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Salt dissolution collapse-subsidence is proposed as the dominant tectono-stratigraphic control on the deposition of major sand trends across the northern Athabasca Oil Sands Deposit. Salt removal along linear dissolution trends 200 m below in the Prairie Evaporite (Middle Devonian) halite beds resulted in the collapse of the overlying Upper Devonian strata. The collapse- induced differential subsidence of the fault blocks formed the floor underlying the McMurray deposits in the 50 km long V-shaped Bitumount Trough extending across the northern area of the Athabasca Oil Sands Deposit. The lower and middle-upper McMurray sand trends filled the accommodation created by collapses of a linear chain of Upper Devonian fault blocks along the northern margin of the western Trough. A pair of tens-of-metres thick and 20-30 km long sand trends developed parallel in overlying accumulations of the lower and middle-upper McMurray Formation (Aptian). This half-graben tilted northward as the dissolution trend in the underlying Prairie Evaporite salt scarp widened, and the scarp margin was deeply embayed. Salt dissolution-induced structures were the principal control that located the large sand complexes exploited by bitumen mining projects. Earlier models of McMurray architecture interpreted the underlying karst collapse to have been largely pre-Cretaceous. This new architectural model reinterprets the spatiotemporal balance between erosion at the pre-Cretaceous surface and within the buried salt beds. Extensive salt removal resulted in collapse of the underlying hypogene karst during the late Aptian age. This resulted in the over-thickened multi- kilometres long McMurray sand trends. The underlying karst collapse resulted in unstable deposition surfaces along the sub-Cretaceous trough floors. This tectono-stratigraphic architecture, called the syndepositional model in this study, is proposed as an alternative to two other models, one of which proposes that deeply incised channel valleys and fills resulted from multiple significant sea-level fluctuations, while the other proposes that stacked parasequences accumulated along overlying shallow channels that meandered across a stable fluvio-estuarine coast. La dissolution de sel causant la subsidence / l'effondrement est proposee en tant que le controle tectonique / stratigraphique dominant de la tendance de la deposition du sable a travers le secteur nord du gisement des sables bitumineux de l'Athabasca. Le retrait du sel le long de tendances de dissolution lineaires a 200 m plus bas dans les lits de halite Prairie Evaporite (Devonien moyen) a cause l'effondrement des strates du Devonien superieur qui se trouvaient au-dessus. La subsidence differentielle, engendree par l'effondrement de blocs de faille, a forme le plancher sous les gisements McMurray dans la fosse Bitmount, laquelle a une longueur de 50 km et une forme en V. Cette fosse s'etend a travers le secteur nord du gisement de sables bitumineux de l'Athabasca. Les tendances de sable inferieures et moyennes-superieures remplissaient l'espace disponible cree par l'effondrement d'une chaine lineaire de blocs de faille (Devonien superieur) le long de la bordure nord de la fosse Ouest. Une paire de tendances de sable de quelques dizaines de metres d'epaisseur et d'une longueur de 20 a 30 km s'est developpee parallelement aux accumulations sus-jacentes de la Formation de McMurray inferieure et moyenne-superieure (Aptien). Ce demi-graben s'est incline vers le nord alors que la tendance a la dissolution dans l'escarpement sous-jacent de sel Prarie Evaporite se developpait et que la bordure de l'escarpement etait grandement decoupee. Les structures causees par la dissolution du sel constituaient le principal controle qui a positionne les vastes complexes de sable exploites par les projets d'extraction du bitume. Selon des modeles anterieurs de l'architecture de la Formation de McMurray, l'effondrement des karsts sous-jacents a eu lieu principalement au pre-Cretace. Le present nouveau modele architectural reinterprete l'equilibre spatio-temporel entre l'erosion a la surface, au pre-Cretace, et a l'interieur des lits de sel enfouis. Le retrait a grande echelle du sel a cause l'effondrement du karst hypogene sous-jacent durant l'Aptien. Cela a donne les tendances de sable sur- epaissies de la Formation de McMurray sur plusieurs kilometres. L'effondrement sous-jacent du karst a donne des surfaces de deposition instables le long des planchers de la fosse sous-jacente au sous-Cretace. Cette architecture tectonostratigraphique, nommee modele synsedimentaire dans la presente etude, est proposee en tant qu'option de rechange a deux autres modeles : l'un propose que les vallees fortement entaillees et les remplissages decoulaient de nombreuses fluctuations importantes du niveau de la mer et l'autre propose que des parasequences empilees se soient accumulees le long de chenaux peu profonds sus-jacents qui serpentaient a travers une cote fluvio-estuarienne stable. [Traduit par le Redaction], Introduction The Lower Cretaceous (Aptian) McMurray Formation strata accumulated the largest known bitumen sand resource across several areas of northeastern Alberta, estimated at nearly 270 billion [m.sup.3] of bitumen-in-place by [...]

We use inverse models of mantle convection to explore the vertical evolution of the Colorado Plateau. By satisfying multiple constraints (seismic tomography, stratigraphy in the western United States and Great Plains, and other structural and volcanic data adjacent to the plateau), the model provides predictions on the continuous history of Colorado Plateau vertical motion since 100 Ma. With the arrival of the flat-lying Farallon slab, dynamic subsidence swept from west to east over the plateau and reached a maximum ca. 86 Ma. Two stages of uplift followed the removal of the Farallon slab below the plateau: one in the latest Cretaceous and the other in the Eocene with a cumulative uplift of ~1.2 km. Both the descent of the slab and buoyant upwellings raised the plateau to its current elevation during the Oligocene. A locally thick plateau lithosphere enhances the coupling to the upper mantle so that the plateau has a higher topography with sharp edges. The models predict that the plateau tilted downward to the northeast before the Oligocene, caused by northeast-trending subduction of the Farallon slab, and that this northeast tilting diminished and reversed to the southwest during the Miocene in response to buoyant upwellings. doi: 10.1130/G30624.1

[1] We use seismic reflection and rock sample data to propose that the first-order physiography of New Caledonia Trough and Norfolk Ridge formed in Eocene and Oligocene time and was associated with the onset of subduction and back-arc spreading at the Australia-Pacific plate boundary. Our tectonic model involves an initial Cretaceous rift that is strongly modified by Cenozoic subduction initiation. Hence, we are able to explain (1) complex sedimentary basins of inferred Mesozoic age; (2) a prominent unconformity and onlap surface of middle Eocene to early Miocene age at the base of flat-lying sediments beneath the axis of New Caledonia Trough; (3) gently dipping, variable thickness, and locally deformed Late Cretaceous strata along the margins of the trough; (4) platform morphology and unconformities on either side of the trough that indicate a phase of late Eocene to early Miocene uplift to near sea level, followed by rapid Oligocene and Miocene subsidence of ~ 1100-1800 m; and (5) seismic reflection facies tied to boreholes that suggest absolute tectonic subsidence at the southern end of New Caledonia Trough by 1800-2200 m since Eocene time. The Cenozoic part of the model involves delamination and subduction initiation followed by rapid foundering and rollback of the slab. This created a deep (>2 km) enclosed oceanic trough, ~2000 km long and 200-300 km across, in Eocene and Oligocene time as the lower crust detached, with simultaneous uplift and local land development along basin flanks. Disruption of Late Cretaceous and Paleogene strata was minimal during this Cenozoic phase and involved only subtle tilting and local reverse faulting or folding. Basin formation was possible through the action of at least one detachment fault that allowed the lower crust to either be subducted into the mantle or exhumed eastward into Norfolk Basin. We suggest that delamination of the lithosphere, with possible mixing of the lower crust back into the mantle, is more widespread than previously thought and may be commonly associated with subduction initiation, such as Cenozoic events in the Mediterranean and western Pacific. doi: 10.1029/2009TC002476

Subsidence is a common cause of amplified relative sea-level rise, flooding, and erosion in coastal environments. In particular, subsidence due to sediment consolidation can play a significant role in relative sea-level rise in large deltas. We use a combination of InSAR (interferometric synthetic aperture radar), leveling, and global positioning system data to map absolute vertical land motion in the Fraser River delta, western Canada. We show that primary consolidation of shallow Holocene sediments is the main cause for the slow subsidence (-1 to -2 mm/a) affecting the delta lowlands. In addition, parts of the delta undergo increased anthropogenic subsidence. Rapid subsidence rates (-3 to -8 mm/a) are associated with recent artificial loads and exhibit a first-order exponential decrease with a time constant of ~20 years, consistent with the theory of consolidation. Assuming two sea-level rise scenarios of 30 or 100 cm by the end of the twenty-first century, natural subsidence will augment relative sea-level rise in the Fraser Holocene lowlands by ~50% or ~15%. Anthropogenic subsidence will augment relative sea-level rise b y ~130% or ~40%, potentially raising it to as much as 1-2 m. In deltaic, lacustrine, and alluvial environments, anthropogenic sediment consolidation can result in significant amplification and strong spatial variations of relative sea-level rise that need to be considered in local planning.

Modeling the shrinkage and subsidence of soils is generally based on the laboratory shrinkage curves established from liquid state to shrinkage limit, rarely exhibited in situ. We studied the vertical behavior of day-dominant soils from the Marais de l'Ouest (France) in the 20 to 100% water content range. The consolidation states were quantified by recording profiles of wet density ([[gamma].sub.b]) and gravimetric water content (W) down to the depth of 2.50 and 2.00 m in a sunflower (Helianthus annuus L.) field and a grassland, respectively. Under the evident surface consolidation, a paleosol was observed at 1.3-m depth in the sunflower field. The W profiles show two superimposed layers: in the upper layer, W increased from the shrinkage limit ([W.sub.s]) to the plasticity limit ([W.sub.p]), the W profiles bounded by the wet and dry season profiles; in the subjacent layer (100% > W > [W.sub.p]), the W profiles were quite constant. The depth of [W.sub.p] marks the end of the downward progression of the shrinkage cracks. The properties of shrinkage were established through drying stages on intact samples. In the [W.sub.s] to [W.sub.p] domain, the linearity of the volume-water content relation allows the modeling of the interseasonal volumetric distribution of the macro-porosity due to the shrinkage cracks. The preliminary model of porosity behavior proposed agrees with the two superimposed layers: the [W.sub.s] to [W.sub.p] domain characterized by isotropic shrinkage (shrinkage geometry factor r = 3), and the W > [W.sub.p] domain characterized by subsidence only (r = 1).

Large deltas are commonly believed to exhibit rapid rates of tectonic subsidence, largely due to sediment loading of the lithosphere. As a result, deltaic plains are prone to accelerated relative sea-level rise, coastal erosion, and wetland loss. Hurricane Katrina's devastation testifies to the severe threat that these processes pose to the Mississippi Delta, but the relative role of tectonics versus other mechanisms causing land subsidence remains elusive. Relative sea-level records derived from basal peat have the potential to quantify differential crustal movements over Holocene time scales with exceptionally high accuracy and precision. Here we present new sea-level index points from two study areas in the southwestern Mississippi Delta that essentially coincide with a recently published detailed relative sea-level record from the eastern part of the delta. Our results show that differential vertical movements among the three study areas have been only ~0.1 mm [yr.sup.-1] We compare our evidence with a recent sea-level compilation from the Caribbean, to a large extent based on data from areas that are tectonically stable. Our sea-level index points nearly coincide with the Caribbean data, showing surprising tectonic stability for considerable sections of the Mississippi Delta. However, the well-documented high subsidence rates in and near the birdfoot of the Mississippi Delta indicate that different conditions prevail there. The rapid wetland loss in coastal Louisiana is likely due, to a considerable extent, to the compaction of Holocene strata. Keywords: Mississippi Delta, sea-level change, subsidence, Holocene.

This study addresses multiple controls on foreland-basin accommodation and contributes to enhanced understanding of the evolution of the northern Andes. The Middle Magdalena Valley Basin (MMVB), Eastern Cordillera, and Llanos Basin are part of a Late Cretaceous-Cenozoic foreland-basin system, east of the Colombian Central Cordillera. Mechanical modeling indicates that the primary control on complex distributions of sedimentary thicknesses, facies, and unconformities was lithospheric flexure in response to crustal loads from the Central and Eastern Cordilleras. Shorter-wavelength folding and paleoaltitude determined the local character of strata. Our mechanical modeling consists of the application of orogenic and sedimentary loads extracted from geologic data on a continuous elastic lithosphere. The results validate two major basin configurations. The first configuration was a Maastrichtian-early Eocene foreland basin coupled with Central Cordillera uplift. Growth strata record continuous sedimentation in the Eastern Cordillera, whereas regional unconformities in the Llanos Basin (distal foreland basin) reflect isostatic adjustments of the basin's amplitude and wavelength to Central Cordillera episodic uplift and tectonic quiescence. The second major basin configuration was characterized by Central Cordillera erosion since middle Eocene times recorded by a regional pediment surface. In the absence of Central Cordillera effective loading, loads from onlapping sediments and Eastern Cordillera piggyback sub-basins provoked post-middle Eocene accommodation in the MMVB and Llanos Basin. Intensified Eastern Cordillera uplift during the Neogene produced basinal tilting recorded by unconformities in the MMVB. This study highlights the importance of assessing the causes of tectonic accommodation as a foundation for interpretation of the evolution of large foreland and intermontane basins. Keywords: basin analysis, subsidence, unconformity, paleogeographic controls, Colombia, Northern Andes.

The conversion of opal A to opal CT is a thermoehemieal diagenetic process that can cause kilometer-scale differential compaction and differential subsidence within elastic sedimentary basins. This is demonstrated for an opal A to opal CT conversion imaged by three-dimensional seismic data on the northeastern Atlantic margin. This diagenetic 'front' has a circular to polygonal ridge-depression morphology. The ridges have a relief of 10-50 m and separate circular to polygonal depressions that have diameters of 1-2 km, some of which link up to form interconnected networks. This morphology initially developed because the host sediments mantled an underlying polygonal fault system and the front tracked deformed stratigraphy. Ridges formed above the tips of the underlying faults, and depressions formed between them. Ridge relief and width then progressively increased due to earlier opal A to opal CT conversion above ridges as well as conversion laterally along beds or bed sets. This caused compaction and concomitant subsidence in the overburden and the development of a circular to polygonal network of overburden troughs aligned with the ridge system. A positive feedback loop was established where additional overburden sediment above the growing ridges reached the depth of conversion ahead of adjacent areas, driving more compaction and differential subsidence. This paper provides the first insights into the large-scale morphological characteristics of opal A to opal CT diagenetic fronts. It demonstrates the potential for a local stratigraphic control on diagenetic front development and morphology and lastly highlights the potential utility of seismic reflection data for understanding diagenetic processes. Keywords: differential compaction, opal A, opal CT, diagenesis, front, differential subsidence.

Since the early 1990s, sinkholes and wide, shallow subsidence features (WSSFs) have become major problems along the Dead Sea shores in Israel and Jordan. Sinkholes are readily observed in the field, but their locations and timing are unpredictable. WSSFs are often difficult to observe in the field. However, once identified, they delineate zones of instability and increasing hazard. In this study we identify, characterize, and measure rates of subsidence along the Dead Sea shores by the interferometric synthetic aperture radar (InSAR) technique. We analyze 16 SAR scenes acquired during the years 1992 to 1999 by the European Remote Sensing ERS-1 and ERS-2 satellites. The interferograms span periods of between 2 and 71 months. WSSFs are observed in the Lisan Peninsula and along the Dead Sea shores, in a variety of appearances, including circular and elongate coastal depressions (a few hundred meters to a few kilometers in length), depressions in ancient alluvial fans, and depressions along salt-diapir margins. Phase differences measured in our interferograms correspond to subsidence rates generally in the range of 0-20 mm/yr within the studied period, with exceptional high rates that exceed 60 mm/yr in two specific regions. During the study period, the level of the Dead Sea and of the associated ground water has dropped by ~6 m. This water-level drop within an aquifer overlying fine-grained, marly layers, would be expected to have caused aquifer-system consolidation, resulting in gradual subsidence. Comparison of our InSAR observations with calculations of the expected consolidation shows that in areas where marl layers are known to compose part of the upper 30 m of the profile, estimated consolidation settlements are of the order of the measured subsidence. Our observations also show that in certain locations, subsidence appears to be structurally controlled by faults, seaward landslides, and salt domes. Gradual subsidence is unlikely to be directly related to the sinkholes, excluding the use of the WSSFs features as predictable precursors to sinkhole formation. Keywords: consolidation, Dead Sea, ground-water level, land subsidence, synthetic aperture radar interferometry