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

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Chapter One: Introduction The study area of the Barbados Accretionary Prism (BAP), also called the Lesser Antilles Accretionary Prism by some workers, is located in a convergent margin setting near the eastern edge of the Caribbean plate. At this location the Caribbean plate is overriding the westward dipping Atlantic plate, moving eastward at a rate of approximately 20 mm a year, (Mann, 1999; Weber, et al., 2001; Perez, et al., 2001) (Figure 1.1). This plate boundary is marked by the presence of classic convergent margin features such as an accretionary prism (The Barbados Accretionary Prism), a volcanic island arc (The Lesser Antilles Island Arc and an associated forearc basin (The Tobago Basin) and a back arc basin (The Grenada Basin). The Barbados Accretionary Prism (BAP) is the considered to be the only hydrocarbon producing prism in the world. One of the goals of this research is to examine the petroleum system of the BAP and determine whether the conditions that have made hydrocarbon production possible are unique or whether they exist within similar settings and can be successfully exploited. The following research problems will be investigated. time? How has the Southern Barbados Accretionary Prism (BAP) developed through What is the sedimentation history of the Southern BAP and what is the composition and timing of the Tobago Forearc Basin fill? What is the nature of the petroleum system of the southern BAP? 1
1. Development history of the southern BAP Convergent margins can be accretionary, erosive or a combination of the two. Accretionary margins are defined as those which are experiencing net accretion over recent geologic time (Clift and Vannucchi, 2004) (Figure 1.2). Even so at margins experiencing net overall accretion, up to 70 % of the sediment may be being subducted (von Heune and Scholl, 1991; Clift and Vannucchi, 2004). In the study area sediments which have accumulated on the Atlantic abyssal plain are accreted to the front of the Caribbean plate, as the Atlantic plate is subducted. This has resulted in the growth of an accretionary prism that is greater than 300 km wide and has sediment thicknesses that exceed 18 km (Torrini and Speed, 1989; Westbrook et al., 1973, Moore et al., 1982; Valery et al., 1985; Speed, 1983; Brown and Westbrook, 1987). Accretionary prisms grow through frontal accretion and underplating. Frontal accretion is the mechanism by which seaward sediments are off-scraped above a basal decollement and incorporated into the growing accretionary prism. In this manner accretionary prisms become wider (Moore and Biju-Duval, 1984, Shipley and others, 1982; DiTullio and Byrne, 1990; Von Heune and Scholl, 1991; Morris et al. 2002). Underplating occurs when off-scraped sediment passes beneath the sediment pile and is added to the base of the prism. This is the mechanism by which prisms thicken (Moore and Biju-Duval, 1984, Shipley et al., 1982; DiTullio and Byrne, 1990; Von Heune and Scholl, 1991; Morris et al. 2002). The Barbados Accretionary prism has an extraordinarily thick sediment pile- up to 18 km (Speed, 1983; Brown and Westbrook, 1987) that may partially be the result of thickening of the prism by underplating. At 20 mm a year, it also is experiencing one of the slowest rates of convergence recorded at accretionary margins world wide (von Heune and Scholl, 1991). The evolution of the Tobago Basin is recorded by the sedimentary units within it that show its steady decrease in size since the Mid-Miocene (Chaderton, 2005). The existence of a broad proto-Tobago Basin (Speed et al., 1983; 2
Page 1 and 2: Copyright by Nysha Chaderton 2009
Page 3 and 4: Sedimentation within the Tobago For
Page 5 and 6: Acknowledgements I would like to th
Page 7 and 8: Table of Contents List of Tables ..
Page 9 and 10: List of Tables Table 2.1: Latitudes
Page 11 and 12: Figure 2.14: Planar parallel lamina
Page 13 and 14: Figure 2.42: Coarse, cobble and peb
Page 15: Figure A.3a: Chalky Mount Ridge mea
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
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Sandy material is primarily quartz
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esult of extension caused by flexur
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1994). The origin of the Oceanic Fo
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Oligocene-age sediments are deposit
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The observation of channel geometri
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Pudsey, (1982) interpreted smectite
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The interpretation of the Scotland
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Figure 1.2: Convergent margins arou
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NSF Study Lines Grenada St. Kitts S
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Figure 2.2: Generalized vertical se
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Figure 2.4: Detailed Geological map
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Figure 2.6: Photographs and illustr
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Figure 2.8: Bedsets on the channel
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S 50 m Figure 2.10: Photo-panorama
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Figure 2.13: Laminated silt and mud
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Figure 2.16a: Measured section at C
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Figure 2.16c: Measured section at C
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Figure 2.18: Correlation of section
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Figure 2.21: Parallel laminated sil
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Wach, Vincent and Chaderton March 2
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Figure 2.24: Channel element identi
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WRB S N Fresh rock face exposed by
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Figure 2.28: Photograph of Diplocra
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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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