Continental Margin

Passive continental margins represent a vast and long-lived exploration domain with huge depository of sediments stored during their evolution.

From: Developments in Petroleum Science , 2012

Basin Evolution and Petroleum Prospectivity of the Continental Margins of India

R. Bastia , K. Radhakrishna , in Developments in Petroleum Science, 2012

one.3.i Types of Continental Margins

Continental margins can be fundamentally divided into three bones types worldwide. These are

i.

The passive continental margins are formed under divergent plate purlieus setting. These are aseismic (less seismic) and often referred as the Atlantic-type margins having a singled-out transition zone betwixt the continental and oceanic crustal regions.

two.

The agile continental margins referred as the Pacific-type margins are the zones of seismically agile convergent plate boundaries. These are characterized by subduction zones formed nether variety of settings such as oceanic–oceanic, oceanic–continental, etc. and are by and large observed along the periphery of the Pacific Ocean.

iii.

Transform continental margins (sheared margins) are formed due to lateral plate movements or shearing motions during the continental breakup procedure in the divergent margin setting. Identifying this category of margins is also in a fashion important, as they represent an original kickoff in the line of continental breakdown and can commonly exist traced laterally into an oceanic fracture zone (Bird, 2001). Further, transform margins are also noticed along the Pacific type continental margins.

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Introduction to Petroleum Geology

Djebbar Tiab , Erle C. Donaldson , in Petrophysics (Fourth Edition), 2016

Convergent Continental Margins

Convergent continental margins develop when two crustal plates collide. When an body of water plate collides with a less dumbo continental plate a marginal basin forms between the island arc and the continent. This basin fills with carbonate deposits from marine animals and clastics from the land mass forming big areas for accumulation of hydrocarbons such as the oilfields of Southeast Asia.

Continual movement of the plates confronting each other will outcome in germination of a long narrow trough (several hundreds of miles long) called a geosyncline. The resulting trough is filled with great thicknesses of sediments that may become uplifted and folded as mountain building (orogeny) begins accompanied by volcanic activity. The Appalachian Mountains in eastern United States and the Ural Mountains in Russia are examples of the effect of convergent continental margins where sediments accumulated and were then uplifted in an orogenic period to form the stable mountains that are eroding today and furnishing sediments to the low land areas on both sides of the mountains.

Some of the petroleum that may accept accumulated in the sediments is lost during the orogenic period considering the seals holding the oil in geologic traps are destroyed allowing the hydrocarbons to migrate to the surface. Folding and faulting of the sediments, nevertheless, too produces structural traps in other areas of the region.

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Legislation and The Futurity

James G. Speight , in Subsea and Deepwater Oil and Gas Scientific discipline and Engineering science, 2015

10.4 Littoral zone management

The continental margins, the geographic region contiguous to and lying seaward of a coastline ( Chapter ii), have become increasingly of import to the crude oil and natural gas industry over the by century. The continental margins consist of three portions: (ane) the continental shelf which has shallow water depths rarely deeper than 650 ft) and extends seaward from the shoreline to distances ranging from 12.3 miles to 249 miles, (two) the continental slope where the bottom drops off to depths of upward to three.1 miles, and (iii) the continental rise which dips very shallowly seaward from the base of the continental slope and is in part equanimous of down-washed sediments deposited at the base of operations of the gradient. The continental margins are of peachy importance for many reasons, not least of which is that they are shortly the source of increasing amounts of crude oil and natural gas supplies.

In the United States, as interest in the commercial evolution of natural gas and oil increased in the 1940s, control over these resources became a major issue, peculiarly in the offshore regions. While these legislative efforts take are used here equally example, the countries of the Eu and other countries take followed suit with similar legislation.

The Congress of the United States somewhen resolved this issue by passage of the Submerged Lands Deed (SLA) in 1953, which established the jurisdiction of the Federal Authorities to (and buying of) submerged lands located on a bulk of the continental margin. States were given jurisdiction over any natural resources within 3 nautical miles (3.45 miles) of the coastline excepting Texas and the west coast of Florida where the SLA extends the states' Gulf of Mexico jurisdiction to 9 nautical miles (10.35 miles).

Passage of the SLA prepared the way for passage of the OCSLA, likewise in 1953, which defined the Outer Continental Shelf (OCS), separate from geologic definitions, as whatsoever submerged land outside country jurisdiction and reaffirmed federal jurisdiction over these waters and all resources they contain. Moreover, the OCSLA outlined the responsibilities of the federal government for managing and maintaining offshore lands subject field to environmental constraints and condom concerns. The Act (OCSLA) authorizes the United States DOI to lease the divers areas for development and to formulate regulations pertaining thereto every bit necessary. Between 1978 and 1998 the OCSLA was amended 6 times to account for irresolute issues and remains the cornerstone of offshore legislation.

On a worldwide basis, the 1994 International Law of the Sea granted the same 200 nautical miles (230 miles) to all countries. Prior to this, countries had claimed jurisdiction to offshore areas in bilateral agreement with neighboring countries. For case, since 1978, the United States and Mexico signed two treaties in order to fully ascertain jurisdictional boundaries in the Gulf of United mexican states. In some instances the International Police force of the Sea provides that jurisdiction over natural resources extends beyond the 200-nautical mile (230-mile) boundary to the border of the geological continental margin based on geological factors such every bit sediment thickness and water depth. For this reason the boundaries associated with Alaska, parts of the East Coast and the Gulf of Mexico extend beyond 200 nautical miles (230 miles), just the Pacific coast has the standard boundary limits (Figure ten.i).

The consequence of the availability of outer continental shelf (OCS) lease areas has been a source of debate, fifty-fifty controversy, over the years. On the ane hand, there are arguments that one side are those who argue that countries (for example, the Us) need to open such areas to crude oil and natural gas production in society to meet futurity energy needs or other policy objectives such as reduced dependence on foreign (imported) oil. On the other hand, there are other arguments related to protection of the ocean and coastal environments from further pollution also as avoiding the potential negative effects on angling or tourism with the caveat that the negative impacts of exploration and evolution needed to extract the natural gas and oil likely outweigh the potential benefits.

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Formation and Distribution of Volcanic Rock

Caineng Zou , ... Wu Xiaozhi , in Volcanic Reservoirs in Petroleum Exploration, 2013

2.1.1.3 Cordilleran Continental Margin Volcanic Arc Zone

The Cordilleran continental margin volcanic arc mainly refers to the Cordilleran mountain range zone in South America, and information technology, together with the due west Pacific volcanic arc zone, composes the circum-Pacific volcanic circle, which has a full length of more than forty,000  km. At that place are 30 active volcanoes in the south section of the Andes, the Cordillera mount arrangement, and 16 active volcanoes in the northward section. The Llullaillaco volcano in the center with an altitude of 6723   g is the highest active volcano in the earth. The characteristics of volcanic rock in the Cordilleran continental margin volcanic arc are like to those in the west Pacific intraoceanic arc; that is, dominated by intermediate andesite, the volcanic rock has apparent horizontal zonality in the direction from trench to land. The main eruption mode is centered eruption.

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Bowl Development and Petroleum Prospectivity of the Continental Margins of India

R. Bastia , G. Radhakrishna , in Developments in Petroleum Science, 2012

3.four.5.5 Seismic Refraction Velocities and Crustal Seismic Transects

The WCMI and the bordering deep oceanic areas of the eastern Arabian Sea consist of numerous structural features namely, the Laccadive ridge, the Laxmi ridge, the Prathap ridge complex, and the Panikkar ridge, which are mostly buried under the sediments (Naini and Talwani, 1982). The Laccadive and Laxmi ridges split up the eastern Arabian Ocean into the Western and Eastern basins (Fig. iii.4). While the geophysical studies indicate that the Western bowl is underlain past oceanic crust (Chaubey et al., 1995; McKenzie and Scalter, 1971; Naini and Talwani, 1982; Whitmarsh, 1974), the nature of crust below the Eastern bowl could not be clearly established.

Seismic data along the WCMI and the deep oceanic parts of the Arabian Sea include broad-angle reflection and seismic refraction surveys carried out by Francis and Shor (1966), Rao (1967), Naini and Talwani (1982), Naini and Kolla (1982), Chaubey et al. (2002a), Krishna et al. (2006), and Minshull et al. (2008). Information on crust/mantle structure forth the W coast of India is available from seven refraction DSS profiles collected by National Geophysical Enquiry Plant, Hyderabad, India, along the Kavali–Udipi profile (Kaila et al., 1979; Reddy et al., 2000; Sarkar et al., 2001), Guhagar–Chorochi profile (Koyna-I) and the Kelsi–Loni profile (Koyna-Ii) in Koyna region (Kaila et al., 1981a,b; Krishna et al., 1991), Mehmadabad-Billimora contour in Cambay basin (Kaila et al., 1981b), Amreli–Navibandar contour in Saurashtra (Kaila et al., 1988), and Kuppam–Palani transect in the Southern Granulite Terrain (SGT) (Reddy et al., 2001; Vijaya Rao et al., 2006), and Dharimana–Gandhinagar profile (Kaila et al., 1990b). The locations of available refraction stations in the eastern Arabian Sea and the DSS profiles in the western Indian shield are shown in Fig. iii.4. The interpreted DSS sections belonging to the west coast are shown in Fig. 3.9.

DSS investigations have clearly shown the unstretched continental crust and its mail-rifting features in the western Indian shield. A few inferences from the DSS studies along the west coast (after Radhakrishna et al., 2002) as revealed from Figs. 3.9 and iii.10 are (i) the velocities for Deccan traps range betwixt four.5 and five.five   km/s and take maximum thickness of 2.0   km. The traps are underlain by Mesozoic sediments having velocities of 4.0   km/s in Saurashtra; (ii) a two-layered continental crust, an upper crust of 10–twenty   km characterized past velocities of 5.8–six.5   km/due south and a lower crust having velocities of 6.vi–6.ix   km/s. The Moho is observed at a depth of 38–42   km in the shield regions; (iii) Moho in general shallowing towards the coast; (iv) high lower crustal velocities (>   7.0   km/s) at 23–25   km depth and a shallow Moho at a depth of 31–33   km below Cambay rift basin; (v) transitional Moho and low-velocity layers in the Koyna region; and (vi) continental type of crust below Saurashtra.

Figure three.9. Various DSS sections (location shown in Fig. 3.iv) close to the Due west Coast of India compiled from different sources. (A) Crustal section (2) along Kavali–Udipi profile (adapted from Kaila et al., 1979 ) and crustal section (3) along Koyna I (Guhagar–Chorochi) profile (adapted from Kaila et al., 1981a ). (B) crustal section (4) along Koyna 2 (Kelsi–Loni) profile (adapted from Kaila et al., 1981b ) and crustal department (5) along the Mehmadabad to Billimora profile in the Cambay basin (adapted from Kaila et al., 1981c ). (C) Crustal department (6) along due north Cambay and Sanchor basins from Mehmadabad to Dharimanna (adapted from Kaila et al., 1990b ) and crustal department (7) along Navibandar-Amreli profile in the Saurashtra peninsula

 (adapted from Kaila et al., 1988).

Figure 3.ten. The compiled velocity models for different DSS profiles along the western Indian shield region and the velocity models for lithosphere below the West Declension in the DVP

 (adapted from Radhakrishna et al., 2002).

The sonobuoy refraction data shown every bit velocity–depth profiles in Fig. 3.11 compiled from Naini and Talwani (1982) show singled-out variations in crustal structure below the western and the eastern basins in the Arabian Sea. A summary of this data indicates that the sedimentary layers are characterized by velocities varying from 1.seven   km/s for top unlithified sediments to four.nine   km/southward for the deeper layers above the acoustic basement, the basal sedimentary layers in the Eastern basin and the Laxmi ridge region show velocities in the range of four.0–4.9   km/s, and the acoustic basement having velocity of v.0   km/s. For the crustal layers, velocities between 5.2 and 7.three   km/s (with predominantly 6.2–half-dozen.4   km/s values) have been observed. A few refraction stations in the Laxmi basin and the Laxmi ridge evidence velocities >  vii.0   km/s in the lower crust, although the Moho could non be mapped. Notwithstanding, the Moho having velocities of 7.9–viii.3   km/s could be mapped in the western basin at several locations at an average Moho depth of 11.five   km. The refraction data unequivocally betoken that the western basin is underlain past oceanic crust with average velocities of 5.5 and half dozen.7   km/southward for oceanic layers two and 3, respectively. While the seismic velocities over the Laxmi ridge bespeak continental affinity of the ridge, unfortunately, in the Laxmi basin region, the velocity data did non provide whatever clues regarding the nature of crust. Miles et al. (1998) interpreted the seismic velocities (as low every bit six.three   km/southward) in the Laxmi bowl as representing the continental crust, whereas Talwani and Reif (1998) attributed the velocities greater than 7.0 km/southward to the presence of initial oceanic crust. Krishna et al. (2006) infer the basin to be underlain by rifted continental crust.

Figure 3.eleven. The velocity–depth profiles obtained from the sonobuoy refraction data in the eastern Arabian Sea

 (redrawn with permission from Naini and Talwani, 1982 © AAPG Publication).

Further, for meliorate understanding of crustal geometry across the western margin, crustal transects have been earlier synthetic by few workers (Radhakrishna et al., 2002; Todal and Eldholm, 1998) past projecting all available seismic information in the nearby areas onto the transect lines (Fig. iii.12). While Todal and Eldholm (1998) synthetic the sections in the offshore (P5 and P8 in Fig. 3.4), Radhakrishna et al. (2002) extended them into the coastal areas of western shield (P7 and P11 in Fig. 3.4) and projected the upper and lower crustal boundary too as the Moho variations known from the DSS sections in the West Coast which provided information on the stretched every bit well as unstretched continental chaff at the margin.

Effigy 3.12. 4 crustal transects (P5, P7, P8, and P11) constructed from seismic data across the WCMI (see Fig. 3.four for location of transects)

 (P5 and P8 adapted from Todal and Eldholm, 1998; P7 and P11 adjusted from Radhakrishna et al., 2002).

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Basin Development and Petroleum Prospectivity of the Continental Margins of Bharat

R. Bastia , M. Radhakrishna , in Developments in Petroleum Science, 2012

6.1 Introduction

The Western Continental Margin of India (WCMI) in contrast to the ECMI discussed in Chapter 5 has a dissimilar evolutionary history. Large onshore basins as well as thick offshore sedimentary depocenters observed along the ECMI are typically absent along the WCMI. The margin consists of five major offshore sedimentary basins (Fig. six.1) such as the Kutch, Saurashtra, Mumbai, Konkan and Kerala basins separated by transverse basement arches (Biswas and Singh, 1988; Singh and Lal, 1993). Further, the eastern Arabian Body of water and the adjoining West Coast of Republic of india contain several structural features which have evolved mostly as a effect of rifting and seafloor spreading betwixt Bharat, Madagascar, and Seychelles (Biswas, 1987; McKenzie and Scalter, 1971; Naini and Talwani, 1982). While the northern office of the W Coast is geologically prominent due to the presence of all-encompassing Deccan alluvion basalt province which masks the preexisting Precambrian geology of the region, the southern part is composed of Archaean charnockites, gneisses, and granites with limited extent of the Tertiary sediments along the coast of Kerala in the far southward. It is very well known that the dominant structural and tectonic trends along the West Declension (Fig. 3.v), such as, the Dharwar trend (NW–SE to NNW–SSE), the Aravalli trend (NE–SW), and the Satpura trend (ENE–WSW to Eastward–West) have a begetting on the north to southward sequential rifting of the Indian Subcontinent during the breakup (Biswas, 1982). In this chapter, a brief description of regional geology, subsurface lithostratigraphic history of the offshore sedimentary basins forth the WCMI, and the development of petroleum systems for the individual basins is provided.

Effigy six.ane. Bathymetric map showing major structural and tectonic features along the WCMI. WCF, West Coast Error. Thick marking onland parallel to the coast indicates the location of Western Ghat scarp. SGT, Southern granulite terrain; DCP, Dharwar Craton Province; DVP, Deccan Volcanic Province

 (adapted from Singh et al., 2007).

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Basin Evolution and Petroleum Prospectivity of the Continental Margins of India

R. Bastia , M. Radhakrishna , in Developments in Petroleum Scientific discipline, 2012

5.3.four.2.1 Connecting Shelf to the Deepwater: Evidences from the East Coast of India

In the example of continental margin, the shelf region acts every bit the main staging expanse for the sediments to disperse into the deepwater areas. Due to tectonic movements and continuous changes in ocean level at the coast, topographic changes takes identify in the shelf as well as slope areas. These changes affect the sediment pathways leading to deepwater basins and therefore influence the deposition of deepwater systems. Equally many canyons observed in the shelf and slope regions human activity as conduit for sediment transportation, connecting shelf to deepwater is an important pace in understanding the deepwater depositional systems. Identification of different stratal terminations from seismic data and interpretation of shoreline shifts are important in the sequence stratigraphic framework. In fact, the sequence stratigraphy is extremely helpful in determining the facies associated with shelf, slope, or basinal part ( Catuneanu, 2005). A shoreline shift tin be transgressive or regressive, which can assistance in characterizing various offshore reservoirs. For example, during transgressive phase, sediments transported to the deepwater are mostly fine grained, while during regressive phase, the aqueduct organisation will be active. The continental shelf along the e coast of India is narrower when compared to the west declension. A number of canyons have been observed in the slope area and the presence of these canyons at the shelf–gradient suspension (Fig. 5.35) acts as inlet for sedimentation to deep basin. The shelf canyons tin be connected to the deepwater channel organisation and a multifariousness of shelf margin and slope processes influence the sediment pathways into the deepwater basins (Figs. v.36 and v.37).

Figure 5.35. Uninterpreted and interpreted seismic sections (left) showing deep shelfal canyon cutting above which progradational and aggradational delta pack was deposited during high stand. A massive shelfal canyon cut of Pleistocene age every bit mapped within the seismic volume

 (adjusted with permission from Bastia, 2007 © Applied science Publications, Dehradun).

Figure five.36. Seismic sections depicting the slope channels and shelfal canyon cutting.

 (adjusted with permission from Bastia, 2007 © Technology Publications, Dehradun)

Figure five.37. Seismic section showing stacked channels (in a higher place left), seismic stage section showing major sequence stratigraphic elements connecting high-stand prograding delta on the shelf, depression-stand wedge and slope/basin floor fan (to a higher place right), and seismic section showing shelf-border delta progradation and low-stand fan complex

 (adjusted with permission from Bastia, 2007 © Technology Publications, Dehradun).

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Basin Development and Petroleum Prospectivity of the Continental Margins of Republic of india

R. Bastia , M. Radhakrishna , in Developments in Petroleum Science, 2012

Abstract

The geological history and evolution of Indian continental margins has close linkages with the breakup and dispersal of eastern Gondwanaland. It is very well established that the continental breakup processes between Republic of india, East Antarctica, Madagascar, and the Seychelles have left their imprints on the continental margins of India equally well as on the adjoining deep bounding main floor. In order to understand the early on breakup history and subsequent development of its constituent margins, several before workers (eastward.g., Reeves and de Wit, 2000) accept reconstructed the continental fragments of the Gondwanaland using the magnetic anomaly identifications, fracture zones and transform fault trends revealed by bathymetry maps, and the paleomagnetic information of continental areas. Though these reconstruction models of the Indian Sea are very well constrained until the Cretaceous, the function of India in the Gondwanaland dispersal remained very uncertain in the Mesozoic due to which edifice upward of a tighter reconstruction becomes very hard. This is basically due to lack of articulate agreement on the nature of crust in certain critical areas of the continental margins as well equally below big aseismic ridges/plateaus, and uncertainties in magnetic anomaly identifications. In this affiliate, we present a brief account of various geological or geophysical constraints obtained through deep body of water drilling efforts in the Indian Ocean, central morphological/tectonic features, Mesozoic magnetic anomaly identifications, and the role of plumes and associated volcanism, for amend understanding of the early breakup history of Eastern Gondwanaland as well every bit the development of the Indian Ocean.

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Basin Development and Petroleum Prospectivity of the Continental Margins of Republic of india

R. Bastia , Grand. Radhakrishna , in Developments in Petroleum Science, 2012

Abstract

The tectonic framework of the present-twenty-four hour period continental margin of Bharat and the wide variations in morphology, structure, sedimentation, volcanic activeness, and and then on observed along its various segments basically reflect that these segments have evolved through a variety of tectonomagmatic processes and varied breakup history (passive/active rifting, shearing) during their evolution. We highlighted in this chapter some of the above issues as they take direct relevance to proper evaluation of petroleum system forth the Indian continental margins. A tabular array summarizing the structural setup and petroleum system of the offshore basins is provided along with a description of reservoir potential of the deepwater depositional system in the Bengal Fan.

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Metallogeny

D.H.C. Wilton , D.F. Strong , in Encyclopedia of Physical Science and Applied science (3rd Edition), 2003

III.B Stage 2: Breakup

In the earliest stages of breakdown, when the continental margin begins to cool and sink, and seawater floods the rift valleys, evaporation of the seawater may consequence in the precipitation of chemic sediments known as evaporites, forming economic deposits of halite, potash, and sulfates. As the continent is dissever into separate plates, the passive continental margins are initially high and rugged, like the opposing coasts of Greenland and Canada. The erosion of these terrains results in the rapid degradation of thick deposits of clastic sedimentary rocks known as turbidites. These evaporites and turbidites are ideal environments for the formation of epigenetic oil and gas deposits, which concentrate in the more porous sedimentary horizons and in structural traps similar anticlines and salt domes. Such situations are well-illustrated by the numerous oil fields around the margins of the North Atlantic, such equally those of the Northward Ocean and the giant Hibernia oil structure off Newfoundland.

In the Norils'g region of Russian federation, plateau basalts intruded into, and intermixed with, sedimentary evaporite sequences to form giant syngenetic nickel and platinum group chemical element deposits.

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