Further Evidence for the Early Cretaceous Breakup of Gondwanaland off Southwestern Australia*

Marine Geology, 26 (1978) 41-48 0 Elsevier Scientific Publishing Company, Amsterdam

- Printed in The Netherlands

FURTHER EVIDENCE FOR THE EARLY CRETACEOUS BREAKUP OF GONDWANALAND OFF SOUTHWESTERN AUSTRALIA* RUDI G. MARKL Lamont-Doherty Geological Observatory of Columbia University, Palisades, N. Y.10964 (U. S. A. ) (Received March 28, 1977)

ABSTRACT Markl, R.G., 1978. Further evidence for the Early Cretaceous breakup of Gondwanaland off southwestern Australia. Mar. Geol., 26: 41-48. Magnetic anomalies adjacent to the northwest margin of the Naturaliste Plateau are identified as Early Cretaceous reversals M-0 through M-4.These lineations indicate that northwestsoutheast sea-floor spreading began off the present Naturaliste Plateau circa 118 m.y. B.P., 8 m.y. later than along the adjacent continental margin off Perth. The Naturaliste and Perth lineation sequences are offset 130 km dextrally by a fracture zone which passes near DSDP Site 257. The data indicate that an intracratonic small ocean basin existed seaward of Perth from about 126 to 118 m.y. B.P.

INTRODUCTION

Recent studies have tended to corroborate the basic DuToit (1937) reconstruction of eastern Gondwanaland, but with an important addition, namely, that pre-drift India extended eastward to Australia. The concept of such an enlarged, or “Greater” India implies that the early drift of India cannot have been exclusively northward, as previously assumed, but must have been northwestward, as suggested by Falvey (1972), Johnstone et al. (1973), Markl (1974a, b), Curray and Moore (1974), Veevers and Heirtzler (1974) and Johnson et al. (1976). Northwestsoutheast sea-floor spreading off Western Australia was demonstrated by the magnetic anomaly investigations of Falvey (1972), Markl (197413) and Larson (1975). These results, corroborated by basement ages determined from Deep Sea Drilling Project (DSDP) Legs 26 and 27 (Davies et al., 1974; Veevers et al., 1974) showed that continental dispersal began off northwestern Australia in Late Jurassic times, and off the southwest coast in Early Cretaceous times. The present study reports additional M-series (Larson and Pitman, 1972) anomalies indicative of northwestsoutheast spreading off southwestern Australia. *L-DGO Contribution No. 2565.

42

A two-week cruise of R/V “Vema” (3304) was devoted to surveying the Naturaliste fracture zone (Markl, 1974a, b, c) and attempting t o determine from morphologic features and magnetic anomalies whether lateral offset exists across the fracture zone. A premise of this search was that the region bounded by the Naturaliste and Diamantina fracture zones was, like the region north of the plateau, formerly occupied by some part of Greater India and, therefore, might yield Mesozoic-seriesanomalies corresponding to those of the Perth sequence (Markl, 1974b). MAGNETIC ANOMALY DATA

A long magnetic profile obtained parallel t o and west of the Naturaliste fracture zone revealed no identifiable anomalies, nor any correlations to the few suitably oriented existing magnetic profiles. However, several tracklines parallel to and east of the Naturaliste fracture zone did reveal Mesozoic anomalies M-0 through M-4, adjacent to the northwest margin of the Naturaliste Plateau (Fig.1). The character of the M-4 anomaly, shown in Fig.2, profile 3304-1, is perturbed by a topographic spur; likewise, anomaly M-4 on profile 3304-3 may be influenced, although less so, by minor relief of the plateau margin. However, there is no disturbing relief on profile 3304-2, which displays the best-developed M-4 anomaly. Existing tracklines R/V “Robert D. Conrad” 1106 and USNS “Eltanin” 48 help define the trend of anomaly M-0 (although they intersect right over it), but anomaly M-0 cannot be positively identified on D/V “Glomar Challenger” cruise 26, nor are anomalies M-2 and M-4 of this sequence observed on GC26. The (half) spreading rate between anomalies M-0 and M-4 is 1.8 cm/yr, which is identical to the average rate of the Perth sequence when the revised time scale of Larson and Hilde (1975) is used. It is apparent from the dextral offset of approximately 130 km between corresponding lineations of the “Naturaliste” anomaly sequence and the Perth sequence, that a northwest-southeast-striking fracture zone exists between these sequences. Unlike the Naturaliste fracture zone, which is in all respects a prominent feature, the magnetic, gravity, and seismic reflection data provide no obvious indication of the precise location of the fracture zone (or zones). The magnetic anomaly data near the plateau would permit the fracture zone t o lie anywhere within a band extmding about 35 km to either side of the GC26 track. DSDP Site 257, in the Cretaceous quiet zone, appears to lie very near the inferred projection of the fracture zone; the age of the basal sediments at Site 257 is approximately 102 m.y. (Davies e t al., 1974). The spreading rate between Site 257 and anomaly M-2 of the Naturaliste sequence is 1.6 cm/yr, whereas the rate computed between Site 257 and anomaly M-2 of the Perth sequence is 2.6 cm/yr (also using the Larson and Hilde (1975) time scale). Both 1.6 and 2.6 are plausible rates, considering present knowledge of global changes in spreading rates in the mid-Cretaceous, so this exercise does not specify whether Site 257 lies east or west of the fracture zone. Acoustic basement dips southeast in a broad

>

28

30

32

Fig.1. The Naturaliste and Perth Early Cretaceous magnetic lineation sequences (separated by the Batavia fracture zone). Ship’s track segments shown by solid lines correspond to the magnetic profiles in Fig.2; other tracklines in the area are dashed. DSDP sites are indicated by large dots. Isobaths (dotted lines) are labelled in kilometers.

IP

w

44

6

-

N

8

m

B

: : I

I

?

c

E

?

M-0

M-2 I GC26

3 0

W +

0 -

a

Fig.2. Observed magnetic profiles of the Naturaliste sequence (“Vema” 3304)projected perpendicular to the strike of the lineations. Trackline GC26 crosses the Batavia fracture zone ( B F Z ) obliquely and does n o t clearly show M-series anomalies of either the Perth or the Naturaliste sequence.

region surrounding Site 257 (Mark1 1974a; 1978). The basement contours indicate a 125-km dextral offset just west of the GC26 track which matches the offset of the magnetic lineations. Also, a steep northwest-southeasttrending scarp exists where the fracture zone is inferred to intersect the plateau. The few basement highs and seamounts known in the area show no pattern which might define the trace of the fracture zone, although Pelsaert seamount lies on its probable trace (Fig.1). This morphologic evidence, in conjunction with the constraints of the magnetic anomaly data, the requirement for parallelism with the Naturaliste fracture zone, and the assumption that relatively constant spreading rates obtained in the adjacent spreading compartments suggests that this fracture zone, henceforth referred to as the “Batavia” fracture zone*, passes east of Site 257. *Dutch merchant ships bound for Batavia (Djakarta) are the first known t o have sailed these waters. They followed the trade winds eastward from Africa, a route pioneered by Henrik Brouwer in 1611, turning northward west of Australia. The difficulty of determining longitude caused many ships, including o n e named “Batavia”, to be wrecked on the Australian coast. The Batavia’s captain, Francois Pelsaert, sailed 1800 miles t o Java in a small boat, returning to find that mutineers had murdered 1 2 5 of the survivors (Joy, 1971; Green, 1975).

45

INTERPRETATION OF DATA

The nature of the crust of the Naturaliste Plateau has yet to be established. Some evidence suggests it is continental (Francis and Raitt, 1967; Heezen and Tharp, 1973; Petkovic, 1975), and other evidence has been interpreted to imply an oceanic origin (Luyendyk and Davies, 1974). An additional unknown factor is whether the plateau has always been fixed in its present relationship to Australia. Markl (1974a) speculated that the plateau may have moved northwest, initially accompanying the Indian plate; Veevers et al. (1975) invoked such a translation. The magnetic anomaly data show that sea-floor spreading began off the present northwestern margin of the Naturaliste plateau in earliest Barremian times (ca. 118 m.y. B.P.), approximately 8 m.y. later than off the nearby Australian margin, where spreading began in late Valanginian times. It seems highly improbable that accretion was not occurring at some location within the Naturaliste spreading compartment (that bounded by the Naturaliste and Batavia fracture zones and their projections) in this 8-m.y. period, during which approximately 290 km of oceanic crust were generated in the adjacent Perth compartment (at a total rate of 3.6 cm/yr). Although opening between India and Western Australia began in the north and progressed southward (Veevers et al., 1971; Markl, 197413; Larson, 1975), the apparent disparity in onset of spreading in the Naturaliste Plateau area cannot be explained by this means. Conceptually, there appear t o be three alternative ways t o account for the disparity: (1)spreading within the Naturaliste compartment occurred somewhere t o the northwest, between the plateau and the northern edge of Greater India, (2) spreading occurred to the southeast, between the plateau and Antarctica, and (3) accretion occurred within the area presently occupied by the plateau. The first two alternatives imply subsequent ridge jumps to the northwest margin of the plateau just prior to M-4 time (118 m.y. B.P.). Alternative (1)presupposes that the Naturaliste Plateau is continental and was fixed to Australia as now; it probably precludes the existence of a rift between the plateau and Antarctica in Early Cretaceous times. According to Veevers et al. (1975), the Tethyan margin of Greater India lay approximately 1800 km northwest of the Naturaliste Plateau. Although magnetic anomaly data (Markl, 1974b; Larson, 1977) document an offset of at least 1000 km along the Wallaby-Perth scarp (transform fault), it is geologically unlikely that the 400-km-wide Perth compartment was bounded on the west by an even longer fault. It is probable that the pre-anomaly M-4 phase of spreading occurred nearer the plateau, or even at its northwestern edge. The bathymetry of the southern Wharton Basin (Markl, 1974c) shows a disproportionate number of seamounts and larger elevations between the projected traces of the Naturaliste and Batavia fracture zones. These include the plateau-like northern extremity of Broken Ridge and a long ridge near 30"s 105"E that subsequent surveying (Markl, 1978) suggests is a volcanic pile. The few magnetic profiles adjacent t o this ridge show no identifiable anomalies, but

46

it is conceivable that it originated at the northwestern edge of the Naturaliste Plateau. Alternative (2), that initial spreading in the Naturaliste compartment occurred south of the Naturaliste Plateau also presumes a continental origin for the plateau, but implies that it formerly lay about 290 km to the southeast, having been carried to its present location as part of the Indian plate. Marked northwest-southeast morphologic trends on the plateau and adjacent Australian margin, together with the observation that the Naturaliste fracture zone extends approximately 200 km southeast of the plateau first raised this possibility (Markl, 1974a). Magnetic profiles between the Naturaliste Plateau and Diamantina fracture zone are dominated by a pair of (unidentified) positive anomalies of larger amplitude (500 gamma) than occur within or south of the Diamantina fracture zone. The anomalies can be correlated between 112" and 114"E, however, the 085" trend of the lineations suggests that they are unrelated t o the Early Cretaceous spreading episode. Alternative (3), the assumption that the Naturaliste Plateau is of oceanic origin, opens a range of possibilities depending upon when and how the plateau formed and whether it has been fixed to Australia. Cores from DSDP Sites 258 and 264 show it t o have been a marine feature since at least 105 m.y. B.P. and above the lysocline since Late Cretaceous times (Davies e t al., 1974; Hayes et al., 1975). Although the former authors discuss the possible Early Cretaceous origin of the plateau as the result of volcanic activity along the incipient rift between Australia and Antarctica, this is difficult to reconcile with the fact that normal oceanic crust was accreting simultaneously in the adjacent Perth compartment. One could postulate that the plateau represents normal oceanic crust (of M-11 to pre-M-4 age) that was subsequently uplifted. An origin of this type appears plausible for Broken Ridge, whose northern flank slopes gently to abyssal depths, but not for the Naturaliste Plateau, which rises abruptly from the deep basin where anomalies M-0 through M-4 occur. Although the evidence is not conclusive, it is probable that the initial rift in the Naturaliste crustal compartment lay northwest of the plateau (alternative 1). However, all of the alternatives appear to have two important results in common. First, that the receding margin of India (in the Perth compartment) was abreast of the (present) northwest margin of the plateau at the time spreading began there. Second, that the crust generated in the Perth compartment prior to M-4 time formed an intracratonic small ocean basin (Fig.3). Wherever the initial rift transected the Naturaliste compartment, it seems certain that it was transformed south-eastward again, along the trace of the Naturalist&fracture zone. The fact that the fracture zone extends considerably south of the plateau and northeastsouthwest basement trends are observed in the triangular area between it and the Diamantina fracture zone suggests that some part of India, rather than Antarctica, formerly lay southwest of the Naturaliste Plateau.

47

Fig.3. Diagrammatic sketch of the junction of Greater India and Australia-Antarctica a t the time spreading began of€ the northwest margin of the Naturaliste Plateau. An intracratonic small ocean basin formed in the Perth compartment during the preceding 8 m.y. ACKNOWLEDGEMENTS

I thank the complement of “Vema” cruise 3304 for their cooperative spirit and professionalism, and S. Cande for review. Data collection and reduction was supported by National Science Foundation grant OCE 7601434 to Lamont-Doherty Geological Observatory of Columbia University.

REFERENCES Curray, J.R. and Moore, D.G., 1974. Sedimentary and tectonic processes in the Bengal deep-sea fan and geosyncline. In: C.A. Burk and C.L. Drake (Editors), The Geology of Continental Margins. Springer, New York, N.Y., pp.617-627. Davies, T.A., Luyendyk, B.P. e t al., 1974. Initial Reports of the Deep Sea Drillihg Project, 26. U.S. Govt. Printing Office, Washington, D.C. DuToit, A.L., 1937. Our Wandering Continents - An Hypothesis of Continental Drifting. Oliver and Boyd, London, 366 pp. Falvey, D.A., 1972. Sea-floor spreading in the Wharton basin (northeast Indian Ocean) and the breakup of eastern Gondwanaland. J. Aust. Pet. Explor. Assoc., 12(2): 86-88.

48 Francis, T.J.G. and Raitt, R.W., 1967. Seismic refraction measurements in the southern Indian Ocean. J. Geophys. Res., 72: 3015-3041. Green, J.N., 1975. The VOC ship ‘‘Batavia” wrecked in 1629. Int. J. Naut. Archeol. Underwater Explor., 4(1): 43-63. Hayes, D.E., Frakes, L.A. e t al., 1975. Initial Reports of the Deep Sea Drilling Project, 28. U.S. Govt. Printing Office, Washington, D.C., pp.19-27. Heezen, B.C. and Tharp, M., 1973. USNS “Eltanin” cruise 55. Antarct. J. U.S., 8(3): 137-14 1. 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. SOC.Am., Bull., 87(11): 1560-1566. Johnstone, M.H., Lowry, D.C. and Quilty, P.G., 1973. The geology of southwestern Australia - a review. J.R. SOC.West. Aust., 56: 5-15. Joy, W., 1971. The Explorers. Rigby, Australia, 159 pp. Larson, R.L., 1975. Late Jurassic sea-floor spreading in the eastern Indian Ocean. Geology, 3: 69-71. Larson, R.L., 1977. Early Cretaceous breakup of Gondwanaland off Western Australia. Geology, 5: 57-60. Larson, R.L. and Hilde, T.W.C., 1975. A revised time scale of magnetic reversals for the Early Cretaceous and Late Jurassic. J. Geophys. Res., 80(17): 2586-2594. Larson, R.L. and Pitman 111, W.C., 1972. World-wide correlation of Mesozoic magnetic anomalies, and its implications. Geol. SOC.Am., Bull., 83: 3645-3662. Luyendyk, B.P. and Davies, T.A., 1974. Results of DSDP leg 26 and the geologic history of the southern Indian Ocean. Initial Reports of the Deep Sea Drilling Project, 26. U.S. Govt. Printing Office, Washington, D.C., pp.909-943. Markl, R.G., 1974a. Bathymetry, Sediment Distribution, and Sea-Floor Spreading History of the Southern Wharton Basin, Eastern Indian Ocean. Thesis, Univ. of Connecticut, Storrs, Conn. (unpublished). Markl, R.G., 1974b. Evidence for the breakup of eastern Gondwanaland by the Early Cretaceous. Nature, 251 (5472): 196-200. Markl, R.G., 1974c. Bathymetric map of the eastern Indian Ocean (southern Wharton basin). In: T.A. Davies, B.P. Luyendyk e t al., Initial Reports of the Deep Sea Drilling Project, 26. U.S.Govt. Printing Office, Washington, D.C., pp.967-968. Markl, R.G., 1978. Basement morphology and rift geometry near the former junction of India, Australia, and Antarctica, in press. Petkovic, P., 1975. Origin of the Naturaliste plateau. Nature, 253: 30-33. Veevers, J.J., Jones, J.G. and Talent, J.A., 1971. Indo-Australian stratigraphy and the configuration and dispersal of Gondwanaland. Nature, 229: 383-388. Veevers, J.J. and Heirtzler, J.R., 1974. Tectonic and paleogeographic synthesis of leg 27. In: J.J. Veevers, J.R. Heirtzler e t al., Initial Reports of the Deep Sea Drilling Project, 27. U.S. Govt. Printing Office, Washington, D.C., pp.1049-1054. Veevers, J.J., Heirtzler, J.R. e t al., 1974. Initial Reports of the Deep Sea Drilling Project, 27. U.S. Govt. Printing Office, Washington, D.C. 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.