Km Of Seismic Lines Research Articles

Sedimentology of Modern Bahamian Carbonate Slopes: Summary and Update

AbstractSlopes adjacent to the Bahamian carbonate platform revealed a large variety of depositional processes. In this study, we present a synthesis summarizing 109,000 km2 of bathymetric and reflectivity data with ∼7,900 km of seismic lines and 311 m of sediment cores that were obtained over the last 50 years. These data are used to develop a conceptual model of sedimentation patterns on Quaternary carbonate slope systems and their interaction with the adjacent shallow‐water carbonate platforms. Our data highlight that during the Quaternary, factors controlling large‐scale sedimentation on Bahamian slopes have numerous similarities as they have higher sedimentation rates during interglacials. At a small scale, every slope has its own characteristics that are contemporary controlled by two main characteristics: (a) facies on the adjacent shallow‐water platform, and (b) the impact of shallow‐ and deep‐water currents. Large‐scale tectonics influence sediment deposition as it determines the position of the islands and impacts platform facies distribution.

Subsurface basement, structure, stratigraphy, and timing of regional tectonic events affecting the Guajira margin of northern Colombia

We have combined previous data from Mesozoic-Cenozoic outcrops in the Guajira Peninsula of northern Colombia with regional gravity, bathymetric, and seismic interpretations to demonstrate the existence of a 280 km long western extension of the Great Arc of the Caribbean (GAC) along the continental margin of Colombia. Seismic data reveal an 80–100 km wide domal-shaped basement high that exhibits internal chaotic seismic facies. This elongate and domal-shaped structure extends 1800 km from the Aves Ridge in the Caribbean Sea to the study area in offshore Colombia. The western extension of the GAC in Colombia and western Venezuela is buried by 700–3000 m of continental margin sedimentary rocks as a result of the GAC colliding earlier with the Colombian margin (Cretaceous-early Paleogene collision) than its subaerially exposed eastern extension along the Leeward Antilles ridge (late Paleogene-Neogene). Our compilation of geologic information from the entire GAC reveals that GAC magmatism occurred from 128 to 74 Ma with magmatism ages progressively younger toward the east. Six upper Eocene to recent marine seismic sequences overlying the domal basement high of the GAC have been mapped by our analysis of 2400 km of seismic lines and 12 well logs. Based on subsurface mapping correlated with well-log information and onland geology in the Guajira Peninsula, these six sequences record four major deformational events: (1) late Eocene rifting in an east–west direction produced half-grabens in the northern part of the area, (2) Oligocene transtension in the southern part of the area expressed by right-lateral Oligocene strike-slip faulting and extensional basin formation, (3) early-middle Miocene transtension, and (4) late Miocene-early Pliocene Andean uplift accompanied by rapid erosion and clastic infilling of offshore basins by the Magdalena delta and deep-sea fan. The significance of this basin framework is discussed for known and inferred hydrocarbon systems.

Predicting the effects of restoring linear features on woodland caribou populations

Predator-prey dynamics are increasingly being modified by the alteration of natural habitats. Such alteration has led to increased predation rates and local extirpation of woodland caribou (Rangifer tarandus caribou) in western Canada. Linear features such as roads or seismic lines (narrow corridors used for petroleum exploration that are cleared of vegetation) increase predation rates on caribou by increasing wolf (Canis lupus) movement rates and by facilitating access into caribou habitat. Linear feature restoration is therefore hypothesised to help reverse caribou declines. However, with the high financial cost to restore approximately 350,000 km of seismic lines within western Canada’s boreal forests, theoretical predictions can clarify the efficacy of such actions. We use a mathematical model based on coupled ordinary differential equations representing predator-prey dynamics to estimate equilibrium densities of caribou, moose (Alces alces) and wolves under various parameter scenarios. Changes in equilibrium density serve as a proxy for the expected effect of linear feature restoration on population densities. Our model captures dynamical feedbacks between caribou and wolf densities, and also includes moose, which are the wolf’s primary prey species. With our best estimates of parameter values, caribou density increased 2.51-fold if all linear features were restored and 1.61-fold if only seismic lines were restored. As a comparison, simulated predator reductions increased caribou densities 3.92-fold, nearly twice the total response of linear feature restoration. The effect of restoration was increased if caribou group size was smaller, yet was less pronounced if carrying capacity for ungulates was higher. By varying the parameter values and fixing population densities, our approach allowed us to partition the caribou populations’ response from restoration into the contributions of the various mechanisms and feedbacks. In particular, contrasting simulation results where wolf densities are kept fixed with those where they are free to respond to prey allowed us to disentangle the relative importance of wolf functional and numerical response. This novel approach indicates that most of the increase in caribou densities after restoration was due to reduced foraging efficiency of wolves, especially reduced habitat overlap. Overall, our results suggest that restoration could substantially benefit caribou populations, but only if all linear features are restored, which is far from realistic. Linear feature restoration alone may not lead to population recovery, and should therefore be coupled with other direct management actions to successfully recover caribou.

Motorized Activity on Legacy Seismic Lines: A Predictive Modeling Approach to Prioritize Restoration Efforts.

Natural regeneration of seismic lines, cleared for hydrocarbon exploration, is slow and often hindered by vegetation damage, soil compaction, and motorized human activity. There is an extensive network of seismic lines in western Canada which is known to impact forest ecosystems, and seismic lines have been linked to declines in woodland caribou (Rangifer tarandus caribou). Seismic line restoration is costly, but necessary for caribou conservation to reduce cumulative disturbance. Understanding where motorized activity may be impeding regeneration of seismic lines will aid in prioritizing restoration. Our study area in west-central Alberta, encompassed five caribou ranges where restoration is required under federal species at risk recovery strategies, hence prioritizing seismic lines for restoration is of immediate conservation value. To understand patterns of motorized activity on seismic lines, we evaluated five a priori hypotheses using a predictive modeling framework and Geographic Information System variables across three landscapes in the foothills and northern boreal regions of Alberta. In the northern boreal landscape, motorized activity was most common in dry areas with a large industrial footprint. In highly disturbed areas of the foothills, motorized activity on seismic lines increased with low vegetation heights, relatively dry soils, and further from forest cutblocks, while in less disturbed areas of the foothills, motorized activity on seismic lines decreased proportional to seismic line density, slope steepness, and white-tailed deer abundance, and increased proportional with distance to roads. We generated predictive maps of high motorized activity, identifying 21,777 km of seismic lines where active restoration could expedite forest regeneration.

Modern and relict sedimentary systems of the semi-arid continental shelf in NE Brazil

This paper describes the carbonate–siliciclastic system of the equatorial continental shelf of NE Brazil (East Ceará) based on X-ray fluorescence (XRF), grain size, CaCO3, shallow seismic and remotely operated vehicle (ROV) analyses. Data were obtained for two sectors: 1) Halimeda Bank (HB), inner shelf (−12 m), and 2) transverse profile (TP), inner to outer shelf-upper slope (−5 to −100 m). In total, 72 samples were collected, and 29 km of seismic lines (HB) and ROV profiles (HB and TP) were surveyed. The main chemical elements were Ca and Si (93%). These elements occur in two types of shallow marine sediments: carbonate (mainly autochthonous) and siliciclastics (terrigenous/allochthonous/relict). With respect to the chemical elements, a strong negative correlation was observed between calcareous (Ca and Sr) and siliciclastic (Si, Al, and K) components. Strontium does not always show a strong positive correlation with Ca. The average CaCO3 contents of 81% and 91% were determined for the HB and TP, respectively. The profiles show a predominance of carbonate sediments; however, the HB demonstrates a greater continental influence (inner shelf). The grain size presents a prevalence of sand (82%) in relation to gravel (18%). This particle size variation is mainly due to the breakdown of Halimeda nodules, siliciclastic sediments in the finer fraction (>2.5Φ), and the presence of gravel with iron coating (relict). Two types of echo-characters have been identified. Both are associated with the large presence of carbonate sediments. Echo I shows the bottom surface with continuity in the sub-bottom without a subsurface reflector. Echo II presents a discontinuous subsurface reflector. The ROV allowed the observation of algae patches in higher floors and gravelly and sandy bioclastics in the lowest sectors. Large patches of calcareous green algae, Halimeda, occur in the inner shelf below the 15 m isobath, mainly due to the semi-arid climate (weak sediment supply from the mainland), geographical position (equatorial) and oceanographic conditions (hydrodynamic and biogeochemistry). It has been concluded that the seafloor of the semi-arid continental shelf of East Ceará (NE Brazil) shows modern predominance of carbonate deposition based on the lack of contaminants, geochemical purity of carbonate sediments, and high percentage of CaCO3. The conditions for exploitation in the intermediate sector are provided. However, it would be ideal to perform punctual extraction and analyze the resilience and regeneration of Halimeda incrassata and the consequences for fisheries (important economic resource of the region).

Early cementation and accommodation space dictate the evolution of an overstepping barrier system during the Holocene

Abstract The morphology and stratigraphic features of a well-preserved drowned barrier system, located on the western coast of Sardinia (Mediterranean Sea), are presented here. The barriers were mapped using a multibeam echosounder. The Digital Terrain Model of the seabed revealed five sub-parallel barriers in a depth range of 18–37 m, with a distance of ~ 300 m between each single barrier. Direct inspection by scuba diving, revealed that the barriers consist of beachrocks, topped by seagrass meadows growing on a biogenic hardground. The inner-most barrier is limited landward by a steep cliff, 10 m high, bordering the back-barrier area. About 200 km of seismic lines were collected along the barrier system using a 0.4–1.0 kJ sparker source and a 3.5 kHz Chirp Subbottom profiler. The seismic data, calibrated with vibrocores, allowed us to recognize the subaerial topographic surface of the last glacial maximum as well as several seismic units interpreted as the Pliocene marine sediments, the pre-Holocene deposits and the Holocene barrier–lagoon complex composed of shoreface, barrier, lagoonal/deltaic and beach deposits. Despite the relatively high seabed gradient (0.3°–0.4°) and the relatively low rate of sea-level rise (10–15 mm y − 1 ), the barriers were well preserved due to the early diagenetic processes which led to a rapid cementation with the formation of beachrocks, and the subsequent overstepping with the rise of the sea level. The development of the overstepping barrier system is strictly related to the antecedent subaerial topography which is, in turn, related to the tectonic setting of the area. The Pliocene seismic unit was lowered by a direct fault at the entrance of the gulf forming a depression filled by sediments. The overstepping barrier system developed following the increase of the seabed gradient and was limited landward by the above-mentioned depression which increased the accommodation space. Following the sea-level rise and the barrier formation, this depression was filled by lagoonal sediments, washover fans and sediments coming from the rivers. The age model of barrier evolution, based on previous sea-level-rise curves during the Holocene, supported by radiocarbon data, highlighted that the whole system evolved over a time period of 1 ka; while the time elapsed from this formation to the drowning of single barriers was estimated to be in the order of magnitude of centuries. Scenarios of short-term evolution of modern barrier–lagoon systems of the adjacent coastal sector, under conditions of accelerated sea-level rise, according to Church et al. (2013) (2013 IPCC report) and Rahmstorf (2007) projections, were elaborated. The study of this ancient analogue suggests that the processes of adaptation of coastal systems to the rising sea level would require times evaluable from centuries to millennia.

Deglacial and postglacial evolution of the Pingualuit Crater Lake basin, northern Québec (Canada)

The Pingualuit Crater, located in the Ungava Peninsula (northern Québec, Canada) is a 1.4-Ma-old impact crater hosting a ~245-m-deep lake. The lake has a great potential to preserve unique paleoclimatic and paleoecological sedimentary records of the last glacial/interglacial cycles in the terrestrial Canadian Arctic. In order to investigate the stratigraphy in the lake and the late Quaternary glacial history of the Pingualuit Crater, this study compiles data from three expeditions carried out in May 2007 (~9-m-long sediment core), in August 2010 (~50km of seismic lines), and in September 2012 (high-resolution terrestrial LiDAR topography of the inner slopes). Despite the weak penetration (~10m) of the 3.5-kHz subbottom profiling caused by the presence of boulders in the sedimentary column, seismic data coupled with the stratigraphy established from the sediment core enabled the identification of two glaciolacustrine units deposited during the final stages of the Laurentide Ice Sheet (LIS) retreat in the crater. Two episodes of postglacial mass wasting events were also identified on the slopes and in the deep basin of the crater. The high-resolution topography of the internal slopes of the crater generated from the LiDAR data permitted the confirmation of a paleolake level at 545m and determination of the elevation of drainage outlets. Together with the mapping of glacial and deglacial landforms from air photographs, the LiDAR data allowed the development of a new deglaciation and drainage scenario for the Pingualuit Crater Lake and surrounding area. The model proposes three main phases of lake drainage, based on the activation of seven outlets following the retreat of the LIS front toward the southwest. Finally, as opposed to other high-latitude crater lake basins such as Lake El'gygytgyn or Laguna Potrok Aike where high-resolution paleoclimatic records were obtained owing to high sediment accumulation rates, the seismic data from the Pingualuit Crater Lake suggest extremely low sedimentation rates after the retreat of the LIS owing to the absence of tributaries.

Architecture of the western margin of the North Adriatic foreland:the Schio-Vicenza fault system

In the Italian Southern Alps, the Lombardic and Venetian chains and related foreland are separated by the Lessini-Berici-Euganei foreland block, which is unaffected by the Neogene-Quaternary shortenings. However, the Veneto-Friuli alluvial plain to the east of this foreland block has been affected by a poly-phase evolution since the Mesozoic era and represents the foreland of three surrounding chains. The area was affected by several flexural cycles related to the diachronous build-up of the External Dinarides to the east (Late Cretaceous-Late Eocene), the Eastern Southern Alps to the north (Late Oligocene-Quaternary), and the Northern Apennines to the southwest (Middle Miocene-Quaternary). The last two chains are currently active, although at different rates. The western margin of the foreland is marked by the Schio-Vicenza fault, which divides the deformed foreland (Veneto-Friuli alluvial plain) from the undeformed foreland (Lessini and Berici Mountains and Euganei Hills). The aim of this work is to unravel the architecture and evolution of this boundary using 2D seismic sections and deep wells acquired by ENI for hydrocarbon exploration. Approximately 1,000 km of seismic lines were interpreted and 10 wells were used to calibrate the seismic interpretation. Seven seismic sections that are sub-orthogonal to the main faults were selected to obtain geological cross-sections through a depth conversion process. The collected data display a complex buried fault system (Schio-Vicenza fault system) that extends with a NW-SE trend from the foot of the Prealps to the Po Delta. In the cross sections, the movement of the fault shows a vertical component with down-throw of its eastern side (hanging wall block). Some faults display a Mesozoic extensional displacement in accordance with the Mesozoic basin and swell architecture of the area. In addition, the Pliocene throw increases from the southeast to the northwest.Therefore, the Schio-Vicenza fault system can be interpreted as an inherited Mesozoic structure that reactivated during the Neogene shortening of the area. In particular, this fault system appears to have been mainly active during the Pliocene-Quaternary flexural cycle that is related to the Northern Apennines subduction, which is when the fault system accommodated a scissor movement between the Veneto-Friuli foreland and the Lessini-Berici-Euganei block.

Transboundary geophysical mapping of geological elements and salinity distribution critical for the assessment of future sea water intrusion in response to sea level rise

Abstract. Geophysical techniques are increasingly being used as tools for characterising the subsurface, and they are generally required to develop subsurface models that properly delineate the distribution of aquifers and aquitards, salt/freshwater interfaces, and geological structures that affect groundwater flow. In a study area covering 730 km2 across the border between Germany and Denmark, a combination of an airborne electromagnetic survey (performed with the SkyTEM system), a high-resolution seismic survey and borehole logging has been used in an integrated mapping of important geological, physical and chemical features of the subsurface. The spacing between flight lines is 200–250 m which gives a total of about 3200 line km. About 38 km of seismic lines have been collected. Faults bordering a graben structure, buried tunnel valleys, glaciotectonic thrust complexes, marine clay units, and sand aquifers are all examples of geological structures mapped by the geophysical data that control groundwater flow and to some extent hydrochemistry. Additionally, the data provide an excellent picture of the salinity distribution in the area and thus provide important information on the salt/freshwater boundary and the chemical status of groundwater. Although the westernmost part of the study area along the North Sea coast is saturated with saline water and the TEM data therefore are strongly influenced by the increased electrical conductivity there, buried valleys and other geological elements are still revealed. The mapped salinity distribution indicates preferential flow paths through and along specific geological structures within the area. The effects of a future sea level rise on the groundwater system and groundwater chemistry are discussed with special emphasis on the importance of knowing the existence, distribution and geometry of the mapped geological elements, and their control on the groundwater salinity distribution is assessed.

Selection and Characterization of Geological Sites able to Host a Pilot-Scale CO2Storage in the Paris Basin (GéoCarbone-PICOREF)

The objective of the GéoCarbone-PICOREF project was to select and characterize geological sites where CO<sub>2<sub/> storage in permeable reservoir could be tested at the pilot scale. Both options of storage in deep saline aquifer and in depleted hydrocarbon field were considered. The typical size envisioned for the pilot was 100 kt CO<sub>2<sub/> per year. GéoCarbone-PICOREF initially focused on a “Regional Domain”, ca. 200 × 150 km, in the Paris Basin. It was attractive for the following reasons: detailed geological data is available, due to 50 years of petroleum exploration; basin-scale deep saline aquifers are present, with a preliminary estimate of storage capacity which is at the Gt CO<sub>2<sub/> level, namely the carbonate Oolithe Blanche Formation, of Middle Jurassic age, generally located between 1500 and 1800 m depths in the studied area, and several sandstone formations of Triassic age, located between 2000 and 3000 m; several depleted oil fields exist: although offering storage capacities at a much lower level, they do represent very well constrained geological environments, with proven sealing properties; several sources of pure CO<sub>2<sub/> were identified in the area, at a flow rate compatible with the pilot size, that would avoid capture costs. 750 km of seismic lines were reprocessed and organized in six sections fitted on well logs. This first dataset provided improved representations of: the gross features of the considered aquifers in the Regional Domain; the structural scheme; lateral continuity of the sealing cap rocks. An inventory of the environmental characteristics was also made, including human occupancy, protected areas, water resource, natural hazards, potential conflicts of use with other resources of the subsurface, etc. From all these criteria, a more restricted geographical domain named the “Sector”, ca. 70 × 70 km, was chosen, the most appropriate for further selection of storage site(s). The geological characterization of the Sector has been as exhaustive as possible, with the reprocessing of additional 450 km of seismic lines, and the collection of a complete well-data base (146 petroleum wells). At this scale a relatively detailed characterization of the sedimentary layers could be done, in particular the formations potentially rich in aquifer units. For the Middle Jurassic carbonates observations were made on analogue sediments outcropping 150 km to the east of the Sector. A geological and numerical 3-D representation of the whole sedimentary pile of the Sector area was built. It forms a basis for constructing grids used by codes able to simulate various processes induced by CO<sub>2<sub/> injection (displacement of the fluids, pressure build-up and release, mechanical deformation, mineral interactions, control of the parameters used to check the local sealing efficiency, etc.). In parallel with that work on aquifers, GéoCarbone-PICOREF has access to all the petroleum data, including production data and reservoir modelling, of the Saint-Martin de Bossenay oil field, localized in the eastern part of the Sector. This was an opportunity to apply a comparable methodology and to test the capabilities of modelling codes to the specific case of a depleted hydrocarbon field, and to show some of the advantages of such a context with respect to a pilot-scale CO<sub>2<sub/> injection.

Destruction of Luzon forearc basin from subduction to Taiwan arc–continent collision

Along offshore to the east of southern Taiwan, different stages of subduction and collision occur simultaneously along strike of the convergent boundary. As a result, the evolution of the Luzon arc and its forearc basin can be studied from the younger subduction zone to the south to the collision zone to the north. Examining more than 8000 km of seismic lines, we analyzed the seismic stratigraphy of strata in a forearc basin and its successive basins in the collision zone, to study the processes related to arc collapse and forearc basin closure. The study area presents three evolutional stages: intra-oceanic subduction, initial arc–continent collision, and arc–continent collision. We divided 9 seismic sequences in the forearc basin and found older, sub-parallel basin-fill sequences (4–9) and younger, divergent sequences (1–3). Isochron maps of the sequences were used to interpret different deformation modes and their areal extends. On the arc side of the basin of the subduction and initial collision zones, we found relatively undisturbed strata, showing little arc deformation. On the trench side, the growth strata in sequences 1 through 3 are the result of recent tectonic wedging along the rear of the accretionary prism. Tectonic wedging and back-thrusts incorporate the forearc strata into the rear of the accretionary prism until they close the forearc basin at a region with a 2200 m basement relief. This relief is not caused by active deformation, as young flat forearc strata lap onto it and mark the transition from initial collision to collision where many growth strata to the north suggest abrupt increase in active arc basement deformation. The (1) deforming basement, (2) back-thrusts, and (3) other sedimentary processes affect the architecture of the successive basins in the collision zone until the arc is juxtaposed to the rear of the fold and thrust belt on land.

Net Community Benefits and Seismic Line Rehabilitation — A Case Study

In 1999 the Petroleum Group of Primary Industries arid Resources South Australia (PIRSA) conducted an audit of seismic lines in the Cooper Basin of South Australia, to assess their condition upon expiry of Petroleum Exploration Licences (PLLsl 5 and 6. A significant number of seismic lines located in gihber plains and residual tablelands to the north of Innamincka were identified as being in poor condition, particularly in regard to active erosion.Detailed assessment of the condition of 1200 km of seismic lines was made using maps produced from low-level aerial videography.Key stakeholders agreed that physical rehabilitation of windrows or erosional gullies would be unlikely to make a significant improvement to the environmental condition of the lines. This is consistent with other published research on rehabilitation attempts in similar terrains. Rather than wasting money and effort by forcing the licensees (primarily Santos Lid) to undertake any physical rehabilitation, PIRSA, Santos, and the Department for Environment and Heritage (DEH) agreed that funding of other environmental projects in the Innamincka Regional Reserve would provide a better net benefit to the local environment.The licensees offered to fund projects to a total of SA660 000 as an offset to undertaking physical rehabilitation. The South Australian Government has accepted this offer. A formal agreement and implementation plan has been developed for the licensees to fund a range of environmental projects within the Innamincka Regional Reserve. In return, the Government agrees that no further rehabilitation of the lines will he required.

Winter Habitat Use by American Marten, &lt;em&gt;Martes americana&lt;/em&gt;, in Western Alberta Boreal Forests

Although the American Marten (Martes americana) is found in most forest regions of Alberta, little is known about its choice of winter habitats. This study investigated winter habitat use by American Marten in Weyerhaeuser’s Grande Prairie Forest Management Area (FMA) using snowtracking along 128.2 km of seismic lines inventoried in winters 1999, 2002, and 2005 with snowmobiles. American Marten tracks (n = 44) occurred significantly less frequently than expected (P &lt; 0.001) in immature/young pole stands, but more frequently than expected (P &lt; 0.02) in mature/old growth mixedwood stands. American Martens apparently used young forests, and mature/old coniferous and deciduous stands, according to their availability. Forest development plans should be developed locally to retain late successional forests that meet the winter habitat requirements of American Marten.

Potential impacts of petroleum exploration and exploitation on biodiversity in a Patagonian Nature Reserve, Argentina

Petroleum exploration and extraction are common on the Patagonian steppe, but their impacts on the native biodiversity have not been properly evaluated. We describe both activities in a Patagonian nature reserve and consider their potential impacts on biodiversity. More than 2025 km of seismic lines inside the reserve resulted in 87.21 m2/ha (0.9%) of directly affected land, and 793 fragments of native habitats were defined with a mean area of 1.26 ± 0.74 km2. Vegetation recovery on seismic lines is extremely poor. We discuss the role of seismic lines as barriers to native species, and their significance in encouraging poaching and the expansion of exotic invasive plants. There is a high degree of overlap between current petroleum activities and areas of special conservation concern (high erosion risk, vegetation diversity, abundance of endemic plant species, and habitat quality for native vertebrates). All these have a significant impact on the efficiency of the conservation area and highlight the urgent need to implement appropriate mitigating actions.

Environmental management in resource-rich Alberta, Canada: first world jurisdiction, third world analogue?

Economic growth is frequently touted as a cure for environmental ills, particularly for those in Third World countries. Here we examine that paradigm in a case study of Alberta, Canada, a wealthy, resource-rich province within a wealthy nation. Through provincial-scale datasets, we examine the increasing pressures of the forest, petroleum, and agricultural industries upon the ecosystems of Alberta within management, economic, and political contexts. We advance the thesis that economic activity leads to environmental degradation unless ecosystem-based management is integrated into economic decision making. Agricultural lands cover 31·7%, and forest management areas leased to industry cover 33·4% of Alberta; both continue to increase in extent. The rate of logging (focused on old-growth by government policy) continues a decades-long exponential rise. Current Alberta annual petroleum production is 52·5million m3crude oil and 117billion m3of gas. As of early 1999, there were ∼199025 oil and gas wells and a conservative total of ∼1·5–1·8million km of seismic lines in Alberta. Fire occurrence data indicate no downward trends in annual area burned by wildfire, which may be characterized as driven by climate and inherently variable. When logging and wildfire are combined, the annual allowable cut in Alberta is unsustainable, even when only timber supply is considered and the effects of expanding agriculture and oil and gas activities are ignored. Ecosystem degradation in Alberta is pervasive and contrasts prominently with a high standard of living. A wealth of ecological data exists that indicates current resource-based economic activities are non-sustainable and destructive of ecosystem health yet these data are not considered within the economic decision making process. Given the complex, compounded, and increasing ecosystem perturbations, a future of unpleasant ecological surprises is likely. We conclude with tentative predictions as to where current trends in Alberta may lead if decisions biased against ecosystems continue.

Tectono‐sedimentary evolution of the northernmost margin of the NE German Basin between uppermost Carboniferous and Late Permian (Rotliegend)

AbstractThe tectono‐sedimentary evolution of the Rotliegend deposits of the northernmost margin of NE German Basin (NEGB) has been analysed on the basis of detailed sedimentary logs of 300 m of core material together with the re‐evaluation of 600 km of seismic lines. Three distinct phases were recognized. During the initial Phase I, basin geometry was largely controlled by normal faulting related to deep‐seated ductile shearing leading to a strong asymmetric shape, with a steep fault‐controlled eastern margin and a gently, dipping western margin. The results of forward modelling along a cross‐section fit the basin geometry in width and depth and reveal a footwall uplift of c. 1000 m. Adjacent to the steep faults, local sedimentation of Lithofacies Type I was confined to non‐cohesive debris flow‐dominated alluvial fans, whereas the gently dipping western margin was dominated by alluvial‐cone sedimentation.During the post‐extensional period (Phase II), cooling of the lithosphere generated additional accommodation space. The sediments of Lithofacies Type II, comprising mainly clast‐supported conglomerates, are interpreted as braided ephemeral stream flow‐surge deposits. Tectonic quiescence and an increase in flood events resulting from wetter climate led to progradation of this facies over the entire region. At the end of this period, the accommodation space was almost completely filled resulting in a level topography.Phase III was controlled by the thermal‐induced subsidence of the southerly located NEGB in post‐Illawarra times. The formerly isolated region tilted towards the SW, thus forming the northern margin of the NEGB during uppermost Havel and Elbe Subgroup times. The sediments of Lithofacies Type III were divided into a marginal sandstone‐dominated environment and a finer‐grained facies towards the SW. The former consists of poorly‐sorted coarse‐grained sandstones of a proximal and medial ephemeral stream floodplain facies. The latter comprise mud flat fines and fine‐grained distal ephemeral stream deposits. The end of the tectono‐sedimentary evolution is marked by the basinwide Zechstein transgression. Copyright © 2001 John Wiley &amp; Sons, Ltd.

Presence of Stratigraphic Traps in the Back Arc Basins of the Southern Shelf of Cuba: ABSTRACT

ABSTRACT For the last ten years the southern shelf of Cuba has been theobject of seismic investigations, mainly in the Ana Maria and Guacanayabo areas. More than 4000 km of seismic lines with 3000% have been shot. These seismic surveys have confirmed the following geological events: Presence of back arc extensional basins as a result of the ocean/ocean subduction. These basins have formed since Middle Cretaceous. Presence of sedimentary sequences with thickness changes of between 3.0-7.0 km. Predominance of an extensional regime since Middle Cretaceous with subsidence, accommodation and extension of the rocks. Development of stratigraphic traps, mainly associated with reef facies and slope fans of Late Cretaceous-Early Tertiary. These traps can reach hundreds of square kilometers. They have very clear dynamic expression in the seismic section and usually form anomaly zones. Over these seismic anomalies some reverberation can be observed which could be related to hydrocarbon flows. The depth of the traps changes between 1.5-3.5 km. More than thirty have been localized. Probably a wrench tectonic system has been present in these basins since Middle Eocene. Oil and gas seepage as well as seal sequences are present in some wells. According to their origin and evolution they can be similar to the great oil basins of Venezuela and Colombia. End_of_Record - Last_Page 478-------

Seismic sequence stratigraphy of the Tertiary sediments, offshore Sarawak deepwater area, Malaysia

A seismic sequence stratigraphic interpretation was carried out in the Sarawak deepwater area with the main objective of developing a workable chronostratigraphic chart that defines stratigraphic boundaries within which depositional systems and lithofacies can be identified, mapped and interpreted. The dataset includes 8,000 km of seismic lines and well data from four drilled locations. . The study has resulted in the identification and correlation of eight seismic horizons representing the tops of eight depositional sequences which are grouped into four mega/supersequences (A, B, C and D) based on regional tectonic events of the South China Sea. Six of the seismic horizons have been tied to the four wells and dated based on paleontologic data. Two other older horizons are dated based on correlation to the global sea-level chart. Higher order sequences are also interpreted from paleontologic, lithologic, paleofacies data and GR-Iogs from the four wells. Seismic facies analysis have also been carried out in the study area where four main seismic facies (Facies I-IV) lunging from non-marine to deepmarine facies are interpreted. Seismic facies maps constructed for lower and upper portions of Oligocene-Lower Miocene Supersequence C indicate that it contains all four main facies. This supersequence is overall transgressive and its paleoshoreline runs in a NW-SE direction. A seismic facies map generated for Middle Miocene-Recent Supersequence D suggests that it contains mainly outer shelf to deepmarine facies (Facies III-IV) and its paleoshoreline runs in an East-West direction. A workable chronostratigraphic chart has been developed where second to fourth-order sequences can be correlated within the study area. The chart is able to correlate the episodic rifting ofRu and Pigott (1986), the local structural history and Shell's sedimentary Cycles I-VIII (Ho, 1978) to the global sea­ level curve (Haq et al., 1988). This study also assisted in identifying potential play-types. Structural traps of non-marine to shallow marine facies are mainly confined to Supersequence C while stratigraphic traps of basin floor fans are located mainly in Supersequence D.

ENVIRONMENTAL SENSITIVITY AND PROTECTION FOR THE NORTHEAST CASPIAN SEA

ABSTRACT An environmental sensitivity and impact analysis was performed for the largest ever two-dimensional marine geophysical survey to be conducted in the Kazakhstan sector of the Caspian Sea. A total of 35,000 km of seismic lines are to be shot covering an offshore area of 100,000 km2. The purpose of the environmental studies is to identify critical environmental sensitivities and to develop operating rules for the seismic work to protect the environment.

Implications of Mesozoic—Recent basin development in the western Inner Moray Firth, UK

A new interpretation of a comprehensive seismic database, consisting of over 5000 km of seismic lines, contradicts the notion that strike-slip motion on the Great Glen Fault (GGF) was the dominant control on Mesozoic basin development in the Inner Moray Firth, UK. It is suggested that the GGF, which may have been active during Palaeozoic times, lay dormant during the Mesozoic and that normal fault systems (such as the Helmsdale-Wick system), formed during two extensional events (pre-Jurassic and Late Jurassic), were the dominant controls on Mesozoic basin evolution. The present expression of the GGF as a discrete, sub-vertical through-going fault attests to its subsequent activity as a divergent wrench structure as part of limited oblique-slip motion after the Early Cretaceous. It seems most likely that such movements occurred in the Tertiary and may have been contemporaneous with regional uplift of the Scottish Highlands during Palaeocene-Eocene (Thulean) events, in response to north-east Atlantic rifting or subsequent Oligo-Miocene (Alpine) tectonism. The new model aids the understanding of the area's general hydrocarbon prospectivity. It can now be demonstrated that the most likely kitchen area for oil resident in the Beatrice Field was centred in the Sutherland Terrace area to the north-west when it formed the site of an active half-graben. Maturation in, and direct up-dip migration from, that area probably took place at the time of maximum burial during the Late Jurassic and Cretaceous, below the half-graben depocentre adjacent to the Helmsdale Fault. Subsequent regional uplift and dissection of the Sutherland Terrace may have served to take the kitchen area out of the maturation window and led to reactivation of several pre-existing structures. Breach and remigration of hydrocarbons is likely to have occurred as a result of the later motions.