A program that constructs geologic cross sections has been linked to a set of routines that permit the user to balance the section interactively as it is constructed. This ability raises important issues for the process of section construction. The present procedure constructs the section first and balances it after the entire section is complete. Although interactive construction and balancing can be done by hand, the task is slow, so it is not a common practice. Drastically cutting the time requires for this procedure opens the way for it to become a standard method. However, the procedure is only possible if the component contains a pin line. This study explores the nature and method of locating such pin lines. The authors also discuss under what conditions, if any, a section should be balanced before construction is completed. Generally, interactive section construction and restoration work best if the deformational sequence is known. Otherwise, the geologist may correct features that appear to be inaccurate, such as fault trajectories with dip angles unacceptably steep, but which in fact may be the product of break-back or fold-first sequences.
Blind thrusts are structures which at no time in their history broke the erosion surface and along which displacement progressively changes upwards. Faults of the stiff layer along which displacement progressively decreases to zero (tip) are one prominent type of blind thrust structure. Shortening above such tips is accommodated entirely by folding whereas shortening below the tip is partitioned between folding and faulting. For these types of faults it is possible to determine the original length of the stiff layer for balancing purposes. A systematic methodology for line length and area restoration is outlined for determining blind thrust geometry. Application of the methodology is particularly suitable for use with microcomputers. If the folded form of the cover is known along with the position of the fault and its tip, then it is possible to locate hanging and footwall cutoffs. If the fault trajectory, tip, and a single hanging wall footwall cutoff pair are known, then the folded form of the cover layer can be determined. In these constructions it is necessary to specify pin lines for balancing purposes. These pin lines may or may not have a zero displacement gradient, depending upon the amount of simple shear deformation. Examples aremore » given from both Laramide structures of the western USA and the Appalachians.« less
A structural interpretation of a part of the central and northern Appalachian foreland, uses the correlation of mechanical twinning, solution cleavage, crenulation cleavage, pencils, joints, and deformed fossils. Such a correlation suggests that within the central Appalachians, the Alleghanian orogeny consists of two major phases: a deformation possibly as old as Pennsylvanian, herein called the Lackawanna phase, and a second deformation, termed the Main phase, which is Permian or younger in age. The Lackawanna phase affects mainly the eastern parts of the foreland, such as the Hudson River Valley and Pocono Plateau, while the Main phase affects most of the Valley and Ridge and Alleghany Plateau. The Lackawanna phase is interpreted as the product of strike-slip motion possibly between the Avalon microcontinent and North America. The Main phase may record the final convergence of Africa against North America and its accredited microcontinents. End_of_Article - Last_Page 1168------------
This paper presents a structural interpretation of a part of the central and northern Appalachian foreland using the correlation in orientation of such deformation features as mechanical twins, solution cleavage, crenulation cleavage, pencils, joints, and deformed fossils. Such a correlation suggests that, within the central Appalachians, the Alleghanian orogeny consists of two major phases: a deformation possibly as old as Pennsylvanian, herein called the Lackawanna phase, and a second deformation, termed the Main phase of Permian or younger age. Effects of the Lackawanna phase deformation are found mainly in the Hudson River Valley and Pocono plateau, while effects in the...
Includes 14 chapters on the Appalachian orogen, 15 of the Ouachita orogen, and a chapter on the connection between them beneath the eastern Gulf Coastal Plain. The Appalachian chapters synthesize the geologic development of the orogen by tectonostratigraphic intervals (pre-orogenic, Taconic, Acadian, Alleghanian, and post-Alleghanian), and also treat Paleozoic paleontologic control, regional geophysics, thermal history of the crystalline terranes, parts of the orogen buried beneath the Atlantic and eastern Gulf coastal plains, regional geomorphology, mineral and energy resources; an integration chapter also is included. The Ouachita chapters cover physical stratigraphy and biostratigraphy of the Paleozoic rocks, structural geology, a synthesis of the subsurface geology beneath the western Gulf Coastal Plain, a review of the mineral and energy resources, regional geophysics, and a tectonic synthesis. Twelve excellent plates provide four-color geologic maps, structural cross sections, tectonic syntheses, and geophysical maps; a black-and-white synthesis of Appalachian mineral deposits, and a reflection seismic cross section.
Research Article| April 01, 1989 Construction of geological cross sections: Techniques, assumptions, and methods Peter A. Geiser; Peter A. Geiser 1Department of Geology, University of Connecticut, Storrs, Connecticut 06268 Search for other works by this author on: GSW Google Scholar Steven E. Boyer Steven E. Boyer 2Standard Oil Production Co., Technical Services Division, Dallas, Texas 75340 Search for other works by this author on: GSW Google Scholar Author and Article Information Peter A. Geiser 1Department of Geology, University of Connecticut, Storrs, Connecticut 06268 Steven E. Boyer 2Standard Oil Production Co., Technical Services Division, Dallas, Texas 75340 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1989) 17 (4): 373–375. https://doi.org/10.1130/0091-7613(1989)017<0373:COGCST>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Peter A. Geiser, Steven E. Boyer; Construction of geological cross sections: Techniques, assumptions, and methods. Geology 1989;; 17 (4): 373–375. doi: https://doi.org/10.1130/0091-7613(1989)017<0373:COGCST>2.3.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 No abstract available 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.
We have developed a novel enhanced geothermal system (EGS) called radiator EGS (RAD-EGS). This system attempts to emulate naturally occurring hydrothermal systems by creating a vertically oriented heat exchanger or vane in the deep subsurface, mimicking a radiator in an internal combustion engine. Water is injected at the bottom of the vane and produced on the top. We propose to build the RAD-EGS in hot sedimentary aquifers (HSAs) with high-permeability vane(s) created in the plane defined by [Formula: see text] and [Formula: see text] (vertical). We have evaluated 3D heat-transfer simulations to better understand the fluid and heat flows that may occur in RAD-EGSs. The simulations account for subsurface heterogeneity including the presence of underlying basement rock, an overlying confining layer, and an ambient hydraulic gradient, which causes background groundwater flow. Our simulations indicate that our induced upward flow in the vane significantly prolongs the lifetime of RAD-EGS when compared with downward flow because hydraulic short circuiting is avoided. Within the vane, convection may occur, and its onset is analyzed in terms of a characteristic Rayleigh number. A critical aspect of RAD-EGS, therefore, is that thermal recharge does not rely solely on heat conduction from the surrounding wall rock, which is typical for EGS built in hot dry rock (HDR). Instead, recharge is also due to heat advection through the surrounding water-saturated aquifer, substantially prolonging the lifetime of the thermal reservoir. Moreover, fluid losses as typical for EGS built in HDR do not occur. It is also possible that cold water injected at the bottom of the vane may sink into deeper rock layers, which displaces hot water from the surrounding aquifer into the RAD-EGS. We suggest that mimicking a natural hydrothermal system is a successful EGS strategy via RAD-EGS.
This chapter explores the critical role that kinematics plays in the construction and analysis of geological cross sections. The structures on any admissible cross section must arise from relative displacements that are consistent with reasonable deformation kinematics. Sections that violate this constraint are physically impossible. The deformation kinematics can be derived from a displacement field, but the scale at which the displacement field is analyzed affects our perceptions of the movement of rocks in the cross section. Microscopic displacement fields associated with grain-scale deformation may be derived by the standard techniques of finite strain analysis, while macroscopic displacement fields may be derived from the geometry of map-scale cross sections in those regions that have undergone uniform area strain.
