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

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PREVIOUS RESEARCH The source terranes of the Scotland Formation were interpreted by Kasper and Laure (1986) to include the Guyana Shield, the Caribbean Mountain System and possibly the Lesser Antilles or predecessor arc. It is important to note that in 1985, workers wrote that the Eocene sandstones exposed onshore Barbados had not been deeply buried (< 40 km) or exposed to high temperatures (< 60˚C) (Larue et al. 1985; Larue, Gortner and Torrini, 1987), based on extensive petrographic analysis of the Scotland Formation sandstones. Larue and Kasper (1986) and Larue, et al. (1987) further stated that the Scotland Formation was no more diagenetically mature “…than the sediments that lay passively on the floor of the Atlantic Ocean for 40 my…” These authors also interpreted the Scotland to represent abyssal plain or trench deposits that were tectonically incorporated into the accretionary prism. It is hard to reconcile these two observations because sediments deposited so distal in the prism to their current outcropping location would require significant tectonic displacement associated with trench subduction, tectonic burial and subsequent uplift. In 1986, Baldwin undertook fission track analysis on the sandstones of the Scotland Formation. She reported that the ages of the youngest populations were 20-90 Ma. The results of her study also showed that the maximum temperature that the Scotland Formation sediments underwent was 80˚C (Baldwin, 1986). Punch (2004) examined 13 samples from the Scotland sandstones onshore Barbados found at the Chalky Mount outcrops and along the East Coast Road outcrops (Previous location Figure 2.3). The analyzed samples ranged from mature quartz arenites to feldspathic sublitharenites, sublitharenites and arkoses. Punch concluded that the sandstones were compositionally mature, but texturally submature and had only been transported a short distance. She observed that formation fluids had caused the dissolution of some but not all of the feldspars. Her conclusion was that the sediments 27
had not been buried deeply or long enough to result in complete dissolution (Punch 2004). All of these previous results lead to the questions of 1. How can sediments deposited in a trench setting now be uplifted to the highest point of the prism core with little or no diagenetic imprint on the sediments? and 2. If they have been subducted in this transport process why do they show limited signs of high pressure and temperature history? To address these questions we needed to reexamine the samples of the Scotland and reassess the diagenetic history of the deposits within the context of their depositional setting and within the context of previous work by Chaderton (2005) regarding the history of Tobago Forearc Basin development. METHODOLOGY Samples were cut and made into thin sections then impregnated with blue dyed epoxy and left unpolished. The sections were then stained for identification of potassium feldspars (yellow) and calcium plagioclase (pink) Forty samples were examined for petrographic content and sandstone characteristics. However, the majority (33) of these samples were measured from a single locality (SGRF) therefore, only 10 samples were chosen for detailed analysis and point counting. The goal of this analysis was to investigate possible variations in petrographic character between localities and between facies. In each of the 10 samples 200 grains were point counted and 100 grains were measured in each sample along the long axis. Pore spaces and grains were not counted separately. The intergranular volume (IGV) was calculated based on the results of point counting using the following formula: IGV= Primary pores + Pore-filling Cements + Matrix 28
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 and 16: 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: Chapter Three: Petrographic Analysi
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 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 107 and 108:
Page 109 and 110:
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
Page 127 and 128:
Figure 2.38d: Inner Turner’s Hall
Page 129 and 130:
Figure 2.39: Spa Hill measured stra
Page 131 and 132:
Juniper Ridge, California Scotland
Page 133 and 134:
Figure 3.1: Fractured quartz grain
Page 135 and 136:
SGRF 1C SGRF 9C Figure 3.5: Measure
Page 137 and 138:
Figure 3.8: Photo of sample SGRF 11
Page 139 and 140:
Figure 3.10: Photo of sample SGRF 1
Page 141 and 142:
Figure 3.12: Photo of sample WRA 16
Page 143 and 144:
Figure 3.14: Photo of sample WRB 8
Page 145 and 146:
Figure 3.16: Photo of sample ITR 9
Page 147 and 148:
Figure 3.19: Photo of sample CMRA s
Page 149 and 150:
Figure 3. 23: Composition of Scotla
Page 151 and 152:
Figure 4.1: Base map showing seismi
Page 153 and 154:
Figure 4.3: Channels within Unit Fi
Page 155 and 156:
Figure 4.5: Seismic reflection prof
Page 157 and 158:
Figure 4.7 Isochron maps of the old
Page 159 and 160:
Figure 4.9: Illustration of the Spe
Page 161 and 162:
Figure 4.11: Illustration of Hypoth
Page 163 and 164:
necessary to clear a path. Keep to
Page 165 and 166:
2006 Figure A.2a: Lidar Ridge measu
Page 167 and 168:
Figure A.3b: Chalky Mount Ridge mea
Page 169 and 170:
2006 Figure A.4a: Chalky Mount Ridg
Page 171 and 172:
2006 Figure A.4c: Chalky Mount Ridg
Page 173 and 174:
2006 Figure A.6: Chalky Mount Ridge
Page 175 and 176:
Figure A.7b: Measured Section of Ch
Page 177 and 178:
2006 Figure A.8a: Sleeping Giant Ri
Page 179 and 180:
2006 Figure A.9: Sleeping Giant Rid
Page 181 and 182:
2006 Figure A.11: Sleeping Giant Ri
Page 183 and 184:
Figure A.13a: Sleeping Giant Ridge
Page 185 and 186:
2006 Figure A.14a: Coast Road Below
Page 187 and 188:
2006 Figure A.14c: Coast Road Below
Page 189 and 190:
2006 Figure A.14e: Coast Road Below
Page 191 and 192:
2006 Figure A.14g: Coast Road Below
Page 193 and 194:
2006 Figure A.15: Ermy Bourne Ridge
Page 195 and 196:
2006 Figure A.17: Spa Hill Fold Mea
Page 197 and 198:
2006 Figure A.19: Ermy Bourne Ridge
Page 199 and 200:
Figure A.20b: Walkers Ridge Measure
Page 201 and 202:
Figure A.21: Walkers Ridge Measured
Page 203 and 204:
Figure A.22b: Walkers Ridge Measure
Page 205 and 206:
2007 Figure A.23b: Inner Turner’s
Page 207 and 208:
2007 Figure A.23d: Inner Turner’s
Page 209 and 210:
Framework grains Quartz Feldspar Ro
Page 211 and 212:
CRIMES, T.P., 1977, Trace fossils o
Page 213 and 214:
MONTGOMERY, S.L., BARKER, C.E., SEA
Page 215 and 216:
RICHARDS, M., BOWMAN, M., and READI
Page 217 and 218:
WEBER, J.C., DIXON, T.H., DEMETS, C
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