- Email: [email protected]
Reefs and Carbonate Platforms of the Pacific and Indian Oceans
Marine and Petroleum Geology 18 (2001) 283±285
www.elsevier.com/locate/marpetgeo
Book Review Reefs and Carbonate Platforms of the Paci®c and Indian Oceans G.F. Camoin, P.J. Davies (Eds.); Special Publication 25 of the International Association of Sedimentologists, Blackwells, 1998, 328 pages, ISBN 0-632-04778-X, £45.00 This compilation of papers is wide ranging but focuses mainly on platforms from the Paci®c Ocean. The book is divided into three main sections that for me were not obvious natural divisions of this topic: Processes Operating, Platform Case Histories, and Oceanic Reef Case Histories. The listing of contributions and a subject index, however gets the reader to those chapters of interest. The book starts with an oppositely placed review of the demise of carbonate platforms. Here, Schlager revisits and takes the reader through the different processes of platform demise, generation of unconformities and platform drowning (exposure and termination, exposure followed by ¯ooding and renewed platform sedimentation, exposure followed by drowning, and simple drowning). A wide range of examples are given of these processes and the sequence stratigraphic interpretations and implications are discussed (e.g. Does simple drowning result in a sequence boundary or just a ¯ooding surface?). Davies and Peerdeman follow with an analysis of the internal structure and age of the Great Barrier Reef in a study that illustrates the dif®culties of interpreting internal platform history from platform slope borehole and seismic data when internal platform geometries are poorly imaged. Their conclusion is that the GBR is signi®cantly younger (,300,000 yr old) than was previously thought. A comprehensive description and discussion of the geological history of the Wodejebato Guyot of the Marshall Islands from ODP Leg 144 follows (Camoin et al.) and the original atoll was found to be rimmed with skeletal and ooid sand shoals rather than reefs. Drowning of this and other guyots drilled on this leg indicate that there are three main periods of drowning (late Albian, late Maastrichtian and mid Eocene) that coincide with periods of high frequency sea-level changes and short-term climatic and oceanographic changes. A similar theme of high stress on organic carbonate building communities during times of high frequency sea-level changes is visited by Taviani. He examines Cainozoic extinction patterns of reef-related molluscs from the IndoWest Paci®c and the Red Sea. The intriguing hypothesis that isolated, coeval oceanic platforms might be used as ocean dip-sticks that record PII: S 0264-817 2(00)00056-8
the history of eustatic sea-level changes is investigated by Cooper using data from the mid Paci®c Leg 143. Because core recovery is poor (ca. 15%) Cooper used down hole logging (gamma, resistivity and sonic data) from thick, platform-top Cretaceous sections. Spectral analysis of the geophysical logs indicate that eccentricity periodicities dominate the spectra in these greenhouse period lagoonal carbonates but that the vertical resolution was insuf®cient to recognize higher frequency cycles. Case Histories are subdivided into ªPlatform Case Historiesº and ªOceanic Reef Case Historiesº. This subdivision was not obvious to this reviewer as most Paci®c platforms contain oceanic reefs and many oceanic reefs contribute to platform formation. However investigation of contents reveals that the former deals with the internal structure or geological history of platforms and the latter with present day platforms. Two ªPlatform Case Historiesº caught my eye: Rohl and Ogg investigate drowned Cretaceous platforms (guyots) of the mid Paci®c because, being far from any continental margin they are unaffected by varying clastic sediment supply, differential marginal tectonic subsidence/ uplift and therefore provide good sites for testing proposed eustatic sea-level changes in the Cretaceous greenhouse world. A theme visited earlier in the volume by Cooper. Their dataset comes from 4 guyots drilled on Legs 143 and 144 (irritatingly their location ®g lacks a scale and gives borehole numbers but the text gives names). However, how do you do this exercise when you only have about 10% borehole recovery? Rohl and Ogg use logs of FM imagery, density, gamma, resisitivity and neutron porosity. These provide information on cementation, and to a lesser extent grain size and therefore act as a proxy for emergence. The gamma spikes, correlating with uranium peaks, are interpreted to represent peritidal microbial facies. Descriptions of each hole are provided but the published scale of the geophysical logs makes it dif®cult to see the evidence for their shallowing-up parasequences and sequence sets. However to be fair the paper comes with an extensive 14 page apppendix which details how each log is interpreted. Some major assumptions have to be made before attempting the correlation between the atolls; that all the atolls drowned synchronously to provide a latest age and that the major .5 m thick cemented layers represent emergent horizons due to eustatic sea-level fall. Despite such problems Rohl and Ogg adventurously provide parasequence level correlation between the platforms which they also correlate with Aptian and Albian sections in France and England. They are
284
Book Review / Marine and Petroleum Geology 18 (2001) 283±285
honest with the pitfalls of such correlations relying as they are in places on sea-level trends that can only be ªvaguely approximatedº. Liu et al. use Kendall's SEDPAK model to test different proposed sea level curves for the origin of the Marion Plateau northeast of the Great Barrier Reef. This plateau has an interesting three stage history marked by major shifts in the platform margin and early Pliocene drowning reminiscent of many southeast Asian platforms. This forward stratigraphic modelling uses inputs derived mainly from one 2D seismic section but unfortunately this is oriented rather oblique to the platform margins. Sensibly they simulate changes in production rates through time as the platform evolves from an Early Miocene cool water carbonate margin with depth dependant production rates estimated at 0±0.1 m/ka through to a tropical system with rates from 0 to 0.6 m/ka. Four colour plates show the simulated sections that are displayed as either depositional sequences or as ªfaciesº (cf. depth of deposition). The major features of the platform margins and drowning history are simulated but any detailed comparison is hampered by the nature and the scales of the displays. The seismic section is in m/s TWT by kilometres and the simulations in metres by kilometres printed at various scales, and all different from the seismic section! A main mismatch appears to be that remarkably little erosion is simulated on the inner Marion Platform during its ca. 8 Ma of emergence and erosion appears to be present on their seismic section. The simulation was run using an Exxon sea-level curve with little success and also a ªstochasticº curve that is not fully explained. The best ®t comes, not surprisingly, from a relative sea-level curve generated from seismic stratigraphic analysis of the Marion Plateau. This has cycles of similar timing to those on the Exxon curve but different magnitudes. This is a useful analysis to show how some controlling rates on platform formation can be bracketed and how different sea-level curves can be tested. Other papers in this section include Flood on the origin of white sucrosic dolomite within shallow water limestones, Hole 866A, Resolution Guyot, Mid Paci®c Mountains; Marshall et al. on Quaternary and sub-tropical carbonate platform development on the continental margin of southern Queensland, Australia (this documents the more southerly sub-tropical carbonate facies that developed synchronously with the tropical Great barrier Reef to the north); and, Iryu et al. on Pleistocene reef complex deposits in the central Ryukyus, southwest Japan. ªOceanic Reef Case Historiesº are subdivided into ªAtolls and Volcanic Islandsº, ªActive Marginsº and ªPassive Margins (all GBR)º and below I give one taster of each of these sections. Dullo et al. provide results from a joint German±French examination of the only study in the book entirely from the Indian Ocean, Comoro Islands. Their aims are to compliment the many records of highstand reefs on uplifted islands with analysis of reef and terrace lowstands. This work was
undertaken at an impressive number of 19 dive sites around the fore-reef slope of Mayotte atoll in a small submersible. Does this represent our most intensively examined forereef slope? All reef slopes start with a steep cliff of coral framestone, cemented grainstones and debris leading to a cemented slope of grainstones and coral debris with sponge covered ledges to a deeper sediment slope of sands and gravels (plus some very large reef derived blocks) passing down to rippled or bioturbated muddy carbonates. This pattern is similar to that of the reef slopes of the Bahamas. Karst levels are observed at 150±155 and 120±125 m and two main levels of drowned reefs were found at 90±100 and 55±65 m. Using global sea-levels curves together with U/Th dating of corals they ®nd evidence for the Last Glacial Maximum (20±22 ka) in the vertical reef wall and lowstand karst features down to 155 m overgrown by corals dated back to 18.6 ka; a rapid post glacial sea-level rise in a bored hardground on the reef wall interrupted by terraces with drowned reef caps at 90±100 m (Bolling Melting Pulse at 14 ka) and at 55±65 m (Post Younger Dryas Melting Pulse at 11.5 ka) followed by the onset of Holocene reef growth at 9 ka in response to a decrease in the rate of sealevel rise. Cabioch et al. provide the only case history from ªActive Marginsº (New Hebrides island Arc), and for completeness it would have been good to have something from Southeast Asia in this section. Drilling of uplifted reef terraces of Espiritu Santo Island provide the data for this study. Here, high Holocene uplift rates (6 m/ka) against a background postglacial sea-level rise result in recently uplifted reefs with a relatively thick stratigraphic section. The reefs initiate on a sand horizon interpreted to be earlier (late Pleistocene) fore reef slope deposits indicating rapid relative sea-level fall corresponding to the Last Glacial Maximum from the earliest U/Th dated reef corals (24,390 cal yr BP). Subsequently, aggradational reef geometries are preserved through to 4.4±4.8 ka when the reefs became emergent. An earlier (from 24 to 12±10 ka) deeper water coral community formed in medium to high energy conditions is replaced up-section by a high energy reef front or upper slope coral/coralline algal community indicating a catch-up to keep-up reef system. The thick, upper, keep-up unit appears to be a response to coral growth being maintained in accommodation space generated by the eustatic Holocene sea-level rise with rates reduced by the tectonic uplift of the island. Slowing of eustatic rise at around 6±5 ka with continued uplift brought to reefs to their present position at 5±30 m ASL. This contribution is therefore a good example of the complex stratigraphic relations that can arise from interactions of rates of reef growth and rates of relative sea-level change. ªPassive marginº reefs are all exempli®ed from the Great Barrier Reef (GBR) with Smith, B.T., et al. on lagoonal sedimentation and reef development on Heron Reef and Rao et al. comparisons between subtropical and temperate carbonate elemental composition. Woolfe and Larcombe
Book Review / Marine and Petroleum Geology 18 (2001) 283±285
investigate the important effects of terrigenous sedimentation on reefs in the GBR and Papua Gulf (PNG). On the inner parts of the GBR suspended sediment from the Burdekin River is transported NE along shelf for some 200 km resulting in high sedimentation rates (,0.8 m/ka) and coastal progradation. Despite this, nearshore reefs (e.g. Palumo Shoals) survive within such turbid waters and have done for much of the Holocene. The critical factor appears to be the presence of a suitable site for initiation of reef growth, in this case former Pleistocene reefs or shoreline terrigenous gravels. High sediment supply rates also characterise Papua Gulf, where the Fly and other rivers supply an astonishing amount of sediment into the gulf (365 Mt/yr) representing six times the sediment yield from the entire Australian continent. The area is relatively unstudied but surprisingly fringing reefs are common in the eastern part of the Gulf. Clearly net sediment supply is not in itself a major control on reef occurrence. They develop a 4D model of controls on reef occurrence dependant on terrigenous accumulation, reef accumulation, terrigenous erosion and carbonate removal. Reefs grow in a ®eld limited by high terrigenous accumulation and erosion. To confuse matters further large amounts of accumulated terrigenous sediment adjacent to reefs in the geological record may not equate to high rates of sediment supply as reef communities tend to baf¯e, and preferentially preserve, terrigenous sediment. The book is correctly described as ªthe ®rst to examine the carbonate platforms of two oceans which offer such a wide diversity of tectonic and climatological variables, so
285
relevant to platform developmentº. The book's title is however rather ambitious because only one study comes from the Indian Ocean and there are no contributions from the Hawaiin Chain so the book really only concerns the central and western Paci®c. However within this there are a large number of different types of largely reef-rimmed platforms and guyots which provide a vast dataset on such topics as climatic/oceanographic variations in carbonate platforms, platform drowning processes, and the responses of platforms to sea-level changes, to terrigenous sedimentation and to tectonics. Anyone interested in these broad topics or in the reefs and platforms of this particular region should buy or ensure that this volume is in their library. My only criticism is the rather idiosyncratic arrangement of the volume, but others may ®nd it easier to follow. This volume was developed out of a 1995 conference but despite the time period from conference to publication the contributions do not appear out of date, they have clearly been written as post-conference papers. The text, ®gures and plates (a few in colour) are all well produced and up to the normal standard expected of a Special Publication of the International Association of Sedimentologists and are also a credit to the editors. D.W.J. Bosence Department of Geology, Royal Holloway University of London, Egham, Surrey, TW20 0EX, UK E-mail address: [email protected]
www.elsevier.com/locate/marpetgeo
Book Review Reefs and Carbonate Platforms of the Paci®c and Indian Oceans G.F. Camoin, P.J. Davies (Eds.); Special Publication 25 of the International Association of Sedimentologists, Blackwells, 1998, 328 pages, ISBN 0-632-04778-X, £45.00 This compilation of papers is wide ranging but focuses mainly on platforms from the Paci®c Ocean. The book is divided into three main sections that for me were not obvious natural divisions of this topic: Processes Operating, Platform Case Histories, and Oceanic Reef Case Histories. The listing of contributions and a subject index, however gets the reader to those chapters of interest. The book starts with an oppositely placed review of the demise of carbonate platforms. Here, Schlager revisits and takes the reader through the different processes of platform demise, generation of unconformities and platform drowning (exposure and termination, exposure followed by ¯ooding and renewed platform sedimentation, exposure followed by drowning, and simple drowning). A wide range of examples are given of these processes and the sequence stratigraphic interpretations and implications are discussed (e.g. Does simple drowning result in a sequence boundary or just a ¯ooding surface?). Davies and Peerdeman follow with an analysis of the internal structure and age of the Great Barrier Reef in a study that illustrates the dif®culties of interpreting internal platform history from platform slope borehole and seismic data when internal platform geometries are poorly imaged. Their conclusion is that the GBR is signi®cantly younger (,300,000 yr old) than was previously thought. A comprehensive description and discussion of the geological history of the Wodejebato Guyot of the Marshall Islands from ODP Leg 144 follows (Camoin et al.) and the original atoll was found to be rimmed with skeletal and ooid sand shoals rather than reefs. Drowning of this and other guyots drilled on this leg indicate that there are three main periods of drowning (late Albian, late Maastrichtian and mid Eocene) that coincide with periods of high frequency sea-level changes and short-term climatic and oceanographic changes. A similar theme of high stress on organic carbonate building communities during times of high frequency sea-level changes is visited by Taviani. He examines Cainozoic extinction patterns of reef-related molluscs from the IndoWest Paci®c and the Red Sea. The intriguing hypothesis that isolated, coeval oceanic platforms might be used as ocean dip-sticks that record PII: S 0264-817 2(00)00056-8
the history of eustatic sea-level changes is investigated by Cooper using data from the mid Paci®c Leg 143. Because core recovery is poor (ca. 15%) Cooper used down hole logging (gamma, resistivity and sonic data) from thick, platform-top Cretaceous sections. Spectral analysis of the geophysical logs indicate that eccentricity periodicities dominate the spectra in these greenhouse period lagoonal carbonates but that the vertical resolution was insuf®cient to recognize higher frequency cycles. Case Histories are subdivided into ªPlatform Case Historiesº and ªOceanic Reef Case Historiesº. This subdivision was not obvious to this reviewer as most Paci®c platforms contain oceanic reefs and many oceanic reefs contribute to platform formation. However investigation of contents reveals that the former deals with the internal structure or geological history of platforms and the latter with present day platforms. Two ªPlatform Case Historiesº caught my eye: Rohl and Ogg investigate drowned Cretaceous platforms (guyots) of the mid Paci®c because, being far from any continental margin they are unaffected by varying clastic sediment supply, differential marginal tectonic subsidence/ uplift and therefore provide good sites for testing proposed eustatic sea-level changes in the Cretaceous greenhouse world. A theme visited earlier in the volume by Cooper. Their dataset comes from 4 guyots drilled on Legs 143 and 144 (irritatingly their location ®g lacks a scale and gives borehole numbers but the text gives names). However, how do you do this exercise when you only have about 10% borehole recovery? Rohl and Ogg use logs of FM imagery, density, gamma, resisitivity and neutron porosity. These provide information on cementation, and to a lesser extent grain size and therefore act as a proxy for emergence. The gamma spikes, correlating with uranium peaks, are interpreted to represent peritidal microbial facies. Descriptions of each hole are provided but the published scale of the geophysical logs makes it dif®cult to see the evidence for their shallowing-up parasequences and sequence sets. However to be fair the paper comes with an extensive 14 page apppendix which details how each log is interpreted. Some major assumptions have to be made before attempting the correlation between the atolls; that all the atolls drowned synchronously to provide a latest age and that the major .5 m thick cemented layers represent emergent horizons due to eustatic sea-level fall. Despite such problems Rohl and Ogg adventurously provide parasequence level correlation between the platforms which they also correlate with Aptian and Albian sections in France and England. They are
284
Book Review / Marine and Petroleum Geology 18 (2001) 283±285
honest with the pitfalls of such correlations relying as they are in places on sea-level trends that can only be ªvaguely approximatedº. Liu et al. use Kendall's SEDPAK model to test different proposed sea level curves for the origin of the Marion Plateau northeast of the Great Barrier Reef. This plateau has an interesting three stage history marked by major shifts in the platform margin and early Pliocene drowning reminiscent of many southeast Asian platforms. This forward stratigraphic modelling uses inputs derived mainly from one 2D seismic section but unfortunately this is oriented rather oblique to the platform margins. Sensibly they simulate changes in production rates through time as the platform evolves from an Early Miocene cool water carbonate margin with depth dependant production rates estimated at 0±0.1 m/ka through to a tropical system with rates from 0 to 0.6 m/ka. Four colour plates show the simulated sections that are displayed as either depositional sequences or as ªfaciesº (cf. depth of deposition). The major features of the platform margins and drowning history are simulated but any detailed comparison is hampered by the nature and the scales of the displays. The seismic section is in m/s TWT by kilometres and the simulations in metres by kilometres printed at various scales, and all different from the seismic section! A main mismatch appears to be that remarkably little erosion is simulated on the inner Marion Platform during its ca. 8 Ma of emergence and erosion appears to be present on their seismic section. The simulation was run using an Exxon sea-level curve with little success and also a ªstochasticº curve that is not fully explained. The best ®t comes, not surprisingly, from a relative sea-level curve generated from seismic stratigraphic analysis of the Marion Plateau. This has cycles of similar timing to those on the Exxon curve but different magnitudes. This is a useful analysis to show how some controlling rates on platform formation can be bracketed and how different sea-level curves can be tested. Other papers in this section include Flood on the origin of white sucrosic dolomite within shallow water limestones, Hole 866A, Resolution Guyot, Mid Paci®c Mountains; Marshall et al. on Quaternary and sub-tropical carbonate platform development on the continental margin of southern Queensland, Australia (this documents the more southerly sub-tropical carbonate facies that developed synchronously with the tropical Great barrier Reef to the north); and, Iryu et al. on Pleistocene reef complex deposits in the central Ryukyus, southwest Japan. ªOceanic Reef Case Historiesº are subdivided into ªAtolls and Volcanic Islandsº, ªActive Marginsº and ªPassive Margins (all GBR)º and below I give one taster of each of these sections. Dullo et al. provide results from a joint German±French examination of the only study in the book entirely from the Indian Ocean, Comoro Islands. Their aims are to compliment the many records of highstand reefs on uplifted islands with analysis of reef and terrace lowstands. This work was
undertaken at an impressive number of 19 dive sites around the fore-reef slope of Mayotte atoll in a small submersible. Does this represent our most intensively examined forereef slope? All reef slopes start with a steep cliff of coral framestone, cemented grainstones and debris leading to a cemented slope of grainstones and coral debris with sponge covered ledges to a deeper sediment slope of sands and gravels (plus some very large reef derived blocks) passing down to rippled or bioturbated muddy carbonates. This pattern is similar to that of the reef slopes of the Bahamas. Karst levels are observed at 150±155 and 120±125 m and two main levels of drowned reefs were found at 90±100 and 55±65 m. Using global sea-levels curves together with U/Th dating of corals they ®nd evidence for the Last Glacial Maximum (20±22 ka) in the vertical reef wall and lowstand karst features down to 155 m overgrown by corals dated back to 18.6 ka; a rapid post glacial sea-level rise in a bored hardground on the reef wall interrupted by terraces with drowned reef caps at 90±100 m (Bolling Melting Pulse at 14 ka) and at 55±65 m (Post Younger Dryas Melting Pulse at 11.5 ka) followed by the onset of Holocene reef growth at 9 ka in response to a decrease in the rate of sealevel rise. Cabioch et al. provide the only case history from ªActive Marginsº (New Hebrides island Arc), and for completeness it would have been good to have something from Southeast Asia in this section. Drilling of uplifted reef terraces of Espiritu Santo Island provide the data for this study. Here, high Holocene uplift rates (6 m/ka) against a background postglacial sea-level rise result in recently uplifted reefs with a relatively thick stratigraphic section. The reefs initiate on a sand horizon interpreted to be earlier (late Pleistocene) fore reef slope deposits indicating rapid relative sea-level fall corresponding to the Last Glacial Maximum from the earliest U/Th dated reef corals (24,390 cal yr BP). Subsequently, aggradational reef geometries are preserved through to 4.4±4.8 ka when the reefs became emergent. An earlier (from 24 to 12±10 ka) deeper water coral community formed in medium to high energy conditions is replaced up-section by a high energy reef front or upper slope coral/coralline algal community indicating a catch-up to keep-up reef system. The thick, upper, keep-up unit appears to be a response to coral growth being maintained in accommodation space generated by the eustatic Holocene sea-level rise with rates reduced by the tectonic uplift of the island. Slowing of eustatic rise at around 6±5 ka with continued uplift brought to reefs to their present position at 5±30 m ASL. This contribution is therefore a good example of the complex stratigraphic relations that can arise from interactions of rates of reef growth and rates of relative sea-level change. ªPassive marginº reefs are all exempli®ed from the Great Barrier Reef (GBR) with Smith, B.T., et al. on lagoonal sedimentation and reef development on Heron Reef and Rao et al. comparisons between subtropical and temperate carbonate elemental composition. Woolfe and Larcombe
Book Review / Marine and Petroleum Geology 18 (2001) 283±285
investigate the important effects of terrigenous sedimentation on reefs in the GBR and Papua Gulf (PNG). On the inner parts of the GBR suspended sediment from the Burdekin River is transported NE along shelf for some 200 km resulting in high sedimentation rates (,0.8 m/ka) and coastal progradation. Despite this, nearshore reefs (e.g. Palumo Shoals) survive within such turbid waters and have done for much of the Holocene. The critical factor appears to be the presence of a suitable site for initiation of reef growth, in this case former Pleistocene reefs or shoreline terrigenous gravels. High sediment supply rates also characterise Papua Gulf, where the Fly and other rivers supply an astonishing amount of sediment into the gulf (365 Mt/yr) representing six times the sediment yield from the entire Australian continent. The area is relatively unstudied but surprisingly fringing reefs are common in the eastern part of the Gulf. Clearly net sediment supply is not in itself a major control on reef occurrence. They develop a 4D model of controls on reef occurrence dependant on terrigenous accumulation, reef accumulation, terrigenous erosion and carbonate removal. Reefs grow in a ®eld limited by high terrigenous accumulation and erosion. To confuse matters further large amounts of accumulated terrigenous sediment adjacent to reefs in the geological record may not equate to high rates of sediment supply as reef communities tend to baf¯e, and preferentially preserve, terrigenous sediment. The book is correctly described as ªthe ®rst to examine the carbonate platforms of two oceans which offer such a wide diversity of tectonic and climatological variables, so
285
relevant to platform developmentº. The book's title is however rather ambitious because only one study comes from the Indian Ocean and there are no contributions from the Hawaiin Chain so the book really only concerns the central and western Paci®c. However within this there are a large number of different types of largely reef-rimmed platforms and guyots which provide a vast dataset on such topics as climatic/oceanographic variations in carbonate platforms, platform drowning processes, and the responses of platforms to sea-level changes, to terrigenous sedimentation and to tectonics. Anyone interested in these broad topics or in the reefs and platforms of this particular region should buy or ensure that this volume is in their library. My only criticism is the rather idiosyncratic arrangement of the volume, but others may ®nd it easier to follow. This volume was developed out of a 1995 conference but despite the time period from conference to publication the contributions do not appear out of date, they have clearly been written as post-conference papers. The text, ®gures and plates (a few in colour) are all well produced and up to the normal standard expected of a Special Publication of the International Association of Sedimentologists and are also a credit to the editors. D.W.J. Bosence Department of Geology, Royal Holloway University of London, Egham, Surrey, TW20 0EX, UK E-mail address: [email protected]