Copyright by Nysha Chaderton 2009 - The University of Texas at ...

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Chapter 5: Conclusions SEDIMENTATION AND HYDROCARBON EXPLORATION WITHIN FOREARC BASINS The study area is a classic forearc basin depositional setting. Hydrocarbons have been produced economically from some forearc basins such as Cook Inlet, Alaska (Bruhn et al., 2000; Clough et al., 2001), and the ancient Great Valley forearc basin in California (Rentschler, 1985; Vermeesch et al., 2006). In addition to conventional hydrocarbon production, there is thought to be up to 245 tcf of gas available in the unconventional resource of coal bed methane in Cook Inlet, Alaska (Clough et al., 2001; Montgomery and Barker, 2003). The re-interpretation of the Scotland Formation as a forearc basin deposit has implications for hydrocarbon exploration onshore and offshore Barbados. It has been accepted for several years that the oil and gas production onshore Barbados is the only example of successful hydrocarbon production from true accretionary prism sediments. The new model presented in this research re-defines the depositional setting of the reservoirs and classifies them as forearc basin plays similar to Alaska or California. Sedimentation within forearc basins is a combination of deposition by turbidity currents travelling parallel to the volcanic arc along the basin axis or travelling perpendicular to the volcanic arc. In the case of island arcs, the sediment sources are usually localized to the volcanic islands (Moore et al., 1980). In the case of the Lesser Antilles volcaniclastic sediments are interbedded with the longitudinal input from the South American continent. Clastic sediments within the Tobago Forearc Basin (TFB) were transported parallel to the Lesser Antilles Island Arc as evidenced from seismic reflectors prograding from south to north and channels that are visible in the strike (east to west) direction across the basin. Sediment input from the volcanic arc was minor, as evident from the small amounts of volcanic rock fragments that have been identified in thin section. 61
Pudsey, (1982) interpreted smectite and kaolinite rich clays within the Scotland Formation as ash fall deposits from the volcanic island arc. Punch, (2004) and Kasper and Larue, (1986) also found a minor volcanic input to the Scotland Formation sediments. The source of the clastic Scotland Formation sediments was the proto-Orinoco which drained from northern South America during Eocene to Oligocene times and deposited sediment into d the proto-TFB. As the Orinoco River shifted eastward, the main source of clastic sedimentation to the TFB ceased and pelagic accumulation became dominant as clastic sedimentation lessened. In the TFB-BAP region, the Oceanic Formation is the unit that is comprised of pelagic muds and marls, with interbedded volcanic ash layers. The reinterpretation of the Scotland Formation means that both the Oceanic Formation and the Scotland Formation are now both interpreted to be forearc basin sediments. Following deposition in the basin of clastic turbidites of the Scotland Formation, the post-Oligocene Oceanic Formation blanketed the basin. Several researchers have noted some confusion regarding the age of the Oceanic Formation (Speed, 1982; Pudsey, 1982; Poole and Barker, 1982). It is probable that the Scotland and the Oceanic formations have an inter-fingering relationship and thus the reason for the age discrepancies that have puzzled researchers in the region for decades. The Cook Inlet, a structurally complex forearc basin, is located between the Alaska Range-Aleutian Volcanic Arc to the northwest and the Chugach-Kenai accretionary prism to the south. The basin is bounded by active faults and has a number of tight asymmetrical folds that form hydrocarbon traps. These folds are associated with reverse faults (Montgomery and Barker, 2003). Although the distant sedimentary source of the reservoir rocks in the Barbados study area differentiates the TFB fill from most forearc basins, the active faults in the area may form traps similar to those in the Cook Inlet. In Barbados, similar traps may exist within the BAP region along the Barbados 62
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Copyright by Nysha Chaderton 2009
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Sedimentation within the Tobago For
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Acknowledgements I would like to th
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Table of Contents List of Tables ..
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List of Tables Table 2.1: Latitudes
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Figure 2.14: Planar parallel lamina
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Figure 2.42: Coarse, cobble and peb
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Figure A.3a: Chalky Mount Ridge mea
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1. Development history of the south
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Formation. This interpretation requ
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DATA AND METHODOLOGY Extensive work
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DESCRIPTIVE METHODOLOGY Each sectio
Page 25 and 26: Two or more channel complexes stack
Page 27 and 28: These poorly sorted sands are later
Page 29 and 30: East Coast Road Although the East C
Page 31 and 32: succession of interlaminated siltst
Page 33 and 34: Mount All The beds of the Mount All
Page 35 and 36: Lobes are non-channelized bodies, 3
Page 37 and 38: Sandy units are the most resistant
Page 39 and 40: SUMMARY DEPOSITIONAL SETTING OF THE
Page 41 and 42: Chapter Three: Petrographic Analysi
Page 43 and 44: had not been buried deeply or long
Page 45 and 46: Feldspars Calcium Plagioclase Felds
Page 47 and 48: Authigenic Minerals Authigenic mine
Page 49 and 50: amounts of chlorite and kaolinite c
Page 51 and 52: Sample: WRA 16 This sample was take
Page 53 and 54: cementation is observed. A number o
Page 55 and 56: COMPARISON WITH PREVIOUS WORK Punch
Page 57 and 58: K feldspar preservation to slightly
Page 59 and 60: CONCLUSIONS 1. No quartz cementatio
Page 61 and 62: The highest point of the island, is
Page 63 and 64: STRATIGRAPHIC FRAMEWORK ONSHORE TO
Page 65 and 66: STRUCTURAL FRAMEWORK OF THE BARBADO
Page 67 and 68: Sandy material is primarily quartz
Page 69 and 70: esult of extension caused by flexur
Page 71 and 72: 1994). The origin of the Oceanic Fo
Page 73 and 74: Oligocene-age sediments are deposit
Page 75: The observation of channel geometri
Page 79 and 80: The interpretation of the Scotland
Page 81 and 82: Figure 1.2: Convergent margins arou
Page 83 and 84: NSF Study Lines Grenada St. Kitts S
Page 85 and 86: Figure 2.2: Generalized vertical se
Page 87 and 88: Figure 2.4: Detailed Geological map
Page 89 and 90: Figure 2.6: Photographs and illustr
Page 91 and 92: Figure 2.8: Bedsets on the channel
Page 93 and 94: S 50 m Figure 2.10: Photo-panorama
Page 95 and 96: Figure 2.13: Laminated silt and mud
Page 97 and 98: Figure 2.16a: Measured section at C
Page 99 and 100: Figure 2.16c: Measured section at C
Page 101 and 102: Figure 2.18: Correlation of section
Page 103 and 104: Figure 2.21: Parallel laminated sil
Page 105 and 106: Wach, Vincent and Chaderton March 2
Page 111 and 112: Figure 2.24: Channel element identi
Page 113 and 114: WRB S N Fresh rock face exposed by
Page 115 and 116: Figure 2.28: Photograph of Diplocra
Page 117 and 118: Figure 2.31: Conglomerate with eros
Page 119 and 120: Figure 2.33: Thalassinoides trace f
Page 121 and 122: Figure 2.35: Mount All measured str
Page 123 and 124: Figure 2.37: Medium grained sand be
Page 125 and 126: Figure 2.38b: Inner Turner’s Hall
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Figure 2.38d: Inner Turner’s Hall
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Figure 2.39: Spa Hill measured stra
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Juniper Ridge, California Scotland
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Figure 3.1: Fractured quartz grain
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SGRF 1C SGRF 9C Figure 3.5: Measure
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Figure 3.8: Photo of sample SGRF 11
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Figure 3.10: Photo of sample SGRF 1
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Figure 3.12: Photo of sample WRA 16
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Figure 3.14: Photo of sample WRB 8
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Figure 3.16: Photo of sample ITR 9
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Figure 3.19: Photo of sample CMRA s
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Figure 3. 23: Composition of Scotla
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Figure 4.1: Base map showing seismi
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Figure 4.3: Channels within Unit Fi
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Figure 4.5: Seismic reflection prof
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Figure 4.7 Isochron maps of the old
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Figure 4.9: Illustration of the Spe
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Figure 4.11: Illustration of Hypoth
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necessary to clear a path. Keep to
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2006 Figure A.2a: Lidar Ridge measu
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Figure A.3b: Chalky Mount Ridge mea
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2006 Figure A.4a: Chalky Mount Ridg
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2006 Figure A.4c: Chalky Mount Ridg
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2006 Figure A.6: Chalky Mount Ridge
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Figure A.7b: Measured Section of Ch
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2006 Figure A.8a: Sleeping Giant Ri
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2006 Figure A.9: Sleeping Giant Rid
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2006 Figure A.11: Sleeping Giant Ri
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Figure A.13a: Sleeping Giant Ridge
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2006 Figure A.14a: Coast Road Below
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2006 Figure A.14c: Coast Road Below
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2006 Figure A.14e: Coast Road Below
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2006 Figure A.14g: Coast Road Below
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2006 Figure A.15: Ermy Bourne Ridge
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2006 Figure A.17: Spa Hill Fold Mea
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2006 Figure A.19: Ermy Bourne Ridge
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Figure A.20b: Walkers Ridge Measure
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Figure A.21: Walkers Ridge Measured
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Figure A.22b: Walkers Ridge Measure
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2007 Figure A.23b: Inner Turner’s
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2007 Figure A.23d: Inner Turner’s
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Framework grains Quartz Feldspar Ro
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CRIMES, T.P., 1977, Trace fossils o
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MONTGOMERY, S.L., BARKER, C.E., SEA
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RICHARDS, M., BOWMAN, M., and READI
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WEBER, J.C., DIXON, T.H., DEMETS, C
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