Richard Corfield - Academia.edu (original) (raw)

Papers by Richard Corfield

Journal of Foraminiferal Research, 1985

... a great deal to this field, and over many years maintained an interest in combining direct ob... more ... a great deal to this field, and over many years maintained an interest in combining direct observation of living foraminifera with isotope ... discussions with NJS, was the fact that the isotopic composition of the test necessarily integrates the continuing calcification throughout the life ...

The oxygen and carbon isotopic composition has been measured for numerous Paleogene planktonic fo... more The oxygen and carbon isotopic composition has been measured for numerous Paleogene planktonic foraminifer species from Maud Rise, Weddell Sea (ODP Sites 689 and 690), the first such results from the Antarctic. The results provide information about large-scale changes in the evolution of temperatures, seasonally, and structure of the upper water column prior to the development of a significant Antarctic cryosphere. The early Paleocene was marked by cooler surface-water conditions compared to the Cretaceous and possibly a less well developed thermocline. The late Paleocene and early Eocene saw the expansion of the thermocline as Antarctic surface waters became warm-temperate to subtropical. The late Paleocene to early Eocene thermal maximum was punctuated by two brief excursions during which time the entire Antarctic water column warmed and the meridional temperature gradient was reduced. The first of these excursions occurred at the Paleocene/Eocene boundary, in association with a major extinction in deep sea benthic foraminifers. The second excursion occurred within the early Eocene at -54.0 Ma. These excursions are of global importance and represent the warmest intervals of the entire Cenozoic. The excursions were associated with fundamental changes in deep-water circulation and global heat transport.

Geological Magazine, 1992

From the unique perspective of the geological record, it appears that the ' Greenhouse Earth' was... more From the unique perspective of the geological record, it appears that the ' Greenhouse Earth' was a feature of climate for up to 80 % of the last 500 Ma, and that therefore our present glacially dominated climate is an anomaly. The Cretaceous in particular was a time of global warmth, an extreme greenhouse world apparently warmer than our current Earth. The geological record provides perspective and constraints against which the success of climate models can be evaluated. At present there are no ways of evaluating model predictions for the future of our ' Greenhouse Earth' until after the event. Retrodicting the past is therefore a very useful way of testing model sensitivity and robustness. The geological record tells us that the characteristics of the Cretaceous greenhouse world were a shallower equator-to-pole temperature gradient, shallow, well-stratified epicontinental seas with a tendency towards periodic dysaerobism, and a well-developed terrestrial flora extending to the high latitudes. Both marine and non-marine data show a global cooling trend throughout Late Cretaceous time, a trend that seems to correlate with declining atmospheric carbon dioxide.

Precambrian Research, 2005

Shallow intracratonic basins developed across a large area of the central part of the Australian ... more Shallow intracratonic basins developed across a large area of the central part of the Australian craton during the Neoproterozoic and continued to accumulate marine sedimentary successions until well into the early Palaeozoic—a half billion year sedimentary record. Carbonate successions ranging in age from Neoproterozoic (Cryogenian) to ostensibly Early Ordovician have been sampled at eleven sites across four of the northernmost of these basins (Amadeus, Georgina, Wiso and Daly Basins). A total of 996 samples were then analyzed for stable carbon (δ13Ccarb) and oxygen (δ18Ocarb) isotopes to develop a regional secular stable carbon isotopic curve. The curve complements earlier work and provides an important framework for global correlation at a critical time in Earth history during which the biosphere and atmosphere were evolving rapidly.At one site in the Amadeus Basin, diagenesis proved to have significantly modified the isotopic composition of the carbonates and the data were eliminated. Analysis of the remaining samples suggests that they reflect the global secular stable carbon isotope curve and tie well with established palaeontological timescales. In particular, key isotopic excursions can be identified in the earliest part of the Neoproterozoic succession, notably the negative excursion following the Sturtian glaciation. In the early Palaeozoic record a major excursion during Ordian–early Templetonian (509–506 Ma) time can be identified across the region as can the so-called SPICE excursion which has been associated globally with the Steptoean Stage of Laurentia (497.5–495 Ma). A smaller late Templetonian–Floran (506–503 Ma) positive excursion has also been recognized. The stable carbon isotope record provides a strong regional correlation in both fossiliferous and unfossiliferous Neoproterozoic and early Palaeozoic successions and allows a global correlation to be established.

Geology, 1993

Differences in depth ecology suggest that some chronospecies are not simply artifacts of taxonomy... more Differences in depth ecology suggest that some chronospecies are not simply artifacts of taxonomy but may have biological reality. ACKNOWLEDGMENTS Supported by National Science Foundation grant EAR 9106108 (to Nor-rie) and by the Department of Earth Sciences, Oxford ...

One of the most continuous and best studied continental stratigraphic sections spanning the Paleo... more One of the most continuous and best studied continental stratigraphic sections spanning the Paleocene-Eocene boundary is preserved on Polecat Bench in the northern Bighorn Basin. The mammalian biostratigraphy of Polecat Bench sediments has been well documented, and includes a major reorganization of faunas at or near the P-E boundary. To complement the existing biostratigraphy, we measured the isotopic composition of paleosol carbonate nodules at soil-by-soil temporal resolution through the P-E boundary interval. These measurements provide a detailed record of the abrupt, transient, carbon isotope excursion that affected atmospheric and oceanic carbon reservoirs at ca. 55 million years before present [Ma]. Tests of soil thickness and diagenesis indicate that trends in the record are primary, and reflect syndepositional changes in the 613C value of atmospheric C02. The carbon isotope record suggests that the 613C value of atmospheric C02 dropped by ca. 8%0 during this interval, and then rebounded. The pattern of change is very similar to that of an independent high-resolution record of Bains et al. (submitted). Changes in the 6180 of paleosol carbonates are consistent with a significant increase in local mean annual temperature during the P-E boundary event. Comparison of biotic and isotopic stratigraphies on Polecat Bench shows that faunal changes at the P-E boundary lag behind major events in the carbon and oxygen isotope records by about 10 thousand years [k.y.]. In: Paleocene-Eocene Stratigraphy and Biotic Change in the Bighorn where R = 1801160. Similarly, 613C is the deviation (in %o) of and Clarks Fork Basins, Wyoming (P. D. Gingerich, ed.), University of the carbon isotope ratio of a sample from that of a standard (V-Michigan Papers on Paleontology, 33: 73-88 (2001). PDB), where R = 13C112C.

Gff, 2000

... Geological Society Special Publication 101. Bains, S., Corfield, RM & Norris, RD, 1999: M... more ... Geological Society Special Publication 101. Bains, S., Corfield, RM & Norris, RD, 1999: Mechanisms of climate warm-ing at the end of the Paleocene. ... Lu, G. & Keller, G., 1993: The Paleocene-Eocene transition in the Antarctic Indian Ocean: Inference from planktic foraminifera. ...

After over 15 m.y. of evolution in near-surface waters of the Western Pacific and Caribbean, plan... more After over 15 m.y. of evolution in near-surface waters of the Western Pacific and Caribbean, planktic foraminifera in the lineage Globorotalia (Fohsella) abruptly invaded thermocline habitats at 13 Ma. Stable isotope data demonstrate that this habitat shift took 50 ka to complete, a duration similar to the fastest measured rates of speciation in marine protistans. The ecological change occurred near the end of a long series of gradual morphological transitions and demonstrates that at least some of the chronospecies in this lineage had distinctive ecologies and were probably biological species. Other than this one shift in depth distribution, skeletal evolution is largely disconnected from depth changes in Globorotalia (Fohsella). Morphological trends of globorotaliid foraminifera may not record changes in depth ecology, contrary to existing models for foraminiferal diversification.

Nature, 2000

The onset of the Palaeocene/Eocene thermal maximum (about 55 Myr ago) was marked by global surfac... more The onset of the Palaeocene/Eocene thermal maximum (about 55 Myr ago) was marked by global surface temperatures warming by 5-7 degrees C over approximately 30,000 yr (ref. 1), probably because of enhanced mantle outgassing and the pulsed release of approximately 1,500 gigatonnes of methane carbon from decomposing gas-hydrate reservoirs. The aftermath of this rapid, intense and global warming event may be the best example in the geological record of the response of the Earth to high atmospheric carbon dioxide concentrations and high temperatures. This response has been suggested to include an intensified flux of organic carbon from the ocean surface to the deep ocean and its subsequent burial through biogeochemical feedback mechanisms. Here we present firm evidence for this view from two ocean drilling cores, which record the largest accumulation rates of biogenic barium--indicative of export palaeoproductivity--at times of maximum global temperatures and peak excursion values of delta13C. The unusually rapid return of delta13C to values similar to those before the methane release and the apparent coupling of the accumulation rates of biogenic barium to temperature, suggests that the enhanced deposition of organic matter to the deep sea may have efficiently cooled this greenhouse climate by the rapid removal of excess carbon dioxide from the atmosphere.

Geology, 1996

ABSTRACT Isotopic analysis of lacustrine carbonates from the Eocene Green River Formation suggest... more ABSTRACT Isotopic analysis of lacustrine carbonates from the Eocene Green River Formation suggests that lake waters were derived partly from snow melt. This evidence for cool climates is in marked contrast to paleontological and model evidence for mild tempera-tures in the ...

Terra Nova, 1992

We have compared detailed planktonic and benthonic foraminiferal carbon and oxygen isotope record... more We have compared detailed planktonic and benthonic foraminiferal carbon and oxygen isotope records from the Palaeocene and early Eocene successions at DSDP Site 577 (Shatsky Rise, North Pacific), a composite section derived from DSDP Leg 74 sites (Walvis Ridge, South Atlantic) and a composite section from ODP Leg 113 sites (Maud Rise, Weddell Sea). The δ13C records of Palaeocene and early Eocene Foraminifera at Site 577 and the Leg 74 sites show that an increase in δ13C values in surface waters at 64 Ma (end of Zone P1) resulted in increased vertical carbon isotope gradients (δ13C) between surface and deeper dwelling planktonic foraminifera, and between surface-dwelling planktonics and benthonic foraminifera which became progressively steeper until the iniddle Late Palaeocene (Zone P4). This steepening also occurs in the latest Palaeocene of the composite Leg 113 section and can be explained by an increase in surface ocean productivity. This increase in productivity probably resulted in an expansion of the oxygen minimum zone (OMZ).Benthonic δ13C values increased during the late Palaeocene in Site 577 and the composite Leg 74 section, suggesting that the Palaeocene carbon isotope maximum was composed of both within-ocean reservoir (increased surface water productivity) and between-reservoir (organic carbon burial) ftactionation effects. The benthonic δ13C increase lags the surface ocean δ13C increase in the early Palaeocene (63–64 Ma) suggesting that surface water productivity increase probably led an increase in the burial rate of organic carbon relative to carbonate sedimentation. Moreover, inter-site δ13C comparisons suggest that the locus of deep to intermediate water formation for the majority of the Palaeocene and the earliest Eocene was more likely to have been in the high southern latitudes than in the lower latitudes.Oxygen isotope data show a decline in deeper water temperatures in the early and early late Palaeocene, followed by a temperature increase in the late Palaeocene and across the PalaeoceneEocene boundary. We speculate that these changes in deeper water temperatures were related to the flux of CO2 between the oceans and the atmosphere through a mechanism operating at the high southern latitudes.

Oxygen and carbon isotope analyses have been performed at close sampling intervals on rocks from ... more Oxygen and carbon isotope analyses have been performed at close sampling intervals on rocks from several exposures that show the boundary between the Wenlock and Ludlow Series in the classic Silurian areas of Wales, the Welsh Borderland, and the West Midlands of England. Our data indicate a monotonic decline in δ13C from positive to negative values across the boundary between the Much Wenlock Limestone Formation (Wenlock Series) and the Lower Elton Formation (Ludlow Series), and correlatives, in all sites investigated. A slightly earlier negative excursion is also present in the upper Wenlock strata of two of these localities. Both negative δ13C excursions appear to be contemporaneous with episodes of increased ocean ventilation and eustatic sea- level lowstand postulated by Kemp. At least one, and possibly both, of the late Wenlock carbon isotope depletions can also be related to the decline in pelagic graptolite diversity. The distribution of the carbon isotope depletion in both carbonate-platform and off-shelf facies implies that this trend is unlikely to have been caused by local diagenetic alteration. Isotope chemostratigraphy may also provide an extra correlation tool that can be integrated with traditional biostratigraphic methods for Silurian strata.

Nature, 2000

The onset of the Palaeocene/Eocene thermal maximum (about 55Myr ago) was marked by global surface... more The onset of the Palaeocene/Eocene thermal maximum (about 55Myr ago) was marked by global surface temperatures warming by 5-7°C over approximately 30,000yr (ref. 1), probably because of enhanced mantle outgassing and the pulsed release of ~1,500gigatonnes of methane carbon from decomposing gas-hydrate reservoirs. The aftermath of this rapid, intense and global warming event may be the best example in the geological record of the response of the Earth to high atmospheric carbon dioxide concentrations and high temperatures. This response has been suggested to include an intensified flux of organic carbon from the ocean surface to the deep ocean and its subsequent burial through biogeochemical feedback mechanisms. Here we present firm evidence for this view from two ocean drilling cores, which record the largest accumulation rates of biogenic barium-indicative of export palaeoproductivity-at times of maximum global temperatures and peak excursion values of δ13C. The unusually rapid return of δ13C to values similar to those before the methane release and the apparent coupling of the accumulation rates of biogenic barium to temperature, suggests that the enhanced deposition of organic matter to the deep sea may have efficiently cooled this greenhouse climate by the rapid removal of excess carbon dioxide from the atmosphere.

Geology, 1992

Carbon isotope excursion near the Wenlock-Ludlow (Silurian) boundary in the Anglo-Welsh area Rich... more Carbon isotope excursion near the Wenlock-Ludlow (Silurian) boundary in the Anglo-Welsh area Richard M. Corfield Department of Earth Sciences, University of Oxford Parks Road, Oxford 0X1 3PR, England Derek J. Siveter Geological Collections, University Museum, ...

Isotopic analysis of lacustrine carbonates from the Eocene Green River Formation suggests that la... more Isotopic analysis of lacustrine carbonates from the Eocene Green River Formation suggests that lake waters were derived partly from snow melt. This evidence for cool climates is in marked contrast to paleontological and model evidence for mild temperatures in the continental interior. Oxygen isotope ratios of carbonates frequently reach -12‰ to nearly -16‰ (Peedee belemnite), which suggests that lake waters probably had δ18O of <-13‰ (standard mean ocean water). Consideration of the evaporative 18O enrichment that typically occurs in modern large saline lakes suggests that the source waters to the Green River basin had a δ18O of <-18‰. These ratios are consistent with snow melt and are too negative to be easily accounted for by distillation in the atmosphere during heavy rainfall. The Green River lakes formed in a closed basin encircled by large mountains; this suggests that the snow melt was locally produced. The mountains surrounding the lake must have been high enough to occasionally supply significant melt water to the much lower lake. Lapse rate calculations suggest minimum altitudes of >3000 m for the mountains encircling the Green River basin.

Journal of Foraminiferal Research, 1985

... a great deal to this field, and over many years maintained an interest in combining direct ob... more ... a great deal to this field, and over many years maintained an interest in combining direct observation of living foraminifera with isotope ... discussions with NJS, was the fact that the isotopic composition of the test necessarily integrates the continuing calcification throughout the life ...

The oxygen and carbon isotopic composition has been measured for numerous Paleogene planktonic fo... more The oxygen and carbon isotopic composition has been measured for numerous Paleogene planktonic foraminifer species from Maud Rise, Weddell Sea (ODP Sites 689 and 690), the first such results from the Antarctic. The results provide information about large-scale changes in the evolution of temperatures, seasonally, and structure of the upper water column prior to the development of a significant Antarctic cryosphere. The early Paleocene was marked by cooler surface-water conditions compared to the Cretaceous and possibly a less well developed thermocline. The late Paleocene and early Eocene saw the expansion of the thermocline as Antarctic surface waters became warm-temperate to subtropical. The late Paleocene to early Eocene thermal maximum was punctuated by two brief excursions during which time the entire Antarctic water column warmed and the meridional temperature gradient was reduced. The first of these excursions occurred at the Paleocene/Eocene boundary, in association with a major extinction in deep sea benthic foraminifers. The second excursion occurred within the early Eocene at -54.0 Ma. These excursions are of global importance and represent the warmest intervals of the entire Cenozoic. The excursions were associated with fundamental changes in deep-water circulation and global heat transport.

Geological Magazine, 1992

From the unique perspective of the geological record, it appears that the ' Greenhouse Earth' was... more From the unique perspective of the geological record, it appears that the ' Greenhouse Earth' was a feature of climate for up to 80 % of the last 500 Ma, and that therefore our present glacially dominated climate is an anomaly. The Cretaceous in particular was a time of global warmth, an extreme greenhouse world apparently warmer than our current Earth. The geological record provides perspective and constraints against which the success of climate models can be evaluated. At present there are no ways of evaluating model predictions for the future of our ' Greenhouse Earth' until after the event. Retrodicting the past is therefore a very useful way of testing model sensitivity and robustness. The geological record tells us that the characteristics of the Cretaceous greenhouse world were a shallower equator-to-pole temperature gradient, shallow, well-stratified epicontinental seas with a tendency towards periodic dysaerobism, and a well-developed terrestrial flora extending to the high latitudes. Both marine and non-marine data show a global cooling trend throughout Late Cretaceous time, a trend that seems to correlate with declining atmospheric carbon dioxide.

Precambrian Research, 2005

Shallow intracratonic basins developed across a large area of the central part of the Australian ... more Shallow intracratonic basins developed across a large area of the central part of the Australian craton during the Neoproterozoic and continued to accumulate marine sedimentary successions until well into the early Palaeozoic—a half billion year sedimentary record. Carbonate successions ranging in age from Neoproterozoic (Cryogenian) to ostensibly Early Ordovician have been sampled at eleven sites across four of the northernmost of these basins (Amadeus, Georgina, Wiso and Daly Basins). A total of 996 samples were then analyzed for stable carbon (δ13Ccarb) and oxygen (δ18Ocarb) isotopes to develop a regional secular stable carbon isotopic curve. The curve complements earlier work and provides an important framework for global correlation at a critical time in Earth history during which the biosphere and atmosphere were evolving rapidly.At one site in the Amadeus Basin, diagenesis proved to have significantly modified the isotopic composition of the carbonates and the data were eliminated. Analysis of the remaining samples suggests that they reflect the global secular stable carbon isotope curve and tie well with established palaeontological timescales. In particular, key isotopic excursions can be identified in the earliest part of the Neoproterozoic succession, notably the negative excursion following the Sturtian glaciation. In the early Palaeozoic record a major excursion during Ordian–early Templetonian (509–506 Ma) time can be identified across the region as can the so-called SPICE excursion which has been associated globally with the Steptoean Stage of Laurentia (497.5–495 Ma). A smaller late Templetonian–Floran (506–503 Ma) positive excursion has also been recognized. The stable carbon isotope record provides a strong regional correlation in both fossiliferous and unfossiliferous Neoproterozoic and early Palaeozoic successions and allows a global correlation to be established.

Geology, 1993

Differences in depth ecology suggest that some chronospecies are not simply artifacts of taxonomy... more Differences in depth ecology suggest that some chronospecies are not simply artifacts of taxonomy but may have biological reality. ACKNOWLEDGMENTS Supported by National Science Foundation grant EAR 9106108 (to Nor-rie) and by the Department of Earth Sciences, Oxford ...

One of the most continuous and best studied continental stratigraphic sections spanning the Paleo... more One of the most continuous and best studied continental stratigraphic sections spanning the Paleocene-Eocene boundary is preserved on Polecat Bench in the northern Bighorn Basin. The mammalian biostratigraphy of Polecat Bench sediments has been well documented, and includes a major reorganization of faunas at or near the P-E boundary. To complement the existing biostratigraphy, we measured the isotopic composition of paleosol carbonate nodules at soil-by-soil temporal resolution through the P-E boundary interval. These measurements provide a detailed record of the abrupt, transient, carbon isotope excursion that affected atmospheric and oceanic carbon reservoirs at ca. 55 million years before present [Ma]. Tests of soil thickness and diagenesis indicate that trends in the record are primary, and reflect syndepositional changes in the 613C value of atmospheric C02. The carbon isotope record suggests that the 613C value of atmospheric C02 dropped by ca. 8%0 during this interval, and then rebounded. The pattern of change is very similar to that of an independent high-resolution record of Bains et al. (submitted). Changes in the 6180 of paleosol carbonates are consistent with a significant increase in local mean annual temperature during the P-E boundary event. Comparison of biotic and isotopic stratigraphies on Polecat Bench shows that faunal changes at the P-E boundary lag behind major events in the carbon and oxygen isotope records by about 10 thousand years [k.y.]. In: Paleocene-Eocene Stratigraphy and Biotic Change in the Bighorn where R = 1801160. Similarly, 613C is the deviation (in %o) of and Clarks Fork Basins, Wyoming (P. D. Gingerich, ed.), University of the carbon isotope ratio of a sample from that of a standard (V-Michigan Papers on Paleontology, 33: 73-88 (2001). PDB), where R = 13C112C.

Gff, 2000

... Geological Society Special Publication 101. Bains, S., Corfield, RM & Norris, RD, 1999: M... more ... Geological Society Special Publication 101. Bains, S., Corfield, RM & Norris, RD, 1999: Mechanisms of climate warm-ing at the end of the Paleocene. ... Lu, G. & Keller, G., 1993: The Paleocene-Eocene transition in the Antarctic Indian Ocean: Inference from planktic foraminifera. ...

After over 15 m.y. of evolution in near-surface waters of the Western Pacific and Caribbean, plan... more After over 15 m.y. of evolution in near-surface waters of the Western Pacific and Caribbean, planktic foraminifera in the lineage Globorotalia (Fohsella) abruptly invaded thermocline habitats at 13 Ma. Stable isotope data demonstrate that this habitat shift took 50 ka to complete, a duration similar to the fastest measured rates of speciation in marine protistans. The ecological change occurred near the end of a long series of gradual morphological transitions and demonstrates that at least some of the chronospecies in this lineage had distinctive ecologies and were probably biological species. Other than this one shift in depth distribution, skeletal evolution is largely disconnected from depth changes in Globorotalia (Fohsella). Morphological trends of globorotaliid foraminifera may not record changes in depth ecology, contrary to existing models for foraminiferal diversification.

Nature, 2000

The onset of the Palaeocene/Eocene thermal maximum (about 55 Myr ago) was marked by global surfac... more The onset of the Palaeocene/Eocene thermal maximum (about 55 Myr ago) was marked by global surface temperatures warming by 5-7 degrees C over approximately 30,000 yr (ref. 1), probably because of enhanced mantle outgassing and the pulsed release of approximately 1,500 gigatonnes of methane carbon from decomposing gas-hydrate reservoirs. The aftermath of this rapid, intense and global warming event may be the best example in the geological record of the response of the Earth to high atmospheric carbon dioxide concentrations and high temperatures. This response has been suggested to include an intensified flux of organic carbon from the ocean surface to the deep ocean and its subsequent burial through biogeochemical feedback mechanisms. Here we present firm evidence for this view from two ocean drilling cores, which record the largest accumulation rates of biogenic barium--indicative of export palaeoproductivity--at times of maximum global temperatures and peak excursion values of delta13C. The unusually rapid return of delta13C to values similar to those before the methane release and the apparent coupling of the accumulation rates of biogenic barium to temperature, suggests that the enhanced deposition of organic matter to the deep sea may have efficiently cooled this greenhouse climate by the rapid removal of excess carbon dioxide from the atmosphere.

Geology, 1996

ABSTRACT Isotopic analysis of lacustrine carbonates from the Eocene Green River Formation suggest... more ABSTRACT Isotopic analysis of lacustrine carbonates from the Eocene Green River Formation suggests that lake waters were derived partly from snow melt. This evidence for cool climates is in marked contrast to paleontological and model evidence for mild tempera-tures in the ...

Terra Nova, 1992

We have compared detailed planktonic and benthonic foraminiferal carbon and oxygen isotope record... more We have compared detailed planktonic and benthonic foraminiferal carbon and oxygen isotope records from the Palaeocene and early Eocene successions at DSDP Site 577 (Shatsky Rise, North Pacific), a composite section derived from DSDP Leg 74 sites (Walvis Ridge, South Atlantic) and a composite section from ODP Leg 113 sites (Maud Rise, Weddell Sea). The δ13C records of Palaeocene and early Eocene Foraminifera at Site 577 and the Leg 74 sites show that an increase in δ13C values in surface waters at 64 Ma (end of Zone P1) resulted in increased vertical carbon isotope gradients (δ13C) between surface and deeper dwelling planktonic foraminifera, and between surface-dwelling planktonics and benthonic foraminifera which became progressively steeper until the iniddle Late Palaeocene (Zone P4). This steepening also occurs in the latest Palaeocene of the composite Leg 113 section and can be explained by an increase in surface ocean productivity. This increase in productivity probably resulted in an expansion of the oxygen minimum zone (OMZ).Benthonic δ13C values increased during the late Palaeocene in Site 577 and the composite Leg 74 section, suggesting that the Palaeocene carbon isotope maximum was composed of both within-ocean reservoir (increased surface water productivity) and between-reservoir (organic carbon burial) ftactionation effects. The benthonic δ13C increase lags the surface ocean δ13C increase in the early Palaeocene (63–64 Ma) suggesting that surface water productivity increase probably led an increase in the burial rate of organic carbon relative to carbonate sedimentation. Moreover, inter-site δ13C comparisons suggest that the locus of deep to intermediate water formation for the majority of the Palaeocene and the earliest Eocene was more likely to have been in the high southern latitudes than in the lower latitudes.Oxygen isotope data show a decline in deeper water temperatures in the early and early late Palaeocene, followed by a temperature increase in the late Palaeocene and across the PalaeoceneEocene boundary. We speculate that these changes in deeper water temperatures were related to the flux of CO2 between the oceans and the atmosphere through a mechanism operating at the high southern latitudes.

Oxygen and carbon isotope analyses have been performed at close sampling intervals on rocks from ... more Oxygen and carbon isotope analyses have been performed at close sampling intervals on rocks from several exposures that show the boundary between the Wenlock and Ludlow Series in the classic Silurian areas of Wales, the Welsh Borderland, and the West Midlands of England. Our data indicate a monotonic decline in δ13C from positive to negative values across the boundary between the Much Wenlock Limestone Formation (Wenlock Series) and the Lower Elton Formation (Ludlow Series), and correlatives, in all sites investigated. A slightly earlier negative excursion is also present in the upper Wenlock strata of two of these localities. Both negative δ13C excursions appear to be contemporaneous with episodes of increased ocean ventilation and eustatic sea- level lowstand postulated by Kemp. At least one, and possibly both, of the late Wenlock carbon isotope depletions can also be related to the decline in pelagic graptolite diversity. The distribution of the carbon isotope depletion in both carbonate-platform and off-shelf facies implies that this trend is unlikely to have been caused by local diagenetic alteration. Isotope chemostratigraphy may also provide an extra correlation tool that can be integrated with traditional biostratigraphic methods for Silurian strata.

Nature, 2000

The onset of the Palaeocene/Eocene thermal maximum (about 55Myr ago) was marked by global surface... more The onset of the Palaeocene/Eocene thermal maximum (about 55Myr ago) was marked by global surface temperatures warming by 5-7°C over approximately 30,000yr (ref. 1), probably because of enhanced mantle outgassing and the pulsed release of ~1,500gigatonnes of methane carbon from decomposing gas-hydrate reservoirs. The aftermath of this rapid, intense and global warming event may be the best example in the geological record of the response of the Earth to high atmospheric carbon dioxide concentrations and high temperatures. This response has been suggested to include an intensified flux of organic carbon from the ocean surface to the deep ocean and its subsequent burial through biogeochemical feedback mechanisms. Here we present firm evidence for this view from two ocean drilling cores, which record the largest accumulation rates of biogenic barium-indicative of export palaeoproductivity-at times of maximum global temperatures and peak excursion values of δ13C. The unusually rapid return of δ13C to values similar to those before the methane release and the apparent coupling of the accumulation rates of biogenic barium to temperature, suggests that the enhanced deposition of organic matter to the deep sea may have efficiently cooled this greenhouse climate by the rapid removal of excess carbon dioxide from the atmosphere.

Geology, 1992

Carbon isotope excursion near the Wenlock-Ludlow (Silurian) boundary in the Anglo-Welsh area Rich... more Carbon isotope excursion near the Wenlock-Ludlow (Silurian) boundary in the Anglo-Welsh area Richard M. Corfield Department of Earth Sciences, University of Oxford Parks Road, Oxford 0X1 3PR, England Derek J. Siveter Geological Collections, University Museum, ...

Isotopic analysis of lacustrine carbonates from the Eocene Green River Formation suggests that la... more Isotopic analysis of lacustrine carbonates from the Eocene Green River Formation suggests that lake waters were derived partly from snow melt. This evidence for cool climates is in marked contrast to paleontological and model evidence for mild temperatures in the continental interior. Oxygen isotope ratios of carbonates frequently reach -12‰ to nearly -16‰ (Peedee belemnite), which suggests that lake waters probably had δ18O of <-13‰ (standard mean ocean water). Consideration of the evaporative 18O enrichment that typically occurs in modern large saline lakes suggests that the source waters to the Green River basin had a δ18O of <-18‰. These ratios are consistent with snow melt and are too negative to be easily accounted for by distillation in the atmosphere during heavy rainfall. The Green River lakes formed in a closed basin encircled by large mountains; this suggests that the snow melt was locally produced. The mountains surrounding the lake must have been high enough to occasionally supply significant melt water to the much lower lake. Lapse rate calculations suggest minimum altitudes of >3000 m for the mountains encircling the Green River basin.