Module 2:Week 1
Introduction to Palaeozoic Britain
Old Lost Sea: The Iapetus Ocean
Wikimedia Commons
Palaeozoic periods
Permian (299–252 Ma)
Carboniferous (359–299 Ma)
Devonian (419–359 Ma)
Silurian (444–419 Ma)
Ordovician (485–444 Ma)
Cambrian (541–485 Ma)
North-South dividePalaeozoic UK partitioned into ‘terranes’:
Scotland, N. Ireland = ‘Laurentian’ (North American)
England, Wales, S. Ireland = Avalonian (Euro-Africa)
Dividing the Early Palaeozoic
V
(Images from Wikimedia Commons)
Rev. Adam Sedgwick
Sir Roderick ImpeyMurchison
Uniting the Early Palaeozoic
Charles Lapworth Charles Walcott
Not to mentionJ. Tuzo Wilson
RichardFortey
RobinCocks
The Cambrian Controversy
Sedgwick vs Murchison
1835: collaboration
&
(Images from Wikimedia Commons)
Sedgwick - Cambrian
Murchison- Silurian
Cambria
Sedgwick studiedgeology of North Wales
Siluria
Murchison studied geology of South Wales
1839-1873:competition
V
(Images from Wikimedia Commons)
Murchison began
encroaching his ‘Lower
Silurian’ on Sedgwick’s
‘Upper Cambrian’
1879: compromise
(Images from Wikimedia Commons)
Lapworth proposes the Ordovician
Cambrian outcrops (Eng & Wal)
Harvey et al. (2011)
Walcott's Cambrian critters
Walcott's Cambrian critters
Puzzling distribution of Euro-American fossils
Wilson's (1966) wonderings
Did the Atlantic close then re-open?
Cocks & Fortey (1982)
Fossils = more precise timings
Cambrian: very differentLaurentia & Avalonia far apart
Ordovician = getting similarL & A converging
Silurian = very similarL & A converged
Wilson Cycles?
Cyclical plate tectonic system
by which oceans open and close
Start of a Wilson Cycle
Hot spot → rifting beneath continent
Middle of a Wilson Cycle
ACTIVE margin PASSIVE margin
End of a Wilson Cycle
Subduction of ocean → continental collision
Late Precambrian
opening of Iapetus Ocean
Start of a Wilson Cycle
Precambrian supercontinent break-up
Cambriangeography
© Ron Blakey (Geosystems)http://cpgeosystems.com/paleomaps.html
Early-Mid Cambrian (Eng & Wal)
Cambro-Ordovician (Eng & Wal)
Hebridean Terrane, NW Scotland
Cambro-Ordovician Scotland
Cambro-Ordovician
strata, Northwest Scotland
Sea-level change
controlled deposition?
Middle of a Wilson Cycle
ACTIVE margin(Eng & Wales)
PASSIVE margin(Scotland)
Late Cambrian
Early CambrianPASSIVE margin
(Scotland)PASSIVE margin(Eng & Wales)
Ordovician volcanism
Borrowdale Volcanic Group
Fiamme textures in ignimbrite, Great Paddy Crag, Buckbarrow
© BGS
Late-stage Wilson Cycle
ACTIVE marginAvalonia
North Wales
West Wales
Lake District
Death of an ocean
Silurian: The closing of Iapetus
LinksPalaeogeographical maps of Europe:http://cpgeosystems.com/euromaps.html
The Wilson Cycle:http://csmres.jmu.edu/geollab/fichter/Wilson/Wilson.html
The Iapetus in Newfoundland:http://theindependent.ca/2011/06/14/gros-mornes-old-lost-sea/