structural modelling of the soapaga fault in the central

Structural Modelling of the Soapaga Fault in the central part of the Eastern

Cordillera, Colombia.

Germán Andrés Pardo Torres

Universidad Nacional de Colombia

Facultad de Ciencias, Departamento de Geociencias

Bogotá, Colombia

2020

Structural Modelling of the Soapaga Fault in the central part of the Eastern

Cordillera, Colombia.

Germán Andrés Pardo Torres

Tesis presentada como requisito parcial para optar al título de:

Magister en Ciencias-Geología

Director:

Guillermo Arturo Camargo Cortés.

Profesor de Geología Estructural

Línea de Investigación:

Geología Estructural


Facultad de Ciencias, Departamento de Geociencias

Bogotá, Colombia

2020

Dedicado a mis amigos Tomás y “Cha-Chan”. La

geología, las artes marciales y los tragos nunca

hubieran sido tan divertidos, osados e irónicos sin

su compañía.

De todo corazón, gracias.

Acknowledgments

For sure, one page is not enough to acknowledge all the people who supported me during my

master’s thesis, but certainly, I’m going to try my best. First, I want to recognize my wife Nathalia

Loaiza, the person behind all these pages and analyses. A load of developing scientific research is

too heavy for just one person. Her love, patience, and compassion every evening and weekend I

worked were one of my most significant supports all this time.

Next, I want to acknowledge my mom, who taught me that being smart and educated doesn’t mean

anything if you are not a fair and compassionate person. My dad gave me the most precious gift a

kid could ever have, the curiosity and love for science. And my brother, who, through his example,

always taught me that love is all we need.

I want to acknowledge my friends who were there at the beginning of this journey, Yeni, and Carlos

“Cacerolo,” two incredible people who were the initial spark to initiate my master’s studies. The

friends who came along the way, “JD,” Karen and Cristian, three fantastic people who always

supported me and turned the job into an incredible place. The friends who were still there, like

Felipe Pastor, who was my field trip partner, my discussion peer, and my gastronomic fellow during

this research. And last, the friends that have left, “Cha-Chan” and Tomas, my most significant

friends with whom I had lived amazing adventures both in the city and in the mountains.

I want to acknowledge my martial arts students and teachers, all the Bushinden Daruma Dojo and

the Komorebi Dojo members, all of you, awesome people who were a gift in my life, thank you for

evoking in me the principles of Judo and Budo through all this time. In my professional life, I want

to acknowledge Juan Carlos “El Pollo” Martínez, my first technical and ethical professor in my

workable life, and Andrea Pablos. They taught me the importance of always doing the best I could.

And last, to my advisor Guillermo Camargo, the professor I debt my passion for structural geology.

I want to thank you for all of you and the rest who do not appear on this page

Resumen

La Falla de Soapaga es una estructura orientada en dirección NNE-SSW, la cual corresponde al

borde oriental del Macizo de Floresta y se ha relacionado con la terminación sur de la Falla de

Bucaramanga. Existen varias interpretaciones estructurales para la Falla de Soapaga como los

modelos cinemáticos de pliegues por propagación de falla, por flexión de falla y tipo buckling, los

cuales buscan dar respuesta a las evidencias de deformación observadas en campo. Sin embargo,

ninguna de estas interpretaciones estructurales explica con claridad características estructurales

como la presencia del Sinclinal de Betéitiva localizado en el bloque yacente de la falla, la posición

vertical a invertida del flanco trasero de este pliegue, y el adelgazamiento estratigráfico

evidenciado en esta parte del pliegue. Por esta razón, he propuesto un modelo cinemático a través

del estilo de pliegues tipo Trishear, que explique la deformación de la Falla de Soapaga en una zona

entre el sector de Paz de Río y Corrales, Boyacá. Para esto, realicé el balanceo de cinco secciones

estructurales asociando las evidencias geológicas observadas en campo a tres episodios

deformativos que interpreté para el sistema de fallas Corrales-Soapaga. En este estudio identifiqué

que existen diferentes interpretaciones de la Falla de Soapaga, las cuales difieren en gran medida

en los estilos deformativos utilizados para explicar la deformación asociada a esta estructura.

Mediante el análisis que realicé, observé que varios de los modelos propuestos para la evolución

de la Falla de Soapaga no concuerdan con mi análisis, debido principalmente a que la Falla de

Corrales se ha descrito como la Falla de Soapaga, tratando estas dos fallas como una sola

estructura. Adicionalmente, el balanceo que desarrollé para el sistema de fallas Soapaga-Corrales

a través del modelo de Trishear, muestra que el acortamiento para estas secciones puede llegar a

ser hasta diez veces menos en comparación con los modelos de pliegues por flexión de falla.

Palabras clave: Trishear, Falla de Soapaga, Falla de Corrales, balanceo de secciones estructurales,

Macizo de Floresta, pliegues por propagación de falla.

Abstract

The Soapaga Fault is the eastern border of the Floresta Massif, oriented in an NNE-SSW trend, and

several authors have linked it to the Bucaramanga Fault's southern termination. There have been

several structural interpretations for this fault, such as the Fault-Propagation, Fault-Bend, and

Buckling folding kinematic models: all of these tried to explain the related deformation observed

in the field. However, none of these structural interpretations clearly explain structural features

such as the Betéitiva Syncline presence in the Soapaga Fault’s footwall, the upright-to-overturned

backlimb, and the stratigraphic thinning of the units at this limb of the fold. Therefore, I have

proposed a kinematic model using the Trishear folding style to explain the Soapaga Fault

deformation in an area between Paz de Río and Corrales localities (Boyacá). For this reason, I have

restored five structural cross-sections, associating the geologic evidence observed in the field to

three inferred deformation stages for the Soapaga-Corrales fault system. In this study, I identify

several structural interpretations for the Soapaga Fault, diverging each other in the kinematic

folding models used to explain the deformation related to this structure. I observed that most of

the proposed models for the Soapaga Fault evolution do not fit with my structural analysis results,

mainly because several authors described both the Corrales Fault and the Soapaga Fault as a single

structure. Besides, the restoration I made for the Soapaga-Corrales fault system through the

Trishear kinematic model shows that the shortening for the five structural cross-sections could be

ten times lesser compared to the fault-bend fold models.

Keywords: Trishear, Soapaga Fault, Corrales Fault, balanced cross-sections, Floresta Massif, fault-

propagation folds

Contents

Pág.

1 Geologic setting of the study area ..................................................................................... 7 1.1 Andean uplift and reactivation of Rift-related structures ................................................. 8 1.2 Stratigraphy of the study area. .......................................................................................... 9

2 Methods......................................................................................................................... 11 2.1 The Trishear modelling ..................................................................................................... 12

3 Results, analysis, and data interpretation. ....................................................................... 15 3.1 The Soapaga Fault features .............................................................................................. 15

3.1.1 Geologic relationships .................................................................................................. 16 3.1.2 Structural and mineralogical processes on the fault’s trace ........................................ 16 3.1.3 The geometric and geomorphic expression of the Soapaga Fault ............................... 18 3.1.4 Kinematic evidence of the Soapaga and Corrales faults .............................................. 21

3.2 Deformation and restoration analysis. ............................................................................ 21 3.2.1 Gravitational deformation and strike-slip faulting....................................................... 24 3.2.2 Compressional fault propagation thrusting ................................................................. 26 3.2.3 Trishear fault-propagation deformation ...................................................................... 30

3.3 Forward Modelling ........................................................................................................... 36

4 Discussion ...................................................................................................................... 39 4.1 The confusion about the Corrales Fault as the Soapaga Fault: an epistemological analysis of defining a fault. ........................................................................................................................ 39

4.1.1 Geometric features. ..................................................................................................... 39 4.1.2 Geomorphic features. .................................................................................................. 41 4.1.3 Fault zone features....................................................................................................... 41 4.1.4 Kinematic features ....................................................................................................... 42

4.2 The Trishear deformation as a realistic kinematic model for the study area .................. 44 4.3 The possibility of a regional fault-propagation fold model with a local Trishear kinematic model 48

5 Conclusions .................................................................................................................... 51 5.1 Conclusions ...................................................................................................................... 51

Image list

Pag. Fig. I- 1 Tectonic framework and geological map of the Floresta Massif and the study area ........... 2

Fig. I- 2. Fault-Bend kinematic models for the Soapaga Fault. .......................................................... 3

Fig. I- 3. Two Fault-Propagation kinematic models for the Soapaga Fault ........................................ 3

Fig. I- 4. Seismic interpretation in the study area of a basement rooted geometry for the Soapaga

Fault, with no evidence of flats or fault bend that supports the FBM. ............................................. 4

Fig. I- 5 Comparison of the two main explanations for the Soapaga Fault. ....................................... 5

Fig. 1- 1. A chronostratigraphic framework of the study area in the Floresta Massif. .................... 10

Fig. 2- 1 Three examples of the Trishear kinematic model applied for thrust, reverse, and normal

faults. ............................................................................................................................................... 13

Fig. 3- 1. Geological map of the study area and images of structural features of primary folds and

faults. In Fig.-G, the arrows point to the bed’s bottom showing the strata polarity. ...................... 17

Fig. 3- 2. The “three-point” solution for the Soapaga Fault. ............................................................ 19

Fig. 3- 3. Relief maps of the Soapaga Fault geomorphic expression. .............................................. 20

Fig. 3- 4. A zoom of the topographic contours in the 20 altitude ranges map to look in detail the

Soapaga Fault's expression on the relief. The black dashed line represents the inferred fault trace

using the geomorphic features. ....................................................................................................... 22

Fig. 3- 5 Kinematic and paleo stress solutions for the fault planes identified in the Soapaga and

Corrales faults hanging wall. ............................................................................................................ 23

Fig. 3- 6. Restoration of the structural cross-section A-A’. .............................................................. 25

Fig. 3- 7. Restoration of the structural cross-section B-B’. .............................................................. 27

Fig. 3- 8. Structural evidence of the Corrales Fault deformation. ................................................... 28

Fig. 3- 9. Restoration of the structural cross-section C-C’ ............................................................... 29

Fig. 3- 10. Restoration of the structural cross-section D-D’. ............................................................ 31

Fig. 3- 11. Exposition of the Betéitiva Syncline and related features in the Colacote Creek. .......... 33

Fig. 3- 12. Restoration of the structural cross-section E-E’ .............................................................. 34

Fig. 3- 13. Forward modeling results for the five structural cross-sections. ................................... 38

Fig. 4-1. The parallelism between the main faults (black lines) and its related folds (red lines) in the

compressive (A) and the 60° oblique convergence (B) analog models. .......................................... 40

Fig. 4- 2. A, fault-scarp control (white dashed lines) in contours and slope image from Konon &

Śmigielski (2006). B, explicit strike-slip fault control over two drainages in China from Lacassin et al.

(1998). .............................................................................................................................................. 42

Fig. 4- 3. Strike-slip separation is caused by the erosion over a normal fault. ................................ 43

Fig. 4- 4. Frohlich’s ternary diagram of the Corrales and Soapaga fault planes. ............................. 44

Fig. 4- 5. Discrete-element modeling showing how a Trishear kinematic model could form a footwall

syncline............................................................................................................................................. 45

Fig. 4- 6. An example of a fault-propagation fold explained with the Trishear model. ................... 46

Fig. 4- 7. A, Erslev’s geometric explanation of area conservation. B, diagram of displacement vector

trajectories within the triangular shear zone. ................................................................................. 47

Table list

Pág.

Table 2- 1 Stratigraphic thickness used for the cross-section ......................................................... 11

Table 3- 1. Upper and lower limits, initial guess, and selected model values for the best-fit

parameters grid search in the Trishear inverse modelling. ............................................................. 35

Table 3- 2. Upper and lower limits, initial guess, and selected model values for the best-fit

parameters grid search in the Trishear forward modelling. ............................................................ 37

Introduction

The Soapaga Fault is an NNE-SSW trending structure located at the central part of the Eastern

Cordillera, Colombia, and together with the Boyacá Fault have been described either as the

southern horsetail termination of the sinistral strike-slip Bucaramanga Fault (Mojica & Villarroel,

1984; Ulloa et al., 2001) or structures captured by the slip of the Bucaramanga Fault (Velandia &

Bermúdez, 2018). In any case, the Soapaga and Boyacá faults show a structural relationship with

the Bucaramanga Faults, transferring the strike-slip displacement into transpressive deformation

(Kammer, 1996; Toro, 1990; Velandia, 2005). The Soapaga Fault separates two structural and

geological domains (Fig. I- 1): at the west, the hanging wall is the eastern flank of the Floresta

Anticlinorium characterized by pre-Cambrian metamorphic schists, Paleozoic intrusive stocks, pre-

Devonian and upper Paleozoic sedimentary units, and Jurassic? red rocks of the Girón Formation;

at the east, the footwall is characterized by Paleogene sedimentary units of the Concentración

Formation folding into the Betéitiva Syncline. For the Soapaga Fault trace, there is not a unique

structural behavior but a compartmentalized framework (Velandia, 2005) that could be related to

a structural inheritance of the Mesozoic distensive regimen (Lozano, 2014)

One could group into two kinematic models the studies about its deformation. First, the Fault-Bend

models (FBM) proposed by Dengo & Covey (1993), Saylor et al. (2012), and Toro et al. (2004). In

these models (Fig. I- 2), they described the Soapaga Fault as a thick-skin structure that faults the

basement, flattens in the Lower Cretaceous units, and then thrusts again until it reaches the

Cenozoic units. On the other hand, the Fault-Propagation model (FPM) is the second and most

common kinematic model used to explain the deformation for the Soapaga Fault, proposed by

Cooper et al. (1995), GEOESTUDIOS (2006), GEOSEARCH (2007), Kammer (1996), Tesón et al.

(2013), Toro (1990), and Ulloa et al. (2001).

2 Introduction

Fig. I- 1 Tectonic framework and geological map of the Floresta Massif and the study area (this work and modified from Ulloa et al. (2001) and Velandia & Bermúdez (2018))

Introduction 3

Fig. I- 2. Fault-Bend kinematic models for the Soapaga Fault.

Fig. I- 3. Two Fault-Propagation kinematic models for the Soapaga Fault

4 Introduction

Moreover, the FBM and the FPM had been tested in different manners to validate and support

these structural interpretations. For instance, Saylor et al. (2012) has restored his FBM model to an

unstrained state using thermochronologic and stratigraphic data, resulting in shortenings about 25

km. In contrast, Rodríguez (2009) tested the FPM of Kammer (1996) through gravimetric and

magnetometric inverse and forward modelings, validating this structural interpretation. Similarly,

Tesón et al. (2013) restored both their structural cross-sections and the Dengo & Covey (1993) FBM

cross-section, suggesting the FPM is most efficient due to the lesser amount of shortening the

restoration required. The seismic interpretation of the Soapaga Fault (Fig. I- 4) showed by Tesón et

al. (2013) supported this statement

I identify that the FPM and the FBM named before do not explain precisely the study area's

geological and structural framework. Features such as the kinematic relationship between the

Soapaga Fault and a footwall syncline, the upright-to-overturned position of the Betéitiva Syncline

backlimb, and the thickness changes of the hanging wall stratigraphic units, are not explained in

these models.

Fig. I- 4. Seismic interpretation in the study area of a basement rooted geometry for the Soapaga Fault, with no evidence of flats or fault bend that supports the FBM. Source: Tesón et al. (2013)

Furthermore, comparing geological maps of the study area, I identified no clarity about the Soapaga

Fault trace, finding two main explanations for the same fault (Fig. I- 5). The first establishes the

Soapaga Fault put in contact the Pre-Cretaceous units in the hanging wall with the Cenozoic and

Cretaceous units in the footwall with a periclinal closure south of Nobsa (Kammer, 1996; Kammer

& Sánchez, 2006; Mojica & Villarroel, 1984; Tesón et al., 2013; Toro, 1990) (Fig. I- 5A). The second

Introduction 5

proposes that the Soapaga Fault put in contact the Cretaceous and Pre-Cretaceous units in the

hanging wall with the Cenozoic units in the footwall, showing this structure propagating southern

of the study area (GEOESTUDIOS, 2006; Saylor et al., 2012; Ulloa et al., 2001) (Fig. I- 5B).

Fig. I- 5 Comparison of the two main explanations for the Soapaga Fault. In both images, the Soapaga Fault is highlighted in red, Pre-Cretaceous units in pale blue, Cretaceous units in green, Cenozoic units in yellow and reference locations as blue stars. A, The Soapaga Fault model of Pre-Cretaceous rocks in the hanging wall and a periclinal closure at the south. B, The Soapaga Fault model of Cretaceous rocks in the hanging wall and a continuous trace through the south.

These cartographic issues evidence a partial understanding of the Soapaga Fault identity and the

study area's kinematic evolution. For this reason, I studied the deformation along the Soapaga Fault

from Paz de Río to Corrales in order to propose a kinematic model that explains the structural

framework observed in the field. In this study, I gathered geological evidence to identify the

Soapaga Fault’s features, such as the trace in the field, the fault blocks, and the related structures.

1 Geologic setting of the study area

The Eastern Cordillera (EC) of Colombia is the easternmost of three north-south trending

topographic highs -the Central Cordillera (CC) and the western Cordillera (WC)- separated at the

east by the Llanos foreland basin (Ll B) and at the west by the Magdalena Valley (MMV) (Fig. I- 1).

The Eastern Cordillera correspond to a bivergent orogen (Cooper et al., 1995; Kammer & Sánchez,

2006; Mora et al., 2013; Toro et al., 2004) related to a complex tectonic history of rifts basin

development, sedimentation, and tectonic inversion in a convergent plate margin setting.

By the Jurassic, the Eastern Cordillera was a compartmentalized-high angle normal faults rift basin,

where shallow marine to coastal sedimentation occurred from the Early Cretaceous to the Late

Paleogene period (Cooper et al., 1995). Then, the filled basin was tectonically inverted between

the Miocene (Cooper et al., 1995) to Oligocene (Caballero et al., 2013; Parra et al., 2012) due to

changes in the stress field (Cortés et al., 2005), driving the orogenic uplifting of the Eastern

Cordillera. The primary record of this tectonic inversion is the thickness changes of synrifts units in

both sides of faults (Cooper et al., 1989) such as the Boyacá (Kammer, 1996; Kammer & Sánchez,

2006; Mojica & Villarroel, 1984; Ulloa et al., 2001), Servitá, and Suarez faults (Tesón et al., 2013)

This orogenic episode cropped out older crystalline basement-sedimentary units arrangements

such as the Floresta Massif as an NNE-SSW anticlinorium located at the central part of the Eastern

Cordillera (Fig. I- 1). Two NNE-SSW trending faults bound this massif, the Boyacá Fault at the west

and the Soapaga Fault at the east, both as east verging structures (Kammer, 1996; Kammer &

Sánchez, 2006; Mojica & Villarroel, 1984; Ulloa et al., 2001). Both flanks of the massif show the

presence of Jurassic and Cretaceous sedimentary units: the Girón and the Tibasosa formations in

the western flank, and the same units plus the Une, Chipaque, and Guadalupe formations in the

eastern flank (Ulloa et al., 2001).

At the core of the structure, crops out the Paleozoic sedimentary units of the Tibet, Floresta, and

Cuche formations, in unconformity over Ordovician to Devonian stocks and Precambrian basement

8 Structural Modelling of the Soapaga Fault in the central part of the Eastern Cordillera, Colombia

schists. Mojica & Villarroel (1984) argued that these Paleozoic sedimentary units were a

sedimentary filling of the paleo topography formed by the faulted basement, due to the thickness

changes of the Tibet Formation. Later, the Paleozoic units were deformed into minor folds that

formed the structural frame for the angular unconformities with both the Girón Formation, as seen

in the Santa Rosa de Viterbo-Floresta road, and the Tibasosa Formations, as seen in the Duitama-

Tibasosa road (Fig. I- 1).

In this geologic context, the Boyacá and the Soapaga faults are inferred as tectonic boundaries in

the Neocomian Rift system (Dengo & Covey, 1993; Mojica & Villarroel, 1984; Tesón et al., 2013)

that isolates blocks in the paleo-Floresta Massif in an up-and-down structural configuration

(Lozano, 2014), and controlled the sedimentation for the Jurassic and Lower Cretaceous units

(Cooper et al., 1995; Kammer & Sánchez, 2006; Tesón et al., 2013). The evidence of the structural

control of these two faults over the sedimentary distribution are thickness differences of the

Jurassic rocks at both sides of the Boyacá Fault (Kammer & Sánchez, 2006; Ulloa et al., 2001) and

of the Lower Cretaceous Tibasosa Formation at both flanks of the Floresta Massif (Cooper et al.,

1995; Ulloa et al., 2001).

1.1 Andean uplift and reactivation of Rift-related structures

The strong crystalline rift basin filled in rheological contrast with weak sedimentary units initiate

its deformation at the Late Maastrichtian to Early Paleocene (Parra et al., 2012): the Eocene

unconformity in the subsurface of the Middle Magdalena Valley and the outcrops at the west of

the Boyacá Faults are evidence of this deformation. Then, Mora et al. (2013) reported a tectonic

quiescence at the Mid-Eocene by the low-to-no sedimentary rates of accumulation in the western

and eastern foothills of the Eastern Cordillera. This quiescence is followed by a tectonic

deformation at the Late Eocene inferred with lag-time detrital zircon analysis (Saylor et al., 2012).

Last, the tectonic advance ongoing at the Oligocene corresponds to the primary orogenic

deformation (Horton et al., 2010; Mora et al., 2010; Parra et al., 2009), with an intensification by

the Miocene (Mora et al., 2013).

It is essential to notice that the tectonic inversion of a rift basin requires the maximum horizontal

stress (σ1) to be oriented obliquely to the preexisting fault planes. This transpressive deformation

is necessary because it is mechanically unviable that a σ1 oriented perpendicular to the high angle

Chapter 1 9

rift faults reactivates them in a tectonic inversion instead of generating a thrust low angle fault

(Handin, 1969). For the Floresta Massif context, palaeostress analyses show how the σ1 was

oriented at the Neogene in a WNW (Cortés et al., 2005) to NE (Velandia & Bermúdez, 2018)

direction, allowing the reactivation of preexisting NE to NNE structures. Kammer (1996) reported

striated fault planes with evidence of transpressive deformation movement near the Soapaga

Fault, supporting the palaeostress analyses' results. Moreover, Kammer & Sánchez (2006) and Ulloa

et al. (2001) described structures such as the Boyacá Fault and the Soapaga Fault as a tectonic-

inverted structure because of the Girón Formation’s thickness changes in both blocks of the fault.

1.2 Stratigraphy of the study area.

Cooper et al., (1995) recognized for the Neocomian Rift System in the Eastern Cordillera two main

depocenters that were separated by the Santander high (Etayo-Serna, 1968): the Tablazo-

Magdalena Basin in the west; and the Cocuy Basin in the east, where the Floresta Massif and the

study area are located. Furthermore, Cooper et al., (1995) separate the stratigraphic units in the

study area into four megasequences based on the tectonic frame: the Synrift Megasequence that

controlled the sedimentation of the Girón (Jurassic?) and Tibasosa (Valanginian to Albian

(Salamanca, 2012)) formations; The Back-Arc Megasequence that controlled the sedimentation of

the Une (Albian to Cenomanian (Ulloa et al., 2001)) and Chipaque (Turonian to early Coniacian

(Villamil & Kauffman, 1993)) formations, and the Guadalupe Group (Coniacian to Maastrichtian

(Hubach Eggers, 1931; Pérez & Salazar, 1978)); The Early Pre-Andean Foreland Basin

Megasequence that controlled the sedimentation of the Guaduas (late Maastrichtian to early

Paleocene (Sarmiento, 1992)), Socha Inferior, Socha Superior, and Picacho formations; and the Late

Pre-Andean Foreland Basin Megasequence that controlled the sedimentation of the

Concentración Formation.

I summarized the stratigraphy and the relationships among sedimentary units along the Soapaga

Fault of the study area in a chronostratigraphic framework (Fig. 1- 1), using field observations plus

the descriptions of Cooper et al. (1995), Mora et al. (2013), Salamanca (2012), Ulloa, Rodriguez, &

Rodriguez (2001). Also, this image shows the unconformities among lower Cretaceous and pre-

Cretaceous units with the Paleozoic and crystalline basement units: the Tibasosa and Cuche

formations unconformity to the south of the study area, the Girón and Floresta unconformity by


the Betéitiva-Otengá road at the central part of the study area, and the Girón and crystalline

Basement unconformity at the north of the study area.

Fig. 1- 1. A chronostratigraphic framework of the study area in the Floresta Massif. Source: this work.

2 Methods

For this study's development, I first conducted a field trip campaign in a narrow zone from Paz de

Río at the north to Corrales at the south, which comprises 117 km2. Here, I recognized the

stratigraphic units and their geologic relationship (regular contact, angular unconformity,

nonconformity), orientation (low angle dipping, upright, overturned), and structural position in

folds and faults. Besides, I described Soapaga Fault’s features such as the fault trace, fault-related

structures, fault rocks, the stratigraphic faulted units, and mineralization in the fault zone. I used

geomorphologic, geologic, and structural criteria such as slope changes (Huggett, 2016; Rivard,

2012), fault rocks and mineralization (Davis et al., 2011), and high fracture density (Petit, Auzias,

Rawnsley, & Rives, 2000) to identify faults zones. I used the movement sense criteria of Petit (1987)

and the kinematic solution for shear planes of Delvaux & Sperner (2003) for the fault planes I

founded in the study area. In some places, such as the Buntía Creek or at the north of Betéitiva

locality, I found fault rocks that I described based on of Woodcock & Mort (2008), and brittle

structures that I classified using the criteria of Gale, Laubach, Olson, Eichhubl, & Fall (2014).

With the field data, I elaborated on a 1:25.000 scale geological map where I identify: reverse, thrust,

and strike-slip faults; primary and secondary folds; and the relationships among the geological units

(Appendix A). Therefore, I described the geometric features of folds such as their flanks' symmetry

and structural positions to relate these geometric features to a kinematic model. I developed five

structural cross-sections across the study area with the geological mapping and structural

description that allowed me to propose deformational stages and styles for the faults and folds

along the Soapaga Fault. To develop the structural cross-sections, I obtained the topographic

profiles from a 30m resolution DEM, the fault throws from the stratigraphic relationships between

the fault blocks, the sedimentary thickness from previous works in the study area (Table 2- 1), and

the structural dip data from the fieldwork. For the geomorphic data analysis, I used Konon &

Śmigielski (2006) and Lacassin et al. (1998) methods using the software QGis.

Table 2- 1 Stratigraphic thickness used for the cross-section


Yes No

Concentración

Formation1368-1554 m

Paz de Río - Cerinza

road1400 m

Picacho Formation 138,8 mCorrales - Paz de

Rio road (1,5 km)150 m

Socha Formations 501 mCorrales - Paz de


Guaduas Formation 392,4 mCorrales - Paz de


Guadalupe Group 236 mCorrales - Paz de


Chipaque

Formation226,4

Betéitiva-Otengá

road230 m

Une Formation 227,8 mBetéitiva-Otengá

road230 m

Tibasosa Formation 514 m

Betéitiva-Otengá

road

Busbanzá -Corrales

road

700 m

Geologic Units

Measured

thickness by Ulloa

et al., (2003)

Measured inside the study area? Thickness used in

this work

With these data, I first restored the gravitational deformation observed in the field by hand using

geological criteria in the software AutoCAD®. Then, I restored the fault’s displacement in the cross-

section with the software AutoCAD® following the methods of Marshak & Mitra (1988) and

Woodward et al. (1991); and for the Trishear retro-deformation, I used the software

FaultFoldForward. To find the best-fit values for the Trishear restoration, I used Cardozo et al.

(2011) algorithms and methods in the software MATLAB®, and to handle and convert the data to

be readable for the algorithms, I used the software Python®. Last, I did quality control of the

restoration process following Groshong (2006) methods and advice.

2.1 The Trishear modelling

The Trishear is a fault-propagation fold kinematic model proposed by Erslev (1991), where a

triangular shear zone located at the fault’s tip deforms both the hanging and the footwall. The

Trishear model explains in simple manner structural and geometric features that traditional

kinematic models do not, such as stratigraphic thick changes in the deformational front, curved

hinges in the fault-related folds, and high-angles in the paired limb of the footwall syncline and the

hanging wall anticline (Fig. 2- 1). To restore a strained section using the Trishear inverse modeling

algorithm, it is necessary the input of five parameters: the propagation/slip ratio (p/s),

Chapter 2 13

displacement (D), Trishear angle (TA), fault tip (FT), and fault angle (FA). Some of those data could

be measured in the field, such as the fault angle, some could be interpreted by geological evidence

such as displacement and fault tip, and some must be found by iterative search processes such as

the propagation/slip ratio and Trishear angle.

Fig. 2- 1 Three examples of the Trishear kinematic model applied for thrust, reverse, and normal faults. Source: Hardy & Allmendinger (2011)

Thus, several possible folds geometries result from the combination of those five parameters, and

a wide range of possible values that could restore a given fold geometry. For this reason, I used the

inverse and forward methods of Trishear restoration analysis showed by Cardozo et al. (2011). For

the inverse model, the algorithm first required dots' input representing a single bed on a cross-

section. With this, the algorithm searched for the best suit of values for the five parameters that

retro-deform the strained bed to an unstrained state with the Trishear kinematic model. Compared

with previous algorithms, the algorithm I have used in this work is not restricted by local minima

and can search for possible solutions in a broader range. Last, I used the forward modelling

algorithm to compare and validate the inverse modelling and the structural interpretation. The

forward algorithm searched for the best geometry and required the inputs of a topographic profile,

the stratigraphic contact and dip position over the profile, a regional dip, and a stratigraphic

thickness values measured in either the hanging or the footwall block: the thicknesses used were

those summarized in the Table 2- 1.

3 Results, analysis, and data interpretation.

In the study area, I identified two structural blocks: the Floresta Massif and the Corrales Foreland.

The Floresta Massif is located west of the Soapaga Fault and is characterized by basement

metamorphic schists, plutonic intrusions, and Paleozoic and Jurassic sedimentary rocks. The

Corrales Foreland, located to the east of the Soapaga Fault, is composed of a thick sedimentary

cover of Cenozoic clastic rocks thrusted by the Corrales, Chiguaza, and Betéitiva faults. In these two

blocks, I identified three main structures for the structural analysis: the Betéitiva Syncline, the

Soapaga Fault, and the Corrales Fault; and minor structures such as the Chiguaza Fault, the

Betéitiva Fault, strike-slips faults, and gravitational folds (Fig. 3- 1 and Appendix A).

However, before I could describe the deformational analysis of the study area's structural settings,

I first develop a profound analysis of the Soapaga Fault’s identity and its differences with the

Corrales Fault. This analysis was required because I proposed the Corrales Fault has been named

and described as the Soapaga Fault, which has generated a misunderstanding about the kinematic

evolution in the deformational front of the Soapaga Fault. In this analysis, I show different types of

evidence that I used to identify the Soapaga Fault in the field and support my statement about

these two faults.

3.1 The Soapaga Fault features

I used four types of evidence to identify the Soapaga Fault: 1, the geological units in the hanging

wall; 2, the structural and mineralogical processes in the fault trace; 3, the geometric and

geomorphic features of the Soapaga Fault, and; 4, the kinematic differences between the Soapaga

and the Corrales faults.


3.1.1 Geologic relationships

The first type of evidence is related to the geologic units that the Soapaga Fault crops out in its

hanging wall. At the north of the study area, close to the Paz de Río locality, the geologic

relationship between the two blocks of the Soapaga Fault is evident: the basement schists,

Paleozoic and Jurassic sedimentary units crop out over the Cenozoic Concentración and Picacho

formations. The same relationship could be followed southward until the Chiguaza Creek, where

the Chiguaza Fault thrusted the Soapaga Fault footwall and cropped out the Guadalupe Group's

upper part and the Guaduas Formation (Fig. 3- 1). However, the Soapaga Fault hanging wall units

still the same as in the north of the area: the red bed of the Girón Formation and the Paleozoic

sedimentary units.

I found a significant change in the Soapaga Fault’s deformational front at 2.5 km NNW from the

Betéitiva locality, where the Corrales Fault branched from the Soapaga Fault and thrusted the

Chiguaza Fault and the Betéitiva Syncline axis and backlimb. Here, the Soapaga Fault initiated the

deformation transference to the Corrales Fault, making the Corrales Fault cropped out the rocks of

the Tibasosa, Une, and Chipaque formations and the Guadalupe Group in an upright to west-high-

angle overturned dipping position. Even though the Soapaga Fault lose all its displacement and

disappear in a periclinal closure at the north of Nobsa locality, the Soapaga Fault shows the same

behavior as in the other studied areas: the red beds of the Girón Formation, the fossiliferous beds

of the Floresta Formation, and the metamorphic schists located in the hanging wall of the fault.

With this description, I want to point out that no matter how the structural setting changes through

the Soapaga Fault footwall, the hanging wall shows the same geologic relationships in the study

area.

3.1.2 Structural and mineralogical processes on the fault’s trace

The second type of evidence is related to the structural and mineralogical process that I found over

the Soapaga Fault trace. To the south of the Chiguaza Creek, the Soapaga Fault shows a fault zone

of 2 to 3 m wide green-foliated fault breccias (Fig. 3- 1C), that separates the red beds of the Girón

Formation in the Soapaga Fault hanging wall from the rocks of the upper part of the Guadalupe

Group and the lower part of the Guaduas Formation in the Chiguaza Fault hanging wall (Fig. 3- 1).

Chapter 3 17

These breccias have low expression in the landscape, and there are few outcrops in the area due

to the friable and low cohesive composition for the weathering processes.

Fig. 3- 1. Geological map of the study area and images of structural features of primary folds and faults. In Fig.-G, the arrows point to the bed’s bottom showing the strata polarity.


On the Otengá-Betéitiva road, I found malachite-azurite mineralization in a minor creek where the

Soapaga Fault put in contact with the red beds of the Girón Formation in a normal-east dipping

position wall with the limestones and mudstones of the Tibasosa Formation in an inverted-west

dipping position. This mineralization appears as a green and deep blue patch over the Girón

Formations (Fig. 3- 1E) in a highly fractured zone where I infer the Soapaga Fault's trace. Even

though one could think it is not necessary the presence of a fault in this location due to the virtual

stratigraphic continuity -the “Jurassic” red beds of the Girón Formation in contact with the Lower

Cretaceous rocks of the Tibasosa Formation- this mineralogic and structural evidence fits with the

description by Ulloa et al. (2001) of a faulted contact between these two units in this place.

Last, on the Busbanzá-Corrales road, I found the occurrence of green-colored mudstones and

siltstones and a high-density fracture zone close to a creek where I identified the Soapaga Fault

trace. With this, I suggested the green-colored fault breccias at the north, the green malachite

patches at the middle, and the green-colored mudstones at the south of the study area, plus the

high-density fracture zones close to these places, are correlated with the Soapaga Fault trace and

its geological processes.

3.1.3 The geometric and geomorphic expression of the Soapaga Fault

The third type of evidence is the Soapaga Fault's geometry and its geomorphic expression in the

landscape. In the Chiguaza Creek, I developed a geomorphic estimation of the Soapaga Fault dip

magnitude comparing the places where either the red rocks of the Girón Formation or the pale

yellow rocks of the Concentración Formation appears on one side of the creek: a simplistic and

visual approximation of the Monte Carlo method (Johansen, 2010) to determine the geometry of

the fault. Fig. 3- 1B shows the result of this visual method, where one can notice an approximation

for the Soapaga Fault geometry -between 50° to 70° to the west. I also developed the “three points”

geometric method in the Chiguaza Creek to validate the visual geometric approximation, and the

results show an angle of 63° for the Soapaga Fault (Fig. 3- 2), that allowed me to describe this fault

as a high angle structure.

Chapter 3 19

Fig. 3- 2. The “three-point” solution for the Soapaga Fault. A, three localities where I estimate the Soapaga Fault appears in the Chiguaza Creek. B, the triangular part of the method to obtain the strike and dip direction of the fault. C, the graphical solution to obtain an average dip value for the Soapaga Fault.

After calculating the Soapaga Fault angle, I wondered how this feature -a high angle fault- be

expressed in the landscape? To answer this, I developed a geomorphic analysis of four relief maps:

images where the altitudes of the landscape are grouped in n ranges, and for each range, the

software assigns a unique color. Fig. 3- 3 shows the geomorphic analysis of these relief maps where:

the red stars represent the places where I identified the Soapaga Fault trace in the field, the purple

line below the stars represents the average trend of the fault, the purple dots represent the places

where I trace the Soapaga Fault based on the geomorphic features, and the red dashed line

represents the boundary of the study area.

At the north on the 5 altitudes range map (Fig. 3- 3A), the “red stars” align with the valley’s apex

trend -“V” shaped landforms in an NNE orientation-, while at the south beyond the study area, the

“red stars” tend to be aligned with a subtle ENE straight topographic feature. In these relief maps,

one could notice that the more the altitude ranges increases, the more these geomorphic features

become evident: the northern “V” shapes valleys start to alienate with straight topographic highs

(Fig. 3- 3B, C), the southern straight topographic features repeats in an offset pattern in the same


map (Fig. 3- 3C, D), and the alienations between the southern and northern geomorphic features

become evident. Fig. 3- 4 is a zoom of the topographic contours on the 20 altitude ranges map that

shows how the Soapaga Fault influences the development of geomorphic features on the

landscape. In this image, I noticed how the “red stars” fit on the straight path generated by the

creeks align, which allowed me to infer the Soapaga Fault trace (black dashed line in Fig. 3- 4).

Fig. 3- 3. Relief maps of the Soapaga Fault geomorphic expression. Each map represents a relief model based in a range of altitudes: A, 5 ranges; B, 10 ranges; C, 15 ranges; D, 20 ranges. The red stars represent the places where I identified the Soapaga Fault and the lines below represent the average fault trend. The purple dots represent the places where I infer the Soapaga Fault trace due to the geomorphic evidence.

Chapter 3 21

3.1.4 Kinematic evidence of the Soapaga and Corrales faults

The fourth type of evidence is the kinematic solutions of the fault planes of the Soapaga and the

Corrales faults blocks. The Fig. 3- 5 shows the kinematic (“beach-ball” diagrams) and paleo stress

(circle and arrows diagrams) solutions for the fault planes identified in the study area. In this figure,

I identified two types of solutions: transpressive and compressive solutions. The Soapaga Fault’s

hanging wall shows only transpressive solutions (Fig. 3- 5 boxes 3 and 4), and this allowed me to

suggest oblique movements as the primary deformational process on this fault. Fig. 3- 1A

corroborates this assumption showing that striae are oriented oblique on the metric fault plane of

the Girón Formation. Moreover, the kinematic solutions show that one of the solution planes is a

high angle plane parallel or semi-parallel to the Soapaga Fault trace. These results support the

previous geometric interpretation of a high-angle related geometry for the Soapaga Fault and are

mechanically consistent due to the need of oblique stress over a high angle fault plane to move the

hanging wall block upwards (Tesón et al., 2013).

On the other hand, the compressive solutions of the kinematic and paleo stress results are

restricted to the Corrales Fault hanging and footwall (Fig. 3- 5 boxes 1,2,5,6,7), this allowed me to

suggest that the primary deformational process on this block is related to a compressive

deformation perpendicular to the Corrales Fault trace. This result is constrained by the low angle

thrust that I identified in the Concentración (Fig. 3- 1H) and the Tibasosa formations (Fig. 3- 1F) in

the field. Moreover, in most cases, the compressive fault planes' kinematic solutions show that one

of the solution planes is a low-angle plane oriented parallel or semi-parallel to the Corrales Fault.

These deformative results allow me to argue that the deformational style and the kinematic

evidence in the field are useful tools to differentiate the Soapaga and the Corrales fault from each

other in the field.

3.2 Deformation and restoration analysis.

After describing the Soapaga Fault in the study area and showed the evidence to identify this fault

in the field, I developed five balanced structural cross-sections in an NNE-SSW trend to explain the

folding relationship of the Betéitiva Syncline with the deformation of the Soapaga Fault. These

structural cross-sections were restored to an unstrained position to identify and describe the

deformational phases in the study area and validate my structural interpretation's plausibility. I


draw the cross-sections close to the maximum shortening direction in the hanging wall of the

Soapaga Fault to reduce the influence of strike-slip movements in 2D structural cross-sections due

to the transpressive influence over this fault block.

I identified four deformational processes to explain the study area's geological and structural

frame: gravitational folding and faulting, strike-slip faulting, compressional fault propagation

thrusting, and Trishear fault-propagation deformation -these deformational phases are listed from

the earliest to the latest.

Fig. 3- 4. A zoom of the topographic contours in the 20 altitude ranges map to look in detail the Soapaga Fault's expression on the relief. The black dashed line represents the inferred fault trace using the geomorphic features.

Chapter 3 23

Fig. 3- 5 Kinematic and paleo stress solutions for the fault planes identified in the Soapaga and Corrales faults hanging wall.


3.2.1 Gravitational deformation and strike-slip faulting

The gravitational folding and faulting are the earliest deformation in the study area. This

deformative process is related to the mechanical instability of rocks at the surface product of the

decreasing ground level due to hinterland uplifting and foreland weathering. I used the description

of flaps folds and slip-sheet faults of Harrison & Falcon (1936) to describe the study area's

deformations. In the Paz de Río-Belén road, I identified a flap-fold due to the abrupt changes of the

Betéitiva Syncline backlimb from an upright to an overturned low angle position (Fig. 3- 11G). The

NE-verging bending of the Soapaga and the Betéitiva faults in the cross-section A-A’ (Fig. 3- 6) and

less evident in the cross-sections B-B’ (Fig. 3- 7) and C-C’ (Fig. 3- 9) are evidence of this process.

On the other hand, south of the study area between Corrales locality and Buntía Creek, I inferred

a slip-sheet fault due to the abrupt change in the dip of the limestones of the Tibasosa Formation,

turning from an upright position to a west-dip overturned position between 35° to 45°. This faulting

process could be noticed from the cross-sections B-B’ to E-E’ as the black dashed-NW dipping listric

faults that abruptly change the strata in the hanging wall from an upright to a lower angle-

overturned position.

I restored these gravitational deformations in the structural cross-sections using geological and

geometrical criterion, rotating de data over the fault planes until it restored the fault blocks'

displacement. This process corresponds to Step 1 on the cross-sections images and shows the

original positions of the strata and faults before the gravitational collapse at the Soapaga Fault’s

deformational front.

Also, in the study area, I observed evidence of strike-slip faulting such as acute changes in the

course of the Chicamocha River to the north of Corrales locality, lateral displacement of

sedimentological units across their strikes on the Betéitiva-Otengá road, and the faulted contact

across the strikes between the Tibasosa and Guaduas formations to the northwest of Betéitiva

locality (Fig. 3- 1D). Even though the structural cross-sections do not include this type of faulting

because of the difficulty of retro-deform strike-slip displacements in a 2D section (Marshak & Mitra,

1988; Woodward et al., 1991), I described it because it influenced the structural frame of the study

area. Last, the strike-slip deformation could respond to the Bucaramanga Fault System's

transpressive deformation over the “horsetail” termination of the Boyacá and the Soapaga faults.

Chapter 3 25

Fig. 3- 6. Restoration of the structural cross-section A-A’.


3.2.2 Compressional fault propagation thrusting

The second deformational stage is related to an in-and-out of sequence faulting in the Soapaga

Fault footwall. In this stage, the Betéitiva, Chiguaza, and Corrales faults thrusted the Corrales

Foreland (Fig. 3- 1) in response to the Floresta Massif's contractional advance over the footwall

Cenozoic units. Step 2 of the cross-section images show the restoration process of these faults

3.2.2.1 Betéitiva Fault

I inferred the Betéitiva Fault was the first structure generated in this stage, growing as an in-

sequence high-angle fault that thrusted the Betéitiva Syncline by its axial plane. In the field, I

described evidence of the Betéitiva Fault such as minor fault planes close to the fault zone at the

upper part of the Colacote Creek (Fig. 3- 1I); drag folds in an interbedded interval of sandstones

and mudstone in the lower part of the Colacote Creek (Fig. 3- 1H); the fast change from a moderate

west-dipping angle in the footwall to an upright-to-overturned west-dipping position in the hanging

wall on the Colacote Creek (Fig. 3- 11); and isolated coal mines with minor development because

of the loss of the ore beds due to the fault throw near to the Divaquía Creek (Fig. 3- 9, cross-section

C-C’).

In the cross-sections A-A’ (Fig. 3- 6), B-B’ (Fig. 3- 7), and C-C’ (Fig. 3- 9), the Betéitiva Fault could be

noticed as the in-sequence fault that cropped out the rocks of the Concentración and the Picacho

formations at the north (cross-section A-A’) and the Socha Formation at the south (cross-section C-

C’). However, at the south of the study area in the cross-sections D-D’ (Fig. 3- 10) and E’-E’ (Fig. 3-

12), the Betéitiva Fault is decapitated by the Corrales Fault showing the out-of-sequence

relationship between these two structures. The restoration of the Betéitiva Fault shows how the

displacement increased through the south, starting with 81 m in the cross-sections A-A’, increasing

from 150 m in the cross-section B-B’ to 260 m in the C-C’ until it reaches to 650 m in the cross-

sections D-D’ and E-E’.

Chapter 3 27

Fig. 3- 7. Restoration of the structural cross-section B-B’.


3.2.2.2 Chiguaza Fault.

Behind the Betéitiva Fault, I described the Chiguaza Fault as an out-of-sequence structure that

thrusted the Betéitiva Syncline back-limb and cropped out the upper part of the Guadalupe Group

and the lower part of the Guaduas Formations. I inferred that this fault grows from north to south,

staying blind in the cross-section A-A’, at the surface in B-B’, and then truncated by the Corrales

Fault between B-B’ and C-C’. The principal evidence of the Chiguaza Fault is the faulted contact

near the Chiguaza Creek between the coal beds of the Guaduas Formation in the hanging wall with

the clastic rocks of the Picacho Formation in the footwall. Like the Betéitiva Fault, the cross-sections

show that the Chiguaza Fault grew from north to south of the study area, and this could be related

to a southward increment of the deformation of Soapaga Fault over the Corrales Foreland.

3.2.2.3 Corrales Fault

I described the Corrales Fault as an out-of-sequence structure behind the Betéitiva Fault that:

thrusted the backlimb of the Betéitiva Syncline, uplifted the Lower Cretaceous units, and truncated

the Betéitiva Fault to the south of the Betéitiva Municipality. In the field, I observed structural

evidence of the deformation of the Corrales Fault such as minor fault planes in the Guadalupe

Group on the Otengá-Betéitiva road (Fig. 3- 8A), highly-strained mudstones in the Chipaque

Formations on the Búntia Creek, and minor faults and folds in the Tibasosa Formation on the

Corrales-Busbanzá road (Fig. 3- 8B and Fig. 3- 1F). In the field, the Corrales Fault's primary

geomorphic evidence is the slope change between the mountain range's foothills and the Corrales

Foreland plains.

Fig. 3- 8. Structural evidence of the Corrales Fault deformation. A, minor normal faults in the Guadalupe Group siltstones on Betéitiva-Otengá road. B, Kink folds in the Tibasosa Formation limestones on Corrales-Busbanzá road.

Chapter 3 29

Fig. 3- 9. Restoration of the structural cross-section C-C’


With the structural evidence, I inferred the Corrales Fault become more relevant in the tectonics

at the south of the study area because of the transference of deformation from the Soapaga Fault

to the Corrales fault. In this way, the cross-sections show how the Corrales Fault’s displacement

increases from north to south: in the cross-section C-C’ (Fig. 3- 9) -at the middle of the study area-

the Corrales Fault locates in the structural wedge between the Betéitiva and the Soapaga Fault,

where it truncates the Chiguaza Fault and crops out the rocks of the Tibasosa, Une and Chipaque

formations; and in the cross-sections D-D’ (Fig. 3- 10) and E-E’ (Fig. 3- 12) the Corrales Fault migrates

toward the east, truncates the Betéitiva Syncline axis and the Betéitiva Fault, and crops out in a

broader zone the Tibasosa and Une formations in the cross-section D-D’ and only the Tibasosa

Formation in the cross-section E-E.

Likewise, the restoration of the Corrales Fault also shows that the fault displacement increases

from north to south, starting with 800 m in the cross-section C-C’ and increasing to 1300 m in the

cross-sections D-D’ and E-E’. One crucial aspect to notice is the presence of a blind fault between

the Corrales and the Betéitiva fault in the cross-sections D-D’ and E-E’. I inferred this fault thrusted

the Betéitiva Syncline's back-limb and uplifted all the Cretaceous and Cenozoic units. I have no field

evidence of this blind fault; however, without this fault, the cross-sections cannot be balanced due

to the lack of stratigraphic units between the Tibasosa Formation in the Corrales Fault hanging wall

and the upper Cenozoic units in the Betéitiva Fault footwall. In consequence, this structure is

peremptory for the structural interpretation and kinematic reliability of the cross-sections.

3.2.3 Trishear fault-propagation deformation

Here, I will present the evidence that allows me to propose the Trishear fault-propagation process

is the best deformative process to explain the Betéitiva Syncline, its features, and the relationship

with the Soapaga Fault. First, the Floresta Massif worked as a massive, resistant, and less

penetrative deformed block, making a rheological difference with the layered, ductile, and shear-

penetrative sedimentary block of the Corrales Foreland. This mechanical contrast was a key factor

for Erslev (1991) to relate structural features such as highly curved geometries and thickness

changes of folds in the deformational front with fault-propagation deformation processes. In the

Trishear model, the fault tip forms a triangular shear zone that simultaneously deforms the hanging

and the footwall.

Chapter 3 31

Fig. 3- 10. Restoration of the structural cross-section D-D’.


Second, at the north of the study area, the parallelism between the Betéitiva Syncline’s axis and

the Soapaga Fault’s trace shows how these two structures are related to each other (Fig. 3- 1).

However, from the middle part to the south of the study area, this parallelism was truncated by a

post-Betéitiva Syncline - compressive-related fault branched from the Soapaga Fault and thrusted

the Betéitiva Syncline axis. This structural setting shows how a multistage deformations process

characterizes the study area.

Third, the Betéitiva Syncline as a frontal fold is located in both the footwall and the deformational

front of the Soapaga Fault. In general, frontal synclines are explained using complex structural

models such as aborted faults in an out of sequence-fault propagation models, or paired anticline-

syncline structures in multi flat-ramp stages in fault-bend models such as the interpretations of

Dengo & Covey (1993) and Saylor et al. (2012). However, I inferred a simple relationship between

the Betéitiva Syncline and the Soapaga Fault that does not require complex assumptions such as

blind anticlines under the Soapaga Fault; The Trishear kinematic model could explain in a simple

way how a fault-propagation related deformation forms a frontal syncline.

Fourth, the stratigraphic thickness changes in the backlimb of the Betéitiva Syncline that I have

identified in the Cretaceous -mainly- and Cenozoic units on the Otengá-Betéitiva road could be

explained simply by neither the fault-propagation nor the fault-bend folds classic models. However,

the Trishear kinematic model could explain and recreates the stratigraphic thickness changes in the

hanging wall anticline-footwall syncline paired limb and maintains area conservation in forward

and inverse models. The stratigraphic thickness changes could be seen mainly in the cross-section

C-C’ for the Cretaceous units on the Otengá-Betéitiva road and in the cross-section B-B’ for the

Cenozoic units on the Chiguaza Creek, where the stratigraphic thickness in the Betéitiva Syncline’s

backlimb is lesser than in the hinge zone.

Last, the Trishear kinematic model could explain better the Betéitiva Syncline geometry. The

Betéitiva Syncline is an NNE close and overturned fold nucleated by Cenozoic sediments of the

Concentración Formation and truncated at the south by the Corrales Fault (Fig. 3- 1). On the

Colacote Creek, the gentle west-dipping forelimb (Fig. 3- 11A) turns into an upright-to-inverted

west-dipping back-limb (Fig. 3- 11B) with a fractured and minor faulted transition zone (Fig. 3- 1I)

where I described the Betéitiva Fault (Fig. 3- 11C).

Chapter 3 33

Fig. 3- 11. Exposition of the Betéitiva Syncline and related features in the Colacote Creek. A, forelimb dipping gently to the SW. B, backlimb in an upright position. C, the panorama of the Betéitiva Syncline geomorphological expression with a geological interpretation.

3.2.3.1 The Trishear grid-search algorithm to find the best-fit values.

To develop the Trishear inverse modeling is necessary to find the best-fit values for the five

parameters (slip, fault angle, Trishear angle, p/s, and fault tip position). I used the simulated

annealing algorithm developed by Cardozo et al. (2011) to found these values. To find the best

values, the algorithm iterates n times until it founds the best values avoiding the samples fall in a

local minimum: this guarantees the algorithm searches in a broader range of possibilities. This grid-

search process requires the input of an upper limit (amax), a lower limit (amin), and an initial guess

(ao) for each parameter. At the end of the iteration process, the last iteration results correspond

to the best set of values to retro-deform a given bed to an unstrained state using the Trishear

kinematic model.


Fig. 3- 12. Restoration of the structural cross-section E-E’

Chapter 3 35

The Table 3- 1 shows the configuration to search the best values -lower and upper limit for the grid

search, and the initial guess- and the selected model to restore each cross-section with the Trishear

model. In Table 3- 1, one can notice that all the cross-sections share the same grid-search limits

and that the parameters with more uncertainty, such as the s/p ratio and the slip, have a broader

search range that those I have more confidence. Furthermore, one could corroborate that the

selected model values correspond to one of the clusters iterations located in the lowest part of the

“y-axis” on the iteration’s diagrams (Appendix B).

I restored the Betéitiva Syncline with the Soapaga Fault deformation using the selected model

values in Table 3- 1. The Trishear retro-deformation -Step 3 on the cross-sections- shows that most

of the beds located in the Betéitiva Syncline restore to and admissible unstrained state in the five

cross-sections: this is an evidence of the plausibility of the Trishear to explain the folding of the

Betéitiva Syncline in relationship with the Soapaga Fault. The retro-deformation and the grid-

search processes show how the Soapaga Fault's deformation changes toward the south: the

southern cross-sections show bigger slip, p/s, displacement, and shortening, evidence of the

increment of the deformation. Finally, it is crucial to notice that the final tip of the fault does not

mean that the fault stops at this point; but is the highest point the Trishear deformation needed to

generate the geometry I proposed in this work

Table 3- 1. Upper and lower limits, initial guess, and selected model values for the best-fit parameters grid search in the Trishear inverse modelling.

Cross Section Lower (amin) and upper (amax) limits

TA p/s FA slip

Initial guess (ao)

TA p/s FA slip

Selected Model (af)

TA p/s FA slip

amin = [40 0,5 60 5]

amax = [60 2,0 70 100]

amin = [40 1,0 60 5]

amax = [60 4,0 70 100]

amin = [40 1,0 60 5]

amax = [60 4,0 70 100]

amin = [40 1,0 60 5]

amax = [60 4,0 70 100]

amin = [40 1,0 60 5]

amax = [60 4,0 60 100]

af = [47 1,1 66 52]

af = [53 1,1 68 52]

af = [53 1,4 69 47]

af = [50 1,2 70 50]

A-A' ao = [60 1,5 60 30] af = [58 0,8 58 60]

B-B'

C-C'

D-D'

E-E'

ao = [60 1,5 60 30]

ao = [60 1,5 60 30]

ao = [60 1,5 60 30]

ao = [60 1,5 60 30]


3.3 Forward Modelling

In the inverse modelling, most of the structural cross-sections' retro-deformed strata show an

admissible undeformed state after the Trishear restoration step; however, some strata show a

remanent of deformation close to the Soapaga Fault, suggesting the geometry of these beds

requires improvement and fine-tuning. This statement allows me to ask: Which is the best

geometry that explains the geologic and structural setting that could be fully restored to an

unstrained state using the Trishear kinematic model?

To validate my structural interpretation and answer the question above, I developed a forward

model to find the best geometry that explains the Betéitiva Syncline. To this, I used the forward-

modeling algorithm of Cardozo et al. (2011) that requires: a topographic profile, the stratigraphic

contact and its dip data over the profile, a stratigraphic thickness of the sedimentary units either

in the hanging or the footwall, a regional dip reference, an upper and lower limit for the grid search

of the best suit of the Trishear parameters, and an initial guess value to initiate the search.

This algorithm feed from the number of stratigraphic contacts and dip data and the Trishear

parameters we use to find the best-fit geometry: the more contacts and dip data available, the

more accurate the model. However, there is a lack of stratigraphic contacts at the Betéitiva

Syncline's forelimb in the study area due to the topography. Because of this, I used both real and

synthetic data to develop the forward model: the real data correspond to the western part of the

topographic profile, the western dips, and stratigraphic contacts, and the stratigraphic thicknesses;

and the synthetic data correspond to the eastern part of the topographic profile and the eastern

stratigraphic contacts and dips.

Table 3- 2 shows the values I used for the search grid and the best-fit parameters to recreate the

Betéitiva Syncline geometry. For the forward modeling, I used the inverse modelling results to

narrow down the upper and lower limits for the grid search values. Here, it is essential to notice

how the best-fit values of the p/s and the slip parameters increase from north to south, showing

how the deformation in the Soapaga Fault changes through its trace.

Chapter 3 37

Table 3- 2. Upper and lower limits, initial guess, and selected model values for the best-fit parameters grid search in the Trishear forward modelling.

Cross Section Lower (amin) and upper (amax) limits

TA p/s FA slip

Initial guess (ao)

TA p/s FA slip

Best-fit parameters (af)

TA p/s FA slip

amin = [40 0,3 60 45]

amax = [80 2,0 70 70]

amin = [40 0,8 60 45]

amax = [55 1,5 70 70]

amin = [45 1,4 60 57]

amax = [65 1,8 70 80]

amin = [45 1,2 60 40]

amax = [65 1,8 70 80]

amin = [40 0,8 60 40]

amax = [60 1,8 70 80]

af = [43 1,4 60 51]

af = [61 1,7 69 57]

af = [63 1,7 67 59]

af = [49 1,7 67 60]

A-A' ao = [50 1,0 65 50] af = [47 0,8 66 50]

B-B'

C-C'

D-D'

E-E'

ao = [50 1,0 65 50]

ao = [50 1,5 65 50]

ao = [50 1,5 65 60]

ao = [50 1,3 65 60]

The Fig. 3- 13 shows the geometric results of the forward modeling where the thick line is the

topographic and the pseudo topographic profile, the white circles are the stratigraphic contacts,

the red circle and triangle are the initial and the final tip of the fault, the red line the Soapaga Fault,

and the thin black lines are the deformed beds. This figure shows that the forward geometry results

are similar to the structural model geometry -the footwall on Step 2 of the cross-sections- that I

proposed, and supports the hypothesis of the Betéitiva Syncline is a Trishear fold related to the

deformation of the Soapaga Fault. Another aspect to point out in the Fig. 3- 13 is how the forward

model shows graphically that the Soapaga Fault increases its deformation southwards because the

northern sections show an initial tip shallower (0 to -1000 m) than the southern sections (-4000 m).

Finally, the forward model shows that the structural model requires a slight enhance in the

geometric model to retro-deform to a complete unstrained stated; however, the proposed model

could be considered a plausible and acceptable model to explain the structural and geological

setting of the study area.


Fig. 3- 13. Forward modeling results for the five structural cross-sections.

4 Discussion

4.1 The confusion about the Corrales Fault as the Soapaga Fault: an epistemological analysis of defining a fault.

Here, I want to discuss the existence of the Corrales Fault, the trace of the Soapaga Fault, and how

this has influenced the structural interpretation of the Betéitiva Syncline. The main issue about

these two faults are the places in the study area -such as the Otengá-Betéitiva road and the

Busbanzá-Corrales road- where geologists argue a stratigraphic continuity between the Jurassic?

red beds of the Girón Formation and the Lower Cretaceous limestones of the Tibasosa Formation:

It looks like they are right in a simple view. For this reason, several authors have changed at the

north of Betéitiva locality, the direction and location of the Soapaga Fault, drawing it where the

fault’s throw is more evident at the field: the fault contact between the Cretaceous and Cenozoic

units. However, their assumption does not consider some geologic, structural, and geomorphic

evidence, generating confusion between the Corrales and the Soapaga faults. What does it mean

to define a fault? How can one name a fault and follow its trace in a region? To answer this, I have

grouped four types of features to identify and characterized a fault regarding Bennison et al. (1997)

and Davis et al. (2011): geometric, geomorphic, fault zone, and kinematics.

4.1.1 Geometric features.

Faults are usually represented as straight planes or curved surfaces, where an appreciable

displacement is evident (Schultz & Fossen, 2008). As geometric objects, they have: a location, a

strike direction, and a dip angle. In a first approach, one could identify and name a fault using its

geometric and geographic properties. Nevertheless, these geometric and geographic criteria are

not enough to distinguish between the Corrales and the Soapaga faults, because both faults show

similar strike directions, similar kinematics, and separates from each other 0.5 km at the north and

1.6 km at the south of the area. Due to these similarities, one could easily misinterpret these two


faults and change the Soapaga Fault’s trace to the Corrales Fault’s trace as Saylor et al. (2012), and

Ulloa et al. (2001) did.

However, one could use the geometric relationship between faults and folds to differentiate similar

faults in the field, as occurred with the Soapaga and the Corrales faults. McClay (2011) showed the

variety of fault-related folds and how their geometric aspects -of faults and folds- are essential to

define the deformation style. Moreover, McClay et al. (2004) showed in analog models how in

compressive to slightly oblique tectonic settings, the folds axis is parallel to the faults related to

(Fig. 4-1).

Using the observations of McClay et al. (2004), one could notice how the Soapaga Fault and the

Betéitiva Syncline are parallel to each other at the north of the area (Fig. 3- 1), but the axis and the

backlimb of the Betéitiva Syncline are truncated from the middle to the south of the area. If the

trace of the Soapaga Fault was as proposed by Saylor et al. (2012) and Ulloa et al. (2001) (Fig. I- 5B),

one could assume that the Betéitiva Syncline as a fault-related fold to the Soapaga Fault, would

change its direction and maintain the parallelism through the area. However, the fold's truncation

shows a post-Betéitiva Syncline deformation that thrusted this fold: this after deformation

corresponds to the Corrales Fault.

Fig. 4-1. The parallelism between the main faults (black lines) and its related folds (red lines) in the compressive (A) and the 60° oblique convergence (B) analog models. The folds were drawn using the map and the cross-section views in the original paper.

Chapter 4 41

4.1.2 Geomorphic features.

Next, Davis et al. (2011) and Huggett (2016) showed that geomorphic expression on the landscapes

is a useful tool for recognizing faults. These geomorphic expressions are fault scarps, fault-line

scarps, lineaments, and drainage control.

Davis et al. (2011) defined fault scarps as “steps in the land surfaces that coincide with the location

of faults” and forms triangular facets when they are well preserved. However, fault-line scarps -a

topographic relief change near the fault trace that shows the differential resistance of the hanging

and the footwall- replaces steps when the weathering erodes it. Konon & Śmigielski (2006) showed

an example of the geomorphic analysis of fault-line scarps, identifying two fault traces where the

contours on the slope image turn from curved to straight patter (white dashed lines in Fig. 4- 2A).

In the study area, the Corrales Fault shows fault line scarp as the relief change between the

resistant Cretaceous units in the hinterland and the low topographic relief of the Cenozoic units in

the foreland. Also, the Soapaga Fault shows fault-line scarps to the south of the study area, where

the relief maps show turns from curved to straight patterns (Fig. 3- 3).

On the other hand, Huggett (2016) defined lineaments as “curved or straight linear features on the

earth surface that are too precise to have arisen by chance…and most are tectonic related”. An

essential aspect of lineaments is these features tent to control the drainages and generate either

lineation from hundreds of meters to several kilometers or offset that changes abruptly the

directions of drainages. Lacassin et al. (1998) showed an example on a false-color satellite image

(cyan-dashed lines in Fig. 4- 2B) of a strike-slip fault system lineament controlling the drainage by

tents of kilometers. From the middle to the south of the study area, the Soapaga Fault shows

control throughout several drainages, aligning these individual creeks with the fault trace.

4.1.3 Fault zone features

Davis et al. (2011) showed some characteristics to identify a fault regarding the fault zone it

produced: fault rocks, mineralization process, intense fractures, and drag folds. Also, Davis et al.

(2011) stated that in fault zones, the width could vary concerning the displacement: the wider the

fault zone, the larger the fault's displacement.


The fault zone of the Soapaga Fault zone vary through it trace showing a different type of evidence:

at the north, I found a 3m wide fault of green-colored, noncohesive, fault breccias close to the

Colacote Creek; at the middle, I found a mineralized zone of malachite and azurite in aligned

drainage on the Otengá-Betéitiva road; and at the south, I found green-colored mudstones in a

highly fractured zone close to the fault trace on the Busbanzá-Corrales road. On the other hand,

the Corrales Fault's fault zone shows minor normal faults perpendicular to the trace of the Corrales

Fault on the Otengá-Betéitiva road, and minor thrusts and drag folds parallel to Corrales Fault on

the Busbanzá-Corrales road.

Fig. 4- 2. A, fault-scarp control (white dashed lines) in contours and slope image from Konon & Śmigielski (2006). B, explicit strike-slip fault control over two drainages in China from Lacassin et al. (1998).

4.1.4 Kinematic features

The most relevant evidence to name and describe a fault in both the field and the subsurface

(Bennison et al., 1997; Davis et al., 2011) is the slip features: the direction, sense, and magnitude

Chapter 4 43

of displacement. When the slip features are unobservable, one could use the separation: the

relative movement of the fault blocks on either a cross-section or a map view. However, Bennison

et al. (1997) and Davis et al. (2011) warned about using the separation to name a fault because of

the virtual movement sense caused by weathering and erosion: a normal fault could show a strike-

slip separation on a map view, or a strike-slip fault could show a thrust separation on a section view

(Fig. 4- 3).

Fig. 4- 3. Strike-slip separation is caused by the erosion over a normal fault. Taken from Fossen (2010)

Because of this, Davis et al. (2011) suggested the analysis of slickensides, drag folds, and tension

fractures to determine the slip of a fault. This statement is supported by the observations of Twiss

& Unruh (1998), who argued that slickensides could be the response of strain (direction and sense

of deformation) rather that stress. Also, Frohlich & Apperson (1992) proposed a ternary diagram

that uses the dip of the P, T, and B axis of the focal mechanism to identify the best fault mechanism

between pure strike-slip, pure thrust, or pure normal. Álvarez-Gómez (2019) showed a

contemporary example of determining an earthquake's main movement using the focal

mechanisms and plotting the results in a Frohlich’s diagram.

For the Soapaga and the Corrales fault issue, the separation does not offer a useful tool to

differentiate between these two faults; yet the kinematic and deformation analysis does. In the

structural analysis, I described the Soapaga Fault as a high-angle - thick skin structure that uplifted

the pre-Cretaceous units. A transpressive stress regimen is necessary for a high angle reverse fault


to make the hanging wall displaces stratigraphically upwards (Tesón et al., 2013). Otherwise, if a

compressional stress regimen acts over a high angle fault, it will drive the formation of a new low-

angle thrusting fault rather than an inversion. Comparing the kinematic solutions in the study area

(Fig. 3- 5), I observed that transpressive solutions characterize the Soapaga Fault hanging wall, and

the Corrales Fault hanging wall is characterized by compressive solutions.

This observation could be supported by plotting the data of the fault planes of the area into the

Frohlich’s diagram with Delvaux & Sperner (2003) methods. Fig. 4- 4 shows how the fault planes'

data on the Corrales Fault hanging wall tent to cluster into the “Thrust” apex; meanwhile, the fault

planes' data on the Soapaga Fault hanging wall clusters into the “Strike-Slip”. These kinematic

solutions represent a structural “fingerprint” that allows the Soapaga Fault and the Corrales Fault

differentiation and supports my structural analysis and interpretation.

Fig. 4- 4. Frohlich’s ternary diagram of the Corrales and Soapaga fault planes.

4.2 The Trishear deformation as a realistic kinematic model for the study area

The Fault-propagation and Fault-bend folding kinematic models proposed for the Soapaga Fault do

not entirely explain how this fault is related to the Betéitiva Syncline characteristics as its structural

location -a footwall syncline-, its geometry, and its stratigraphic thinned backlimb. In this work, I

stated the Trishear kinematic modelling explains these structural key factors for understanding the

fault kinematic evolution and the study area's structural setting.

Chapter 4 45

First, the Trishear model allowed me to explain how a fault-propagation deformation style forms a

syncline below the fault plane. In this kinematic model, the triangular shear zone at the tip of the

fault deforms and rotates the hanging and the footwall blocks simultaneously. The rotation uses

the triangular shear zone's bisector as a fulcrum, making the particle trajectories forms an anticline

in the hanging wall and a syncline in the footwall. The volume of deformed rock in the hanging and

the footwall depends on the TA parameter. Hardy & Allmendinger (2011) shows an example of

discrete-element of how a footwall syncline could be explained in a simple manner using the

Trishear kinematic model (Fig. 4- 5). In this work, I showed how one could recreate a syncline below

the Soapaga Fault with the geometrical characteristic of the Betéitiva Syncline using values of TA

between 47°-58° for the inverse model and 47°-63° for the forward model.

Fig. 4- 5. Discrete-element modeling showing how a Trishear kinematic model could form a footwall syncline. After Finch et al., (2003) in Hardy & Allmendinger (2011).

Second, the deformation in the triangular zone of the Trishear model could explain the geometry

features of the Betéitiva Syncline: a fast change from a gentle west-dipping forelimb to an

overturned west-dipping backlimb, a narrow hinge zone, an asymmetrical fold shape, a close

interlimb angle, and a moderately inclined axial plane. The oblique particles’ trajectories

constrained by the p/s parameter could explain the listed features: the bigger the p/s value, the

longer particles’ trajectories from the hanging wall to the footwall, and the more strata rotates in

the fault blocks. Galup (1951) in Hardy & Allmendinger (2011) shows a natural example of a Trishear

fault-propagation fold in which geometric and structural characteristics are similar to those of the

Betéitiva Syncline: a footwall-asymmetric syncline with an overturned backlimb and thickness

changes into the deformational front. In the study area, a range of p/s values between 0.8 and 1.4


for the inverse modelling and 0.8 and 1.7 for the forward modelling allowed me to explain how the

Soapaga Fault's deformation could explain the structural features of the Betéitiva Syncline.

Fig. 4- 6. An example of a fault-propagation fold explained with the Trishear model. After Gallup (1951) in Hardy & Allmendinger (2011).

Third, the way the particles move in the Trishear model offers a mechanical explanation about the

thickness changes observed in the backlimb of the Betéitiva Syncline. The algorithms used to

recreate the Trishear deformation based in three statements: 1, the hanging wall is assumed as a

rigid mobile block where the particles move parallel to the fault and at the same velocity; 2, the

footwall is assumed as a rigid static block where the particles have zero velocity and; 3, the area is

conserved in the triangular shear zone affecting the hanging wall and the footwall.

The Trishear deformation conserves the area in both fault blocks throughout the volume

movement from the hangingwall to the footwall (Fig. 4- 7A). This movement occurs because the

velocity field in the triangular shear zone comprises equal velocity-radial areas that decrease in

magnitude toward the footwall: the particles move faster in the upper areas and slower in the

lower areas (Fig. 4- 7B). Furthermore, the displacement vectors within the triangular shear zone

are not parallel to each other, making the particles flow from the hanging wall to the footwall

thinning the folds' paired limb and thickening the syncline hinge zone. Therefore, even rigid strata

of limestones or sandstones could change its thicknesses through this deformational process if

mechanical and physical processes such as the velocity field, temperature, heat fluids, and

deformation rate (p/s parameter) maintain through the deformation for millions of years. In this

way, I explained the stratigraphic thickness changes in the backlimb of the Betéitiva Syncline using

the Trishear method.

Chapter 4 47

Fig. 4- 7. A, Erslev’s geometric explanation of area conservation. B, diagram of displacement vector trajectories within the triangular shear zone.

And fourth, the restoration I made showed the Trishear kinematic model implied lesser shortenings

than the FBF kinematic model for the Soapaga-Corrales fault system. The cross-section restorations

results show shortenings for the Soapaga-Corrales fault system of 1.92 km at the north of the area

and 3.43 km at the south of the area; 7.6 to 13 times lesser than the 25 km shortening of the FBF

model (Saylor et al., 2012). These differences in the shortenings between the Trishear and the FBF

models cannot be related to differences in the data used for the restoration process: both models

used similar geologic maps, gathered similar structural field data, and restored the same main

structures such as the Soapaga Fault and the Betéitiva Syncline. However, the Trishear model

requires less structural complexity to restore and explain the same structural and geological setting

than the FBF model, showing that the first kinematic model offers a plausible and more efficient

explanation than the latter.

This last observation implies a new way of thinking about traps and reservoirs for the petroleum

exploration in the study area: the structural model has been a helpful tool due to the low seismic

resolution related to the irregular-mountainous landscape and the high angle position of the strata.

In conclusion, a plausible and efficient structural interpretation that best explains the geological

settings on the area could better understand the structural traps and reservoirs' geometry in the

petroleum exploration.


4.3 The possibility of a regional fault-propagation fold model with a local Trishear kinematic model

The Soapaga Fault has been described as the eastern boundary of the Floresta Massif (Kammer,

1996; Mojica & Villarroel, 1984; Ulloa et al., 2001) that cropped out and formed a 17 km wide

anticlinorium in a fault-propagation deformative style (Kammer, 1996; Kammer & Sánchez, 2006;

Tesón et al., 2013). The fault-propagation fold model explains the kinematic relationship between

the Soapaga Fault and the Floresta Anticlinorium in regional scope. However, this model does not

explain the folding of the Betéitiva Syncline or its structural and geometric characteristics in a local

scope. In contrast, the Trishear kinematic model that I proposed in this work, supported by the

inverse and forward modeling, could explain in a local scope how the Betéitiva Syncline and its

characteristics are related to the deformation of the Soapaga Fault. However, in a regional scope,

a Trishear kinematic deformation could not explain the deformation of a structure of such

dimensions as the Floresta Anticlinorium. If the Floresta Anticlinorium and the Betéitiva Syncline

relate each other as paired structures product of the same deformative style, they would have

similar dimensions; however, the 2 km wide Betéitiva Syncline is not comparable with the 17 km

wide Floresta Anticlinorium.

If the fault-propagation fold model explains in a regional scope the folding of the Floresta

Anticlinorium, but the Trishear kinematic model explains in a local scope the folding of the Betéitiva

Syncline, how could one choose which is the best model for the Soapaga Fault? I propose there is

not a kinematic model that explains, in general, the formation of the Betéitiva Syncline and the

Floresta Anticlinorium at the same time; but scope-restricted models that explain either the

Betéitiva Syncline or the Floresta Anticlinorium.

Allmendinger et al. (2004) pointed out the idea of scope-restricted models to explain either

regional or local folds related to the same fault. These authors show examples of how the structure

could be better explained with a fault-propagation model on a regional scale even though the

Trishear model could better explain the structure on a local scale. Therefore, it is important to

notice two points: 1, the Betéitiva Syncline and the Floresta Anticlinorium cannot be either related

as paired structures nor explained in the same deformative style, and 2, for the structural modeling

of the Betéitiva Syncline, there is no need for a regional cross-section in order to understand the

local deformation of the Betéitiva Syncline. There is no parameter that one could found for a local

Chapter 4 49

Trishear restoration in a regional cross-section that explains better the structures with the fault-

propagation model.

5 Conclusions

5.1 Conclusions

I identify the Soapaga Fault as the eastern boundary of the Floresta Massif that cropped out the

Paleozoic and Jurassic? Sedimentary formations and the metamorphic and igneous basement end

to the south of the study area near the Sogamoso city in a periclinal close. Furthermore, the

Soapaga Fault shows geological and structural characteristics such as a fault zone of green-colored

breccias or malachite-azurite mineralization, geomorphic features related to a high angle fault

plane as drainage alignments and straight topographic features, and transpressive deformation

evidence located on the hanging wall.

On the other hand, I identified the Corrales Fault as a later-branched structure from the Soapaga

Fault that cropped out the Cretaceous sedimentary units and shows evidence of compressive-

related structures the hanging wall. I also distinguish between the Corrales Fault and the Soapaga

Fault in the geological map, showing how the misunderstood between these two faults makes

some author changes the Soapaga Fault’s trace with the Corrales Fault's trace.

The Trishear kinematic model explains better how the Soapaga Fault folds the Corrales Foreland

into the Betéitiva Syncline. This kinematic model explains simply the geometric and geological

characteristics of the Betéitiva Syncline, such as the fast change from a low angle-west dipping

forelimb to a high angle-to-overturned west-dipping backlimb, or the stratigraphic thickness

changes in the forelimb of the fold. Compared to classical structural models, the Trishear model

could efficiently explain the Corrales-Soapaga fault system, reducing the shortenings from 26 km

in the fault-bend model to 2-3.5 km in the Trishear model.

The restoration of structural cross-sections as well as the inverse and the forward modeling show

how the deformation of the Soapaga Fault changes from north to south, where the northern cross-


sections show less shortening, faults displacements, and Trishear kinematic parameters values such

as p/s and slip in comparison with the southern cross-sections that show higher values.

The Trishear inverse modeling of the Betéitiva Syncline restores the fold to an admissible

unstrained state, even though the results show a remaining strain in some beds close to the fault

suggesting the cross-sections requires fine-tuning to restore to a flat unstrained state. However,

the forward modeling results support my structural model showing a close similarity between the

forward and the proposed geometries.

Even though the Betéitiva Syncline and the Floresta Anticlinorium are related to the Soapaga Fault,

these two structures cannot be explained at the same time by one kinematic model. Nonetheless,

these two structures respond to individual kinematic models: the Trishear model better explains in

a local scope the Betéitiva Syncline and the Fault-propagation model better explain in a regional

scope the Floresta Anticlinorium.

A. Appendix: Geological map of the study area at 1:25.000 scale

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Chic

amoc

haR

iver

Divaquia

Creek

SOA 66

SOA 55

SOA 15

SOA 12

TO CORRALES

TO TASCO

TO PAZ DEL RÍO

SOA 92

SOA 83

Bet

eiti

vaFa

ult

Bet

eitiv

aFa

ult

Bet

éit

iva

Syn

clin

e

2500

27

00

25

50

2700

28

00

29

00

24

00

2400

3000

23

00

3100

32

00

31

00

3300

33

00

34

00

2400

2900

3000

25

00

29

00

2900

2850

2800

25

00

2600

280028

00

2700

2700

2600

2500

27

00

2700

26

00

30

00

24

00

2500

33

00

29

50

29

50

3000

3100 25

00

2500

30

50

2600

25

00

3000

26

00

2300

2700

27002700

26

00

28

00

2600

27

00

2700

2800

30

00

2700

3000

2600

2900

3100

Corr

ales

Fau

lt

Chig

uaza

Fau

lt

Soa

pa

ga F

aul

t

Soap

aga

Faul

t

Soap

aga

Faul

t

CORRALES

BETEITIVA

BUSBANZA

Jg

Pgc

Cc

Kit

pD?so

Pgc

Kiu

Pgs

Pgp

Kit

PCA?nb

PCA?nb

PCA?nb

Ksc

KPgg

Kiu

PCA?nb

Pgp

Ksg

Pgs

Ksg

Pgp

Kit

Cc

Kiu

40

30

40

55

22

8584 57

80856969

3935

53

4442

50

44

8982

32

18

22

47

26

77

46

42

66

517225

42

53

43

52

66

46

31

43

66

52 54

57

34

81

55

39

4050

78

6076

40

26

53

2548

3956

3748

41 19

43

59

28

34

6782694153

21

18

36

24

SOA 2

SOA 3

SOA 4

SOA 6

SOA 7

SOA 11

SOA 13

SOA 17

SOA 18

SOA 20

SOA 21

SOA 23

SOA 26

SOA 29 SOA 30

SOA 32

SOA 35

SOA 36

SOA 37

SOA 38

SOA 43

SOA 44

SOA 45

SOA 47

SOA 48

SOA 50

SOA 52

SOA 53

SOA 54

SOA 56

SOA 57 SOA 58

SOA 58

SOA 59

SOA 60

SOA 61

SOA 62

SOA 63

SOA 65

SOA 67

SOA 68

SOA 69

SOA 70

SOA 71

SOA 72

SOA 73

SOA 74

SOA 75

SOA 76

SOA 79 SOA 80

SOA 81

SOA 82

SOA 84

SOA 85

SOA 86

SOA 88

SOA 89 SOA 90

SOA 91

SOA 95

SOA 96

SOA 97

SOA 98

72°44'W72°46'W

72°52'W

6°2'N

6°2'N

6°N

6°N

5°58'N

5°58'N

5°56'N

5°56'N

5°54'N

5°54'N

5°52'N

5°52'N

5°50'N

5°50'N

72°44'W

72°46'W

72°48'W

72°48'W

72°50'W

72°52'W

±

Legend

Formations

Concentracion Formation

Picacho Formation

Socha Formation

Guaduas Formation

Guadalupe Group

Chipaque Formation

Une Formation

Tibasosa Formation

Giron Formation

Cuche Formation

Otenga Stock

Gneiss

Geography

Locations

Topographic Contour

Roads

Waterways

Dip data

o Bedding

s Overturned

Cross-Sections

Cross-Sections

Folds

F Anticline

M M M Syncline

Faults(( (( Thrust

Strike-Slip

Lithologic Contacts

Normal

Unconformity

EE EE Angular Unconformity

DD DD DD DD Intrusive

Appendix AGeological Map of the study area

From the M.Sc. Thesis:Structural Modelling of the Soapaga Fault

in the central part of the Eastern Cordillera,Colombia

Author:Germán Andrés Pardo Torres


20200 740 1.480 2.220 2.960370

Meters

Scale: 1:25.000

DATUM Colombia BogotaProjection: Transverse Mercator

False Easting: 1.000.000 False Northing: 1.000.000Central Meridian: -74,077 Latitude of Origin: 4,596

Scale Factor: 1Linear Unit: Meter

Geology of the eastern side of the Floresta Massif

E

E'

DD'

C

C'

BB'

A

A'

Jg

Cc

pD?so

pCA?nb

Kit

Kiu

Ksc

Ksg

KPgg

Pgs

Pgp

Pgc

Chicam

ocha

Riv

er

BuntiaCr ee

k

Soapaga River

Colacote Creek

Chiguaza Creek

B u sban

zaCr

eek

54 Título de la tesis o trabajo de investigación

B. Appendix: Iterations of the best-fit parameter values grid search process

56 Structural Modelling of the Soapaga Fault at the northern of Easter Cordillera

References 57

References 59


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