The soil temperature survey is an inexpensive exploration method in groundwater and geothermal resource investigations. In its simplest form, temperatures measured in shallow holes are analyzed to deduce variations in material properties. Typical interpretation schemes are based on simple, one‐layer solutions to the Fourier conduction equation using the annual solar cycle as a surface heat source. We present a solution to the more complicated two‐layer problem that can be computed using inexpensive personal computers and spreadsheet software. The most demanding mathematical requirement is the ability to manipulate a [Formula: see text] matrix. Testing the solution over a range of thermal diffusivity values expected in common soils and rocks reveals that the solution is very sensitive to variations in the thermal diffusivity of the surface layer and to the depth of the interface with the lower layer. When the boundary to the lower layer is less than about 10 m deep, a soil temperature survey is expected to be sensitive to the diffusivity variations in the lower layer. Because variations in shallow thermal properties often can be significant, this two‐layer method should be useful in areas with distinct shallow layering, (e.g., where there is a shallow water table or a thin soil layer).
Sea level changes are related to both climatic variations and tectonic movements. The fractal dimensions of several sea level curves were compared to a modern climatic fractal dimension of 1.26 established for annual precipitation records. A similar fractal dimension (1.22) based on δ( 18 O/ 16 O) in deep‐sea sediments has been suggested to characterize climatic change during the past 2 m.y. Our analysis indicates that sea level changes over the past 150,000 to 250,000 years also exhibit comparable fractal dimensions. Sea level changes for periods longer than about 30 m.y. are found to produce fractal dimensions closer to unity and Missourian (Late Pennsylvanian) sea level changes yield a fractal dimension of 1.41. The fact that these sea level curves all possess fractal dimensions less than 1.5 indicates that sea level changes exhibit nonperiodic, long‐run persistence. The different fractal dimensions calculated for the various time periods could be the result of a characteristic overprinting of the sediment record by prevailing processes during deposition. For example, during the Quaternary, glacio‐eustatic sea level changes correlate well with the present climatic signature. During the Missourian, however, mechanisms such as plate reorganization may have dominated, resulting in a significantly different fractal dimension.
Research Article| December 01, 1987 Origin of cratonic basins George deV. Klein; George deV. Klein 1Department of Geology, University of Illinois at Urbana-Champaign 245 Natural History Building, 1301 W. Green Street, Urbana, Illinois 61801-2999 Search for other works by this author on: GSW Google Scholar Albert T. Hsui Albert T. Hsui 1Department of Geology, University of Illinois at Urbana-Champaign 245 Natural History Building, 1301 W. Green Street, Urbana, Illinois 61801-2999 Search for other works by this author on: GSW Google Scholar Author and Article Information George deV. Klein 1Department of Geology, University of Illinois at Urbana-Champaign 245 Natural History Building, 1301 W. Green Street, Urbana, Illinois 61801-2999 Albert T. Hsui 1Department of Geology, University of Illinois at Urbana-Champaign 245 Natural History Building, 1301 W. Green Street, Urbana, Illinois 61801-2999 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1987) 15 (12): 1094–1098. https://doi.org/10.1130/0091-7613(1987)15<1094:OOCB>2.0.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation George deV. Klein, Albert T. Hsui; Origin of cratonic basins. Geology 1987;; 15 (12): 1094–1098. doi: https://doi.org/10.1130/0091-7613(1987)15<1094:OOCB>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Tectonic subsidence curves show that the Illinois, Michigan, and Williston basins formed by initial fault-controlled mechanical subsidence during rifting and by subsequent thermal subsidence. Thermal subsidence began around 525 Ma in the Illinois Basin, 520–460 Ma in the Michigan Basin, and 530–500 Ma in the Williston Basin. In the Illinois Basin, a second subsidence episode (middle Mississippian through Early Permian) was caused by flexural foreland subsidence in response to the Alleghanian-Hercynian orogeny. Resurgent Permian rifting in the Illinois Basin is inferred because of intrusion of well-dated Permian alnoites; such intrusive rocks are normally associated with rifting processes.The process of formation of these cratonic basins remains controversial. Past workers have suggested mantle phase changes at the base of the crust, mechanical subsidence in response to isostatically uncompensated excess mass following igneous intrusions, intrusion of mantle plumes into the crust, or regional thermal metamorphic events as causes of basin initiation. Cratonic basins of North America, Europe, Africa, and South America share common ages of formation (around 550 to 500 Ma), histories of sediment accumulation, temporal volume changes of sediment fills, and common dates of interregional unconformities. Their common date of formation suggests initiation of cratonic basins in response to breakup of a late Precambrian super-continent. This supercontinent acted as a heat lens that caused partial melting of the lower crust and upper mantle followed by emplacement of anorogenic granites during extensional tectonics in response to supercontinent breakup. Intrusion of anorogenic granites and other partially melted intrusive rocks weakened continental lithosphere, thus providing a zone of localized regional stretching and permitting formation of cratonic basins almost simultaneously over sites of intrusion of these anorogenic granites and other partially melted intrusive rocks. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
The effects of variable viscosity on flow dynamics within spherical shells are investigated using a finite-element thermal convection model, and preliminary result for cases with relatively low Rayleigh numbers and small viscosity contrasts are reported. These results demonstrate some general effects of viscosity variation on mantle dynamics, and, in particular, the generation of toroidal energy. Since lateral viscosity variations are necessary in the generation of toroidal motion in a thermally driven convective system, it is not surprising our results show that flows with greater viscosity contrasts produce greater amounts óf toroidal energy. Our preliminary study further shows that solutions become more time-dependent as viscosity contrasts increase. Increasing the Rayleigh number is also found to increase the magnitude of toroidal energy. Internal heating, on the other hand, appears to lead to less toroidal energy compared wth bottom heating because it tends to produce a thermally more uniform interior and thus smaller viscosity variations.
