- Email: [email protected]
Rifted arch basins and post-breakup rim basins on passive continental margins
Tectonophysics, 41 (1977) Tl-T5 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
Tl
Letter Section Rifted arch basins and post-breakup rim basins on passive continental margins J.J. VEEVERS
School of Earth Sciences, ~ac~aarie
~~iversi~,
North Ryde, N.S. W. ~Aus~a~ia~
(Submitted October 18, 19’76; revised version accepted February 17, 1977)
ABSTRACT Veevers, J.J., 1977. Rifted arch basins and post-breakup rim basins on passive continental margins. Tectonophysics, 41: Tl-Tg.
In its evolution by plate divergence to a passive continental margin, a ~ntinent~ arch marked by narrow rift valleys (intra-arch basins) and flanked by broad basins (inter- and extra-arch basins) is most likely to break up along a rift valley boundary fault. The resulting dismembered arch at the continental margin is a rim that constitutes the oceanward flank of a rim basin, and the rim basin succeeds one or other of the basins related to the previous arch. In offshore Western Australia, the juxtaposition of Mesozoic reservoir rock at a rift shoulder and source rock of the succeeding rim basin provide a mechanism for concentrating a large gas deposit.
Superimposed on the broad uplift of the Central Plateau of East Africa are rifted arches bearing tbe Western and Gregory Rifts, with a shallow sag between occupied by Lake Victoria (Holmes, 1965, p. 1056) (Fig. 1). In relation to the arches, the modem depositional basins of East Africa may be classed as within arch (Western and Gregory Rift Valleys), between (Lake Victoria), and outside (Congo River basin), for which I propose the terms i~tr~-u~c~, i~~e~~~c~, and ex~~u~~c~ basins. In the postulated evolution of a continental interior to a continental margin by plate divergence (Schneider, 1969; Dewey and Bird, 1970), the continent is most likely to break up along one or other of the rift valley boundary faults (Kinsman, 1975). It follows that a rifted continent should bear a dismembered arch or half-arch along its margin. Thanks to a very thin (generally < 1 km) cover of post-breakup sediment on the western margin of Australia, the surface of the continent at breakup - 160 m.y. ago (Late Jurassic) along the northwest margin (Veevers and Heirtzler, 1974; Larson, 1975; Powell, 1976) and 125 m.y. ago (Early Cretaceous) along the southwest margin (Veevers and Heirtzler, 1974; Johnstone et al., 1973; Markl, 1974; Johnson et al., 1976) -and the contemporaneously generated adjacent oceanfloor are clearly seen in seismic profiles (Veevers and Cotterill, in preparation) and have been penetrated in several
T2
Fig. 1. Profile of Central Plateau of East Africa (data from Atlas of the World, 1974) from a point (4”N, 27*E) near Niangara, Zaire, to Mombasa, Kenya (4”S, 40°E), across the Western Rift arch at Lake Albert, the sag of Lake Victoria, and the Gregory Rift arch at Lake Natron. Rift valley fill dotted. Only part of the extra-arch basin of Zaire is shown; the extra-arch basin of Kenya and Tanzania is truncated by the Indian Ocean. Vertical exaggeration X 10. Ticks on seaievel datum spaced 100 km.
C
sectron line of Fig. 3
25
30,
ANTARCTICA
t
35
Fig. 2. Reconstruction of Western Australia and adjacent parts of Gondwanaland, including Greater India (Veevers et al., 1975), in the Jurassic before breakup, showing Permian to Jurassic Perth, Meriinleigh, and Dampier intra-arch Basins (dotted) and the extra-arch Browse Basin (shown by a synolinal axis) behind what became the western margin of Australia, and the inferred rifted arch system on the other side of the line of breakup (double lines). Note the broad inter-arch regions of the Exmouth plateau and Carnarvon Terrace. Present coastline and geographical co-ordinates for reference only.
T3
drill-holes (Veevers, 1974; Powell, 1976; Veevers, Heirtzler et al., 1974 a)* By these means, the western margin of Australia before breakup is found to have a configuration of rifted arches and associated basins (Fig. 2) that match those of modem East Africa (Veevers and Cotter& 1976). Breakup by plate divergence took place presumably along a boundary fault of a rift valley or intra-arch basin (Fig. 3u,b), after the fashion described by Kinsman (1975). The half-arch is recognized as a rim at the edge of the continental margin, constituting the oceanward flank of a depositional basin, which I a
i%E - BREAKUP
ARCH .
inter-arch
ARCH
basin
extraarch basm
1
b incipient
BREAKUP Rimmed ~~fain
. . ocean” rift L,:‘;‘:_.___. ::‘j” Y Y
rim
basin
c rim
basm
rim
I :::::: ” ” Y :, j”“” d initial fill .).,,.
IO
200 km
300 I
400 8
500 1
Fig. 3. Schematic sections (from Veevers and Cotterill, in preparation) showing evolution of the multiple rifted arch system of the Exmouth Plateau-Dampier Basin, located in Fig. 2. Vertical exaggeration X 10. Rift valley fill dotted. Lines of coarse dots in a---%represent continent that dispersed after break-up. a. 200-165 m.y. ago: stage of rifted arch systems (cf. Fig. 1). b. Incipient breakup (160 m.y. ago): marked uplift of incipient ocean rift arch. c. A few million years after breakup: generation of ocean rift, development of half-arch forming marginal rim and rim basin. d. 140 m.y. ago: subsidence of oceanfloor and adjacent margin, and initial fiil of rim basin in depression between shoulders of preceding rift valley. e. 120 m.y. ago: submergence of rim and seaward migration of axes of rim basin by subsidence of oceanfloor and margin. f. Present day: progradation of sediment (mainly carbonate) outward since submergence of rim.
T4
propose to call a rim basin (Fig. 3c-e). The half-arch is best seen along the outer part of the Exmouth Plateau and Camarvon Terrace (Branson, 1974; Veevers et al., 1974 b; Veevers, 1974; Wilcox and Exon, 1976) (Fig. 2). At different places, the rim basin succeeded an inter-, intra-, or extra-arch basin or two or more of these. In the sections shown in Fig. 3, the rim basin succeeded first the eastern rift valley or intra-arch Dampier Basin, and then, by oceanward migration of the rim basin axis, the inter-arch basin of the Exmouth Plateau. The rim and its associated rim basin lasted some 30-40 m.y. after breakup until the rim subsided below sealevel (Fig. 3e), seen in detail in the time--space diagrams of Powell (1976), whereafter sediment transport became grossly centrifugal from the rimless continent without damming or deflection (Fig. 3f). The half-arch is a member of the class of structures that dam sediment at the edge of continental margins (Hedberg, 1970). That rim basins and the preceding rifted arch basins are common on other passive margins is suggested by cross-sections of the margin of eastern North America (Sheridan, 1974), southeast (Kent, 1974) and southwest (Emery et al., 1975) Africa, and southern Australia (Falvey, 1974; Boeuf and Doust, 1975). In the Dampier Basin (Fig. 2), the juxtaposition of reservoir rock (Late Triassic rift valley fluvio-deltaic sandstone) at a rift shoulder and source rock (Late Jurassic claystone deposited in a restricted marine environment) of the rim basin, and the sealing of the source and reservoir by Early Cretaceous marine claystone have led to the concentration of estimated recoverable reserves of about 0.34*10i2m3 of gas (Powell, 1976). The recognition of rim basins on other passive margins may therefore provide a guide in exploration for petroleum. ACKNOWLEDGEMENTS
I thank J.G. Jones and C. McA. Powell for valuable comments, and the Australian Research Grants Committee for support. REFERENCES Atlas of the World, 1974. Comprehensive Edition. Times Books, London. Boeuf, M.G. and Doust, H., 1975. Structure and development of the southern margin of Australia. Aust. Pet. Explor. Assoc. J., 15: 33-43. Branson, J.C., 1974. Structures of the western margin of the Australian continent. Oil and Gas (Sydney), 20 (9): 24-35. Dewey, J.F. and Bird, J.M., 1970. Mountain belts and the new global tectonics. J. Geophys. Res.,75: 2625-2647. Emery, K.O., Uchupi, E., Bowin, C.O., Phillips, J. and Simpson, E.S.W., 1975. Continental margin off Western Africa: Cape St. Francis (South Africa) to Walvis Ridge (South-West Africa). Am. Assoc. Pet. Geol. Bull.,59: 3-59. Falvey, D.A., 1974. The development of continental margins in plate tectonic theory. Aust. Pet. Explor. Assoc. J., 14: 95-106. Hedberg, H.D., 1970. Continental margins from the viewpoint of the petroleum geologist. Am. Assoc. Pet. Geol. Bull.,54 : 3-43.
T5
Holmes, A., 1965. Principles of Physical Geology. Nelson, London, 1288 pp. Johnson, B.D., Powell, C. McA. and Veevers, J.J., 1976. Spreading history of the eastern Indian Ocean, and Greater India’s northward flight from Antarctica and Australia. Geol. Sot. Am. Bull., 87: 1569-1566. Johnstone, M.H., Lowry, D.C. and Quilty, P.G., 1973. The geology of southwestern Australia - a review. J. R. Sot. W. Aust., 56: 5-15. Kent, P.E., 1974. Continental margin of East Africa - a region of vertical movements. In: C.A. Burk and C.L. Drake (Editors), The Geology of Continental Margins. Springer, New York, pp. 313-320. Kinsman, D.J.J., 1975. Rift valley basins and sedimentary history of trailing continental margins. In: A.G. Fischer and S. Judson (Editors), Petroleum and Global Tectonics. Princeton Univ. Press, Princeton, pp. 83-126. Larson, R.L., 1975. Late Jurassic sea-floor spreading in the Eastern Indian Ocean. Geology, 3: 69-71. Markl, R.G., 1974. Evidence for the breakup of eastern Gondwanaland by the Early Cretaceous. Nature, 251: 196-199. Powell, D.E., 1976. The geological evolution of the continental margin of northwest Australia. Aust. Pet. Explor. Assoc. J., 16: 13-23. Schneider, E.D., 1969. Models for rifted and compressional continental margins. Geol. Sot. Am., Abstr., 7: 291-292. Sheridan, R.E., 1974. Atlantic continental margin of North America. In: CA. Burk and C.L. Drake (Editors), The Geology of Continental Margins. Springer, New York, pp. 391-407. Veevers, J.J., 1974. Western continental margin of Australia. In: C.A. Burk and C.L. Drake (Editors), The Geology of Continental Margins. Springer, New York, pp. 605616. Veevers, J.J. and Cotterill, D., 1976. Western margin of Australia: a Mesozoic analog of the East African rift system. Geology, 4: 713-717. Veevers, J.J. and Heirtzler, J.R., 1974. Tectonic and paleogeographic synthesis of Leg 27. Initial Report Deep Sea Drilling Project, 27: 1049-1054. Veevers, J.J., Heirtzler, J.R. and others, 1974a. Initial Reports of the Deep Sea Drilling Project, 27. Veevers, J.J., Falvey, D.A., Hawkins, L.V. and Ludwig, W.J., 1974b. Seismic reflection measurements of Northwest Australian margin and adjacent deeps. Am. Assoc. Pet. Geol. Bull., 58: 1731-1750. Veevers, J.J., Powell, C. McA. and Johnson, B.D., 1975. Greater India’s place in Gondwanaland and in Asia. Earth Planet. Sci. Lett., 27: 383-387. Willcox, J.J. and Exon, N.F., 1976. The regional geology of the Exmouth Plateau. Aust. Pet. Explor. Assoc. J., 16: l-11.
Tl
Letter Section Rifted arch basins and post-breakup rim basins on passive continental margins J.J. VEEVERS
School of Earth Sciences, ~ac~aarie
~~iversi~,
North Ryde, N.S. W. ~Aus~a~ia~
(Submitted October 18, 19’76; revised version accepted February 17, 1977)
ABSTRACT Veevers, J.J., 1977. Rifted arch basins and post-breakup rim basins on passive continental margins. Tectonophysics, 41: Tl-Tg.
In its evolution by plate divergence to a passive continental margin, a ~ntinent~ arch marked by narrow rift valleys (intra-arch basins) and flanked by broad basins (inter- and extra-arch basins) is most likely to break up along a rift valley boundary fault. The resulting dismembered arch at the continental margin is a rim that constitutes the oceanward flank of a rim basin, and the rim basin succeeds one or other of the basins related to the previous arch. In offshore Western Australia, the juxtaposition of Mesozoic reservoir rock at a rift shoulder and source rock of the succeeding rim basin provide a mechanism for concentrating a large gas deposit.
Superimposed on the broad uplift of the Central Plateau of East Africa are rifted arches bearing tbe Western and Gregory Rifts, with a shallow sag between occupied by Lake Victoria (Holmes, 1965, p. 1056) (Fig. 1). In relation to the arches, the modem depositional basins of East Africa may be classed as within arch (Western and Gregory Rift Valleys), between (Lake Victoria), and outside (Congo River basin), for which I propose the terms i~tr~-u~c~, i~~e~~~c~, and ex~~u~~c~ basins. In the postulated evolution of a continental interior to a continental margin by plate divergence (Schneider, 1969; Dewey and Bird, 1970), the continent is most likely to break up along one or other of the rift valley boundary faults (Kinsman, 1975). It follows that a rifted continent should bear a dismembered arch or half-arch along its margin. Thanks to a very thin (generally < 1 km) cover of post-breakup sediment on the western margin of Australia, the surface of the continent at breakup - 160 m.y. ago (Late Jurassic) along the northwest margin (Veevers and Heirtzler, 1974; Larson, 1975; Powell, 1976) and 125 m.y. ago (Early Cretaceous) along the southwest margin (Veevers and Heirtzler, 1974; Johnstone et al., 1973; Markl, 1974; Johnson et al., 1976) -and the contemporaneously generated adjacent oceanfloor are clearly seen in seismic profiles (Veevers and Cotterill, in preparation) and have been penetrated in several
T2
Fig. 1. Profile of Central Plateau of East Africa (data from Atlas of the World, 1974) from a point (4”N, 27*E) near Niangara, Zaire, to Mombasa, Kenya (4”S, 40°E), across the Western Rift arch at Lake Albert, the sag of Lake Victoria, and the Gregory Rift arch at Lake Natron. Rift valley fill dotted. Only part of the extra-arch basin of Zaire is shown; the extra-arch basin of Kenya and Tanzania is truncated by the Indian Ocean. Vertical exaggeration X 10. Ticks on seaievel datum spaced 100 km.
C
sectron line of Fig. 3
25
30,
ANTARCTICA
t
35
Fig. 2. Reconstruction of Western Australia and adjacent parts of Gondwanaland, including Greater India (Veevers et al., 1975), in the Jurassic before breakup, showing Permian to Jurassic Perth, Meriinleigh, and Dampier intra-arch Basins (dotted) and the extra-arch Browse Basin (shown by a synolinal axis) behind what became the western margin of Australia, and the inferred rifted arch system on the other side of the line of breakup (double lines). Note the broad inter-arch regions of the Exmouth plateau and Carnarvon Terrace. Present coastline and geographical co-ordinates for reference only.
T3
drill-holes (Veevers, 1974; Powell, 1976; Veevers, Heirtzler et al., 1974 a)* By these means, the western margin of Australia before breakup is found to have a configuration of rifted arches and associated basins (Fig. 2) that match those of modem East Africa (Veevers and Cotter& 1976). Breakup by plate divergence took place presumably along a boundary fault of a rift valley or intra-arch basin (Fig. 3u,b), after the fashion described by Kinsman (1975). The half-arch is recognized as a rim at the edge of the continental margin, constituting the oceanward flank of a depositional basin, which I a
i%E - BREAKUP
ARCH .
inter-arch
ARCH
basin
extraarch basm
1
b incipient
BREAKUP Rimmed ~~fain
. . ocean” rift L,:‘;‘:_.___. ::‘j” Y Y
rim
basin
c rim
basm
rim
I :::::: ” ” Y :, j”“” d initial fill .).,,.
IO
200 km
300 I
400 8
500 1
Fig. 3. Schematic sections (from Veevers and Cotterill, in preparation) showing evolution of the multiple rifted arch system of the Exmouth Plateau-Dampier Basin, located in Fig. 2. Vertical exaggeration X 10. Rift valley fill dotted. Lines of coarse dots in a---%represent continent that dispersed after break-up. a. 200-165 m.y. ago: stage of rifted arch systems (cf. Fig. 1). b. Incipient breakup (160 m.y. ago): marked uplift of incipient ocean rift arch. c. A few million years after breakup: generation of ocean rift, development of half-arch forming marginal rim and rim basin. d. 140 m.y. ago: subsidence of oceanfloor and adjacent margin, and initial fiil of rim basin in depression between shoulders of preceding rift valley. e. 120 m.y. ago: submergence of rim and seaward migration of axes of rim basin by subsidence of oceanfloor and margin. f. Present day: progradation of sediment (mainly carbonate) outward since submergence of rim.
T4
propose to call a rim basin (Fig. 3c-e). The half-arch is best seen along the outer part of the Exmouth Plateau and Camarvon Terrace (Branson, 1974; Veevers et al., 1974 b; Veevers, 1974; Wilcox and Exon, 1976) (Fig. 2). At different places, the rim basin succeeded an inter-, intra-, or extra-arch basin or two or more of these. In the sections shown in Fig. 3, the rim basin succeeded first the eastern rift valley or intra-arch Dampier Basin, and then, by oceanward migration of the rim basin axis, the inter-arch basin of the Exmouth Plateau. The rim and its associated rim basin lasted some 30-40 m.y. after breakup until the rim subsided below sealevel (Fig. 3e), seen in detail in the time--space diagrams of Powell (1976), whereafter sediment transport became grossly centrifugal from the rimless continent without damming or deflection (Fig. 3f). The half-arch is a member of the class of structures that dam sediment at the edge of continental margins (Hedberg, 1970). That rim basins and the preceding rifted arch basins are common on other passive margins is suggested by cross-sections of the margin of eastern North America (Sheridan, 1974), southeast (Kent, 1974) and southwest (Emery et al., 1975) Africa, and southern Australia (Falvey, 1974; Boeuf and Doust, 1975). In the Dampier Basin (Fig. 2), the juxtaposition of reservoir rock (Late Triassic rift valley fluvio-deltaic sandstone) at a rift shoulder and source rock (Late Jurassic claystone deposited in a restricted marine environment) of the rim basin, and the sealing of the source and reservoir by Early Cretaceous marine claystone have led to the concentration of estimated recoverable reserves of about 0.34*10i2m3 of gas (Powell, 1976). The recognition of rim basins on other passive margins may therefore provide a guide in exploration for petroleum. ACKNOWLEDGEMENTS
I thank J.G. Jones and C. McA. Powell for valuable comments, and the Australian Research Grants Committee for support. REFERENCES Atlas of the World, 1974. Comprehensive Edition. Times Books, London. Boeuf, M.G. and Doust, H., 1975. Structure and development of the southern margin of Australia. Aust. Pet. Explor. Assoc. J., 15: 33-43. Branson, J.C., 1974. Structures of the western margin of the Australian continent. Oil and Gas (Sydney), 20 (9): 24-35. Dewey, J.F. and Bird, J.M., 1970. Mountain belts and the new global tectonics. J. Geophys. Res.,75: 2625-2647. Emery, K.O., Uchupi, E., Bowin, C.O., Phillips, J. and Simpson, E.S.W., 1975. Continental margin off Western Africa: Cape St. Francis (South Africa) to Walvis Ridge (South-West Africa). Am. Assoc. Pet. Geol. Bull.,59: 3-59. Falvey, D.A., 1974. The development of continental margins in plate tectonic theory. Aust. Pet. Explor. Assoc. J., 14: 95-106. Hedberg, H.D., 1970. Continental margins from the viewpoint of the petroleum geologist. Am. Assoc. Pet. Geol. Bull.,54 : 3-43.
T5
Holmes, A., 1965. Principles of Physical Geology. Nelson, London, 1288 pp. Johnson, B.D., Powell, C. McA. and Veevers, J.J., 1976. Spreading history of the eastern Indian Ocean, and Greater India’s northward flight from Antarctica and Australia. Geol. Sot. Am. Bull., 87: 1569-1566. Johnstone, M.H., Lowry, D.C. and Quilty, P.G., 1973. The geology of southwestern Australia - a review. J. R. Sot. W. Aust., 56: 5-15. Kent, P.E., 1974. Continental margin of East Africa - a region of vertical movements. In: C.A. Burk and C.L. Drake (Editors), The Geology of Continental Margins. Springer, New York, pp. 313-320. Kinsman, D.J.J., 1975. Rift valley basins and sedimentary history of trailing continental margins. In: A.G. Fischer and S. Judson (Editors), Petroleum and Global Tectonics. Princeton Univ. Press, Princeton, pp. 83-126. Larson, R.L., 1975. Late Jurassic sea-floor spreading in the Eastern Indian Ocean. Geology, 3: 69-71. Markl, R.G., 1974. Evidence for the breakup of eastern Gondwanaland by the Early Cretaceous. Nature, 251: 196-199. Powell, D.E., 1976. The geological evolution of the continental margin of northwest Australia. Aust. Pet. Explor. Assoc. J., 16: 13-23. Schneider, E.D., 1969. Models for rifted and compressional continental margins. Geol. Sot. Am., Abstr., 7: 291-292. Sheridan, R.E., 1974. Atlantic continental margin of North America. In: CA. Burk and C.L. Drake (Editors), The Geology of Continental Margins. Springer, New York, pp. 391-407. Veevers, J.J., 1974. Western continental margin of Australia. In: C.A. Burk and C.L. Drake (Editors), The Geology of Continental Margins. Springer, New York, pp. 605616. Veevers, J.J. and Cotterill, D., 1976. Western margin of Australia: a Mesozoic analog of the East African rift system. Geology, 4: 713-717. Veevers, J.J. and Heirtzler, J.R., 1974. Tectonic and paleogeographic synthesis of Leg 27. Initial Report Deep Sea Drilling Project, 27: 1049-1054. Veevers, J.J., Heirtzler, J.R. and others, 1974a. Initial Reports of the Deep Sea Drilling Project, 27. Veevers, J.J., Falvey, D.A., Hawkins, L.V. and Ludwig, W.J., 1974b. Seismic reflection measurements of Northwest Australian margin and adjacent deeps. Am. Assoc. Pet. Geol. Bull., 58: 1731-1750. Veevers, J.J., Powell, C. McA. and Johnson, B.D., 1975. Greater India’s place in Gondwanaland and in Asia. Earth Planet. Sci. Lett., 27: 383-387. Willcox, J.J. and Exon, N.F., 1976. The regional geology of the Exmouth Plateau. Aust. Pet. Explor. Assoc. J., 16: l-11.