The Cretaceous Period (145- to 65 million years ago) was hot and steamy. There was no ice at the poles. Global temperature is estimated to have been about 18 F warmer than today. Atmospheric carbon dioxide began a 145-million-year decline from about 2,000 ppm to the 380 ppm of today, in part, due to carbon sequestration by formation of coal deposits. Flowering plants appeared.

The North American continent was split by a sea connecting the Gulf of Mexico with the Arctic Ocean. Transgressions and regressions of this sea formed conditions ripe for coal formation similar to those in the Paleozoic Era. In Southern Arizona, the lower Cretaceous Bisbee Group, consisting of the basal Glance conglomerate, the Morita formation sandstones and mudstones, the distinctive Mural Limestone (which forms the cliffs just east of Bisbee), and the sandstones and mudstones of the Cintura Formation record the changes in sea level. Upper Cretaceous rocks, the Fort Crittenden Formation lie unconformably (representing erosion or structural change) upon the Bisbee Group. The lower Fort Crittenden is dominated by marginal wetland to deep-water lake deposits, whereas the upper Fort Crittenden is characterized by wetland to deltaic deposits. These rocks contain organic geochemical evidence of wildfires which suggest that seasonal aridity and wildfires were common occurrences.

There are no early Cretaceous rocks recognized in northern Arizona. Thick sequences of upper Cretaceous rocks were deposited on what is now the Colorado Plateau. These represent near-shore marine, coastal, and river-deposited sands, mudstone, and coal. Coal is mined from the Dakota sandstone at Black Mesa in Navajo County, AZ. This is overlain by the Mancos Shale, and several other sedimentary formations.

The Laramide orogeny of late Cretaceous to early Tertiary time (80- to 40 million years ago) built the Rocky Mountains and closed the inland Cretaceous sea. Subduction of oceanic crust under continental rocks along the west coast caused compression and uplift of the continent.

This was the time of emplacement of most of the porphyry copper deposits in the western U.S. Volcanism was extensive, and included the volcano that produced the rocks of the Tucson Mountains. (See the Tucson Mountain story).

 Dinosaurs roamed the land, including Arizona’s Sonorasaurus thompsoni, a new species of brachiosaurid dinosaur whose remains were first discovered in the Whetstone mountains by UofA graduate geology student Richard Thompson in 1994. Sonorasaurus is estimated to have been about 50 feet long and 27 feet tall, about one third of the size of other brachiosaurus. It may have been a juvenile or just a small dinosaur species. Sonorasaurus was an herbivore. Tooth gouges on its bones suggest it was killed and eaten by a larger dinosaur. A single blade-like tooth of a huge meat eater called Acrocanthosaurus was found near the bones and suggests that this was the predator that killed Sonorasaurus. You can see an exhibit dedicated to Sonorasaurus at the Arizona-Sonora Desert Museum.

The end of the Cretaceous Period saw another major extinction of life. Dinosaurs, pterosaurs, many marine reptiles, some marine invertebrates, some groups of mammals, and a few plant groups became extinct. The reasons are still controversial. We know that an asteroid impacted near Yucatan, Mexico and formed the Chicxulub crater about 65 million years ago. The impact is said to have vaporized rock into clouds of dust, that cooled temperatures, and created clouds of sulfurous gas, which may have killed plants with acid rain. The impact is also said to have deposited a thin clay layer containing iridium and strained quartz. However, the extinction occurred during an 800,000-year eruption of basalts that form the Deccan Traps in India. Volcanic eruptions can also product dust and sulfur dioxide emissions (and layers of iridium which characterize the K/T boundary). More precise dating shows that the Chicxulub impact occurred 300,000 years before the mass extinction. Evidence suggests that the extinctions occurred over a period of several million years.

Cretaceous Trivia:

The white cliffs of Dover, England are Cretaceous age chalk deposits.

Paul Spur, a rail stop between Bisbee and Douglas exists because Mural limestone was mined for smelter flux.

Hills carved from Cretaceous beds east of Bisbee. View is northward across Mule Gulch. The prominent white band is the upper member of the Mural limestone, forming the top of Mural Hill on the left and showing the dislocation due to the Mexican Canyon fault. Cochise County, Arizona. December 1, 1902. Plate 9-B in U.S. Geological Survey. Professional paper 21. 1904, figure 7 in U.S. Geological Survey Folio 112. 1904.

See more of geologic history:

Precambrian, Early Paleozoic, Late Paleozoic, Triassic, Jurassic

Arizona Geological History 7: The Cenozoic Era

References:

Dickinson, W.R., et al., 1989, Cretaceous Strata of Southern Arizona, in Geologic Evolution of Arizona, Arizona Geological Society Digest 17.

Finkelstein, D.B, et al., 2005, Wildfires and seasonal aridity recorded in Late Cretaceous strata from south-eastern Arizona, USA, Sedimentology, Volume 52, Issue 3 , Pages587 – 599, International Association of Sedimentologists

Krantz, R.W., 1989, Laramide Structures of Arizona, in Geologic Evolution of Arizona, Arizona Geological Society Digest 17.

Nations, J.D., 1989, Cretaceous History of Northeastern and East-Central Arizona, in Geologic Evolution of Arizona, Arizona Geological Society Digest 17.

Arizona warms from ice age, becomes tropical again, gets flooded by the ocean, suffers another ice age, warms up, makes coal, and suffers a major extinction of life.

In this chapter we will complete the Paleozoic Era with four periods: Devonian (416- to 359 million years ago), Mississippian (359-318 mya), Pennsylvanian (318- 299 mya), and the Permian (299-251 mya). In the European classification, the Mississippian and Pennsylvanian are, together, called the Carboniferous period because it was during this time that most coal deposits were formed.

After recovery from the Ordovician ice age (about 440 mya), Arizona was apparently a highland on the southwest edge of a continental mass, about 30 degrees south of the equator. I say apparently, because there is no record from the Silurian period (444- to 416 mya ), so Arizona may have been dry land that was subject to erosion.

During the last four periods of the Paleozoic, Arizona was mainly under water. The rocks deposited during this time represent deposition on a continental shelf environment. There were several episodes of transgression (encroaching) and regression of the sea from the west. Only what is now the northeastern corner of the state remained above sea level for most of the time. The rise and fall of the sea was due to both tectonic shifting of land and changes in water volume from the glacial epochs.

Limestone was the principal rock deposited during this time along with relatively minor shale and sandstones. All the formations contain fossils. These limestones currently make up most of the mountain ranges south of Tucson.

Mississippian rocks rest unconformably (not at the same angle or with evidence of erosion) on Devonian and older rocks. This means that there was some tectonic adjustment and erosion between the two Periods. (And by the way, the geologic Periods are usually defined by their distinct fossil assemblages). The principal formation of the Devonian is called the Martin Formation with type area in Bisbee. The principal Mississippian limestone is called the Redwall Limestone near the Grand Canyon and the Escabrosa Limestone in southern Arizona. Kartchner caverns are in the Escabrosa Limestone, but the caves formed recently.

Pennsylvanian and Permian rocks represent complex cycles of transgression/regression by the sea, caused by changes in water volume due to glacial epochs, and by tectonic uplift and sinking of the continent. This tectonic shifting was the result of the collision of Gondwana on the south with Pangea on the north. Carbonate rocks dominate in the northwest and southeast, while sandstones and conglomerates dominate in central and northeast Arizona.

 Most coal deposits developed during the Carboniferous period. Arizona caught some of this in the northeastern part of the state. Coal is mostly carbon accumulations from fossil plant material deposited in swamps so devoid of oxygen that bacteria and other critters couldn’t survive to feed on their remains. This implies that climate was warm and wet, and that the cyclic transgressions/regressions of the sea were relatively quick enough to bury the swamps before the luxuriant plant life could be destroyed.

Arizona coal was formed about 300 million years ago. It is mined in Navajo county, and, according to the Arizona Department of Mines and Mineral Resources, ranks second only to copper in economic importance.

Worldwide coal formation stripped the atmosphere of carbon dioxide. Beginning in mid- Devonian time, about 380 mya, through early Mississippian time, atmospheric carbon dioxide dropped from around 4,000 ppm to near current levels of 400 ppm by 340 million years ago. Temperature, however, remained high (about 68 F world average vs 57 F today). But near the Pennsylvania-Permian boundary time, about 270 million years ago, the planet was plunged into another ice age. Note the 70-million-year gap between lowered carbon dioxide and decreased temperature. By the end of the Permian, temperatures rose again to an average of about 63 F, soon followed by a rise in carbon dioxide to just under 3,000 ppm. (Rising temperature causes more carbon dioxide to be exsolved from the oceans.) Volcanism contributed to the rising carbon dioxide.

The first known land vertebrates, amphibians, appeared in late Paleozoic time. Devonian rocks contain fossils of amphibians called stegocephalians (roofed head) because of flat, broad heads. Most were one- to two inches long, but later forms became as large as a crocodile and most were probably carnivorous judging by the teeth.

Reptile fossils appear in Pennsylvanian rocks. The first were small like amphibians, but later Permian reptiles got up to eight feet long. One group, the Therapsids, had teeth differentiated into incisors, canines, and molars similar to present-day mammals.

The Permian ended with a mass extinction in which about 90% of species disappeared, including marine fauna, plants, and terrestrial animals. The reason for this extinction is unknown although there are many speculative theories. This extinction happened over a period of several million years and is coincident with the coalescing of continents and extensive volcanism.

When Pangea and Gondwana collided is reduced marine habitats and brought deep, oxygen-poor ocean water to near surface environments. Major volcanism, in what is now Siberia, lasted for about one million years and annually spewed billions of tons of sulfur dioxide and carbon dioxide into the atmosphere. These two events are probably contributory to the extinctions.

But, with the dawning of the new Mesozoic era, life rebounded and became more diverse and more robust.

PHOTO: Omphalotrochus (snail) from the Permian Colina formation, collected about 2 miles southeast of the Tombstone airport. Notice also the pits made by rain drops differentially eroding the limestone.

See Chapter 1: the Precambrian, and Chapter 2, the Cambrian and Ordovician periods.

Chapter 4: the Triassic Period

President Obama says he favors “Clean Coal.” Coal produces 49% of the electricity generated in the United States. But burning coal puts carbon dioxide into the atmosphere and that scares the politically correct and the carbon cultists, including Barack Obama and John McCain. Their solution is to capture carbon dioxide, transport it to a storage site, and bury it. That comes at considerable cost in both dollars and in additional coal burned to produce the energy needed for the process. But “clean coal” is now the political panacea, even though there is no evidence that CO₂ emissions significantly affect temperature. In fact, additional atmospheric CO₂ would be beneficial by making plant life more robust.

Coal-fired plants are much cleaner than they were in 1970 when Congress passed the Clean Air Act Amendments. Since that time, coal-fired electrical generation increased by 180% while SO₂ emissions decreased by 80% and NO_x decreased by 70% (in pounds per megawatt-hour) according to the EPA. According to the Department of Energy’s National Energy Technology Laboratory, a new pulverized coal plant (operating at lower, “subcritical” temperatures and pressures) reduces the emission of NO_x by 86 percent, SO₂ by 98 percent, and particulate matter by 99.8 percent, as compared with a similar plant having no pollution controls.

Carbon Capture Technology

The most promising technology for CO₂ capture is called Integrated Gasification Combined Cycle. But the cost of building a power plant with this technology to capture 90% of the CO₂ generated is 47% higher than that for a traditional power plant, according to a 2006 study by the EPA.

According to the Department of Energy (DOE), existing capture technologies are not cost-effective when considered in the context of sequestering CO₂ from power plants. Most power plants and other large point sources use air-fired combustors, a process that exhausts CO₂ diluted with nitrogen. Flue gas from coal-fired power plants contains 10%-12% CO₂ by volume, while flue gas from natural gas combined cycle plants contains only 3%-6% CO₂. For effective carbon sequestration, the CO₂ in these exhaust gases must be concentrated and separated.

CO₂ is currently recovered from combustion exhaust by using amine absorbers and cryogenic coolers. The cost of CO₂ capture using current technology is on the order of $150 per ton of carbon – much too high for carbon emissions reduction applications according to DOE. Analysis performed by SFA Pacific, Inc. indicates that adding existing technologies for CO₂ capture to an electricity generation process could increase the cost of electricity by 2.5 cents- to 4 cents/kWh depending on the type of process. That would about double the cost of natural gas and coal produced electricity, making it almost as expensive as electricity produced from wind energy.

The EPA, which usually underestimates costs, says that capturing CO₂ imposes a cost of about $24 per ton, much less than DOE. Even at that lower estimate, however, the largest U.S. power plant which emits about 25 million tons of CO₂ annually, would incur an extra cost of $600 million per year. For all U.S. coal-fired power plants, which emit a total of more than 2.2 billion tons annually, the cost would be $52 billion per year. Passing along the capital and operating costs to consumers would raise electricity prices by almost 40% according to the EPA.

Carbon Storage

The capture cost is only part of the story. The gas must be compressed, transported, and buried.

Where would it be stored? Several types of geological reservoirs theoretically provide sufficient storage capacity. According to the National Energy Technology Laboratory (NETL), “more than 88 billion metric tons of geologic storage potential exists in 9,667 oil and gas reservoirs distributed over 27 states and 3 Canadian provinces.”

Unmineable coal seams can be drilled to collect the methane for use in energy applications. Once the methane is recovered, CO₂ could be pumped into the wells, where it is preferentially stored in the coal, releasing additional methane. “More than 180 billion metric tons of CO₂ sequestration potential exists in unmineable coal seams…distributed over 24 states and 3 provinces,” according to NETL.

Deep saline formations could provide another storage option. An analysis by the Massachusetts Institute of Technology in 2006 showed that wells deep underground consisting of porous rock, such as limestone or sandstone, saturated with saltwater, would form an effective trap for injected CO₂. Geologically, over time, some CO₂ would react with rock minerals to form solid carbonates, further immobilizing it. Deep saline aquifers could potentially store between 3,300 to more than 12,200 billion metric tons of CO₂, according to NETL.

Pipe Dreams

In theory, there appears to be plenty of potential underground storage for captured carbon dioxide, but the theoretical is different from the practical. Location relative to the power plants makes much of these reservoirs impractical to actually use.

Getting the carbon dioxide from the power plants to the storage areas is problematic and expensive. And, of course, Greenie extremists are likely to oppose construction of the many high-pressure pipelines that would be required. A report from the nonpartisan Congressional Research Service (CRS), entitled “Pipelines for Carbon Dioxide (CO₂) Control: Network Needs and Cost Uncertainties” (Jan. 10, 2008) shows several hypothetical examples of CO₂ pipelines running from the 11 largest CO₂ emitters in Indiana, Kentucky, Maryland, Michigan, Ohio, Pennsylvania, and West Virginia — all coal-fired electric power plants emitting over 9 million metric tons of CO₂ annually — to potential regional sequestration sites.

In the least expensive scenario, it would take an estimated $66 million to build pipelines each with a capacity of 10 million tons of CO₂ annually from the 11 plants to a nearby geological formation called Rose Run. Unfortunately, as the CRS points out, Rose Run may not have the capacity to accept all the CO₂ produced, and injecting pressurized CO₂ may cause minor earthquakes. While the earthquakes may create additional capacity for CO₂, they may also produce permanent conduits for leakage.

Unmineable coal beds in the same general area as Rose Run are another option but their capacity falls far short of Rose Run’s.

The 10 largest local depleted oil and gas fields have an average capacity of 251 million tons of CO₂, but the 30-year CO₂ output of the 11 plants is estimated to range from 270 million tons to 491 million tons at current emission levels. Not only is their capacity lacking, but the oil and gas fields pose a significant risk of leaking.

A final option considered by CRS is piping the CO₂ hundreds of miles west to a geological area in Michigan, Indiana and western Ohio known as the Mt. Simon formation. The average cost of building each pipeline would be $150 million.

That’s a bargain, however, compared to a geographically disadvantaged area like North Carolina. A Duke University study estimated it would cost $5 billion to transport CO₂ from North Carolina’s electric utilities to sequestration sites in other states.

The CRS report emphasized an August 2007 decision by the Minnesota Public Utilities Commission to reject a 450-mile pipeline to a Canadian oil field costing over $635 million as “not in the public interest.”

According to the Business & Media Institute, Stanford Professor Ken Caldeira, an IPCC Report Author, estimates that the annual cost to capture carbon from power plants worldwide, will be $800 billion.

Another study by Xina Xie, University of Wyoming, and Michael Economides, University of Texus, The Impact of Carbon Geological Sequestration, says that carbon capture sequestration for just Kyoto Protocol-type CO₂ cuts in the U.S. would require the drilling of 161,429 injection wells by 2030 at a cost of 1.61 trillion dollars — and there’s no guarantee that the CO₂ would stay sequestered, much less accomplish anything for the climate.

Boon or Boondoggle

While carbon capture and storage may be technologically possible, it makes no sense either economically or scientifically. It is a solution seeking a problem; it is utter wastefulness. But bureaucrats, politically correct and stupid politicians, and industry, will suck up to the trough of public money to promote these wasteful schemes in an attempt to quell the phantom menace of carbon dioxide. Raising the cost of electricity 50% to 100% should make us feel all warm and fuzzy since “clean coal” will assuage our carbon guilt.

And just to make it interesting, the Center for Biological Diversity has just formed a new law institute in San Francisco with the goal of stopping all electrical generation from use of fossil fuels. I hope they will not be hypocrites and actually use fossil-fuel-produced electricity during their campaign.