PRECAMBRIAN ROCKS AND TIME

Precambrian constitutes about 85% of geologic time;  first 4,000,000,000 years  (4.6 to 0.54 Ga) but we don’t know as much about it as Phanerozoic Eon; only about 20% of exposed rock is PC, highly metamorphosed, and few diagnostic fossils; subdivision mainly awaited absolute dating techniques:

Precambrian Rocks form the cratons or central, stable, thick "cores" of continents; mainly composed of metamorphosed and deformed PC rocks; where covered by veneer of Phanerozoic sedimentary rock Precambrian is referred to as basement

exposed portions of Precambrian rocks are called shields; mainly low relief, broad areas near interiors of continents:

 Baltic Shield: (Scandinavia )

 Anabar and Aldan Shields (Siberia)

 Ethiopian Shield, Bushveld (Africa)

 Guyana Shield (South America)

 Pilbara and Yilgarn Shields (Australia)

Canadian Shield**  (central Canada, very minor outliers in the US; Adirondacks)  largest area of exposed Precambrian in the world

Smaller areas of PC exposed in basement uplifts, including:

 a) intracratonic arches/domes  (e.g. Ozarks, Adirondacks; Black Hills)

b) "thick-skinned" tectonic uplifts (e.g. Berkshire, Green Mtns., Rockies
 
 
 

PRECAMBRIAN EONS, ERAS, OROGENIES

Basic framework is two eons divided into two or three eras; in Canada boundaries of eras correspond approximately to major orogenies- metamorphic and igneous events that reset many age dates

Phanerozoic Eon  Paleozoic-Cenozoic      544 to 0  Ma

      Hadrynian (Neoproterozoic)   1000 to 544 Ma
        Grenville Orogeny
Proterozoic Eon  Helikian* (Mesoproterozoic) 1600 to 1000 Ma
        Hudsonian Orogeny
      Aphebian (Paleoproterozoic)   2500 to 1600 Ma
        Kenoran Orogeny

Archean Eon   Early and Late        3800 Ma = 3.8 Ga

Hadean Eon                4600 Ma = 4.6 Ga
(Ma=mega-annum; million years;  Ga= giga-annum; billion  years)

* Canadians recognize two divisions of Helikian  Era split by orogeny:

  Neohelikian
      Elsonian Orogeny      ~1300 Ma
  Paleohelikian
 

Precambian terranes are divided into structural-geochronologic provinces:

a) clustering of age dates (particularly K/Ar dates) reflects metamorphic age; times of extensive metamorphism, heating and resetting of dates

b) similar structural trends reflect common compressional direction and vergenz

e.g. Pan African 550 Ma and Eburnian province boundary in S.Am/Africa

Canadian shield and US subsurface divided into several provinces:

Superior,  northern Gt. Lakes area; largest dates about 2.5 Ma, strong NE-SW trend of "greenstone" belts (metamorphosed by Kenoran Orogeny)

Slave: NW Territories; Gt. Slave Lake, ~600 km west of Hudson Bay; similar age as Superior; greenstone belts (metamorphosed by Kenoran Orogeny)

Wyoming-Hearn-Rae (sometimes Hearn-Rae  combined in Churchill Province in Canada): exposed in Black Hills, Rockies; ancient Archean reworked about 1.6 Ga; major gold-producing area; may continue in eastern Antarctica, Australia, Siberia ?

Bear: Yukon, NWT, early Proterozoic; metamorphosed by Wopmay Orogeny); major gold producer

Nain: Quebec, Labrador, much of Greenland;  partly Archean, partly mid Helikian; metamorphosed in Elsonian

Trans-Hudson: suture area between Wyoming-Churchill  and Superior provinces; metamorphosed during Hudsonian Orogeny (1.6 Ga)

Granite-Rhyolite (Central) Province:  under mid-continent US; Ohio (west)  subsurface; 1.6-1.8. Ga

Grenville: long belt NE-SW, Adirondack Mtns.(NY); most of Ontario shield ; Ohio (east) subsurface;  Llano Uplift, Texas; much of Ireland, Scotland; metamorphosed by 1 Ga ? Grenville Orogeny

Continental Accretion:

Note that older parts of craton tend to be near center, with younger belts outward;  continents have built up through time by suturing of formerly separate terranes, microcratons, and cratons,  and by stabilizing of mobile belts (compression thickening, metamorphism, intrusion of volcanic arcs, forearc basins, etc.

e.g. Africa made up of many smaller cratons welded together in Pan-African orogeny in latest Proterozoic-Early Cambrian;

Laurentia (ancestral North America) started as discrete Archean cratons sutured during early Proterozoic, with Central and Grenville provinces added on later then Phanerozoic fold belts
 
 
 
 

ARCHEAN EON

Archean: 4.0 (to 4.6) to 2.5 billion years ago;  45% of geologic time:

Where to find Archean rocks?
Superior, Slave, Wyoming-Hearn provinces;
(oldest rocks on Earth: Acosta  Formation, NW Territories, Slave Province)

Isua Supergroup; Greenland; 3.8 Ga; BIF; evidence for life

 Pilbara shield of Australia (oldest fossil-bearing rocks: Warawoona Group)

Typical rocks: mafic rocks: komatiites;  granulite terranes;  graywacke sandstones, shales; banded iron formation (BIF) (some); extensive terrestrial sediments only in southern Africa; only minor carbonates; no evaporites or redbeds known;

A distinct motif of Archean is greenstone belts, alternating with
granulite terranes

Greenstones are weakly metamorphosed ultramafics, pillow basalts, lesser amounts of felsic volcanics, and overlying metasediments; metaconglomerates contain clasts of granitic gneiss,  but:

They are also surrounded by and in places intruded by granitic gneiss; which came first? And why are greenstone belts confined to Archean ?

General  model:
Granulite terranes represent remnants of microcontinents which were sometimes partially melted and remobilized during collisions;

Greenstone belts represent  deformed "mobile belts" including island arcs and forearc basin sediments that were compressed during microcontinental collisions

Most important:  early Archean crust/lithosphere was very mobile because of 2X heat flow relative to present; very active microplate tectonics, small ocean basins opened and closed frequently

Only in late Archean was substantial amount of crust stabilized into larger cratons, southern Africa:
Pongola Supergroup  (2.5-2.7 Ga) tidal flat cycles tens of meters of shallow water siliciclastics

Witwatersrand  (2.7-2,8 Ga) braided stream gravels up to 5 miles thick; rich in placer gold derived from earlier greenstone belts

Archean life:

Indirect evidence back to 3.8 Ga
Oldest fossils, including cells in chert and stromatolites 3.3-3.5 Ga  Warawoona Group (Australia)

FigTree Chert of Barberton Mountain land also shows early bacteria

Stromatolites first abundant in Bullawayo Group South Africa ~2.8 Ga

Entirely prokaryotic; archebacteria and eubacteria, including cyanobacteria
If eukaryotes evolved they were small, simple and are mistaken for bacteria
 
 
 
 

PALEOPROTEROZOIC (APHEBIAN)

Bounded by a series of crustal thermal events worldwide stabilized larger cratons, metamorphosed and underplated rocks with massive granitic intrusions around 2.5 Ga; in Canada this has been called Kenoran Orogeny, but it was not a standard modern-style orogeny;
Slave and Superior cratons stabilized

Paleoproterozoic was time of still minor or no eukaryotes but much more extensive limestone deposition and widespread diverse stromatolites
Also 85% of banded iron formations precipitated up to about 1.9 Ga

Major iron ores ("Superior type" ores); mined in Minnesota and elsewhere must be fluxed with limestone to remove silica from jasper (chert);

BIFs indicate  that deep sea was still anoxic; volcanic eruptions in deep sea released reduced (ferrous) Fe and silica; when contacted oxygenated water in photic zone Fe oxides precipitated out ; Fe, S, OM were MAJOR OXYGEN SINKS; unclear what caused the banding cyclic upwelling; climatic or seasonal shifts in water oxygen content ??
 
 

Other  Paleoproterozoic (Aphebian) Events:
a) 2.3 Ga  First continental glaciation:  Gowganda conglomerate at base of Huronian Supergroup (north of L. Huron) is oldest extensive tillite, Aphebian, about 2.3 Ga;  shows temperatures had cooled substantially; other tillites known at about same age in Wyoming, Finland, S. Africa and India

b) 2.0 Ga: Largest meteor impact craters: Sudbury Crater, centered near Sudbury, Ontario; impact of a large (10 km) asteroid about 2.0 billion years ago; crater is over 140 km in diameter; famous nickel mining area near Sudbury shows shatter cones and carbonaceous material that is claimed to contain "bucky balls" (fullerenes-spherical carbon capsules) from space with primordial He inside??
A similarly large crater of almost same age is Vredofort,  South Africa

c) ~ 2.0- 1.8 Ga: First Red Beds; decline of BIFs: red terrestrial sediments imply oxygenic atmosphere with ~ 5% present O2 levels;  no more detrital pyrite in subaerial sediments; decline of BIFs seems to imply that marine waters were becoming oxygenic; Fe sinks were becoming filled, allowing free oxygen from photosynthesis to escape and build up; also carbon burial

d) 1.9 Ga First modern-style orogeny: Wopmay Orogen; collision of island arc, with outer side of Slave Province (~1000 km west of Hudson Bay)  created fold and thrust belt and peripheral foreland basin; shows all features typical of later orogenic belts:

i) Paired metamorphic belts: Deformed but unmetamorphosed fold and thrust belt west of Slave Craton

ii) Shelf succession shows inversion of topography and evolution of deposits from passive shelf to a peripheral  foreland basin filled with flysch and molasse:

a) at base of succession is an arkose filled rift;  b) followed by mature quartz sandstones and stromatolitic carbonates (orthoquartzite-carbonate), then transition to siliciclastics,
c) black shale and turbidites (flysch: underfilled peripheral foreland basin);
 d) finally this passes upward into molasse: marginal to non marine siliciclastics  that overfill the basin , coarsen and shallow upward as sediment is shed from the outboard mobile belt (in this case west of the foreland basin)

e) 1. 6 Ga Hudsonian (Mazatzal) Orogeny slightly later; welded Slave-Churchill-Superior cratons together; major continent-cont. collisions
These events related to first major accretion of continents; early "Pangea"
 
 
 
 

Paleoproterozoic life

2. 1 Ga: Gunflint Chert: Well preserved microflora of bacteria, including filamentous nostoccales  blue greens with heterocysts for N fixation; imply some oxygen in atmosphere; Kackebeckia colonial iron bacteria.  Also, stromatolites achieved their greatest diversity

recently also Grypania , a possible multicellular eukaryotic algae; would push eukaryotes back to 2 billion years;
 
 

Evolution of Eukaryotes
a major step in life history now appears to have taken place as far back as Paleoproterozoic; share common ancestor with archebacteria and eubacteria;  evolved from larger cells; most prokaryotes only a few tens of microns ; cells > 25 microns generally eukaryotic;

began to develop invaginations along cell membrane to accommodate AV problem; such vacuoles may have pinched off to encapsulate DNA:nucleus
SET theory; serial endosymbiosis; hypothesis of Lynn Margulis; now well accepted:

organelles of eukaryotic cells evolved by symbiosis with small bacterial cells:

Flagella: possibly from spirochaete bacteria

Mitochondria: small aerobic bacteria: modern Pelomyxa lacks true mitochondria but picks up bacteria that function in  this way; mitochondria have their own DNA;
gave cells the ability to cope with oxygen;
their appearance may signal "oxygen holocaust"; buildup in atmosphere of this toxic gas; mitochondria evolved ability to undergo aerobic metabolism

Chloroplasts: from symbiotic small cyanobacteria; also have distinct DNA;
Eukaryotic algae evolved after heterotrophic protists
 
 

MIDDLE PROTEROZOIC (HELIKIAN)

The great Hudsonian Orogeny of Canadian  Shield provides a reference point for dividing Paleoproterozoic form Mesoproterozoic or Helikian
Atmosphere was now oxygenic with 10-15% present levels; eukaryotic protista well established

Major outpourings of anorthosite around 1.3 Ga suggest mantle changes

While Paleoproterozoic was time of continental collision, Mesoproterozoic appears to have been a time of (failed) extension or rifting:

a) 1.4 Ga: Belt and Amargosa failed rifts; developed actively subsiding basins in what is now Montana, California; Belt Supergroup  nearly 10  miles thick; well exposed in Glacier National Park; shows evidence of inland sea or lake? Enormous thicknesses of dark shales, some coarser sediments; well laminated (no burrowers yet!); some shallow water sandstones and carbonates;

b) 1.2- 1.1 Ga Mid-Continent Failed rift: apparent 3-way rift developed in mid-continent; associated with Mid-continent gravity high;  enormous outpourings of mafic rocks loaded crust (e.g. Duluth Gabbro); may have initiated subsidence of Michigan Basin; Keweenawan Supergroup; thick arkosic conglomerates, quartz arenites, redbeds,(Nonesuch Formation) basalts; source of famous native copper deposits of Michigan UP;

A rift graben East Continent Rift in subsurface under Tristates area may be related; recently geologists discovered thick (~1900') red sandstone basalt succession ?Middle Run Formation in what had been thought to be crystalline basement; appears to be overthrust by Grenville (1 Ga) rocks

The rifting failed, Laurentia was not torn apart and shortly thereafter compressional tectonics took over

c) 1.1-0.9 Ga (~ 1 billion years ago): Grenville Orogeny: A major tectonic and thermal event affected a large strip of eastern Laurentia east of sharp line that may pass under Cinn.-Grenville front; (Grenville Province)
Rocks well exposed in Adirondacks and eastern Canada plus Green Mtns., Berkshires; are high grade metamorphics; include metasediments and meta-igneous (include: meta-anorthosites of Mt. Marcy highlands; finally  intruded by late stage granites

Very major event;seems to have been a "Himalaya style" collision in which eastern Laurentia was overthrusted by the edge of another continent (like India overthrust by Asia); formerly sedimentary successions were buried up to 25 km tectonically: subjected to high T and high P regimes

What collided?  is unxertain but latest reconstructions suggest that this was western South America and possibly also Baltica; whatever it was had rifted away before the Paleozoic Era

Grenville was one part of the assembly of a new supercontinent: Rodinia which stayed together for a few hundred million years before rifting

Grenville such a  major event that it is used to demarcate the end of the Mesoproterozoic and begin of Neoproterozoic

Mesoproterozoic Life:

Eukaryotes well established:

Oldest acritarch fossils in 1.4 Ga Beck Springs Dolostone (California); became diversified in later Helikian

 possible carbonized remnants of multicellular algae  1.3 Ga in Belt Supergroup of Montana

Stromatolites still abundant
 
 
 
 

NEOPROTEROZOIC (HADRYNIAN)

From 1.0 to .544, very important interval associated with a) assembly of "proto-Pangea" (Rodinia) and perhaps a later supercontinent;  enormous glaciations, first mass extinctions (of acritarchs) and origin of metazoans-multicellular animals

Grenville Orogeny was an important component of  formation of Rodinia; with Laurentia sutured to w South America and probably Baltica; Grenville extends into British Isles

SWEAT hypothesis: SW Laurentia sutured to east Antarctica-Australia (East  Gondwanaland); further north Siberia attached to NW Laurentia by 1 Ga
West Gondwanaland  still not fully assembled;  association of microplates
Subsequently, at about 700 Ma major rift developed through present western interior US (Idaho to Arizona) East Gondwana plate separated and moved eastward to collide with West Gondwana near end of Protoerozoic (in Pan-African Orogeny ~ 550-530 Ma)

The assembly of supercontinents typically associated with slowing of seafloor spreading and this, in turn, leads to cooling and subsidence of  MORs; deepening  of ocean basins; this leads to regression of seas from continents

Hadrynian was time of major global regression; supersequence boundaries reflect erosion of most cratonic interiors; with no vegetation to hold weathered debris in place; more rapid erosion than at present; continents denuded to peneplane surfaces

Global cooling and near "Runaway Icehouse" Effect

a) Extensive weathering must have drawn large quantities of CO2 from atmosphere; this leads to "icehouse" cooling

b) C isotopes indicate burial of large amounts of organic carbon in sediments; further draws down CO2; more icehouse effect

b) Drainage of shallow seas led to more severe "continent-dominated" climates: land has lower heat capacity than water; less moderating effect

c) "Bright" land surface would have had much higher albedo (reflectance) than dark water; especially in  Proterozoic, pre-vegetation world; and once snow began accumulating this would have a self-propagating effect; lots of light reflected rather than absorbed

These cooling effects nearly rendered the Earth a frozen snowball

On at least four separate occasions there was very extensive continental glaciation 800 Ma, 700 Ma, 650 Ma, 600 Ma,

The last glaciation called Varanger (from a Scandinavian location) was most extensive glacial episode in Earth history; glacial deposits on every continent (except Antarctica !); good deposits in  White Russia, Scandanavia still unconsolidated; Cordillera (Arizona, Utah, Wyoming, Montana); glaciers to within 30 NS of Equator

Major excursions in 13C/12C ratios with light values during glacial intervals, heavy during non-glacial times suggests mass burial of organic carbon during non-glacial times when seas became stratified and anoxic in bottom water

 (Note: photosynthetic organisms fractionate carbon isotopes; preferentially incorporate lighter isotope, 12C; of organic matter then decays aerobically the 12C is relapsed back to water. But if OM is buried in sediment this process depletes water in 12C;  it gradually becomes enriched in 13C;  any carbonate precipitated from this water will have heavy isotopic ratio

During glacial times; improved ventilation of deep seafloor by cold, well oxygenated currents; this allowed aerobic decay of stored organic matter, released light 12CO2 back to water; lowered ratios in carbonates)

There is evidence that considerable burial of OM took place after Varanger glacial time; this eliminated a major oxygen sink; (decay sops up a lot of O2), therefore allowing O2 to build up in atmosphere (probably):

Amazingly, there were brief intervals of renewed precipitation of BIF, associated with the glacials; perhaps during stagnant times dissolved  Fe+2 may have built up in deep anoxic bottom water; then in transition to glacials this water upwelled into oxygenated zone and Fe+3 was precipitated

This  increase in oxygen may have triggered rise of larger metazoans after about 600 Ma;  maybe !

Neoproterozoic Life:

Acritarchs abundant in early portion of Neoproterozoic but underwent mass extinction around 600 Ma, maybe due to glacial cooling; stromatolites also declined

First trace fossils around this time very simple forms (though Seilacher reported 1.1 Ga traces from India in 1998 and there were reports of fecal pellets in early Hadrynian; shows presence of a gut) but then there is a big gap of nearly 400 million years without record

Ediacaran  (Vendian) large soft-bodied metazoans:
 

EDIACARA BEDS: (LATE PROTEROZOIC; VENDIAN  (570-550 Ma),  AUSTRALIA , NAMIBIA, ENGLAND, NEWFOUNDLAND ETC.)

Impressions of some of the oldest  large soft bodied soft-bodied organisms in sandstones;includes true animals (e.g. Kimberella) and enigmatic forms :

Cloud wanted to add Ediacarian Period (=~Vendian of Russians or Sinian of Chinese)

Vendozoa controversy of Seilacher; "taphonomic window"; few scavengers or predators; "Garden of Ediacara"

Were these really animals or large quilted lichens even  an entirely different kingdom ("Vendozoa")?

In any case, there were animals around; 1998 discovery of phosphatized fossil embryos from China;
show cell cleavage patterns typical of modern animals;

Also oldest (Vendian) sponges reported in 1997

Why the abrupt appearance of these large organisms after nearly 4 billion years?

Evolution of sexuality and increased rates of change? BUT eukaryotes ith sex had been around since at least 1.5 Ga

Cropping of dominant algae communities? BUT implies first evolution of grazers, and would algae compete with animals?

Transgression of shallow seas with abundant nutrients?  Did occur at end of glacial times and because continental rifting (seafloor spreading) was increasing again, BUT had occurred many times before.

Rise in oxygen? Direct evidence based on carbon isotopes (Knoll); BUT the excess O2 must have been partly sopped up by increased weathering rates
 
 
 
 
 
 

PRELUDE TO THE PALEOZOIC: THE RIFTING OF RODINIA

Early in the Neoproterozoic (Hadrynian) the continent of Rodinia had assembled but then began to rift apart about 700 Ma

Rifting of Rodinia involved several steps:

1) ~ 700 Ma  East Gondwana rifted from west side of Laurentia (Ancestral North America) forming Protopacific; these created a long-lasting passive (trailing) margin along western Laurentia

2)  ~ 600 Ma West Gondwana (northern South America) rifted from eastern Laurentia creating Protoatlantic (Iapetus) and subsiding passive margin in eastern Laurentia

3) Baltica ( Ancestral Europe) may have rifted from NE Laurentia

4) Avalonia may have rifted from northern Gondwana (N Africa);

All of this renewed seafloor spreading apparently associated with major sea level rise of the Sauk transgression over deeply eroded cratons

Pan African Orogeny

During latest Proterozoic, at same time Rodinia was continuing to rift,  a new supercontinent was assembling, East and West Gondwana came together as did several minor cratons in the African area

Pan African Orogeny produced supercontinent of Gondwanaland

So, by beginning of Paleozoic several land masses existed and were becoming shallowly submerged by transgressing seas:

Gondwanaland (straddling the south pole),

Laurentia straddling the equator rotated about 90 degrees from now

Baltica in southern hemisphere near Gondwanalad

Siberia, parts of China, Kazahkstan, and micro-continent of Avalonia
 
 

Major regression of seas associated with the assembly of continents in Rodinia  configuration, reduced seafloor spreading rates and, at times, very extensive continental glaciers caused most of Rodinia to be exposed to weathering and erosion for tens of millions  of years forming very widespread unconformity

"Lipalian Unconformity" (Wolcott’s name for what was thought to be a worldwide unconformity) forms base of first (mostly) Phanerozoic supersequencee, as sea-level rose in late Hadrynian shallow marine sediments accumulated over erosion surface, forming: Sauk Supersequence

In western North America: Classic late Proterozoic successions:
Windermere Supergroup; thick succession of arkosic to quartz arenite ‘ basalts; also probable tillites; esp. in Montana, Alberta, BC

Grand Canyon Supergroup: thick succession of red marginal marine to non-marine sands, shales; possible fossil algae; shows non-conformity with older Proterozoic Vishnu Schist below and angular unconformity with overlying Cambrian Tapeats Sandstone

All these clastics indicate rapid erosion of rift shoulder following rifting of Antarctica- Siberia away from Laurentia

In eastern North America:  The best record is in Blue Ridge and Smokies;
Metabasalts (Catoctin "greenstone", nr Wash., DC); conglomerates, including 600 Ma tillites and arkosic sandstones; Ocowee and Chilhowie supergroups  (late Neoproterozoic to Early Cambrian) of Smokies

Excellent late Proterozoic tillites and overlain by thick turbiddite succession with datable bentonites and Ediacaran type fossils (Mistaken Point) in Newfoundland; looks like another rift succession but probably not involving N America but rifting of Avalonia from Gondwanaland ?
 

Basically  Climate was warming; perhaps still cool in Early Cambrian; going into a long non-glacial interval in Cambrian to Late Ordovician
Greenhouse conditions; high sea level; active SFS; lots of CO2  emitted
Still no life on land; in seas animal life just about to burst forth with diverse skeletonized groups
 
 
 
 

EARLY PALEOZOIC HISTORY

Recall that the term "Paleozoic" ("age of ancient animal life") was proposed by Adam Sedgewick in (1838) who recognized the Paleozoic Era bounded below by (putatively) unfossiliferous rocks and above by the great Permo-Triassic extinction

The Paleozoic Era as now defined, ranges from about 544 to 250 million years ago, and includes six (or seven in North America): Cambrian to Permian

Recently the base of the Paleozoic- base of Cambrian- has been debated in several ways:

1) some have tried to add a new period to the base Vendian or Ediacaran- so that the oldest fossils of metazoans would be in included;  this has not been widely accepted

2) more ancient shelly fossils and large (trilobite) trace fossils have been discovered and used to redefine and extend back the base of the Cambrian
(now based on lowest occurrence of trace fossil Phycodes pedum

3) New dates on zircons from newly discovered bentonites from near the biostratigraphic base of the Cambrian gave more precise dates: ~544 Ma
for the base of the Paleozoic prior to 1990s dates of (higher horizons for) the base of the Cambrian were around 570 million years-but were based on altered samples.
 

CAMBRIAN PERIOD (544 to 495 Ma)

Name: Cambria: Roman name for Wales; A. Sedgewick (1834)
 

1) Very critical time in history of life: "Cambrian Explosion"

2) No glaciers: warming climates; entering long "greenhouse" phase

3) Rising sea level much of continents shallowly submerged, very widespread carbonate deposition

4) Protoatlantic (Iapetus) was opening during Cambrian

5) Little tectonic action in Laurentia; passive margins all around; many relict features from  late Proterozoic rifting; some of these still persist in crust today (rifting creates deep "wounds" in crust which are very "slow to heal"):

6) Oklahoma (Anadarko) aulacogen (Oklahoma); Reelfoot graben (Tennessee); Rome trough (Kentucky), St. Lawrence aulacogen (Quebec); these are failed third arms or lateral rifts from the Hadrynian (Neoproterozoic) rifting of Protoatlantic;

other features probably "built in" to  N. American craton during rifting; e.g. Cincinnati-Findlay- Algonquin-Kankakee arch; Kentucky River fault; etc. some of these features  became reactivated later; most important feature in early Paleozoic was Transcontinental Arch: "backbone of N Am"

7) Tectonics continued in Gondwanaland with Pan African Orogeny ending in earliest Cambrian and Adelaide Orogeny in Tasman belt of Australia

 8) Carbonates extremely widespread Great American carbonate bank

Mixed siliciclastic shales and carbonate turbidites, debris flows off the carbonate banks; passing off craton into "starved continental slope and rise", these were eventually incorporated into an accretionary wedge,  now seen in rocks that were thrust westward up onto the craton during the later, Mid Ordovician, Taconic Orogeny

9) Evaporites widespread especially in area of Salt Range of Pakistan
 

Sauk Supersequence :

Recall that L. Sloss (1963) defined a series of cratonic sequences in the Phanerozoic of North America; each bounded by major unconformities (Sauk, Tippecanoe, Kaskaskia, Absaroka, Zuni, Tejas  supersequences)

First is  Sauk which includes rocks of late Neoproterozoic through Early Ordovician age;

Sauk is bounded below by Wolcott’s "Lipalian Unconformity" (typically a nonconformity between Cambrian sedimentary rocks and older crystalline rocks; in a few places around the cratonic margins there is a nearly conformable passage from late Proterozoic into Cambrian; due to high subsidence rates and heavy sedimentation
 

Sauk is bounded at top by Knox unconformity, typically an erosional (karstic) disconformity between Lower and Middle Ordovician carbonates

Sea level rose onto deeply weathered, peneplaned Laurentian craton;
shallow subtropical seas reworked residual debris weathered from cratonic sialic rocks;  i.e. quartz, oxides, clay minerals; what was the fate of these sediments?

With no vegetation to hold soils in place; may have had huge dust storms which carried must fine clay-sized sediment offshore dropped over oceans (such as Protoatlantic) to form hemipelagic clays (shales);  residual material was mainly quartz sand and gravel; minor silt

Shallow shoreface reworked these  sands to form blankets of highly mature (compositionally and texturally) quartz arenites and some offshore siltstones and shales; classic transgressive sands overlie the Lipalian unconformity; e.g. Tapeats, Flathead (W US) and Potsdam Ss ((E US)
Under Cincinnati Mt. Simon Sandstone

As transgression continued siliciclastics diminushed in shallow offshore areas (due to coastal sequestering and coverage of source areas by water and carbonate blankets

Quartz sands and shales pass upward into limestone and dolostone; much of this is sparsely fossiliferous. HYPERSALINE conditions? North America straddling equator; carbonate banks lay N and S of equator

Typical Successions:

Parallel successions up through the Cambrian on either side of Transcontinental Arch

SW USA:  White-Inyo Mtns, California; continuous thick succession from Neoproterozoic upward into basal Cambrian siliciclastics give way to carbonates; Early Cambrian archecyathan reefs

Arizona: famous transgressive (diachronous) succession:

Tapeats Sandstone-Bright Angel Shale-Muav Limestone
EARLY PALEOZOIC LIFE: CAMBRIAN EXPLOSION
Terrestrial: No terrestrial organisms known yet, possible lichens, moss but probably barren landscapes

Marine Life:: The Ediacarian faunas were largely gone from the fossil record by Cambrian, but in last year a few Ediacaran forms have been found in Australia.  A very abrupt burst of adaptive radiation of skeletonized multicellular animals in Cambrian known as Cambrian Explosion.  10 million years almost all known phyla had appeared

Why?  a ) Geochemistry of oceans, but all skeletal mineralogies appear almost simultaneously; phosphatic, silica, calcite, aragonite

b) Coming out of sediment: need rigid skeletons to support larger bodies

c) Rise of Predators: need for skeletal protection; there is direct evidence for Cambrian predators, including 2 m long Anomalocaris

Cambrian Explosion took place in three phases:

Earliest Cambrian 544-540 Ma; low diversity faunas a few odd small tubular skeletons; conodontd (=chordates, probably vertebrates) trilobite-like trace fossils increased bioturbation

Tommotian: age of "small shellies" diverse plates, spines, hooks, rods, tubes, plus first gastropods, hyolithids, brachiopods, conodonts

Botomian-later Early Cambrian: first trilobites; diversification of arthropods and soft worms in Chengjiang fauna
 of China

Later Cambrian Faunas

Archeocyathans: sponge-like double walled cups with perforations
May be separate phylum; built reefs in symbiosis with certain algae, in tropics  but largely gone by end of early Cambrian

Sponges: siliceous hexactinellids and demosponges common in some environs

Corals: very rare Early Camb. Cothoniids; newly discovered tabulates in
Australia; some jellyfish, possible anemones

Brachiopods: both lingulids (phosphatic) and simple articulates

Mollusks: first gastropods, bivalves. Tiny nautiloid cephalopods

Echinoderms:  Carpoids (non-symmetrical)  helicoplacoids (ancestral stock) for edrioasteroids, eocrinoids);  possibly first crinoids

Arthropods: "age of trilobites" high diversity; includes tiny, eyeless agnostids, and much larger, multisegmented polymerids up to a meter long became very diverse and common; in western US find a series of abrupt extinctions followed by new diversifications from offshore ancestral stocks:
Biomeres (useful in biostratigraphy)

Other arthropods: earliest chelicerates (Sanctacaris), crustaceans, include. Ostracodes with appendages. first gooseneck barnacles;  Uniramians;(Cambropodus marine ancestors of millepedes)  Plus many bizarre forms:

Best record of these and many other groups from Middle Cambrian Burgess Shale: most famous of all Lagerstatten; Gould’s Wonderful Life
British Columbia: Canadian Rockies

Probable muddy seafloor banked up against carbonate escarpment
Rapid burial in dysoxic sediment, preservation of soft tissue as films of organic matter

Among other oddities:

Worms: Priapulids, spiny annelids: Wiwaxia

Anomalocaris large predator with "pineappple slice" mouth, swimming flukes; and "great appendages" to push stuff in mouth

Opabina: odd organims with several eyes and a "trunk",

Onychophorans (intermed between annelids and arthropods ?) Ayshea (looks quite like some moderns);  more spectacular is Hallucigenia  with spines

Pikea: early chordate-survived: conodonts also apparently vertebrate teeth; the chordates managed to survive Late Cambrian extinctions while many other more abundant groups:  Gould’s point about contingencies