Subsidence Curves Research Articles

Evidence for a synchronous circum‐Iberian subsidence event and its relation to the African‐Iberian plate convergence in the Late Cretaceous

Subsidence curves from Mesozoic sedimentary basins at the southern Iberian margin (Betic Cordilleras) display pronounced changes in subsidence rates around 85 Ma (chron 34, Late Cretaceous, Santonian to earliest Campanian). The subsidence events correlate with changes in the bulk and clay mineral composition in these basins, as well as with an Eoalpine high‐pressure metamorphic event in the western Mediterranean region. The synchroneity with subsidence events observed in basins around the Iberian microplate suggests a causal relationship with the regional plate tectonic setting. We propose that the circum‐Iberian subsidence event was largely controlled by the convergence and incipient collision of the Iberian microplate with Africa.

Error Estimation in Decompacted Subsidence Curves

Subsidence curves, based on decompacted sediment thicknesses, are generally displayed without indicating depth or age errors. This makes their interpretation ambiguous, leading to incorrect identification of subsidence pulses and incorrect identification of periods of steady subsidence. Error analysis should also form part of thermal maturation studies based on such subsidence curves. Formal error analysis of subsidence curves is a complex problem because of the iterative and nonlinear nature of the decompaction calculations. This paper presents an alternative approach, based on Monte Carlo simulation, that allows subsidence curves to be calculated along with error estimates. We also show that identification of subsidence pulses and identification of periods of steady subsidence cannot be made on the basis of such subsidence curves, even when errors are shown, because errors on successive points on the subsidence curves are correlated. Instead, an ensemble of subsidence rate curves must be calculated at the same time as the ensemble of subsidence curves so that a mean subsidence rate curve can be calculated along with associated error estimates.

On the origin of the Southern Permian Basin, Central Europe

A detailed study of the structural and stratigraphic evolution of the Southern Permian Basin during latest Carboniferous to Early Jurassic times, supported by quantitative subsidence analyses and forward basin modelling for 25 wells, leads us to modify the conventional model for the Rotliegend–Zechstein development of this basin. The Late Permian–Early Jurassic tectonic subsidence curves are typical for a Permian to Early Triassic extensional stage that is followed by thermal subsidence. However, a purely extensional model is extremely problematic because active faulting during this time is ‘minor’ and generally hard to document. Using inverse techniques to model the subsidence curves, we quantitatively show that a significant component of Late Permian and Triassic tectonic subsidence can be explained by thermal relaxation of Early Permian lithospheric thinning, and by delayed infilling of paleo-topographic depressions that developed during the Early Permian. In this interpretation, Stephanian–Autunian wrenching resulted in thermal destabilisation of the lithosphere, deep fracturing of the crust, disruption and erosion of its sedimentary cover and regional uplift of the area of the future Southern Permian Basin. Upon termination of wrench tectonics and associated volcanism, towards the end of the Autunian, the Southern Permian Basin began to subside in response to thermal contraction of the lithosphere. The evolving basin was isolated from the World oceans and had subsided possibly up to some 700 m below their level at the beginning of Upper Rotliegend sedimentation. After catastrophic flooding of this paleo-topographic depression at the beginning of the Zechstein, changing sea level, sedimentation and subsidence rates remained essentially in balance. Although the effects of Triassic rifting overprinted parts of the Southern Permian Basin, its overall subsidence pattern persisted well into the Jurassic. In contrast to the remainder of the Southern Permian Basin, Permian and Triassic crustal extension contributed significantly to the subsidence of the Polish Trough.

Quantifying the timing and sense of fault dip slip: New application of biostratigraphy and geohistory analysis

The timing and sense of the dip-slip component of a fault9s motion can be quantified by using geohistory analysis. Geohistory analysis traditionally is used to quantify tectonic subsidence or uplift of marine basins, but is newly applied to evaluate phases of activity of individual faults, including blind faults. Intermittent fault activity and changing sense of dip slip emerge, particularly for faults reactivated under changing kinematic regimes. Through the use of outcrop or core data from two fault blocks on either side of a major fault, the vertical component of displacement can be isolated. Steps of geohistory analysis include generation of (1) a rock-accumulation curve consisting of stratal thicknesses as a function of age, (2) a decompacted sediment-accumulation curve as a function of age, and (3) a total-subsidence curve with paleobathymetry inferred from fossil assemblages and sedimentary structures. Because errors on the inferred water depths are considered to be 20% of the water depth, the method is limited to large-scale faults. The analysis is repeated on both sides of the fault to determine which block subsided or was uplifted faster, thus isolating both the sense of dip slip and its relative magnitude. If both blocks display parallel subsidence curves within the error margins, a period of fault inactivity or pure strike slip is inferred. If the sense of dip slip changed, the subsidence curves cross. If the dip direction of the fault plane is interpreted from field or subsurface data, a change—for example, from an extensional component to a contractional component—also emerges, and the timing of basin inversion is detectable. As a case study, fault activity was evaluated for a mosaic of faults cutting the Messaras basin of Crete, Greece, a Neogene forearc basin that underwent extension followed by transpression. This approach is applicable to neotectonics or ancient tectonics and pertains to subsurface or exhumed faults as well as active faults offshore that generate contrasting water depths across a fault zone.

Late Carboniferous tectonic subsidence in South Wales: implications for Variscan basin evolution and tectonic history in SW Britain

Detailed stratigraphic data have been used to backstrip seven sections from the Carboniferous South Wales coal basin. Resulting tectonic subsidence curves for the interval 319–305 Ma (Namurian–Westphalian D) are convex‐up, indicating increasing subsidence rate with time, with rates between 130 and 250 m Ma −1 , suggesting a foreland basin setting. Forward modelling of subsidence due to flexural loading in front of a propagating orogenic wedge shows that an orogenic load migrating in a north‐northeasterly direction across SW England between 319 and 305 Ma could have generated the backstripped subsidence patterns. Sensitivity tests show that while many of the forward model parameters are poorly constrained, and the model results non‐unique, backstripped subsidence patterns allow reasonable constraint on the different model cases, so that model predictions can be treated as one possibility in a limited range. The predicted load evolution is consistent with current knowledge of tectonic and stratigraphic features of SW England. These results suggest that subsidence in other Late Carboniferous UK basins may also have been influenced by flexure due to a propagating orogenic load.

Modelling rates and distribution of subsidence due to dynamic topography over subducting slabs: is it possible to identify dynamic topography from ancient strata?

Dynamic topography formed over subducting oceanic lithosphere has been proposed as a mechanism to explain certain otherwise anomalous long‐wavelength patterns of subsidence inferred from ancient strata. Forward modelling of mantle flow in response to a subducting slab predicts amplitudes and distributions of dynamic topography that may occur due to various subducting slab geometries and histories. Plotting calculated dynamic topographies at a point against time produces tectonic subsidence curves. These subsidence curves show features such as evolution from convex to concave shape, amplitudes up to ~2000 m, subsidence rates up to ~220 m Myr−1, and a general decrease in subsidence amplitude away from the subduction zone, over a distance of ~2000 km. On many convergent continental margins, dynamic topography is likely to be superimposed on other subsidence mechanisms. In back‐arc basins, subsidence due to dynamic topography should be distinguishable from that due to extensional tectonics based simply on the temporal subsidence evolution expressed in the subsidence curve shapes. In a foreland basin setting, comparing dynamic topography models with forward models of flexural loading suggest the two processes can generate similar temporal subsidence patterns, but that dynamic topography causes subsidence over significantly greater wavelengths. Matches between calculated subsidence due to dynamic topography and backstripped subsidence patterns from Upper Cretaceous strata of the Western Interior Basin, USA, support the hypothesis that a long‐wavelength ‘background subsidence’ was caused by dynamic topography.

Late Vendian–Early Palæozoic tectonic evolution of the Baltic Basin: regional tectonic implications from subsidence analysis

Subsidence analysis was performed on 43 boreholes penetrating the Upper Vendian–Lower Palaeozoic sedimentary succession of the Baltic Basin. The results were related to lithofacial and structural data to elucidate subsidence mechanisms and the regional tectonic setting of basin development. Tectonic subsidence patterns are consistent throughout the basin for the time period studied. An extensional tectonic subsidence event, possibly of two phases, is indicated from the Late Vendian to the beginning of the Middle Cambrian. This event is seen in the southwestern part of the Baltic Basin (Peri-Tornquist zone) until the earliest Cambrian after which it is also observed in the SW–NE-trending Baltic Depression part of the basin. Basin development during this time is interpreted as recording the latest stages of break-up of the Precambrian super-continent Rodinia and ultimately the formation of the Tornquist Sea. The late Middle Cambrian to Middle Ordovician tectonic subsidence pattern of the Baltic Basin is characteristic of post-rift thermal subsidence of the newly formed passive continental margin of Baltica, developed along its southwestern edge. A gradual increase in subsidence rate is observed from the (Middle?) Late Ordovician and throughout the Silurian (particularly for Ludlow and Pridoli times) creating subsidence curves with convex shapes typical of foreland basin development. The rate of Late Silurian tectonic subsidence increases significantly towards the southwest margin of the Baltic basin, adjacent to the present location of the North German–Polish Caledonides. The Baltic Basin therefore appears to have developed primarily as a flexural foreland basin during Silurian oblique collision of Baltica and Eastern Avalonia. A foreland setting is supported by the influx of distal turbidites into the basin from southwest sources in the Late Silurian. Compressional deformation structures of Early Devonian (Lochkovian) age are seen in seismic sections in the central part of the Baltic Basin (Lithuania). These, together with a change in subsidence pattern, mark the end of the Caledonian stage of basin development of the Baltic Basin.

Evolution of the Northeast German Basin — inferences from a 3D structural model and subsidence analysis

A 3D structural model of the Northeast German Basin was evaluated with special emphasis on its evolution as an intracontinental depression. The study includes investigations on subsidence history and structural setting of the basin. Thickness evolution and calculated tectonic subsidence volumes of Permian to Quaternary sediments in the Northeast German Basin indicate that the subsidence history was related to five stages of basin evolution which differ in their subsidence mechanisms. For the initial rift phase in the Late Carboniferous to Early Permian, a dominant thermal event and subordinate horizontal stresses were indicated by thickness variation evolution and by structural evidence. The main part of basin subsidence occurred in a NW–SE-oriented basin in the subsequent phase of thermal relaxation with maximum subsidence from Early Permian (Rotliegend) to Middle Triassic (Muschelkalk). From Middle Triassic the thermal subsidence pattern was superposed by further tectonic events. In the Middle Triassic regional extension led to a reconfiguration of the southern part of the basin, where new NNE–SSW-trending troughs (Rheinsberg and Gifhorn Troughs) developed. In the Jurassic the northwestern part of the basin was uplifted while in the south the Keuper subsiding areas continued to sink and NW–SE-trending depressions, related to salt margins, became important. Differentiation continued into Cretaceous times when regional compression caused uplift of the southeastern part of the basin and basin margins. A final subsidence phase occurred in the Cenozoic. This was accompanied by intensive salt movement. Recent basin configuration reflects the superposition of structural elements resulting from different evolution stages. The main structural characteristics of the basin are: (1) a vertical tectonic zonation in a pre-Zechstein succession, which lacks significant internal structures, and a strongly deformed post-Zechstein succession, which was decoupled due to the thick Zechstein salt; and (2) a marked asymmetry of the basin with a shallow northern slope and a steep bounding fault at the southern margin (Elbe Fault System). The northwestern part of the basin shows the structural properties of an intracratonic sag basin with persisting subsidence and with minor salt mobilisation. In contrast, initial structures in the southeastern part are strongly overprinted by younger tectonic events including Middle Triassic to Jurassic extension, Late Cretaceous inversion and Late- to post-Cretaceous salt movements. Tectonic elements that deform the whole sedimentary succession are restricted to the basin's southern, eastern and northeastern margins where salt thickness decreases. Combined volumetric and backstripping investigations show that 2/3 of the total subsidence was induced by the sediment load and 1/3 was caused by tectonics. The tectonic subsidence history varies laterally across the basin. While tectonic subsidence curves in the northwestern part of the basin show fast subsidence during the Permian, and Early Triassic decreasing exponentially with time, subsidence curves in the southeastern part indicate repeated tectonic activity. However, the tectonic subsidence volume created during Permian to Late Triassic is significantly higher than the tectonic subsidence during younger phases of basin history.

Gravity anomalies, subsidence history and the tectonic evolution of the Malay and Penyu Basins (offshore Peninsula Malaysia)

To demonstrate the extensional origin of the Malay Basin and calculate the stretching factor (β), Madon & Watts (1998) conducted subsidence-history backstripping on more than 60 wells. The resulting backstripped basement depths through time were then matched to best-fit theoretical subsidence curves, suggesting a McKenzie (1978)-type basin with rapid extensional subsidence (\\\'synrift\\\') followed by slower thermal subsidence (\\\'postrift\\\'). However, the match is only \\\'relatively poor\\\' (p. 381) for the first half of the basin\\\'s 35-0 Ma history (see subsidence curves, Madon & Watts 1998, fig. 7). In the second half, the match looks better on cursory inspection of the subsidence curves, but this is partly an artefact of lacking basement-depth data points over part of this time interval (e.g. 19-0 Ma in well M-6; 7-0 Ma in all 12 illustrated wells).

Evolution of the North Caucasus foredeep: constraints based on the analysis of subsidence curves

Using a database of more than 130 wells the Alpine evolution of the North Caucasus foredeep can be described in three main periods. (1) The Early Jurassic to Middle–Late Cretaceous (including the Cenomanian) relates to the initial rifting phase and was characterised by succession of comparatively high rates of subsidence and uplift. During this stage, many events in the eastern and western parts were synchronous, whereas some of them appeared to be smoothed in the Stavropol high. The southern border of the area had a more complex behaviour often moving in the opposite direction relative to the rest of the area. The main peculiarities of evolution of the Great Caucasus region can be explained if we adopt the hypothesis of Stamply and Pillevuit (1993)and suppose that the Early Jurassic extension of the trough was accompanied by a strong left-lateral transform movement. As a result the central part of the Great Caucasus trough formed as a pull-apart basin. Analysis of the style of movements of the southern border of the Scythian plate as well as data on tectonics and volcanism in the Great and Lesser Caucasus showed that other regional compressional and extensional Mesozoic events could also have a transform component. Shear stresses within the lithosphere of the Great Caucasus can be due to oblique subduction or even transform movements at the plate boundary to the south of the Caucasus region ( Dercourt et al., 1993). (2) The period from the Late Cretaceous to the Middle Eocene (from the Turonian to the Bartonian) relates to the oceanic suture of the Lesser Caucasus and was characterised in the Great Caucasus area by alternating subsidence and uplift events of considerably lower amplitude (at least up to the Maastrichtian). Beginning in the Late Paleocene, subsidence curves for almost all the area reflect the same events, but in the western part and also in the north of the central part the rate of movements was considerably higher and since the Late Paleocene short term events in this area took place on the background of rather fast subsidence at nearly constant rate. We believe that this subsidence and formation of the East Black Sea depression have the same origin. We consider strong differences in evolution of the eastern, western and central parts during the second stage to be due to closure of the Lesser Caucasus oceanic basin and arrival of the Nakhichevan block. This led to changes of configuration of the plate boundary and resulted in reorganisation of stress and displacements within the Caucasus region. This reorganisation was a reason for the opening of the East Black Sea depression and rapid subsidence of the western and central parts of the area at the end of the second stage. (3) The period from the Middle Eocene to the present relates to the development of a foreland basin coeval with shortening and uplift in the adjacent Great Caucasus range. It was characterised by alternation of relatively short uplift and longer subsidence events. An important feature of this stage is that although the amplitude of movements varied from place to place, these events were synchronous in all parts of the foredeep (at the Stavropol region sediments preserved only for the beginning of this stage). Formation and evolution of the foredeep during the third stage can not be explained exclusively by elastic flexure. To do this we used the model of a small-scale convection within the asthenosphere ( Mikhailov et al. 1996, 1999). By the comparison of numerical results with the data on the evolution of the North Caucasus foredeep we concluded that there were four main stages of compression in the processes of formation of the Great Caucasus mountain belt. The first compression took place before the Maykopian (between 39.5 and 36.0 Ma). The other three were in the Tarkhanian (16.6–15.8 Ma), Konkian–Early Sarmatian (14.3–12.3 Ma) and Pontian (7.0–5.2 Ma). The different width of the Great Caucasus trough by the beginning of the compression, as well as variations in thickness of the lithosphere and a different thermal state can cause interruption of the formation of the foredeep at the Stavropol high.

A Multi-Week Basin-Analysis Lab for Sedimentary Geology

We describe a multi-week basin-analysis lab for sedimentary geology that utilizes construction, analysis, and interpretation of 1) sedimentary facies and structures, 2) paleocurrent data, 3) subsurface data, 4) paleogeographic data, 5) bio- and magnetostratigraphic data, and 6) subsidence curve(s) associated with a hypothetical sedimentary basin. Students collect most of the data in the field during trips that occur prior to and during the lab, and analyze their data by hand and with the aid of selected computer programs. Ultimately, students synthesize an integrated analysis and discuss a series of questions about basin history (for example, paleogeography, paleotectonics) and economic potential (for example, hydrocarbon systems). Students individually collect and analyze most of the data but orally present selected aspects of their synthesis in teams. The exercise allows students to develop their skills in field-data collection, and analysis and interpretation of a variety of sedimentarygeology data types, and provides an opportunity for them to integrate such data into a general synthesis of a basin's history.

Vendian-Cambrian subsidence of the passive margin of western Baltica - application of new stratigraphic data from the Scandinavian Caledonian margin

Stratigraphic information from the Neoproterozoic to Cambrian cover sequences at the Caledonian margin in central Scandinavia has been compiled from the literature and our own data. Four flooding events can be recognized in the autochthonous cover rocks and parts of the eastern Caledonian Lower Allochthon: one, at the base of the Vendian at 590 Ma, two Early Cambrian events (540 and 530 Ma), and the fourth at the base of the Mid Cambrian and the alum shales (518 Ma). Stratigraphic successions of the western Baltica margin from northern Sweden to southern Norway are correlated using these flooding events. Based on these correlations, depth and time sections are constructed and subsidence curves calculated. Although Early Cambrian flooding events lead to temporarily higher sedimentation rates, the subsidence appears to have decreased through time. Such a decrease is consistent with models of lithospheric stretching and subsequent thermal subsidence. A review of available age data on tectonic events suggests a transition from continental rifting to ocean-floor formation off western Baltica at ca. 600 Ma ago. Accordingly, the Vendian to Cambrian evolution of the western Baltica continental margin is interpreted as a stage of post-rift subsidence showing the 'steer's head' geometry characteristic of sequences onlapping from an older zone of active rifting and of ocean-floor formation farther west. The gradual decrease in thermal subsidence through Cambrian time also shows that the Baltica lithosphere was essentially thermally re-equilibrated prior to earliest Caledonian tectonic activity in Early Ordovician time.

Two diamictites, two cap carbonates, two δ13C excursions, two rifts: The Neoproterozoic Kingston Peak Formation, Death Valley, California

Research Article| April 01, 1999 Two diamictites, two cap carbonates, two δ13C excursions, two rifts: The Neoproterozoic Kingston Peak Formation, Death Valley, California A. R. Prave A. R. Prave 1Crustal Geodynamics Group, School of Geography and Geosciences, University of St Andrews, St Andrews, Fife KY16 9ST, UK Search for other works by this author on: GSW Google Scholar Geology (1999) 27 (4): 339–342. https://doi.org/10.1130/0091-7613(1999)027<0339:TDTCCT>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation A. R. Prave; Two diamictites, two cap carbonates, two δ13C excursions, two rifts: The Neoproterozoic Kingston Peak Formation, Death Valley, California. Geology 1999;; 27 (4): 339–342. doi: https://doi.org/10.1130/0091-7613(1999)027<0339:TDTCCT>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Stratigraphic mapping of the Neoproterozoic glaciogenic Kingston Peak Formation (Death Valley, California) provides evidence for two temporally discrete extensional deformation episodes. These episodes are bracketed by the Sourdough Limestone and Noonday Dolomite, the facies characteristics and δ13C data (ranging between 2.15 and −2.56‰ and −1.88 and −4.86‰, respectively) of which make them equivalent to Sturtian and Varangian age cap carbonates, respectively. This constrains the two extensional episodes along the southwestern margin of Laurentia to ca. 700 Ma and ca. 600 Ma. These observations and data show that the field evidence for mid-Neoproterozoic breakup and the predictions from tectonic subsidence curves for a latest Neoproterozoic breakup are both correct. Thus, Neoproterozoic plate reconstructions must account for two discrete rift episodes separated by 100 m.y. or more. Confining rifting to within the Kingston Peak Formation thereby places the younger Proterozoic rocks of the southwestern Great Basin in the rift to drift tectonic phase. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Continental accretion of the Iran Block to Eurasia as seen from late Paleozoic to early Cretaceous subsidence curves : Saidi A., Brunet M.-F. & Ricou L.-E., Geodinamica Acta, 1997, 10/5 (189–208)

Continental accretion of the Iran Block to Eurasia as seen from late Paleozoic to early Cretaceous subsidence curves : Saidi A., Brunet M.-F. & Ricou L.-E., Geodinamica Acta, 1997, 10/5 (189–208)

Subsidence of the Atlantic Moroccan margin during the Mesozoic

This paper presents a combined study based on seismic interpretation, sequence stratigraphy, and the evaluation of subsidence that aims to characterize the structure and development of the Essaouira Basin in Morocco. Located in the coastal Meseta adjoining the continental margin, this basin records an initial Carnian-Hettangian deformation phase during rifting in the central part of the North Atlantic region. The geometry of the basin as a function of time shows a succession of half-grabens and horsts that developed westwards from reactivated Hercynian structures. The postrift stage is characterized by an aggrading sedimentary sequence, as shown by concordant seismic sequences stacking over the onshore part of the basin. The Upper Cretaceous coincides with a sequence showing a transition towards a prograding regime that leads to the topography of the present-day margin. Using the high-resolution analysis provided by sequence stratigraphy, it is possible to recognize fine-scale stratigraphic variations in the sedimentary succession. The well-to-well correlation of sedimentary cycles forms a dataset for evaluating subsidence. Residual subsidence curves reveal a differential behaviour between the present onshore and offshore areas. Although the computed subsidence rates are low across the onshore zone, curves for the western offshore part of the basin follow theoretical lithospheric cooling curves that are compatible with a stretch factor ( beta ) of nearly 1.4. Steep temporary gradients on the computed curves may be correlated with tectonic phases documented across the North Atlantic region that exerted a tight control on the development of the Essaouira Basin from Triassic rifting until the uplift of the Atlas Mountains during the Cenozoic.

Grain‐size trends, basin subsidence and sediment supply in the Campanian Castlegate Sandstone and equivalent conglomerates of central Utah

Reconstructions of grain‐size trends in alluvial deposits can be used to understand the dominant controls on stratal architecture in a foreland basin. Different initial values of sediment supply, tectonic subsidence and base‐level rise are investigated to constrain their influence on stratal geometry using the observed grain‐size trends as a proxy of the goodness of fit of the numerical results to the observed data. Detailed measurements of grain‐size trends, palaeocurrent indicators, facies and thickness trends, channel geometries and palynological analyses were compiled for the middle Campanian Castlegate Sandstone of the Book Cliffs and its conglomerate units in the Gunnison and Wasatch plateaus of central Utah. They define the initial conditions for a numerical study of the interactions between large‐scale foreland basin and small‐scale sediment transport processes. From previous studies, the proximal foreland deposits are interpreted as recording a middle Campanian thrusting event along the Sevier orogenic belt, while the stratal architecture in the Book Cliffs region is interpreted to be controlled by eustatic fluctuation with local tectonic influence. Model results of stratal geometry, using a subsidence curve with a maximum rate of ≈45 m Myr−1 for the northern Wasatch Plateau region predict the observed grain‐size trends through the northern Book Cliffs. A subsidence curve with a maximum rate of ≈30 m Myr−1 in the Gunnison–Wasatch Plateaus best reproduces the observed grain‐size trends in the southern transect through the southern Wasatch Plateau. Eustasy is commonly cited as controlling Castlegate deposition east of the Book Cliffs region. A eustatic rise of 45 m Myr−1 produces grain‐size patterns that are similar to the observed, but a rate of eustatic rise based on Haq et al. (1988) will not produce the observed stratal architecture or grain‐size trends. Tectonic subsidence alone, or a combined rate of tectonic subsidence and a Haq et al. (1988) eustatic rise, can explain the stratal and grain‐size variations in the proximal and downstream regions.

Forward modelling of the sequence stratigraphic architecture of shelf cyclothems: application to Late Pliocene sequences, Wanganui Basin (New Zealand)

We demonstrate a procedure for forward modelling of the sequence stratigraphic architecture (i.e. positions of systems tract boundaries) of shelf cyclothems as observed at outcrop sites or in well logs. The 1-D model is based on the fact that the deposition of facies within shelf sequences and those defining the key stratigraphic surfaces between systems tracts, respond directly to changes in depth between the sea surface and seafloor. This accommodation-bathymetry model incorporates three reference surfaces, sea surface, seafloor and lower sequence boundary, each of which varies independently as a result of changes in the rates of eustatic sea level, sedimentation and subsidence. The model input and boundary conditions are an eustatic sea-level curve (i.e. late Cenozoic deep-sea δ 18O record), an independent chronology for the outcrop or well section and a subsidence curve; the model outputs are changes in accommodation and palaeobathymetry throughout the sequence, and the time ‘missing’ at erosional sequence boundaries. The main variable in the model, i.e. sedimentation rate, is established by comparison of a model output (bathymetry) with the model target (palaeobathymetry) established from the faunal and facies content of the sequence being modelled. When the model output and target are compatible, the model sedimentation rate curve is adopted and the theoretical positions of the systems tract boundaries can be read off the model in relation to the lower sequence boundary, and compared with independent field-based interpretations of their stratigraphic position. The model is designed to predict the architecture of sequences as they appear at particular outcrop sites or in well sections. Its usefulness lies in establishing the timing of accumulation of systems tracts in relation to stages in a eustatic sea-level cycle; in particular, distinguishing between units deposited during highstand versus regressive systems tracts. The model is applied to 6th-order (41 ka) Plio-Pleistocene cyclothems in Wanganui Basin (New Zealand), where it distinguishes the boundary between highstand systems tracts (HST) and regressive systems tracts (RST). The modelling has implications for the definition of systems tracts, especially in late Cenozoic successions for which the record of eustatic sea-level changes is known independently.

Quantified vertical motions and tectonic evolution of the SE Pyrenean foreland basin

Abstract Local isostatic backstripping analysis is performed across the eastern part of the Ebro foreland basin between the Pyrenees and the Catalan Coastal Ranges. The subsidence analysis is based on two well-dated field-based sections and four oil-wells aligned parallel to the tectonic transport direction of the eastern Pyrenean orogen. The marine infill of the foreland basin is separated into four, third-order, transgressive-regressive depositional cycles. The first and second depositional cycles are located in the Ripoll piggy-back basin and the third and fourth ones are located south of the syn-depositional emergent Vall-fogona thrust. Subsidence curves display a typical convex-up shape with inflection points recording the onset of rapid tectonic subsidence. Inflection points coincide roughly with the base of depositional cycles. Rates of tectonic subsidence are less than 0.1 mm a −1 in distal parts of the basin and up to 0.53 mm a −1 in proximal parts during second depositional cycle. Younger depositional cycles show maximum rates of tectonic subsidence of 0.26 mm a −1 . The locus of subsidence within the basin migrated southward at a rate of c . 10 mm a −1 . This flexural wave crossed the complete Ebro foreland basin in 10–11 Ma. The intraplate Catalan Coastal Ranges at the southeastern margin of the Ebro foreland basin produced an increase of tectonic subsidence rate at 41.5 Ma. Maximum rates of tectonic subsidence coincide with deep-marine infill of the basin, maximum rates of shortening and thrust front advance, and low topographic relief orogenic wedge. Transgressive-regressive depositional cycles can be controlled partly by reductions of available space within the basin during tectonic thickening of the sedimentary pile by layer parallel shortening, folding and thrusting. Although much less constrained, an approximation of post-thrusting exhumation and isostatic and tectonic uplift, as well as a first determination of possible amounts of eroded material of parts of the Ebro basin illustrate the impact of post-depositional erosion and uplift on the foreland.

Subsidence analysis in thrust tectonics. Application to the southeastern Pyrenean foreland

This case-study conducted in the Pyrenees examines the application of 1D-subsidence analysis in thrust tectonics. By integrating subsidence analysis with sequence stratigraphy and structure, significant changes between the subsidence curves of the southeastern Pyrenean thrust sheets are seen to occur bearing a close relationship to regional unconformities and variations in the sedimentary record of each thrust sheet. A comparative study examining the correlation between the tectonic subsidence curves of the thrust sheets and those of the autochthon shows that the essential structure of the southward sequence of thrust sheets (Palaeozoic Axial Zone not included) was piggy-back developed in only 6 m.y. The northern Garrotxa antiformal stacks started to emplace ∼50.7 Ma ago, as can be interpreted from their linear-shaped curve and anomalously low subsidence rate (∼7 cm/ka), and preservation of continental platform, whereas the southern Cadí thrust sheet underwent strong subsidence acceleration (up to ∼60 cm/ky) related to the development of a deep starved continental slope. Comparison between coeval platform sections (with good palaeobathymetric constraints) and slope sections provides an estimate for slope palaeobathymetry up to 650–900 m. The Cadí thrust sheet was emplaced at about ∼49.5 Ma, as can be deduced from dramatic subsidence deceleration in its curves related to shallowing, resumption of siliciclastic sedimentation and broad erosion of the continental platform areas of the Cadí thrust sheet. Meanwhile, the curves of the Serrat thrust sheet and those of the autochthon recorded significant subsidence acceleration (∼30–40 cm/ka and ∼15 cm/ka, respectively). Finally, the Serrat thrust sheet was emplaced at ∼45 Ma, as can be inferred from the decelerated subsidence in its curve, associated with shallowing, emergence and broad molasse sedimentation, whereas in the foreland plate, the subsidence accelerated and was related to the onset of marine sedimentation.

Continental accretion of the Iran Block to Eurasia as seen from Late Paleozoic to Early Cretaceous subsidence curves

Subsidence analysis is used here to get a better understanding of the Eo-Cimmerian continental accretion to Eurasia of a block (the Iran Block) of Gondwanian origin. The drift of the block from Gondwana to Eurasia is classically considered as a late Triassic event but the lack of unquestionable age evidence leads to investigate the whole Permian to Jurassic history. Indeed, the subsequent Alpine deformation along the proposed suture that should mark the Eo-Cimmerian collision forbids to characterize the collisional event without ambiguity. Moreover, the Iran block is presently represented by different continental slivers that are disconnected from each other, being in places separated by Cretaceous ophiolites, and it makes unclear if one or several blocks should be taken into account. Subsidence analysis is introduced to solve the problem, in the hope that the sedimentary history in any part of the slivers has registered important crustal events such as breakup and collision and that the few well-preserved stratigraphic sections bear the corresponding subsidence signals. Subsidence analysis is thus applied to geologically disconnected objects in a manner that departs from its traditional use in basin analysis. However, as it introduces quantified data on the behaviour of the crust in response to tectonics, it was shown to be an efficient tool in sorting out the major events amongst various local evidences for crustal unstability. Major results are: – dating the breakup as Early Permian and collision as Middle Triassic; – showing that the accretion of the Iran Block to Eurasia was accompanied by a new breakup that formed a passive margin in Nayband to the Southeast, in contrast to the new active margin that was established along the Abadeh, south-western side; – emphasising the tectonic instability that controlled the continental Jurassic deposits upon the new continent before stabilisation was reached during Late Jurassic-Early Cretaceous times.