Volumen 2 Amaga-cauca-patia Basins

PETROLEUM GEOLOGY OF COLOMBIA

AMAG, CAUCA AND PATA BASINS

Gloria M. SierraMaria I. Marn-Cern

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AGENCIA NACIONAL DE HIDROCARBUROS

COLOMBIA

Editor, Fabio Cediel

AMAGA Correciones 7 Abr19.indd 1 21/04/12 8:14

Copyright

UNIVERSITY EAFITDepartment of Geology

ChairmanGeovany Bedoya Sanmiguel, MSc.

Project Manager

www.eafit.edu.coCarrera 49 No. 7 sur 50, Avenida Las Vegas

Tel: (57-4) 2619330Medelln - Colombia

Printed by Impresos El DaMedellin

December 2011

GEOLOGY AND HYDROCARBON POTENTIAL REGIONAL GEOLOGY OF COLOMBIA


PETROLEUM GEOLOGY OF COLOMBIAEditor, Fabio Cediel

Geology and Hydrocarbon Potential

AMAG, CAUCA AND PATA BASINSGloria Sierra

Mara I. Marn-Cern


Minister of Mines and Energy

General Director ANH

Technical Sub-director

Chief Geologist

ORLANDO CABRALES SEGOVIA

MAURICIO CRDENAS SANTAMARIA

President of the Republic of ColombiaJUAN MANUEL SANTOS CALDERN

CAROLYNNA ARCE HERNNDEZ

CLEMENCIA GMEZ GONZLEZ

AGENCIA

NACIONAL DE HIDROCARBUROS

COLOMBIA


PETROLEUM GEOLOGY OF COLOMBIAGeology and Hydrocarbon Potential


ACPB, Amag Cauca - PatiaATB, Atrato

CATB, CatatumboCAYB, Cayos

CPB, Caguan - PutumayoCRB, Cesar - RancheraECB, Eastern Cordillera

GUB, GuajiraLIAB, Llanos

LMB, Lower - MagdalenaMMB, Middle Magdalena

SIB - SJAB, Sin San JacintoSJUB, San Juan

TUB, TumacoUMB, Upper Magadalena

URB, UrabVAB, Vaups - Amazonas


PETROLEUM GEOLOGY OF COLOMBIA

Editor, 1Fabio Cediel, Co-Editor, 2Germn Y. Ojeda, Co-Editor, 3Fabio Colmenares

VOL. TITTLE - BASIN AUTHOR PAGES FIGURES

1 Regional Geology of Colombia1Cediel, F., H. 4-6Leal-Meja,5-6R.P. Shaw, 6J.C. Melgarejo,

7P.A. Restrepo-Pace224 67

2 Amag - Cauca - Pata, ACP 1Sierra, G.M., 1M.I. Marn-Cern 104 74

3 Atrato - San Jun Urab, AT-SJU-UR 1Cediel, F., 8I. Restrepo Correa 112 92

4 Cagun - Putumayo, CP 9Montenegro, G., Barragan M. 126 70

5 Catatumbo, CAT 3Pedraza, P.E., 3Y. Ramrez 136 86

6 Cesar - Ranchera, CR 3Mesa, A.M., Rengifo, S.E. 160 86

7 Eastern Cordillera, EC 10Sarmiento, L.F. 140 87

8 Guajira - Cayos, GU-CAY 11Aguilera, R. 174 107

9 Eastern Llanos, LLA 10Sarmiento, L.F. 185 135

10 Lower Magdalena, LM12Arminio, J.F., 12F. Yoris, 12L. Porras, 12E. Garca,

12M. Diluca218 148

11 Middle Magdalena, MM 10Sarmiento, L.F. 194 85

12 Sin - San Jacinto, SI-SJA 11Aguilera, R. 110 87

13 Tumaco, TU 1Marn-Cern, M.I.,1 G.M.Sierra 80 46

14 Upper Magdalena, UM 3Roncancio, J.H., 3M. Martnez 182 104

15 Vaups - Amazonas, VA 13Kroonenberg, S., 13C.V. Reeves 104 74

Chapter Petroleum Systems (in each basin)

14Mora, C., 14P. Parra, 14D. Sanabria, 14W. Guzmn

1 Department of Geology, University EAFIT, Medelln

2 LAEFM Colombia, Ltda., Subsuelo 3D, Bogot

3 Geosearch Ltd., Bogot

4 Greenfields Exploration, AngloGold Ashanti Colombia S.A.,

University of Barcelona

5 Exploration Geologist, Medelln

6 - MINRESOUR, Faculty of Geology, University of Barcelona

7 - Mubadala Oil & Gas Malaysia, Kuala Lumpur

8 ECOPETROL, Bogot

9 Lithoil Ltd., Bogot

10 Consultant, Bogot

11 RaGeologia E.U.

12 Pacific Rubiales Energy, Bogot

13 Delft University of Technology

14 Gems Ltda.


Pag.

CONTENTS

13 1. INTRODUCTION14 1.1 BaSIN LOCaTION aND pREvIOUS STUDIES17 1.2 ExpLORaTION HISTORy

23 2.GEOLOGy24 2.1 REGIONaL OvERvIEw25 2.2 STRaTIGRapHy26 2.2.1 Pre CenozoiC basement 26 2.2.2 CenozoiC26 2.2.3 Lower eoCene28 2.2.4EocEnEoligocEnESEquEncES31 2.2.5oligocEnEMiocEnESEquEncES35 2.2.6uppErMiocEnE35 2.2.7pliocEnE-rEcEnt35 2.3 STRaTIGRapHIC SUmmaRy35 2.3.1 environment36 2.3.2DrillEDwEllSinthEcaucapataarEa39 2.3.3DrillEDwEllSinthEaMagarEa40 2.4 STRUCTURaL GEOLOGy40 2.4.1SouthErnarEa:pataSub-baSin44 2.4.2cEntralarEa:caucabaSin47 2.4.3northErnarEa:aMagbaSin54 2.5 majOR STRUCTURaL ELEmENTS54 2.5.1roMEralFaultSyStEM54 2.5.2caucaFaultSyStEM54 2.5.3piEDEcuEStaFault54 2.5.4FaultingwithnE-SwDirEction54 2.5.5rEgionalFolDingnnEDirEction57 2.6 GRavImETRy aND maGNETOmETRy57 2.7 STRUCTURaL map

63 3. TECTONIC EvOLUTION OF THE amaG CaUCa paTa BaSIN64 3.1 LaTE TRIaSSIC64 3.2JurassicEarlycrEtacEous66 3.3latEPalEocEnE-EarlyEocEnE66 3.4 EOCENE TO EaRLy mIOCENE 67 3.5latEMiocEnEPliocEnE68 3.6 QUaTERNaRy68 3.7 BaSIN DEvELOpmENT

73 4. pETROLEUm SySTEm75 4.1 HyDROCaRBON ELEmENTS aND pROCESSES75 4.1.1SourcErockS75 4.1.2rESErvoirrockS75 4.1.3 eaL rockS75 4.1.4hyDrocarbontrapS


CONTENTSPag.

75 4.1.5 OVERBURDEN ROCkS75 4.2 EVENTS CHART75 4.3 SOURCE ROCk PROPERTIES75 4.3.1 ORGANIC MATTER CONTENT75 4.3.2 oRGanic MattER quality 75 4.3.3 THERMAL MATURATION OF ORGANIC MATTER75 4.3.4 HYDROCARBON GENERATION POTENTIAL75 4.3.5 PETROLEUM SYSTEM MODELING 76 4.4 PETROLELUM SYSTEM DEFINITION 76 4.5 PEtrolEuM systEMs of thE CAuCA suB-BAsin77 4.5.1 ELEMENTS AND PROCESSES78 4.5.2 ORGANIC MATTER CONTENT78 4.5.3 oRGanic MattER quality79 4.5.4 THERMAL MATURATION OF ORGANIC MATTER79 4.5.5 HYDROCARBON GENERATION POTENTIAL79 4.6 HYDROCARBON ExTRACT PROPERTIES 81 4.7 PETROLEUM SYSTEMS MODELING81 4.8 PETROLEUM SYSTEMS DEFINITION83 4.9 PEtrolEuM systEMs of thE PAtA suB-BAsin83 4.9.1 ELEMENTS AND PROCESSES84 4.10 EVENTS CHART84 4.10.1 SOURCER ROCk PROPERTIES85 4.10.2 OIL SEEPS AND ROCk ExTRACT PROPERTIES 85 4.10.3 SYNTHESIS OF OIL SEEPS AND ROCk ExTRACT PROPERTIES 87 4.11 PETROLEUM SYSTEMS MODELING88 4.12 PETROLEUM SYSTEMS DEFINITION

91 5. CONCLUSIONS

95 REFERENCES


Figure 1 Geographical location of Amag Cauca Pata Basin.Figure 2. Geological Map and location of Amag Cauca Pata Basin.Figure 3. Base map of studies carried out in the Amag Cauca Pata basin.Figure 4. Seismic lines location in the Amag Cauca Pata Basin Sub basin. Figure 5. Geological index map from Geological Survey of Colombia (INGEOMINAS).Figure 6. Geodynamics of the South American plate and the Caribbean and Nazca plates Cediel, et al., 2003). Figure 7. Chronostratigraphic Chart for ACP basin. (Modified from Barrero, and Laverde, 1998; Hincapie et al; 2010).Figure 8. Pea Morada Formation and Mosquera Formation, Syntetic stratigraphic column (Geoestudios 2008).Figure 9. Chimborazo Formation and Guachinte Formation, Syntetic stratigraphic column. (Geoestudios 2008).Figure 10. Mosquera Formation and Esmita Formation, Syntetic stratigraphic column (Geoestudios 2008). Figure 11. Guachinte Formation Syntetic stratigraphic column (Geoestudios 2008).Figure 12. Lower Cinta de Piedra Formation Syntetic stratigraphic column (Geoestudios 2008).Figure 13. Lower member of the Amag Formation (Unit 1 and 2).Figure 14. Esmita Formation Syntetic stratigraphic column (Geoestudios 2008).Figure 15. a) and b). Upper member of the Amag Formation.Figure 16. Cenozoic magmatism in the ACP basin.Figure 17. Ferreira Formation, Syntetic stratigraphic column (Geoestudios 2008).Figure 18a. Schematic paleo reconstruction sedimentary enviroments of the Pea Morada FormationFigure 18b. Schematic paleo reconstruction sedimentary enviroments of the Chimborazo Formation.Figure 18c. Schematic paleo reconstruction sedimentary enviroments of the La Cima Member and lower member of the Amaga Formation.Figure 18d. Schematic paleo reconstruction sedimentary enviroments of the Cinta de Piedra Formation.Figure 18e. Schematic paleo reconstruction sedimentary enviroments of the Guachinte Formation.Figure 18f. Schematic paleo reconstruction sedimentary enviroments of the La Rampla member.Figure 18g. Schematic paleo reconstruction sedimentary enviroments of the Mosquera Formation.Figure 18h. Schematic paleo reconstruction sedimentary enviroments of the Esmita Formation.Figure 19. Interpreted Seismic Profiles CP-90-1450 showing style of deformation and regional unconformities in the Pata Sub-basin (Modified from

Barrero and Laverde, 1998).Figure 20. Interpreted Seismic Profile CP-90-1200, showing large displacement along thrust and regular relation of Upper Cretaceous strata with the

Lower Eocene Pea Morada Fm., that documents the folding/thrusting deformationduring the Paleogene Collision in the Pata Sub-basin. (Modified from Barrero and Laverde, 1998).

Figure 21. Geoseismic Profile showing structural style in the Cauca sub-basin. (Modified from Barrero and Laverde, 1998).Figure 22. TWT structural map of the Lower Eocene unconformity Pata sub-basin (Modified from Barrero and Laverde, 1998).Figure 23. TWT Structural map of the Lower Eocene unconformity Cauca sub-basin. From Barrero. D, and Laverde, F., 1998.Figure 24a. North stratigraphical correlation Cauca sub-basin.Figure 24b. South stratigraphical correlation Pata sub-basin.Figure 25. Seismic Profile VC-79-10 showing structural style, regional unconformities and seismic secuences in the Cauca sub-basin. (Modified from

Barrero and Laverde, 1998).Figure 26. Geological map of Amag sub-basin.Figure 27. Cross-sections of the Amaga sub-basin. Figure 28. Geological map of the Cauca-Pata sub-basins.Figure 29. Regional structural map in the ACP basin.Figure 30. Pole reduced Total Magnetic Intensity (Modified from Carson Helicopters, 2006).Figure 31. Gravity_Seismic Depth.Figure 32. Top of Cretacic Basement map.Figure 33. Gravimetry map Amag sub-basin.Figure 34. Magnetometric map Amag sub-basin.Figure 35. Cross section geological profile close to Manizales city. (Modified from Suter 2008).

LIST OF ILLUSTRATIONS


Figure 36. Romeral Blue Schist Belt (Compiled by Cediel, 2011).Figure 37. Paleomagnetic site mean declination (the black wedges are a previous study and the red ones are the present one) for the late tertiary

intrusions form two distintct groups (northern and souther of the Amaga Sub basin) of different treands but approximately parallel to trend of adjacent Romeral suture zone. Late Tertiary intrusions are stippled.

Figure 38. Standard F diagrams (dedding poles, righthand column) define structural trends of domains for the folded Tertiary strata of the North Ama-ga Cauca Patia basin. In the left column, the symmetry plane found by eigenvalue method is great circle representing the bedding poles. Dots in the lefthand column represent the minimum eigenvector, representing the normal to the great circle and therefore corresponding to the fold axis for the bedding poles of the right column. The fold axes is approximately parallel to the Romeral Structure zone.

Figure 39. Models for coherent vertical axis rotation of northern group of intrusions relative to southern group by kinking of the zone of intrusions.Figure 40. Models for incoherent horizontal axis rotation of lenticular masses of Tertiary intrusions. Rotation of massive lenticular intrusive bodies in

the plane of the fault system produces irregular dispersion of remanence vector in the vertical plane.Figure 41. Sketch diagram of possible movements of Cauca Romeral fault System mid- Eocene Pleistocene. A). Extension phase with sedimentation,

detachment, and clockwise rotation associated with right -lateral slip at a right stopover. b) Compression phase, with folding, thrusting, and clockwise rotation during ninistral slip at right stopover.

Figure 42. Scheme of the origin and evolution of the Amaga Cauca Pata basin in the upper Cretaceous.Figure 43. Scheme of the origin and evolution of the Amaga Cauca Pata basin in late Cretaceous to Eocene. Figure 44. Scheme of the origin and evolution of the Amaga Cauca Patia basin in the Early Eocene - Middle Eocene.Figure 45. Scheme of the origin and evolution of the Amaga Cauca Patia basin in the in the Miocene to Pleistocene.Figure 46. Location of active coal mines in the Amag Basin.Figure 47. Chart of events of the unconventional hydrocarbon system of the Amag Basin. The hypothetical burial curve for the Paleogene unit is rep-

resented by the red line.Figure 48. Maximum temperature (Tmax) vs hydrogen index (HI) diagram for the Amag Basin. Note that HI values indicate the existence of kerogen

type III, and type II in a lesser proportion. The analyzed samples are immature (modified from UNAL and ANH, 2009).Figure 49. Synthesis diagram properties of the source rock of the Amag Basin. Note that the Amag Formation is a gas prone unit.Figure 50. Location of wells and geochemical data of the Cauca Sub-Basin.Figure 51. Petroleum events Chart for the Cauca Sub-Basin. The burial curve is represented by the red line.Figure 52. Modified Van Krevelen diagram of the stratigraphic succession of the Cauca Sub-Basin. The evaluated stratigraphic succession presents a

mixture of kerogens type II and III. Figure 53. Maximum temperature (Tmax) vs hydrogen index (HI) diagram for the source rocks of the Cauca Sub-Basin. The Cinta de Piedra and Agua

Clara Formations are considered immature and over-matuer, respectively, whereas the Chimborazo, Guachinte, and Ferreira Formations are in the oil generation window.

Figure 54. Total organic carbon (%TOC) vs generation potential (S1+S2) of the Cauca Sub-Basins source rocks. Note that the Guachinte and Ferreira Formations show favorable generation potential values. Data from Geoestudios Ltd. (2008) and Hincapi et al. (2009).

Figure 55. Synthesis of geochemical properties of the main source rocks of the Cauca Sub-Basin. Note that the Guachinte Formation shows the best characteristics as a source rock.

Figure 56. Phytane/nC18 vs pristane/nC17 diagram for organic matter extracts of the Cauca Sub-Basin. Extracts correlate with an oxic environment with a mixture of organic matter corresponding to a kerogen type II and III (marine and terrestrial).

Figure 57. Pristane/Phytane vs oleanane/C30 hopane diagram for hydrocarbon extracts of the Cauca Sub-Basin. Note that they correlate with an oxic depositional environment.

Figure 58. Maximum burial curves for the stratigraphic succession of the Cauca Sub-Basin. Note that the maximum burial depth occurs in the Holo-cene.

Figure 59. Vitrinite reflectance (%Ro) through time for the stratigraphic succession of the Cauca Sub-Basin. Note that the Cinta de Piedra Formation reached a temperature equivalent to the liquid hydrocarbons generation peak to a late maturation.

Figure 60. Expulsion generation processes. Note that the Cinta de Piedra Formation did not reache a stage of development.Figure 61. Petroleum systems map of the Cauca Sub-Basin. Note the depocenter at the top of the basement, and the hypothetical area of influence of

the petroleum systems.Figure 62. Location of geochemical data from the Pata Sub-Basin. Figure 63. Events Chart for the petroleum systems of the Pata Sub-Basin. The burial depth curve is indicated with the red line.Figure 64. Modified Van Krevelen diagram for the Pata Sub-Basin. Note how the Esmita and Mosquera Formations have the best organic matter qual-

ity, with mixture of kerogens II and III, and a gas and oil generation capacity. Data from Geoestudios Ltd (2008) and Hincapi et al. (2009).


Figure 65. Maximum temperature (Tmax) vs the hydrogen index (HI) for the stratigraphic succession of the Pata Sub-Basin. Note that some samples of the Esmita and Mosquera Formations have values in the liquid hydrocarbon generation window. Data from Geoestudios Ltda (2008) and Hincapi et al. (2009).

Figure 66. Total organic carbon (%TOC) vs generation potential (S1+S2) diagram for the Pata Sub-Basin. Note that the units with a better generation potential are the Esmita, Mosquera and Chapungo Formations. Data from Geoestudios Ltda (2008) and Hincapi et al. (2009).

Figure 67. Synthesis diagram of the geochemical properties of the main source rocks of the Pata Sub-Basin.Figure 68. Phytane vs pristane diagram for the stratigraphic succession of the Pata Sub-Basin. Note that rock extracts from the Chapungo Formation

suggest an oxidating environment, whereas that organic matter seeps suggest a more reducing depositional environment.Figure 69. Pristane/Phytane vs oleanane/C30 hopane diagram for the stratigraphic succession of the Pata Sub-Basin. Note that samples from the Pea

Gorda and Chapungo Formations reflect a marine, siliciclastic depositional environment.Figure 70. Ternary diagram of esteranes (C27, C28 and C29) for the Pata Sub-Basin. The increase in the C29 fraction indicates a major supply of terres-

trial organic matter.Figure 71. Burial curve depths for the stratigraphic succession of the Pata Sub-Basin. Note that the maximum depth has been reached in the Holo-

cene.Figure 72. Vitrinite reflectance (%Ro) profile through time for the stratigraphic succession of the Pata Sub-Basin. Note that the Esmita Formation was

not submitted to enough temperature to reach the liquid hydrocarbon generation window.Figure 73. Expulsion processes for the stratigraphic succession of the Pata Sub-Basin. Note that the Esmita Formation did not experienced them.Figure 74. Petroleum systems map for the Pata Sub-Basin. Note the depocenter at the top of the basement, the oil seeps, and the hypothetical area

of influence of the petroleum systems.

TABLE LISTTable 1. Seismic programs in the ACP basin.Table 2. CBM exploration wells in the Amag sub-basin. (ANH, 2011).Table 3. Synthesis of extracts and crude oil seeps from the Pata Sub-Basin.


1. INTRODUCTION


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1 - INTRODUCTION

1.1 BASIN LOCATION AND PREVIOUS STUDIES

The Amag Cauca Pata basin (ACP) in western Colombia lies between the Central Cordillera to the east and The Western Cordillera to the west, between 1 20 and 635 North latitude (Figure 1). The basin is mapped as an elongated depression that extends for about 588 kilometers in direction N 24 E, and averages 40 kilometers east west. The maximum width is about 55.4 kilometers close to the town of Cartago, narrowing to the North (3.5 kilometers) near the town of Santa F de Antioquia. The Cauca Valley terminates in the north at the junction of the Central and Western Cordilleras, where the Cauca - Romeral fault systems converge.

In the south the ACP basin trends NNE and then switches to NNW in the north. It separates the Central and Western Cordilleras and largely controls the course of the Cauca and Pata rivers. Currently, remnants of molassic continental and marine sediments that filled the depression during the Tertiary period are dominant in the North Amag, in the central part of Valle del Cauca and in the southern Pata sub-basins. Between these basins, small bodies of Tertiary sediments are exposed as geological windows surrounded by thick volcano-clastic and Volcanic deposits. Locally, lacustrine and marine environments took place during the Cenozoic which are erosion remnants resting on pre- Tertiary rocks (Figure 2).

The ACP basin is the result of the accretion and collision of oceanic terrains along the Romeral suture zone (McCourt and Aspden 1984; Pindell and Barrett 1990; Cediel et al., 2003). The stratigraphical and sedimentological histories of these basins show signatures related to the tectonic activity in western Colombia. The ACP basin developed through a process that started with a rifted continental margin, followed by oblique subduction of oceanic lithosphere and a sequential collision of an intra oceanic island arc (Strorey, et al. 1991; Nivia, A., 1989; Sierra et al, 1996; Kerr et al., 1997b, 1998; Barrero and Laverde, 1998; Moreno, and Pardo, 2003 Kerr, and Terney, 2005). This collision event may have triggered thrust-faulting and dextral strikeslip displacement mainly along the Romeral suture, inducing the formation of structures such as the Amag pull apart basin. Most of the ACP basin margins are shaped by inverse regional faults and that direct Cauca-Romeral fault system. These faults are the boundary between the Cenozoic sedimentary filling, the Paleozoic metamorphic rocks and the Cretaceous oceanic affinity bodied complexes.

The information provided by five wells (Candelaria-1, Juga-1; Patacore-1; Salsa-1 and Bereju-1) drilled in the southern and central part of The ACP basin made it possible to understand the principal bioestratigraphic units and provide a general stratigraphic framework for the basin (Figure 3). The presence of oil seeps and hydrocarbons indicates that the source rocks could not have achieved the thermal maturity necessary to produce

Figure 1. Geographical location of Amag Cauca Pata Basin


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Figure 2. Geological Map and location of The Amag Cauca Pata Basin


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Figure 3. Base map of studies carried out in the Amag Cauca Pata basin.


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oil and gas. In order to evaluate any petroliferous system the available geochemical information was reinterpreted and a preliminary model of hydrocarbon generation and expulsion is proposed. A new play related to the non-conventional hydrocarbon exploration is also proposed, mainly related to the Coal Bed Methane (CBM) associated with the Amag basin (ANH, 2011), where seven wells have been drilled: Venecia-1, El Cinco-1A, El Cinco-1B, Torreblanca-1, Rincn Santo-1, Damasco-1 and La Loma -1.

1.2 ExPLORATION HISTORY

The ACP basins have been studied by various authors, including Hincapi et al., 2010, Geoestudios, 2008; Barrero et al., 2007; Moreno and Pardo, 2003; Bravo et al., 2004; Pardo et al, 2004; Buzar Consultor Limitada, 1993; Mantilla and Arias, 2001; Dueas et al., 2000; Villalobos and Aranzazu, 1994; Alfonso, 1993; Oxy Exploration, 1991; Gonzlez, 1991; Keith et al., 1988; Galindo and Gonzlez, 1982; Rodriguez and Velandia, 1980; Van der Hammen, 1958; and Grosse 1935, 1926.

The work carried out by the Hincapie et al (2010) includes a summary of the Cauca Pata basin, as well as an extensive bibliography that mentions seismic, gravimetric, and aeromagnetometric studies, drilled wells and their results, and regional geological studies. A Base Map was compiled (Figure 4), showing the main field studies, the seismic programs, and five exploratory wells that have been drilled: Candelaria-1 (1965) drilled by the International Petroleum Limited Company and the other four wells: Juga-1; Patacore-1; Salsa-1 and Bereju-1 were drilled during the period 1997-1998 by Trinity Gas Colombia INC Company.

The most significant aeromagnetric and seismic reflection studies of the Cauca-Pata area were carried out during 1979 1990. The names of the seismic programs are: Valle Del Cauca-79, Valle Del Cauca-80, Pata-81, and Cauca-Pata-90. The total length of the seismic programs cover 905.934 km and a total of 33 seismic lines (see Table 1). Figure 5 shows the geological map index from Ingeominas.


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Figure 4. Seismic lines location in the Cauca Pata, Sub basin.


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Figure 5. Geological index map from Geological Survey of Colombia (INGEOMINAS).


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Program Seismic Line Length (Km) Total Length of the Program (Km)

Cauca Pata - 90

CP- 1990 - 1160 25,2CP- 1990 - 1200 35,5CP- 1990 - 1300 44,3CP- 1990 1300A 11,8CP- 1990 1300B 14,3CP- 1990 - 1450 26,4CP- 1990 - 1600 15,1CP- 1990- 1850 23,3CP- 1990 - 2015 14,2

Subtotal 210,0

Pata - 81

P-1981 - 1100 24,1P-1981 - 1150 27,1P-1981 - 1460 5,5P-1981 - 1600 8,5P-1981 - 1640 5,7P-1981 - 1800 5,5

Subtotal 76,3

Valle del Cauca 79

VC-1979 01 - L 30,0VC-1979 01 - N 29,7VC-1979 - 01- S 21,6VC-1979 - 02 34,5VC-1979-03 73,7VC-1979 - 4 41,5VC-1979 - 5 69,9VC-1979- 6 36,3VC-1979- 8 42,2VC-1979- 10 36,7VC-1979 - 12 35, 4

Subtotal 451, 3

Valle del Cauca 79

VC- 1980 - 660 17,5VC-1980 -840 16,2VC- 1980 -1150 19,6VC- 1980-1260 16,3VC- 1980-1300 51,5VC- 1980-1350 47,3

Subtotal 168,3TOTAL 905,9

Table 1. Seismic programs in the ACP basin.


2. GEOLOGY


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CHAPTER 2 - GEOLOGY

2.1 REGIONAL OVERVIEw

The northwestern part of the northern Andes is formed from the tectonic interactions between the South American, Caribbean and Nazca Plates (Figure 6).

The ACP basin is located in the Cauca depression between the Cauca and Romeral Fault Systems, in an area where rocks of different characteristics are juxtaposed in fault contact. Also, the region is a former continental margin, set by the Cauca-Romeral fault system. The ACP is bordered by the Romeral-Peltetec and Cauca fault system and is inside of the so-called Romeral-Peltetec Terrain (Cediel et al., 2003). The Romeral-Peltec and Cauca fault systems form a suture between the Cajamarca-Valdivia (CA-VA) - Romeral (RO) terraines, and Romeral- Dagua-Pin oceanic terraines (e.g Cediel et al, 2003). In Colombia, the Cauca system outcrops along almost its entire length and thus is cartographically well defined. The generally right-lateral strike-slip character of the fault (Sierra G., 1994; Ego et al., 1995; MacDonald et al., 1996,) varies along the strike and the dextral component can only be inferred at some local sites.

The Cauca system appears to correlate with the dextral Pujili-Pallantanga system in southern Ecuador (e.g.Van Thournout et al., 1992). Interpretation is inhibited to some degree by deformation and abundant recent volcanic cover that distort and mask the faults structure along the Inter-Andean depression. Regardless, occurrences of ophiolite along the fault (e.g., the Pujili ophiolite; Litherland et al., 1994) suggest a suture origin.

The seismic profiles of the Cauca fault system in the Cauca-Pata area indicate the dominance of west-verging thrust displacement in the subsurface (e.g. Cediel et al., 1998). This interpretation is corroborated by observed thrust emplacement of Paleozoic Cajamarca-Valdivia schist over siltstone and shale of the Oligocene Esmita Formation near Almaguer town in the southern part of the basin and Eocene Amag Formation near Santa Fe de Antioquia in the northern part of the basin. These observations contrast markedly with the traditional interpretation of the region as an arc-axial depression or structural graben (e.g. Sillitoe et al., 1982; Aspend et al., 1987). Thrust faults in the seismic profiles appear to truncate middle Miocene hypabyssal intrusive bodies, implying late or post-Miocene reactivation of the Romeral-Cauca system. Instead, Romeral fault arrival and oblique docking is temporally and geometrically constrained by five independent observations:

Sierra (1994) conducted paleomagnetic studies in the Irra area and described both dextral and sinestral movements along the Romeral Fault systems, the dextral movements are predominant.Ego et al., (1995) confirms that the movement along the Romeral fault is clearly dextral.

Radiometric dating of phengite and glaucophane schists of the El Oro ophiolite (Raspas sector), Ecuador, Colombia and the Jambal areas, respectively, returned K-Ar dates of about 132 and 125 Ma (McCourt and Feininger, 1984). These units are contained in the Romeral suture and mlange and the dates are interpreted to indicate the time of collision and emplacement of the Romeral terrain (Litherland et al., 1994).

Regional uplift and erosion in the Eastern Cordillera and elsewhere is registered by the stratigraphic gap of the Aptian. This unconformity appears to represent tectonic response to Romeral docking. Initial dextral reactivation of the Palestina fault system during the Aptian was documented by Feininger et al., (1970). This reactivation indicates transpressive dextral docking stress relay into preexisting structures of the Cajamarca-Valdivia terrain.

Figure 6. Geodynamics of the South American plate and the Caribbean and Nazca plates Cediel , et al., 2003)


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Faults in this system are the boundaries of structural complexes from East to West: polymetamorphic complex of the Central Cordillera, Cajamarca complex, Quebradagrande complex, Amaime complex and Western Cordillera oceanic affinity complexes (e.g Maya & Gonzalez 1995; Moreno & Pardo 2003). The last two complexes comprise the majority of the basement of the ACP basin and consist of imbricate blocks of oceanic crust formed in the Cretaceous during the accretion to the South American plate (Millward et al., 1984; Nivia 1989; Kerr et al. 1996; Sinton et al. 1998; Cediel, et al., 2003; Pindell et al. 2006;). The sediments embedded in these complexes were deposited in marine environments during the Coniacian to Maastrichtian (Keizer 1954; Leon et al., 1973; Orrego et al., 1976; Pardo et al., 2004).

The continuing convergence of the South American and Nazca plates resulted, during the Cenozoic in a syntectonic sedimentation in shallow locally marine, lacustrine, deltaic, and river environments; reverse faults and regional folds were also developed. Later on, the middle Miocene volcanic sedimentation process also became important. Associated with this volcanic activity a large number of intrusive small bodies were emplaced in the ACP basin, along the Cauca-Romeral fault system structures.

2.2 Stratigraphy

The ACP basin is composed in the north part by the Amag sub-basin that is separated by the Armenia fan, in the central part is separated by the Popayn high basement and in the south it is made up by the Pata sub-basin. Figure 7 shows in a general manner the lithology, age, stratigraphic relations and nomenclature of the rocks in the basin.

The stratigraphy of the basin records a siliciclastic-dominated Upper Campanian to Holocene section more than 3000m thick (Barrero and Laverde, 1998), overlying an Upper Jurassic - Lower Campanian section of basaltic units interbedded with polymictic rocks. The basement unit has been named the Amaime- Chaucha complex by Moreno and Pardo (2003). The Amaime-Chaucha complex terrain crops out at the western and eastern side of the basin and corresponds mostly to the western flank of the Central Cordillera (Figure 2). The Amaime heterolithic complex represents a tectonic stacking of ocean basalts and sediments, trench deposits and slivers of dismembered ophiolites (Barrero and Laverde, 1998).

Figure 7. Chronostratigraphic Chart for ACP basin. (Modified from Barrero, and Laverde, 1998; Hincapie et al; 2010).


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The major stratigraphic units and sequence boundaries were dated based on paleontological and palinological information cited by Orrego et al. (1980), Perez (1980b), Moreno et al. (1993), Pardo et al. (1993) and Blau et al. (1995), Zegarra, 1993; Geoestudios 2008; Sierra et al. (2011). Some unconformities observed in the field are also traced on seismic profiles carried out in the Cauca and Pata sub basins. There are no seismic lines available in the Amag sub basin. The Cenozoic basin fill was divided into five stratigraphic sequences that cover the time-span from early Eocene to the present. A chart for the ACP basin is presented in Figure 7 and explained below.

2.2.1 PRE CENOZOIC BASEMENT

Resting on the Amaime complex is a sequence of upper Campanian-lower Paleocene age composed of the Marilopito Formation and the lower segment of the Rio Guabas succession in the Pata sub-basin, and the Nogales Formation in the Cauca sub-basin. In the Amag sub basin there is no record of this time (Figure 7).

The Nogales formation consists of three different segments (Pardo et al., 1993; Moreno et al., 1993 and Blau et al., 1995). The lower segment is composed of matrix-supported conglomerates, calcareous sandstones, mudstone and claystone. The petrofacies of this segment indicates a source of sediment from the Central Cordillera. Said deposits were laid down from debris flow, most probably in the proximal part of a fan delta (fan delta-front facies). The middle segment consists of sandstones, siliceous claystone and chert beds. Sedimentary structures indicate deposition from turbidity currents during a time of limited sediment supply. The upper segment is dominated on its lower part by claystones and cross-bedded sandstones. Conglomerates and claystones of red and green color suggesting transition to continental deposits dominate the upper part of this segment. This segment is interpreted to be deposited in the fan delta transition zone front to alluvial fan facies (e.g. Moreno and Pardo 2003).

2.2.2 CENOZOIC

The transition from an oceanic remnant to a collisional basin setting began as the intra- oceanic island arc terrain collided with the Ecuadorian and southern Colombia margin. The collisional basin is represented by five depositional sequences (Figure 7).

2.2.3 LOWER EOCENE

The lower Eocene deposition is recorded in the Pata sub-basin by the 200m thick clast supported polymictic conglomerates of the Pea Morada Formation (Figure 8). In the Cauca sub-basin the occurrence of more than 400 m of similar lithofacies alternating with sedimentary breccias, siltstones and carbonaceous shale is referred to as the Chimborazo Formation (Figure 9). In the southern Pata sub-basin, Leon et al. (1973) identified a sedimentary succession 650 m thick that is composed of sedimentary breccias, conglomerates, sandstones and mudstones, named Upper Rio Guabas sequence.

Figure 8. Pea Morada Formation and Mosquera Formation, Syntetic stratigraphic column (Geoestudios 2008).


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Figure 9. Chimborazo Formation and Guachinte Forma-tion, Syntetic stratigraphic column. (Geoestudios 2008).

The ruditic petrofacies of these units consist of pebbles and boulders of diabase, basalt, chert, dacite and granitoids. This assemblage strongly suggests provenance of sediments from the Western Cordillera Island Arc with a minor contribution from the Central Cordillera. These three units are herein interpreted as time equivalent facies deposited as alluvial fans, fan-deltas and sub-marine fans during a period of high tectonic activity and sediment supply.


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2.2.4 EocEnE oligocEnE SEquEncES

The upper Eocene-lower Oligocene Mosquera and Guachinte Formations in the Pata sub - basin (250 m and 700 m thick) consist of fining upward units of quartz rich conglomeratic sandstones, quartz arenites, fossiliferous mudstones, coal seams and shales (Figure 10 and 11). The basal part of the Mosquera Formation is made up of massive quartzose conglomerates alternating with thin polymictic conglomerates.

Equivalent lithofacies were recognized in the basal part of the Lower Cinta de Piedra Formation (at least 300 m thick, Figure 12) of the Cauca sub-basin (Ecopetrol-ESRI, 1988). In this region, the fining upward trend is also present, but with an additional mudstone dominated segment (500 m thick) at the top of the unit. A shallow marine fossiliferous limestone (Vijes Formation 40-50m thick) grading upwards into fine-grained siliciclastics, locally crops out in the Cauca sub-basin. Despite the fossil content (Heterostegina, Miogypsina, Lepidocyclina, and Porites sp.), the age of this limestone is still a matter of controversy.

The equivalent lithofacies were recognized in the lower member (300 m thick) of the Amag Formation in the Amag Sub basin (Sierra et al; 2005; Silva et al, 2008; Figure 13). It is characterized by poorly selected and quartz-rich conglomerates, well sorted sub lithoarenites with high content of quartz, massive grey siltstones and layers of coal.

The siliciclastic lithofacies of this sequence seems to have been deposited in a delta plain environment. The high content of quartz clearly indicates a provenance of sediments from the Central Cordillera.

Figure 10. Mosquera Formation and Esmita Formation, Syntetic stratigraphic column (Geoestudios 2008).


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Figure 11. Guachinte For-mation Syntetic stratigraphic column (Geoestudios 2008).

Figure 12. Lower Cinta de Piedra Formation Syn-tetic stratigraphic column (Geoestudios 2008).


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Figure 13. Lower member of the Amag Formation (Unit 1 and 2).


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2.2.5 OLIGOCENE MIOCENE SEQUENCES

The upper Oligocene-Miocene sequence is composed of three major lithostratigraphic units: Esmita in the Pata sub-basin (Figure 14), the Ferreira and upper Cinta de Piedra Formations in the Cauca sub-basin and the upper member of Amag formation in the Amag sub-basin (Figure 15). The South, Central and Northern sequences were intruded by numerous porphyritic stocks (Figura 16).

The Ferreira Formation consists of quartz-rich conglomerates and sandstones, siltstones and carbonaceous shales. The main clasts constituents of the conglomerates are of quartz, chert and quartzite (Figure 17).

The Esmita Formation consists of a lower part made of siltstones, mudstones, thin layers of limestone and local coal beds. The upper part of the Esmita Formation shows different petrofacies dominated by graywackes with few layers of quartz arenites.

The upper Cinta de Piedra consists of quartz-rich conglomerates and sandstone followed by a succession of claystones.

The upper member of the Amag Formation consists of lithic wackes, feldspathic lithoarenites and siltstone of reddish and greenish colors (Figure 15).

The quartz-rich composition of the four lithofacies described above, together with the metamorphic origin for some of the components, strongly suggests a source of sediments from the Central Cordillera and a drastic change of Oligocene weathering conditions. The sediment dispersal system for this sequence was probably longitudinal and transversal as well.

Figure 14. Esmita Formation Syntetic stratigraphic column (Geoestudios 2008).


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Figure 15a and b. Upper member of the Amag Formation. b)a)


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Figure 16. Cenozoic magmatism in the ACP basin.


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Figure 17. Ferreira Formation, Syntetic stratigraphic column (Geoestudios 2008).


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2.2.6 UPPER MIOCENE

The upper Miocene deposition is recorded in the Pata sub-basin by the Pata Formation, in the Cauca sub-basin by the conglomeratic member of the Upper Esmita Formation and La Paila Formation, and by the lower part of the Combia Formation in the Amag sub-basin. These four units exhibit similar petrofacies consisting of thick successions of polymictic conglomerates, massive cross-bedded sandstones, minor shales, tuffaceous deposits, and woody fragments in its upper part. The conglomerates are made of clasts of granitoids, diabase, basalt, chert, quartzite, schist and pyroclastic rocks. These mixed petrofacies indicate multiple sources of sediments in the Central and Western Cordillera.

The shape of these deposits in cross-section is that of a wedge with the thickest part close to the Romeral suture zone, as a result of a tilting of the basin toward the east due to tectonic loading and thermal subsidence of the oceanic crust.

The upper Miocene deposits are considered the tectonic signature produced by the collision of the Panama Arc against the northwestern corner of South America. The presence of abundant volcanic material in the lower part of the sequence is the record of the intense plutonic/volcanic activity that began at 19 Ma until 6 Ma (Figure 16).

2.2.7 PLIOCENE - RECENT

The Galen and Popayn Formations in the Pata sub-basin, the Zarzal, Jamundi, Armenia Formations in the Cauca sub-basin and the upper part of the Combia Formation in the Amag sub-basin represent the upper Pliocene to Holocene sedimentary successions of the basin. These sedimentary units form the youngest sequence in the basin and overlie and unconformably coalesce with older sequences (Alfonso et al., 1994, Sierra et al., 1995, Sierra et al, 2011).

Seismic reflection data indicates a post- kinematic character for this sequence. The sequence was deposited after final collision of the island arc took place, ca. 3.6-3.1Ma (Kroonenberg et al., 1990). The main lithofacies are composed of polymictic conglomerates, volcanoclastic sandstones and diatomaceous deposits of the Zarzal Formation; tuffaceous deposits of the Popayn Formations and alluvial fan and glacio-fluvial deposits of the Jamundi- Armenia Formations, and tuffaceous deposits and alluvial fluvial deposits of the Upper part of the Combia Formation.

2.3 STRATIGRAPHIC SUMMARY

2.3.1 ENVIRONMENT

Paleoenvironmental reconstructions of the analyzed units (Figures 18), and their potential source areas are outlined below in a schematic way and without scale. The absence of paleocurrents and areas of provenance, the register of high dip directions, the lack of detailed maps and in consequence, the impossibility of having an acceptable structural model, among other factors, limits the paleo-environment interpretation. The interpretations are based on lithofacies arranged in the studied stratigraphic columns from the different authors, combined with age-dating from palynomorphs and geochemical, petrophysical and petrographical information from secondary information.

The sediments of the Pea Morada Formation of Paleogene age in the Pata area are interpreted as deposited in two different environments: the calcareous member was deposited in a shallow platform dominated by carbonates; and the conglomeratic member deposited in deltaic fans dissecting the shelf area (Figure 18a). Concentrations of clasts and calcareous sandstones that demonstrate the processes of erosion to the base of the sequence of conglomeratic member can be seen in the registry (Geoestudios 2008).

The oldest sediments in the southern sector of the Cauca basin correspond to the upper part of the Chimborazo Formation, Loma Larga Member and in a northern sector of the basin (Antioquia), the lower member of the Amag Formation, which accumulated during the Middle Eocene in areas with an alluvial system of fans, braided rivers, flood plains and meandering system rivers, which were transient on a delta plain associated with tectonic pulses (Figure 18b). Samples of fine sediments with gastropods and bivalves, indicating proximity to marine or transitional areas, have been collected toward the base of the members.

La Cima Member accumulated in fields of braided rivers and towards the top, meandering systems with poor preservation of fine facies associated with flood plains, possibly due to high migration of channels producing a stacking by reworked sediments where only the coarse fraction is preserved (Figure 18c).

In the northern Cauca and Antioquia area during the Oligocene the sediments of Cinta de Piedra Formation and the upper member of the Amag Formation were accumulated mainly in continental areas of meandering systems and, with less development, distal braided rivers and flood plains. Marginally, the sediments present toward the top of the column accumulated during the Lower Miocene were deposited in areas of swamps and marshes(Figure 18d). Marginally, the sediments presented


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in the superior part of the column were deposited in areas of swamps and marshes during the lower miocene. Is an approximate distribution of the different environments, which accumulated in the Cinta de Piedra Formation and upper member of Amag Formation.

Of the Guachinte Formation were clearly deposited in marginal marine environments in areas of marshes, swamps, and shallow ponds, while La Leona Member represents shore face environments, the presence of glauconite in the sediments corroborating the marine conditions (Figure 18e). This may indicate a transgressive event, represented by the increase in the level of the sea or a larger rate of basin subsidence, which allowed the migration of the coastline to the East and as a result, the migration of the environments. La Rampla Member accumulated in continental flood plains and marshes with some developments of meanderformes and braided rivers deposits (Figure 18f). Registers the paleoenvironments in transition zones for the accumulation of Los Chorros and La Leone members, close to the continental areas where sediments of La Rampla Member were deposited, indicating a regressive event as a result, of westward migration of the shoreline.

Acording to Geoestudios (2008), the Surez member and the lower part of Ferreira Formation demonstrate the continuity of the regressive process with a clearly continental domain at the base and braided rivers in the middle and upper intervals. Among the thick conglomerates and sandstones deposits are decametric beds with carbonaceous mudstones and coal, which were accumulated in fields of marshes and swamps. Such alternation can mean that while there is an overall regressive process, intermittent marine incursions occurred. Figure 18c represents the geographical distribution of environments of braided rivers, meanderforms, swamps and marshes to this unit.

The sediments of the Pea Morada Formation of Paleogene (?) age in the Pata area are interpreted as accumulated in two different environments: the calcareous member in a shallow platform dominated by carbonates and a conglomeratic member in deltaic fans. Concentrations of clasts and calcareous sandstones that demonstrate the processes of erosion to the base of the sequence of the conglomeratic member can be seen in the registry.

Figure 18g represents a possible distribution of environments, showing areas where fan deltas cut a shallow platform dominated by mud and carbonates (Orrego, 1975). The decametric conglomerates packages must be associated with faulting and tectonic pulses. The Mosquera sequences indicate that the unit accumulated in alluvial continental areas involving proximal and distal fans mainly in the section El Boquern; braided rivers and meandering river systems transient on flood plains, and swamps with marginal marshes are dominant environments in the Guanabanal and La Despensa stream sections.

The presence of the thickest deposits to the south and a gradation northward suggest a possible subsidence proceding northward. In addition, the Boquern section presents a gradation in size and composition of the clasts, indicating a change in the type of source rock. The absence of lithological bodies of enriched quartz close to the area of the uprising may indicate that there was exhumation and erosion of the whole body that originated the conglomerates. Figure 18g shows that the paleo-reconstruction of Mosquera Formation and of the upper member of Amaga Formation are similar.

The basal interval of the Esmita Formation, called Limoltico Member, is characterized by the abundance of bivalves and gastropods. It was accumulated in an estuarine system where the facies of the Guanabanal section displays greater marine influence. It shows marshes, intertidal plains, tidal channels and beach deposits of shallow platform environments (Figure 18h). In El Boquern and La Despensa stream sections, the Limoltico Fosilfero Member developed in marshes, locally reaching intertidal plain environments. Such a relation could be established by comparing the sets of ichnofacies found in the three sections, in which there is a wide variety of ichonofacies that correspond to the Skolithos and Cruziana ichnofacies in the Guanabanal section. The other two sections are associated with mudstones and carbonaceous shales, indicating ichonofacies Skoyenia - associated environments with continental influence (Geoestudios, 2008).

The Arenceo and Limoltico Members were accumulated in purely continental areas, associated with meandering currents that were cutting in extensive flood plains. These deposits are the final stages of the processes of the sedimentary basin accumulation. Figure 18f presents a paloenvironmental reconstruction that shows the absence of marine influence and indicates a westward migration.

2.3.2 DRILLED WELLS IN THE CAUCA PATA AREA

In the Cauca Pata area there are five exploratory wells; the first one was the Candelaria-1 well located by gravimetric interpretation and drilled in 1965 by the International Petroleum Company; the other wells, Juga-1, Patacore-1, Salsa-1 and Bereju-1, were drilled in 1997 and 1998 by Trinity Gas Colombia Inc., and were located by gravimetric and seismic interpretation acquired between 1979 and 1990. In the Amag area, there are six drilled wells with exploration of CBM OBJETIVED. A brief description of each well in the Cauca Pata area is presented below.

There is some information about Candelaria-1, Juga-1 and Patacore-1 wells, as shown in the following paragraphs. Less informationis available for Salsa-1 and Berej-1 wells.


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Figure 18c. Schematic paleo reconstruction sedimentary enviroments of the La Cima Member and lower member of the Amaga Formation.

Figure 18b. Schematic paleo reconstruction sedimentary enviroments of the Chimborazo Formation.

Figure 18a. Schematic paleo reconstruction sedimentary enviroments of the Pea Morada Formation.

Figure 18d. Schematic paleo reconstruction sedimentary enviroments of the Cinta de Piedra Formation.


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Figure 18e. Schematic paleo reconstruction sedimentary enviroments of the Guachinte Formation.

Figure 18f. Schematic paleo reconstruction sedimentary enviroments of the La Rampla member.

Figure 18g. Schematic paleo reconstruction sedimentary enviroments of the Mosquera Formation.

Figure 18h. Schematic paleo reconstruction sedimentary enviroments of the Esmita Formation.


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Candelaria-1 well

The Candelaria-1 well started in alluvial Quaternary deposits, and ended at 5.028 feet, in sediments of Cretaceous age corresponding to the Diabasic Group. A summary of the formation tops and ages in this well are listed in Table 1 where several gas manifestations were observed (weak and strong).

The interval 3.762-4.576 (Guachinte / Formation) has high content of organic matter, appropriate for the generation of gas. On the other hand, the thermal maturity tests show a type of organic matter between immature and mature, which can be observed under the geometric gradient: 1.33 oF/100 ft. The well was not tested, since the manifestations found indicated the presence of gas (methane).

Juga-1 well

Quaternary deposits were drilled in the Juga-1 well; these are mainly made up of sand, clay and gravel intercalations (from the surface up to 2.030). On the other hand, the Amaime complex is made up of volcanic rocks (basaltic lavas, andesites towards the top and basalts and ultramafic diabases (from 2.030 to T.D. and 3.761).

Patacore-1 well

Quaternary deposits were drilled in the Patacore-1 well; these are mainly made up of sand, clay and gravel intercalations (from the surface up

to 2.090). La Paila Formation is made up of intercalations of conglomerate sandstones, conglomerates, claystones and locally of shales (from 2.090 to 5.156); the Cinta de Piedra formation is made up of intercalations of sandstones, mudstones and conglomerates (from 5.156 to 7.210); and the Guachinte formation, fining succession, mainly consists of mudstones with two quartz sand-conglomerate levels, in the lower part (La Cima Member) and towards the middle; between these two levels the biggest number of coal layers are found (from 7.210).

2.3.3 DRILLED WELLS IN THE AMAG AREA

Recent projects done by EAFIT Unviersity in the Amag area have been focused in the CBM exploration (ANH, 2011). Up to now, seven wells have been drilled as shown in Table 2, the analyzed samples related to the gas content range from 10 to 90 Tcf.

Well Depth (m) East NorthVenecia-1 467.5 811067 1153153El Cinco-1A 278 820029 1150821El Cinco-1B 340 819902 1150923Damasco-1 85.4 832309 1133795Rincn Santo -1 247.50 809915 1153645Torreblanca-1 513,13 813691 1153752La Loma-1 313,92 830762 1135694

Table 2. CBM exploration wells in the Amag sub-basin. (ANH, 2011).


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2.4 STRUCTURAL GEOLOGY

The ACP basin seems to have behaved like a tectonic unit from the Middle Eocene. The fact that the Amag and the Cauca Pata sub-basins developed in similar environments but in different morphological conditions suggests a tectonic control for both sedimentation and the morphology of the basins .

Andean folding and uplift in the middle Miocene characterizes the western Colombian region. This tectonic process gave individual development to the Amag, Cauca and Pata sub-basins. The main differences between these sub-basins result from pure and simple shear that can be demonstrated by the paleomagnetic date.

Structurally, the ACP basin is characterized by a dominant NE structural trend, which is offset by ENE trending right - lateral and NW trending left lateral structures. NE - trending faults are either dip slip or oblique thrusts, generated as a result of transpressive regime active since at least Paleogene (?) times. NW- trending faults are considered to be reactive pre Cretaceous extensional structures. Right lateral shear on ENE trending faults has resulted from oblique convergence between the Nazca Plate and the northern Andes. Major changes in the geometry of the oblique plate convergence between the Nazca and South American plate generated the stress strain partition within the mountain belt. These strike slip structures have exerted important control on the sedimentation, source rock distribution, fluid flow and ore mineralization during the Cenozoic. The interpretation of the ACP basin affected by strike slip deformation provides a structural context in which to reassess resource exploration.

The Amag and Cauca sub-basins are separated by Pliocene volcanic -clastic sediments: The Cauca and Pata sub-basins are separated by the Popayn high, which is a poorly known structural feature that may represent either a basement-cored uplift, like those described by Alfonso et al. (1994), or a paleo-topographic high of the old accreted oceanic crust (Barrero and Laverde 1998).

The three sub-basins have changed in orientation, structural style and thickness of the sedimentary infill. Shortening in the Amag and Pata sub basin is greater than in the Cauca sub-basin, and this is probably related to a thicker sedimentary infill and to differences in style of deformation in the sub-basins.

The seismic records are restricted to the Cauca-Pata area and were used to describe the structural style. Table 1 summarizes the main seismic programs; the Candelaria-1 well and 600km of 2D seismic data were interpreted by Barrero and Laverde (1998), following stratigraphic sequence concepts from Van Wangoner et al. (1990). Five regional

unconformities are recognized throughout much of the Cauca-Pata basin. These unconformities were calibrated with surface geology in the Pata sub-basin and the Candelaria-1 well in the Cauca sub-basin. Due to the non-existence of seismic data in the Amag sub-basin, paleomagnetism, boreholes and surface data were used.

2.4.1 SOUTHERN AREA: PATA SUB-BASIN

The Pata sub-basin is bounded to the east by the over-thrust Amaime complex and to the west by the Cauca fault system, a major east-vergent suture, composed of several footwall imbricates that uplifted rocks of the Western Cordillera island arc over Neogene deposits of the basin. The breaking forward imbricates suggest that they developed at depth, conclusion supported by seismic data (Figures 19, 20, 21). The Cauca Pata thrust faults or Bellavista fault named by other authors (e.g. Barrero and Laverde, 1998.) is interpreted to be a branch from a west-vergent basal detachment within oceanic crust, marking a possible suture zone (Figures 20 and 21). Surface geology mapping shows that the Pata area is characterized by thrust and related folds showing a clear west vergence. The fold and thrust belt is ca. 150 km long and 40 km wide and is composed of four major thrust sheets separated by the Chorea, Guayabillas, El Bordo and Miraflores faults. The main outcropping units in the thrust sheets are the Paleogene Mosquera Formation and the Neogene Esmita Formation. Cenozoic intrusive bodies crop out mostly toward the east, in the hanging wall of the Guayabillas fault (Figures 20, 21). Four major west-vergent thrust sheets associated with local back-thrust are imaged on seismic records. The thrust faults, folded Cretaceous basement and a thick Paleogene and Neogene sedimentary sequence, have a ramp-flat geometry and follow a staircase trajectory. They are steep to the east and gentle to the west.

Shortening is greater to the east as evidenced by the geological map and the seismic lines (Figures 19, 20, 21). This suggests that the deformation developed in a forward breaking sequence towards the west. Minor east-directed back thrusts are also present and in some cases it looks as if they were decapitated by some of the west vergent-thrusts (Figures 20, 21). However, the most frontal zone of deformation to the west forms a triangular zone, which suggests that east- and west-directed thrusts share a common detachment at depth, with probably a simultaneous development of both vergences (Barrero and Laverde 1998).

The structural map at the level of the sub-lower Eocene unconformity indicates that the major thrust faults that trend NE-SW are at least 50 km long and form closures in anticline structures (Figure 21). Four seismic sequences were identified in this sub-basin base on seismic character and unconformities of regional extent. Because of the absence of well penetrations in the Pata sub-basin, the unconformities that define the


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sequence boundaries were correlated with the stratigraphic record described from outcrops (Barrero and Laverde 1998).

The seismic sequence 1 below the sub- Lower Eocene unconformity is characterized by strong discontinuous reflectors that are truncated by the overlying unconformity (Figures 19, 20, 21). The uppermost reflectors are interpreted to represent the upper Campanian-Maastrichtian Aguaclara and Marilopito Formations overlying the basaltic (non-stratified) rocks of the Amaime complex.

Seismic sequence 2 is composed of two stratigraphic sequences separated by the Middle Eocene unconformity (Figures 19, 20, 21). The basal part of the seismic sequence corresponds to the Paleogene molasse and shows a reflection proper of mounded seismic facies. The upper

part of the sequence has parallel continuous reflectors, some of them of high amplitude probably representing shales and coals of the Mosquera Formation (Figures 19, 20, 21).

Seismic sequence 3 is limited at the top by the Sub-Middle Miocene unconformity, and is ca. 700 ms two-way-time thick. It has a lower part of high amplitude, parallel, continuous reflectors and an upper part of chaotic seismic configuration. These seismic facies correspond to the silty and sandy members of the Lower Esmita Formation (Barrero and Laverde 1998).

Seismic sequence 4 is the youngest outcropping seismic unit in the Pata sub-basin, the reflection patter is chaotic and in some places mounded, and presents the conglomeratic member of the Esmita Formation (Figures 19, 20, 21).


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Figure 19. Interpreted Seismic Profiles CP-90-1450 showing style of deformation and regional unconformities in the Pata Sub-basin (Modi-fied from Barrero and Laverde, 1998).


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Figure 20. Interpreted Seismic Profile CP-90-1200, showing large displacement along thrust and regular relation of Upper Cretaceous strata with the Lower Eocene Pea Morada Fm., that documents the folding/thrusting deformationduring the Paleogene Collision in the Pata Sub-basin. (Modified from Barrero and Laverde, 1998).

Figure 21. Geoseismic Profile showing structural style in the Cauca sub-basin. (Modified from Barrero and Laverde, 1998).


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2.4.2 CENTRAL AREA: CAUCA BASIN

The Cauca sub-basin is limited to the east by an inner fold-and-thrust belt of basement core uplifts (Alfonso et al., 1994) and to the west by the Cauca fault system. There are only few outcrops of Tertiary units. Quaternary deposits cover most of the interior of the sub-basin. In the Cauca sub-basin, the thrust belt is oriented NNE-SSW and is ca. 235 km long and 45 km wide.

The first interpretation of this sub-basin as a fold-and-thrust belt was done by Alfonso et al. (1994). He described it as a west-vergent thick - skin thrust belt in a stacked imbricate fashion of basement highs transported over Miocene strata, formed during the Oligocene upper Miocene.

The seismic profiles in this region show a consistent structural style of west-vergent imbricates, in a similar way to the Pata sub-basin. Here, the deformation propagated to the west, from the Central Cordillera, which acted as a back-stop (Barrero and Laverde 1998). The structural map at the level of the sub-lower Eocene unconformity shows that thrust system trend is mainly N-S and that it is at least 70 km long. (Figure 22 and 23). There is less back thrusting in this sub-basin compared to the Pata sub-basin, the thrusts involve mainly Cretaceous sections and have passively deformed the Cenozoic section. Most of the thrusts stop at the sub-Upper Miocene unconformity, but the section below shows good examples of syn-kinematic deposition (growth strata). Since growth strata are present in the footwall of the thrusts, from uppermost Cretaceous to Middle Miocene, we argue that thrusting in this sub-basin was a continuous process and that this growth strata record the history of collision. The Cenozoic sequence has an overall wedge shape, thicker to the west suggesting tilting of the basin by tectonic loading (Figure 24a and 24b).

Five seismic sequences were identified in this sub-basin based on the character and interpretation of the Candelaria-1 well by Barrero et al.,(2007). (Figure 25).

Seismic sequence 1 is composed of strong discontinuous reflectors that are folded and truncated by the sub-Lower Eocene unconformity. The reflectors in the upper part of the sequence my represent the upper Campanian Paleocene Nogales Formation. The chaotic reflection character of the lower part corresponds to volcanic basement.

Seismic sequence 2 is composed of two stratigraphic sequences separated by the middle Eocene unconformity. The basal part of the sequence shows mounded reflections onlapping the underlying sequence, and represents the Paleogene molasse deposition of the Chimborazo Formation. The upper reflectors are parallel and discontinuous and represent the prospective Guachinte Formation. The entire sequence is

Figure 22. TWT structural map of the Lower Eocene unconformity Pata sub-basin (Modified from Barrero and Laverde, 1998).

200 to 400 ms two-way-time, considerably thinner than its coeval section in the Pata sub basin.

Seismic sequence 3 is composed of continuous, parallel, high amplitude reflectors. The basal part of the sequence shows reflectors onlapping the underlying sequence. The upper reflectors are more continuous and in general are tilted to the east. The sequence is wedging within each thrust sheet, becoming thicker to the east. It records progressive growth of the structures, during time of deposition of the Ferreira and upper Cinta de Piedra Formations.


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Figure 23. TWT Structural map of the Lower Eocene unconformity Cauca sub-basin. From Barrero. D, and Laverde, F., 1998.


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Figure 24b. South stratigraphical correlation Pata sub-basin.

Figure 24a. North stratigraphical correlation Cauca sub-basin.


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Seismic sequence 4 is composed of parallel discontinuous reflectors and is 200 ms two-way-time in average shows little deformation and is interpreted to represent the Neogene molasse, a result from the final collision. Deformation of this sequence has been documented close to the Central Cordillera.

Seismic sequence 5 is composed of parallel, sub-horizontal continuous reflectors wave-shaped at the base of the sequence, and chaotic pattern to the east (Figure 25). The overall geometry of this sequence is a wedge shape that thickens to the east from 100ms to 600ms two-way-time. It shows no deformation on the seismic profile VC-79-10. However, the fieldwork observations indicate faulting is present in this sequence close to the Central Cordillera.

2.4.3 NORTHERN AREA: AMAG BASIN

The Amag sub-basin is limited to the east by an inner fold-and-thrust belt of basement core uplifts and to the west by the Cauca fault system. There are only few outcrops of Tertiary units. Most of the interior of the sub-basin is covered by the Combia Formation deposits (Figure 26). In the Amag sub-basin the thrust belt is oriented N 34 E and is 230 km long and 6.6 km wide in the northern part, 40km wide in the middle part and 12 km in the southern part.

The first interpretation of this sub-basin as a fold-and-thrust belt was done by Grosse (1926). It was described as a thrust of basement highs transported over Miocene strata, formed during the Oligocene to upper Miocene (Figure 27a, b, c, d, e).

Figure 25. Seismic Profile VC-79-10 showing structural style, regional unconformities and seismic secuences in the Cauca sub-basin. (Modified from Barrero and Laverde, 1998).


Figure 26. Geological map of Amag sub-basin.


INSERTAR MAPA PLEGABLE

ARCHIVO ADJUNTO

(Amag Pg.49 plegable.pdf)


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Figure 27 a). Cross-sections of the Amaga sub-basin.


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b)


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c)


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d)


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2.5 MAJOR STRUCTURAL ELEMENTS

The Pata sub-basin is essentially a wide synclinorium developed in the Cenozoic sedimentary sequence. The Cretaceous basement complex is exposed on the flanks of this structure in the western foothills and East of the Cordillera Central and Western respectively. The structural regional trend of the Pata sub-basin is N - NE / S - SW. The most important structural elements are: Romeral Fault System, to the East, Cali - Pata Fault system to the west, a system of transverse faults with NE - SW direction and a set of folds with azimuth N - NE, developed between the systems of faults of Romeral and Cali - Pata (Figure 28). The regional structural features are summarized in the Figure 29 and described as follows:

2.5.1 ROMERAL FAULT SYSTEM

This fault system is generally accepted as the boundary between oceanic and continental crusts and was initially recognized by Grosse (1926) in the Antioquia region. It has been described in numerous works such as: (1) strike-slip system (Campbell, 1968; Case and others, 1971); (2) inverse system of high angle; (3) Western vergence (McCourt and Millward, 1984); (4) right-lateral strike-slip system (McCourt and Aspden, 1984, MacDonald et al., 1996, Sierra, G., 1994); (5) transtensional system with left lateral movement (Kellog et al., 1983) and (6) a system with transpressional compressive and direction components (Afonso et al., 1994).

On the other hand, ECOPETROL / ESRI (1988) studies indicate the presence of Paleozoic metamorphic rocks in the hanging wall and Cretaceous rocks in the footwall of the fault suggesting this structure was a thrust from its origin. To the north of the Basin, Alfonso (1993) recognizes a belt folded and faulted with azimuths N - NE, on the east flank of the Cauca sub-basin, consisting of a series of basement highs with en echelon geometry, and westward vergence, which constitute an embedded system associated with Romeral Fault System.

The Romeral fault system, which includes San Jernimo, Silvia - Pijao and Cauca Almaguer faults, is noted with an arched, concave line westward, consistent with a moderate inclination towards the East and a direction of tectonic transport to the west (see Geological maps Figures 26, 28).

2.5.2 CAUCA FAULT SYSTEM

This fault system is called Cali Pata in the Cauca-Pata sub-basins (Mosquera et al., 1998). There is no consensus on the definition of the fault system, which has been described interchangeably by various authors.

Murcia and others (1991) interpret these feactures as an extensional system, formed in the area of flexure of the oceanic crust adjacent to the old mid- Cretaceous subduction zone; Cline et al. (1981) argue that the system is part of the Dolores Megashear System, which extends from Ecuador as an anastomosing system of faults, which are vertical and that dip both east and west. ECOPETROL / ESRI (1988) suggests that Cauca and other associated faults that cut the Tertiary rocks along the eastern flank of the Cordillera Occidental deliver a thrust of dominantly western vergence. On the other hand, Orrego and Paris (1999) described the system as a group of reverse, high angle, NE-trending faults, dipping to the East, with important horizontal displacements.

2.5.3 PIEDECUESTA FAULT

The Piedecuesta Fault was mapped and named by Grosse (1926) in the Amag sub-basin. This Fault lies west of the principal trace of the Romeral Fault. The fault is a truly remarkable geological boundary, it separates blocks of very dissimilar geology and lithology. Estrada et al., (1998) shows that the trace of the fault is a reverse fault dipping to the east. The Piedecuesta fault trend is somewhat irregular (anastomosing pattern).

2.5.4 FAULTING WITH NE - SW DIRECTION

A third system of major faults is a series of transverse structures of NE - SW trend. The cartographic relations indicate that they are more recent structures related to N S direction movements.

2.5.5 REGIONAL FOLDING N NE DIRECTION

A series of anticlines and synclines with preferential direction N NE are developed, in Neogene rocks. The synclines dominate over anticlines and are the most prominent structures mapped.

The folds are parallel or sub parallel to the faults, and are tight, asymmetric, with westward vergence; the direction of thrust axes is not very continuous. The general trend of faulting for the Cauca-Pata watershed varies between 30-43 NE-SW. The axes of folding, anticlines and synclines, are parallel to that trend. Strikes of NS direction that extend to the northernmost part north of the Amag basin can be seen approximately at the latitude of Manizales. A third train of fault tend, evidenced in two basins, with trend N 30 W can be observed.


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Figure 28. Geological map of the Cauca-Pata sub-basins.


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Figure 29. Regional structural map in the ACP basin.


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2.6 GRAVIMETRY AND MAGNETOMETRY

A magnetic study was done at 4750m above sea level by Carson Helicopters (2006) and interpreted by Graterol. The magnetic and Bouguer gravity anomaly data are well correlated with the igneo-metamorphic Pre-Cretaceous basement. The Bouguer anomaly with a density of 2.30 Grs/cc Bouguer density, also shows a clear close relationship with the density contrasts between the Tertiary sequences and the Cretaceous basement.

Along the Cauca Valley river, there are negative Bouguer anomalies, indicating the great thickness of the Quaternary Tertiary sequence to the North. A positive anomaly in the middle of the Valley with a large extension to the west border correlates with the Cretaceous basement. The eastern border has negative values and correlates with the metamorphic nucleus of the Central Cordillera. Figure 30 shows the pole-reduced total magnetic intensity, which correlates well, with the gravity seismic depth map (Figure 31), and with positive Bouguer anomalies associated with the igneous-metamorphic Cretaceous basement rocks. The top of the Cretaceous basement is shown in Figure 32.

The geophysical information in the Amag sub-basin is shown in Figures 33 and 34. Both maps are well correlated with the main fault systems and with the surface lithology. A possible depocenter in the basin is interpreted south of the Arma fault where the overlying Combia Formation has its maximum thickness.

2.7 STRUCTURAL MAP

The structural contour analysis associated with the 3D gravimetric inversion with the geological control was the basis of the structural interpretation of the Cretaceous basement. This map clearly shows the Tertiary-Quaternary thickness and the main fault trends. There is a large structural complexity of the Cretaceous basement top that outcrops along the Eastern and Western border and the Cauca river Valley and close to the Juda-1, Patacore-1 and Bereju-1 wells. The greatest thicknesses of the Quaternary-Tertiary sequences is observed close to the Candelaria-1 (3000m) well and to the Southeast of Armenia city (1500m). These values indicate that there is not enough Tertiary sedimentary sequence for hydrocarbons generation. However, if migration from other sources occurs in the valley, the best possibilities for their retention will occur in the Cretaceous basement structural traps.

The gravimetric-magnetometric models, and the structural interpretation of the top of the Cretaceous basement, show that the dominant structural trend in North-Northeast direction in the Cauca River is related to the Central and Western Cordillera emplacement.

Figure 30. Pole reduced Total Magnetic Intensity (Modified from Carson Heli-copters, 2006).


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Figure 31. Gravity_Seismic Depth.


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Figure 32. Top of Cretacic Basement map.


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Figure 33. Gravimetry map Amag sub-basin.


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Figure 34. Magnetometric map Amag sub-basin.


3. TECTONIC EVOLUTION OF THEAMAG, CAUCA AND PATA BASINS


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CHAPTER 3 - TECTONIC EVOLUTION OF THE AMAG CAUCA PATA BASIN

The model presented here is intended to be a synthesis of all the available information of the evolution of the Western Colombia region. Nevertheless, the scarcity of radiometric, biostratigraphic and geochemistry data, the structural complexity, and the lithologic similarities of diachronous units, result in basin reconstructions of variable detail for particular periods of time.

The ACP basin developed during the Paleogene and Neogene time, adjacent to the Romeral suture zone, as result of diachronous oblique collision of an intra oceanic island arc with the irregular margin of north western South America. The basin is located between the Cayo Arc Continental Ecuador collision zone to the South, and the Panama Arc Antioquia collision zone to the North (Barrero and Laverde 1998; Cediel et al., 2003; Moreno and Pardo, 2008).

The plate tectonic events that play an important role in the evolution of the Western Colombia region and in the origin of the ACP are: (1) Late Triassic event, related to Pangea breakup; (2) a Jurassic-Early Cretaceous event: western Colombia underwent oblique subduction by the Farallones plate; (3) a Late Paleocene- early Eocene event: major tectonism in Ecuador could be caused by collision of the Cayo remnant arc with the continental margin; (4) an Eocene- early Miocene event: the island arc migrated and rotated about 130 degrees from its original position to finally collide with the Antioquia promontory in western Colombia,

Discontinuous uplift and erosion of the ancestral Central and Western Cordilleras and the closure of the basin to the marine influence during the Cenozoic allow us to propose that the ACP basin could be better classified as a collision related basin.

3.1 LATE TRIASSIC

Bacause of the break up of Pangea, the continental margin of northwest South America was very irregular, due to the alternation of coastal promontories and re-entrants. The geometry is now expressed by two promontories separated by a pronounced re-entrant that probably existed since Triassic time: The Ecuadorian promontory, extending from Gulf of Guayaquil to southern Colombia; the Manizales re-entrant and the Antioquia promontory extending from the north of Manizalez as far as the northern part of Cerro Matoso. This configuration of the Triassic continental margin has big implications in the kinematics and geometry of the different events. (Storey, et al., 1991; Nivia, A., 1989; Kerr, A. C., at al., 1997, 1998; Moreno, and Pardo, 2003; Cediel et al., 2003; Barrero et al, 2003, Kerr, and Tarney, 2005.)

3.2 JuraSSic Early crEtacEouS

East-dipping subduction was the dominant process during evolution of the northwest continental margin of South America for this time. During this period, the continental margin of western Colombia underwent oblique subduction by the Farallones plate. The evidence of these events is now mapped as a highly deformed accretionary prism that extends along the Romeral suture. This accretionary prism is well exposed in the Manizales reentrant and the evidence includes: slivers of oceanic crust (Figure 35), dismembered ophiolite suites, glaucophane schists, retrograde eclogites and calcareous unit. The above mentioned suture is well explained by the so-called Romeral Blueschist Belt (Figure 36). Surface geology and seismic data indicate a west-vergent fold-and thrust structural style of deformation

Figure 35. Cross section geological profile close to Armenia city. (Mod-ified from Suter 2008).


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Figure 36. Romeral Blue Schist Belt (Compiled by Cediel, 2011).


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CHAPTER 3 - TECTONIC EVOLUTION OF THE AMAG CAUCA PATA BASIN

(Figure 37). This accretionary prism that crops out east of the Cauca-Pata basin and, most-likely form the basement of its Paleogene- Neogene fill, has been named Amaime terrain (McCourt and Aspden 1985).

3.3 latE PalEocEnE- Early EocEnE

The late Paleocene- early Eocene major tectonism in Ecuador could be caused by collision of the Cayo remnant arc with the continental margin. The collision zone extends from southern Ecuador to the south of Colombia. This situation created a remnant ocean basin between the arc and the continental margin of Colombia at that time. The continued migration of the arc in a north-east direction results in a clockwise rotation of about 55 degrees in the Ecuadorian portion of the arc (Roperch et al., 1987). The upper Paleocene middle Eocene is marked by a regional hiatus in the ACP, and by the development of silici-clastic deposits (Figure 38).

3.4 EOCENE TO EARLY MIOCENE

From Eocene to early Miocene times, the island arc migrated and rotated about 130 degrees from its original position to finally collide with the Antioquia promontory in western Colombia. Evidence for rotation of the Colombia portion of the Costa Rica-Ecuador island arc is given by the paleomagnetic studies done in the El Horno pillow basalt (86+/- 3 Ma) of the Gorgona terraine (Estrada, 1995). The collision zone with the Antioquia promontory extends from the south of Antioquia as far north to Cerro Matoso. This zone is geologically very complex and thrusting of the arc over the Central Cordillera was probably the result of this Miocene collision, and more importantly, this event closed the remnant ocean and determined the final geometry of the ACP basin. The above description of the Cenozoic evolution of the western continental margin of Colombia allows us to propose that the ACP basin is better classified as a collision related basin (Figure 39).

Figure 37. Paleomagnetic site mean declination (black wedges previous study and red wedges these study) for the late tertiary intrusions form two distintct

groups (northern and souther of the Amaga Sub basin) of different treands but approximately parallel to trend of adjacent Romeral suture zone. Late Tertiary

intrusions are stippled.


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Volumen 2 Amaga-cauca-patia Basins