Phanerozoic

Unconformity-Related Deposits. Deposits of the unconformity-related type occur spatially close to significant unconformities. These deposits usually developed during the period about 1800—800 million years ago in intracratonic basins. Deposits also developed during Phanerozoic time. Examples of unconformity-related deposits include the ore bodies at Cluff Lake, Key Lake, and Rabbit Lake in northern Saskatchewan, Canada, and those in the Alligator Rivers area in northern AustraHa (12). 

High and low stands of sea level are directly recorded as sedimentary coastal onlap sequences and as erosional terraces. These records are complicated in regions of crustal instability, and the rate and nature of crustal deformation determines whether evidence of short-term or long-term sea-level fluctuations are preserved and how easily this evidence is interpreted. Because continental basement warps and fractures through time, and because evidence of sea level is erased by erosion, the interpretation of this evidence to produce sea-level curves for the Phanerozoic has been a subject of considerable debate. 

Fischer, A. G. (1983). The two Phanerozoic supercycles. In "Catastrophies in Earth History The New Uniformitarianism" (W. Berggren and J. Van Couvering, eds), pp. 129-150. Princeton University Press, Princeton, New Jersey. 

Holland, H. D. (1974). Marine evaporites and the composition of sea water during the Phanerozoic. In "Studies in Paleo-oceanography (W. W. Hay, ed.), pp. 187-192. Society of Economic Paleontologists and Mineralogists, Tulsa, Oklahoma, Special Publication 20. 

Berner, R, A. (1990). Atmospheric carbon dioxide levels over Phanerozoic time. Science, 249, 1382-1386. 

Holland, H.D., Horita, J. and Seyfried, W.E. Jr. (1996) On the seawater variations in the composition of Phanerozoic marine potash evaporites. Geology, 24, 993-996. 

Frakes, L.A., Francis, J.E. and Syktus, J.I. (1992) Climate Modes of the Phanerozoic. Cambridge University Press, 274 pp. 

Reymer A, Schubert G (1984) Phanerozoic addition rates to the continental cmst and crastal growth. Tectonics 3 63-77... 

Dickson, J.A.D. (2002). Fossil echinoderms as monitor of the Mg/Ca ratio of phanerozoic oceans. 

Parrish, J. T. 1985. Latitudinal distribution of land and shelf and absorbed solar radiation during the Phanerozoic, Open-File Report 85-31. Washington, D.C. U.S. Department of the Interior, Geological Survey. 

Elliott, C.G. 1996. Phanerozoic deformation in the stable craton, Manitoba, Canada. Geology, 24, 909-912. 

Let us first introduce some important definitions with the help of some simple mathematical concepts. Critical aspects of the evolution of a geological system, e.g., the mantle, the ocean, the Phanerozoic clastic sediments,..., can often be adequately described with a limited set of geochemical variables. These variables, which are typically concentrations, concentration ratios and isotope compositions, evolve in response to change in some parameters, such as the volume of continental crust or the release of carbon dioxide in the atmosphere. We assume that one such variable, which we label/ is a function of time and other geochemical parameters. The rate of change in / per unit time can be written... 

Michard, A., Gurriet, P., Soudan, M. Albarede, F. (1985). Nd isotopes in French Phanerozoic shales external vs. internal aspects of crustal evolution. Geochim. Cosmochim. Acta, 49, 601-10. 

C02 is a major factor in the cycles that built up our mineral resources. Fossil fuels developed over several hundred million years during the Phanerozoic era. There was abundant life for about 600 million years. 

Figure 12. Models and data showing variations in the concentration of Ca in the oceans over Phanerozoic time. Figure adapted from Horita et al. (2002), who used the mineralogy of evaporite deposits to infer the values shown as filled circles and bars.

Horita J, Zimmermann H, Holland HD (2002) Chemical evolution of seawater during the Phanerozoic implications from the record of marine evaporates. Geochim Cosmochim Acta 66 3733—3756 Inghram MG, Brown H, Patterson C, Hess DC (1950) The branching ratio of K-40 radioactive decay. Phys Rev 80 916-917... 

As shown in Figure 17.7, the volume of evaporites in the rock record increases from the Proterozoic (2.6 to 0.6 bybp) into the Phanerozoic (0.6 bybp to present), although... 

Timeiine of marine evaporite deposition during the Phanerozoic. Shown are the volumes of NaCI (halite, dark line) and CaS04 (gypsum and anhydrite, dashed line) deposited over time in km . The arrows mark the current volumes of NaCi and CaS04 contained in modern ocean water. These are approximately 1.8 x 10 and 9 x 10 km , respectively. Source After Holser, W. T. (1984). Patterns of Change in Earth Evolution, Springer, pp. 123-143. 

The ancient evaporites of the Phanerozoic eon were deposited at rates as fest as 100 m per lOOOy. These rapid rates are thought to have been caused by a lowering of sea level associated with tectonic activity and glaciation. Some of the largest of the salt giants are the Messinian evaporites that formed in the Mediterranean Sea during the late Miocene epoch, 5.5 to 6.5mybp. 

Improvements in analytical techniques have made possible reconstruction of ancient seawater composition from fluid inclusion trapped in marine halites. This has forced marine chemists to accept that the major ion composition has changed significantly— at least over the past 500 million years. Since marine halites older than 500 million years are rare, little is known about the major ion composition of seawater prior to the Phanerozoic eon. Thus, current modeling effiarts are directed at simulating changes in seawater composition over the Phanerozoic. 

Additional material on this subject is provided in the supplemental information for Chapter 25.4 that is available online at http //elsevierdirect.eom/companions/9780120885305. Key topics covered are the role of tectonism in the geologic carbon cycle and how the evolution of pelagic calcifiers in the Phanerozoic led to the development of feedbacks, some stabilizing and some destabilizing, that act on the atmospheric COj reservoir. Also included is a short summary of how the global carbon cycle interacts with the atmospheric O2 and sulfur cycles. 

The kinetic interpretation of the chemistry of oceanic waters (kinetics of inputs of primary constituents interactions between biologic and mixing cycles) leads to the development of steady state models, in which the relatively constant chemistry of seawater in the recent past (i.e., Phanerozoic cf. Rubey, 1951) represents a condition of kinetic equilibrium among the dominant processes. In a system at... 

---