlock

WC

WC-23a

WC-25a

-2000m

U1457

U1456Arabian Basin

L a x m i R i d g e

Laxmi BasinAbyssal Basin

Shelf-Margin

S

646666646464˚

2020˚̊̊̊̊̊̊̊̊̊̊̊

22222222222222222222222˚̊̊ India

RRRSRRRRRRSRSRSRSRRRRRRSSRSRSRRRRRRRSR

PPPPPSPSPPPPSSSSPSPSSSPPSSSPSPSSSP

N

100km

Figure 1. Regional bathymetry (m) map of the western continental margin of India (WCMblack lines) used in this study. Solid black triangles with superscripted numbers denote locwhite triangles denote locations of Sites (U1456 and U1457) from IODP expedition 355 (Pa(2002). Solid red circles denote locations of seismic refraction stations (after Naini and TalwHigh. White dashed lines represent possible locations of Continent Ocean Boundary (COB)

Please cite this article in press as: Pandey, D.K., et al., Basement tectonicsGeoscience Frontiers (2016), http://dx.doi.org/10.1016/j.gsf.2016.10.006

to examine creation of accommodation space vis-a-vis flexuraladjustments in the basin which is poorly understood at themoment. Role of eustatic changes as well as sediment loading frompossible ‘sources’ such as Indus fan and denudational dischargefrom peninsular India since its inception is examined. Based on newdeep penetratingmulti-channel seismic (MCS) data and constraintsfrom industry boreholes from WCMI, we reconstruct the verticaltectonics since initiation of late Cretaceous rift-drift process.

2. Regional setting and tectonic framework

TheWCMI, surrounded by adjoining ocean basins in the ArabianSea, is a passive continental margin extending more than 2000 kmlong from Gujarat coast in the north to Kerala coast in the south(Fig. 1). The breakup of East Gondwana initiated in early Jurassic c.a.150 Ma (Courtillot et al., 1986; Storey et al., 1995) followed byseparation of Greater India (IndiaeMadagascar) from Africa ca.130e120 Ma (Reeves and de Wit, 2000). Later, IndiaeMadagascarbreak-up occurred at ca. 88 Ma which is considered as the firstmajor rifting event that modified the WCMI (Agrawal et al., 1992;Storey et al., 1995; Chand and Subrahmanyam, 2003; Yatheeshet al., 2009). Subsequently, a ridge jump in Mascarene Basin dur-ing the late Cretaceous led to the break-up of Seychelles and India(Norton and Sclater, 1979; Naini and Talwani, 1982; Schlich, 1982;Biswas, 1999; Chaubey et al., 2002; Yatheesh et al., 2009). Theemplacement of Deccan flood basalts at ca. 65 Ma is opined to becontemporaneous with the rifting between Seychelles and India(McKenzie and Sclater, 1971; Hooper, 1990; Venkatesan et al., 1993;Subrahmanya, 1998; Pande et al., 2001). The rifting episode is

70˚

70˚

72˚

72˚

74˚

74˚

14˚

16˚

18˚

20˚

22˚

eters

1

34

5 6 8

9

urashtra

Goa

WC-20WC-19

-18

WC-17

W

444WC-1W

774477744744W

1716

15 144

10

11

12 13

Narmada Rift

Mumbai

Dharw

ar trend

Surat

Depressio

n

Ratnagiri F

ault Basinhelf Platform

2

WWGGWWGGGGGGGGWWWWGWGWGWWWWWWGGWWGGWWGGGGGGGGGGGGGWWGGGGGGGWGWGG

BH

I). Superposed are the major tectonic elements and locations of seismic profiles (solidations of the commercial wells in the region (see Table 2 for more information). Solidndey et al., 2016) in the Arabian Sea. Magnetic anomalies are plotted after Royer et al.ani, 1982); RS-Raman Seamount; WG-Wadia Gyot; PS-Panikkar Seamount; BH-Bombaydepending upon the nature of crust in between.


D.K. Pandey et al. / Geoscience Frontiers xxx (2016) 1e16 3

considered to have finally led to the sea floor spreading in theArabian Sea. Although offshore extent of the Deccan flood basalts isyet to be precisely identified nevertheless published literature ar-gues in favour of substantial offshore extent (Biswas, 1982; Mohan,1985; NELP, 2007; Pandey et al., 2011). In addition, Jerram andWiddowson (2005) expressed that it is likely that much of theDeccan flood basalt lava erupted onto existing Precambrian Dhar-war cratonic crust around WCMI (Fig. 1).

The east-west stretch of WCMI varies remarkably from north(ca. 300 km) to south (ca. 80 km) (Zutshi et al., 1993). The presentday shelf break alongWCMI occurs at an average water depth of ca.200 m. A very broad shelf platform in the north makes it as one ofthe largest continental terraces in the world (Fig. 1). The NWeSEtrending horst and grabens are bounded by normal faults. Biswas(1982, 1989) reported disjointed NEeSW trending cross faultssegregating different tectonic blocks (Figs. 1 and 2). From north tosouth these tectonic blocks include the Surat depression, BombayPlatform (i.e. Shelf Platform), Ratnagiri Block, a Shelf Margin Basin,and Abyssal Basin. The paleo (Miocene) shelf edge is reportedmuchlandward with several horst and graben patterns within the MOB(Raju et al., 1981; Rao and Srivastava, 1981; Biswas, 1989). The MOBoccupies a large part of the shelf as well as adjoining deep-waterbasins (Figs. 1 and 2). Existing information (Biswas, 1982; Mitraet al., 1983; Rao and Srivastava, 1984; Mohan, 1985; Whitinget al., 1994; Gombos et al., 1995; Nair and Pandey, in preparation)and interpretation of new high quality multi-channel seismic dataand sediment thickness isopach maps from this study (Fig. 3)suggest that the stratigraphic fill of the basin, covering an area of ca.120,000 km2, consists of Tertiary and Quaternary sediments withsediment thickness varying between 0.1e5 km. Thickest sedimentson the shelf are hosted in coast parallel grabens ca. 50e100 kmoffshore (Fig. 3). High sediment loading since inception of the MOB

64˚

64˚

66˚ 68˚

68˚

14˚

16˚

18˚

20˚

22˚

28n27n

26n

Gop-Basin

SaurashtraHigh

Kachchh-SauBlock

W

WC-1

WC-23a

WC-25a

-2000m

U1457

U1456Arabian Basin

L a x m i R i d g e

Laxmi BasinAbyssal Basin

Shelf-Margin B

Sh

RRRRSRRRRRRRRRRRSRSRSRSRSSSSRRRSSRSRSRSRSRSRSRSRSRSRRRRRRRRSSRRRRRRSRRRRRRRR

PPPPPPPPPSPSPPSSSSSSSPPSPSSPSSSSSPSSSSSPSPPSPSSSSPSSSSPSPPPP

N

100km

−120 −80 −40 0 4

Figure 2. Free air gravity anomaly map of the region derived from satellite altimetry (Sandwsync with various structural highs and lows corresponding to the horst and graben pattern


appears to have structurally modified its shape (Biswas, 1982; Nairand Pandey, in preparation). The sediment depocentres, structuralplays and their potential implications in hydrocarbon explorationmake it crucial to understand overall subsidence behavior of thismargin. Outcome of such studies would be extremely relevant inunderstanding stratigraphic development and basin evolution ofMOB over long periods.

2.1. Seafloor morphology and gravity anomaly

The present day water depth in the study area (Fig. 1) variesbetween shallow (<100 m on the Shelf Platform) to moderatedepths in the Margin Basin (ca. 2000 m) to deep in the AbyssalBasin (>3000 m). Coast parallel variations in the 2000 m isobathdemarcate the present day shelf break (Fig. 1). Several highs andlows are observed on the bathymetric data along the coast whichare attributed to the horst and graben structures (Biswas, 1982).Distinctly elevated morphological features (seamounts) are alsoevident along Panikkar Ridge in the Laxmi Basin (west of AbyssalBasin, Figs. 1 and 2). These include Raman Seamount (RS); WadiaGuyot (WG) and Panikkar Seamount (PS) (Krishna et al., 2006;Mukhopadhyay et al., 2008).

Satellite derived free air gravity anomaly data (Sandwell andSmith, 2009) from the MOB is presented in Fig. 2. Eastewestalternating high and low gravity anomalies demarcate the coastparallel ridge and basin structures (Biswas, 1982). The elevatedseamounts in the Laxmi Basin exhibit distinct high gravity anom-alies embedded in a broad gravity low (Fig. 2). The Shelf Platformshows gravity highs, which gradually decrease in the Shelf MarginBasin before again attaining higher values towards the west (Fig. 2).The regional gravity lows along the northern parts of the conti-nental shelf are associated with graben type structures followed by

70˚

70˚

72˚

72˚

74˚

74˚

14˚

16˚

18˚

20˚

22˚

1

34

5 6 8

9

rashtra

Goa

C-20WC-19

8

WC-17

W

444WC-1W

774477744744W

1716

15 144

10

11

12 13

Narmada Rift

Mumbai

Dharw

ar trend

Ratnagiri F

ault

asinelf Platform

2

WWGGGGGGWGGGGGGGGGWWWWWWWWWWWWWGWGWGWGGWWWWWWWWWGGWWWWGGWWWGGGWWGGGWWGGGGGGGGWWWWWWG

BH

mgal0 80

ell and Smith, 2009). Alternating coast parallel high and low gravity anomalies are ins (see text). Abbreviations are same as Fig. 1.


Figure 3. Sediment thickness isopach (km) maps of the MOB corresponding to different time periods (aeg) obtained from interpreted seismic profiles (seismic tracks are shown inred). Present day total sediment thickness (km) is shown in bottom right map (h).


highs associatedwith the horsts in the south along the Shelf MarginBasin (Fig. 2.).

2.2. Seafloor magnetic anomalies

Identification of seafloor magnetic anomalies is a widely usedtool to evaluate rift-drift transition along a margin that canconstrain the amount of continental extension leading to the sea-floor spreading (or the failure). The oldest undisputed seafloormagnetic anomaly in the Arabian Sea is considered to be C27n (ca.60.9 Ma) lineations (Royer et al., 1992; Miles et al., 1998) (Figs. 1 and2). Some studies also report presence of C28ny (ca. 62.5 Ma) southof Laxmi Ridge (Miles and Roest, 1993; Chaubey et al., 2002). Shortsegments of even older (though debatable) magnetic anomalies inthe Laxmi Basin in the Arabian Sea have been proposed byBhattacharya et al. (1994) (C33neC28neC33n corresponding to ca.79.5e 62.5 Ma); Yatheesh et al. (2009) (C31reC25rneC31r orC29reC25rneC29r) and Eagles and Wibisono (2013) (C29n-C28n-C29n). Decisive magnetic anomalies have not yet been identified inMOB east of Laxmi Basin (Fig. 2). In view of inconclusive identifi-cation of magnetic anomalies, its evolutionary history remainselusive. Consequently, precise estimates of extension along WCMIand the nature of crust in the basin are still underdetermined.

2.3. Stratigraphy and sedimentation history

The MOB has evolved through multi-phases extensional tec-tonics since earlyelate Cretaceous ca. 88e64 Ma rifting betweenIndia, Madagascar and Seychelles (Norton and Sclater, 1979; Storeyet al., 1995). Previous studies suggest presence of Precambrianbasement at various locations on the shelf, in sync with the deepeststratigraphic layer onshore (Jerram and Widdowson, 2005; NELP,2007; Singh and Mishra, 2015). However, subsequent large-scalebasaltic volcanism at ca. 65 Ma is considered to have spread


across central western India as well as adjoining offshore basinsand therefore modified the existing basement stratigraphy (Pandeyet al., 2011). Past studies have also opined that the nearby BombayHigh (Fig. 1) remained close to sea level/paleo-high since Precam-brian therefore barring any Mesozoic sediments on top (Mohan,1985; Agrawal and Rogers, 1992). Under such circumstances,seismic reflections off the acoustic basement (i.e. late Cretaceousbasaltic basement) can be considered as the regional basement forthe purpose of subsidence estimation. The Paleocene syn-rift sed-iments have been identified in various morpho-tectonic de-pressions during earlyelate Paleocene (Biswas, 1982; Mishra et al.,2011; Pandey and Pandey, 2015). Broadly, MOB has SWeNE-trending coast parallel horstegraben patterns along entire shelf(Fig. 2). Seismic studies from MOB suggest that grabens are boun-ded by normal faults, and the horsts/ridges are dissected byNEeSW-trending cross faults (Biswas, 1982; Mishra et al., 2011).The broad stratigraphy deciphered from the nearest IODP SiteU1457 (Pandey et al., 2016) and DSDP site 219 (Whitmarsh, 1974)also confirmed the oldest sediments above basement as Paleoceneclayey siltstones and volcaniclastic deposits.

Regional paleo-facies studies (Nair et al., 1992; Mathur and Nair,1993; Zutshi et al., 1993; Mishra et al., 2011) proposed that themajor part of theWCMI shelf was laid by first marine strata over thebasaltic basement. Sediments were deposited in deltaic torestricted marine and shallow marine environments (Basu et al.,1982; Zutshi et al., 1993). Detailed faunal studies using data fromcommercial boreholes (Fig. 2) suggest that, the basement reliefs onthe Shelf Platform started submerging below sea level for the firsttime during the early Oligocene (Mohan, 1985; Zutshi et al., 1993).Paleo-bathymetry estimates (Mohan, 1985; Raju et al., 1999) indi-cate that the early sedimentation in Shelf Platform region initiatedat shallow depths (<200 m). Mohan (1985) reported the paleo-bathymetry of the shelf during early Paleocene through late mid-dle Miocene remained shallower than 100 m below mean sea level


Table 1Details of various stratigraphic parameters used for 2-D reverse post-rift flexuralbackstripping for the present study.

Horizon at the baseof stratigraphic unit

Age of the baseof lithologicalunit (Ma)

Initialporosity (%)

Compactionconstant(km�1)

Matrixdensity(gm/cm3)

Seabed 0 - - -PlioceneeRecent 5.33 59 0.44 2.68Late Miocene 7.24 57 0.45 2.69Mid Miocene 13.8 60 0.44 2.67Late Oligocene/

Early Miocene23.0 61 0.46 2.68

Late Eocene 33.9 58 0.47 2.72Late Palaeocene 56.0 60 0.45 2.74Top basement 65.0 - - 2.80


before deepening further. Results from MCS data interpretationfrom the MOB reveal that the shelf margin has prograded/agradedupto ca. 100 km basinward since the Oligocene (Whiting et al.,1994).

The early Oligocene transgressions are reported to have coveredmost parts of the Abyssal Basin and inundated parts of BombayPlatform (Mathur and Nair, 1993). Major unconformities since latePaleocene have been discussed by Nair and Pandey (in preparation).Sea level rise during early Miocene submerged large areas of thebasin and terminated the Oligocene delta progradation (Clift, 2006).The middle Miocene transgression marks the last phase of thewidespread carbonate sedimentation in the MOB region (Basu et al.,1982; Zutshi et al., 1993). Sediment provenance studies show thatthe large scale unroofing of the sediments from Himalayan regionthrough various Indus tributaries also contributed to the sedimen-tation in the region during Oligocene till Recent post-rift-phase (Cliftet al., 2002). The morphology of theWCMI has beenmodified by thepresence of sediments discharged from WCMI as well as throughIndus Fan (Naini and Kolla, 1982; Kolla and Coumes, 1987; Clift et al.,2002). Further west in the deep offshore region, the Arabian Seaexhibits rather smooth topography.

3. Data and methodology

Regional MCS data is utilized to document history of sedimen-tation in the MOB. Further, role of sediment loading in modifyingthe basin architecture is investigated through post-rift subsidenceanalyses. In this study we have used three SWeNE seismic profilesWC-17,WC-19 andWC-20 (Fig.1) of variable lengths (220e350 km)out of more than ca. 4000 line km of close grid MCS data from theMOB. The MCS reflection data were acquired by Directorate generalof Hydrocarbons (DGH), India using 6000 m long streamer with arecording length of 8s two way travel time, (TWT) and 25 m shotspacing. Coast perpendicular (dip lines) seismic profiles arepreferred over coast parallel (strike) profiles for the subsidenceanalyses as they cross over the shelf, slope and the Abyssal Basinand provide a good control on regional sedimentation pattern.Various morphological features in the basin are shown on theregional bathymetric map (Fig. 1).

Each interpreted seismic section was converted from a two waytravel-time to a depth scale using interval velocities derived fromstacking velocities during the MCS data processing (Nair andPandey, in preparation). The interval velocities used for the depthconversion are in good agreement with those reported by seismicrefraction studies (Naini and Talwani, 1982), constraints from theknown stratigraphic information (Kolla and Coumes, 1987; Mishraet al., 2011; Mohanty et al., 2013; Pandey et al., 2015) and regionalboreholes (Mohan, 1985; Whiting et al., 1994; NELP, 2007).Considering high data quality and constrained velocity analyses,the uncertainties in time-depth conversion are estimated to bewithin 10% (Nair and Pandey, in preparation).

Various seismic horizons, and faults were marked using King-dom� software. Seven seismic sequences overlying the basementwere identified (Table 1). Nair and Pandey (in preparation) havedescribed an in-depth interpretation of the acquired MCS profilesusing integrated seismo-gravity modelling. The sediment thicknessisopachmaps corresponding to various time periods shown in Fig. 3(aeg) provide an overview of present day sediment thickness in theMOB since Paleocene as well as total sediment thickness (Fig. 3h).

In this article we focus on examining the basement tectonics byway of unloading the sediment through time using flexural back-stripping modelling approach (Kusznir et al., 1995; Roberts et al.,1998). Our modelling strategy considers both tectonic as well asthermal subsidence since syn-rift phase of the basin (ca. 65 Ma).The flexural backstripping technique has been successfully applied


to other passive margins in the past (Baxter et al., 1999; Kuszniret al., 2004; Roberts et al., 2013 and references therein). Details ofmodelling parameters used in this study are listed in Table 1 anddiscussed in following sections.

The MCS sections used in this study show variable sedimentarycover (Paleocene to Recent) above the igneous basement alongWCMI (Fig. 3). Interpreted layers from bottom to top correspond tothe late Paleocene, Eocene, early Oligocene, mid Miocene, lateMiocene and PlioceneeRecent respectively (Table 1). Identifiedhorizons on the depth converted seismic sections were constrainedby available stratigraphic knowledge and lithology data fromboreholes (Mohan, 1985; NELP, 2007; Mishra et al., 2011). Theircorresponding ages were assigned using the revised GeologicalTime Scale 2012 (Gradstein et al., 2012) indicating their time offormation based on correlation with the log data (Mohan, 1985;Agrawal and Rogers, 1992). The chronostratigraphic correlationpublished by Mathur and Nair (1993) and Zutshi et al. (1993) werealso employed to deduce basinwide stratigraphic picture. Forreverse post-rift subsidence modelling it is important to accountfor the water filled space lying above the sediment in a subsidingbasin. Such estimates are usually difficult because paleo depth in-dicators may have considerable uncertainties. Lithofacies and thetype of benthic fauna are broadly used to constrain paleo-waterdepths. The stratigraphy and paleo-bathymetry of MOB has beenpreviously discussed based on sporadic seismic and well data bynumber of researchers (Rao and Talukdar, 1980; Basu et al., 1982;Mohan, 1985; Nair et al., 1992; Mathur and Nair, 1993; Singhet al., 2009). Nair and Pandey (in preparation) presented an inte-grated interpretation using existing knowledge as well as newseismic data from MOB.

4. Flexural reverse post-rift modelling

Flexural backstripping or reverse post-rift modelling approach(Kusznir et al., 1995; Roberts et al., 1998) using Flexdecomp� isadopted to determine temporal and spatial subsidence variationson interpreted seismic profiles. Using interpreted cross sectionsand lithological parameters this multi-step process was achievedby removing the topmost (present day) stratigraphic unit andallowing stepwise decompaction (effect of dewatering) of theremaining deeper lithologies. The sediment dewatering model ofSclater and Christie (1980) has been applied for decompactedsediment thickness estimation. The net removed mass of sedimentmatrix and water is estimated as a consequence of the removal ofthe top layer. Further, incremental post-rift tectonic and thermalsubsidence corresponding to the ages of removed stratigraphicunits is computed using stretching factor (b) and rift age (McKenzie,1978). Next, flexural isostatic response due to the removed mass ofsediment matrix and water, as well as thermal subsidence is


Table 2List of wells from Mumbai Offshore Basin along western continental margin of India used for the present study. See Fig. 1 for their locations.

Serial No. Well Name T.D/D.D (m below seafloor) Lowest reflector (Age) Lithology

1 BRDW-4-1 3250 (DD) E. Paleocene2 C-45-1 2977 (TD) L. Oligocene Shale/Sandstone/Limestone/Claystone3 SM-1-1 >3000 Eocene Limestone4 SM-1-2 3985 (TD) Eocene Limestone recrystalised5 MB4-A1 4200 U. Cretaceous Basalt6 MD-1 4544 (TD) M. Eocene Silt7 MDS-1 2880 (TD) E. Miocene Shale, siltstone, Sandstone/Limestone8 MB5-C1 2016 (TD) M. Miocene Limestone9 MB1-05-03 - - -10 SM-2-1 4014 (TD) Paleocene Trap-Derivatives Weathered Basalt11 SM-79-1 3283 (DD) L. CretaceouseE. Paleocene Trap-Derivatives Weathered Basalt12 R-1-1 1520 L. CretaceouseE. Paleocene Basalt13 R-29-1 1550 Mid-Eocene Limestone14 D-4-1 4600 Paleocene Basalt15 D-1-2 4100 Early Eocene Limestone16 B-1-1 3532 Early Oligocene Limestone/Shale alterations17 B107-1 3119 Early Oligocene Limestone/Shale alterations

Figure 4. Eustatic sea level change since late Cretaceous (after Haq et al., 1987) andpaleo-bathymetry variations. Dotted paleobath curve (after Mohan, 1985) and grayzones (after Whiting et al., 1994). These reference data were incorporated in the post-rift subsidence modelling.


determined. This process is repeated sequentially until all post-riftstratigraphic units have been removed. The resulting section afterunloading the basement in above manner provides knowledgeabout the basement depth that would be today had there been nosediment deposition since its formation. Details of sub-surfacestrata and their physical parameters used in reverse post-riftmodelling are described in Table 1. Flexural backstripping model-ling tends to be sensitive to the paleo-bathymetry variationsespecially in regions close to the continental slope (i.e. Shelf MarginBasin due to water depths exceeding 2000 m). Paleo-bathymetrydata proposed by Mohan (1985) based on biostratigraphic infor-mation from several boreholes in MOB have been reliably used forsubsequent work. Therefore, we have incorporated paleo-bathymetric observations from faunal facies analyses from MOB(Mohan, 1985; Nair et al., 1992; Mathur and Nair, 1993; Zutshi et al.,1993). Though the eustatic sea-level fluctuation has less influenceon backstripping compared to the variations of paleo-bathymetry,eustatic curves of Haq et al. (1987) has been incorporated whilemodelling in order to make an integral assessment of subsidence(Fig. 4).

5. Results and discussion

A depth converted and interpreted profile showing variousseismic horizons along WC-19 is shown in Fig. 5. The stretchingfactor (McKenzie, 1978) is a significant attribute in controllingrestoration of the section by flexural backstripping and reverse post-rift modelling. Using a known b stretching factor flexural back-strippingmay allow us to predict palaeo-bathymetry, or vice versa inan iterative fashion (Kusznir et al., 1995; Roberts et al., 1998). Theconventional 1-D backstripping approaches use borehole litholog-ical data (or pseudo-wells) to deduce a constant stretching factor.However, rifting/extension along continental margins may not belaterally uniform. Thus, post-rift modelling ought to incorporate alaterally varying extension, if required. The 2-D modelling approachemployed here has the flexibility to choose uniform as well as alaterally varying b profile to determine the best fit restored section.In order to examine model sensitivity we performed restorationalong profile WC-17 for uniform as well as laterally varying b profileand results are shown in Fig. 6a. We shall discuss the suitably ofuniform versus variable b profile subsequently.

The b stretching factor is a function of the lithospheric flexuralstrength defined by effective elastic thickness Te. Different values ofTe can render different magnitudes and geometries of deflection.Low Te values can generate large amount of flexure over short


distances and large (Te) values result in low flexural response overgreater distances. In order to demonstrate sensitivity of reversepost-rift modelling to lithospheric flexural rigidity, a range of Tevalues (Te ¼ 0, 5, 15 and 25 km) have been used and the sediment


Figure 5. (a) Interpreted present day (0 Ma) depth converted seismic section for line WC-19. Various sequences are colour coded as indexed; (b) Free air gravity anomaly variationsalong seismic track WC-19.


unloaded basement depths (for thermoetectonic as well as thermalsubsidence only) are shown in Fig. 6b. A Te value of zero wouldcorrespond to the local isostasy. The modelling results show thatthe sediment unloaded present day depth to the basement and thederived paleo-bathymetry seems to be rather insensitive to the Tevalues close to zero. Rifted margins (as the case here) are learnt tohave low flexural rigidity for several million years after the end ofactive extension (Karner andWatts, 1982; Allen and Allen, 2006). Inview of this, a low Te ¼ 5 km was chosen for reverse post-riftmodelling which is consistent with the recommended values forother passive margins (Kusznir et al., 1995).

The flexural backstripping analysis has been applied to the diplines WC-17, WC-19 and WC-20 each 220 km, 350 km and 250 kmlong respectively. These dip lines are preferred over strike lines forbackstripping analyses as they traverse through wide domain andthereby permitting us to determine effects of spatial variations insediment loading through time.

5.1. Reverse post-rift modelling of WC-19

Firstly, we discuss the flexural backstripping and reverse post riftmodelling of the longest (350 km) seismic profile WC-19. Thisprofile traverses through the Shelf Platform in the east marked withsignificant bathymetric highs, Shelf Margin Basin in the central partand the Abyssal Basin in the west (Fig. 1). Although the exact age ofthe extension initiation in this region is still unclear, the earliestphase of rifting in the WCMI is generally considered to start in thelate Cretaceous to early Paleocene (Biswas, 1982; Bhattacharya andYatheesh, 2015). Paleogeographic reconstructions and prior mag-netic studies suggest that rifting along northern part of WCMIinitiated ca. 68 Ma and ceased during late Paleocene (ca. 56 Ma)(Eagles and Wibisono, 2013; Bhattacharya, and Yatheesh, 2015; andreferences therein). Since, the span of late Cretaceous rifting alongWCMI under consideration may have lasted less than 20 Myr theassumption of an instantaneous stretching holds valid (Jarvis andMcKenzie, 1980). Accordingly the reverse post-rift modelling hasbeen carried out to examine post rift developments since late


Paleocene (ca. 56 Ma). Moreover, we have restricted our modellingto a post-rift scenario because there aren’t enough deeper con-straints (such as wells penetrating the basement) to allow usproperly document the syn-rift developments in the basin. Occur-rences of earlier Mesozoic strata underlying the basement werereported from adjoining regions (e.g. Kachchh and Saurashtra),however their extension further south in the MOB is not confirmed(Mohan, 1985). Backstripping with reverse thermal subsidencemodelling (as compared to tectonic subsidence only) (Fig. 6b) allowschoosing post-rift models consistent with the paleo-bathymetricknowledge (Mohan, 1985; Agrawal and Rogers, 1992). Takinginherent effects of an earlier extensional phase (India-Madagascarseparation at ca. 88 Ma) along WCMI into account our modellingincludes an inherited stretching with b ¼ 1.3 corresponding to anage ca. 88 Ma (Agrawal and Rogers, 1992; Yatheesh et al., 2009).

A series of restored cross sections from present day to ca. 56 Mafor lineWC-19 is shown in Fig. 7. Applying a uniform b factor of 1 to3 for late PaleoceneeRecent phase, post-rift restorations predictemergent topography on the eastern end of the profile whereaslarge residual bathymetry (>3.5 km) on the western end of theprofile (see sensitivity test for various uniform b values in Fig. 6).Such circumstances, if true, would have lead to an erosional con-dition on the Shelf Platform. This does not seem to be consistentwith paleo-bathymetry observations from the bore holes on theShelf (Mohan, 1985; Whiting et al., 1994). This implies that a vari-able b profile along the section is required to restore top post-riftstrata close to the sea level in order to be consistent with paleo-bathymetric observations. Our preferred sequence of restorationswith above parameters (Fig. 7) restores the top of Paleocene (ca.56 Ma) close to the sea level towards the eastern end of the profile.However, the preferred model predicts variable water depths of ca.1e2 km on the western end of the profile (ca. 200 km west of theShelf Platform). A laterally varying lithospheric b factor rangingfrom 1 (i.e. no stretching) on the eastern parts to very highstretching (b ¼ 5) on the SW end which lies close to the COB (Nairand Pandey, in preparation). Further, allowing post-rift tectonicsubsidence only and not allowing any thermal subsidence fails to


Figure 6. (a) Sensitivity analysis for post-rift flexural backstripping (WC-17) for varying uniform beta factors. A variable beta profile that successfully restores most part of the ShelfPlatform to the sea level (z ¼ 0) has been used for the present study (Figs. 7e9); (b) Sensitivity test of 2-D post-rift backstripping (WC-19) for variable flexural strengths (Te). A Tevalue of 5 applicable to rifted margin that successfully restores most part of the Shelf Platform to the sea level (z ¼ 0) has been used for the present study. Solid lines representthermo-tectonic subsidence while broken lines represent tectonic subsidence only (WC-19). The black dotted line shows present day seabed depth along seismic profile WC-19. Thelight blue bar on top demarcates regions of zero bathymetry (z ¼ 0) and above.


restore entire section consistent with the paleo-bathymetry esti-mates (Mohan, 1985; Agrawal and Rogers, 1992). On the other handreverse post-rift modelling with total subsidence (tectonic andthermal) successfully restores the eastern Shelf Platform close tothe sea level (Fig. 7). Accordingly we revise our backstripping pa-rameters to include a laterally varying b profile (Fig. 7) constrainedthrough forward modelling vis-a-vis paleo-bathymetric knowledgefrom previous studies.

The gradually reducing b factor from oceanic/transitional part ofthe profile in the west to the continental end of the profile in theeast is also consistent with observations from other passive mar-gins (Kusznir et al., 1995; Roberts et al., 1998; Clift et al., 2002). Onthe Shelf Platform modelled b values are moderate, ranging be-tween 1.5e1.8. These are relatively low b values typical of conti-nental rift basins (Roberts et al., 2013). Across the central part of theprofile, b factors surge to the range of 3e4. This intermediate tohigh b factor is indicative of a highly stretched and attenuated crustclose to the continental margin (Pandey and Pandey, 2015; Pandeyet al., 2016). Very high b factors at SW end are required to restorethe top Paleocene horizon. This can be attributed to the proximityof western end of this profile to the oceanic crust in the Arabian Seatowards west. This is in conformity with the published geological


models for the eastern Arabian Sea characterising highly stretchedcrust in this part (Naini and Talwani, 1982; Krishna et al., 2006;Pandey and Pandey, 2015 and references therein). Seismo-gravitymodelling also suggests possibility of intermediate crustal thick-ness in the Abyssal Basin part of the profile (Nair and Pandey, inpreparation; Pandey et al., 2016).

It is noteworthy that the top of the Paleocene in the western endof the profile WC-19 could not be restored close to the sea level. Nounanimous views exist about the time and precise location of sea-floor opening in the Eastern Arabian Sea and creation of an oceaniccrust prior to ca. 56 Ma (Pandey et al., 2015 and references therein).Assuming that if an oceanic crust indeed was created in the AbyssalBasin prior to ca. 56 Ma, the depth to the ocean floor after initial ca.10e12 Ma of ‘normal’ subsidence would have been greater than ca.3.7 km based on subsidence curves of Stein and Stein (1992). Oneshould therefore expect to find continental crust in the Abyssal Basinat water depths of 3.7 km or shallower in absence of sedimentation.Going by the subsidence analyses data, the unloaded water depthfrom our study (ca. 2.5e3 km) supports such a possibility (Fig. 7).Further, our knowledge from new oceanic crust at mid ocean ridgessuggest that the zero-age oceanic crust under ca. 2e3 km of water isin equilibrium with a ‘standard’ continental lithospheric column.



Using the equation for the initial subsidence (McKenzie, 1978; Allenand Allen, 2006), the stretch factor required to produce ca. 2.5 km ofsubsidence is larger than 3. This in turn could reduce the crust to ca.9e10 km thick andwill most likely be highly fractured, therefore it isprobable that the asthenosphere would upwell and may piercethrough when this depth was reached. White and McKenzie (1989)and subsequently, Roberts et al. (2013) showed that the waterloaded initial subsidence can be computed as a function of crustalthickness, crustal density and the melt thickness at a rifted margin.Subsequently, possible melt addition as a function of thinning (1e1/b)/stretching factor (b) and canbe estimated.During a riftingprocess,sufficiently large b factor (e.g.>3) can lead to addition of 7e10 km ofmelt at the base of lithosphere (Roberts et al., 2013) and cause sub-sidence of more than 2 km at a rifted margin. Such a situation couldrepresent the continenteocean transition in the Abyssal Basin. Theanomalously high beta factors (Fig. 7), and other corroborating evi-dences (Pandey and Pandey, 2015) imply that the basin must havebeen hyper-stretched. Therefore, it may be possible that the openingof seafloor in the Arabian Sea occurred in late Cretaceous/earlyPaleocene further westward of these seismic profiles in the ArabianSea (consistent with the magnetic anomalies C28n, Fig. 1), withsignificant crustal underplating (Krishna et al., 2006; Minshull et al.,2008) in the Abyssal Basin and marking the underlying crust in theAbyssal basin as highly attenuated and transitional type (Pandey andPandey, 2015). However, we do recognise that such a proposition isfar from straightforward and requires further supporting observa-tions. We further explored the possibility of water loaded post-rifttransient thermal uplift of ca. 2000 m. The results suggest thatincluding ca. 2000 m of transient thermal uplift at ca. 56 Ma doesrestore the western part of the profile to zero bathymetry at the costof substantial erosional surfaces on the eastern parts of the profile(diagram not included here). It is also significant to note that suchunusually large magnitude of post-rift thermal uplift (e.g. plume) atca. 56 Ma or younger would have to be observed basin wide in theMOB. Incorporating ca. 2000 m uplift would also elevate the ShelfPlatform much above the sea level, consequently leading to erosionand removal of Paleocene sequences. Most importantly, recentpaleogeographic reconstructions at ca. 56 Ma suggest that the studyarea had moved far enough (>1000 km) to have been influenced bythe possible source of a thermal uplift (i.e. Reunion plume)(Bhattacharya and Yatheesh, 2015). Therefore, we discard the pos-sibility of a large post-rift transient thermal uplift in MOB to explainanomalous subsidence in the Abyssal Basin.

Thus, by constraining the late Paleocene water depth under theShelf Platform (Mohan, 1985), a satisfactory restoration of thewestern end of the profile WC-19 requires inclusion of an addi-tional subsidence event younger than ca. 68 Ma leading to a re-sidual bathymetry>2000m at late Paleocene. The long wavelength(ca. 150 km) of the residual bathymetry also precludes large scaleupper crustal faulting (Fig. 7) during late PaleoceneeEocene in theAbyssal Basin area. Therefore an alternative mechanism for addi-tional post-rift subsidence of ca. 2000 m could be through thinningof the lower continental crust west of ca. 200 km of the profile WC-19 during pre/syn-rift stage. Thinning of the lower continental crustduring extensional phases leading to crustal underplating is quitecommonly observed on other margins (Hopper and Buck, 1996;Allen and Allen, 2006; Roberts et al., 2013). Lithospheric stretch-ing may be accompanied by magmatism, producing dyke swarms,plutons and extensive basaltic sills (Royden and Keen, 1980; Whiteand McKenzie, 1989). Emplacement of large volumes of basalticmelt into the crust (or along its base) should produce transientuplift, followed by subsidence as the extruded, intruded or under-plated material cools. In view of this it is proposed that thinning ofthe lower crust after rift initiation (ca. 68Ma) could have resulted inexcess subsidence in the Abyssal Basin in addition to that generated


from post-rift subsidence. Such processes are widely reported onpassive margins wherein inclusion of lower crustal magmaticunderplating/dikes during rifting process is commonly suggested(Krishna et al., 2006; Roberts et al., 2013; Misra et al., 2015).Furthermore, possibility of considerable subsidence caused byemplacement of large seamounts (ca. 2 km relief) in the proximalLaxmi Basin (southwest of the profile WC-19) perhaps coetaneouswith syn-rift phase, could not be ruled out. Alternatively, the re-sidual bathymetry of ca. 2000 m could be linked to an earlier phaseof Mesozoic rifting. However, such propositions can only be verifiedonce deeper seismic reflection data are available where Mesozoicreflectors have been imaged.


The profileWC-20 extends in SWeNE direction perpendicular tothe coast and is ca. 250 km long. It is the northernmost profile usedin this study (Fig. 1). The eastern end of the profile lies on the ShelfPlatform, central part traverses through the Shelf Margin Basin andthe western end lies in the Abyssal Basin (proximal to Laxmi Basin).

The depth converted section along this profile (Fig. 8) exhibitspresent day stratigraphic set up along this profile. Seven differentstratigraphic layers have been identified corresponding to the latePaleocene to Recent sediments in the basin. The depth to the pre-sent day basement varies from ca. 3 km in the central part of theprofile to >5 km on either sides of the profile (Fig. 8). The presentday water-filled depth to the basement under the Shelf is ca. 6 km(Fig. 3) exhibiting a large sediment depocentre towards the edge ofthe section. A large basement uplift (>2000 m) is observed be-tween 100e200 km of the profile. Several volcanic intrusive areobserved in the central part of the profile. Details about identifiedstratigraphic horizons are provided in Table 1.

The reverse post-rift restoration to the top of Paleocene (ca.56 Ma) along this profile is shown in Fig. 8. Much like the profileWC-19, the preferred restoration requires very high b factor (ca. 6)between 0e50 km of the profile in the west and graduallydecreasing (ca. 1) towards the eastern end close to the Shelf MarginBasin. The eastern end of the section is restored close to the sealevel which is consistent with the Paleo-bathymetric observationsfrom nearby borehole data (Mohan, 1985). However, the westernsegment of the section within the COT domain exhibits a residualpaleo-bathymetry of ca. 2 km.


The profile WC-17 is the southernmost suite of seismic profilesused in this study for subsidence modelling (Fig. 1). The profile is220 km long and extends in SWeNE direction. The eastern end ofthe profile is close to the Shelf Margin Basin whereas the westernend lies in the Laxmi Basin. Previous studies suggest that the crustlying west of ca. 150 km is of transitional nature due to hyper-stretching associated with the late Cretaceous rifting process inthe Laxmi Basin (Pandey and Pandey, 2015). The industry boreholeSM-1-2 is located close to the eastern edge of the profile (Fig. 1).

The present day depth to the basement alongWC-17 is shown inthe depth converted section (Fig. 9).The depth to the present daybasement varies from ca. 3 km in the east to ca. 6 km in the westernend of the profile. Details about seven identified stratigraphic ho-rizons are provided in Table 1.

The reverse post-rift restoration to the top of Paleocene (ca.56 Ma) along this profile is shown in Fig. 9. Like the other twoprofiles, the preferred restoration requires an extremely high b

factor (>5) in the western end of the profile and graduallydecreasing (ca. 1.2) towards eastern end close to the Shelf MarginBasin. The extent of high b factor along this profile is much longer as



Please cite this article in press as: Pandey, D.K., et al., Basement tectonics and flexural subsidence along western continental margin of India,Geoscience Frontiers (2016), http://dx.doi.org/10.1016/j.gsf.2016.10.006

Figure 8. (a) Present day (0 Ma) interpreted seismic section along profile WC-20; the profile is oriented SWeNE direction and is 250 km long (location in Fig. 1). Variousdepositional units are colour coded as indexed in Fig. 5. (b) Variable b factor used for post-rift restoration of this profile; (c) Restored cross section using reverse post-rift modellingwith above b factor on top of the Paleocene (ca. 56 Ma) for WC-20 at different geological times based on 2-D reverse post rift flexural backstripping analyses. Note that the ShelfPlatform is successfully restored close to the sea level on top of Paleocene, however, Abyssal basin shows a residual bathymetry of ca. 2 km; (d) Free air gravity anomaly variationsalong this profile.


compared to WC-20 because this profile has maximum extent inthe Abyssal Basin and least coverage under the Shelf Platform.Reverse post-rift backstripping shows that the short segment of theeastern end of the profile is restored close to the sea level. Theseestimates are consistent with the Paleo-bathymetric observationsfrom nearby borehole data (Mohan, 1985; Whiting et al., 1994;NELP, 2007). On the other hand like WC-19 and WC-20, the west-ern segment of the section within the COT domain exhibits a re-sidual paleo-bathymetry of ca. 2 km.

Figure 7. Restored cross sections for WC-19 at different geological times based on 2-D reversfactor (b) along the profile; (c) at 5.33 Ma; (d) at 7.25 Ma; (e) at 13.82 Ma; (f) at 23 Ma; (g) atNote that the Shelf Platform is successfully restored at close to the sea level, however, Abys


5.4. Basement tectonics

Two dimensional reverse post-rift modelling through stepwiseunloading of sediment using interpreted seismic profiles from MOBprovides depth to the top of Paleocene formation as well as knowl-edge about the basement topography through time. Based on ob-servations from basement tectonics and subsidencemodelling alongWCMI, it is inferred that the MOB has undergone a highly complexevolutionary history since initiation of late Cretaceous break-up.

e post rift flexural backstripping analyses. (a) Modern daye0 Ma; (b) variable stretching33.9 Ma; (h) at 56 Ma. Various depositional units are colour coded as indexed in Fig. 5.sal Basin shows a residual bathymetry of ca. 2 km on top of the Paleocene (ca. 56 Ma).


Figure 9. (a) Present day (0 Ma) interpreted seismic section along profile WC-17; The profile is oriented SWeNE direction and is 220 km long (location in Fig. 1). Refer to Fig. 5 forvarious colour coded horizons. (b) Variable b factor used for post-rift restoration of this profile; (c) Restored cross section using reverse post-rift modelling with above b factor ontop of late Paleocene (ca. 56 Ma) for WC-17 at different geological times based on 2-D reverse post rift flexural backstripping analyses. Note that the Shelf Platform is successfullyrestored close to the sea level on top of Paleocene, however, Abyssal basin shows a residual bathymetry of ca. 2 km; (d) Free air gravity anomaly variations along this profile.


The seismic data presented in this study show that the majortectonic episodes including scattered late stage volcanic intrusionsalong WCMI are primarily restricted to the early Paleocene tomiddle Miocene period (Figs. 7e9). The basal reliefs along thedeepest reflectors towards the east of the Abyssal Basin appear tobe accompanied by numerous normal faults. Based on continuity ofthese faults, it is inferred that the basal reliefs (Figs. 7e9) couldhave been caused by intrusions of volcanic material along the zonesof weaknesses (Gopala Rao et al., 2010). Such zonesmay have arisendue to varied stretching of continental crust during late Cretaceouswhen SeychelleseIndia separation took place. This was followed bythinning and rupturing of continental crust resulting in dyke in-jection/underplating associated volcanism. The basement faulting


close to the Shelf in MOB also appears to have led to the formationof smaller sag basins. Some of them could be attributed to thepossible reactivation during riftedrift process.

Wepropose that spatial and temporal variations in themagnitudeof subsidence on MOB were caused by interplay of several coeta-neous geodynamic factors. The most significant of these include (1)flexural undulations caused by the considerable emplacement ofload on top; and (2) spatial variations in the strength of the basementand underlying lithosphere. Post-rift reverse modelling from MOBsuggests that ever since the rift initiation, the Shelf Platform hasremained close to the sea level most likely under photic conditions.On the other hand, moving westward, near the present day conti-nental slope, the Shelf Margin Basin appears to have largely



experienced mid bathyal environs during late Paleocene. Furtherwest, contemporarily the Abyssal Basin seems to have developedfull-fledged bathyal surroundings. The residual bathymetry in theAbyssal Basin obtained fromourmodelling is also consistentwith thepaleo-facies map of Nair et al. (1992) (Fig. 10). Results from 2-Dsubsidence modelling demonstrate extremely large lithosphericstretching factors under WCMI especially the MOB. The variable b

factors deduced from such analyses indicate that continental riftingmay have initiated in the proximity to the present day Abyssal Basin,though it may not have finally succeeded in formation of a fulloceanic crust at this site as evident by relatively low stretching fac-tors and lack of undisputable seafloor spreading type magneticanomalies (Miles and Roest, 1993; Miles et al., 1998; Chaubey et al.,2002; Royer et al., 2002; Krishna et al., 2006; Bhattacharya andYatheesh, 2015). However, these inferences need corroborationwith further geophysical data such as detailed identification of sea-floor magnetic lineations. Enormously high and increasing b factorstowards west of the seismic profiles implies that stretching wouldhave eventually led to infinitely large b values over present dayoceanic crust in the Arabian Basin. A laterally varying b factors alongWCMI inferred from this study is not unprecedented on passivemargins. Observations from other analogous continental margins inNorthAtlantic such as the Faeroes ShetlandBasin, VoringMargin andRockall Trough (White and Smith, 2009; Eccles et al., 2011; Roberts

Figure 10. Paleo-facies distribution map of the Mumbai Offshore Basin during PaleoceneeEare overlain on the map in red.


et al., 2013) also suggest variably high b factors (z10) for hyper-stretched crust within a passive continental margin setup.

Majority of previous workers support that the onshore rapideruption of Deccan Traps (ca. 65 Ma) predated the initiation ofrifting process in the Arabian Sea (Courtillot et al.,1986; Venkatesanet al., 1993; Pande et al., 2001). Although in absence of precisechronological measurements uncertainties exist about thesequence of events that led to the continental break up alongWCMI(Pandey et al., 2015, 2016). Nonetheless, general consensus arisesthat the adjoining rifts and connected basins in the Arabian Seahave undergone pre/syn/post-rift tectonic as well as thermal sub-sidence for ca. 68 Myr (Mohan, 1985). By assuming original crustalthickness ca. 36 km, same as that under peninsular India (Rao andTewari, 2005), the extent of thinning (i.e. 1-1/b) during continentalbreakup alongWCMI can be computed using the laterally varying b

profile (Figs. 7e9). The above facts in conjunctionwith the regionalstratigraphic data presented here and reverse post-rift subsidencemodelling allows estimation of total accommodation space as wellas the amount of extension.

Reverse post-rift backstripped sections pertaining to the seismicprofiles WC-19, WC-20 and WC-17 are shown in Figs. 7e9. A steepincrease in the unloaded depth to the top Paleocene formation nearShelf Margin Basin indicates a distinct boundary between150e200 km wide relatively less extended crust in the east and

ocene (modified after Nair et al., 1992; NELP, 2007). Seismic profiles used in this study



highly extended crust in the west. Fault-related structures are moreevident under the Shelf Platform than those under the Shelf MarginBasin or Abyssal Basin. The basement in the Abyssal Basin appearsto have been intruded at places with volcanic rocks. The sedimentunloaded subsidence history and the resulting paleo-bathymetry inand beyond the transitional parts of the crust is quite similar to thatof an extremely stretched crust (Kusznir et al., 1995). However,presence of the Laxmi Ridge to the west (a widely agreed conti-nental block) and lack of conspicuous magnetic anomalies in theLaxmi Basin (west of Abyssal Basin) makes the issue furthercomplicated. The modelling results presented here support hyper-stretching in the Abyssal Basin as proposed earlier by Pandey andPandey (2015). However, more precise measurements of exten-sion in the Laxmi Basin would emerge from the recently concludedIODP expedition-355 in the Arabian Sea (Pandey et al., 2015). An-alyses of basement cores collected from IODP drill Sites (Fig. 1) areexpected to throw more light on its precise nature.

5.5. Sediment accumulation rates

The unloaded sediments along each profile also provide quan-titative estimates of sedimentation rates on the Shelf Platform,Shelf Margin Basin and Abyssal Basin. We performed calculation ofsedimentation rates based on the geohistory analyses deducedfrom post-rift subsidence modelling using seismic profiles. Resultsof accumulation rates calculation along seismic profile WC-19 areshown in Fig. 11. Computations are performed using backstrippedsediment load for various periods assuming pseudo-wells for threesectors (Abyssal Basin: 0e150 km; Shelf Margin Basin:150e250 km; Shelf platform: 250e350 km). The results show twomain spatially distinct components (Fig. 11). Spatial and temporalvariations in accumulation rates demonstrate that large volumes ofthe sediments were deposited in MOB during the Paleocene andNeogene. The Shelf Platform has in general received higher masssediment flux in comparison to the Shelf Margin and Abyssal ba-sins. The primary reason attributed to such variations could be dueto available post-rift accommodation space on the Shelf Platformwas much more dynamic through time (Biswas, 1982; Nair et al.,1992).

Comparison among three different provinces along the profileshows that sedimentation rapidly increased to a maximum in thelate Miocene, before slowing down again in last ca. 5 Myr (duringPlioceneeRecent). The peak sedimentation during the late Miocenereached almost ca. 2e4 times higher. Such high sedimentation isinterpreted to have been resulted from enhanced influx through

Figure 11. Calculated mass accumulation rates for various periods using pseudo-wellsalong seismic line WC-19 on Shelf Platform: 0e150 km (green), Shelf Margin Basin:150e250 km (dark red) and Abyssal Basin: 250e350 km (blue). See Fig. 1 for locations.


Indus fan as well as western continental margin of India. Such in-crease in sediment supply could be evident by the progradation ofthe paleo-shelf along our seismic profiles (Figs. 7e9). Clift andGaedicke (2002) proposed a 2e3 fold increase in rate of sedimen-tation in the Arabian Sea during midelate Miocene period relatingto the accelerated mass flux from Indus during that period. Uplift ofthe Himalayas and Tibetan Plateau (ca. 10e8 Ma) has been pro-posed to be the main cause of the origin of late Miocene intensi-fication of the Indian monsoon system (Clift and Gaedicke, 2002;Gupta et al., 2004). Our observations of late Miocene increase insedimentation rates on MOB are consistent with earlier observa-tions based on sedimentological, and geochemical responses to lateMiocene uplift of Himalayas and Tibetan Plateau and intensificationof Indian Monsoon system from Bay of Bengal as well as ArabianSea (Kroon et al., 1991; Rea, 1992; Davies et al., 1995; Gupta et al.,2004 and references therein).

6. Conclusions

New seismic data in combination with the commercial bore-hole information from the Mumbai Offshore Basin have beenexamined to understand basement tectonics and cumulativesubsidence alongWCMI since late Paleocene. The 2-D reverse postrift flexural backstripping modelling was performed usingSWeNE extending depth converted multi-channel seismic pro-files. By adapting tectonic, paleo-bathymetry and eustatic sealevel fluctuation settings from previous studies, modelling resultsdemonstrate that the rates of subsidence have varied throughoutthe Neogene and Paleogene in this basin. Backstripping anddecompaction derived sediment accumulation rates show thatmaximum sedimentation occurred during late Miocene. Such anincrease in sedimentation rate is in conformity with previousstudies linking late Miocene HimalayaneTibetan uplift and sub-sequent intensification of Indian monsoon system (Singh andMishra, 2015). Based on the restored sections, it is inferred thatthe parts of the crust in the Abyssal Basin has undergone extremestretching (with very high b factors) whereas the Shelf Platformhas experienced relatively less stretching since late Paleocene.This observation is consistent with the presence of transitionalcrust in the proximal areas of Abyssal Basin and oceanic crust to itswest in the Arabian Basin. The observations from present studytogether with existing geological and geophysical knowledgesuggest that the dominant process responsible for the evolution ofWCMI was the extensional tectonics. The sediment unloadedsections on top of ca. 56 Ma horizon exhibit varying residualtopography. Such residual depth-anomalies are attributed topossible uplift and subsidence of the crust associated to lowercrustal flows and underplating as a responsible mechanisminstead of a thermal anomaly (plume) prior to the initiation ofrifting process along WCMI. Potential magma intrusion/under-plating in the lower crust during syn-rift/drift phase is expected tohave further weakened the crust. Consequently, localised strain insuch zones is likely to have led to higher subsidence. The largeaccommodation space and coeval sediment supply would lead toanomalously high subsidence on continental margins such asWCMI.

Acknowledgements

The authors are thankful to the Director, NCAOR for kindlyallowing this manuscript to be published. We are also grateful toDGH India for providing us the MCS data for this study. Academiclicense of seismic interpretation software IHSeKingdom� isgratefully acknowledged. Authors thank Dr. Alan Roberts and Prof.Nick Kusznir for their help with the FLEX-DECOMP� package. Ms.



Bincy P. K. is acknowledged for preparation of sediment thicknessisopach maps. The manuscript benefitted significantly fromconstructive reviews from anonymous reviewers and the editor.This is NCAOR contribution No. 30/2016.

References

Agrawal, A., Rogers, J.J.W., 1992. Structure and tectonic evolution of the westerncontinental margin of India: evidence from subsidence studies for a 25e20 Maplate reorganization in the Indian Ocean. In: Basement Tectonics 8: Charac-terization and Comparison of Ancient and Mesozoic Continental Margins-Proceedings of the 8th International Conference on Basement Tectonics.Kluwer Academic Publishers, Dordrecht, The Netherlands, pp. 583e590.

Agarwal, P.K., Pandey, O.P., Negi, J.G., 1992. Madagascar: a continental fragment ofthe paleo-super Dharwar craton of India. Geology 20, 543e546.

Allen, P.A., Allen, J.R., 2006. Basin analysis: Principles and Applications. BlackwellPublishing Ltd., Oxford, 549 pp.

Anderson, D.L., 2001. Top-down tectonics. Science 293, 2016e2018. http://dx.doi.org/10.1126/science.l065448.

Basu, D.N., Banerjee, A., Tamhane, D.M., 1982. Facies distribution and petroleumgeology of the Bombay offshore basin, India. Journal of Petroleum Geology 5 (1),51e75.

Baxter, K., Cooper, G.T., Hill, K.C., O’brien, G.W., 1999. Late Jurassic subsidence andpassive margin evolution in the Vulcan Sub-basin, northwest Australia: con-straints from basin modelling. Basin Research 11, 97e111.

Bhattacharya, G.C., Chaubey, A.K., Murty, G.P.S., Srinivas, K., Sarma, K.V.L.N.S.,Subrahmanyam, V., Krishna, K.S., 1994. Evidence for seafloor spreading in theLaxmi Basin, northeastern Arabian Sea. Earth and Planetary Science Letters 125,211e220.

Bhattacharya, G.C., Yatheesh, V., 2015. Plate-tectonic evolution of the deep oceanbasins adjoining the western continental margin of India e a proposed modelfor the early opening scenario. In: Mukherjee, S. (Ed.), Petroleum Geosciences:Indian Contexts, Springer Geology. http://dx.doi.org/10.1007/978-3-319-03119-4_1.

Biswas, S.K., 1999. A review on the evolution of the rift basins in India duringGondwana with special reference to Western Indian basins and their hydro-carbon prospects. Proceedings of Indian National Science Academy 65,261e283.

Biswas, S.K., 1989. Hydrocarbon exploration in western offshore basins of India.Geological Survey of India. Spl. Pub, 24, 185e194.

Biswas, S.K., 1982. Rift basins in western margin of India and their hydrocarbonprospects with special reference to Kutch Basin. Bulletin American Associationof Petroleum Geologist 66, 1497e1513.

Buck, W.R., 2001. Can flow of dense cumulate through mushy upper gabbros pro-duce lower gabbros at fast spreading ridges. GSA Spec. Paper 349. In: Dilek, Y.,Moores, E., Elthon, D., Nicolas, A. (Eds.), Ophiolites and Ocean Crust: New In-sights from Field Studies and Ocean Drilling, pp. 121e128.

Chand, S., Subrahmanyam, C., 2003. Rifting between India and Madagascar-mechanism and isostasy. Earth and Planetary Science Letters 210, 317e332.

Chaubey, A.K., Gopala Rao, D., Srinivas, K., Ramprasad, T., Ramana, M.V.,Subrahmanyam, V., 2002. Analyses of multichannel seismic reflection, gravityand magnetic data along a regional profile across the central-western conti-nental margin of India. Marine Geology 182, 303e323.

Clift, P.D., 2006. Controls on the erosion of Cenozoic Asia and the flux of clasticsediment to the ocean. Earth and Planetary Science Letters 241, 571e580.

Clift, P.D., Gaedicke, C., 2002. Accelerated mass flux to the Arabian Sea during theMiddle-Late Miocene. Geology 30, 207e210.

Clift, P.D., Gaedicke, C., Edwards, R., Lee, J.I., Hildebrand, P., Amjad, S., White, R.S.,Schülter, H.U., 2002. The stratigraphic evolution of the Indus Fan and the historyof sedimentation in the Arabian Sea. Marine Geophysical Research 23 (3),223e245.

Courtillot, V., Besse, J., Vandamme, D., Montigny, R., Jaeger, J.J., Cappetta, H., 1986.Deccan flood basalts at the Cretaceous/Tertiary boundary? Earth and PlanetaryScience Letters 80, 361e374.

Davies, T.A., Kidd, R.B., Ramsey, A.T.S., 1995. A time slice approach to the history ofCenozoic sedimentation in the Indian Ocean. Sedimentary Geology 96, 157e197.

Eagles, G., Wibisono, A.D., 2013. Ridge push, mantle plumes, and the speed of theIndian plate. Geophysical Journal International 194, 670e677.

Eccles, J.D., White, R.S., Christie, P.A.F., 2011. The composition and structure ofvolcanic rifted continental margins in the North Atlantic: further insight fromshear waves. Tectonophysics 508 (1e4), 22e33. http://dx.doi.org/10.1016/j.tecto.2010.02.001.

Gombos, A.M., Powell, W.G., Norton, I.O., 1995. The tectonic evolution of WesternIndia and its impact on hydrocarbon occurrences d an overview. SedimentaryGeology 96, 119e129.

Gopala Rao, D., Paropkari, A.L., Krishna, K.S., Chaubey, A.K., Ajay, K.K., Kodagali, V.N.,2010. Bathymetric highs in the mid-slope region of the western continentalmargin of IndiaeStructure and mode of origin. Marine Geology 276, 58e70.

Gradstein, F.M., Ogg, J.G., Schmitz, M., Ogg, G., 2012. The Geologic Time Scale 2012,2-volume set. Elsevier.

Gupta, A.K., Singh, R.K., Joseph, S., Thomas, E., 2004. Indian ocean high-productivityevent (10e8 Ma): linked to global cooling or to the initiation of the Indianmonsoons? Geology 32, 753e756.


Haq, B.U., Hardenbol, J., Vail, P.R., 1987. Chronology of fluctuating sea levels since theTriassic. Science 235, 1156e1167.

Hooper, P.R., 1990. The timing of crustal extension and the eruption of continentalflood basalts. Nature 345, 246e249.

Hopper, J., Buck, W.R., 1996. Effects of lower crustal flow on continental extensionand passive margin formation. Journal of Geophysical Research 101,20175e20194.

Jarvis, G.T., McKenzie, D.P., 1980. Sedimentary basin formation with finite extensionrates. Earth and Planetary Science Letters 48, 42e52.

Jerram, D.A., Widdowson, M., 2005. The anatomy of continental flood basaltprovinces: geological constraints on the processes and products of floodvolcanism. Lithos 79, 385e405.

Karner, G.D., Watts, A.B., 1982. On isostasy at Atlantic-type continental margins.Journal of Geophysical Research 87 (B4), 2923e2948. http://dx.doi.org/10.1029/JB087iB04p02923.

Kolla, V., Coumes, F., 1987. Morphology, internal structure, seismic stratigraphy, andsedimentation of Indus Fan. American Association of Petroleum GeologistBulletin 71, 650e677.

Krishna, K.S., Rao, D.G., Sar, D., 2006. Nature of the crust in the Laxmi Basin (14�-20�), western continental margin of India. Tectonics 25. http://dx.doi.org/10.1029/2004TC001747.

Kroon, D., Steens, T., Troelstra, S.R., 1991. Onset of monsoonal related upwelling inthe western Arabian Sea as revealed by planktonic foraminifers. In: Prell, W.L.,Niitsuma, N., et al. (Eds.), Proceedings of the Ocean Drilling Program, ScientificResults, vol. 117. Ocean Drilling Program, College Station, Texas, pp. 257e263.

Kusznir, N.J., Hunsdale, R., Roberts, A.M., 2004. Timing of depth-dependent litho-sphere stretching on the S. Lofoten rifted margin offshore mid-Norway: pre-breakup or post-breakup? Basin Research 16 (2), 279e296. http://dx.doi.org/10.1111/j.1365-2117.2004.00233.x.

Kusznir, N.J., Roberts, A.M., Morley, C., 1995. Forward and reverse modelling of riftbasin formation. In: Lambiase, J. (Ed.), Hydrocarbon Habitat in Rift Basins,Geological Society, London, Special Publications, vol. 80, pp. 33e56.

Mathur, R.B., Nair, K.R., 1993. Exploration of Bombay offshore basin. In: Proceedingsof the 2nd Seminar on Petroleum Basins of India, vol. 2. KDMIPE and ONGC,Indian Petroleum Publishers, Dehradun, India, pp. 365e396.

McKenzie, D.P., 1978. Some remarks on the development of sedimentary basins.Earth and Planetary Science Letters 40, 25e32.

McKenzie, D.P., Sclater, J.G., 1971. The evolution of the Indian Ocean since the lateCretaceous. Geophysical Journal of the Royal Astronomical Society 24, 437e528.

Miles, P.R., Munschy, M., Segoufin, J., 1998. Structure and early evolution of theArabian Sea and East Somali Basin. Geophysical Journal International 134,876e888.

Miles, P.R., Roest, W.R., 1993. Earliest sea-floor spreading magnetic anomalies in thenorth Arabian Sea and the oceanecontinent transition. Geophysical JournalInternational 115, 1025e1031.

Minshull, T.A., Lane, C.I., Collier, J.S., Whitmarsh, R.B., 2008. The relationship be-tween rifting and magmatism in the northeastern Arabian Sea. Nature Geo-science 1, 463e467. http://dx.doi.org/10.1038/ngeo228.

Mishra, J., Singh, G., Paul, R., Rath, B.K., Phukan, R.K., 2011. Facies Analysis of EarlyMiocene Bombay Formation in Panna-Bassein-Heera Area, Mumbai OffshoreBasin, 2nd South Asain Geoscience Conference and Exhibition, GEO India 2011,12e14th Jan, 2011, Gearter Noida, New Delhi, India.

Misra, A.A., Sinha, N., Mukherjee, S., 2015. Repeat ridge jumps and microcontinentseparation: insights from NE Arabian Sea. Marine and Petroleum Geology 59,406e428. http://dx.doi.org/10.1016/j.marpetgeo.2014.08.019.

Mitra, P., Zutshi, P.L., Chourasia, R.A., Chugh, M.L., Ananthanarayanan, S., Shukla, B.,1983. Exploration in western offshore basins. Petroleum Asia Journal 4, 15e24.

Mohan, M., 1985. Geohistory analysis of Bombay high region. Marine and PetroleumGeology 2, 350e360.

Mohanty, S.N., Jain, M., Jamkhindikar, A., 2013. New Insight to Hydrocarbon Po-tential of Shelf Margin Basin West of DCS Area in Mumbai Offshore Basin, India,10th Biennial Conference on Hydrocarbon exploration and exposition, Kochi,India. p. 243.

Mukhopadhyay, R., Rajesh, M., De, Sutirtha, Chakraborty, B., Jauhari, P., 2008.Structural highs on the western continental slope of India: implications forregional tectonics. Geomorphology 96 (1e2), 48e61.

Naini, B.R., Kolla, V., 1982. Acoustic character and the thickness of the Indus fan andthe continental margin of western India. Marine Geology 47, 181e195.

Naini, B.R., Talwani, M., 1982. Structural framework and the evolutionary history ofthe continental margin of western India. In: Watkins, J.S., Drake, C.L. (Eds.),Studies in Continental Margin Geology, vol. 34. American Association of Pe-troleum Geology Memoir, pp. 167e191.

Nair, N., Pandey, D. K., Cenozoic sedimentation in the Bombay Offshore basin: im-plications for tectonic evolution of western continental margin of India (inpreparation).

Nair, K.M., Singh, N.K., Ram, J., Gavarshetty, C.P., Muraleekrishanan, B., 1992. Stra-tigraphy and sedimentation of Bombay offshore basin. Geological Society ofIndia 40 (5), 415e442.

NELPVII, 2007.MumbaiOffshoreBasinDocument (Accessed3 June2016) http://www.infraline.com/ong/upstream/nelp-vii/mumbai-offshore_basin_nelp_vii.pdf.

Norton, I.O., Sclater, J.G., 1979. A model for the evolution of the Indian Ocean andthe breakup of Gondwanaland. Journal of Geophysical Research 84, 6803e6830.

Pande, K., Sheth, H.C., Bhutani, R., 2001. 40Ar/39Ar age evidence for pre-DeccanUpper Cretaceous volcanic activity in southern India: the St. Mary’s Islandsfelsic volcanics. Earth and Planetary Science Letters 193, 39e46.


http://refhub.elsevier.com/S1674-9871(16)30147-5/sref1














http://dx.doi.org/10.1126/science.l065448

http://dx.doi.org/10.1126/science.l065448














http://dx.doi.org/10.1007/978-3-319-03119-4_1

http://dx.doi.org/10.1007/978-3-319-03119-4_1















































http://dx.doi.org/10.1016/j.tecto.2010.02.001

http://dx.doi.org/10.1016/j.tecto.2010.02.001



































http://dx.doi.org/10.1029/JB087iB04p02923






http://dx.doi.org/10.1029/2004TC001747

http://dx.doi.org/10.1029/2004TC001747






http://dx.doi.org/10.1111/j.1365-2117.2004.00233.x

http://dx.doi.org/10.1111/j.1365-2117.2004.00233.x

























http://dx.doi.org/10.1038/ngeo228







http://dx.doi.org/10.1016/j.marpetgeo.2014.08.019




























http://www.infraline.com/ong/upstream/nelp-vii/mumbai-offshore_basin_nelp_vii.pdf

http://www.infraline.com/ong/upstream/nelp-vii/mumbai-offshore_basin_nelp_vii.pdf











Pandey, A., Pandey, D.K., 2015. Mechanism of crustal extension in the Laxmi Basin,Arabian Sea. Geodesy and Geodynamics 6 (6), 409e422. http://dx.doi.org/10.1016/j.geog.2015.12.006.

Pandey, D.K., Clift, P.D., Kulhanek, D.K., the Expedition 355 Scientists, 2016. ArabianSea monsoon. In: Proceedings of the International Ocean Discovery Program,vol. 355. International Ocean Discovery Program, College Station, TX. http://dx.doi.org/10.14379/iodp.proc.355.2016.

Pandey, D.K., Clift, P.D., Kulhanek, D.K., Andò, S., Bendle, J.A.P., Bratenkov, S.,Griffith, E.M., Gurumurthy, G.P., Hahn, A., Iwai, M., Khim, B.-K., Kumar, A.,Kumar, A.G., Liddy, H.M., Lu, H., Lyle, M.W., Mishra, R., Radhakrishna, T.,Routledge, C.M., Saraswat, R., Saxena, R., Scardia, G., Sharma, G.K., Singh, A.D.,Steinke, S., Suzuki, K., Tauxe, L., Tiwari, M., Xu, Z., Yu, Z., 2015. Expedition 355Preliminary Report: Arabian Sea Monsoon. International Ocean DiscoveryProgram. http://dx.doi.org/10.14379/iodp.pr.355.2015.

Pandey, D.K., Pandey, A., Rajan, S., 2011. Offshore extension of Deccan Traps inKachchh, central western India: implications for geological sequestrationstudies. Natural Resources Research 20 (1), 33e43.

Raju, D.S.N., Bhandari, A., Ramesh, P., 1999. Relative sea-level fluctuations duringCretaceous and Cenozoic in India. Bulletin ONGC 36, 185e202.

Raju, A.T.R., Sinha, R.N., Ramakrishna, M., Bisht, H.S., Nashipudi, V.M., 1981. Struc-ture, tectonics and hydrocarbon prospects of Kerala-Laccadive Basin. In:Rao, R.P. (Ed.), Workshop on Geological Interpretation of Geophysical Data,pp. 123e127.

Rao, P.R., Srivastava, D.C., 1984. Regional seismic facies analysis of Western OffshoreIndia. Bulletin ONGC 21, 83e96.

Rao, R.P., Srivastava, D.C., 1981. Structure, tectonics and hydrocarbon prospects ofKerala-Laccadive Basin. In: Rao, R.P. (Ed.), Workshop on Geological Interpreta-tion of Geophysical Data, pp. 49e57.

Rao, R.P., Talukdar, S.N., 1980. Petroleum geology of Bombay High field, India. In:Halbouty, M.T. (Ed.), Giant Oil and Gas Fields of the Decade 1968e1978, vol. 30.American Association of Petroleum Geology Memoir, pp. 487e506.

Rao, G.S.P., Tewari, H.C., 2005. The seismic structure of the Saurashtra crust in NWIndia and its relationship to Reunion hot-spot. Geophysical Journal Interna-tional 160, 318e330.

Rea, D.K., 1992. Delivery of Himalayan sediment to the northern Indian Ocean andits relation to global climate, sea level, uplift, and seawater strontium. In:Duncan, R.A., et al. (Eds.), Synthesis of Results from Scientific Drilling in theIndian Ocean: American Geophysical Union Geophysical Mono-graph, vol. 70,pp. 387e402.

Reeves, C.V., de Wit, M., 2000. Making ends meet in Gondwana: retracing thetransforms of the Indian Ocean and reconnecting continental shear zones. TerraNova 12 (6), 272e280. http://dx.doi.org/10.1046/j.1365-3121.2000.00309.x.

Roberts, A.M., Kusznir, N.J., Cornfield, R.I., Thompson, M., Woodfine, R., 2013. Inte-grated tectonic basin modelling as an aid to understanding deep-water riftedcontinental margin structure and location. Petroleum Geoscience 19, 65e88.http://dx.doi.org/10.1144/petgeo2011-046.

Roberts, A.M., Kusznir, N.J., Yielding, G., Styles, P., 1998. 2D flexural backstripping ofextensional basins; the need for a sideways glance. Petroleum Geoscience 4,327e338.

Royer, J.Y., Chaubey, A.K., Dyment, J., Bhattacharya, G.C., Srinivas, K., Yatheesh, V.,Ramprasad, T., 2002. Paleogene plate tectonic evolution of the Arabian and


Eastern Somali basins. Geological Society, London, Special Publications 195 (1),7e23.

Royden, L., Keen, C.E., 1980. Rifting process and thermal evolution of the continentalmargin of eastern Canada determined from subsidence curves. Earth andPlanetary Science Letters 51, 343e361.

Sandwell, D.T., Smith, W.H., 2009. Global marine gravity from retracked Geosat andERS-1 altimetry: Ridge segmentation versus spreading rate. Journal ofGeophysical Research: Solid Earth 114 (B1). http://dx.doi.org/10.1029/2008JB006008.

Schlich, R., 1982. The Indian Ocean: aseismic ridges, spreading centers and oceanbasins. In: The Ocean Basins and Margins. Springer, US, pp. 51e147.

Sclater, J.G., Christie, P.A.F., 1980. Continental stretching: An explanation of the Post-Mid-Cretaceous subsidence of the central North Sea Basin. Journal ofGeophysical Research 85 (B7), 3711e3739. http://dx.doi.org/10.1029/JB085iB07p03711.

Singh, S., Jain, A.K., Barley, M.E., 2009. SHRIMP UePb c. 1860 Ma anorogenicmagmatic signatures from the NW Himalaya: implications for Palae-oproterozoic assembly of the Columbia Supercontinent. Geological Society,London, Special Publications 323 (1), 283e300.

Singh, A.P., Mishra, O.P., 2015. Seismological evidence for Monsoon induced microto moderate earthquake sequence beneath the 2011 Talala, Saurashtra earth-quake, Gujarat, India. Tectonophysics 661, 38e48.

Storey, M., Mahoney, J.J., Saunders, A.D., Duncan, R.A., Kelley, S.P., Coffin, M.F., 1995.Timing of hotspot-related volcanism and the breakup of Madagascar and India.Science 267, 852e855.

Subrahmanya, K., 1998. Tectono-magmatic evolution of the west coast of India.Gondwana Research 1 (3), 319e327. http://dx.doi.org/10.1016/S1342-937X(05)70847-9.

Stein, C.A., Stein, S., 1992. A model for the global variation in oceanic depth andheatflow with lithospheric age. Nature 359, 123e129.

Venkatesan, T.R., Pande, K., Gopalan, K., 1993. Did Deccan volcanism pre-date theCretaceous transition. Earth and Planetary Science Letters 119, 181e190.

Watts, A.B., 2001. Isostasy and Flexure of the Lithosphere. Cambridge UniversityPress, Cambridge, U.K., 472 pp.

White, R.S., McKenzie, D., 1989. Magmatism at rift zones: The generation of volcaniccontinental margins and flood basalts. Journal of Geophysical Research 94,7685e7729.

White, R.S., Smith, L.K., 2009. Crustal structure of the Hatton and the conjugate eastGreenland rifted volcanic continental margins, NE Atlantic. Journal ofGeophysical Research 114, B02305. http://dx.doi.org/10.1029/2008JB005856.

Whitmarsh, R.B., 1974. Some Aspects of Plate Tectonics in the Arabian Sea. InitialReports of the Deep Sea Drilling Project, vol. 23, pp. 527e535.

Whiting, B.M., Karner, G.D., Driscoll, N.W., 1994. Flexural and stratigraphic devel-opment of the West Indian continental margin. Journal of Geophysical Research99 (B7), 13791e13811. http://dx.doi.org/10.1029/94JB00502.

Yatheesh, V., Bhattacharya, G.C., Dyment, J., 2009. Early oceanic opening off westernIndia Pakistan margin: the Gop basin revisited. Earth and Planetary ScienceLetters 284, 399e408. http://dx.doi.org/10.1016/j.epsl.2009.04.044.

Zutshi, P.L., Sood, A., Mohapatra, P., Ramani, K.K.V., Dwivedi, A.K., Srivastava, H.C.,1993. Lithostratigraphy of Indian Petroliferous Basins. Documents-V, BombayOffshore Basin, 383.


http://dx.doi.org/10.1016/j.geog.2015.12.006

http://dx.doi.org/10.1016/j.geog.2015.12.006

http://dx.doi.org/10.14379/iodp.proc.355.2016

http://dx.doi.org/10.14379/iodp.proc.355.2016

http://dx.doi.org/10.14379/iodp.pr.355.2015



































http://dx.doi.org/10.1046/j.1365-3121.2000.00309.x

http://dx.doi.org/10.1144/petgeo2011-046














http://dx.doi.org/10.1029/2008JB006008

http://dx.doi.org/10.1029/2008JB006008




















http://dx.doi.org/10.1016/S1342-937X(05)70847-9

http://dx.doi.org/10.1016/S1342-937X(05)70847-9













http://dx.doi.org/10.1029/2008JB005856




http://dx.doi.org/10.1029/94JB00502

http://dx.doi.org/10.1016/j.epsl.2009.04.044




Date post:	01-Jun-2020
Category:	Documents
Upload:	others
View:	4 times
Download:	0 times