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Doctoral Dissertations Student Theses and Dissertations
Summer 2019
Origin of Periclines in the Ozark Plateau, Missouri: A field and numerical modeling
Chao Liu
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ORIGIN OF PERICLINES IN THE OZARK PLATEAU, MISSOURI: A FIELD AND
NUMERICAL MODELING
by
CHAO LIU
A DISSERTATION
Presented to the Faculty of the Graduate School of the
MISSOURI UNIVERSITY OF SCIENCE AND TECHNOLOGY
In Partial Fulfillment of the Requirements for the Degree
DOCTOR OF PHILOSOPHY
in
GEOLOGY AND GEOPHYSICS
2019
Approved by:
John Hogan, Advisor Andreas Eckert Jonathan Obrist-Farner Marek Locmelis Klaus Woelk
2019
Chao Liu
All Rights Reserved iii
ABSTRACT
A series upright sub-horizontal folds in sandstones of the early Ordovician
Roubidoux Formation are exposed in road cuts along US Highway 63 in the northern part
of the Salem Plateau of central Missouri for over a distance of approximately 10 km.
These folds are in marked contrast to the more typical horizontal to sub-horizontal
Ordovician strata of the Ozark Plateau. The origin of those folds remains enigmatic. The
inspection of the characteristics of these folds using stereographic analysis revealed a non- cylindrical geometrical pattern than a near cylindrical fold. Structural data of 54 folds indicate an alternating basin and dome pattern. However, acceptance of more traditional classification and interpretation as a viable explanation for the origin of these folds ultimately only serves to heighten the enigma. Combing the results of numerical models, a more realistic hypothesis is proposed to explain the occurrence of those localized folds.
The result of numerical models implies a localized stress enhancement in the transpression zone and the basin and dome periclines is formed by applying unidirectional shortening. We propose that these folds are periclines formed in a transpression zone as a result of reactivation of basement faults with left-lateral slip during the late Paleozoic Alleghenian Orogeny which provides an E-W far-field compression.
iv
ACKNOWLEDGMENTS
I would like to thank Dr. Hogan for his guidance and advice. His sparking suggestions and encouragements are critical for this project. I would like to thank Dr.
Eckert for his guidance on numerical models, which provides a brand new aspect to investigate the research problems.
I would like to thank professors in my committee, Dr. Obrist, Dr. Locmelis and
Dr. Woelk. They provided some brilliant ideas that inspired me. Also, I would like to thank those colleagues who offered assistance for the field work.
I would like to acknowledge the financial support from a Geological Society of
America Research Grant and the University of Missouri University of Science and
Technology Radcliffe endowment.
Finally, thanks to my parents, for their support and love.
v
TABLE OF CONTENTS
Page
ABSTRACT ...... iii
ACKNOWLEDGMENTS ...... iv
LIST OF ILLUSTRATIONS ...... vii
LIST OF TABLES ...... viii
SECTION
1. INTRODUCTION ...... 1
2. GEOLOGIC SETTING ...... 5
2.1. REGIONAL GEOLOGY ...... 5
2.1.1. The Ozark Plateau ...... 5
2.1.2. The Ozark Dome ...... 5
2.1.3. Regional Fault Trends ...... 6
2.1.4. Regional Fold Trends ...... 9
2.2. LOCAL GEOLOGY ...... 11
2.2.1. Stratigraphy ...... 11
2.2.2. Fault Trends ...... 14
3. INITIAL WORKING HYPOTHESES ...... 15
3.1. KARST COLLAPSE HYPOTHESIS ...... 15
3.2. TECTONICS INDUCED BUCKLE FOLDS ...... 17
4. METHODOLOGY ...... 18
4.1. FIELD WORK ...... 18
vi
4.2. STRUCTURAL ANALYSIS...... 19
4.3. FINITE ELEMENT MODELS ...... 19
4.4. OTHER ATTEMPTS...... 20
5. HUTCHINSON CEMETERY FOLDS ...... 21
5.1. AREA ONE ...... 22
5.2. AREA TWO...... 24
5.3. AREA THREE ...... 26
5.4. AREA FOUR ...... 28
6. DISCUSSIONS ...... 31
6.1. KARST COLLAPSE ...... 31
6.2. "BASIN AND DOME” FOLD INTERFERENCE PATTERN ...... 33
6.3. CONICAL FOLDS ...... 34
6.4. NUMERICAL MODELING APPROACH ...... 38
6.4.1. 2D Transpression Model ...... 38
6.4.2. 3D Pericline Model ...... 40
7. CONCLUSIONS ...... 44
APPENDICES
A. FIELD DATA OF HUCHISON CEMETERY FOLDS ...... 46
B. GOVERNERING EQUATIONS ...... 64
C. PALEOMAGNETIC FOLD TEST ...... 67
BIBLIOGRAPHY ...... 71
VITA ...... 80
vii
LIST OF ILLUSTRATIONS
Figure Page
2.1 Map of the study area in the Ozark Plateau and structural trends...... 7
2.2 The localized map of study area...... 10
2.3 Stratigraphic column of Canadian Series, Ordovician...... 13
3.1 Conceptual sketches of initial hypotheses ...... 17
5.1 Area one, showing a road sketch, stereograms and a rose diagram...... 22
5.2 Area two, showing a road sketch, stereograms and a rose diagram...... 26
5.3 Area three, showing a road sketch, stereograms and a rose diagram...... 27
5.4 Area four, showing a road sketch, stereograms and a rose diagram...... 30
6.1 Rose diagram of all hinge lines, showing the trends of fold structure...... 35
6.2 2D transpression model...... 40
6.3 Three-dimentional model sketch and resutls...... 43
viii
LIST OF TABLES
Table Page
5.1 Field data of Hutchison Cemetery folds...... 23
6.1 Material properties for each unit of the 3D pericline model...... 43
1. INTRODUCTION
Within the central interior of the gently rolling terrain of the Ozark Plateau, in the
Midcontinent of North America, sandstones of the early Ordovician Roubidoux
Formation are deformed into a series of low (<2m) and varying amplitude and
wavelength buckle-folds. Exposure of these folds are confined to discontinuous road-cuts
along US Highway 63, for a distance of approximately 10 km, just south of the border
between Phelps and Texas counties in the state of Missouri. Informally, these folds are
referred as the “Hutchinson Cemetery” folds where they are best exposed in a road-cut below the cemetery. Although previously noted, the Hutchinson Cemetery folds received little attention (Heller, 1954; Thompson, 1991, 1995). This likely reflects, that even though gentle open folding of Ordovician strata in the Ozark Plateau is recognized, considerable more attention has focused on deformation related to karst and sink-hole collapse or folding closely spatially associated with displacement on faults (Spreng and
Proctor, 2001). Deformation associated with karst is common in Missouri (Bretz, 1950;
Heller, 1954; Elliott and Ashely, 2005; Weary and Doctor, 2014). However, concentrated zones of tectonic-related deformation, including asymmetrical anticlines, monoclines, and broad anticlines and synclines of low structural relief (e.g., Eureka-House Springs structure, Lincoln fold) are also well known within the Ozark Plateau (Marshak et al.,
2000, 2003; Harrison and Schultz, 2002). These tectonic forced-folds are attributed to reactivation of Precambrian basement-faults as a result of “far-field” forces transmitted into the mid-continent from colliding continental terranes along the eastern and southern margins of North America during the late Paleozoic (Cox, 1995; Harrison and Schultz,
2002; Marshak et al., 2000, 2003). Thus, the origin of the Hutchinson Cemetery folds
2 was considered ambiguous in that either they may be tectonic or the result of karst
collapse (Spencer, 2011).
The Hutchison Cemetery folds are considered enigmatic and worthy of investigation for several reasons. Immediately adjacent to this localized zone of deformation, exposed Canadian series Ordovician strata (e.g., Gasconade Dolomite,
Rubidoux Fm., Cotter-Jefferson City Dolomite) record low to little strain and are commonly sub-horizontal (Heller, 1954; Thompson, 1991, 1995). The Gasconade
Formation, which underlies the Roubidoux Formation, is well known for karst features
(Orndorff et al., 2001). However, evidence for karst collapse (e.g., chaotic breccia, circular faulting) associated with these folds is absent in these road-cuts and a tectonic origin for the Hutchison Cemetery folds is favored. However, the preliminary investigation of these folds indicated they are atypical of tectonic folds described from the Ozark Plateau in both their geometrical form and lack of a close-spatial association
with displacement on steep regional faults. Rare, very low displacement, faults, confined
to steeper dipping limbs where the sandstone layers have locally failed are present for a
couple of the Hutchinson Cemetery folds. In contrast, large through-going faults,
associated with strike-slip “flower structures”, that bound the zone of folding or cross-cut
monoclines, or drape folds, as is common in the Ozark Plateau (see Marshak et al., 2000;
2003), are absent. In addition, rather than forming long linear drape folds or monoclines,
the Hutchinson Cemetery folds consistently define two, and possibly three, fold axes
orientations, that are inconsistent with the more commonly documented mid-continent
fold and fault trends (Marshak and Paulsen, 1996; Cox, 2009). The multiple trends for
fold axes is consistent with a basin and dome pattern. The suggestion of such a pattern is
3 consistent with initial field observations where adjacent folds in the same road cut exhibit opposing plunge directions. Basin and domes are commonly interpreted as an interference pattern that forms as a result of multiple non-coaxial deformation events (See
Ramsay and Huber 1987). This additional complexity, potentially necessitating multiple deformation events is puzzling given that Ordovician strata immediately adjacent to these folds is largely un-strained and sub-horizontal. Finally, the Hutchinson Cemetery folds define simple to complex π-diagram stereogram patterns, including great circles, small circles, and “fish-hook” patterns. Traditionally, these π-diagrams would been interpreted as defining the presence of cylindrical folds and non-cylindrical “conical-folds” in the mid-continent.
The Hutchinson Cemetery folds, despite their small stature, and to an extent due to limited exposure, present a significant challenge to traditional structural analysis and interpretation. Are these folds the result of local or far-field tectonic stresses? If they are tectonic in origin, then why are these folds spatially restricted within a domain surrounded by relatively unstrained strata? What is the significance of the seemingly complex geometry of these folds in which both basin and dome patterns and conical folds occur within the same fold system? Are multiple, non-coaxial, tectonic deformation events required to produce these folds? To address these questions this study presents the results of the combined fieldwork, structural analysis, and numerical dynamic modelling of these structures. Welker et al., (2019) utilizing this approach demonstrate that “conical folds” while being a mathematically permissible solution for π-diagrams with small circles is a geomechanically unrealistic geometry for folds. They show that the
Hutchinson Cemetery folds, among other folds, have geometrical forms best described as
4 “periclines” which are elongated, doubly plunging, anticlines (domes) and synclines
(basins). This study extend the work of Welker et al., (2019) to present a more comprehensive field characterization and structural analysis, from multiple exposures, of the Hutchinson Cemetery folds (periclines). This study then utilizes geomechanically realistic dynamic modelling to demonstrate these periclines are most likely to have formed in a localized zone of transpression as a result of left-lateral slip on a set of northwest-south east striking that border these folds. Marshak et al., (2000, 2003) suggested similar movement on this fault set, as part of the late Ancestral Rockies deformation, to form other tectonic forced-folds in the mid-continent. The integrated field and numerical modelling approach accounts for the apparent complexity of the geometry of the Hutchinson Cemetery folds and removes the ambiguity in their origin.
Collapse of paleocave systems can lead to deformation in the overlying strata (see
Loucks, 2007 for a review). In contrast to deformation commonly associated with epigenic karst collapse, such as chaotic breccia or faulting (e.g., circular faults), the coherent continuous sandstone layers can be traced through multiple synclines and anticlines. The anticlinal forms of the Hutchison Cemetery Folds are also inconsistent with an origin as “accidental anticlines” occupying the space between adjoining “sag- synclines” (see Tewksbury et al., 2017) that form directly over dissolution features such as solution-widened joints.
Traditionally, many secondary structures in the Roubidoux Fm. have commonly been ascribed to dissolution (Heller, 1954; Spreng and Proctor, 2001).
5 2. GEOLOGIC SETTING
2.1. REGIONAL GEOLOGY
In this section, the regional geology of the Ozark Plateau will be discussed,
including the topography of the Ozark Plateau, the Ozark Dome and the fault and fold
trends in the midcontinent.
2.1.1. The Ozark Plateau. The Ozark Plateau (OP) is a prominent physiographic
region of the southern mid-continent of North America (Bretz, 1965). The OP extends
over 130,000 km2 in area and includes portions of northwestern Arkansas, northeastern
Oklahoma, and most of southern Missouri (Figure. 2.1). It consists of five sub provinces
or topographic surfaces of varying elevation and topography (Fenneman, 1938). The
highest region is the rugged terrain of the Boston Mountains of northern Arkansas, with
peaks over 760 m. In Missouri, the Springfield Plateau is characterized by elevations just
over 515 m and closer to 485 m, and the Salem Plateau, where the study area is located,
is slightly lower with elevations closer to 395 m. The Salem Plateau surrounds the
Mesoproterozoic crystalline rocks of the St. Francois Mountain. The St. Francois
Mountains are host to the highest elevations in Missouri (e.g., Taum Sauk Mountain 540
m). Both the Springfield and Salem Plateaus are characterized by considerably gentler
and more rolling topography, and sparser bedrock exposures, than either the Boston or St.
Francois Mountains.
2.1.2. The Ozark Dome. The OP is underlain by a thin veneer, rarely exceeding
800 m, of clastic and carbonate Paleozoic sedimentary “cover-rocks” deposited on
Mesoproterozoic crystalline “basement” along an extensive, continent-wide, non- conformity “The Great Unconformity” (Middendorf, 2003; Thompson, 1995;). This non-
6 conformity is locally well exposed on ca. 1.47-1.38 Ga Eastern Granite-Rhyolite
Province in the St. Francois Mountains (Van Schmus et al., 1996; DeLucia et al., 2017;
Joel, 2018). The entire OP has been gently deformed into a broad, elliptical, epeirogenic upwarp, with outward dipping Paleozoic strata – “the Ozark Dome” (OD) (Middendorf,
2003; Marshak et al., 2016). The OD is bounded to the northwest by the mid-continent rift system – an intracratonic Precambrian rift (Van Schmus and Hinze, 1985; Figure.
2.1). Immediately to the east, the OD is the intracratonic Illinois Basin (McBride and
Nelson, 1999; Marshak et al., 2016) and further east the Paleozoic Appalachian fold and thrust belt (Hatcher, 2010). Along the southeastern edge of the OD is the late Proterozoic
Reel-foot Rift (Tuttle et al., 2002; Guccione et al., 2005; Csontos and Van Arsdale, 2008;
Calais et al., 2010; Van Arsdale et al., 2013). The late Paleozoic Ouachita Fold and
Thrust Belt occurs to the southwest of the OD (Thomas, 1985; Hatcher, 2010;
Bartholomew and Whitaker, 2010). Possible driving mechanisms for intracratonic epeirogenic uplift of the OD include broad flexure of the crust related to loading associated with the Ouachita fold and thrust belt (Quinlan and Beaumont 1984; Root and
Onasch, 1999; Harrison and Schultz, 2002) or alternatively broad mantle upwelling associated with lithospheric delamination following supercontinent assembly (DeLucia et al., 2017).
2.1.3. Regional Fault Trends. The OD is transected by two prominent fault trends; a set of northwest-southeast striking faults and a set northeast-southwest striking faults (Figure. 2.1). These faults are inherited from a large system of intracratonic faults that originated during two or more distinct periods of crustal extension associated with the break-up of Proterozoic super-continents (Marshak and Paulsen 1996; Timmons et
7 al., 2001; Thomas, 1991, 2011; Harison and Schultz, 2002). The northwest-southeast trend has been associated with the late Mesoproterozoic Mid-continent rift and Grenville
Orogeny. However, in Missouri these faults are also suggested to have originated as transform faults related to the Cambrian Reel-foot rift (Horrall et al. 1983; Marshak et al.,
2000; Thomas, 1991, 2011). The northeast-southwest faults are also associated with rifting, first during the breakup of Rodinia in the Neoproterozoic, and again in the late
Neoproterozoic to early Cambrian, with the breakup of Pannotia. In Missouri, northeast- southwest faults are rift-parallel with the early Cambrian Reel-foot Rift (Hildenbrand and
Hendricks, 1995; Marshak and Paulsen 1996; Thomas, 2011, Figure. 2.1).
Figure 2.1. Map of the study area in the Ozark Plateau and structural trends (Compiled from McBride and Nelson, 1999; Marshak and Paulsen, 1996; Middendorf, 2003; Duchek et al., 2004; Cox, 2009).
8 The northeast striking Commerce fault system and geophysical lineament has
also been related to a major Mesoproterozoic plate-boundary or rifted continental margin
(Hildenbrand et al., 2002) that was reactivated again during Reelfoot rift extension
(Clendenin et al., 1993; Harrison and Schultz, 1994, 2002) and continues to be a locus for accumulating and releasing strain in the Holocene. Together these two dominant fault sets divide the Proterozoic basement of the Mid-continent into rectilinear blocks that have been episodically reactivated several times during the Phanerozoic, Mesozoic, and
Cenozoic, and some (e.g., The New Madrid Seismic Zone, Commerce Geophysical lineament) continue to localize strain today (Harrison and Schultz, 2002; Hildenbrand et al., 2002; Marshak et al., 2000, 2003).
Detailed kinematic studies of these two prominent faults of the OD are challenging due to the limited, to sparse, commonly weathered, bedrock exposures, and low displacements (Harrison and Schultz, 2002; Marshak et al., 2003). The two prominent fault sets typically record distinct periods of oblique-slip displacement, a dip- slip component, and an associated component of either right-lateral slip or left-lateral slip depending on their orientation. In the “Old Lead Belt” of southeastern Missouri these fault are typically steeply dipping with near-horizontal to low angle slickensides (Snyder and Gerdemann, 1968). In general, the northeast striking fault set dominantly record a right-lateral component of displacement (Clendenin and Diehl, 1999; Hudson, 2000). For example, Holocene sediments are displaced along the Commerce fault zone, and where the fault is exposed, kinematic indicators demonstrate right-lateral strike-slip displacement (Harrison et al., 1999; Harrison and Schultz, 20002). In contrast, the northwest striking fault set, which transect the study area along the border of Phelps and
9 Texas counties, Missouri (Figure. 2.1 and Figure. 2.2), record a left-lateral component of displacement (Horrall et al., 1983; Clendenin et al., 1989; Clendenin et al., 1993;
Harrison and Schultz, 2002). Clendenin et al. (1989) documented a left-lateral component of displacement on northwest striking faults during the late Paleozoic, including the Ste.
Genevieve, Simms Mountain, Black, Ellington, and Shannon County faults. Left-lateral slip is also documented for the northwest-striking Eureka fault system (Clendenin et al.,
1993). Several faults also record complex deformations histories. The Ste. Genevieve fault records multiple episodes of displacement, including both right- and left-lateral slip, during the Paleozoic (Cox, 2009; Nelson and Lumm, 1985; Schultz et al., 1992; Harrison and Schulz, 2002). A detailed study on northeast striking Grays Point fault zone (a segment of the Commerce fault system) also records polyphase reactivation during the
Paleozoic (Clendenin and Diehl, 1999).
2.1.4. Regional Fold Trends. Rare to sparse folds within the Midcontinent, including those in the OD, are related to subsequent reactivation of these two sets of basement faults (Marshak and Paulsen, 1997; Marshak et al., 2000; Harrison and Schultz,
2002). Typically, steeply dipping to near vertical, basement faults (Mateker and Segar,
1965) display normal dip-slip displacement along the basement-cover contact and propagate upwards through the overlying cover rocks where several splays develop to form a “flower-structure” or an en-echelon fault zones on the order of 100-600 km long and 2-20 km wide (Marshak et al., 2003). The fault propagation folds that form above these faults are typically faulted asymmetrical anticlines or monoclinal folds, locally with several 100’s m of structural relief, or broad anticlines and synclines of low structural relief (Harrison and Schultz, 2002). Examples include the Lincoln fold, the Cap au Gres
10 faulted monocline, and the Eureka-House Springs structure (Clendenin et al., 1992;
Harrison and Schultz, 2002; Liu et al., 2018) or belts of en-chelon domes or anticlines
related to restraining bends along right-lateral strike-slip segments of the Cottage-Grove fault system (Nelson and Krausse, 1981).
Figure. 2.2. The localized map of study area (from Middendorf, 2003).
Although these faults are likely to have been reactivated episodically throughout the Paleozoic, Mesozoic, and Cenozoic, the major period of reactivation, and timing of fold formation, is associated with late Pennsylvanian to Permian “Ancestral Rockies” deformation and possibly with the Laramide Orogeny as well (Harrison and Schultz,
11 2002; Marshak et al., 2003). Cox (1995) and Harrison and Schultz (2002) relate
displacement along the different faults, that lead to formation of fault propagation folds,
to changes in the orientation of the stress-field as a resulting of rotation and migration of
the continental terrane colliding along the southern margin of North America during the
late Paleozoic. Alternatively, Marshak et al., (2003) suggested the rectilinear pattern
defined by the two major fault sets divides a strong-basement and thin overlying cover
into a mosaic of blocks that jostle (see Davis, 1978; Tikoff and Wojtal, 1999) with
respect to one another during the Alleghenian-Ouachita Orogeny. The complex sense of
displacement on these faults reflects the local geometry, orientation, and linkage of the
system of faults that define the blocks. Faults with different types of displacement
(normal and reverse slip, and right- and left-lateral strike slip) can form at the same time within the same regional stress field, as the blocks are jostled by collisions along the distance continental margin. The low displacement on these faults reflecting the relatively strong nature of the lithosphere inhibiting transfer of strain from the continental margins into the interior (Marshak et al., 2003).
2.2. LOCAL GEOLOGY
The Hutchinson Cemetery folds are exposed discontinuously in road-cuts along
Missouri Highway-63 near the Phelps County – Texas County line (Figure. 2.1 and
Figure. 2.2). In this section, the local stratigraphy, fault and fold trends will be discussed.
2.2.1 Stratigraphy. The study area, along the southern portion of the Salem
Plateau, is characterized by very low-relief, gently rolling farm-land with extremely sparse bedrock exposure. Here, rocks of the lower Ordovician Canadian Series crop-out
12 as sub horizontal strata with contacts that generally follow the topographic contours.
Figure 2.3 shows the stratigraphic column of Canadian Series, Ordovician in Missouri.
The oldest unit, the lower Ordovician Gasconade Formation crops out outside of the immediate study area within valleys formed by the Big Piney and Current rivers and their tributaries (Figure. 2.2). It is approximately 90 m thick, and dominantly comprised of light brownish gray to brown, medium to coarsely crystalline dolomite, finely crystalline dolomite, and cherty dolomite (Thompson, 1995). Caves and springs are common in the
Gasconade Formation (Bertz, 1950; Spencer, 2011). The lower Ordovician Roubidoux
Formation (host to the Hutchison Cemetery fold) overlies the Gasconade Fm. along a disconformity. Regionally, the Roubidoux Fm. is dominantly comprised of cherty dolomite, sandy dolomite, dolomitic sandstone, and sandstone, with some beds containing oolitic sandy chert and varies in thickness from 30m to 75m (Thompson, 1995). Lee
(1913) subdivided the Roubidoux Fm. into seven members. However, in the study area, as well as in the nearby Rolla Quadrangle, the Roubidoux typically crops out as two distinct layers of sandstone, each approximately 4 – 7.5m thick separated by a thin clay- rich mudstone. Spreng and Proctor (2001) informally referred to them as the “upper” and
“lower” sandstone even though they occur near the top of the formation. The sandstones are typically fine to medium grained, sub-rounded, and poor to well-sorted quartz sand.
They are white on a fresh surface and weather to a light gray to tan, or a rusty-red brown along some joint planes. In many places, primary structures, including mud cracks, current ripple marks, rain-drop imprints, and cross-bedding are very well preserved in the
Roubidoux Fm (Spreng and Proctor, 2001). Stratigraphically, above the Roubidoux Fm., in a gradational contact, is the early Ordovician Jefferson City Formation with an average
13 thickness of approximately 60m (Thompson, 2001). The Jefferson City Fm. does not crop out in the immediate study area but forms the cap rock on the nearby slightly higher elevations of the Salem Plateau. The Jefferson City Fm. is dominantly comprised of light brown to brown, fine to medium crystalline, dolomite and argillaceous dolomite, with thin, laterally discontinuous sandstone lenses (Martin et al, 1961; Thompson, 2001).
Figure 2.3. Stratigraphic column of Canadian Series, Ordovician (Depicted from Thompson, 1995).
14 2.2.2 Fault Trends. The Salem Plateau, near Licking, Missouri, is cross-cut by
several faults (Figure. 2.2). Within this area, the faults all exhibit northwest-southeast trends. Direct evidence for deformation associated with displacement on regional scale faults, such as truncation or off-set of stratigraphic contacts or fault-rocks were not observed within the immediate study area where the folds are exposed. However, just to the north of the study area is the Bradford Branch Fault, and to the south is the Licking
Fault (Figure. 2.2). The study area occurs within the right-stepping overlap zone these two faults. Displacement on the regional northwest-southeast trending faults is consistently left-lateral displacement (Horrall et al., 1983; Clendenin et al., 1989;
Clendenin et al., 1993; Harrison and Schultz, 2002). If both of these faults, or all the faults in this area underwent left-lateral slip at the same time the study area would be in a localized zone of tranpsression.
15 3. INITIAL WORKING HYPOTHESES
Two major divisions of thoughts have been brought up by previous studies. Spencer
(2011) suggests two possible explanations of Hutchison Cemetery folds, as either karst- related deformations or tectonic deformations. Initial working hypotheses are formulated based up those two distinct branches of thoughts. However, detailed investigations and studies are still needed to provide evidence for the origin of those folds.
3.1. KARST COLLAPSE HYPOTHESIS
Heller (1954) claims local structures of the Roubidoux Formation are ascribed to the solution of underlying formations, so do other irregularities of bedding planes. Given the pervasive distribution of karst collapses throughout Missouri (Bretz, 1950; Elliott and
Ashley, 2005; Weary and Doctor, 2014; Gramlich 2015), one hypothesis to explain these folds is that the Roubidoux Formation beds sagged into collapsed caverns (Figure. 3.1A).
The underlying Gasconade Dolomite Formation has dissolved away and form void spaces for the collapse to occur. Therefore, the fold distribution passively depends on the location of karst collapse, especially, a rigorous circumstance is required to form an anticline.
Sagging into a collapsed cavern, only the syncline will be formed unless another sagged syncline is formed nearby at an appropriate distance, then an “accidental anticline” could be produced (Figure. 3.1A). A random and irregular pattern on stereograms would be expected.
Some field examples in Missouri are documented as following (Spencer, 2011): 1)
Wea Shale syncline at the west end of the ramp from Raytown Road to westbound
US50/I-470; 2) Chouteau Group Limestone anticline in a road cut along the westbound
16 lanes of US50, 0.5 miles west of Cooper County Route A near Otterville; 3) Jefferson
City Dolomite: a) along the westbound lanes of US50 at Cole County Route D; b) at the
third cut east of the MO 28 South junction, about 0.4 miles west of the Gasconade River; c) along the northbound lane of US 63 halfway between Maries County Route A and MO
28 North; 4) Cedar Valley Limestone along the westbound lanes of US 50 west of the
Moreau River; and 5) Pennsylvanian limestones in a road cut about 2 miles east of Route
Y and 2 miles west of Route C, Franklin County.
Another karst-related possibility is that those Roubidoux layers are deposited on a wavy, eroded surface of Gasconade Dolomite after karst collapse. The geometry of this type of structure is highly depended on the underlying surface and the resulting amplitude is low in common. Similar geological structures also can be found in Missouri (Spencer,
2011): 1) The St. Peter Sandstone along I-44 between mile markers 254.9 and 255.2; 2)
The unconformity between the Proterozoic Grassy Mountain Ignimbrite and the
Cambrian Lamotte Sandstone in a road cut along the eastbound lane of MO 72, about 1.6 miles west of US 67.
3.2. TECTONICS INDUCED BUCKLE FOLDS
Alternatively, the Hutchison Cemetery folds could be produced by a completely different mechanism. A second hypothesis is that Hutchison Cemetery folds are the result of tectonic events. Localized tectonics furnished layer-parallel compression in the study area, initializing buckling of Roubidoux beds and eventually formed Hutchison Cemetery folds (Figure. 3.1B). Certain systematic trends on stereograms, yielding to the stress field are expected in this case.
17
Figure 3.1. Conceptual sketches of initial hypotheses. A) Karst collapse model B) tectonics buckle folding model.
Furthermore, the following questions should be addressed to support this hypothesis: 1) What is the driving force of Hutchison Cemetery folds? 2) How many deformation events are contributing to form Hutchison Cemetery folds? 3) What is the depth of the deformation? 4) What are the timing and origin of the driving force? And, 5) what are the evidence to answer the questions above?
18 4. METHODOLOGY
Guided by initial working hypotheses, different approaches have been applied to test hypotheses and explain the possible origin of the Hutchison Cemetery folds in the study area, including field work, structural analysis, finite element modeling, paleomagnetic fold test, and other attempts.
4.1. FIELD WORK
As one of the most fundamental and important methods to understand structures in
the study area, fieldwork lays the foundation and provide ground truth data for other
following analysis. Careful field data measurement and field observation are essential and
critical for the study.
There are nine discontinuous fold exposures along the road cuts in the study area.
Field work of this study comprises of four major parts. They are: 1) the field observations
throughout the study area; 2) Four selected well-exposed areas to conduct field data measurement; 3) the similar structure hunting in the nearby area (approximately 10 miles in both directions along US Highway 63); 4) the typical Roubidoux Formation near Rolla, Mo for reference study.
Four well-exposed areas are selected to investigate in details, including rock type identification, wavelength measurement, amplitude estimation, bedding attitudes measurement of fold limb (RHR). More than 500 pieces of fold attitude data from 52 folds are collected for structural analysis. Each fold is documented with photo and stereogram data in the previous report (Liu, 2016).
19 4.2. STRUCTURAL ANALYSIS
To quantitatively identify the structure and the architecture of Roubidoux Folds, the stereographic analysis is applied (Ramsay and Huber, 1987; Davis et al., 2011,
Allmendinger, 2011). The collected field data is processed with stereographic analyses. For each individual fold, its hinge line and axial surface orientation have been calculated by plotting its limb attitudes as poles. Rose diagrams are plotted to demonstrate fold trend directions and principal stress orientations in this area. The results of the structural analysis are used to test the proposed hypothesis and reconstruct the fold structure in 3D.
4.3. FINITE ELEMENT MODELS
Field data and stereographic analyses provide fundamental knowledge to constrain
fold geometry and boundary conditions (Smith et al., 2013). The results are used to
examine the possibilities of proposed models. The general workflow of a finite element
analysis includes following steps: 1) build a conceptual model sketch to demonstrate the
problem; 2) field work and literature review; 3) build model geometry and discretized to
finite element mesh; 4) apply material properties and boundary conditions to the model; 5)
Run analysis; 6) Sanity check of the model results; and 7) interpret the results. In this study,
software HyperWorkTM is used to build model geometry and export code file. The edited
code file is run in software AbqusTM. The purposes of these models are not to reproduce
what exactly happened in the field, but to test the possibilities that folding is able to occur
at given setups. A two-dimension map-view model is built to test the transpression hypothesis. Also, a three-dimensional pericline model is created to constrain the
conditions that is required to form periclines.
20 4.4. OTHER ATTEMPTS
Some other attempts have been made to investigate the study area from different
aspects. Such as published well data from USGS and free digital elevation images in this
area. However, the limited resolution of the data provides little useful information to investigate the Hutchison Cemetery folds. In addition, Paleomagnetic fold test is applied as
a powerful tool to constrain the timing of those deformations (Cochran and Elmore, 1987;
Blumstein et al., 2004; Elmore et al., 2010). Paleomagnetic fold test will help to determine whether the magnetizations of Roubidoux Folds are pre-, syn- or post-folding (Weil and
Van der Voo, 2002).
21 5. HUTCHINSON CEMETERY FOLDS
The Hutchinson Cemetery folds crop out in nine discontinuous road cuts over an
area that extends for 10.2 kilometers along highway U.S. Route 63, from the border of
Phelps and Texas Counties to just north of Licking, Missouri (Figure. 2.2). Here Rt. 63 provides a north-south, two-dimensional transect, at a constant elevation, through the zone folded sandstones. The zone of folding being bounded at both ends (North end: 15S
600374.75 m E, 4163448.55 m N; South end: 15S 600509.23 m E, 4153286.82 m N) by exposures of Roubidoux sandstones characterized by sub-horizontal sedimentary layering.
Within this zone, fold amplitude and tightness gradually decreases to the north and to the south away from the folds exposed in the road cut below Hutchison cemetery. The overall form of the folds within this zone vary from gentle to open cylindrical folds to non-cylindrical “conical folds” (however, see discussion section). In addition, several folds are asymmetric south verging folds characterized by longer, gentler dipping northern limb and a shorter, steeper dipping southern limb. The limbs of these folds may also preserve kinks. Four areas, covering a distance over two kilometers within the central portion of the zone of folding, were selected for detailed field investigation. In several of the road cuts two distinct layers of sandstone separated by a thin layer of a clay-rich mudstone can be observed and are informally referred to here as the “upper” and “lower” sandstone (see also Spreng and Proctor, 2001). Direct observation and measurement of these folds are restricted to road cuts, as the surrounding area is covered by forest or gently rolling farmland. Detailed stereograms for each area is listed in
Appendix A.
22 5.1. AREA ONE
Area one is located at [15S 600392.70 m E 4162363.26 m N] where the
Roubidoux Fm. is exposed in road cuts on both sides of the highway for a distance of approximately 150 m. Locally, the road cuts are degraded by slumping of large blocks of the sandstone, however there is sufficient intact outcrop to structurally characterize the folds, which are better exposed on the east side than the west side of the highway (Figure.
5.1). On the east side the upper sandstone preserves three upright sub-horizontal folds
(Fleuty, 1964) all plunging to the southwest less than ten degrees based upon a great circle fit to the π-diagram. The lower sandstone is covered by talus and vegetation.
Figure. 5.1. Area one, showing a road sketch, stereograms and a rose diagram.
23 Alternatively, orientation data for both anticlines can also be fit by small circles on the π-diagram and tangent diagrams (Bengston, 1980) and allow for classification as non-cylindrical folds with crestal lines also gently plunging to the southwest (Figure. 5.1, Table 5.1).
Table 5.1. Field data of Hutchison Cemetery folds.
24 Both the upper and lower sandstone are exposed in the road cut on the west
side of the highway. Here the continuation of the folds are very subtle and the dips are
low. Folds are preserved as upright sub-horizontal folds, plunging to the northeast less
than five degrees (Fleuty, 1964). A nearly horizontal upper sandstone layer is exposed
between the lower sandstone anticline and the upper sandstone anticline.
5.2. AREA TWO
Area two is located at [15S 600399.79 m E, 4161606.15 m N] where both the
upper and lower sandstone of the Roubidoux Fm. are exposed in road cuts on both sides
of the highway for a distance of approximately 290 m. On the east side of the highway,
the sandstones define ten upright sub-horizontal to gently plunging folds (Fleuty, 1964)
with all folds plunging less than 15o based upon a great circle fit to the π-diagram (Figure.
5.2). We treated the folds in the upper and lower sandstones, from the same location in
the road-cut, independently as a check on coherency. A slight difference in orientation of
the upper and lower fold (Figure. 5.2, Table 5.1) may reflect slippage facilitated by
reduced friction due to the clay-rich mudstone present between the two sandstone layers.
Similarly, ten folds are recognized on the west side, seven anticlines and three syncline, with four of the nine folds classified as upright sub-horizontal folds. One of the folds is gently plunging at 24o which is a relatively high value for the Hutchinson Cemetery folds.
Within this road-cut fold orientation and plunge direction can vary abruptly (Figure. 5.2).
This can be seen from the map and from a rose diagram of the strike orientation and
plunge direction (most plunge values are less than 10o) of the hinge lines. Most of the folds strike and plunge in a westerly direction, with a few striking and plunging in a
25 southeasterly direction. Two considerable small-scale faults on the east are noticed by having an abrupt change to their adjacent dipping layers (Figure. 5.2). The north side of
the north fault shows a 21o dipping layer in 088. The last three folds on the west side
recorded little strain show a very low amplitude but still visible. Locally, the alternating
pattern of opposing plunge directions is suggestive of a “basin and dome” fold
interference pattern (Figure. 5.2).
Figure. 5.2. Area two, showing a road sketch, stereograms and a rose diagram.
In area two, orientation data plotted on π-diagrams defines several types of
patterns and fold-types reflecting the variety of fold shapes observed in the road cut
(Figure. 5.2). The largest anticline exposed in the road-cut is a typical example of the
26 asymmetric, south verging form, with a long, shallowly dipping, kinked, northern limb
and a short, steeper dipping, southern limb. In contrast, smaller synclines can appear
symmetrical. Folds also vary in form from cylindrical, to near cylindrical, to non-
cylindrical based upon the fit of the data to either a great or small circle on π-diagrams
(Davis et al., 2011). Cylindrical folds are exemplified by orientation data that exhibits a close-fit to a great-circle (e.g., fold A in Figure. 5.2). In contrast, π-diagrams for several folds have orientation data that are best fit by small circles which have previously been used to interpret non-cylindrical fold forms as “conical folds” (Bengston, 1980).
5.3. AREA THREE
Area three [15S 600412.11 m E, 4160829.25 m N] is located approximately 800m south of area two. The intervening area is covered by vegetation. Here folds in both the upper and lower sandstone of the Roubidoux Fm. are exposed in road cuts on both sides of the highway for a distance of approximately 230 m. The folds are longer wavelength and lower in amplitude then folds typical of areas one or two. The lower sandstone just crops out in the core of the anticlines and structural data is reported only from the well exposed upper sandstone. On the east side of the highway, the sandstones define six upright sub-horizontal plunging folds (Fleuty, 1964) with all folds plunging less than 10o,
and most less 5o, based upon great circle fits to π-diagrams (Figure. 5.3). At the northern,
and southern end, of the east road-cut the two anticlines flank a syncline, separated by an intervening zone of 50m of vegetation. Similarly, seven upright sub-horizontal plunging folds are recognized on the west side road cut. The synclines are also flanked by anticlines. However, the position of folds are offset from the folds in the opposing road
27 cut (Figure. 5.3). All of the folds plunge less than 10o, and most less 5o, based upon great circle fits to π-diagrams (Figure. 5.3).
Figure 5.3. Area three, showing a road sketch, stereograms and a rose diagram.
The orientation and plunge direction of folds in both road-cuts varies abruptly.
This can be observed in the structural map and the rose diagram of the strike orientation and plunge direction (most plunge values are less than 10o) of the hinge lines (Figure.
5.3). Most of the folds strike and plunge in either a westerly or easterly direction, with a few striking and plunging in a southwesterly direction. Similar to area two, the alternating pattern of opposing plunge directions is suggestive of a “basin and dome” fold interference pattern (Figure. 5.3).
28 In area three, orientation data plotted on π-diagrams defines several types of
patterns and fold-types reflecting the variety of fold shapes observed in the road cut. The
largest anticline exposed in the road-cut also displays the asymmetric, south verging form, with a characteristically long, shallowly dipping, kinked, northern limb and a shorter, steeper dipping, southern limb into a tighter syncline. Folds also vary in form from cylindrical, to near cylindrical, to non-cylindrical based upon the fit of the data to either a great or small circle on π-diagrams (Davis et al., 2011). Cylindrical folds are exemplified by orientation data that exhibits a close-fit to a great-circle (e.g., fold A in Figure. 5.3). In
contrast, π-diagrams for several folds have orientation data that are best fit by small circles which have previously been used to interpret non-cylindrical fold forms as
“conical folds” (Bengston, 1980).
5.4. AREA FOUR
Area four [15S 600425.79 m E, 4159835.18 m N] is located approximately
1000m south of area two. The intervening area is covered by vegetation. Here folds in sandstone of the Roubidoux Fm. are exposed in discontinuous road cuts, separated by vegetation, on both sides of the highway for a distance of approximately 290m (Figure.
5.4). The folds exhibit variable wavelength and amplitude, and are more similar to area three than area two. Folds on the east side of the highway, expose both the lower and upper sandstones, in low-relief, vegetated, road cuts. Five folds, three anticlines flanking two synclines, are recognized. All five folds are upright sub-horizontal plunging folds.
All of the folds plunge less than 10o based upon great circle fits to π-diagrams (Figure.
5.4). Nine upright, sub-horizontal plunging folds are recognized on the west side road cut.
29 All of these folds plunge less than 10o, and most less 5o, based upon great circle fits to
π-diagrams (Figure. 5.4). One syncline is an upright, moderately plunging (32o) fold,
which is atypical of the Hutchinson Cemetery folds, an approximately 21% shortening is
recorded by unfolding process. The synclines are also flanked by anticlines or the
adjacent area is vegetated. Correlation of anticlines and synclines across the road shows a
variety of combinations, including similar fold type and plunge direction, similar fold
type and opposite plunge directions, and different fold types opposing each other (Figure.
5.4). The orientation and plunge direction of folds in both road-cuts can vary abruptly or
more gradually. This can be observed in the structural map. The rose diagram of the
strike orientation and plunge direction (most plunge values are less than 10o) of the hinge
lines show folds plunge in either a westerly or easterly direction, but with a greater
variation than the other three areas (Figure. 5.4). Similar to the other three areas, the alternating pattern of opposing plunge directions is suggestive of a “basin and dome” fold interference pattern (Figure. 5.4).
In area four, orientation data plotted on π-diagrams defines several types of patterns and fold-types reflecting the variety of fold shapes observed in the road cut. The largest anticline exposed in the road-cut also displays the asymmetric, south verging form, with a longer, shallower dipping, northern limb and a shorter, steeper dipping, southern limb into a tighter, moderately plunging, syncline. Folds also vary in form from cylindrical, to near cylindrical, to non-cylindrical based upon the fit of the data to either a great or small circle on π-diagrams (Davis et al., 2011). Cylindrical folds are exemplified by orientation data that exhibits a close-fit to a great-circle (e.g., fold A in Figure. 5.4). In
contrast, π-diagrams for several folds have orientation data that are best fit by small
30 circles which have previously been used to interpret non-cylindrical fold forms as
“conical folds” (Bengston, 1980).
Figure 5.4. Area four, showing a road sketch, stereograms and a rose diagram.
31 6. DISCUSSIONS
Cursory, contrasting, interpretations for the origin of the Hutchinson Cemetery folds as either being the result of karst collapse or tectonic in origin has been previously proposed (Spencer, 2011). In this section, we discuss the characteristics of these folds, including fold style, distribution, orientation, and form, as presented in this study, to better constrain the origin and significance of the occurrence of these unusual folds with the Ozark Dome. We present evidence supporting that these folds are the response to far- field tectonic forces. However, acceptance of more traditional classification and interpretation as a viable explanation for the origin of these folds ultimately only serves to heighten the enigma. To better assess their nature and significance we integrate field observations and measurements with realistic numerical modeling. The purpose of the numerical models is to assess reasonable tectonic processes that will lead to formation of folds that are similar, but not required to be an exact duplication, of these folds. Our resulting model for the tectonic origin, and the form, of the Hutchinson Cemetery folds is consistent with current understanding of the tectonic evolution of the Ozark Dome
(Middendorf, 2003; Marshak et al., 2016).
6.1. KARST COLLAPSE
Deformation related to collapse of epigenic karst (e.g., sink-holes, caves, cave passages, solution-widened joints) is well known in Missouri (Bretz, 1950; Heller, 1954;
Elliott and Ashely, 2005; Weary and Doctor, 2014). Typically associated with this near- surface phenomenon are localized, small displacement faults and poorly sorted, collapsed breccias commonly composed of angular blocks of country rock, some many meters
32 across, set in a finer-grained matrix. If the failure is not catastrophic, as in solution widening of joints, the overlying strata can deform to form a localized isolated “sag- syncline”. Collapse of extensive paleocaves and cave passages from the weight of overlying strata lead to the formation of sag-synclines (Loucks, 1999, 2007; McDonnell et al., 2007). Sag-syncline that form in this manner cover a more extensive region in the overlying sedimentary rocks and are also considerably wider than the original cave system (Tewksbury et al., 2017). The intervening “accidental-anticlines” (see Tewksbury et al., 2017) flanked by the sag-synclines are characterized by sub-horizontal strata and exist simply as a result of sharing limbs with the sag-synclines.
The origin of the Hutchinson Cemetery folds as a result of deformation solely attributed to the collapse of underlying karst-features is inconsistent with several characteristics of these folds. The upper and lower sandstone beds of the Roubidoux Fm., where exposed, can be traced continuously through the Hutchinson Cemetery folds without disruption. Rare faults observed in the sandstone, record very low displacement and are spatially associated with the tightest folds, consistent with localized brittle failure of these limbs. In addition, these synclines are not associated with chaotic collapsed breccias, and although the possibly for karst features due to dissolution (e.g., sinkholes) of the underlying Gasconade Dolomite exists in this area karst-related features were not observed. Finally, the anticlines associated with the Hutchinson Cemetery folds have complex fold shapes, characterized as both cylindrical and non-cylindrical folds, defined by deformed strata observed over a ten-kilometer “cross-section” through the folds; features which are inconsistent with an origin as “accidental-anticlines”. We conclude the
33 Hutchison Cemetery folds, even though they are not intimately spatially associated
with faults (see Marshak et al., 2000, 2003) are also the result of far-field tectonic forces.
6.2. “BASIN AND DOME” FOLD INTERFERENCE PATTERN
The Hutchinson Cemetery folds are gentle upright folds with plunges rarely
exceeding 10o. This allow for spatial orientation of the folds to be characterized using
statistical analysis of the hinge line orientations from structural maps and rose-diagrams
(Figure. 5.1 to 5.4). The general orientation of the strike of the anticlines and synclines is
East-West with plunge directions being either East or West (Figure. 6.1). The alternating
direction of plunging hinge lines is suggestive of a “Basin and Dome” fold interference
pattern (Ramsay, 1967). Typically multiple deformation events are invoked to generate fold
interference patterns. A basin and domes pattern requiring the initial period of folding as a
result of shortening to be followed by a ninety-degree rotation of the stress field; the subsequent period of folding occurs as a result of shortening along a direction orthogonal to the first (Ramsay, 1967; Treagus and Treagus, 1981; Marinin and Sim, 2015). The origin of the Hutchinson Cemetery folds as a result of multiple deformation events related to an orthogonal rotation of the far-field stresses is inconsistent with several observations for these folds. The buckled sandstones of the Roubidoux formation are spatially restricted to localized area (~10 km) in the Ozark Dome. The immediately surrounding strata, including the Roubidoux Fm. are relatively un-deformed and sub-horizontal. Allen et al., (2001) presented a model for how dome and basin fold interference patterns may generated by
“transpressive inversion”. In this model reactivation of transpressional strike-slip fault systems in a reverse sense (e.g., right-lateral followed by left-lateral slip) can produce a
34 first set of upright, gently plunging, folds between the two fault traces with hinges
inclined c. 45o to the fault trace followed by a second set of upright, gently plunging, folds that forms at c. 45o in the opposing sense that overprint the first fold set resulting in the basin and dome interference pattern. In the Ozark Dome reactivation of basement faults as a result of far-field forces has produced strike-slip deformation in the overlying cover rocks
(Harrison and Schultz, 2002; Hildenbrand et al., 2002; Marshak et al., 2000, 2003). While some faults exhibit evidence for multiple senses of slip (e.g., Ste. Genevieve), most faults
that are oriented NW-SE record left-lateral displacement whereas faults oriented NE-SW record right-lateral displacement (Clendenin et al., 1989; Clendenin et al., 1993;
Clendenin and Diehl, 1999; Hudson, 2000; Harrison and Schultz, 2002). Although the
Hutchinson Cemetery folds are not immediately spatially associated with faults, NW-SE faults occur to the north and to the south of the zone of folding (Figure. 2.2). However, these faults do not entirely bound the zone of folding as required by the transpressive inversion model of Allen et al., (2001) to produce a dome and basin interference pattern.
Instead the faults define a right-stepping pattern with the Hutchinson Cemetery folds cropping our within the zone of fault overlap (Figure. 2.2). While this overlap zone would result in localized transpression during left-lateral slip on these faults, a second deformation event of right-lateral slip would lead to transtension rather than transpression and a second deformation of orthogonal shortening as required by the model is unlikely.
6.3. CONICAL FOLDS
Confinement of exposures of the Hutchinson Cemetery folds to discontinuous
road-cuts presents additional challenges in the classification of these folds. Structural data
35 through these three-dimensional geometric surfaces is restricted to a random, narrow
(<6m and more typically <2m) vertical, two-dimensional slice, through these folds along
U.S. Route 63. π-diagrams for these folds (Figure. 5.1 to 5.4) consistently display three types of fold patterns (see Davis et al., 2011).
Figure. 6.1. Rose diagram of all hinge lines, showing the trends of fold structure.
36 For several folds, poles-to-bedding planes display a reasonable fit to a great circle and are classified as cylindrical to near-cylindrical folds. Within the same road-cut, other folds (10 folds out of all 54 folds) have poles-to-bedding planes on a π-diagrams that are best fit by a small circle and are classified as non-cylindrical folds. Non- cylindrical folds represented by small circles in π-diagrams are traditionally classified as
“conical-folds” as this pattern is consistent with the intersection of half a sphere with a geometric cone (Dahlstrom 1954; Bengston, 1980). For many folds, the poles-to-bedding planes display a reasonable fit to a either a great circle or a small-circle and classification based upon stereograms is ambiguous. Bengston (1980) introduce the use of polar tangent diagrams as a means for resolving this ambiguity between cylindrical to non- cylindrical folds. On tangent diagrams, cylindrical fold surface orientation data define straight lines and non-cylindrical folds that define portions of arcs and are classified as
“conical folds”. Rare examples of folds with π-diagrams that define “fish-hook” patterns are also present.
The classification of the geometric shape of non-cylindrical folds as “conical folds” based upon interpretation of patterns on -diagrams and tangent diagrams has led to wide-acceptance and recognition among structural geologists of “conical folds” as a special class of folds (see Twiss and Moores, 1992, p. 221; Groshong, Jr., 2006, p. 111;
Davis et al., 2011, p. 365). However, a more realistic interpretation for the shape of such folds is that of the pericline (Welker et al., 2019). Periclines are elongated, doubly plunging, antiforms (domes) or synforms (basins) (Price and Cosgrove, 1990; Cosgrove and Ameen, 2000). Welker et al., (2019) using synthetic stereograms, tangent diagrams, and curvature analysis of two-dimensional transects through periclines, demonstrated that
37 small portions of periclines are “cylindrical folds” the remainder are “non-cylindrical folds”. The non-cylindrical portions of periclines yield stereograms and tangent diagrams with patterns on π-diagrams where a “cone” is a mathematically permissible solution, but not an accurate representation of the geometry of the folded surface (Welker et al., 2019).
The three-types of patterns displayed by π-diagrams of the Hutchinson Cemetery folds, including those with “fish-hook” patterns, are readily reproduced by orientation data collected along transect across a pericline fold produced by a dynamic modeling of buckling and plotted on synthetic stereogram and tangent diagrams (Welker et al., 2019).
A complete three-dimensional characterization of the Hutchinson Cemetery folds using geophysics is beyond the scope of this study. However, we contend the strong similarity of the patterns of π-diagrams and tangent diagrams from the random two-dimensional cross-section through these folds is consistent with those of the synthetic plots produced from pericline folds (Welker et al., 2019).
In addition, while several conceptual models are proposed to explain conical fold formation (Ross, 1962; Rickard, 1963; Stauffer, 1964; Becker, 1995; Harris et al., 2002;
Pastor-Galan et al., 2012) true dynamic models, using realistic relationships among force, stress, strain, and mechanical strength properties of rocks do not exist. In contrast, realistic dynamic models of buckling of rocks, within a locally uniform horizontal strain field, produces pericline folds with a single deformation event (Fernandez and Kaus,
2014; Liu et al., 2016).
Although poorly exposed, the most realistic interpretation for the geometry of the
Hutchinson Cemetery folds is that they are periclines.
38 6.4. NUMERICAL MODELING APPROACH
More traditional interpretations for the character and origin of the Hutchinson
Cemetery folds (e.g., karst-collapse, basin and dome interference pattern, conical folds) which initially appear plausible, in part due to restricted exposure of these three- dimensional folds along essentially a two-dimensional transect limited to discontinuous highway road-cuts, have fatal flaws and are eliminated from further consideration. Instead, field observations and structural analysis of these folds is consistent with their having a form best described as a “pericline” – an elongated, doubly plunging dome or basin (Price and Cosgrove, 1990; Cosgrove and Ameen, 2000). Liu et al., (2016), using realistic dynamic models of buckling of rocks, within a locally uniform horizontal strain field, produce pericline folds in a single deformation event. In this section, we present the results of 2-D and 3-D numerical modeling to provide an alternative model for the formation of the Hutchison Cemetery folds that is consistent with their geometric form, restricted spatial occurrence, and current understanding of regional tectonics for the
Ozark Dome. The purpose of this model is to demonstrate the high plausibility of producing these folds as a result of a single episode of transpression rather than faithfully reproduce the exact nature of Hutchinson Cemetery folds.
6.4.1. 2D Transpression Model. The Hutchinson Cemetery folds crop out within the overlap zone of two NW-SE striking faults that cross-cut the Paleozoic cover (Figure.
2.2). Throughout Missouri the NW-SE fault system, where exposed, consistently display left-lateral displacement (Horrall et al., 1983; Clendenin et al., 1989; Clendenin et al.,
1993; Harrison and Schultz, 2002). The spatial arrangement of the faults in this area define a right-stepping, en-echelon pattern, such that during periods of left-lateral slip the
39 fault overlap zone should be subjected to transpression (Allen et al., 2001; Davis et al.,
2011). In order to verify that the interaction of the two faults results in a higher degree of localized compression, and an increased likelihood of buckling, we constructed a 2D plane stress finite element model using the commercial software package ABAQUSTM
(Figure. 6.2). In this model, we include six northwest striking fault segments, the location and strike of the faults are digitized from the geologic map (Figure. 2.2) and the model area is sufficient to avoid edge-effects. The fault geometry is simplified as smooth, vertical interfaces with a friction coefficient of 0.6, cutting a flat-plane. Elastic homogenous material property parameters (i.e., Young’s modules of 10 GPa and
Poisson’s ratio of 0.25) are applied uniformly across the model. A ten percent east-west compressional deformation is applied; the model is constrained in the north-south direction to allow in plane displacements along the east-west direction. This simulates the far-field stress produced by the Late Paleozoic Alleghenian Orogeny to create left-lateral slip (see Clendenin et al., 1989). Figure 6.2b shows the difference in the mean stress (i.e., the background mean stress obtained from a model without implementing the faults is subtracted) developed after compression is applied. The results show that the Hutchinson
Cemetery folds along US Hwy 63 are located along a corridor (yellow box) of elevated mean stress (i.e., ~20 – 40 MPa). From the results, the location of the Hutchinson
Cemetery folds are consistent with forming as buckle folds as a result of increased compressional stress within a zone of transpression generated by the contractional step- over of the bounding Bradford and North-Branch Faults.
40
Figure. 6.2. 2D transpression model. a) the model sketch showing the boundary conditon b) the model result showing the mean stress distribution in the study area.
6.4.2. 3D Pericline Model. Traditional geology 2D approach along the road cut is
not sufficient enough to illustration the overall architecture of the basin and dome
periclines in the study area. The road cuts provide the exposures in the nearly
perpendicular orientation to the far field shortening direction. The correlations across the
road are necessary to reconstruct the geometry of the Hutchinson Cemetery folds. And
such correlations can be clearly recognized in the field. By connecting the marker layers
across the road, the maximum shortening direction is estimated in NWW (293o) to SEE
(113o).
The geometry of the Hutchinson Cemetery folds is consistent with the geometry
of pericline folds. Here we present the results of a 3D visco-elastic modeling (see
Mancktelow, 1999; Zhang et al., 2000; Schmalholz et al., 2001; Liu et. al., 2016) to
demonstrate how periclines, which have a basin and dome geometry, are readily produced
41 during a single deformation event of unidirectional compression as a result of
transpression (see previous section). We use the approach of Eckert et al. (2014) and Liu
et al. (2016) to construct a linear Maxwell visco-elastic 3D model to simulate potential
outcomes for the proposed model setup by applying single layer and effective single layer
visco-elastic bucking theory. Effective stress analysis is applied by considering pore
pressure and assuming an incompressible fluid and rock grains utilizing a Biot coefficient
α=1 (see Biot and Willis, 1957; Nur and byerlee, 1971). 3D finite analysis utilizing
ABAQUSTM simultaneously solves equations of equilibrium, conservation of mass, constitutive equations, and pore fluid flow (See Eckert et al., 2014; Liu et al., 2016 for
details).
Similar to the 2D numerical modeling, the purpose of the 3D modeling is to
demonstrate the feasibility of producing folds with pericline geometry as a result of
localized transpression rather than reproducing an exact replica of the Hutchison
Cemetery folds. Our model includes three folded stratigraphic layers, the upper sandstone
(5m), intervening weak clay-rich mudstone layer (1m), and the lower sandstone layers (3m)
respectively (Figure. 6.3). The three layers are considered as an effective single layer model, and they are embedded within a relatively incompetent matrix host rock. The elastic material property parameters for these homogenous layers are shown in Table 6.1. The geometry of the initial perturbation is a central dome with a 1:5 aspect ratio (short axis/long axis) surrounded by six, similar, half domes in a 221m x 276m XY plane and a
314m Z direction before compression. The amplitude of initial perturbation is 8.3% of the total thickness of the competent layer (Damasceno et al, 2017). After an initial pre-
stressing step, layer parallel compression is applied along the X-direction of the model at a
42 constant strain rate of 10-14 and the model is constrained along the Y-direction as well
as along the lower boundary of the model. Unfolding of the tightest Hutchinson Cemetery
folds yield estimates of ~21% shortening and we present model results for 15%, 20%, and
25% shortening for comparison (Figure. 6.3).
3D numerical modeling of layer-parallel shortening during a single contractional deformation event produces a field of buckle folds with an overall basin and dome pattern
(Figure. 6.3). We suggest, that if fully exposed, the Hutchinson Cemetery folds would have a similar form to these periclines. A linear transect through these folds (e.g., the road-cuts of Highway 63) would intersect several alternating domes and basins creating the appearance of anticlines and synclines plunging in alternating directions (i.e., see Figure.
5.1 to 5.4) depending upon which side of the fold is transected. In addition, Welker et al.,
(2019) demonstrated that structural data collected along such transects through pericline folds will produce π-diagrams characterized by great circles, small circles, and “fish-hook” patterns. The characterization and origin of the Hutchinson Cemetery folds as a field of periclines generated in a single contractional deformational event is consistent with the results of our simplified, but realistic, 3D numerical modelling.
43
Figure.6.3. Three-dimentional model sketch and resutls.
Table 6.1. Material properties for each unit of the 3D pericline model.
Folded layer Properties (Roubidoux Sands) Clay Matrix Specific gravity 2.2 1.9 2.7 Visocosity 1021 (Pa s) 1019 (Pa s) 2x1019(Pa s) Young's modulus 33.7(GPa) 10 (MPa) 3.37(GPa) Poisson's Ratio 0.25 0.25 0.25 Permeablity 1.02x10-16 (m2) 1.02x10-13 (m2) 1.02x10-15 (m2) Strain rate 10-14 10-14 10-14
44 7. CONCLUSIONS
The origin of the Hutchison Cemetery folds, a series of isolated buckle folds in the upper sandstones of the Ordovician Roubidoux formation, remained an enigma due to their isolation in the middle of the relatively unreformed strata of the Ozark Plateau and their limited exposure being confined to discontinuous, low road-cuts along U.S. Route
63 just north of Licking, Missouri. Using a combination of field structural analysis and
numerical modeling, we propose these folds formed as a result of a single localized
contractional deformation event within in a zone of transpression. In the study area, two
northwest striking faults, the Bradford Branch fault and the Licking fault (Figure. 2.2),
border the mapped area to the north and south. NW-SE striking faults throughout Missouri
consistently record left-lateral slip (Horrall et al., 1983; Clendenin et al., 1989; Clendenin
et al., 1993; Harrison and Schultz, 2002). The right-stepping, en-echelon geometry of these
faults created a localized area of transpression when they were reactivated by far field
stresses, in east-west direction. This localized unidirectional shortening stress field within
the transpression zone initiated layer-parallel buckling, of ~21% strain, of the Ordovician
Roubidoux Formation sandstones to form periclines.
The essentially two-dimensional transect through these folds, provided by isolated
road cuts along U.S. route 63, erroneously creates the appearance of a basin and dome fold
interference pattern, as well as the presence of both cylindrical and non-cylindrical folds
(i.e., conical folds). In contrast, integrating the results of field mapping, structural analysis,
and 2D, and 3D numerical modelling suggest these folds are best represented as periclines
(see also Welker et al., 2019).
45 The timing of formation of the Hutchinson Cemetery folds, is consistent with
deformation of the interior of the mid-continent as a result of far-field stresses generated by plate collisions associated with the Alleghenian or Ancestral Rockies Orogenies
(Clendenin,et al., 1989; Harrison and Schultz, 2002; Marshak et al., 2003).
46
APPENDIX A.
FIELD DATA OF HUCHISON CEMETERY FOLDS
47 Fifty-four folds from four areas area investigated in detail. Their attitude data are collected and plotted in stereograms for the hinge line and axial surface calculations.
Each stereogram is shown as following:
Figure A.1. Stereograms of folds in area one on the east.
48
Figure A.2. Stereograms of folds in area one on the west.
49
Figure A.3. Stereograms of folds in area two on the east (part one).
50
Figure A.4. Stereograms of folds in area two on the east (part two).
51
Figure A.5. Stereograms of folds in area two on the east (part three).
52
Figure A.6. Stereograms of folds in area two on the west (part one).
53
Figure A.7. Stereograms of folds in area two on the west (part two).
54
Figure A.8. Stereograms of folds in area two on the west (part three).
55
Figure A.9. Stereograms of folds in area three on the east (part one).
56
Figure A.10. Stereograms of folds in area three on the east (part two).
57
Figure A.11. Stereograms of folds in area three on the west (part one).
58
Figure A.12. Stereograms of folds in area three on the west (part two).
59
Figure A.13. Stereograms of folds in area four on the west (part one).
60
Figure A.14. Stereograms of folds in area four on the west (part two).
61
Figure A.15. Stereograms of folds in area four on the west (part three).
62
Figure A.16. Stereograms of folds in area four on the east (part one).
63
Figure A.17. Stereograms of folds in area four on the east (part two).
64
APPENDIX B.
GOVERNING EQUATIONS
65 Governing equations
Following the studies of Mancktelow (1999), Zhang et al. (2000), Schmalholz et
al. (2001), Liu et.at (2016), the visco-elastic behavior of geologic deformations of the
study area is simulated. In this study, Linear Maxwell visco-elastic model is used to
simulate the potential outcomes with proposed model setups by applying a single layer
and effective single layer visco-elastic bucking theory. Effective stress analysis is applied by considering pore pressure and assuming an incompressible fluid and rock grains (Biot coefficient α=1, Biot and Willis, 1957; Nur and byerlee, 1971). 2D plane strain finite analysis and 3D finite analysis (via the commercial software package ABAQUSTM) are
utilized to solve the equations of equilibrium, conservation of mass, constitutive
equations and pore fluid flow. See Eckert et al. (2014) for more details on the system of
governing equations and its derivations.
Dominant wavelength
To select the appropriate dominant wavelength, the competence contrast (R)
(Schmalholz and Podladchikov, 1999; Schmalholz et al., 2001) is introduced to determine
whether the buckle folds behave viscously (R<1) or elastically (R>1). R is defined by the
ratio of the viscous dominant wavelength, , to the elastic dominant wavelength, .
For the single layer and effective single layer model:
(1)
where µl is the viscosity of the competent layer is, is the viscosity of the matrix, G is
the shear modulus an P0 is the Initial layer parallel stress (P0=4µlέ) (Schmalholz and
66 Podladchikov, 1999). A constant strain rate of 10-14 s -1 is applied for all models (Twiss
and Moores, 2007).
Both 2D cross-section models and 3D pericline model develop in viscous behavior for R is smaller than 1. Different models with different viscosities and Young's modulus result in the different values of R as shown in Table 1. The dominant wavelength is given by:
a) For the single layer model:
(2) where h is the thickness of the competent layer.
b) For a single effective model:
(3)
(4)
where H is the thickness of multilayer, consisting of alternating stiffer and softer layers of
viscosity u1 and u2, α is the occupying fraction of the total thickness (Hudleston and
Treagus, 2010).
67
APPENDIX C.
PALEOMAGNETIC FOLD TEST
68 Paleomagnetic fold test is conducted to constrain time of those deformations.
However, not publishable quality results are achieved during the data process. The results may not useful to constrain the timing, but it fits with the range of proposed hypothesis to some degrees.
Many pieces of data do not show clear linear decay (Figure. C.1A and C.1B), indicating too much noise in the specimens. Only data with clear linear decay may contribute to the analysis (Figure. C.1C). However, among all collected the specimens, only a few of them are usable. Stereonet analysis of paleomagnetic directions of specimen does not have a circular distribution (Figure. C.2). Both the precision (κ) and
α95 (95% probability that the unknown true mean is within the α95 of the calculated mean) do not meet the criteria of Paleomagnetic statistics. For Roubidoux Samples, α95 is 47.7o (typically, less than 15o is good), leading to the results that do not match any known polar wander path.
There are two possibilities that can explain the noise in data. One could be unstable magnetization, which is common in whitish sandstone, particularly if sandstone is soft. Alternatively, the results could be the interference of multiple components. SE direction indicates late Paleozoic age and West direction indicates Ordovician age.
Because of the huge uncertainty in the Paleomagnetic result, time of Roubidoux deformations cannot be constrained by this method.
69
Figure. C.1. A) a specimen with poor linear decay; B) a specimen with sort of linear decay but not clear enough; C) a specimen with good linear decay, which will contribute to the further stereonet analysis
70
Figure. C.2. Stereographic distribution of paleomagnetic data.
71 BIBLIOGRAPHY
Allmendinger, R. W., Cardozo, N., & Fisher, D. M. (2011). Structural geology algorithms: Vectors and tensors. Cambridge University Press.
Bamford, M. L., & Ford, M. (1990). Flexural shear in a periclinal fold from the Irish Variscides. Journal of structural geology, 12(1), 59-67.
Bartholomew, M. J., Whitaker, A. E., Tollo, R. P., Hibbard, J. P., & Karabinos, P. M. (2010). The Alleghanian deformational sequence at the foreland junction of the Central and Southern Appalachians. From Rodinia to Pangea: The Lithotectonic Record of the Appalachian Region: Geological Society of America, Memoir, 206, 431-454.
Becker, A. (1995). Conical drag folds as kinematic indicators for strike-slip fault motion. Journal of Structural Geology, 17(11), 1497-1506.
Bengtson, C. A. (1980). Structural uses of tangent diagrams. Geology, 8(12), 599-602.
Biot, M. A., & Willis, D. G. (1957). The elastic coefficients of the theory of consolidation. J. appl. Mech, 24, 594-601.
Biot, M. A. (1961). Theory of folding of stratified viscoelastic media and its implications in tectonics and orogenesis. Geological Society of America Bulletin, 72(11), 1595- 1620.
Blay, P., Cosgrove, J. W., & Summers, J. M. (1977). An experimental investigation of the development of structures in multilayers under the influence of gravity. Journal of the Geological Society, 133(4), 329-342.
Blumstein, A. M., Elmore, R. D., Engel, M. H., Elliot, C., & Basu, A. (2004). Paleomagnetic dating of burial diagenesis in Mississippian carbonates, Utah. Journal of Geophysical Research: Solid Earth, 109(B4).
Bretz, J. H. (1950). Origin of the filled sink-structures and circle deposits of Missouri. Geological Society of America Bulletin, 61(8), 789-834.
Bretz, J. H. (1965). Geomorphic history of the Ozarks of Missouri: Missouri Geol. Survey and Water Resources, 41.
Calais, E., Freed, A. M., Van Arsdale, R., & Stein, S. (2010). Triggering of New Madrid seismicity by late-Pleistocene erosion. Nature, 466(7306), 608.
Clendenin, C. W., Niewendorp, C. A., & Lowell, G. R. (1989). Reinterpretation of faulting in southeast Missouri. Geology, 17(3), 217-220.
72 Clendenin, C. W., Middendorf, M. A., Thompson, T. L., & Whitfield, J. W. (1993). Structural style of the Eureka fault system, eastern Missouri. Geological Society of America, Abstracts with Programs;(United States), 25(CONF-9303210--).
Clendenin, C. W., & Diehl, S. F. (1999). Structural styles of Paleozoic intracratonic fault reactivation: a case study of the Grays Point fault zone in southeastern Missouri, USA. Tectonophysics, 305(1-3), 235-248.
Cochran, K. A., & Elmore, R. D. (1987). Paleomagnetic dating of Liesegang bands. Journal of Sedimentary Research, 57(4), 701-708.
Cosgrove, J. W. (1998). The role of structural geology in reservoir characterization. Geological Society, London, Special Publications, 127(1), 1-13.
Cosgrove, J. W., & Ameen, M. S. (1999). A comparison of the geometry, spatial organization and fracture patterns associated with forced folds and buckle folds. Geological Society, London, Special Publications, 169(1), 7-21.
Cox, R.T., 1995. Intraplate deformation during the Appalachian-Ouachita orogeny as recorded by mesoscale structures on the Ozark Plateau of North America. Unpublished doctoral dissertation, University of Missouri, Columbia, 229 pp.
Cox, R. T. (2009). Ouachita, Appalachian, and Ancestral Rockies deformations recorded in mesoscale structures on the foreland Ozark plateaus. Tectonophysics, 474(3-4), 674-683.
Craddock, J. P., & Relle, M. (2003). Fold axis-parallel rotation within the Laramide Derby Dome fold, Wind river basin, Wyoming, USA. Journal of Structural Geology, 25(11), 1959-1972.
Csontos, R., & Van Arsdale, R. (2008). New Madrid seismic zone fault geometry. Geosphere, 4(5), 802-813.
Dahlstrom, C.D.A., (1954). Statistical analysis of cylindrical folds. Trans. Can. Inst. Min.Metall. 57, 140–145.
Damasceno, D. R., Eckert, A., & Liu, X. (2017). Flexural-slip during visco-elastic buckle folding. Journal of Structural Geology, 100, 62-76.
Davis, G. H. (1978). Monocline fold pattern of the Colorado Plateau. Laramide folding associated with basement block faulting in the western United States: Geological Society of America Memoir, 151, 215-233.
Davis, G. H., Reynolds, S. J., Kluth, C. F., & Kluth, C. (2011). Structural geology of rocks and regions. John Wiley & Sons.
73 DeLucia, M. S., Guenthner, W. R., Marshak, S., Thomson, S. N., & Ault, A. K. (2017). Thermochronology links denudation of the Great Unconformity surface to the supercontinent cycle and snowball Earth. Geology, 46(2), 167-170.
Dubey, A. K., & Cobbold, P. R. (1977). Noncylindrical flexural slip folds in nature and experiment. Tectonophysics, 38(3-4), 223-239.
Duchek, A. B., McBride, J. H., Nelson, W. J., & Leetaru, H. E. (2004). The Cottage Grove fault system (Illinois basin): Late Paleozoic transpression along a Precambrian crustal boundary. Geological Society of America Bulletin, 116(11-12), 1465-1484.
Eckert, A., Connolly, P., & Liu, X. (2014). Large‐scale mechanical buckle fold development and the initiation of tensile fractures. Geochemistry, Geophysics, Geosystems, 15(11), 4570-4587.
Elliott, W. R. and Ashley, D. C. 2005. Caves and karst. – In: Nelson, P. (ed.), The terrestrial natural communities of Missouri. Missouri Natural Areas Committee, pp. 474–491.
Elmore, R. D., Burr, R., Engel, M., & Parnell, J. (2010). Paleomagnetic dating of fracturing using breccia veins in Durness Group carbonates, NW Scotland. Journal of Structural Geology, 32(12), 1933-1942.
Fernandez, N., & Kaus, B. J. (2014). Fold interaction and wavelength selection in 3D models of multilayer detachment folding. Tectonophysics, 632, 199-217.
Fenneman, N. M. (1938). The Ozark Plateaus. Physiography of eastern United States.
Fleuty, M. J. (1964). The description of folds. Proceedings of the Geologists' Association, 75(4), 461-492.
Groshong Jr, R. H. (2006). 3-D structural geology (pp. 305-371). Springer-Verlag Berlin Heidelberg.
Guccione, M. J., Marple, R., & Autin, W. J. (2005). Evidence for Holocene displacements on the Bootheel fault (lineament) in southeastern Missouri: Seismotectonic implications for the New Madrid region. Geological Society of America Bulletin, 117(3-4), 319-333.
Harris, L. B., Koyi, H. A., & Fossen, H. (2002). Mechanisms for folding of high-grade rocks in extensional tectonic settings. Earth-Science Reviews, 59(1-4), 163-210.
Harrison, R. W., & Schultz, A. (1994). Strike‐slip faulting at Thebes Gap, Missouri and Illinois: Implications for New Madrid tectonism. Tectonics, 13(2), 246-257.
74 Harrison, R. W., & Schultz, A. (2002). Tectonic framework of the southwestern margin of the Illinois basin and its influence on neotectonism and seismicity. Seismological Research Letters, 73(5), 698-731.
Robert D. Hatcher, Jr., 2010. "The Appalachian orogen: A brief summary", From Rodinia to Pangea: The Lithotectonic Record of the Appalachian Region (Vol. 206), Richard P. Tollo, Mervin J. Bartholomew, James P. Hibbard, Paul M. Karabinos, Geological Society of America
Heller, R. L. (1954). Stratigraphy and paleontology of the Roubidoux Formation of Missouri.
Hildenbrand, T. G., & Hendricks, J. D. (1995). Geophysical setting of the Reelfoot rift and relations between rift structures and the New Madrid seismic zone (No. 1538- E).
Hildenbrand, T. G., McBride, J. H., & Ravat, D. (2002). The Commerce geophysical lineament and its possible relation to Mesoproterozoic igneous complexes and large earthquakes in the central Illinois basin. Seismological Research Letters, 73(5), 640- 659.
Horrall, K.B., Hagni, R.D., and Kisvarsanyi, G., 1983, Mineralogical, textural and paragenetic studies of selected ore deposits of the Southeast Missouri lead-zinc- copper district, and their genetic implications: International conference on Mississippi Valley type lead-zinc deposits. Proceedings volume: Rolla, University of Missouri-Rolla Press, p. 289–316.
Hudson, M. R. (2000). Coordinated strike-slip and normal faulting in the southern Ozark dome of northern Arkansas: Deformation in a late Paleozoic foreland. Geology, 28(6), 511-514.
Joel, L. (2018), Erasing a billion years of geologic time across the globe, Eos, 99, https://doi.org/10.1029/2018EO092065. Published on 05 February 2018.
Kaus, B. J., & Schmalholz, S. M. (2006). 3D finite amplitude folding: implications for stress evolution during crustal and lithospheric deformation. Geophysical Research Letters, 33(14).
Lee, W. (1913). The geology of the Rolla quadrangle: Rolla. Missouri Division of Geology and Land Survey, 13.
Liu, C. (2016). Periclinal folding in Ozark plateau: A record of local karst collapse or regional tectonic forces? Masters Theses. 7607.
75 Liu, J. (2018) Origin and Structural Geometry of Folding In the Eureka-House Springs Structure. Poster session presented At North-Central - 52nd Annual Meeting of Geological Society of America, Ames, Iowa.
Liu, X., Eckert, A., & Connolly, P. (2016). Stress evolution during 3D single-layer visco- elastic buckle folding: Implications for the initiation of fractures. Tectonophysics, 679, 140-155.
Loucks, R. G. (1999). Paleocave carbonate reservoirs: origins, burial-depth modifications, spatial complexity, and reservoir implications. AAPG bulletin, 83(11), 1795-1834.
Loucks, R. G. (2007). A review of coalesced, collapsed-paleocave systems and associated suprastratal deformation. Acta Carsologica, 36(1).
Mancktelow, N. S. (1999). Finite-element modelling of single-layer folding in elasto- viscous materials: the effect of initial perturbation geometry. Journal of Structural Geology, 21(2), 161-177.
Marinin, A. V., & Sim, L. A. (2015). The contemporary state of stress and strain at the western pericline of the Greater Caucasus. Geotectonics, 49(5), 411-424.
Marshak, S., & Paulsen, T. (1996). Midcontinent US fault and fold zones: A legacy of Proterozoic intracratonic extensional tectonism?. Geology, 24(2), 151-154.
Marshak, S., & Paulsen, T. (1997). Structural style, regional distribution, and seismic implications of midcontinent fault-and-fold zones, United States. Seismological Research Letters, 68(4), 511-520.
Marshak, S., Karlstrom, K., & Timmons, J. M. (2000). Inversion of Proterozoic extensional faults: An explanation for the pattern of Laramide and Ancestral Rockies intracratonic deformation, United States. Geology, 28(8), 735-738.
Marshak, S., Nelson, W. J., & McBride, J. H. (2003). Phanerozoic strike-slip faulting in the continental interior platform of the United States: examples from the Laramide Orogen, Midcontinent, and Ancestral Rocky Mountains. Geological Society, London, Special Publications, 210(1), 159-184.
Marshak, S., Abert, C. C., & Larson, T. H. (2016). Geological and geophysical maps of the Illinois Basin-Ozark Dome region. Illinois Map 23.
Martin, J. A., Knight, R. D., & Hayes, W. C. (1961). Ordovician system. The Stratigraphic Succession in Missouri, 40, 20-32.
Mateker, E. J., & Segar, R. L. (1965). Gravity investigation along the eastern flank of the Ozark uplift. Transactions of the American Geophysical Union, 46, 160.
76 McBride, J. H., & Nelson, W. J. (1999). Style and origin of mid-Carboniferous deformation in the Illinois Basin, USA—Ancestral Rockies deformation?. Tectonophysics, 305(1-3), 249-273.
McDonnell, A., Loucks, R. G., & Dooley, T. (2007). Quantifying the origin and geometry of circular sag structures in northern Fort Worth Basin, Texas: Paleocave collapse, pull-apart fault systems, or hydrothermal alteration?. AAPG bulletin, 91(9), 1295-1318.
Middendorf, M. (2003). Geologic Map of Missouri-Sesquicentennial Edition. Missouri Division of Geology and Land Survey.
Nelson, W. J., Krausse, H. F., & Bristol, H. M. (1981). Cottage Grove Fault System in southern Illinois (No. PB-83-174433). Illinois Inst. of Natural Resources, Champaign (USA). State Geological Survey Div..
Nelson, J., & Lumm, D. (1985). St. Geneviene fault. Nuclear Regulatory Commission Report. NUREG/CR-4333, 94 p. In.
Nur, A., & Byerlee, J. (1971). An exact effective stress law for elastic deformation of rock with fluids. Journal of Geophysical Research, 76(26), 6414-6419.
Orndorff, R. C., Weary, D. J., & Sebela, S. (2001). Geologic framework of the Ozarks of south-central Missouri—Contributions to a conceptual model of karst. Proceedings, Water-Resources Investigations Report, 1(4011), 18-24.
Price, N. J., & Cosgrove, J. W. (1990). Analysis of geological structures. Cambridge University Press.
Pastor-Galán, D., Gutiérrez-Alonso, G., Mulchrone, K. F., & Huerta, P. (2012). Conical folding in the core of an orocline. A geometric analysis from the Cantabrian Arc (Variscan Belt of NW Iberia). Journal of Structural Geology, 39, 210-223.
Quinlan, G. M., & Beaumont, C. (1984). Appalachian thrusting, lithospheric flexure, and the Paleozoic stratigraphy of the Eastern Interior of North America. Canadian Journal of Earth Sciences, 21(9), 973-996.
Ramsay, J. G., & Huber, M. I. (1987). The techniques of modern structural geology: Folds and fractures (Vol. 2). Academic press.
Rickard, M. J. (1963). Analysis of the strike swing at crockator mountain, co. donegal, eire. Geological Magazine, 100(5), 401-419.
Ross, J. V. (1962). The folding of angular unconformable sequences. The Journal of Geology, 70(3), 294-308.
77 Root, S., & Onasch, C. M. (1999). Structure and tectonic evolution of the transitional region between the central Appalachian foreland and interior cratonic basins. Tectonophysics, 305(1-3), 205-223.
Schmalholz, S. M., Podladchikov, Y. Y., & Schmid, D. W. (2001). A spectral/finite difference method for simulating large deformations of heterogeneous, viscoelastic materials. Geophysical Journal International, 145(1), 199-208.
Schultz, A., Baker, G. S., & Harrison, R. W. (1992). Deformation associated with the Ste. Genevieve fault zone and mid-continent tectonics. Geological Society of America, Abstracts with Programs;(United States), 24(CONF-921058--).
Smith, I.M., Griffiths, D.V. and Margetts, L., 2013. Programming the finite element method. John Wiley & Sons.
Snyder, F. G. and Gerdemann, P. E. (1968). Geology of the southeast Missouri lead district. In: Ridge, J.D. (Ed.), Ore Deposits of the United States; the Graton-Sales Volume, vol. 1. American Institute of Mining, Metallurgy and Petroleum Engineers, pp. 326–358.
Spencer, G. C., (2011) Roadside Geology of Missouri. Missoula, Mont: Mountain Press Pub. Co, 1- 273.
Spreng, A. C., and Proctor, P. D. (2001). “Geologic map of the Rolla 7.5″ quadrangle.” Missouri Dept. of Natural Resources, Division of Geology and Land Survey, Geological Survey Program.
Stauffer, M. R. (1964). The geometry of conical folds. New Zealand Journal of Geology and Geophysics, 7(2), 340-347.
Tewksbury, B. J., Tarabees, E. A., & Mehrtens, C. J. (2017). Origin of an extensive network of non-tectonic synclines in Eocene limestones of the Western Desert, Egypt. Journal of African Earth Sciences, 136, 148-167.
Thomas, W. A. (1985). The Appalachian-Ouachita connection: Paleozoic orogenic belt at the southern margin of North America. Annual Review of Earth and Planetary Sciences, 13(1), 175-199.
Thomas, W. A. (2011). The Iapetan rifted margin of southern Laurentia. Geosphere, 7(1), 97-120.
Thompson, T. L. (1991). Paleozoic succession in Missouri. Part 2. Ordovician System. Report of Investigations, 70(2).
Thompson, T. L. (1995). The stratigraphic succession in Missouri. Missouri Department of Natural Resources Division of Geology and Land Survey, 40.
78 Thompson, T. L. (2001). Lexicon of Stratigraphic Nomenclature in Missouri. Missouri Department of Natural Resources, Division of Geology and Land Survey.
Tikoff, B., & Wojtal, S. F. (1999). Displacement control of geologic structures. Journal of Structural Geology, 21(8-9), 959-967.
Timmons, J. M., Karlstrom, K. E., Dehler, C. M., Geissman, J. W., & Heizler, M. T. (2001). Proterozoic multistage (ca. 1.1 and 0.8 Ga) extension recorded in the Grand Canyon Supergroup and establishment of northwest-and north-trending tectonic grains in the southwestern United States. GSA Bulletin, 113(2), 163-181.
Treagus, J. E., & Treagus, S. H. (1981). Folds and the strain ellipsoid: a general model. Journal of Structural Geology, 3(1), 1-17.
Tuttle, M. P., Schweig, E. S., Sims, J. D., Lafferty, R. H., Wolf, L. W., & Haynes, M. L. (2002). The earthquake potential of the New Madrid seismic zone. Bulletin of the Seismological Society of America, 92(6), 2080-2089.
Turner, F. J. (1963). Structural analysis of metamorphic tectonites, Francis J. Turner, Lionel E. Weiss. McGraw-Hill. New York. US.
Twiss, R. J., & Moores, E. M. (1992). Structural geology. Macmillan. Uken, R. (1998). The geology and structure of the Bushveld Complex metamorphic aureole in the Olifants River area (Doctoral dissertation).
Van Arsdale, R., Pryne, D., & Woolery, E. (2013). Northwestern extension of the Reelfoot north fault near New Madrid, Missouri. Seismological Research Letters, 84(6), 1114-1123.
Van Schmus, W. R., & Hinze, W. J. (1985). The midcontinent rift system. Annual Review of Earth and Planetary Sciences, 13(1), 345-383.
Van Schmus, W. R., Bickford, M. E., Turek, A., Van der Pluijm, B. A., & Catacosinos, P. A. (1996). Proterozoic geology of the east-central Midcontinent basement. SPECIAL PAPERS-GEOLOGICAL SOCIETY OF AMERICA, 7-32.
Weary, D. J., & Doctor, D. H. (2014). Karst in the United States: A digital map compilation and database. US Department of the Interior, US Geological Survey.
Webb, B. C., & Lawrence, D. J. D. (1986). Conical fold terminations in the Bannisdale Slates of the English Lake District. Journal of Structural Geology, 8(1), 79-86.
Weil, A. B., & Van der Voo, R. (2002). The evolution of the paleomagnetic fold test as applied to complex geologic situations, illustrated by a case study from northern Spain. Physics and Chemistry of the Earth, Parts A/B/C, 27(25-31), 1223-1235.
79 Welker, A. J., Hogan, J. P., Eckert, A., Tindall, S., & Liu, C. (2019). Conical folds–An artefact of using simple geometric shapes to describe a complex geologic structure. Journal of Structural Geology.
Zhang, Y., Mancktelow, N. S., Hobbs, B. E., Ord, A., & Mühlhaus, H. B. (2000). Numerical modelling of single-layer folding: clarification of an issue regarding the possible effect of computer codes and the influence of initial irregularities. Journal of Structural Geology, 22(10), 1511-1522.
Zulauf, J., Zulauf, G., & Zanella, F. (2016). Formation of dome and basin structures: Results from scaled experiments using non-linear rock analogues. Journal of Structural Geology, 90, 1-14.
Zulauf, G., Zulauf, J., & Maul, H. (2017). Quantification of the geometrical parameters of non-cylindrical folds. Journal of Structural Geology, 100, 120-129.
80 VITA
Chao Liu was born in Karamay, Xinjiang, China. In September 2009, he received
his offer from China University of Petroleum (Huadong) and finished his first three years
majoring in Geology. In August 2012, He went to Missouri University of Science and
Technology, Rolla, Missouri, USA as a transfer student by “two plus two transfer student
program”. In May 2014, he received his B.S. degree in Geology and Geophysics from
both China University of Petroleum (Huadong) and Missouri University of Science and
Technology. In August 2014, he enrolled as a master student at Missouri University of
Science and Technology. In December 2016, he received his M.S. degree in Geology and
Geophysics from Missouri University of Science and Technology. In January 2017, he
enrolled as a doctoral student at Missouri University of Science and Technology
Starting in summer 2012, he was a teaching assistant for geologic field trips,
structural geology, remote sensing technology, and igneous and metamorphic petrology.
His studies were focused on periclinal folds in the Ozark Plateau. In 2015, he received
$1,500 funding from Geological Society of America (GSA) for study on folds in the
Ozark Plateau. In July 2019, he received his Ph.D. degree in Geology and Geophysics
from Missouri University of Science and Technology.