Atlas Symposium 2011 Abstracts
Prang Sinhabaedya, Octavian Catuneanu
The Exmouth Plateau is a part of the Northern Carnarvon Basin, offshore northwest Australia. It evolved from a pre-rift stage in the late Paleozoic, passing through syn-rift sub-basins in the Mesozoic to a passive margin in the Cenozoic. The Exmouth Plateau is 250 km away from the present-day coastline, and it lies 800 m below the sea level. The plateau covers 300,000 sq. km.
Within the Exmouth Plateau, the study area is a significant gas exploration target, identified as the Chandon Field. The Chandon-1 well was drilled in 2006 and is the only well that provides borehole data in this study. The seismic data penetrates up to 6 seconds two-way travel time, and covers an area of 1000 sq. km. The information regarding the basin evolution in the Paleozoic is scarce, as the main exploration interest rests with the Mesozoic and the Cenozoic sections.
In order to understand the evolution of the depositional environments and the paleogeography, 3D seismic data have been interpreted by means of horizon slicing. In this study, most of the time was dedicated to the generation and analysis of horizon slices. The interpretation of ten seismic horizon slices unfolds information about the provenance of sediments, which are derived from various sources of Triassic, Jurassic, Cretaceous and Cenozoic age. Early results of 3D seismic interpretation also reveal that sedimentation of the succession studied in the Chandon Field took place primarily in a deep-water setting.
Khalid M. Javaid
The Kennetcook-Windsor Basin is a part of the large composite Maritimes Basin in Atlantic Canada. Subsurface structural geometries interpreted on the available seismic dataset include: tilted fault-blocks bounded by high angle normal and reverse faults at the basement level; both negative and positive flower structures; imbricate structures bounded by overlapping listric reverse faults within the Horton Group rocks; structural collapses or dissolution features within the basal Windsor Group indicating evaporite mobility that initiated diapiric movement. Structural collapse features within the Windsor Group indicate a major post-Visean extensional episode in the basin that caused evaporite withdrawal and created accommodation space for the Pennsylvanian sediments in the basin. Flower structures mapped in the subsurface clearly indicate a strike-slip setting that remained active during the entire history of the basin and controlled the development and structures in the basin. Subsurface seismic data indicate a very complex basinal history in terms of syn-depositional deformation and superimposition of numerous episodes of fault reactivation in the basin. Faults mapped and correlated at various levels can be subdivided into six categories: normal faults; reverse faults; normal inverted faults that have normal offset at the top of basement and a reverse offset component up-dip; and reverse inverted faults that have reverse offset at the top of basement and normal offset up-dip. TWT structure map at the top of basement shows tilted fault-blocks stepping down to north and northeast. Faults in the west and south show intense inversion and caused uplift of the top of basemen. TWT maps at the tops of the Horton Bluff and the Cheverie formations show a structural low in the central area and rising in the northeast, west, and south. However, the structural low on the top of the Cheverie Formation is narrower and indicates that the faults in the northeast were inverted much as compared to those on the top of the Horton Bluff Formation. Comparison of the thickness maps of the Horton Bluff and the Cheverie formations indicate an overall thickening in the north and northeast. Probably oblique movement (SW-NE) on the Minas Fault affected the basement architecture and the opening of the basin. Wrench tectonics caused the tilting of the fault-blocks and controlled the syndepositional deformation in the basin. Deposition of the Horton Bluff Formation in an extensional setting represented by faults of category I marks the initial development of the basin and the first episode of extension. The second category of faults marks a short break in an overall extensional setting prevailed in the beginning of the basin development. Inversion along the basement-cutting faults (category II) indicate second episode of deformation which was restricted to the basal part of the Horton Bluff Formation. Third episode in the southern part of the Maritimes Basin (study area) provided an extensional setting until the deposition of the Upper Horton Group (Cheverie Formation) in the basin. The faults in category III having normal offsets at basement and the shallower levels mark this third episode in the basin. . Inversion along the faults of category IV suggests that there was uplift in the basin after the deposition of the Cheverie Formation. This uplift and erosion of the upper part of the Horton Group marks the fourth episode in the basin. Most of the faults interpreted within the Windsor Group terminate within the group and do not extend up-dip or down-dip into the older or younger sediments except some listric normal faults that extend up-dip and cut through the Scotch Village Formation. Intense deformation within the Windsor Group could be attributed to the fifth episode in the basin. Gently dipping to almost horizontal seismic reflections within the Cumberland Group (Scotch Village Formation) indicate that the deformation is post-Mississippian and related to an extensional episode (sixth) in the basin.
The Lower Triassic Montney Formation consists primarily of shoreface and turbidite deposits which accumulated along the north-western coast of Pangea. It records the deposition of sandstone, siltstone and dolomitic packstone/grainstone (coquina) with a mineral content consisting dominantly of quartz, dolomite, potassium feldspar, plagioclase, and mica (primarily muscovite). Clay minerals rarely occur in excess of 2 to 8%. In addition to numerous conventional oil and natural gas reservoirs, in the past several years the Montney Formation has become one of the primary focuses of unconventional gas exploration. Despite this recent interest in the ‘shale’ intervals of the Montney, however, the overall composition remains poorly understood. Past publications have focused largely on the conventional reservoir intervals (such as the Coquinal Dolomite Member and the Montney Turbidite interval) which comprise less than 10% of Montney Formation. Fine-grained intervals, despite comprising the bulk of the Montney’s thickness, have received scant attention and thus our understanding of the sedimentologic and stratigraphic evolution of the Montney Formation remains lacking. Until this void is filled, regionally predictive facies models will remain conjectural. By using a micro-computed tomographic (micro-ct) scanner, in partnership with an electron microprobe, 3-D analyses of the mineral composition and fabric of the Montney fine grained intervals have been attained.
Samples of the Upper Montney Formation (obtained from core from the Kobes area of northeastern British Columbia, Canada) are utilized in this study. Mineral phases have been correlated with specific density signatures identified with the micro-ct scanner, thereby characterizing the mineralogy of fine-grained Montney samples. Traditional techniques such as point counting are generally used to determine the mineral content in fine grained successions (such as the Montney), however these techniques are time intensive and may be inaccurate. By calibrating measurements obtained in the micro-ct scanner with elemental maps obtained with an electron microprobe, problems associated with traditional thin section analysis, where grain size can be misinterpreted because of random grain orientation, can be avoided. The scanner has the ability to measure at resolutions as high as 1um allowing for very small mineral grains to be quantified.
Robynn Dicks, S.E. Dashtgard, J. Suter, M. Gingras
The Columbia River Delta, northwest U.S.A. is a complex depositional environment, wherein the neoichnological and sedimentological character of fluvially dominated, tide-influenced brackish-water subenvironments can be established. Although several neoichnological studies have considered bioturbation in brackish-water, the neoichnological characterization of very-low-salinity fluvial-tidal settings has not been presented in the literature.
The aim of this study is to identify and interpret neoichnological trends of tide-influenced bars along a longitudinal transect of the Columbia River Delta (i.e., from the fluvial-dominated through to the tide-dominated regions of the distributary). The collected dataset includes: ichnological observations from x-rays and sediment peels, grain-size analyses, total organic carbon (TOC), and salinity concentrations. The first-order control on ichnological distributions appears to be salinity, which decreases very gradually landwards. Trace assemblages throughout the Columbia River Delta are typical of the Teichichnus Ichnofacies (c.f. Pemberton et al., 2010), and the diversity of traces decreases landwards. Near the mouth of the delta (i.e., 5 km inland from the Pacific Ocean), at salinities of 12 ppt, trace diversity is comparably high, and includes modern burrows akin to Skolithos, Arenicolites, Polykladichnus, Palaeophycus, and Siphonichnus. Twenty to 40 km landward, salinity reaches only 2 ppt, but the river still experiences notable tides. The trace assemblage here is lower in diversity, and includes Skolithos, Arenicolites, and Planolites; although in some sheltered locales, the trace assemblage also includes Thalassinoides and Polykladichnus. Locally, very high bioturbation intensities are observed. Fifty km inland, fluvial processes progressively dominate with maximum salinities of approximately 0.5 ppt. At this landward position, the trace assemblage includes Skolithos, Arenicolites, Planolites, and locally Siphonichnus.
The longitudinal mapping of neoichnological distributions of the Columbia River Delta reveals a decrease in trace diversity with decreasing salinity. At near-freshwater salinities, a brackish-water trace assemblage is still prominent, providing evidence for marine larval recruitment into fluvial-dominated regions of the delta.
Luke McHugh, John-Paul Zonneveld, William S. Bartels, Greg G. Gunnell
The Green River Basin of southwestern Wyoming preserves a continental succession of fluvial and lacustrine deposits. Extensive outcrop exposures of the Early Eocene Cathedral Bluffs Tongue of the Wasatch Formation occur at the northern margin of the basin near South Pass, Wyoming. The succession is dominated by fluvial floodplain and channel deposits with subordinate lacustrine interbeds. Coarser fluvial sediments occur proximal to the Wind River mountain range, with the proportion of lacustrine interbeds increasing to the south. Climatic and tectonic influences caused a regression of Paleolake Gosuite, resulting in dominantly fluvial deposition within the study interval. Intermittent movement along the thrust fault caused periodic lake-level fluctuations resulting in occasional lacustrine oil shale interbeds.
Correlations using traditional methods such as detailed facies analysis and spectral gamma are inadequate for this succession. This is in part due to the complexity of the succession, where abrupt lateral facies changes are intercalated with unconformities, making basin-wide correlations difficult. As a result, alternative methods have been utilized to correlate the units. Detailed whole-rock geochemistry has been used to identify elemental changes and trends throughout the Cathedral Bluffs Tongue. Samples were taken at one-meter intervals and analyzed for 61 elements using Inductively Coupled Plasma Mass Spectrometer (ICP-MS).
Specific intervals show distinct chemical features, which assist in splitting the sections into chemostratigraphic zones. Each zone has a certain geochemical signature that has been identified and correlated across the study area. The chemical characteristics for each facies change vertically through the section and demarcate important stratigraphic positions. These changes in elemental concentrations are linked to subtle changes in sediment provenance, caused by tectonic activity during this time. Other factors, including weathering and diagenesis, may significantly alter the original geochemistry of the succession during burial. These post-depositional factors must be taken into consideration when studying a geochemical dataset.
Daniel Brown, Gerhard Reuter
The Athabasca oil sands development in northeast Alberta has disturbed more than 500 km2 of boreal forest through surface mining and tailings ponds development. This paper examines the effect of the oil sands development on the temperature, precipitation, and lightning. We compared temperature and precipitation at a weather station within the oil sands development with those away from the oil sands. Lightning activity near the oil sands was also compared with lightning further away. We conclude that the oil sands development does not significantly affect lightning or precipitation, but does significantly affect the temperature regime. Over the past 17 years, the summer daytime high temperatures near the oil sands have decreased about 0.7 °C compared to the regional average, while the overnight low temperatures have increased about 1.2 °C. This is consistent with changing the land cover to a lake, and is likely a result of the construction of large tailings ponds.
Carolyn Currie, Murray K. Gingras
The proposed depositional model for the Cold Lake oil sands deposit is an estuarine incised valley fill comprising of fluvial deposits through tidal bar sediments. Thereby much of the Clearwater Formation in the area display low-diversity brackish-water trace-fossil suites that are dominated by Planolites, Teichichnus, Cylindrichnus, Terebellina, Skolithos, Palaeophycus, and in some settings Gyrolithes. However, detailed core analysis — including documentation of physical and biogenic sedimentary structures — reveals comparably diverse ichnofaunal assemblages are identified in the medial sequence of the Clearwater Formation in the Cold Lake area. The trace-fossil assemblage observed includes Planolites, Teichnichnus, Thalassinoides, Skolithos, Cylindrichnus, Asterosoma, and Arenicolites. Also seen in many of the core were traces such as Rhizocorallium, Siphonichnus, Scolicia, and Asterosoma. Most of the observed trace fossils are sporadically distributed throughout the interval, however Asterosoma and Rhizocorralium are most abundant in the lower part of the sequence. The reported trace assemblage is more consistent with sedimentation and animal colonization in fully marine conditions. Thus, the presence of these traces in the majority of core examined suggest that the proposed depositional model—i.e. tidal estuary—is questionable at the studied interval. We assert that the depositional setting occupied an embayed area that received sediment from the Clearwater hinterland, but generally maintained a marine salinity. This hypothesis leads to stratigraphic implications including that the medial strata may represent high-stand sedimentation rather than the transgressive sediment accumulation associated with incised valley fill.
Daniel Brown, Gerhard Reuter
Jenna Phillips, Mark Caplan, Murray K. Gingras, George S. Pemberton
The Lower Cretaceous McMurray Formation is host to a significant bitumen resource within the MacKay River area of the Athabasca Oil Sands in north-eastern Alberta. This clastic succession is situated west of the main valley fairway, within one of several clastic catchments entrenched into the underlying Devonian paleo-surface. The McMurray Formation comprises a complex succession of northwest-trending, amalgamated, tidal sand bars that erosionally truncate a thinly preserved package of estuarine deposits. These laterally continuous embayment-filling marine tidal sand bar complexes depart from the conventional, laterally heterogeneous fluvio-estuarine point bar sands observed in the main valley fairway.
Integrated sedimentologic, ichnologic, and stratigraphic studies of over 55 cores and 200 well logs from the MacKay River area has resulted in a depositional framework that comprises 7 facies associations (FA1-FA7). Estuarine deposits (FA1-FA2) are dominated by heterolithic media and are characterized by a brackish-water trace fossil suite dominated by Cylindrichnus, Gyrolithes and Teichichnus. Bay-fill deposits (FA3-FA6) are dominated by linear sand bodies representing amalgamated, laterally accreting bay-margin- and island-attached tidal bars and highly burrowed fair-weather / interbar areas. These deposits illustrate higher diversities and larger marine traces of an overall proximal Cruziana ichnofacies. Lower shoreface to distal offshore deposits of the Wabiskaw Member (FA7) overlie deposits of the McMurray Formation and are separated by a widespread erosional surface.
The McMurray Formation accumulated in a secondary northwest-trending paleo-valley and reflects a transition from an estuary to a broad marine embayment. Middle McMurray estuarine deposits occur at the base of the succession and represent the initial transgression and filling of the paleo-valley, where distribution was controlled largely by Devonian structure. These deposits reflect a tide-dominated marginal marine setting that was confined within an alluvial valley. Overlying Upper McMurray deposits reflect tide-dominated to mixed wave-tide influenced sedimentation and are separated from the underlying estuary by a regionally extensive ravinement surface. The upper McMurray reflects deposition that was unconfined, within a shallow marine embayment, infrequently affected by storms. This setting is further characterized by a free exchange of fully marine waters, a complete marine source of sedimentation, and negligible fluvial input.
Rui Wang, Jeremy Richards
The Himalayan-Tibetan orogen had a complex early geological history, and is a natural laboratory to study continent-continent collision tectonism and magmatism. Understanding its evolution is of importance to our comprehension of continental tectonics. In addition, there are several metallogenic belts in the orogen including the porphyry Cu-Mo, orogenic Au, complex REE, and vein-type Zn-Pb-Cu-Ag deposits. In order to understand their evolution and constitute the framework of continental metallogenesis, it is necessary to understand the tectonomagmatic evolution within the Tibetan margin from pre-collision, through collision, to post-collision.
A review of tectonomagmatic evolution of the Tibet margin from pre-collision, through collision, to post-collision suggests the Tibetan margin, as an active margin during the subduction of Neo-Tethys, has a complex geological history. The Paleozoic and Mesozoic tectonic histories have a strong influence on the Cenozoic history and strain distribution in the Himalayan-Tibetan.
During the Late Carboniferous and Early Permian, rifting occurred along the northern margin of the Lhasa terrane causing the separation of the Qiangtang block, and the opening of the Bangong-Nujiang Ocean. The southern margin of the Lhasa terrane experienced a rifting event during Permian- Late Triassic, which caused the initial separation of the Lhasa block from India and the opening of the Neo-Tethys Ocean. The Bangong-Nujiang Ocean was still in the process of active opening and closed in Late Jurassic. The Lhasa terrane drifted northward and collided with the Qiangtang terrane during the Late Jurassic-Early Cretaceous. The Gangdese granitoids and Linzizong volcanic rocks located in the southern Tibet have been widely regarded as the products of Andean-type northward subduction of the Neo-Tethyan oceanic lithosphere under Asia. The onset of the Indo-Asian collision at ca.40-60 Ma led to a significant north-south crustal shortening and major deformation events. A large amount of potassic-ultrapotassic volcanic rocks, adakitic rocks and leucogranites developed in the Indo-Asian post-collisional environment.
Dennis Rippe, Martyn Unsworth
The Himalaya and the Tibetan plateau have been formed by the collision of the Indian and Asian plates(1). Several geodynamic models have been suggested to explain the evolution of the Himalayan orogen and the Tibetan plateau and define the overall mass balance required in this continent-continent collision. The observed deformation may occur through tectonic processes that range from brittle deformation with a discrete set of crustal blocks to ductile deformation with spatially continuous distribution.
Models invoking ductile deformation through topography-induced flow in a weak lower crustal layer have been successful in explaining a number of geological and geophysical observations (2,3). Geophysical observations indicate that this weak layer at mid- to lower crustal depths in Tibet may be the result of partial melting (4). Laboratory studies indicate a one order reduction in strength for melt fractions of 5 to 10 percent (5). By relating these laboratory studies to magnetotelluric observations, which are sensitive to the presence of partial melts, it is possible to estimate the flow parameters associated with flow in this weak lower crustal layer (6).
For the Central Tibetan Plateau, if the weak lower crustal layer consists of partially molten felsic rocks, calculations show that conductances in the range 7000 - 27,000 S will produce flow velocities of the order 1 cm/a. Beneath the southern part of the Lhasa block and the Qiangtang terrane magnetotelluric studies indicate conductances of up to 20,000 S (7,8). These conductances suggest effective viscosities of 2.5·10 (18) - 3·10 (20) Pa s, corresponding to flow velocities between 0.02 and 4.5 cm/a (6). Together with higher pressure gradients near the margins of the plateau these flow parameters clearly support ductile deformation through crustal flow in these parts of Tibet.
Beneath the northern Lhasa block lower conductances of 3000 S are reported (9). Assuming a felsic rock composition, the minimum effective viscosity of the weak lower crustal layer beneath the northern Lhasa block is estimated as 3·10 (20) Pa s. The corresponding flow velocities do not exceed 0.04 cm, making deformation by crustal flow in this region unlikely (6).
Letian Zhang, Gaofeng Ye, Wenbo Wei, Sheng Jin
SinoProbe is a Chinese government-funded scientific program with the overall aim of investigating the structure and evolution of the continental crust and lithospheric mantle beneath China. This will use the latest geophysical technologies for real-time data acquisition, with a focus on imaging the deep crustal and upper mantle structures with the highest resolution possible. These data, along with advanced methods of computation and modeling, will allow scientists to address some of the outstanding questions about the deep structures and evolution of the Chinese continental lithosphere. The initial 5 year phase of SinoProbe will take place from 2008 to 2012, with an integrated program aimed at improving exploration techniques, data acquisition and storage, and developing an appropriate computing environment.
A sub-project of SinoProbe is focused on the tectonic study of North China and Tibetan Plateau using a 3D MT observational network. This is planned to use a grid of 330 MT grid nodes, with MT data recorded at a total of 3630 MT locations. The MT data will be collected in two regions with a spatial distribution of 1° × 1° during the initial 5 year phase of SinoProbe (2008 -2012). Field work for data acquisition of all 1375 MT sounding sites in North China was completed in January 2011. The next phase of MT data collection on the Tibetan Plateau will begin in spring 2011. Some primary inversion results will be presented and discussed in this presentation.
Matthew J. Comeau, Letian Zhang, Martyn Unsworth
The Tibetan plateau is the largest topographic feature on Earth, and has a crustal thickness up to 85 km and an average elevation of 5 km. The plateau was formed by the ongoing continent-continent collision between India and Asia.
The tectonic processes that occur during continent-continent collisions are not fully understood and many models have been proposed to explain them. Horizontal motions are clearly important, as evidenced by the major strike faults that characterize the Northern and Eastern parts of the Tibetan Plateau. However, the contribution of horizontal motion on these faults to the overall mass balance of the orogen is still not resolved.
The INDEPTH project has undertaken a series of integrated geological and geophysical studies across the Tibetan Plateau since 1993. The final stage of the INDEPTH study has been focussed on the dynamics of the Northern Tibetan Plateau. As part of this study, a series of magnetotelluric (MT) profiles have been collected across the Altyn-Tagh Fault in Qinghai and Gansu provinces.
The MT method has been previously used to study strike-slip faults and shear zones and can delineate subsurface fluids through their influence on crustal and upper mantle electrical resistivity. Results of the Altyn-Tagh Fault MT study will be presented and their tectonic significance discussed.
Yan Zhan, Martyn Unsworth, Zhao Guoze, Wang Weimao, Wang Jijun, Xiao Qibin
The northeastern margin of the Tibetan Plateau is a region where the ongoing collision between of Indian and Asia causes both crustal thickening and strike slip motion. A series of major strike slip faults accommodate the eastern motion of the crust (Altyn Tagh, Kunlun and Haiyuan Faults). The Haiyuan Fault is the most northerly of these faults and has generated a number of major earthquakes in the last century.
Magnetotelluric exploration is a powerful tool for imaging crustal structure in regions undergoing active tectonics. This study presents a new magnetotelluric dataset that has been used to study the shallow fault zone structure of the Haiyuan fault and its regional tectonic context. The study area is 99º-110ºE, 33º-40ºN, and encompasses several major tectonic units including the Bayankala block, Qaidam block, Alashan block and Ordos block.
The study reveals a region of low resistivity is present in the crust to the south of the Haiyuan fault zone, but is absent to the north. This implies a major reduction in strength and a change in the mode of deformation across the Haiyuan fault. This pattern of resistivity variation has also been observed on other margins of the Tibetan Plateau.
Dunia Blanco, Rui Zhang, Vadim A. Kravchinsky, Leping Yue
Detailed paleomagnetic studies done on Burqin (44 to 25 Ma, 48.0°N/86.7E°) and Tieersihabahe (25 to 17 Ma, 46.7°/88.5°) sections of the northern Junggar Basin, china are presented. Magnetostratigraphy and paleontology give a high resolution chronology which suggests a relatively low rate of sedimentation that gradually increased from 0.76 cm/kyr at 45 Ma to 2.9 cm/kyr at 23 Ma. Our results demonstrate counterclockwise tectonic rotations in Burqin and Tieersihabahe (–17.2 ± 9.6° and –11.8 ± 6.1°, respectively) as well as considerable northward latitudinal displacement (12.2 ± 6.5° and 9.7 ± 4.1°, respectively) with respect to Europe. Results are consistent with the motions of adjacent blocks in the same geological time interval (India, north and south China, Tarim, Amuria, and Kazakhstan). From 40 Ma to 20 Ma no significant intracontinental shortening or vertical-axis rotation is observed for the Junggar block. Our results suggest that major intracontinental rotation and compression between Junggar and northern Europe occurred after 20 Ma due to continuous penetration of India into Asia. We interpret that such intracontinental compression and relative rotations lead to the formation of the Lake Baikal rift system and the uplift of the Altay Mountains.
Chelsea Fefchak, John-Paul Zonneveld
The Upper Triassic (Late Ladinian- Mid Carnian) Charlie Lake Formation is a prolific producer of hydrocarbons in northeastern British Columbia. The lithological fabric is composed of a diverse assemblage of unfossiliferous siliciclastic, carbonate, and evaporite rocks. Historically, these rocks have been interpreted to represent a sabhka or back barrier depositional environment (Arnold, 1994; Higgs, 1990). Petroleum production from the Charlie Lake Formation commonly occurs in 3 main reservoir types: transgressive shoreface units, dolomitic mudstone/siltstones, or aeolian dunes (Zonneveld, 2008).
Sedimentological observations of core data from the Brassey Field indicate that the reservoir flow units are wind induced dune structures. The preservation of these aeolian dune facies is controlled by a variety of factors including, but not limited to, wind direction, sediment supply, and water table-sediment interaction. Within the Brassey Field, our correlation strategy of reservoir units enables us an opportunity to offer a new model of reservoir predictability for aeolian reservoirs in the Charlie Lake Formation. Comparison of subsurface data from the Brassey Field with two outcrop exposures near Williston Lake, British Columbia offered similar observations with regards to the sedimentology and depositional fabric. This unique methodology of combining outcrop and core data permitted new insights into the facies relationships, geological history, and depositional controls of the aeolian dune facies during the Upper Triassic.
Alexandra Der, Brian Jones
Grand Cayman, like many islands throughout the Caribbean Sea, has a Tertiary succession that developed on an isolated bank that was surrounded by deep oceanic water. Given that facies development on that bank was controlled primarily by water depth, the succession can be viewed as a “oceanic dip-stick” that reflects changes in sea level. The challenge is to interpret those changes and determine if they reflect eustatic and/or tectonic controls.
Grand Cayman is a small (about 196 sq. km.) island located on the Cayman Ridge that delineates the southern boundary of the North American Plate. The Bluff Group, formed of Brac Formation (Lower Oligocene), Cayman Formation (Middle Miocene), and the Pedro Castle Formation (Pliocene), is a sequence of carbonates that developed through a succession of deposition-erosion cycles. Core and well cuttings from wells on the eastern part of Grand Cayman, to depths of 275 m, encompass eight facies that are based mainly on the coral assemblages, matrix compositions, and other allochems.
Despite pervasive dolomitization of the succession, original facies are still evident. Facies range from benthic foraminifera mudstone/wackestone to benthic foraminifera packestone/graintstone and coral-rhodolite floatstone. The abundant colonial corals throughout the succession indicate that deposition took place on a bank within the photic zone. There is no evidence of reef development other than isolated thickets of Porites and/or Stylohpora that grew in shallow, low-moderate energy settings. Although rhodolites are found across the bank, they are more common on the bank edge where higher energy levels existed. Large benthic foraminifera are most abundant in shallow water facies whereas planktonic foraminifera are found only in the deeper water facies.
The Tertiary succession evident in the 245 m of strata available from the wells, records two shallowing-upward sequences in the Cayman Formation. In each sequence, deeper water coral assemblages with planktonic foraminifera grade into shallower water coral assemblages and benthic foraminifera sand. These sequences, which correlate roughly with known sea-level curves for the Middle Miocene, indicate that there were two shallowing events in the Middle Miocene followed by a significant lowstand in the Late Miocene. This lowstand is probably the Messinian lowstand event, which probably formed the Cayman unconformity at the top of the formation.
Hongwen Zhao, Brian Jones
On Cayman Brac, the Oligocene Brac Formation (> 60 m thick) is formed of intercalated limestones and dolostones whereas the Miocene Cayman Formation (~ 100 m thick) is formed entirely of dolostone. The dolostones are formed of low-Ca calcian dolomite (LCD < 55 mol% CaCO3) and high-Ca Calcian dolomite (HCD > 55 mol% CaCO3). The Brac Formation is formed of sucrosic, coarsely crystalline dolostone (crystals up to 1.5 mm long) with fabric-destructive textures, whereas fabric-retentive, finely crystalline (crystal size < 20 μm long) dolostones dominate the Cayman Formation.
Dolostones from the Brac Formation have δ13C ranging from 1.4 ‰ to 3.1‰ and δ18O from 1.4 ‰ to 3.0‰, Sr from 56 ppm to 820 ppm, Fe from 52 ppm to 340 ppm, and Mn from 9 ppm to 114 ppm. Dolostones from the Cayman Formation have δ13C ranging from 1.6‰ to 3.5‰ and δ18O from 1.5‰ to 4.0‰, Sr from 174 ppm to 275 ppm, Fe from 92 ppm to 254 ppm, and Mn from 7 ppm to 38 ppm. There is an inverse correlation between the δ18O values and mol % CaCO3 (r2=0.61) and a positive correlation between the Sr content and mol % CaCO3 (r2=0.72). These correlations probably reflect kinetic effects rather than extrinsic factors linked to the composition of the dolomitizing fluids. Calculations based on δ18O, corrected for possible biases associated with the mol % CaCO3 and phosphoric acid fractionation, indicate that the dolostones in both formations formed from normal seawater-like fluids at temperatures of 25 – 28°C. The Sr, Fe, and Mn contents of the dolostones indicate that dolomitization was mediated by normal seawater in surface environments without the influence of hydrothermal fluids. The lack of correlation between δ13C and δ18O indicates that meteoric water did not play a significant role in the dolomitization processes.
Based on 87Sr/86Sr ratios, a two-episode dolomitization model is proposed with the first phase in the Late Miocene (6-10 Ma) and the second phase in the Pliocene to Early Pleistocene (1-5 Ma). The lack of correlation between the 87Sr/86Sr ratios and other geochemical data indicates that the each phase of dolomitization was mediated by fluids of similar compositions. The first episode of dolomitization event caused partial dolomitization of the basal part of the Cayman Formation and the Brac Formation. The second dolomitization event completed dolomitization of the Cayman Formation and may have partly influenced the top of the Brac Formation. The stratigraphic distribution of the dolostones, their geochemical signatures, and time of formation indicate that dolomitization was ultimately controlled by changes in sea level.
Tibor Lengyel, Benjamin Rostron
Understanding the geothermal field of the Phanerozoic strata of Saskatchewan is important for many reasons including: predicting hydrocarbon generation/ migration, assessing geothermal energy resources; and selecting CO2 storage sites. The last major study of the geothermics of Saskatchewan was conducted in the early 1990s as part of a larger geological mapping project on the Western Canada Sedimentary Basin (1). That study utilized only bottom-hole temperature-values (BHT) measured during geophysical logging. Many studies have shown that temperatures mapped from BHTs are notoriously unreliable and there is no consensus on methods to correct BHT-derived temperatures.
Since the 1990s there have been numerous developments that merit further investigation of the geothermal field of Saskatchewan. Those developments include: an increased interest in temperature fields for utilization of geothermal energy; many additional (deeper) temperature data, prompted by deep rights reversal in 1997; studies identifying errors in case of BHTs (2) not taken into account in earlier geothermal work in Saskatchewan; and several recently-published techniques for correcting BHT data. For the aforementioned reasons a new study of the geothermics of Saskatchewan has been undertaken.
Within the frameworks of the present investigation newer BHT’s have been added to the older data. As a new approach other types of temperature measurements that give a better representation of formation temperature have been obtained as well: temperature measurements from drill stem tests; production tests; temperature logs; and potash mine-temperature measurements. These data are less thermally disturbed than BHT’s. Consequently, one major question to be addressed was the way, how different types of measurements can be integrated and used together.
For addressing this question first temperature data have been filtered for erroneous values with newly developed culling methods (e.g. for seasonal variation in data). Then values are homogenized with statistical fitting similar to what was utilized in different earlier studies (4). Temperatures thus obtained will be plotted on maps for major aquifers.
This talk will highlight the characteristics of the newly-obtained different data types and their integration methods, and some of the newest results of the study.
Rameses D'Souza, Larry Heaman, Tom Chacko
Mafic dykes are thought to be feeders to the high-volume, short-lived, and as yet poorly understood phenomenon of Large Igneous Provinces (LIPs), and they are commonly the only indication we see of Paleozoic and older LIPs. Proterozoic mafic dykes at Tsu Lake (NT; 1), and Uranium City (SK; 2,3) have been tentatively correlated with the 1827 Ma (4) Sparrow Dyke Swarm (NT; 5), on the basis of their roughly similar ages and petrography (1,2,3,4). No geochemical comparisons were possible due to lack of such data from the Sparrow Dykes, however dykes at Tsu Lake trend parallel to the Sparrow Dyke Swarm (i.e. 130°), supporting their correlation. The regional extent of dykes with this trend is at least 70,000 square kilometers, with the Tsu Lake locality at the southwest edge of the area.
In this presentation, preliminary geochemical analyses of samples recently collected from all three dyke suites will be used to test the previous authors' correlations. These data indicate that the samples fall into at least two distinct geochemical groups. Samples from a single locality may occur in just one such group, or be distributed between groups. This invokes two possible scenarios; one in which the dykes were emplaced in two short-lived events, tapping two different sources; or a single, long-lived event, with a single source whose composition changes with time and/or degree of crustal contamination. Neodymium isotopic data indicate that the latter is a more likely situation.
Certain dykes from the Northwest Territories and from around Uranium City exhibit abnormally elevated chondrite-normalized REE profiles and, in Saskatchewan, are spatially associated with copper-nickel mineralization (6). These dykes are petrographically unique, but similar to each other, and plot in a distinct geochemical field. The only other contemporaneous magmatic rocks in the region are the ultrapotassic volcanic rocks of the Christopher Island Formation (7).
Daniel Tersmette, Tom Chacko, Larry Heaman, Andy DuFrane
The Queen Maud block (QMB) is a subdivision of the Canadian Shield’s Churchill craton. The QMB is bounded to the west by the Thelon magmatic zone, which divides the Churchill and Slave cratons. Despite its key tectonic position at the boundary between these two cratons, the QMB remains relatively understudied. Early studies conducted by the Geological Survey of Canada revealed that the area is dominated by granitoid rocks that have been metamorphosed under upper amphibolite- to granulite-facies conditions (1, 2). In 2005-2007, a reconnaissance geochronological and geochemical study of the northeastern corner of the QMB was conducted by Michael Schultz, a former graduate student at the University of Alberta (3, 4). This study revealed that much of the area is underlain by the 2.45-2.50 Ga Queen Maud granitoids and metasedimentary rocks that were deposited between 2.45-2.39 Ga and tectonically buried and metamorphosed at granulite-facies conditions at around 2.39 Ga. The tectonism and metamorphism are associated with the Arrowsmith Orogeny, an important but heretofore poorly understood orogenic event that affected many parts of the western Churchill Craton in this time period.
There are two principal goals of this study. First, it is a westward continuation of the transect of the QMB conducted by Schultz and co-workers. Second, it is a detailed investigation of the metamorphic history of the QMB aimed at documenting the pressure-temperature conditions and age of metamorphism. In order to accomplish these goals, field-work was conducted in the summer of 2010 in an east-west transect of the spectacularly exposed rock outcrops along the southern Queen Maud Gulf coast. 60 rock samples were collected in the field work, a subset of which have been selected for quantitative geothermobarometry and U-Pb zircon and monazite dating by in-situ U-Pb dating by laser ablation-multi collector-inductively coupled plasma mass spectrometry (LA-MC-ICP-MS).
Several previously unknown aspects of QMB geology have been discovered through the present work, including the identification of an undeformed granitoid body (2.32 Ga) and associated gabbroic pluton that post-dates the Arrowsmith Orogeny, Mesoarchean crust present in the western QMB, as well as a preliminary estimate of the spatial extent of the Queen Maud granitoids. Upcoming detrital zircon studies from two metasedimentary samples will place maximum age constraints of the timing of sedimentation. Investigation into the metamorphic conditions and history of the QMB has revealed peak pressures of between 7 and 9 kbar, or approximately 25-30 km depth, and minimum temperatures of peak metamorphism of approximately 700-800C. No fewer than three episodes of monazite growth, each thought to be associated with metamorphism, have been identified. The oldest episode of growth is dated at around 2.46 Ga and is thought to be the result of either contact metamorphism during intrusion of the Queen Maud granitoids, or magmatic growth within these granitoids. The principal period of monazite growth, thought to represent the timing of regional granulite-facies metamorphism due to the Arrowsmith Orogeny, occurs at 2.36 Ga. A spreading of ages between 2.36 and 2.1 Ga may be the result of Pb loss and additional monazite growth during the 1.9-2.0 Ga Thelon Orogeny. A final period of monazite growth occurred at around 1.88 Ga and is likely the result of minor and perhaps local reworking during the Trans-Hudson Orogeny.
Shauna Coombs, Tom Chacko
Lower crustal xenoliths play a critical role in the study of crustal formation processes, particularly in Archean terrains where the lower crust is an important interface between the upper and middle crust and the cool lithospheric mantle keel underlying Archean cratons. Research on lower crustal xenoliths from the Slave craton provides an opportunity to gain insight into the age, composition and thermal history of this interface within the craton. In this study we present data from three lower crustal xenoliths suites collected in a northeast to southwest transect across the Slave craton. The samples are from the Artemisia kimberlite, located in the Coronation diamond district of the northwestern Slave (Nunavut), the Ekati kimberlite from the central Slave (NWT) and the Munn Lake kimberlite of the southeastern Slave (NWT). Samples from the Artemisia Suite have a range of bulk composition but the majority are intermediate in composition and compromise Garnet + Plagioclase ± K-feldspar and significant amounts of retrograde hydrous minerals that likely pseudomorph orthopyroxene. As well, there are accessory grains of rutile, zircon and monazite. The garnet in these samples is characterized by relatively low grossular contents. One sample from this suite contains Garnet + Cordierite + Plagioclase + Biotite and is similar in mineralogy and appearance to metagreywackes that are widespread throughout the Slave. In contrast to the Artemisia xenoliths, the Ekati and Munn Lake samples are garnet-bearing mafic granulites with a primary mineralogy of Garnet + Clinopyroxene + Plagioclase ± Orthopyroxene ± Amphibole ± Rutile ± Ilmenite. Based on Fe-Mg geothermobarometry, it has been determined that all three suites equilibrated at ~700-800 °C. As well, pressure constraints of ~10-13 kbars have been determined for the pyroxene bearing samples of the Ekati and Munn Lake suites. Additionally, U-Pb ages of ~1900 Ma, ~2100 Ma and ~2400-2600 Ma were obtained by laser ablation ICP Mass Spectrometry of zircon and monazite grains from the Artemisia suite.
David van Acken
Jason Hong, C.D.K. Herd, R.G. Cavell
Nakhlites are basaltic martian meteorites that have been shown to contain aqueous alteration products (1). Among the alteration products is the mineral jarosite (KFe3(OH)6(SO4)2), which was discovered in the Miller Range (MIL) 03346 nakhlite (2,3). Jarosite formation requires an acidic and oxidizing environment (4), and its occurrence in the MIL 03346 nakhlite provides an opportunity to study possible ancient martian environments and related martian near-surface processes in the lab. In this study, we have located multiple occurrences of jarosite using electron microprobe methods (X-ray mapping) in two separate MIL 03346 thin sections. These areas of alteration are on the order of 10’s of microns in size and are typically found within the mesostasis and along fractures that run through augite and olivine grains. This study uses a combination of various analytical techniques to further characterize the jarosite in order to determine the depositional environment and conditions of its formation.
Two light sources, the Advanced Photon Source (APS) at Argonne National Laboratory and the Canadian Light Source (CLS) were used to provide synchrotron X-ray fluorescence. The purpose of SXRF was to determine the minor and trace element concentrations in both terrestrial and martian jarosite samples. Direct comparison of the jarosite in the meteorite to the terrestrial samples will show if any differences could provide evidence for a pre-terrestrial origin. Ion probe measurements for hydrogen isotopes were performed to determine the origin of the jarosite.
The initial studies using the electron microprobe showed that the jarosite in the MIL 03346 martian meteorite is not widespread throughout the entire specimen. The distribution of the jarosite precipitate provides evidence that the K and S were mobilized by outside waters flowing through the host rock during jarosite formation. The use of synchrotron radiation to obtain quantitative XRF trace element data of the martian meteorites was not successful due to a number of issues. These include the overshadowing Fe signal in the jarosite and that the beam was too large to generate a clear signal on the small and often patchy areas of alteration. This study shows that even with the recent advancements in modern synchrotron capabilities, the application of these techniques to analyze jarosite within the martian meteorites is limited and requires further experimentation. Measurements of D/H ratios in the jarosite using ion probe analysis appear to be the most reliable method of determining the origin of formation.
Jennifer Peats, T. Stachel, R.A. Stern, K. Muehlenbachs, J. Armstrong
The northern Churchill Province has become the locus of avid diamond exploration activity in Canada. However, little is known about the mantle sources and residence history of diamonds in this area. We studied diamonds smaller than 1.1mm (-1DTC) from the ES-1 kimberlite sheet on the Aviat property, Melville Peninsula. The diamonds were analyzed for their carbon isotopic composition, nitrogen content and aggregation state to characterize their sources and residence history in the lithospheric mantle beneath the northern Churchill.
Carbon isotopic composition in some instances can be used to differentiate between peridotitic and eclogitic source parageneses for diamond. Both conventional and SIMS techniques were used to obtain δ13C values for the Aviat diamonds. Combining both techniques, the diamonds yielded δ13C values ranging from -29.7 to -0.7‰. A pronounced mode is present at -5‰, the value for mantle derived carbon, and this mode is characteristic for both peridotitic and eclogitic diamonds worldwide. The large range of δ13C values below -5‰ is indicative of at least a partially eclogitic paragenesis for Aviat diamonds. One diamond recovered from an eclogite xenolith, and hence of proven paragenesis, produced δ13C values around -5‰, perhaps indicating that the mode at -5‰ is made up of eclogitic diamonds.
Zonation was observed in several of the diamonds, with two trends in δ13C: (1.) Highly negative δ13C values in diamond cores and rim values around -5‰ with evidence for a stage of diamond resorption between the two growth stages. (2.) Core compositions with a δ13C around -5‰ and slightly (0.7-2.0‰) more negative values for the rims, again with evidence for resorption between the two growth events.
Nitrogen aggregation, quantified as %B (relative percentage of fully aggregated B component), was measured using FTIR, and nitrogen content was measured using both FTIR and SIMS techniques. Aviat diamonds display higher than average nitrogen contents with point analyses ranging from 10-1700 at.ppm and %B components (from FTIR) ranging from 0-98%. A plot of nitrogen vs. %B (FTIR data) reveals that the diamonds span a range of time averaged mantle residence temperatures from ~1050 -1300°C, indicating derivation of diamonds from sources of various depths at Aviat.
In concert, the nitrogen characteristics and the carbon isotopic composition of the Aviat diamonds advocate for multiple growth events involving fluids from multiple sources beneath the northern Churchill Province.
Karen Smit, Thomas Stachel, Michael Seller
The Victor kimberlite, the first diamond mine on the Archaean Superior craton and in Ontario, provides the unique opportunity to study the association of a diamond deposit with a post-Archaean rift system (the 1.1 Ga Keweenawan Midcontinent Rift). Victor forms part of the Attawapiskat kimberlite cluster, which was emplaced at ~170–180 Ma (1,2), subsequent to the Midcontinent Rift. Details of the history and composition of the lithospheric mantle below the Superior craton are not well constrained, due to a general scarcity of mantle xenoliths. In particular, the impact of the 1.1 Ga Keweenawan Midcontinent Rift on diamond-bearing lithospheric mantle beneath the Superior Craton is poorly understood. Preliminary results from garnet xenocrysts from the Kyle Lake (~1.1 Ga) and Victor kimberlites (3,4,5) indicate that the composition of local lithospheric mantle was modified after emplacement of the Kyle Lake kimberlites, possibly in association with the Midcontinent Rift.
Here we present initial major and trace element results from a suite of xenocrysts from the Victor kimberlite, comprising olivine, orthopyroxene, clinopyroxene and garnet. Olivine with two distinct colours and compositions were analysed – green olivine with a more depleted composition (Mg# 0.90 – 0.94) and brownish-green olivine with less depleted compositions (Mg# 0.89 – 0.91). Geothermobarometry on Cr-diopsides (6) yielded a local geotherm equivalent to ~ 38 mW/m2 surface heat flow at 180 Ma, cooler than the geotherm calculated for Kyle Lake (~ 44 mW/m2 at 1.1 Ga).
Garnet xenocrysts have lherzolitic compositions with Cr-in-grt barometry indicating their origin in the shallow lithosphere (< 4 GPa; 7). Garnet REE patterns normalised to a primitive mantle garnet composition (REEJ4) as well as Y and Zr contents of garnet record both depleted compositions and metasomatic overprint. Depleted garnets have low Y and Zr contents (< 5 ppm and 25 ppm, respectively) and are HREE depleted with positive ErJ4 – YbJ4 slopes. Garnets with metasomatic overprint show increased Y and Zr and are enriched in LREE. REE content indicate that the lithosphere below this portion of the Superior craton has been modified by both fluid and melt metasomatism. Garnets considered to be melt metasomatised have MREE to HREE of primitive mantle garnet abundance.
Theodore Oramah, Jeremy Richards
Despite the abundance of solid mineral deposits, Nigeria only earns about 0.5–1% of its current Gross Domestic Product (GDP) from the solid minerals sector. This is as a result of the dominance of the oil and gas industry, which has negatively affected the competitiveness of other sectors of Nigeria’s economy. The dominance of this industry has resulted in unemployment, poverty, hunger, domestic price inflation, corruption, unstable government, and higher exchange rates. These impacts are typical for economies suffering from the effects of “Dutch Disease” and the “Resource Curse”. Small-scale mining offers hope as an economic activity that can create wealth, employment, reduce hunger and poverty, and provide basic amenities for rural communities with solid minerals endowment. This study presents preliminary results of ongoing research into the prospects of using small-scale mining in a developing country like Nigeria to move towards rural sustainable development.
Darrin Molinaro, S. Gibb, B.D.E. Chatterton
Cornuproetus and Diademaproetus represent common proetid trilobite genera found throughout the Lower and Middle Devonian. Both genera display a relatively simplistic morphology (in terms of Devonian trilobites) of a crescent shaped cephalon with prominent librigenal spines, blunt thoracic pleurae, and a very short and wide pygidium with distinct axis (rhachis). Since being originally described (1,2) numerous species have been erected and added to both genera, many being based on very partial or imperfect specimens. Increase in species numbers, and thus diversity, resulted in the proposal of multiple phylogenetic relationships within and between these taxa. Alberti (3) took this to an extreme by classifying Diademaproetus and fifteen other cornuproetid-like genera as all sub-genera of Cornuproetus. Current accepted classification considers Diademaproetus, Cornuproetus, and all other cornuproetid-like taxa as valid genera (4). Despite this consensus in regards to classification though, the phylogeny of cornuproetids still remains unclear and in need of revision.
Commercial mining of Morocco’s southern Anti-Atlas region trilobite beds has produced numerous, exquisitely preserved (complete and fully articulated) specimens of cornuproetids. Such a large and well preserved collection allows for examination of cornuproetid relationships and revision of some taxa’s description and diagnosis. Specifically, new material permits phylogentic analysis using primarily complete and whole specimens, something not possible until now. Preliminary analysis results, along with character coding, suggest that many of the previously assumed diagnostic characters for genera are not as informative as originally implied. In turn, other characters such as cephalic border size, eye socle size, and pygidial shape are more important towards generic level classification than originally thought.
Furthermore, the phylogenetic analysis provides insight towards character assessment, selection and coding at not only the generic level and below, but also higher taxonomic levels. Ultimately, results of this analysis and new Moroccan specimens will play a significant role in understanding trilobite evolution within the Proetida and through the Devonian.
When conducting research using data structured as a series of samples consisting of various objects, a sample sizes that is too small will lead to erroneous conclusions. However, increasingly larger sample sizes will eventually result in diminishing returns in terms of improving any pattern revealed by the data. Here, I used 30 paleoecological datasets to determine that a minimum sample size of 50 individuals is required for research on communities of marine invertebrate organisms. This is evidence that smaller sample sizes may be applied in any field of research using multivariate statistical methods.
Community Paleoecology uses complete fossil assemblages to determine the mechanisms of spatiotemporal ecological and environmental variation, leading to insights into the processes that structure ecosystems and the possible causes for ecosystem collapse and extinction (1,2,3).
Previous paleoecological studies estimated sample size requirements to be 200 or more individuals per sample, based on the probability of acquiring a representative sample from various proportions of a hypothetical complete population (4,5,6). However, examining probability does not take into account relationships between sampling units or taxa (e.g., the interaction of taxa within a community or evolutionary changes of taxa through time).
Using 30 datasets from the Paleobiology Database and the literature, I present evidence that the minimum required sample size for paleocommunity research is 50 individuals. Each sample within each dataset was randomly subsampled 1000 times to five proportional sizes (50%, 25%, 10%, 5%, 2.5%). Each of the 1000 subsampled datasets created for each proportional sample size was correlated with its corresponding 100% dataset using two multivariate methods: the Mantel test and Pearson’s Product Moment Correlations of non-metric multidimensional scaling ordination axis scores. All Mantel R-statistics are above 0.92 for median sample sizes greater than 25 individuals, and Pearson’s r-values for NMDS axis-one scores are above 0.86 for median sample sizes greater than 50 individuals. Thus, the multivariate paleocommunity signal, for each dataset respectively, is consistent for all median sample sizes greater than 25 to 50 individuals.
The results of this study may be extended to any discipline that uses multivariate statistical methods to analyze series of samples. Using the same subsampling protocol employed here, evidence may be found allowing smaller samples sizes to be collected, reducing the overall cost, in time and funds, of sampling.
Donald C. Wehlage, J. Gamon, D. Hildebrand
Rangeland ecosystems are often subjected to extremely variable weather. The summers of 2009 and 2010 in Alberta provided a natural demonstration of this phenomenon, with the growing season in 2009 being an extremely dry year and 2010 receiving very large amounts of rainfall. The goal of this project was to evaluate the effect of this variability on rangeland productivity. The two extremely different moisture regimes in these years provided the opportunity to see if changes in productivity created by varying rainfall are detectable with available remote sensing techniques. A combination of ground-based optical remote sensing, satellite optical remote sensing and biomass harvests were utilized to analyze productivity in two southern Albertan grazing reserves. Rainfall and temperature data were obtained from the closest Environment Canada weather stations to the research sites. Moisture regime had a large effect on the harvested biomass, with the yields from every month in the 2010 growing season being much higher than the yields during the corresponding 2009 growing season. Vegetation indices derived from ground based optical remote sensing followed a similar trend, demonstrating the ability of the method to monitor the effect of environmental variability on the productivity of rangelands. Remaining goals of the study include placing a dollar value on carbon, and evaluating the confounding effects of grazing and biomass carryover from the previous year.
Cassidy Rankine, A. Sanchez-Azofeifa
Tropical forests and woody savannas account for an estimated 50% of global forest cover and are responsible for approximately 60% of global terrestrial photosynthesis; accurate assessment of gross primary production (GPP) in these environments is important for reducing uncertainties in global ecosystem flux modeling and carbon stock appraisal. Estimates of ecosystem GPP can be made through indirect measurements of photosynthetic rates using optical remote sensing methods. The fraction of photosynthetic active radiation absorbed by a vegetative canopy (fAPAR) is an indicator of canopy structure and an important vegetative growth and carbon uptake model parameter. Landscape scale fAPAR is widely monitored via several satellite platforms but remotely sensed vegetation estimates in tall heterogeneous environments, such as tropical forests, frequently contain high errors; therefore, field based, or in situ, measurements of fAPAR are necessary to validate satellite data and improve ecosystem GPP models. Our wireless sensing networks (WSNs) are equipped with optical and thermal sensors to observe micro-meteorological variables in high temporal and spatial resolution. This study explores the use of in situ WSNs to better monitor the seasonal canopy/understory light environments and plant growth variables of tropical forests so as to enhance multi-dimensional fAPAR estimates and improve ecosystem productivity models.
Steven D. Mamet, Peter Kershaw
The climate in the Subarctic is changing and biological systems are evolving in response to these changing conditions. Recognizing how patterns and processes of subarctic vegetation are responding to recent climate change is paramount to understanding the future trajectory of northern terrestrial ecosystems. The subarctic forest-tundra ecotone represents a transition from northern boreal forest or lichen woodland to tundra vegetation taxa, and contains the Arctic “treeline”—an important biogeographical boundary. Treeline is the northernmost position of arboreal tree growth; beyond this “line”, trees persist as prostrate mats or shrubs and are not coupled with atmospheric conditions due to their low stature. Treeline is predicted to shift northward with warming, and cause a positive feedback with warming through various mechanisms such as albedo, moisture balance and carbon budget alterations.
Dendroclimatological and dendroecological techniques were used to evaluate the forest-tundra transition within the Hudson Bay Lowlands of northern Manitoba. The focus of this presentation is on research completed in the Churchill Wildlife Management area and Wapusk National park since 2003. Several studies at scales ranging from landscape (100s of km) to site (100s of m) scale provide convincing evidence that trees are responding positively to warming during the last several decades, and treeline has advanced and continues to advance in the Churchill area. However, climatic forcing of tree growth and treeline advance may be mitigated by site- and species-specific traits, illustrating the biocomplexity of the region in the context of a warming climate.
Quiang Wang, Xianmin Hu, Paul G. Myers, Andrew B.G. Bush
The Canadian Arctic Archipelago (CAA) is a complex network of straits and basins connecting the Arctic Ocean and the Atlantic Ocean. To identify flow pathways through the Canadian Arctic Archipelago, results of a regional model of the Canadian Arctic Ocean and a Pan Arctic OceanModel have been examined. The two models capture much of the observed spatiotemporal variability of sea ice and the basic features of the circulation in the Canadian Arctic Archipelago. The model results reveal that the southward flow in M’Clintock Channel is the topographically controlled. The analysis of vorticity dynamics also shows that the stratification have strong impact on the circulation in eastern Lancaster Sound.
Laura Castro de la Guardia, Arjen D. Terwisscha van Scheltinga, Paul G. Myers, Andrew E. Derocher, Nick Lunn
The sea ice in Hudson Bay (HB) undergoes a seasonal cycle, going from a complete ice covered from December to June to ice-free from August to October. The timing of the cycle is critical to polar bear’s survival in HB. Polar bears spend the winter hunting seals on the ice, but once the bay starts to breakup they retreat on land until HB refreezes. Survival on land is largely a function of the fat reserves accumulated during the hunting/ice period. The warming of the past 30 years has changed the timing of freezing and breakup of the sea ice in HB, increasing the ice-free period, and leading to a decreased survival of polar bears. To determine the impact of global warming on polar bear populations it is essential to predict future ice changes and seasonality in HB. To achieve this goal we work with a high resolution sea ice model. Here we present the validation of a sea ice model over HB region. The model simulates the sea ice concentration in good agreement with the Canadian Ice Service and PMW data. And the presence/absence of sea ice simulated by the model is in 94% agreement with the western HB polar bear telemetry data . The results suggest that the sea ice model is ready to be use to predict the response of HB sea ice to global warming.
Ben Lange, J. Beckers, C. Haas, S. Hendricks, C. Michel, A. Niemi
Arctic sea ice is changing. Satellite observations show an 11%/decade decline in sea ice extent over the past several decades. Furthermore, the oldest and thickest ice is disappearing and average thickness of sea ice in the Arctic is decreasing. The decreasing extent of sea ice allows more solar radiation to be absorbed, leading to changes in the biogeochemical properties of the ice and ocean. However, unlike sea ice extent which can be accurately monitored from space, measurements of sea ice properties such as thickness and structure remain limited. Current and past satellite remote sensing methods of estimating sea ice thickness are based on altimetry measurements of sea ice surface height, which is affected by variability in properties of the overlying snowpack and the sea ice itself. Additionally, uncertainties in signal penetration depth cause considerable uncertainty in thickness estimates. Airborne electromagnetic measurements provide accurate measurements of sea ice thickness along transects 100s of kilometers long with high spatial density and accuracy. Results from airborne and ground based thickness measurements conducted during the CASIMBO 2010 campaign north of CFS Alert, Ellesmere Island and around Cornwallis Island, Nunavut will be presented. In addition, biogeochemical analysis on cores collected in Alert, performed in collaboration with the Freshwater Institute of Fisheries and Oceans Canada, are presented in comparison with physical core data. Finally, airborne EM results from the Fram Strait and Norwegian Arctic, collected in collaboration with the Norwegian Polar Institute and the Centre for Ice Climate and Ecosystems (ICE), will be summarized.
B. Clarke Burchfiel
The evolution of the Tibetan plateau can be interpreted as consisting of three tectonic episodes with gradational boundaries: 1. Cretaceous to early Cenozoic development of a pre-collisional Andean margin along the Eurasian margin, 2. Early Cenozoic extrusion of continental fragments from southern Tibet into SE Asia with growth of the plateau northward, and 3 Late Cenozoic rotation around the eastern Himalayan syntaxis, shortening and left-slip in the NE part of the Plateau, and development of present day high topography, mostly related to lower crustal flow from central Tibet. The post-collisional tectonics of Tibet is related two dynamic systems, India-Eurasia intracontinental shortening and roll back in the West Pacific/Indonesia subduction systems.
Plate reconstructions indicate perhaps 3600 km of post collisional shortening north of the India indenter at the eastern Himalayan syntaxis. However, the time of collision remains uncertain especially in the eastern Himalaya. The plateau was probably already elevated in the south during pre-collisional Andean development. Shortening of early Cenozoic age within plateau indicate minor shortening in the NE and less than 100% in the central and southern plateau. Our paleomagnetic evidence indicates continental fragments in SE China have moved from southern Tibet to the SE more than 750 km indicating that extrusion played an important role in early Cenozoic India/Eurasia intracontinental convergence with the SE motion facilitated and accommodated by trench roll back in the Indonesian subduction system.
Late Cenozoic intracontinental shortening resulted in clockwise rotation around the eastern Himalayan syntaxis crosscutting early Cenozoic extrusion structures. Left-slip movement on the Altyn Tagh fault and associated transfer to shortening south of the fault began in the NE part of the plateau and is ongoing today. The crustal motions to the NE led to the 2008 Sichuan earthquake; a small area of the eastern plateau moves eastward more or less with South China. All this deformation is related to the flow to the SE and NE of lower crust from central Tibet, and to the east where it was resisted by low ductility crust below the Sichuan basin leading to divergent flow around the basin crust and creation of the steep eastern topographic margin of the plateau. Central Tibet is characterized by strike-slip and extensional faults that mark the area from which flow takes place, however, whether the crust in this area is thickening or thinning remains unknown.
If lower crustal flow, perhaps also involving upper mantle of the lithosphere, is as extensive as implied, then the lithosphere and mantle below the low ductility zone would be decoupled to varying degrees from upper crustal/lithospheric structure. This presents one of the most important problems in tectonics: How to determine the geometry, kinematics and dyanmics of such a decoupled system.
B. Clarke Burchfiel
China is earthquake country: The Xian earthquake of 1556 produced one of the greatest natural disasters on record with the loss of ~ 830,000 lives. Earthquakes in China are numerous and are related to broad plate boundary intracontinental deformation within the India/Eurasia collision zone. They cause a major loss of property and life not only because of seismic activity, but often largely because of secondary effects of the earthquake. Understanding of these secondary effects is necessary for hazard assessment. Three examples: the Haiyuan/Guyuan earthquakes (1920), the Sichuan earthquake (2008), and the potential earthquake risk at Gejiu yield data critical for hazard assessment. The Haiyuan earthquake (M=8.7?) had a left-slip offset of more than 10 m, a surface rupture length of more than 200 km and was responsible for more than 220,000 deaths. An aftershock of M=7 occurred near Guyuan and because of liquefaction at the base of a 1+ km-wide loess terrace the terrace dislocated at its base and flowed into the adjacent valley burying numerous villages. This secondary effect of the aftershock probably would not have been anticipated, but now that we know of such phenomena it must be considered in any seismic risk assessment. The 2008 Sichuan earthquake (M=7.9-8.0) was not anticipated because of its long recurrence interval (2,000 to 5,000 yrs) and slow rate of convergence measured by GPS (1-2 mm/yr), but should have been suspected because of the steep topography, steepest topographic front of anywhere around the Tibetan plateau. More than 80,000 people died. The secondary effects of the earthquake were many; landsliding, landslide river dams and and liquefaction. The town of Gejiu in Yunnan lies within a narrow half graben along a N-S trending splay of the major Xianshuihe-Xiaojiang fault system where it passes through a regional karst terrain. While no major earthquakes have occurred here in historical times, the town lies within a precarious geological setting. Most interesting is that the Gejiu graben has mostly internal drainage in a climatic belt of high monsoon rains and the entire area may underlain by large caverns and underground rivers. The potential exists for massive subsidence and cave-ins that might be triggered by an earthquake.
Neotectonic study of each of these areas contributes to major regional tectonic interpretations. The relations between the Haiyuan strike-slip fault and the transfer of slip to folds and thrust faults suggest these structures are detached at shallow crustal levels and raises the question whether similar interpretations can be applied to large faults such as the Altyn Tagh fault zone. Study of the E-W shortening across the Longmen Shan and Sichuan basin cannot explain the development of the 5 km high plateau to its west. However, the geology of this area strongly supports a tectonic model for eastward flow of lower ductile crust that is resisted by the less ductile lithosphere below the Sichuan basin causing the steep topographic front of the Longmen Shan. A neotectonic study of the Gejiu basin and associated fault will help us understand the regional tectonic problem of how the numerous splays of the Xianshuihe-Xiaojiang fault system lose displacement southward and end at the cross cutting active Red River fault. However, the geology and GPS measurements indicate the left-shear on the N-S fault system continues across the Red River fault and continues west into SE Asia. How the crust absorbed the strain in this area is a common regional tectonic problem.