J.J. Veevers

Late Paleozoic glacial episodes in Gondwanaland reflected in transgressive-regressive depositional sequences in Euramerica

The Late Paleozoic glaciation of Gondwanaland comprised two short episodes, in the Famennian (I) and Visean (II) confined to Brazil and adjacent northwest Africa, and a long episode that started in the Namurian (IIIA) of eastern Australia and Bolivia/Argentina, expanded to cover much of Gondwanaland in the Stephanian/Asselian (IIIB), and collapsed in the early Sakmarian (IIIC). Dropstones in eastern Australia indicate that small ice centers lingered to the Kazanian. Across the belt of low latitudes north of Gondwanaland, short-ranging fossils in widespread shallow-marine and paralic deposits indicate synchronous deposition of transgressive-regressive sequences in different parts of Euramerica. These sequences correlate with glacial events in Gondwanaland at three levels: (a) four major regressions in Euramerica, in the Famennian (1), Visean (2), Namurian (3), Stephanian (4), and the Tastubian transgression that preceded the Sterlitamakian regression (5), also recorded in Gondwanaland, correlate with glacial episodes I, II, and IIIA, IIIB, and IIIC; (b) the time-interval of cyclothemic deposition in Euramerica (Brigantian or latest Visean to Sterlitamakian) correlates with that of glacial episode III; and (c) the dominant period of the Euramerican cyclothems, as estimated from the Middle and Late Pennsylvanian deposits of the mid-continent of North America, and of the thickest known Gondwanaland glacigenic sediment (the earliest Permian Lyons Group of Western Australia) is 0.4 Ma, equivalent in turn to the long orbital-eccentricity period of the Quaternary ice age, and the dominant period of fluctuation of the late Miocene Antarctic ice cap. The three levels of correlations confirm Wanless and Shepard9s (1936) hypothesis that the Late Paleozoic cyclothems are controlled largely by sea-level fluctuations related to the Gondwanaland glaciation.

Pre-breakup continental extension in East Gondwanaland and the early opening of the eastern Indian Ocean

Abstract Extension of continental crust by up to 360 km on a north-northeast azimuth in the Great Australian Bight occurred prior to the Middle Cretaceous (96 Ma) onset of seafloor spreading between Australia and Antarctica. This large amount of continental extension is constrained to the Late Jurassic (≈ 160 Ma)-Middle Cretaceous interval, about a pole estimated to lie about 40° southeastward of southeastern Australia. Using bathymetric data combined with seismic and magnetic determinations of the continent-ocean boundaries off Australia, India and Antarctica, we determine a revised fit of East Gondwanaland prior to continental extension, and at various stages thereafter. In the first stage from 160 to 132.5 Ma (≈ M11), India-Australia rotated from Antarctica with continental crustal extension between Australia and Antarctica and largely transform motion between the Coromandel Coast margin of India and the Kron Prins Olav Kyst margin of Antarctica. In the second stage, from 132.5 to 96 Ma, India rotated northwestward away from Australia-Antarctica, producing M10 and younger magnetic anomalies along the western margin of Australia. Continental extension was greatest between Australia and Antarctica during this stage. The newly determined 132.5-96 Ma rotation between India and Australia provides an improved fit between the orientation of observed M10-M0 magnetic anomalies and the southward decrease in spreading rate off the western Australian margin. Together with bathymetry, the new rotation parameters lead to identification of the abandoned 96 Ma spreading ridge along the Lost Dutchmen and Dirck Hartog ridges. The Naturaliste Fracture Zone is found to lie nearly parallel to the Early Cretaceous transform direction between India and Antarctica suggesting that slow seafloor spreading, required between Australia and Antarctica to accommodate the continental extension further east, occurred between Naturaliste Fracture Zone and the M4-M0 anomalies adjacent to the Naturaliste Plateau. The revised fit of India in East Gondwanaland reduces the eastward extent of Greater India to 95° E but does not change its extent as far north as the Cape Range Fracture Zone. The new pole determined for the Early Cretaceous rotation between India and Australia-Antarctica lies within 15° of the southern tip of India, significantly closer than in previous determinations, thereby reducing the amount of seafloor spreading generated between Africa and Antarctica by the India-Antarctica rotation, and thus offering a possible solution to the perceived spreading-rate problems between M11 and M0 in the Somali, Mozambique and Antarctic basins.

Review of seafloor spreading around Australia. I. synthesis of the patterns of spreading

The existing data on Late Mesozoic and Cenozoic seafloor spreading isochrons (reviewed in the companion paper by Veevers & Li) and fracture zone trends provide the basis for 12 reconstructions of the seafloor around Australia that spread during the dispersal of Argo Land, India, Antarctica, Lord Howe Rise/New Zealand and the Papuan Peninsula. The major changes of plate geometry in the Jurassic, Early Cretaceous, mid‐Cretaceous, early Paleocene and early Eocene reflect global events. The pattern of spreading around Australia was determined by two long‐standing (earlier Phanerozoic) factors that operated in a counter‐clockwise direction: (1) penetration from the northwest by the Tethyan divergent ridge; and (2) rotation from the northeast of the Pacific convergent arc and back‐arc. The only new feature of the modern pattern is the deep penetration by the Indian Ocean ridge into eastern Gondwanaland to fragment it into continents in contrast with the pattern up to 160 Ma ago of breaking off micro‐continents.

Spreading history of the eastern Indian Ocean and Greater India's northward flight from Antarctica and Australia

Recent information from magnetic surveys and from deep-sea drilling allows Sclater and Fishers Late Cretaceous and Cenozoic reconstructions of the eastern Indian Ocean to be extended back almost to the beginning of the Cretaceous Period. After a short phase of spreading off northwestern Australia in Middle and Late Jurassic time, Greater India and Antarctica-Australia dispersed near the beginning of Cretaceous time (130 m.y. B.P.) with the opening between them of a landlocked sea; between 110 to 120 and 105 m.y. B.P., Greater India cleared Antarctica-Australia, and the sea floor generated between them became continuous with the rest of the Indian Ocean. In Santonian time (80 m.y. B.P.), a new pattern of rapid spreading (as much as 17.5 cm/yr) began and caused an oceanic part of the Indian plate to be transferred to the Antarctic-Australian plate. Rapid spreading continued nearly to the end of Paleocene time (53 m.y. B.P.). With the inception at this time of spreading between Antarctica and Australia, three plates (Indian, Antarctic, and Australian) spread at a slow rate until the end of early Oligocene time (32 m.y. B.P.). At 32 m.y. B.P., the separate Indian and Australian plates became united, as they are today, while Antarctica remained a separate plate. Together with paleomagnetic and other determinations that show that Southeast Asia lay at or north of the Equator, the trail of sea floor generated during Greater Indias northward flight implies that Southeast Asia rotated westward across this trail to its present position no earlier than middle to late Miocene time (10 m.y. B.P.).

Breakup of Australia and Antarctica estimated as mid-Cretaceous (95 ± 5 Ma) from magnetic and seismic data at the continental margin

Abstract A positive magnetic anomaly marks the seaward edge of the magnetic quiet zone along the southern margin of Australia eastward between 114° and 131°E and along the conjugate Antarctic margin between 105° and 132°E. This anomaly was originally interpreted as the oldest seafloor-spreading anomaly—A22, revised by Cande and Mutter to A34—in the Southeast Indian Ocean, but is better modelled as the edge effect at the continent-ocean boundary (COB) constrained by seismic data. Continental crust abuts the oceanic sequence of normal and reversed spreading blocks, truncated within the Cretaceous normal interval at an extrapolated age of 96 Ma, rounded to 95 ± 5 Ma to take into account the uncertainty of the initial spreading rate and of the location of the COB. The occurrence of the anomaly on both margins defines this as the age of breakup. Farther east between 131° and 139°E on the Australian margin, the COB anomaly is modelled as due to the same kind of effect but with successively younger ages of truncation to 49 Ma, interpreted as indicating the most recent ridge-crest jumping to the Australian COB. The magnetic data from the conjugate sector of Antarctica, albeit scanty, are consistent with this interpretation. The 95 ± 5 Ma age of breakup coincides with that of the breakup unconformity in southern Australia, expressed by a short mid-Cretaceous lacuna in the Otway Basin between faulted Early Cretaceous rift-valley sediments of the Otway Group and the overlying Late Cretaceous Sherbrook Group, and by an unconformity of similar age in the Great Australian Bight Basin.

Tectonic-climatic supercycle in the billion-year plate-tectonic eon: Permian Pangean icehouse alternates with Cretaceous dispersed-continents greenhouse

Abstract The earth alternates in a supercycle 400 m.y. long from a single continent (Pangea) and ocean (Panthalassa) with an icehouse climate to many continents and oceans with a greenhouse climate. The supercycle is driven by the heat that accumulates beneath the insulator of Pangea, and the greenhouse is made by the excess CO2 vented from the mantle during the faster rate of plate activity. In the current supercycle (A) since the mid-Carboniferous (320 Ma), the growth and decay of Pangean heat is observed in globally synchronous cratonic sedimentary sequences that represent, in ascending order: (1) a stratigraphic gap, (2) sagging, (3) rifting, (4) fast, and (5) slow seafloor spreading. Stages 4 and 5 of the previous supercycle (B) are observed back to the start of the Phanerozoic; in the Proterozoic, earlier stages of B are postulated back to 720 Ma and a third supercycle (C) to 1100 Ma. The big glaciations of the latest Proterozoic (700-600 Ma) and Late Palaeozoic (320-260 Ma) are confined to the icehouse state during stages 1–3; the Sturtian (800 Ma), latest Ordovician (440 Ma), and Quaternary (2-0 Ma) glaciations fall within greenhouse states during stage 5 of slow seafloor spreading. The next icehouse glaciation is expected 80 Ma hence. The problem of long-term past (and future) climate change is soluble by global studies. Urgently needed are (1) global stock-takes of (a) the rate of granite emplacement, which serves as a proxy via plate activity for the mantle source of atmospheric CO2, and (b) carbonate sinks and other sedimentary indicators of CO2; and (2) the extension of the sea-level curve back past 570 Ma to the start of the plate-tectonic eon 1100 Ma ago. From such studies, environmental baselines for past climatic states can be drawn for gauging present and future “background” variations.

Western margin of Australia: Evolution of a rifted arch system

The 4,000-km-long western Australian margin and adjacent ocean floor are probably unique among older (>100 m.y.) passive margins and adjacent oceans in having such a thin ( 4 ) are thus traceable in seismic-reflection profiles across the ocean-continent boundary, and in many places are a continuous surface. Drilling shows that the oldest oceanic crust adjacent to the margin is almost the same age as the oldest part of the continental break-up unconformity. Two types of margin are distinguished by the shape of R 4 : stepped , in which R 4 is offset at the ocean-continent boundary by a long transform fault, and smooth , including the transition from normal ocean floor through oceanic upgrowths, called epiliths, that developed after the start of sea-floor spreading. The marginal plateaus of the western margin originated variously as epiliths or from the post–break-up subsidence of regions that originally lay between rifted arches. After 100 to 150 m.y. of rifting along a multiple rift valley arch system analogous to that of modern East Africa, with concomitant deposition in inter-arch and extra-arch basins, the northwestern margin was initiated by plate divergence 160 m.y. ago (Late Jurassic time) and the southwestern margin 125 m.y. ago (Early Cretaceous time). After break-up, a diachronous clay was deposited on the newly generated sea floor and behind the subsiding continental rim or half-arch (the former rift valley shoulder) in what is called a rim basin. The rim subsided below sea level 30 to 45 m.y. after break-up, and thereafter sediments were dispersed seaward across the entire margin.

Review of seafloor spreading around Australia. II. Marine magnetic anomaly modelling

This paper updates the models of seafloor spreading magnetic anomalies in the oceanic lithosphere of the Indo‐Australian Plate and adjacent plates around Australia. The regions are the eastern Indian Ocean (Argo, Gascoyne, Cuvier and Perth Abyssal Plains), the southeast Indian Ocean (off the southern margin of Australia and the conjugate Wilkes Land margin of Antarctica), the southwest Pacific Ocean (Tasman Sea, Coral Sea and Woodlark Basins) and the Banda Sea, at the southeast edge of the Eurasian Plate. Included in the models for the eastern and southeast Indian Ocean are the magnetic anomaly at the continent‐ocean boundary, modelled as the edge‐effect of a strongly magnetized oceanic crust abutting a weakly magnetized or deeply buried continental crust. A newly compiled Australian apparent polar wander path (Appendix) provides the values of the remanent‐field parameters (inclination and declination) of the magnetic block models. The model dates are confirmed by deep sea (oceanic) drilling. The inceptio...

A revised fit of East and West Gondwanaland

Abstract Recently available evidence provides the basis for a revised fit between East and West Gondwanaland before break-up in the Late Jurassic: deep-sea drilling shows that the entire Falkland Plateau is probably underlain by continental crust, marine geophysical studies off southeast Africa indicate large areas of thinned continental or transitional crust; palaeomagnetic studies show that the western side of Madagascar lay alongside equatorial East Africa; and from the pattern of sea-floor spreading between Madagascar and India we deduce that the southern half of the western margin of India cannot have lain, as customarily shown, alongside the eastern margin of Madagascar, but must have lain farther south. This information about Madagascar provides the crucial link between East (Antarctica, Australia, India) and West (South America, Africa) Gondwanaland. The rest of East and West Gondwanaland is brought into contact so that the Falkland Plateau opposes the margin of Antarctica between 10° and 15°E and the southern part of South America fits without deformation into the Weddell Sea re-entrant of Antarctica. In terms of the continuity of geological features and the cluster of pre-break-up palaeomagnetic poles, the revised fit is at least as favourable as that of Smith and Hallam (1970). In its close match of the continental outlines and its harmony with the pattern of subsequent sea-floor spreading, the revised fit is superior to previous reconstructions.

Early spreading history of the Indian Ocean between India and Australia

Abstract A revised model of seafloor spreading between India and Australia from the inception of spreading 125 m.y. to the change to a new system at 90 m.y. stems from the wider recognition of the M-series of magnetic anomalies off the southwestern margin of Australia, from a revised pole of opening between Australia and Antarctica, and by the extension in the central Wharton Basin of the Late Cretaceous set of magnetic anomalies back to 34. The phase of spreading represented by the later anomalies has been extended back to 90 m.y. in order to give a resolved pole that describes the rotation of India from Australia consistent with the M-series anomalies, DSDP site ages, and fracture zone trends. An abandoned spreading ridge in the Cuvier Abyssal Plain indicates a ridge jump within the first ten million years of spreading. Elsewhere, two kinds of ridge jump (one to the continental margin of Australia or India, the other by propagation of the spreading ridge into adjacent compartments thereby causing them to fuse), are postulated to account for other observations.