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“THE AZOLLA STORY: HOW AN AMAZING PLANT CHANGED OUR CLIMATE 50 MILLION YEARS AGO”
by Jonathan Bujak
The talk is split into two because of its length.
The presentation describes a remarkable event that occurred in the Arctic 50 million years ago, when a unique floating freshwater plant called Azolla repeatedly covered the surface of the ocean for almost a million years. Due to its phenomenal growth, Azolla sequestered enormous quantities of the greenhouse gas carbon dioxide, and changed the Earth’s climate from a greenhouse world towards our modern icehouse climate with its permanent ice and snow at both poles. ‘The Arctic Azolla Event’ was discovered by the Arctic Coring Expedition (ACEX) when it recovered sediments beneath the North Pole in 2004. The discovery was featured in the New York Times (November 20, 2004) and National Geographic (May 2005), and its validity has now been confirmed by international teams of scientists who have investigated and published on the cores, including a series of papers in the scientific journal ‘Nature’.
The talk was presented by Dr Jonathan Bujak as the invited Keynote Address and various symposia, as well as lecture tours in Europe and North America.
The Arctic Azolla Event
The modern icehouse world is characterised by bipolar glaciation, resulting from relatively low levels of atmospheric CO2 and thermal isolation of the poles from warm lower latitude oceanic currents. In contrast, the Mesozoic greenhouse world had no permanent glaciation at either pole, with the greenhouse state continuing through the K/T boundary into the Paleocene.
At the end of the Paleocene, extreme warming during the Paleocene Eocene Thermal Maximum (PETM) was triggered by high levels of greenhouse gases due to extensive volcanism associated with the Greenland mantle plume, and the expulsion of submarine methane hydrates. This resulted in the highest temperatures known for the Cenozoic, characterising a supergreenhouse state that persisted through the Early Eocene. It is therefore surprising that various independent parameters indicate that the supergreenhouse climate was truncated in the earliest Middle Eocene by the initial shift towards modern icehouse regime. Estimates of atmospheric CO2 values show a major decrease at this time, but this cannot be explained by ‘normal’ sequestration processes. Instead, a unique geological event is proposed to explain this fall, centred on processes within the Arctic Ocean Basin.
“The Azolla Model” is based on ACEX (Arctic Coring Expedition) cores from Lomonosov Ridge plus unpublished data from 65 Arctic petroleum exploration wells. The model combines oceanographic reconstructions for the basin with a major decrease in greenhouse gases during the middle Eocene. The Early Eocene Arctic Ocean Basin was largely enclosed following uplift of the Greenland Mantle Plume, with elevated temperatures, evaporation and precipitation leading to increased runoff and the development of extensive surface freshwater plumes. These were colonised in the earliest Middle Eocene by floating mats of the opportunistic freshwater fern Azolla, which occurred periodically for about a million years as a series of repeated cyclical events.
Modern Azolla is one of the fastest growing plants on the planet and draws down large quantities of carbon and nitrogen. Calculations of carbon drawdown combined with the large potential areas of Azolla development in the Arctic, plus the million year time frame indicate levels of CO2 sequestration that are easily sufficient to shift the world from Mesozoic-Early Eocene greenhouse towards the modern icehouse world. The model also indicates the deposition of potentially widespread petroleum source rocks across the Arctic due to the massive carbon drawdown. It is currently being tested by multidiscipilinary teams at ACEX and various universities worldwide, and it has already attracted considerable attention including articles in the New York Times (November 20, 2004), National Geographic (May 2005) and Nature (2006 to 2011).
“ARCTIC CENOZOIC BIOSTRATIGRAPHY. TOWARDS A BASIN-WIDE SCHEME“
by Jonathan Bujak
Biostratigraphic zonation of the Arctic Mesozoic is facilitated by rich marine and nonmarine assemblages that reflected the warm greenhouse temperatures, but this situation altered dramatically during the Cenozoic. Temperature changes accompanying the greenhouse to icehouse shift had a massive impact in the Arctic, resulting in impoverished assemblages that are difficult to correlate with those from lower-latitudes using traditional biostratigraphic techniques.
It is therefore essential to use a scheme that integrates the shifts in sea-surface and air temperatures with changes in marine and nonmarine biotas. The resulting climatic-biostratigraphic scheme has Arctic-wide application because the Arctic Basin was centered on the North Pole throughout the Cenozoic and underwent similar temperature changes across the entire region. One exception is in the Oligocene of the Barents Sea which had warmer conditions due local inflow of the proto-Gulf Stream.
The succession of Cenozoic temperature changes documented in lower latitudes is replicated in the Arctic where they have a much stronger expression. The Arctic succession begins with a Paleocene to Early Eocene greenhouse state inherited from the Mesozoic, but marine dinoflagellates are less diverse than to the south, suggesting lower Arctic salinities due to large freshwater input and restricted marine inflow. At the end of the Paleocene, the PETM is well represented by an influx of the warm-water dinoflagellate Apectodinium, providing high-resolution correlation with lower-latitudes.
Following the base Middle Eocene Azolla Event, a series of cooling steps characterized the Middle and Late Eocene. These ended with major cooling at the Terminal Eocene Event, which affected both marine and nonmarine populations and resulted in the extinction of over 90% of dinoflagellate and angiosperm taxa across most of the Arctic. The succeeding Oligocene cold phase was truncated by increased Arctic temperatures that reflected global warming during the Miocene. This allowed dinoflagellates and angiosperms to migrate back into the Arctic, providing marine and nonmarine zonal markers that can be correlated southwards. Major cooling through the Plio-Pleistocene finally led to their decline across the region, and also resulted in the succession of orbitally-induced glacial-interglacial cycles that characterize today’s climate.
“PALEOCENE EOCENE OCEANOGRAPHY AND CLIMATE OF THE NORTH ATLANTIC: THE KEY TO A REGIONAL BIOSTRATIGRAPHIC SCHEME“
by Jonathan Bujak
The North Atlantic region underwent enormous changes during the Paleogene that affected marine and terrestrial biotas, as well as sedimentation and basin configuration. Open marine conditions during the Early Paleocene became increasingly restricted during the Late Paleocene due to uplift of the Greenland Mantle Plume. This uplift, and the extrusion of enormous quantities of subaerial and submarine basalts, resulted in separation of the North Atlantic region into three marine systems: the North Atlantic, North Sea and Baffin systems, separated by land bridges that permitted the migratory exchange of North American and Eurasian mammals.
At its peak, the basin separation resulted in the ‘End Paleocene Biotic Crisis’, with extreme basin restriction resulting in water stratification and bottom-water dysaerobia or local anoxia within the North Sea and Baffin systems. This affected both the benthic and planktonic populations: the latter were extinguished or restricted to extreme low-diversity agglutinated foraminiferal assemblages, whereas planktonic microfossils are represented by a few pyritized Coscinodiscid diatoms and dinoflagellate assemblages dominated by mainly carnivorous peridinioids.
Bottom-water anoxia and plankton blooms due to large-scale nutrient runnoff also resulted in the deposition of sapropel-rich sediments that are prospective liquid petroleum source rocks in both the North Sea and Baffin Systems. These have been buried deeply enough to be locally mature in some areas of the North Sea System, and they can also be predicted within the largely unexplored Baffin System.
The biotic crisis was overprinted by the Paleocene Eocene Thermal Maximum (PETM), aka the Early Eocene Thermal Maximum (EETM), which was triggered by the emission of enormous quantities of carbon dioxide greenhouse gas by the Greenland Mantle Plume. The resulting increased air and sea-surface temperatures (SST) released methane clathrates (gas hydrates) from rocks, and this potent greenhouse gas increased temperatures further during the PETM/EETM. This allowed the warm-water dinoflagellate genus Apectodinium to migrate from lower latitudes during peak warming when it became abundant in mid latitudes (the ‘Apectodinium acme event’), even reaching the Arctic and Antarctic polar regions where it is seen as an Apectodinium spike. Lush forests preserved as far north as Ellesmere Island in the Arctic attest to mean annual temperatures of 15oC, with the remains of cold-blooded turtles and alligators indicate that temperatures rarely fell to freezing.
Following the PETM/EETM, temperatures fell slightly, but remained high during the remainder of the Early Eocene (Ypresian) during the ‘Early Eocene Climatic Optimum’. This greenhouse world then shifted towards greenhouse due to the ‘Arctic Azolla Event’, when large areas of the mainly enclosed Arctic Ocean were repeatedly covered by the freshwater floating fern Azolla. Azolla was able to do this because of extensive surface freshwater plumes associated with high temperatures, rainfall and river discharge. The Arctic Azolla Event lasted for almost a million years and sequestered enormous quantities of atmospheric carbon dioxide, reducing values from between 2500 to 3500 ppm (parts per million), to less than 1750 ppm. This sequestration continued during the remainder of the Cenozoic, due to a combination of changing oceanographic currents and mountain uplift, eventually resulting in pre-industrial values of 285 ppm and our modern bipolar icehouse world with it succession of glacial-interglacial cycles.
Greenland Mantle Plume collapse occurred in the earliest Early Eocene (Ypresian) when restricted oceanographic connection was re-established between the Atlantic Basin and the North Sea and Baffin Systems. The North Sea and Baffin Systems experienced cooler water conditions than the Atlantic System during the Middle and Late Eocene, so that temperature-sensitive dinoflagellate species have different stratigraphic range, even in the Rockall and Faroe-Shetland basins that were just a few kilometres apart, but separated within the North Atlantic and North Sea systems respectively.
The ranges of temperature-sensitive dinoflagellate species can be plotted geographically and stratigraphically, providing mapable sea-surface isotherms, and this methodology can be extended into the Arctic Ocean where assemblages became increasingly impoverished due to temperature fall.
The ‘Terminal Eocene Event’ at the Eocene-Oligocene boundary resulted from a sudden and dramatic fall in temperature associated with oceanic isolation of the Antarctic landmass due to its plate tectonic separation from South America. This initiated the ‘Oceanic Global Conveyor’, first recognized by Wally Broecker, which sequestered atmospheric carbon dioxide to values below 1000 ppm, increasing Antarctic continental glaciation and lowering global sea-levels. The resulting ‘Grande Coupure’ marked large-scale extinction and floral and faunal turnover at the beginning of the Oligocene.
The Paleogene of the North Atlantic region therefore illustrates the intimate relationship between plate tectonic, volcanic, oceanic, atmospheric and biotic processes. It is not possible to fully understand and appreciate any of these individual processes without treating them all as a single inter-related unit.
“OFFSHORE NEWFOUNDLAND: SOUTH WHALE BASIN SOURCE ROCK STUDY”
by Jonathan Bujak
Upper Jurassic shales are generally considered to be the primary source for oil discoveries in the Grand Banks area of offshore eastern Canada. Biostratigraphic analysis indicates that these rocks are of Oxfordian to early Kimmeridgian age, coeval with the primary oil source in northeast Atlantic basins including the North Sea, Faeroe-Shetland and Porcupine basins. The Grand Banks of Newfoundland are underlain by a number of Mesozoic basins with hydrocarbon potential. These include the South Whale, Whale, Horseshoe and Jeanne d’Arc basins. The drilling of more than 70 wells has resulted in 15 significant oil discoveries, all located in the Jeanne d’Arc Basin. No hydrocarbon discoveries have been made in the Whale or Horseshoe basins, where much of the Upper Jurassic-Lower Cretaceous section is missing due to early Cretaceous (Avalon) uplift and erosion.
However, the South Whale Basin was located southwest of the axis of maximum uplift, and a more complete Upper Jurassic-Lower Cretaceous section has been preserved. n this basin, oil was discovered in Upper Cretaceous Petrel limestone in Heron H-73, with 22 bbl of 7-11.5°API oil being recovered on test. A small gas discovery has also been made in Tors Cove D-52, located in the cap rock (Iroquois Formation) of a salt diapir. All but one of the 13 wells drilled so far in the South Whale Basin have been located over salt diapirs, volcanic or basement highs, encountering incomplete Upper Jurassic-Lower Cretaceous sections with only limited data collected on prospective source rock and reservoir intervals.
Although the number of oil discoveries outside the Jeanne d’Arc Basin has been very small, previous stratigraphic and kerogen analysis has highlighted the presence of potential oil-prone source rocks in the Upper Jurassic section of the South Whale, Whale and Horseshoe Basin wells. In contrast, similar studies of Upper Jurassic rocks from Scotian Shelf wells do not appear to include a significant source for liquid hydrocarbons due to the predominance of gas-prone organic material. This ‘herbaceous-woody’ kerogen is quite different to the ‘amorphous sapropelic’ kerogen that characterizes oil-prone source rocks.
The principal objective of this study therefore was to investigate the source rock potential of Upper Jurassic rocks in the South Whale Basin area. This work has been carried out in three phases:
- Stratigraphic interpretation of the Jurassic-Cretaceous section in a suite of wells from the South Whale and Whale basins, calibrated with data from selected wells in the Horseshoe and Jeanne d’Arc basins, and the Scotian Shelf.
- Paleoenvironmental interpretation of these well data to identify paleoceanographic and other geologic events in the stratigraphic record.
- Production of a suite of paleogeographic and paleoceanographic maps for a series of late Jurassic and early Cretaceous time slices.