Subsidence Of Sedimentary Basins Research Articles

Quantifying Postrift Lower Crustal Flow in the Northern Margin of the South China Sea

AbstractPostrift subsidence of sedimentary basins in the northern margin of the South China Sea exceeds more than 2,.000 m, which points toward anomalous postrift crustal deformation. Previous studies have proposed lower crustal flow to explain this observation; however, this hypothesis has never been confirmed quantitatively. Here, we calculate the initial crustal structure and thermal lithospheric thickness of the northern margin of the South China Sea on the basis of recently measured heat flow data, tectonic subsidence curves, and present‐day crustal structure. Crustal thinning processes during rifting and reduced thickness of the lower crust in the postrift are also calculated by the strain rate inversion method and thermal isostasy. Our results show that the initial (Early Cenozoic) crustal thickness of the northern margin of the South China Sea varies between 27.7 and 36.3 km, and the average proportion of the lower crust is 67%. The initial thermal lithospheric thicknesses decrease from ~118 to ~81 km from the shelf to the sea, which indicates that the offshore margin has high temperatures and low strength and is more easily stretched and deformed. The average stretching factor the margin during rifting is 1.24. The lower crust reduces in thickness during the postrift phase by values between 1 and 11 km, which increases gradually from the shelf to deep water. We suggest that the thicker weak crust and hot lithospheric structure therefore make positive contribution to the lower crustal flow, the direction of which is from the oceanic basin to the shelf.

Using bar preservation to constrain reworking in channel-dominated fluvial stratigraphy

Fluvial deposits comprising more than 80% channel facies are often thought to have accumulated during intervals of relatively slow subsidence in sedimentary basins. This interpretation stems from the conceptual model that migrating and avulsing rivers rework their own deposits during times of limited accommodation creation, preferentially removing and bypassing fine floodplain deposits. Alternatively, channel-dominated stratigraphy may reflect avulsion patterns that favor channel preservation over floodplain preservation, or channel networks fed by sand-rich sediment sources that never deposited significant floodplain sediments. These potential origins of channel-dominated stratigraphy cannot be differentiated without a way of independently assessing how ancient rivers eroded and reworked their own alluvium. Here we propose a new method that uses fluvial-bar preservation as a proxy for reworking in channel-dominated stratigraphy. We apply this approach to the lower Castlegate Sandstone (Upper Cretaceous, Utah, USA) and use geometric modeling to investigate the degree to which sediment supply and avulsion dynamics influence fluvial deposit preservation. Castlegate exposures in central Utah show up to 80% bar preservation in some localities, suggesting that, in contrast to previously published interpretations, Castlegate channel deposits are not heavily reworked and accommodation-creation rates during Castlegate deposition might have been relatively high. Model comparisons indicate that well-preserved Castlegate deposits could have resulted from random avulsions in a rapidly aggrading basin with a sand-dominated sediment supply, or under lower aggradation conditions if river avulsions avoided previously occupied locations. This approach represents a new advance for interpreting the relationships between basin accommodation, sediment supply, and avulsion dynamics on ancient landscapes and provides a new method for estimating sediment reworking and bypass from ancient river deposits.

Earthquake-induced transformation of the lower crust.

The structural and metamorphic evolution of the lower crust has first order effects on the lithospheric response to plate tectonic processes involved in orogeny, including subsidence of sedimentary basins, stability of deep mountain roots, and extension of high topography regions. Recent research shows that prior to orogeny most of the lower crust is dry, impermeable, and mechanically strong1. During an orogenic event, the evolution of the lower crust is controlled by infiltration of fluids along localized shear or fracture zones. In the Bergen Arcs of Western Norway, shear zones initiate as faults generated by lower crustal earthquakes. Seismic slip in the dry lower crust requires stresses at a level that can only be sustained over short timescales or local weakening mechanisms. However, regular earthquake activity in the seismogenic zone produces stress pulses that drive aftershocks in the lower crust2. Here, we show that the volume of lower crust affected by such aftershocks is very significant and that fluids driving associated metamorphic and structural transformations of the lower crust follow in the wake of these earthquakes. This provides a novel ‘top-down’ effect on crustal geodynamics and connects processes operating at very different time scales.

BasinVis 1.0: A MATLAB®-based program for sedimentary basin subsidence analysis and visualization

Stratigraphic and structural mapping is important to understand the internal structure of sedimentary basins. Subsidence analysis provides significant insights for basin evolution. We designed a new software package to process and visualize stratigraphic setting and subsidence evolution of sedimentary basins from well data. BasinVis 1.0 is implemented in MATLAB®, a multi-paradigm numerical computing environment, and employs two numerical methods: interpolation and subsidence analysis. Five different interpolation methods (linear, natural, cubic spline, Kriging, and thin-plate spline) are provided in this program for surface modeling. The subsidence analysis consists of decompaction and backstripping techniques. BasinVis 1.0 incorporates five main processing steps; (1) setup (study area and stratigraphic units), (2) loading well data, (3) stratigraphic setting visualization, (4) subsidence parameter input, and (5) subsidence analysis and visualization. For in-depth analysis, our software provides cross-section and dip-slip fault backstripping tools. The graphical user interface guides users through the workflow and provides tools to analyze and export the results. Interpolation and subsidence results are cached to minimize redundant computations and improve the interactivity of the program. All 2D and 3D visualizations are created by using MATLAB plotting functions, which enables users to fine-tune the results using the full range of available plot options in MATLAB. We demonstrate all functions in a case study of Miocene sediment in the central Vienna Basin.

Early Paleozoic mafic magmatic events on the eastern margin of the Siberian Craton

Neoproterozoic and Devonian mafic flows, sills and dykes associated with synchronous rifting events are widely distributed along the long-lived Mesoproterozoic to Mesozoic passive eastern margin of the Siberian Craton. Early Paleozoic magmatic events are also present, but are poorly studied, including Early Cambrian volcanic rocks in the Kharaulakh Range and ca. 450Ma age mafic intrusions of the Suordakh event in the Sette–Daban Range. Both suites of early Paleozoic magmatic rocks are characterized by high Ti concentrations (>3wt.% TiO2), ocean island basalt (OIB)-type trace element and rare earth element (REE) patterns, and high εNd(t) values that generally vary between 6 and 9. The Kharaulakh magmas were formed during low degree partial melting of an enriched region of mantle at depths >90km, generating a suite of alkaline basalts. In comparison, the Suordakh magmas were formed during higher degree partial melting of less enriched mantle at depths <90km, forming alkaline to subalkaline basalts. Both suites are characterized by εNd(t) values suggestive of interaction between enriched and depleted magmas and both were emplaced in within-plate tectonic settings. Although Kharaulakh and Suordakh magmatic rocks have relatively small areal extents, significant parts of them are likely hidden below clastic rocks of the Lower Carboniferous–Jurassic Verkhoyansk Complex. The Kharaulakh magmatic rocks may have counterparts in the Canadian Cordillera, that together could be of sufficient scale to define a Large Igneous Province (LIP). Early Cambrian mafic volcanic rocks in the study area are associated with locally distributed terrigenous units in both the Kharaulakh and Sette–Daban ranges, suggesting that this magmatism was related to a rifting event. Modeling of sedimentary basin subsidence in the Sette–Daban area is also supportive of an Early Cambrian rifting event. However, the intrusive rocks associated with the ca. 450Ma Suordakh mafic magmatic event are not related to any rift-related sediments or structures. Contemporaneous granites may be interpreted as silicic magmatism associated with a LIP event.

Stagnant lid convection and the thermal subsidence of sedimentary basins with reference to Michigan

The thermal subsidence of basins formed above thick continental lithosphere differs from that of young passive margin basins and of young oceanic crust in that stagnant lid convection supplies significant heat flow from the asthenosphere. The lithosphere eventually approaches thermal equilibrium where the convective heat added to its base balances the heat lost by conduction to the surface. This paper presents a simple parameterization that quantifies these effects for modeling basin subsidence. The convective heat flow scales with the current lithosphere thickness squared while the conductive heat flow scales inversely to current lithospheric thickness. The predicted thermal subsidence rate scales to the difference between the conductive and convective heat flows and wanes gradually over hundreds of millions of years. The formalism can be modified to represent thermal subsidence where plume material has ponded within a catchment of locally thinned lithosphere. The base of the plume material forms a stable stratification that suppresses convective heat flow from below while heat continues to conduct to the surface by conduction. The predicted initial thermal subsidence rate scales with the large difference between conductive and zero convective heat flow. It is thus much greater than beneath lithosphere underlain by ordinary asthenosphere for a given amount of total eventual thermal subsidence. The paper compares thermal subsidence predictions from the models with and without plumes with sedimentation data from the Michigan basin. Observed initial Late Cambrian through Lower Devonian sedimentation in the Michigan basin is rapid as expected from the plume model, but the Ordovician sedimentation rate is slower than before and after. It is conceivable that this irregularity in the sedimentation curve is associated with low eustatic sea level and sediment‐starved conditions at the basin center in the Ordovician and Early Silurian periods, as opposed to irregular tectonics. Sedimentation poorly resolves a long tail of gradual subsidence that may extend to the present.

Potential role of strain hardening in the cessation of rifting at constant tectonic force

Abstract In this study the cessation of rifting at constant tectonic force is discussed from the viewpoint of lithospheric rheology using a simple one-dimensional numerical model. The behaviour of the conventionally adopted constant force model re-examined in this study contradicts some general features in the development of sedimentary basins. Strain hardening is implemented to explain the contradictions, in which the viscosity of the mantle is a function of not only the strain rate and temperature but also the total strain. The roles of various strain hardening parameters in rifting dynamics are examined, including the strain required for the onset of hardening, the strain interval required for the completion of hardening and the factor controlling the increase in mantle viscosity. It is shown that a model with strain hardening can explain many characteristic features of sedimentary basin formation better than the conventional constant force model. There are a variety of ways in which rifting can be terminated by the strain hardening model, depending on the initial lithospheric structure, magnitude of tectonic force and the hardening process. One possible strain hardening mechanism involves the switch from wet to dry rheology associated with decompressional melting, though the implemented strain hardening formula could be generally applicable to any hardening phenomenon and could therefore be physically interpreted as such. The results of this study also provide important insights into sedimentary basin subsidence in relation to rifting dynamics. The end of an initial rapid (“syn-rift” like) subsidence phase is not necessarily equivalent to the end of actual rifting as in the constant force model. The transition from initial rapid subsidence to long-term, more subdued (“post-rift” like), subsidence is actually marked by the onset of deceleration of rifting. Since significant extension still continues for some time thereafter, the subsequent long-term subsidence includes some mechanical effect of crustal thinning.

A plume model of transient diachronous uplift at the Earth's surface

Convection in the Earth's mantle appears to be strongly time-dependent on geological time scales. However, we lack direct observations which would help constrain the temporal variation of convection on time scales of 1–10 Ma. Recently, it has been demonstrated that transient uplift events punctuated the otherwise uniform thermal subsidence of sedimentary basins which fringe the Icelandic plume. In the Faroe–Shetland basin, three-dimensional seismic reflection surveys calibrated by well logs have been used to reconstruct a ∼55 million year old transient event. The minimum amount of uplift is 490 m, which grew and decayed within 2 Ma. This event has also been mapped 400 km further east in the North Sea basin, where peak uplift with an amplitude of 300 m occurred 0.3–1.6 Ma later. Neither observation can be explained by glacio-eustatic sea-level changes or by crustal shortening. We describe a simple fluid dynamical model which accounts for these transient and diachronous observations. In this model, we assume that the Icelandic plume was already in existence and that it had an axisymmetric geometry in which hot (e.g. 1400 °C) asthenospheric material flows away from a central conduit within a horizontal layer. A transient temperature anomaly introduced at the plume centre flows outward as an expanding annulus. Its geometry is calculated using radial flow between two parallel plates with a Poiseuille cross-stream velocity profile. The expanding annulus of hot asthenosphere generates transient isostatic uplift at the Earth's surface. Stratigraphic observations from both basins can be accounted for using a plume flux of 1.3×108 km3 Ma−1 for a layer thickness of 100 km. Plume flux is broadly consistent with that required to account for Neogene (0–20 Ma) V-shaped ridges south of Iceland, although our transient temperature anomalies are larger. We suspect that the stratigraphic expression of transient convective behaviour is common and that a careful examination of appropriate records could yield important insights.

The evolution of the North German Basin and the metamorphism of the lower crust

In an integrated analysis, metamorphic processes in the accreted crust, potential field anomalies, temperature field and subsidence history are summarized into a model for the development of the North German Basin. The model integrates observed phenomena such as the high nitrogen content in natural gases in Permian sandstone reservoirs and the structure of the crust with model calculations. Rock density increase, subsequent volume reduction and loss of volatiles during metamorphism lead to a depression at the surface of the Earth. The load of the sediments, which will be deposited in the depression, enhances the subsidence and the ongoing metamorphism. The model provides an alternative to the application of existing tectonic stretching models for the explanation of the subsidence of sedimentary basins.

Effect of mineral phase transitions on sedimentary basin subsidence and uplift

Metamorphic phase transitions influence rock density, which is a major parameter affecting lithosphere dynamics and basin subsidence. To assess the importance of these effects, we have computed realistic density models for a range of crustal and mantle mineralogies from thermodynamic data by free-energy minimization. These density distributions are incorporated into one- and two-dimensional kinematic models of basin subsidence. The results demonstrate that, compared to models in which density is solely temperature dependent, phase transitions have the effect of increasing post-rift subsidence while decreasing syn-rift subsidence. Discrepancies between our model results and those obtained with the conventional uniform stretching models can be up to 95% for reasonable parameter choices. The models also predict up to 1 km of syn-rift uplift as a consequence of phase transitions. Mantle phase transitions, in particular the spinel–garnet–plagioclase–lherzolite transitions are responsible for the most significant effects on subsidence. Differences in mantle composition are shown to be a second-order effect. Parameterized density models are derived for crustal and mantle rocks, which reproduce the main effects of the phase transitions on subsidence.

Differential compaction and subsidence in sedimentary basins due to silica diagenesis: A case study

The conversion of opal A to opal CT is a thermochemical diagenetic process that can cause kilometer-scale differential compaction and differential subsidence within clastic 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 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.

TURCOTTE, D. L. &amp; SCHUBERT, G. 2002. Geodynamics, 2nd ed. xv + 456 pp. Cambridge, New York, Melbourne: Cambridge University Press. Price £75.00, US $110.00 (hard covers); £29.95, US $45.00 (paperback). ISBN 0 521 66186 2; 0 521 66624 4 (pb).

Perhaps the most remarkable feature of the second edition of Turcotte & Schubert’s classic Geodynamics is that it is now published by Cambridge University Press in a much more generally affordable softback format compared to its hardback Wiley predecessor. Turcotte & Schubert’s preface states that little revision of the first edition was necessary because fundamental physical processes do not change. But the fact is that such was the breadth of the first edition that, some twenty years on, the authors have needed only to introduce fairly minor changes. Thus, the second edition now includes much more material on planetary morphology, particularly Earth’s Moon and the Galilean satellites of Jupiter. There are new discussions of synthetic aperture radar interferometry and the crustal stretching model for sedimentary basin subsidence, and there is a brand new chapter on chemical geodynamics – analysis of the concentrations of radioactive isotopes and their daughter products as a means of inferring mantle dynamics. What sets Geodynamics apart from other textbooks on a comparable theme is the emphasis throughout on developing a quantitative understanding of the fundamental physical processes that underlie geological phenomena.Consequently, to get the most out of this book, familiarity with partial differential equations is essential. That …

Two‐dimensional inverse modeling of sedimentary basin subsidence

Recently developed mathematical models of subsidence in extensional basins provide a good basis for forward modeling. However, the large number of parameters to be specified by the user makes it difficult not only to do the modeling itself, but also to judge the meaning of the results. We present a new method for automatic searching of the best‐fitting parameter set of a 2D basin formation model. Weighted goal functions are used in the minimization process by the inverse problem solver algorithm. The nominal parameter set in the present case includes profiles of the crustal and subcrustal thinning factors, and the level of lithosphere necking. The method was tested on synthetic data with parameters that were perturbed beforehand. With some restrictions, the algorithms are capable of resolving such perturbations. The inversion technique has been applied to two profiles crossing the Dnieper‐Donets Basin (Ukraine). The crustal thinning factors obtained argue for a scissors‐like style of basin opening. High subcrustal thinning values are necessary in order to explain the abnormally thick Carboniferous section in the basin. These values should be treated as cumulative ones due to the currently unresolvable influence of other rifting‐related processes, particularly phase transitions.

Land subsidence and hydrodynamic compaction of sedimentary basins

Abstract. A one-dimensional model is used to investigate the relationship between land subsidence and compaction of basin sediments in response to sediment loading. Analysis of the model equations and numerical experiments demonstrate quasi-linear systems behaviour and show that rates of land subsidence due to compaction: (i) can attain a significant fraction (&gt;40%) of the long-term sedimentation rate; (ii) are hydrodynamically delayed with respect to sediment loading. The delay is controlled by a compaction response time τc that can reach values of 10-5-107 yr for thick shale sequences. Both the behaviour of single sediment layers and multiple-layer systems are analysed. Subsequently the model is applied to the coastal area of the Netherlands to illustrate that lateral variability in compaction-derived land subsidence in sedimentary basins largely reflects the spatial variability in both sediment loading and compaction response time. Typical rates of compaction-derived subsidence predicted by the model are of the order of 0.1 mm/yr but may reach values in excess of 1 mm/yr under favourable conditions.

The thermal blanketing effect of sediments on the rate and amount of subsidence in sedimentary basins formed by extension

The thermal blanketing effect of sediments on the rate and amount of subsidence in sedimentary basins formed by extension

Experience from the Ecors program in regions of complex geology

The French Ecors program was launched in 1983 by a cooperation agreement between universities and petroleum companies. Crustal surveys have tried to find explanations for the formation of geological features, such as rifts, mountains ranges or subsidence in sedimentary basins. Several seismic surveys were carried out, some across areas with complex geological structures. The seismic techniques and equipment used were those developed by petroleum geophysicists, adapted to the depth aimed at (30–50 km) and to various physical constraints encountered in the field. In France, Ecors has recorded 850 km of deep seismic lines onshore across plains and mountains, on various kinds of geological formations. Different variations of the seismic method (reflection, refraction, long-offset seismic) were used, often simultaneously. Multiple coverage profiling constitutes the essential part of this data acquisition. Vibrators and dynamite shots were employed with a spread generally 15 km long, but sometimes 100 km long. Some typical seismic examples show that obtaining crustal reflections essentialy depends on two factors: (1) the type and structure of shallow formations, and (2) the sources used. Thus, when seismic energy is strongly absorbed across the first kilometers in shallow formations, or when these formations are highly structured, standard multiple-coverage profiling is not able to provide results beyond a few seconds. In this case, it is recommended to simultaneously carry out long-offset seismic in low multiple coverage. Other more methodological examples show: how the impact on the crust of a surface fault may be evaluated according to the seismic method implemented ( vibroseis 96-fold coverage or single dynamite shot); that vibrators make it possible to implement wide-angle seismic surveying with an offset 80 km long; how to implement the seismic reflection method on complex formations in high mountains. All data were processed using industrial seismic software, which was not always appropriate for records at least 20 s long. Therefore, a specific procedure adapted to deep seismic surveys was developed for several processing steps. The long duration of the vibroseis sweeps often makes it impossible to perform correlation and stack in the recording truck in the field. Such field records were first preprocessed, in order to be later correlated and stacked in the processing center. Because of the long duration of the recordings and the great length of the spread, several types of final sections were replayed, such as: (1) detailed surface sections (0–5 s), (2) entire sections (0–20 s) after data compression, (3) near-trace sections and far-trace sections, which often yield complementary information. Standard methods of reflection migration gave unsatisfactory results. Velocities in depth are inaccurate, the many diffractions do not all come from the vertical plane of the line, and the migration software is poorly adapted to deep crustal reflections. Therefore, migration is often performed graphically from arrivals picked in the time section. Some line-drawings of various onshore lines, especially those across the Alps and the Pyrenees, enable to judge the results obtained by Ecors.

The thermal blanketing effect of sediments on the rate and amount of subsidence in sedimentary basins formed by extension

The thermal blanketing effect of sediments with finite thermal conductivity on the rate and amount of subsidence in rift basins is presented, in contrast with Mckenzie's (1978) model, which assumed infinite thermal conductivity of the sedimentary covers. The post-rift cooling of the lithosphere is shown to be very slow owing to the blanketing effect. Even 200 m.y. after extension ceases, there is still an enormous amount of residual heat in the lithosphere. With moderate thermal conductivity of the sediments ( k s = 2.0 W/mK), the maximum discrepancy in subsidence predicted by the two models (i.e. the present model and that of Mckenzie) are 2 km, 2.6 km and 3.2 km for thinning factors of 1.5, 2 and 3 respectively. Subsidence is moderately sensitive to k s when k s is greater than 2.0 W/mK, becoming more sensitive to k s when k s is less than 2.0 W/mK. The presence of mudstone would further slow down the cooling. The thermal conductivity of the sediment is shown to govern the temperature gradient of rift basins, although it has little influence on heat flow. The heat production of the upper crust and sediment comprises an important component of heat flow. Unless heat absorption in rift basins is unusually high, subsidence is insensitive to the heat production of sediments. When the thinning factor is less than 2, the mean temperature gradient of rift basins is shown to decrease quickly over a few million years, and as a result such basins are not favourable as regards hydrocarbon maturity. The Central Graben of the North Sea is chosen to test the model. The model satisfactorily predicts the subsidence history and thermal evolution, with the base Zechstein as the basement and the Cenozoic subsidence as the thermal subsidence. The best-fit value of the mean thermal conductivity of the sediments in the graben is 1.67 W/mK, and the thinning factor is about 2.

Correlation between Plate Motions and Tectonic Subsidence of Sedimentary Basins in Africa

From the early Mesozoic until the Holocene, the African continent was generally in a state of extension, based on plate tectonic reconstructions and sedimentary basin subsidence studies. Beginning with the breakup of Gondwana in the Permian-Triassic, this resulted in the formation of the present-day African continental margins and a series of intracontinental rift basins, located mainly on older (late Proterozoic) shear zones. Numerous wells from marginal, as well as intracontinental rift basins, have been backstripped to elucidate their Mesozoic and Tertiary tectonic histories. They show a generally consistent patterns of subsidence and uplift phases in all basins. During the evolution of these basins, the direction of African plate motion changed several times. This was related to the differential opening of the central and south Atlantic oceans, changes in spreading rates in both the Atlantic and Indian oceans, and the collision between Africa and Europe. Episodes of compressional deformation related to these plate tectonic changes are revealed in backstripped tectonic subsidence curves.

Right place, wrong time: anomalous post-rift subsidence in sedimentary basins around the North Atlantic Ocean

Abstract The central and northern North Sea Basin was formed as a result of at least two extensional episodes, the latest of which took place during the Late Jurassic. During the Early Tertiary, some 80 Ma later, the basin experienced a dramatic acceleration in subsidence. Subsidence acceleration of Early Tertiary age has also been reported from a number of other extensional basins, on both sides of the North Atlantic, in which stretching had ceased several tens of millions of years previously. This phenomenon is not in agreement with the published models of extensional basin formation, which predict that the rate of thermal subsidence should progressively decline following extension. It is possible that the predicted pattern of thermal subsidence was obscured by the effects of a mantle hot spot beneath the North Atlantic lithosphere during the Cretaceous to Early Tertiary. However, it is difficult to explain the subsidence phenomena observed in basins around the North Atlantic Ocean using simple hot spot models. It is concluded that the relationships between hot spot activity, continental break-up and vertical crustal movements in the North Atlantic region are subtle and complex, but that subsidence history analysis can yield valuable insights into these relationships.

Phase changes and thermal subsidence in intracontinental sedimentary basins

A model of tectonic subsidence is developed to explain the late acceleration of subsidence observed in some intracratonic sedimentary basins. The proposed mechanism combines the effect of thermal contraction of an initially hot lithosphere with the effect of a subcrustal phase transformation that moves under changing pressure and temperature conditions. The subsidence following a sudden change in temperature at the base of the lithosphere is calculated. The calculations show that: (1) phase changes, if present and activated, contribute substantially to the subsidence of sedimentary basins; (2) because the effect of phase change is delayed, subsidence accelerates after a time on the order of 20 Myr; and (3) the duration of the subsidence is on the order of 100 to 150 Myr. During the late stages of subsidence, the phase change is the dominating mechanism. An application to the Michigan basin is presented. The calculated sediment accumulation history fits the record well when the effect of sea-level changes is included in the model.