Australia: The Land Where Time Began

A biography of the Australian continent 

LIPs - Brito-Arctic flood basalts/North Atlantic Igneous Province

Rifting between northern Europe and Greenland in the early Tertiary produced the youngest of the large CFBPs, the Brito-Arctic Province, and the North Atlantic Igneous Province. Estimates of the volume range from 2 million km³ to as high as 6 million km³ if offshore submarine flows are included in the total (Saunders et al., 1997). As was the case with the Siberian Traps, and possibly the CAMP, several subprovinces comprise the Brito-arctic Province with distinct eruption histories. About 61 Ma the earliest, very brief eruption interval began in West and Southeast Greenland and in northwest Britain (Saunders et al., 1997; Storey et al., 1998). About 56 Ma a second voluminous phase of volcanism began during which basalt flows were emplaced in East Greenland, the Faroes as well as other extensive areas of the margin of the North Atlantic where at present they reflectors, that are seawards dipping, in offshore seismic lines (Saunders et al., 1997). The Faroe-Greenland volcanics erupted with unusual violence by the standards of flood basalt provinces, and basaltic tuffs are commonly found in the successions (Knox & Mortan, 1988). With the development of the Balder Formation in the latest Palaeocene, which is a major airfall ash deposit that covers large areas of the North Sea and west of the Shetland Islands, pyroclastic activity peaked (Eldholm & Thomas, 1993). The North Atlantic was not the only site where major pyroclastic activity occurred in the later Palaeocene, a brief phase (<10⁵) years of intense explosive activity in the Caribbean region around 55.0 Ma has been recorded (Bralower et al., 1997).

Wignall suggests the Brito-Arctic volcanicity may coincide with some dramatic environmental changes, though not with an associated mass extinction event. A gradual shift to a warmer climate that typifies much of the Eocene marked the late Palaeocene, though it was punctuated by an extraordinarily intense short-lived climatic event, the Late Palaeocene Thermal Maximum (LPTM) (aka Palaeocene-Eocene Thermal Maximum (PETM)) (Kennett & Stott, 1991; Koch et al., 1992; Robert & Kennett, 1994; Norris & Röhl, 1999). It is revealed by both δ¹⁸O and δ¹³C that at about 54.0 Ma there was a brief negative spike, with the latter showing the development of a - 3‰ inflection in only a few thousand years followed by a “gradual” return to pre-excursion values in 120 kyr (Norris & Röhl, 1999). This event coincides with a temporary increase in deep sea and high latitude waters temperatures by as much as 7^oC (Kennett & Stott, 1991), and an influx into the ocean of waters of clays that were rich in kaolinite that probably resulted from increased weathering in conditions that were warmer and more humid (Robert & Kennett, 1994). At this time there was a major immigration of mammals into North America, which may also be a response to a warming event (Koch et al., 1992). The only significant extinctions, however, were among deep sea foraminifera. It appears these losses were related to the development of bottom waters that were low in concentrations of oxygen (Kennett & Stott, 1991; Eldhom & Thomas, 1993; Kaiho, 1994).

It is suggested by the comparison of timing of the LPTM (PETM) and volcanic events that the 2 phenomena may be related (Kennett & Stott, 1991; Dickens et al., 1995). The initial phase of volcanism occurred long before the event of the Late Palaeocene, whereas it appears the second phase began about 1 Myr prior to the event. According to Wignall the magnitude of the excursion of δ¹³C is too great to have been caused by volcanic CO₂. And it is widely regarded that methane hydrate supplied the light C (Dickens et al., 1995; Norris & Röhl, 1999; Bains et al., 1999; Katz et al., 1999; Dickens, 1999), though volcanic CO₂ eruptions are a potential cause of the warming event required to trigger the dissociation of hydrate (clathrate). The LPTM (PETM) potentially may also have been terminated by sulphate aerosols during the widespread interval of pyroclastic volcanism in the region of the North Sea and the Caribbean (Beerling & Jolly, 1998).

Sources & Further reading

Wignall, P. B. (2001). "Large igneous provinces and mass extinctions." Earth-Sci. Rev. 53: 1-33.