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

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located off the east coast of the modern island of Barbados see Fig. 4.4), has played a significant role in the emergence of the island. In Eocene times the proto-Tobago Basin was originally very broad with ill-defined margins. Data from Woodbourne oilfield onshore Barbados support this extended east margin of the Tobago Basin, showing today that the basin deposits extended eastward, well beyond the basin’s present margins. However, today this older basin has been segmented into the present-day Tobago Basin and several smaller, more eastwardly located piggyback basins with well-defined margins. The largest of these segmented basins is the Barbados Basin, which lies to the east of the Barbados Ridge. This ridge is composed partly of Tobago Forearc Basin (TFB) sediments, consisting of clastic deep-water sands of the Scotland Formation and the deep pelagic muds that overlie them (Oceanic Formation). It is herein interpreted that the Barbados Ridge was once much deeper than it is today. Data supporting this observation include (1) lower to upper Miocene deep-water units stratigraphically draping the Barbados Ridge and (2) biostratigraphic data on the aforementioned deposits that compose the modern, subaerially exposed Barbados Ridge, which indicate deposition in water depths of 2,000 to 4,000 m (Saunders et al., 1985) (Chaderton, 2005; Chaderton and Wood, 2006). Both observations suggest a significant uplift occurring throughout the Tertiary in the interior of the accretionary prism. Although two hypotheses have been put forward to explain the occurrence of the Oceanic Formation onshore Barbados, only one of these hypotheses is supported by the data and all of the geological observations contained in this dissertation. Data suggest that the channelized deposits of the Scotland Formation were deposited within the TFB in its present position and the Oceanic Formation was deposited conformably on top. 59
The observation of channel geometries within the TFB along with the presence of a regional depocenter during Eocene to Oligocene times suggest a clastic sediment fairway within the broader proto-Tobago Forearc Basin. These sediments would then have been incorporated into the present day western BAP on the eastern margin of the TFB. As the TFB closed the sediments on the basin margin became uplifted and deformed. These observations helped us to expand upon the premise of the second hypothesis. Deepwater background sedimentation is pelagic mud and marl such as those that comprise the Oceanic Formation (that appear layered in seismic reflection profiles). Upon initiation of clastic sedimentation within the basin, a mud-rich submarine fan system was deposited within the broader TFB (Scotland Formation). When clastic sedimentation within the Tobago Forearc Basin ceased, pelagic sedimentation dominated once more (Oceanic Formation) (Figure 4.11). Continued closure of the basin and underplating of sediments uplifted the Scotland and Oceanic Members to their present day position onshore Barbados. Both of these sedimentary packages were later uplifted with the rest of the Barbados Ridge to form the newly defined margin of the shrinking Tobago Basin. CONCLUSIONS The Tobago Forearc Basin was broader prior to the Middle Miocene than it is in the present day. It has been segmented into smaller basins with the TFB being the largest. The Oceanic Formation was deposited in situ and not thrust into place over the Scotland Formation. 60
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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
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 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: Oligocene-age sediments are deposit
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
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
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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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