Really Rapid Inertial-Interchange True Polar Wander During mid-Ediacaran Time: 
A possible trigger for massive sea-level and carbon isotopic excursions.

Joe Kirschvink, Caltech
 
 
[The following abstract is from the Proceedings of the Gondwana XII conference, 
Mendoza, Argentina, Nov. 2005:   Kirschvink, J.L., Mound, J., Mitrovitca, J.X., 
Raub, T.D., Evans, D.A.D., Kopp, R.E.  2005.  Rapid Inertial-Interchange True 
Polar Wander During Ediacaran Time Induced by Intrusion of the Sept-Îles 
Intrusive Suite, Quebec, Canada: A possible trigger for massive sea-level and 
carbon isotopic excursions.: http://cig.museo.unlp.edu.ar/gondwana/ ]
 
ABSTRACT 

The middle of the Ediacaran period (older than ca. 550 Ma) contains one of the 
largest negative carbon isotopic excursions yet discovered, the ‘Shuram’ event, 
with up to a 12%o drop in δ13C preserved in marine carbonates.  Sedimentary 
successions of broadly similar age in Australia and Laurentia record unique 
episodes of massive (> 1 km) and rapid (< ~5 Myr) sea-level draw-downs, 
reflected by incised canyons in the Wonoka Formation and correlative units of 
Australia (Williams and Gostin, 2000) and the Johnnie Formation of California 
and Nevada (Abolins, 1999).  Christie-Blick interprets the Australian canyons 
as the result of local, Messinian-style evaporative drawdown, whereas Williams 
& Gostin interpret them as resulting from transient uplift associated with 
eruption of a plume head.  Neither of these mechanisms would explain the 
existence of putatively coeval canyons in California. Furthermore new age 
constraints on the Table Hill volcanics of Australia’s Officer Basin and 
extrabasinal correlatives (suggested by Williams & Gostin to manifest the plume 
responsible for Wonoka exhumation) suggest they are remnants of the early/middle 
Cambrian (ca. 510 Ma) Kalkarinji large igneous province (summarized by Veevers, 
2004, p. 4).

Whatever their cause, we note here that sea-level fluctuations of the magnitude 
and speed inferred from the stratigraphic constraints are capable of producing 
isotopic anomalies like the Shuram event through the depressurization release of 
methane clathrates and/or the oxidative weathering of sedimentary organic carbon 
exposed transiently on shelves.  Hence, to understand all of these features it 
is important to find a mechanism capable of producing regional sea-level 
fluctuations of the sort preserved in the rock record.

A study of the Sept-Îles intrusive suite in Québec reporting data from 
paleomagnetic, rock magnetic, zircon U/Pb, apatite (U-Th-Sm)/He, and conodont 
alteration indices from overlying Ordovician limestone (Kirschvink et al., 2005) 
indicates that Laurentia moved from the Equator to high latitude between ~564 and 
~561 Ma.  The 80-km diameter center of this intrusive complex, which punched 
through the Laurentian craton, has been interpreted as the eruptive site of a 
major plume head (Higgins, 2005), with a volcanic field (now almost completely 
eroded) which could have been ~ 2000 km in diameter.   Although expanded analysis 
of the APW paths suggests that there may have been several IITPW events in the 
Cryogenian – Cambrian interval (e.g., (Evans, 1998; Kirschvink et al., 1997), 
this event is constrained to be particularly rapid (ca. 1 Myr or less). An 
Inertial Interchange True Polar Wander (IITPW) event on this time scale is 
capable of driving regional sea-level fluctuations of up to +/- 4 km (Mound 
et al., 1999). The amplitude and geometry of the fluctuation is dependent on the 
rate and orientation of the TPW and on the viscoelastic structure of the Earth 
(effective elastic plate thickness, mantle viscosity). The global perturbation 
may also have led to conditions that favored radiation or preservation of the 
Ediacara fauna II, containing the first clear bilaterian animals.

A similarly large and sharp negative carbon isotope anomaly spans the Early/Middle 
Cambrian boundary (Montanez et al., 2000), which has been dated recently to slightly 
younger than 511±1 Myr.  As the age of this anomaly is indistinguishable from the 
emplacement of the Kalkarinji large igneous province in Australia, emplacement of 
the Kalkarinji volcanic province might have triggered another Sept-Îles style rapid 
IITPW episode, as well as the early/middle Cambrian mass extinction event.

 

References:
Abolins, M.J., 1999, I. Stratigraphic constraints on the number of discrete 
neoproterozoic glaciations and the relationship between glaciation and ediacaran 
evolution. [PhD thesis]: Pasadena, California, California Institute of Technology.

Evans, D.A., 1998, True polar wander, a supercontinental legacy: Earth and Planetary 
Science Letters, v. 157, p. 1-8.

Higgins, M.D., 2005, A new model for the structure of the Sept Iles Intrusive suite, 
Canada: Lithos. 83: 199-213.

Kirschvink, J.L., Higgins, M.D., Evans, D.A., Condon, D., Raub, T.D., Bowring, S.A., 
Nowlan, G.S., Macdonald, F.A., and Farley, K.A., 2005, Ediacaran Rapid True Polar 
Wander: Constraints on a Possible Driving Mechanism From the Paleomagnetism and 
Geochronology of the Sept-Îles Intrusive Suite, Quebéc, Canada: EOS Trans. 
American Geophysical Union, v. 86, p. Abstract GP21A-05.

Kirschvink, J.L., Ripperdan, R.L., and Evans, D.A., 1997, Evidence for a large-scale 
Early Cambrian reorganization of continental masses by inertial interchange true 
polar wander.: Science, v. 277, p. 541-545.

Montanez, I.P., Osleger, D.A., Banner, J.L., Mack, L.E., and Musgrove, M.L., 2000, 
Evolution of the Sr and C isotope composition of Cambrian Oceans: GSA Today, v. 10, p. 1-7.

Mound, J.E., Mitrovica, J.X., Evans, D.A.D., and Kirschvink, J.L., 1999, A sea-level test 
for inertial interchange true polar wander events: Geophysical Journal International, 
v. 136, p. F5-F10.

Williams, G.S., and Gostin, V.A., 2000, Mantle plume uplift in the sedimentary record: 
origin of kilometre-deep canyons within large Neoproterozoic successions, South Australia.: 
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