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

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and Westbrook, 1987), are thought to be responsible for the 3,000 m of rise on the prism’s interior. Brown and Westbrook (1987) identified the presence of WNW- ESE Atlantic basement ridges beneath the prism using long-range side-scan sonar images and seabeam bathymetry. Their investigations show a correlation between the orientation of these basement ridges and the structural features of the prism. The west- and east-facing thrust faults and associated piggyback basins and sediment ridges are oriented roughly parallel to the deformation front. However, at oblique angles to these roughly north-south features are the NW-SE-trending extensional faults of the Barbados Ridge, which have a similar orientation to that of these basement ridges. Compression and thrust faulting occur on the west side of the Barbados Ridge, where basement ridges act as a buttress to westward movement, causing thrusting and uplift to occur. Inner Forearc Deformation Front The Inner Forearc Deformation Front (IFDF) delimits the east margin of the Tobago Forearc Basin and forms the boundary between the highly deformed sediments of the accretionary prism and the relatively undeformed sediments of the Tobago Forearc Basin (Figures 4.4 and 4.6). It is characterized by east dipping thrust faults that are the result of interaction between the downgoing Atlantic Plate and the strong crystalline basement. Tobago Forearc Basin The Tobago Forearc Basin, filled with as much as 12 km of sediment, shows little evidence of deformation at its center (Figure 4.6). Several small-scale normal faults along the west and north margins of the basin, confined to the youngest part of the section have very minor throw and appear to terminate at a common shallow horizon. It is not uncommon for normal faults to occur on the stable flanks of forearc basins, and it has been speculated that they form as a 53
esult of extension caused by flexural loading of the crust in response to encroaching fold belts (Harding and Lowell, 1979; Harding and Tuminas, 1989). Dickinson (1995) noted that these faults may act to step the basin downward from the elevated island arc high as localized extension occurs across the forearc belt. The large Barbados Fault (previously discussed) is an example of one of these faults. TIMING AND PROCESSES IN THE EVOLUTION OF THE TOBAGO BASIN Observations from Seismic Data The Tobago Basin is the largest sedimentary accumulation within the basins of Barbados Accretionary Prism system. Nine horizons were mapped across the basin, and six fill units were identified. Isochron maps created on these units show that the basin has evolved from a proto-Tobago Basin that was quite broad, into segments that are the present-day Tobago Forearc Basin (TFB) and more eastward piggyback basins of the Barbados Ridge. Pre-Eocene-age TFB sediments (Unit One of Figure 4.6 and Figure 4.7a) are thickest in the northeast parts of the present-day basin, whereas Eocene to early-Oligocene-age sediments (Unit Two of Figures 4.6 and 4.7b) were deposited within a more central depocenter. This later unit is found south of the older depositional center, suggesting a migration of subsidence to the south part of the basin. During the early Oligocene to early Miocene (Unit Three of Figures 4.6 and 4.7c), sediments were deposited across a broad area, extending as far as the present-day zone of piggyback basins. The thickest sediment deposition at that time was in the southeast part of the basin, adjacent to the present-day Inner Forearc Deformation Front. Sediments deposited after initiation of the closure of the TFB and the emergence of the Barbados Ridge, were confined to a smaller TFB. Isochron 54
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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
Page 17 and 18: 1. Development history of the south
Page 19 and 20: Formation. This interpretation requ
Page 21 and 22: DATA AND METHODOLOGY Extensive work
Page 23 and 24: 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: Sandy material is primarily quartz
Page 71 and 72: 1994). The origin of the Oceanic Fo
Page 73 and 74: Oligocene-age sediments are deposit
Page 75 and 76: The observation of channel geometri
Page 77 and 78: Pudsey, (1982) interpreted smectite
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
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Figure 2.33: Thalassinoides trace f
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Figure 2.35: Mount All measured str
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Figure 2.37: Medium grained sand be
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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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