1. During the late Proterozoic, the global supercontinent began to break up so that by early Cambrian time, all the continental fragments were surrounded by slowly subsiding passive margins.

2. Information gathered from rock exposures, subsurface drilling and geophysical measurements allow geologist to reconstruct how the continents may have looked during the Early Paleozoic.

3. The Cambrian continents were barren and devoid of all vegetation. The lifeless, barren landscape was blanketed by blowing sand, silt and clay. Cratons were low in relief and characterized by broad, gentle warping of the crust.

4. Extensive sequences of Cambrian marine sediments (sandstone, shale & fossil-bearing limestone) indicate that the continents were at times flooded by great shallow seaways. North America was almost completely drowned in Late Cambrian time by what came to be known as the Sauk transgression.

5. Continental interiors experienced deposition of thin and discontinuous marine sequences within shallow basins. The subsiding margins of continents, on the other hand, accumulated thick packages of shallow marine sediment.

6. Mature quartz sandstone derived from deep continental weathering and wind erosion, were flooded by invading seas and reworked into broad sheet-like deposits. Extensive marine deposits indicate that the Cambrian seas flooded a barren continental surface of very low relief.

7. Paleomagnetic data indicate that North America was near the equator during the Early Paleozoic, suggesting a warm climate that fostered the proliferation of shallow-water marine life (invertebrates such as trilobites, archeosyathids and bryozoans).

8. The occurrence of Cambrian oolites, shelly limestone and local evaporite deposits suggest a warm climate for North America during this period.

9. By Late Cambrian time, carbonate-secreting organisms took over the vast shallow epicontinental seaways and deposited great quantities of limestone throughout the North American craton.

1. Figure 10.2: During the late Proterozoic, the global supercontinent (Rodinia) began to break up so that by early Cambrian time, all the continental fragments were surrounded by slowly subsiding passive margins.

2. Figures 10.3, 10.4 & 10.7: The North American Phanerozoic Craton displays profound thickening of strata around the margins of the continent. Cambrian strata dramatically thicken from the craton interior towards the margins.

3. Information being obtained today from surface outcrops, deep drilling and geophysical measurements indicate that during the Cambrian, the North American craton was characterized by broad, gentle warps consisting of raised areas (arches) and depressed areas (basins). These structures may have been formed by:

a) flexing of the craton in response to thermal subsidence of rifted continental margins.

b) compression of the craton margins by colliding island arcs and continents.

4. Basins and arches are important:

a) in accumulating oil and gas

b) isolating bodies of water that, when evaporated, precipitate salts and pure limestone.

5. Figure 10.7: The transcontinental arch is an extension of the Canadian Shield and consists of a long belt of Cryptozoic rock extending from Lake Superior to Arizona. Cambrian sandstone lap unconformably against the margins of the transcontinental arch but are entirely missing on the arch itself, indicting that the arch stood high above the Cambrian shallow seas that flooded most of continent during this period.

6. Figure 10.8: The abundant Cambrian sandstone bordering the transcontinental arch suggest that the arch was a high feature and a major sediment source for the shallow sea that lapped against its margins.

7. The crest of the transcontinental arch is devoid of Cambrian strata, but is overlain by younger (post-Cambrian) rocks. These post-Cambrian rocks reflect marine sedimentary layers that are punctuated by unconformities, suggesting that the arch experienced periodic flooding and sediment deposition alternating with exposure and erosion. This indicates that the arch underwent several spasms of warping after Cambrian times.

1. Figure 10.11: Compared with basins, arches typically contain thinner stratigraphic sequences interrupted by many unconformities, indicating that the arches are areas of little to no subsidence and instead prone to repeated uplifts and erosion. Basins, on the other hand, are areas of subsidence that often accumulate great thicknesses of sediments.

2. Differential warping caused thickening of strata in basins and thinning over arches. Unconformities on arches indicate periods of subareal exposure and erosion when the arches stood as islands protruding above the shallow continental seas.

1. Figure 10.9: By the end of Cambrian time, most of the North American continent was flooded by the vast inland Sauk Sea during the Sauk Transgression. This transgression helped redistribute extensive amounts of clastic sediments throughout the craton.

2. Figures 10.23 & 10.8: Shallow-water sandstone and limestone, evident today around southeastern U.S., were deposited extensively on the North American Craton during the Cambrian.

1. Cambrian cratonic sandstone ranks among the most mature in the world.

2. Erosion of the cratonic surface over the previous half a billion years created a huge volume of clastic material available for redistribution by wind, rivers and the invading shallow seas.

3. Figure 8.14: Quartz grains that were extensively sorted and rounded during long periods of erosion and reworking were afterwards spread throughout the Cambrian craton as thin, immense sheets by wind action and the invading shallow seas.

4. The extensive sorting exhibited by Cambrian sandstone indicate that the primary agents of deposition were wind, surf and vigorous marine currents. Wind played a dominant role in the abrasion of sand grains.

5. Figure 10.15: Cambrian sandstone was deposited in a variety of environments as indicated by different types of fossils and ripple marks preserved in the rock record. Sandstone containing marine fossils indicate final deposition in shallow seas. Cambrian sandstone without fossils and displaying very low, asymmetrical ripples indicate wind deposition. Other types of ripple marks in non-fossil Cambrian sandstone indicate deposition by rivers.

6. Cross stratification in Cambrian sandstone helps geologists determine the direction of wind or water current at the time of sediment deposition.

7. Based on various lines of evidence preserved in the rock record, Cambrian sandstone appears to have first been distributed by wind and rivers. The Sauk transgression that followed caused marine reworking of much of that sand.

1. Figure 10.9: The North American Craton gradually became submerged during the Late Cambrian Sauk transgression until eventually, so little land remained exposed that deposition of terrigenous clastic material virtually ceased.

2. During Late Cambrian time, carbonate rocks had been forming already for millions of years in areas of the craton margin not affected by clastic sedimentation. However when most of the land area became submerged and the sources of clastic sediments were choked off, carbonate deposition became extensive throughout the shallow Sauk Sea.

3. The rock record basically indicates that the Sauk Sea was warm and shallow.

4. Flooding by the Sauk Sea continued into the Early Ordovician. Much of the Sauk limestone was deposited in agitated, oxygenated clear water as evidenced by the abundant marine invertebrate fossils contained in them.

5. Sauk limestone deposited during the Early Ordovician often contain fragmented fossils, scattered quartz grains, carbonate pebbles and ripple marks indicating considerable water agitation during deposition. The presence of spherical, sand-sized carbonate grains called oolites further indicate significant rolling and agitation in warm, carbonate rich shallow waters by extensive tidal action.

6. Not all regions of the Sauk Sea, however, experienced significant agitation. Over the central craton, sparse fossil remains, complete dolomitization and scattered evidence of evaporate minerals indicate areas of restricted circulation and high evaporation of seawater within semi-isolated basins.

7. There were also areas of the sea floor where deposition was slow and chemical reactions sluggish as evidenced by the presence of the mineral glauconite in some Late Cambrian and Early Ordovician sediments. Glauconite only forms in waters where sediment deposition is very slow, thus allowing sluggish chemical reactions to convert clays and other minerals to this green-colored silicate mineral.

1. Figure 10.28: Marine sediments deposited in the ancient Sauk sea indicate long periods of fair weather characterized by slow sedimentation, steady wave action, burrowing by marine organisms and growth of the mineral glauconite. Some of these sediments, however, show evidence of infrequent, violent storm events that occasionally interrupted these fair-weather processes.

2. Figure 10.26: Near Baraboo Wisconsin, there are exposures of coarse Cambrian conglomerates and well-rounded boulders interstratified with sandstone adjacent to cliffs of Precambrian rock. These Precambrian rock cliffs are interpreted to be ancient islands that stood high above the Cambrian Sea and were the source of the conglomerates and boulders. The rapid dumping of pebbles and boulders in otherwise relatively calm water may have resulted from violent Cambrian storms.

3. In other places, there is evidence of shelly layers formed by the winnowing away of sand by strong currents and wave action. These shelly layers formed in water depths not typically affected by waves and currents. This suggests that occasional violent storms were strong enough to generate the deep-water currents that produced the shelly layers.

4. Figure 10.27: There are also occurrences of isolated Cambrian sedimentary layers containing structures resembling symmetrical wave-formed ripples or hummocky stratification. These features may have been formed by unusually large waves that could stir the sea bottom briefly at depths greater than the depths normally reached by fair-weather waves.

5. Figure 10.25: These occasional Cambrian, Early Ordovician storms are analogous to hurricanes that occur today striking North America.

6. The Sauk Sea was in a tropical location and therefore one would expect episodic, violent hurricanes to churn up the waters and cause extensive wave damage.

7. It is also suggested that during the Cambrian, the moon was much closer to the earth than it is today. The stronger gravitational pull by the moon may have contributed to the stronger tidal currents and storm-driven currents evident in Cambrian rocks.