INTRODUCTION:    Unlike its paleontological record (which only spans some 350Ma), the geological record of Vancouver Island can be traced back perhaps another 70Ma or more, to the Lower Silurian Period of the Paleozoic Era, more than 420 million years ago. The oldest rocks from this period are igneous in nature. They undoubtedly record the initial and explosive birth of the Island in the southwestern Pacific Ocean, and as such form the foundation for the accumulation of volcanic arc (not unlike the modern Hawaiian Islands), oceanic, and clastic wedge (sediments eroded from pre-existing rock) deposits that occurred during the periods of the Paleozoic, Mesozoic, and Cenozoic Eras which were later to follow the Silurian Period.    The last 200 or so million years of the Paleozoic Era witnessed the final reassembly of the continental masses into the single supercontinent known as Pangea ("all Earth"), anchored at the south pole and stretching nearly to the north. During this immense span of time, the planet was subjected to a bewildering variety of other geographic transformations as well. Extending from north-west Europe to north-east North America, the Caledonian Mountains were completed, as were the Appalachians and the mountains of South America and central Western Europe. It was also a time of widespread flooding by the world's oceans; indeed, at several different times throughout the latter part of the Paleozoic Era, most of Asia and the margins of all the other continents were completely submerged by these shallow, warm, tranquil seas. They were eventually responsible for depositing huge tracts of thick limestone, which today can be found covering much of Europe, Asia, and North America.    Although glacial deposits are known from the northern hemisphere (North America, Europe, the Baltic States, and Siberia), it left by far its greatest mark upon the southern hemisphere (South America, Africa, India, Australia, Antarctica, and South East Asia). At times these enormous ice sheets extended northward nearly twice the diameter of the current Antarctic ice sheet, lowering the sea levels by as much as 100m (330ft) and as they did so. However, as the Era came to a close some 248 million years ago, and with it many of the world's intercontinental seaways, these ice sheets were replaced by bogs and peat swamps, and a hot, arid climate quickly predominated over large areas of the Pangean interior.    Click on the rotating globe to access a geographical map of each Paleozoic Period.

SIMPLIFIED PALEOZOIC GEOLOGY OF VANCOUVER ISLAND:
(MINOR VOLCANIC EPISODES OMITTED):

THE PERMIAN PERIOD: GLOBAL:    The Permian Period is characterized by the final assembly of the great supercontinent of Pangea, and the dramatic global effects of this reunion. With the northward progression of Laurentia and Gondwana bringing them in contact with the southwestward progression of Angara, the world was, for the first time since the Precambrian supercontinent of Rodinia, composed of a single immense landmass, extending from the south pole to the north.    Not only did the subsequent closure of the various seaways reposition the ocean currents, but the realignmnent of the various mountain chains also blocked the moist, easterly tropical winds, thereby creating extensive rainshadows into the Pangean heartland. This served to create more distinct climatic zones than had existed in the Mississippian or Pennsylvanian Periods before it, and, as the continental areas emerged as much as 100m (330ft) further above sea level, great tracts of desert and inland salt seas began to replace the earlier coal swamps in the tropics. In addition, the Gondwana icesheet reached its maximum coverage in the Lower Permian, but then gradually retreated as the cooler ocean currents and winds were redirected elsewhere and the planet warmed.    The close of the Permian Period, some 248 million years ago, also marked the end of the Paleozoic Era. VANCOUVER ISLAND:    The Insular Superterrane, composed of both the Alexander and Wrangellia Terranes, resembled a stable limestone-mantled plateau, submerged >100m (>330ft) below the ocean's surface. It remained some distance south of the equator during this Period, deep within the Tropic of Capricorn.

The Sicker Assemblage:    The Sicker Assemblage encompasses the entire sequence of Paleozoic rocks that are exposed on Vancouver Island. The sequences of igneous and sedimentary material record not only the Island's birth, but also its alternating transformation from submerged volcanic plateau to low archipelago surrounded by crinoidal barrier reefs and shallow, tropical seas; and finally the start of its long, northeastward migration toward the west coast of North America. The Assemblage is comprised of great thicknesses of lava, argillite (weakly metamorphosed mudstone or shale), graywacke (coarse-grained sandstone deposited by submarine landslides), and limestone, deposited exclusively into a MARINE setting.

STAGES:                (Ma) Tatarian        248 Kazanian        253 Ufimian         250 Kungurian       258 Artinskian      263 Sakmarian       268 Asselian        279

Buttle Lake Formation (~265 - 313 Ma): Sedimentary rock; well-bedded sequences of grey or white crinoidal limestone, alternating with argillite, siltstone, volcanic sandstone, and local beds of exotic limestone blocks, indicating a prolonged, quiet phase of erosion and deposition of sediments into relatively shallow water, isolated from oceanic influence by possible presence of reefs? or other barriers; <200m (<660ft) depth; 300m - 500m (990ft - 1650ft) unit thickness.

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THE PENNSYLVANIAN PERIOD: GLOBAL:    Laurentia continued to rotate counter-clockwise throughout the early stages of the Pennsylvanian Period, and in doing so came into increasing contact with the whole of northwestern Africa. This collision, in turn, initiated the first stage in the final amalgamation of Pangea, whose two massive supercontinental blocks were to remain locked together until well into the Mesozoic Era, and forced more of the southern landmass of Gondwana deeper into the Antarctic Circle. Shortly thereafter, an ice-sheet began to form in southern Africa, extending to Argentina, southern Arabia, India, Antarctica, Australia, and across central Africa to Madagascar, which was ultimately responsible for lowering the global sea level. The shallow marine environment, which had persisted along the coastlines of the northern Laurentia since the latter part of the Mississippian Period, finally drained away to be replaced by more or less permanent coastal deltas and swamps. VANCOUVER ISLAND:    Proceeding northwestward at an average speed of 3 - 5 cms/year (~1.25 - 2 inches/year), Wrangellia gradually became incorporated into a microcontinental mass with the slightly older Alexander Terrane that was preceeding it. This resulted in the new Insular Superterrane, a coherent tropical archipelago around which lime-secreting organisms began to flourish during the latter quarter of the Paleozoic Era.

The Sicker Assemblage:    The Sicker Assemblage encompasses the entire sequence of Paleozoic rocks that are exposed on Vancouver Island. The sequences of igneous and sedimentary material record not only the Island's birth, but also its alternating transformation from submerged volcanic plateau to low archipelago surrounded by crinoidal barrier reefs and shallow, tropical seas; and finally the start of its long, northeastward migration toward the west coast of North America. The Assemblage is comprised of great thicknesses of lava, argillite (weakly metamorphosed mudstone or shale), graywacke (coarse-grained sandstone deposited by submarine landslides), and limestone, deposited exclusively into a MARINE setting.

STAGES:                (Ma) Noginskian      286 Klazminskian Dorogomilovskian Chamovnicheskian Krevyakinskian Myachkovskian   296 Podolskian Kashirskian Vereiskian Melekesskian Cheremshanskian Yeadonian       315 Marsdenian Kinderscoutian

Buttle Lake Formation (~265 - 313 Ma): Sedimentary rock; well-bedded sequences of grey or white crinoidal limestone, alternating with argillite, siltstone, volcanic sandstone, and local beds of exotic limestone blocks, indicating a prolonged, quiet phase of erosion and deposition of sediments into relatively shallow water, isolated from oceanic influence by possible presence of reefs? or other barriers; <200m (<660ft) depth; 300m - 500m (990ft - 1650ft) unit thickness.

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THE MISSISSIPPIAN PERIOD: GLOBAL:    Geographically, the Mississippian Period was dominated by three major continental blocks. Laurentia, composed of North America, north-west Europe, Greenland, and Russia west of the Urals, was positioned along the equitorial tropics. Further north, Angara, comprising Asiatic Russia, Siberia, and parts of China, lay partly in the temperate zone and stretched north into the Arctic circle. Gondwana, made up of the remaining southern continents, remained firmly anchored to the southern pole.    Geologically, the Mississippian was characterized by two great events. First was the collision of Laurentia and Gondwana. As North America turned counter-clockwise and abraded against northwestern Africa and southern Europe, great masses of seafloor and continental sediments were thrust upward. This marked the construction of the Appalachian range of Europe and North America, and the old Hercynian mountains of Europe, the main remnants of which include the Bohemian Massif, the Harz Mountains, and the hills of the Ardennes. Once completed, erosion of these new structures created large deposits of sandstones and shales that flooded the shallow ocean basins between them. And second was the immense acculmulation of limestone throughout the shelf areas of North America and northern Europe. These huge beds often alternate with much thinner bands of sandstone and shale, indicating that the shallow seas periodically withdrew to create coastal deltas and swamps. VANCOUVER ISLAND:    Some ten thousand kilometres (~6200 miles) to the west of Laurentia, Wrangellia began its slow northeastward migration toward its present location. Propelled by upwelling convection currents in the planet's mantle beneath it, the mass of volcanic islands, seamounts, and plateaus was one of the last exotic terranes to vacate the Panthalassan mid-oceanic spreading ridge and proceed toward the west. This new phase marked the temporary cessation of widespread volcanic activity on the ancestral Vancouver Island.

The Sicker Assemblage:    The Sicker Assemblage encompasses the entire sequence of Paleozoic rocks that are exposed on Vancouver Island. The sequences of igneous and sedimentary material record not only the Island's birth, but also its alternating transformation from submerged volcanic plateau to low archipelago surrounded by crinoidal barrier reefs and shallow, tropical seas; and finally the start of its long, northeastward migration toward the west coast of North America. The Assemblage is comprised of great thicknesses of lava, argillite (weakly metamorphosed mudstone or shale), graywacke (coarse-grained sandstone deposited by submarine landslides), and limestone, deposited exclusively into a MARINE setting.

STAGES:                (Ma) Alportian       320 Chokierian Arnsbergian Pendleian Brigantian      333 Asbian Holkerian Arundian Chadian Ivorian         352

Unnamed Chert Unit (~352 - ~360? Ma): Sedimentary rock; alternating, thinly-bedded sequences of argillite, siltstone, chert, graywacke, and calcarenite (a limestone composed of cemented, limy sand), indicating a short, quiet phase of erosion and deposition of sediments along submarine slopes into relatively deep water; 200m - 1000m (660ft - 3300ft) depth; unmeasured unit thickness.

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THE DEVONIAN PERIOD: GLOBAL:    Geologically, the Devonian Period was a time of erosion and deposition. As soon as the mountain-building episode of the Caledonian Mountains in northern Europe and North America came to a close near the end of the Silurian, great masses of sand and mud began to accumulate in the shallow basins between them. In Europe, where these river and lake deposits are best exposed, they are known as the Old Red Sandstone. VANCOUVER ISLAND:    Locally, the initial formation of Wrangellia was nearing completion. As further rifting and subsequent upwelling of volcanic material from below continued unabated, the oceanic rocks that would one day comprise Vancouver Island and the Queen Charlotte Islands began to assume a single coherent landmass. To an observer, this may have resembled a mixture of volcanic islands, seamounts, and submerged plateaus, a wedge of rising seafloor perhaps as much as 600km (375 miles) from north to south (comparable in size and shape to the North African nation of Morocco).

The Sicker Assemblage:    The Sicker Assemblage encompasses the entire sequence of Paleozoic rocks that are exposed on Vancouver Island. The sequences of igneous and sedimentary material record not only the Island's birth, but also its alternating transformation from submerged volcanic plateau to low archipelago surrounded by crinoidal barrier reefs and shallow, tropical seas; and finally the start of its long, northeastward migration toward the west coast of North America. The Assemblage is comprised of great thicknesses of lava, argillite (weakly metamorphosed mudstone or shale), graywacke (coarse-grained sandstone deposited by submarine landslides), and limestone, deposited exclusively into a MARINE setting.

STAGES:                (Ma) Famennian       360 Frasnian        367 Givetian        374 Eifelian        380 Emsian          387 Siegenian       394 Gedinnian       401

Myra Formation (~370 - ~400? Ma): Igneous rock; interbedded massive and well-bedded lava and local pillow lava, with commonly multi-coloured volcanic debris, and alternating thin- to thick-bedded and massive argillite, siltstone, graywacke, and minor conglomerate, indicating explosive volcanic episodes with periods of deep water deposition of eroded sediments; 200m - 1000m (660ft - 3300ft) depth; 750m - 1000m (2475ft - 3300ft) unit thickness.

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THE SILURIAN PERIOD: GLOBAL:    The major global event that marked the Silurian Period was the culmination of the Caledonian orogeny (mountain building episode) in northern Europe, Norway, Spitzbergen, south-eastern Canada, and north-eastern United States. This complex series of geological events was the result of the collision of North America with northern Europe and the Baltic States, and the closing of the shallow ocean basin that had, until then, divided them. Globally, two great landmasses, separated by various arms of the Tethys Sea, persisted from the earlier Ordovician Period. The northern, more or less equatorial supercontinent was composed of North America, Northern Europe, the Baltic States, and Siberia, dwarfed by the much larger supercontinent of South America, Africa, Arabia, India, Antarctica, South East Asia, and Australia anchored to the south pole, but extending northward beyond the Tropic of Cancer. The rest of the globe was composed of the great sea called Panthalassa, bissected north of Australia by a mid-oceanic spreading ridge extending toward the northern pole. VANCOUVER ISLAND:    Along its southernmost limit, this submerged volcanic ridgeline was responsible for the creation of a large number of exotic terranes (blocks of rock unrelated to the rocks in which they are presently found) that would one day find themselves pushed northeastward and welded along the westernmost edge of North America. These include the Quesnellia, Stikinia, Cache Creek, and Alexander Terranes, and, of considerable importance to Vancouver Island, Wrangellia, the name given to the rocks that comprise its foundation. During the mid-Silurian Period, Wrangellia apparently began its explosive existence as a submerged arc of volcanoes and volcanic plateaus, perhaps as old as 430 million years. Periodically, the great upwelling pressures that persisted beneath it would force magma into the ocean depths above. These rocks, found today throughout the Cowichan Lake area, and from Horne Lake to Saltspring Island, record the initial birth of Vancouver Island, and so comprise the basement rocks of the Sicker Assemblage.

The Sicker Assemblage:    The Sicker Assemblage encompasses the entire sequence of Paleozoic rocks that are exposed on Vancouver Island. The sequences of igneous and sedimentary material record not only the Island's birth, but also its alternating transformation from submerged volcanic plateau to low archipelago surrounded by crinoidal barrier reefs and shallow, tropical seas; and finally the start of its long, northeastward migration toward the west coast of North America. The Assemblage is comprised of great thicknesses of lava, argillite (weakly metamorphosed mudstone or shale), graywacke (coarse-grained sandstone deposited by submarine landslides), and limestone, deposited exclusively into a MARINE setting.

STAGES:                (Ma) Pridoli         408 Ludfordian      414 Gorstian Gleedon         421 Whitwell Sheinwoodian Telychian       428 Fronian Idwian Rhuddanian

Nitinat Formation (~408 - ~430 Ma): Igneous rock; dark, unconsolidated debris rock with locally pillowed lava indicating explosive volcanic episodes with minor, though massive, submarine flows; >1000m (>3300ft) depth, ~2000m - ~3000m (~6600ft - ~9900ft) unit thickness. This formation records the violent birth of Wrangellia on the ocean floor.