The Alberta foreland basin: relationship between stratigraphy and Cordilleran terrane-accretion events

1989 ◽  
Vol 26 (10) ◽  
pp. 1964-1975 ◽  
Author(s):  
Douglas J. Cant ◽  
Glen S. Stockmal
Keyword(s):  
Sea Level ◽  
Foreland Basin ◽  
Temporal Correlation ◽  
Sediment Supply ◽  
Passive Margin ◽  
Sea Level Fluctuations ◽  
Lithospheric Flexure ◽  
Half Wavelength ◽  
Bending Stresses ◽  
Clastic Wedges

A foreland-basin sequence resulting from accretion of a terrane to a continental passive margin ideally should be unconformity bounded, with a shallowing-upward pattern, like the classic Flysch to Molasse sequence of Alpine foreland basins. The basal unconformity is cut as the peripheral bulge associated with lithospheric flexure migrates cratonward ahead of the basin and the advancing overthrusts. The shallowing occurs because sediment supply at first is low – early stages of accretion near the continental slope generate little or no topography above sea level; later stages result in significant tectonic uplift, and much sediment is shed into the foreland, filling the basin. The upper unconformity is cut as lithospheric bending stresses are relaxed following overthrusting, and reduction of the flexural load on the lithosphere through erosion and (or) tectonic denudation of the overthrusts causes regional uplift or basin "rebound". Actual sequences show differences from this idealized version in that (i) basal unconformities may not develop under conditions of high eustatic sea level; and (ii) they may not shallow upward in all cases. These differences can occur because later terranes that accrete onto the seaward side of a previously accreted terrane may simply push it farther onboard, thus initiating sediment supply as rapidly as the load-induced subsidence. Also, in this way, a small terrane can influence the filling of a foreland basin that is more than one "lithospheric flexural half-wavelength" away from the site of accretion.The stratigraphy of the Alberta basin has been divided after comparison with the idealized sequence resulting from an individual accretion event. The six clastic wedges recognized (Fernie–Kootenay, Mannville, Dun vegan, Belly River, Edmonton, and Paskapoo) show a temporal correlation with the times of accretion of terranes (Intermontane superterrane, Bridge River, Cascadia, Insular superterrane, Pacific Rim – Chugach, and Olympic, respectively) in the Cordillera. Therefore, the stratigraphy of the foreland basin may be best interpreted in terms of Cordilleran tectonics rather than sea-level fluctuations. Eustatic sea-level variations are believed to affect the internal stratigraphy and sedimentology of some clastic wedges and are responsible for the deposition of some thin units, but they appear to operate on time scales that differ from those of the clastic wedges identified here.

scholarly journals Impact of sea-level fluctuations on the sedimentation patterns of the SE African margin: implications for slope instability

2019 ◽  
Vol 500 (1) ◽  
pp. 267-276 ◽  
Author(s):  
Aaron Micallef ◽  
Aggeliki Georgiopoulou ◽  
Andrew Green ◽  
Vittorio Maselli
Keyword(s):  
South Africa ◽  
Sea Level ◽  
Coastal Region ◽  
Passive Margin ◽  
Slope Instability ◽  
Bottom Current ◽  
The South ◽  
Sea Level Fluctuations ◽  
International Ocean Discovery Program ◽  
Seismic Reflection Profiles

AbstractThe sheared-passive margin offshore Durban (South Africa) is characterized by a narrow continental shelf and steep slope hosting numerous submarine canyons. Supply of sediment to the margin is predominantly terrigenous, dominated by discharge from several short but fast-flowing rivers. International Ocean Discovery Program Expedition 361 provides a unique opportunity to investigate the role of sea-level fluctuations on the sedimentation patterns and slope instability along the South African margin. We analysed >300 sediment samples and downcore variations in P-wave, magnetic susceptibility, bioturbation intensity and bulk density from site U1474, as well as regional seismic reflection profiles to: (1) document an increase in sand input since the Mid-Pliocene; (2) associate this change to a drop in sea-level and extension of subaerial drainage systems towards the shelf-edge; (3) demonstrate that slope instability has played a key role in the evolution of the South Africa margin facing the Natal Valley. Furthermore, we highlight how the widespread occurrence of failure events reflects the tectonic control on the morphology of the shelf and slope, as well as bottom-current scour and instability of fan complexes. This information is important to improve hazard assessment in a populated coastal region with growing offshore hydrocarbon activities.

scholarly journals Quantitative stratigraphic analysis in a source-to-sink numerical framework

2018 ◽  
Author(s):  
Xuesong Ding ◽  
Tristan Salles ◽  
Nicolas Flament ◽  
Patrice Rey
Keyword(s):  
Sea Level ◽  
Trajectory Analysis ◽  
Rate Of Change ◽  
Sediment Supply ◽  
Passive Margin ◽  
Shelf Edge ◽  
Analysis Method ◽  
Source To Sink ◽  
Sedimentary Architecture ◽  
Thermal Subsidence

Abstract. The sedimentary architecture at continental margins reflects the interplay between the rate of change of accommodation creation (δA) and the rate of change of sediment supply (δS). As a result, stratigraphic interpretation increasingly focuses on understanding the link between deposition patterns and changes in δA/δS. Here, we use the landscape modelling framework pyBadlands to assess the respective performance of two well-established stratigraphic interpretation techniques: the trajectory analysis method and the accommodation succession method. In contrast to most Stratigraphic Forward Models (SFMs), pyBadlands provides self-consistent sediment supply to basin margins as it simulates erosion, sediment transport and deposition in a source-to-sink context. We present a landscape evolution that takes into account periodic sea level variations and passive margin thermal subsidence over 30 million years, under uniform rainfall. We implement the two aforementioned approaches to interpret the resulting depositional cycles at the continental margin. We first apply both the trajectory analysis and the accommodation succession methods to manually map key stratigraphic surfaces and define stratigraphic units from shelf-edge (or offlap break) trajectories, stratal terminations and stratal geometries. We then design a set of post-processing numerical tools to calculate shoreline and shelf-edge trajectories, the temporal evolution of changes in accommodation and sedimentation, and automatically produce stratigraphic interpretations. Comparing manual and automatic stratigraphic interpretations reveals that the results of the trajectory analysis method depend on time-dependent processes such as thermal subsidence whereas the accommodation succession method does not. In addition to reconstructing stratal stacking patterns, the tools we introduce here make it possible to quickly extract Wheeler diagrams and synthetic cores at any location within the simulated domain. Our work provides an efficient and flexible quantitative sequence stratigraphic framework to evaluate the main drivers (climate, sea level and tectonics) controlling sedimentary architectures and investigate their respective roles in sedimentary basins development.

Ample and recurrent sea-level fluctuations during the Bajocian: A hint towards middle Jurassic glacio-eustatism

2020 ◽  
Author(s):  
Stéphane Bodin ◽  
Jan Danisch ◽  
Malte Mau ◽  
Francois-Nicolas Krencker ◽  
Alexis Nutz ◽  
...  
Keyword(s):  
Sea Level ◽  
Middle Jurassic ◽  
Sediment Supply ◽  
Medium Term ◽  
High Atlas ◽  
Sea Level Fluctuations ◽  
R Packages ◽  
Central High ◽  
Central High Atlas

<p><span>Mesozoic sea-level fluctuations have been a matter of debate for several decades, especially the extend and origin of sea-level cycles that have a periodicity of about 1 Myr or less. The debate lies in the main driving mechanism for sequence development (global sea-level or sediment flux variations) as well as the reason behind water exchanges between the continents and the oceans (glacio- or aquifer-eustatism). In this study, we focus on the carbonate-dominated sedimentary record of the Bajocian (Middle Jurassic) in the Central High Atlas Basin of Morocco. Several aspects make this basin an appropriate location for discussing Middle Jurassic sea-level changes. Firstly, the outstanding exposures of the High Atlas Mountains, with continuous exposures for 10s of kilometres, allow to describe and track sedimentary packages and their bounding surfaces from proximal to distal settings. Moreover, a combination of ammonite and brachiopod biostratigraphy with carbon-isotopes chemostratigraphy allows to temporarily constrain their development, which permits to correlate and compare the Central High Atlas sedimentary record to other basins. Finally, due to high-subsidence rates, thick Bajocian sedimentary sequences have accumulated, minimizing condensation and hiatus that might prevail in other basins due to a lack of accommodation space creation. Two Bajocian long-term transgressive-regressive (T-R) packages are observed throughout the basin. They are modulated by several medium-term T-R packages, that have each an approximate duration of 1 Myr. These sequences can also be correlated on a basinwide scale. Combined with sedimentological and facies analyses, architectural evidence along proximal-to-distal transect illustrates that several of the medium-term sequences are characterized by the presence of a falling stage and lowstand systems tracts, demonstrating that medium-term T-R stacking patterns are not solely linked to fluctuation in sediment supply, but also to episodes of relative sea-level fall of at least 30m of amplitude. This is confirmed by backstripping analysis performed in a composite section from the center of the Basin. Comparison with Bajocian deposits from France and Scotland, where good biostratigraphic dating is also available, shows that similar contemporaneous sea-level fall can be observed, highlighting their potential global character. The two long-term Bajocian sequences are more difficult to correlate on a global scale, suggesting that they are rather primarily linked to fluctuation in regional sediment supply or dynamic topography processes. The exact cause of the Bajocian medium-term sea-level falls is currently unknown, but it is here interesting to note that a relatively cool globate climate has been postulated for the Middle Jurassic, suggesting that glacio-eustasy was their most likely driver.</span></p>

scholarly journals Lower Badenian coarse-grained Gilbert deltas in the southern margin of the Western Carpathian Foredeep basin

2018 ◽  
Vol 69 (1) ◽  
pp. 89-113 ◽  
Author(s):  
Slavomír Nehyba
Keyword(s):  
Sea Level ◽  
Foreland Basin ◽  
Sediment Supply ◽  
Coarse Grained ◽  
Basal Surface ◽  
Relative Sea Level ◽  
Sediment Delivery ◽  
Southern Margin ◽  
Stratigraphic Architecture ◽  
Carpathian Foredeep

AbstractTwo coarse-grained Gilbert-type deltas in the Lower Badenian deposits along the southern margin of the Western Carpathian Foredeep (peripheral foreland basin) were newly interpreted. Facies characterizing a range of depositional processes are assigned to four facies associations — topset, foreset, bottomset and offshore marine pelagic deposits. The evidence of Gilbert deltas within open marine deposits reflects the formation of a basin with relatively steep margins connected with a relative sea level fall, erosion and incision. Formation, progradation and aggradation of the thick coarse-grained Gilbert delta piles generally indicate a dramatic increase of sediment supply from the hinterland, followed by both relatively continuous sediment delivery and an increase in accommodation space. Deltaic deposition is terminated by relatively rapid and extended drowning and is explained as a transgressive event. The lower Gilbert delta was significantly larger, more areally extended and reveals a more complicated stratigraphic architecture than the upper one. Its basal surface represents a sequence boundary and occurs around the Karpatian/Badenian stratigraphic limit. Two coeval deltaic branches were recognized in the lower delta with partly different stratigraphic arrangements. This different stratigraphic architecture is mostly explained by variations in the sediment delivery and /or predisposed paleotopography and paleobathymetry of the basin floor. The upper delta was recognized only in a restricted area. Its basal surface represents a sequence boundary probably reflecting a higher order cycle of a relative sea level rise and fall within the Lower Badenian. Evidence of two laterally and stratigraphically separated coarse-grained Gilbert deltas indicates two regional/basin wide transgressive/regressive cycles, but not necessarily of the same order. Provenance analysis reveals similar sources of both deltas. Several partial source areas were identified (Mesozoic carbonates of the Northern Calcareous Alps and the Western Carpathians, crystalline rocks of the eastern margin of the Bohemian Massif, older sedimentary infill of the Carpathian Foredeep and/or the North Alpine Foreland Basin, sedimentary rocks of the Western Carpathian/Alpine Flysch Zone).

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