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The uplift of the southern African Plateau with its average elevations of ~1000 m is often attributed to mantle processes, but there are conflicting theories for the timing and drivers of topographic development. Evidence for most proposed plateau development histories is derived from continental erosion histories, marine stratigraphic architecture, or landscape morphology. Here we use a landscape evolution model to integrate a large dataset of low-temperature thermochronometry, sediment flux rates to surrounding marine basins, and current topography for southern Africa. We explore three main hypotheses for surface uplift: 1) southern Africa was already elevated by the Early Cretaceous before Gondwana breakup, 2) uplift and continental tilting occurred during the mid-Cretaceous, or 3) uplift occurred during the mid to late Cenozoic. We test which of these three intervals of plateau development are plausible by using an inversion method to constrain the range in erosional and uplift model parameters that can best reproduce the observed data. Results indicate four regions of parameter space that fall into two families of uplift histories are most compatible with the data. Both uplift families have limited initial topography with some topographic uplift and continental tilting starting at ~90-100 Ma. In one acceptable scenario, nearly all of the topography, >1300 m, is created at this time with little Cenozoic uplift. In the other acceptable scenario, ~400-800 m of uplift occurs in the mid- Cretaceous with another ~500-1000 m of uplift in the mid-Cenozoic. The two model scenarios have different geodynamic implications, which we compare to geodynamic models.

©2018. American Geophysical Union. All Rights Reserved. Western North America has an average elevation that is ∼2 km higher than cratonic North America. This difference coincides with a westward decrease in average lithospheric thickness from ∼240 to 260 basaltic samples. Forward and inverse modeling of carefully selected major, trace, and rare earth elements were used to determine melt fraction as a function of depth. Basaltic melt appears to have been generated by adiabatic decompression of dry peridotite with asthenospheric potential temperatures of 1340 ± 20 °C. Potential temperatures as high as 1365 °C were obtained for the Snake River Plain. For the youngest (i.e.

Next generation gravity missions are expected to improve the accuracy of temporal gravity models significantly. The periodic signals and trends retrieved by these missions are induced by mass redistribution in the Earth system, carrying essential information on dynamic processes in the atmosphere, cryosphere, continental hydrosphere, the oceans and the solid Earth. While temporal gravity signals induced by deep Earth's processes are commonly thought to lie below the observational threshold of satellite gravity missions, as one assumes them to be small in amplitude and restricted to the longest spatial and temporal scales, there exists evidence from the geologic record for rapid uplift and subsidence events at regional scales, especially along passive continental margins, related to flow in the underlying mantle. Here we explore novel mantle flow retrodictions for geodynamically plausible, compressible, high resolution Earth models with ≈ 670 million finite elements. These time-dependent Earth models link to geologic observables in the late Paleogene that can be tested independently, while at the same time indicating mantle flow induced geoid rates on the order of 5 μm/year, at spatial scales of 1000 km. We assess the signal retrievability of the modeled rates in closed-loop numerical simulations, with different satellite gravity retrieval mission assumptions, including GRACE, GRACE-FO and a next generation gravity mission. We find the modeled deep Earth signal to be on the edge of detectability, but coming into the range of detectability in future temporal gravity field solutions, suggesting the use of satellite gravity data to validate geodynamic Earth models. Importantly, the application of forward modeled dynamic mantle signals seems to be essential for improved de-aliasing and signal separation in future gravity missions.

A family of geophysical lineaments have been identified in ∼15,000 km 2 in central Kerala between 9°30′N to 10°45′N and 76°00′E to 77°30′E, integrating geophysical data with geological and geomorphological features. The characteristics of these lineaments in the magnetic and gravity fields and their derivatives have been analysed. The evolution of the lineaments has been traced to the temporal phases of global evolution of the region. A group of these faults have formed by reactivation of the deep-seated distensional fractures associated with and accompanying dyke emplacements during the episodic breakup of Gondwana at ∼90 and 65 Ma under distinctive mantle thermal regimes. It is possible that reactivation of these distensional faults may have started during the cooling interval of time between the two distensions in the 90 and 65 Ma and post 65 Ma periods and later in the Cenozoic, when the lineaments were enlarged to their present dimension, possibly under the influence of forces that led to the uplift of the western Ghats. These may extend down to the crust-mantle interface. A cluster of younger geophysical lineaments has been generated by reactivation along the weak planes of transformation of the charnockitic rocks of the Precambrian. They seem to have a strike-slip character. They are devoid of any dyke association and were formed on a cold crust. They may be confined to the upper-middle crust. They were generated in the high intensity intra-plate palaeo-stress fields of the triple forces arising from (1) the back-thrust from the Himalayan Collision; (2) the impact of epeirogenic forces and related isostatic uplift of the Western Ghats and (3) the flexural isostatic uplifts due to surface loads of late Mesozoic basaltic lavas and Cenozoic sedimentation in the coastal rifted basins in late Cenozoic, probably in the time span of 20 Ma to the present, when the palaeostress fields were most intense.

Erosional unconformity surfaces are key indicators for the variations in eustatic sea level, ocean dynamics and climatic conditions which significantly affect depositional environments of sedimentary successions. Using a dense grid of 2D seismic data, we present new evidence from a frontier basin, the offshore Durban Basin, of a mid-Miocene age erosional unconformity that can be correlated with analogous horizons around the entire southern African continental margin. In the Durban Basin, this unconformity is typified by the incision of a mixed carbonate-siliciclastic wedge and ramp margin by a series of submarine canyons. Epeirogenic uplift of southern Africa characterised this period, with erosion and sediment bypass offshore concomitant with increases in offshore sedimentation rates. Although epeirogenic uplift appears to be the dominant mechanism affecting formation of the identified sequence boundary, it is postulated that an interplay between global eustatic sea-level fall, expansion of the east Antarctic ice sheets, and changes in deep oceanic current circulation patterns may have substantially contributed to erosion during this period.

Mantle plumes have been proposed to exert a first-order control on the morphology of Earth's surface. However, there is little consensus on the lifespan of the convectively supported topography. Here, we focus on the Cenozoic uplift and exhumation history of the British Isles. While uplift in the absence of major regional tectonic activity has long been documented, the causative mechanism is highly controversial, and direct exhumation estimates are hindered by the near-complete absence of onshore post-Cretaceous sediments (outside Northern Ireland) and the truncated stratigraphic record of many offshore basins. Two main hypotheses have been developed by previous studies: epeirogenic exhumation driven by the proto-Iceland plume, or multiple phases of Cenozoic compression driven by far-field stresses. Here, we present a new thermochronological dataset comprising 43 apatite fission track (AFT) and 102 (U–Th–Sm)/He (AHe) dates from the onshore British Isles. Inverse modelling of vertical sample profiles allows us to define well-constrained regional cooling histories. Crucially, during the Paleocene, the thermal history models show that a rapid exhumation pulse (1–2.5 km) occurred, focused on the Irish Sea. Exhumation is greatest in the north of the Irish Sea region, and decreases in intensity to the south and west. The spatial pattern of Paleocene exhumation is in agreement with the extent of magmatic underplating inferred from geophysical studies, and the timing of uplift and exhumation is synchronous with emplacement of the plume-related British and Irish Paleogene Igneous Province (BIPIP). Prior to the Paleocene exhumation pulse, the Mesozoic onshore exhumation pulse is mainly linked to the uplift and erosion of the hinterland during the complex and long-lived rifting history of the neighbouring offshore basins. The extent of Neogene exhumation is difficult to constrain due to the poor sensitivity of the AHe and AFT systems at low temperatures. We conclude that the Cenozoic topographic evolution of the British Isles is the result of plume-driven uplift and exhumation, with inversion under compressive stress playing a secondary role.

Peninsular India is a cratonic region with asymmetric relief manifest by eastward tilting from the 1.5 km high Western Ghats escarpment toward the floodplains of eastward-draining rivers. Oceanic residual depth measurements on either side of India show that this west-east asymmetry is broader scale, occurring over distances of >2,000 km. Admittance analysis of free-air gravity and topography shows that the elastic thickness is 10 ±3 km, suggesting that regional uplift is not solely caused by flexural loading. To investigate how Indian physiography is generated, we have jointly inverted 530 river profiles to determine rock uplift rate as a function of space and time. Key erosional parameters are calibrated using independent geologic constraints (e.g. emergent marine deposits, elevated paleosurfaces, uplifted lignite deposits). Our results suggest that regional tilt grew at rates of up to 0.1 mm a– 1 between 25 Ma and the present day. Neogene uplift initiated in the south and propagated northward along the western margin. This calculated history is corroborated by low-temperature thermochronologic observations, by sedimentary flux of clastic deposits into the Krishna-Godavari delta, and by sequence stratigraphic architecture along adjacent rifted margins. Onset of regional uplift predates intensification of the Indian monsoon at 8 Ma, suggesting that rock uplift rather than climatic change is responsible for modern-day relief. A positive correlation between residual depth measurements and shear wave velocities beneath the lithosphere suggests that regional uplift is generated and maintained by temperature anomalies of ±100°C within a 200 ±25 km thick asthenospheric channel. This article is protected by copyright. All rights reserved.

Apatite fission track (AFT) and (U-Th)/He (AHe) thermochronometry data are reported and used to unravel the exhumation history of crystalline basement rocks from the elevated (>1000 m a.s.l.), but low relief Tanzanian Craton. Coeval episodes of sedimentation documented within adjacent Paleozoic to Mesozoic basins of southern Tanzania and the Congo basin of the Democratic Republic of Congo (DRC) indicate that most of the cooling in the basement rocks in Tanzania was linked to erosion. Basement samples were from an exploration borehole located within the craton, and up to 2200 m below surface. Surface samples were also analysed. AFT dates range between 317 ± 33 Ma and 188 ± 44 Ma. Alpha (Ft)-corrected AHe dates are between 433 ± 24 Ma and 154 ± 20 Ma. Modelling of the data reveals two important periods of cooling within the craton; one during the Carboniferous-Triassic (340 -220 Ma) and a later, less well constrained episode, during the late Cretaceous. The later exhumation is well detected proximal to the East African Rift (70 Ma). Thermal histories combined with the estimated geothermal gradient of 9 °C/km constrained by the AFT and AHe data from the craton and a mean surface temperature of 20 °C, indicate removal of up to 9 ± 2 km of overburden since the end-Paleozoic. The correlation of erosion of the craton and sedimentation and subsidence within the Congo basin in the Paleozoic may indicate regional flexural geodynamics of the lithosphere due to lithosphere buckling induced by far-field compressional tectonic processes, and thereafter through deep mantle upwelling and epeirogeny tectonic processes.

The origin of Iberia's topography is examined by combining gravity, magmatic, topographic and seismological observations with geomorphic considerations. We have four principal results. First, highest coherence between free‐air gravity and topography is at wavelengths ≲250 km where admittance indicates that elastic thickness of Iberia's plate is 20 ± 3 km. These results imply that flexural and sub‐plate support of Iberian topography could be expressed at wavelengths of O(100) km. Secondly, P‐to‐S receiver functions and simple isostatic calculations indicate that whilst crustal thickness variations and flexural loading (e.g. as a result of plate shortening) partially explain the elevation of Pyrenean, Betics, Cantabrian, Spanish Central System and Iberian Chain topography, they fail to explain the elevation of large parts of Iberia. Thirdly, a new full waveform shear wave tomographic model and velocity to temperature conversions suggest that the asthenosphere beneath Iberia is anomalously slow and has excess temperatures of up to 162 ± 14°C. Simple isostatic calculations indicate asthenospheric support of topography of up to 1 km. Neogene‐Recent (∼23–0 Ma) extrusive magmatism (e.g. Calatrava, Catalan) sit atop many of the slow shear wave velocity anomalies. Finally, biostratigraphic data, combined with inversion of 3217 river profiles, show that most of Iberia's topography grew during the last ∼30 Ma at rates of up to 0.3 mm yr−1. Best‐fitting theoretical rivers have a low residual rms misfit (=0.96) and calculated uplift is consistent with an independent inventory of stratigraphic and biostratigraphic observations. We suggest that Neogene‐Recent growth of most of central Iberia's topography was a result of asthenospheric support.

The Grand Canyon region provides an excellent laboratory to examine the interplay between river incision, magmatism, and the geomorphic and tectonic processes that shape landscapes. Here we apply U-series, Ar–Ar, and cosmogenic burial dating of river terraces to examine spatial variations in incision rates along the 445 km length of the Colorado River through Grand Canyon. We also analyze strath terrace sequences that extend to heights of several hundred meters above the river, and integrate these with speleothem constrained maximum incision rates in several reaches to examine any temporal incision variations at the million-year time frame. This new high-resolution geochronology shows temporally steady long-term incision in any given reach of Grand Canyon but significant variations along its length from 160 m/Ma in the east to 101 m/Ma in the west. Spatial and temporal patterns of incision, and the long timescale of steady incision rule out models where geomorphic controls such as climate oscillations, bedrock strength, sediment load effects, or isostatic response to differential denudation are the first order drivers of canyon incision. The incision pattern is best explained by a model of Neogene and ongoing epeirogenic uplift due to an eastward propagating zone of increased upper mantle buoyancy that we infer from propagation of Neogene basaltic volcanism and a strong lateral gradient in modern upper mantle seismic structure.

[1] The Hangay mountain range, a dome in central Mongolia, provides a window into understanding how climate influences the erosion and resulting geomorphic and sedimentary signatures of continental topography. Specifically, asymmetric erosion of the Hangay, associated with a distinct orographic precipitation gradient, offers a natural experiment for exploring uplift, erosion, and the isostatic response to erosional unloading. The flat-topped Hangay peaks preserve low-relief remnant surfaces that provide markers of rock uplift. This makes it possible to map the deformation of a former planar surface during doming and hence to estimate the total extent of erosion by the difference from present day topography. Erosion into the Hangay surface has been significant but incomplete; the morphology of the range indicates a nonequilibrium landscape that may have persisted for millions to tens of millions of years, implying a long response time in this semiarid climate. The extent of erosion across the range correlates with mean annual precipitation. Variability in present-day peak heights across the north-south climatic and erosional gradient provides empirical support for the generally accepted theory that climate-driven erosion will increase the height of mountain peaks by generating greater surface uplift through isostasy. Correction for this isostatic response makes it possible to reconstruct primary surface uplift of the Hangay. Results highlight the importance of considering the interplay between climate, erosion, and uplift in shaping intracontinental topography and thus when interpreting the geomorphic, sedimentary, and geodynamic signatures associated with such topography.

[1] Quantifying long-term erosion of tropical shields is crucial to constraining the role of lateritic regolith covers as prominent sinks and sources of CO 2 and sediments in the context of long-term Cenozoic climate change. It is also a key to understanding long-term landform evolution processes operating over most of the continental surface and their control onto the sediment routing system. We study the surface evolution of West Africa over three erosion periods (~ 45–24, ~ 24–11 and ~ 11–0 Ma) recorded by relicts of three subcontinental-scale lateritic paleolandsurfaces whose age is bracketed by 39 Ar/ 40 Ar dating of lateritic K-Mn oxides. Denudation depths and rates compiled from 380 field stations show that despite heterogeneities confined to early-inherited reliefs, the subregion underwent low and homogeneous denudation (~ 2–20 m Ma –1) over most of its surface whatever the considered time interval. This homogeneity is further documented by a worldwide compilation of cratonic denudation rates, over long-term, intermediate and modern Cenozoic time scales (10 0 –10 7 yr). These results allow defining a steady state cratonic denudation regime that is weathering-limited, i.e., controlled by the thickness of the (lateritic) regolith available for stripping. Steady state cratonic denudation regimes are enabled by maintained compartmentalization of the base levels between river knick points controlled by relief inheritance. Under such regimes, lowering of base levels and their fossilization are primarily imposed by long-term eustatic sea level fall and climate rather than by epeirogeny. The expression of steady state cratonic denudation regimes in clastic sedimentary fluxes remains to be investigated. Components: 9,200 words, 13 figures, 2 tables.

[1] Despite its importance, the spatial and temporal pattern of dynamic topography generated by mantle convective circulation is poorly known. We present accurate estimates of dynamic topography from oceanic basins and continental margins surrounding Australia. Our starting point is measurement of residual depth anomalies on the oldest oceanic floor adjacent to the continental shelf. These anomalies were determined from a combined dataset of ~200 seismic reflection and wide-angle images of well-sedimented oceanic crust. They have amplitudes of between −1 km and +0.5 km, and their spatial variation is broadly consistent with long-wavelength free-air gravity and shallow seismic tomographic anomalies. Along the Northwest Shelf, a regional depth anomaly of −300 to −700 m intersects the adjacent continental shelf. The temporal evolution of this anomaly was determined by analyzing the stratigraphic architecture of an extensive carbonate platform, which fringes the shelf and records a dramatic switch from progradation to aggradation during Neogene times. Three-dimensional seismic mapping calibrated by boreholes was used to calculate water-loaded subsidence histories at rollover points of clinoforms along the shelf. At 9 ± 3 Ma, the rate of subsidence increases from 5 to up 75 m Myr−1, generating a subsidence anomaly of −300 to −700 m. The amplitude of this anomaly varies along the shelf and cannot be generated by glacio-eustatic sea-level variation. Instead, we propose that a regional subsidence episode, which affects both the proximal shelf and the distal oceanic basin, was generated by convective drawdown. By combining our results with other published estimates of uplift and subsidence, a map of Australia, which shows the spatial and temporal pattern of dynamic topography is presented. Most, but not all, of Australia's epeirogeny can be attributed to rapid northward motion of the Australian plate over a pre-existing pattern of convective circulation.

SUMMARY Receiver functions have been calculated from teleseismic events recorded by an array of seismometers deployed on an E-W transect between the coasts of central Norway and Sweden. Forward and inverse modelling and migration of the receiver functions yields models for the subsurface velocity structure along the profile which have the crust thickening from c. 32 km at the Norwegian coast to c. 43 km beneath the central Scandinavian mountain range and then remaining constant beneath Sweden. There is some evidence for a low-velocity layer in the upper 10 km of the crust beneath parts of Norway and western Sweden and good evidence for a high-velocity lower crust underlying much of Sweden which thins to the west beneath Norway. Inverting the seismic velocities to density results in a very good correspondence between calculated and observed gravity anomalies. The results of this study do not support the presence of a significant crustal root providing buoyant support for the mountain range. Low topography and thick crust beneath Sweden are maintained by the high-velocity, high-density lower crustal layer. The upper crustal low-velocity layer is consistent with models based on existing refraction profiling and known geology and physical properties of the crust. There is no direct correlation between properties of the crust and topography suggesting that recent epeirogenic uplift has not resulted from modification of the crust.

Geodynamic models predict that deep mantle buoyancy forces exert important control on the vertical motion history of continents, but it is difficult to isolate the effects of dynamic topography in the geologic record. Here we apply low temperature thermochronometry to exposed Precambrian basement samples across an ~ 1300 km long tract of the western Canadian shield to resolve the thermal imprint, thickness, spatial extent, and evolution of missing portions of the Phanerozoic sedimentary record. New and published apatite (U–Th)/He and fission-track data from three study areas indicate a pronounced heating and cooling event in Paleozoic–early Mesozoic time. This pattern, coupled with geologic observations, indicates that an extensive region of the continent was inundated and buried by sedimentary rocks in Paleozoic time, followed by significant Paleozoic–early Mesozoic unroofing that removed these strata from the rock record. This burial and unroofing history is opposite that expected from eustatic sea level chronologies. A process that can induce long-wavelength (> 1000 km) elevation change in a continental interior region without significant crustal deformation therefore appears required to explain our results. These characteristics of the vertical motions largely eliminate plate margin tectonism as a probable mechanism, and point toward dynamic topography as a likely cause. To evaluate the hypothesis of a dynamic control on the rise and fall of this cratonic region, we compare the 400 to 150 Ma burial and unroofing histories with the evolution of dynamic topography in the western Canadian shield predicted by a three-dimensional model of thermochemical convection. The histories of burial and unroofing mimic the predicted history of elevation change to first order, indicating that dynamic topography is a viable cause for the vertical motions. A phase of significant burial before ~ 350 Ma may be due to cold mantle downwellings that produced subsidence during Pangea assembly, followed by unroofing between ~ 350 Ma and 250 Ma induced by development of warm mantle upwellings after Pangea amalgamation. While a fuller range of mantle dynamic models must be explored to more completely understand the causes of cryptic elevation change in the North American continental interior, our study highlights the utility of cratonic thermochronometry data for testing and calibrating dynamic models, and for evaluating mantle and surface process interactions deep in Earth history.

We use teleseismic waveform inversion, along with depth phase analysis, to constrain the centroid depths and source parameters of large African earthquakes. The majority of seismic activity is concentrated along the East African Rift System, with additional active regions along stretches of the continental margins in north and east Africa, and in the Congo Basin. We examine variations in the seismogenic thickness across Africa, based on a total of 227 well-determined earthquake depths, 112 of which are new to this study. Seismogenic thickness varies in correspondence with lithospheric thickness, as determined from surface wave tomography, with regions of thick lithosphere being associated with seismogenic thicknesses of up to 40 km. In regions of thin lithosphere, the seismogenic thickness is typically limited to ≤20 km. Larger seismogenic thicknesses also correlate with regions that have dominant tectonothermal ages of ≥1500 Ma, where the East African Rift passes around the Archean cratons of Africa, through the older Proterozoic mobile belts. These correlations are likely to be related to the production, affected by method and age of basement formation, and preservation, affected by lithospheric thickness, of a strong, anhydrous lower crust. The Congo Basin contains the only compressional earthquakes in the continental interior. Simple modelling of the forces induced by convective support of the African plate, based on long-wavelength free-air gravity anomalies, indicates that epeirogenic effects are sufficient to account for the localization and occurrence of both extensional and compressional deformation in Africa. Seismicity along the margins of Africa reflects a mixture between oceanic and continental seismogenic characteristics, with earthquakes in places extending to 40 km depth.

Analysis of a 1.15 km deep apatite fission track (AFT) thermochronology profile at the Underground Research Laboratory (URL), in the southwestern Canadian Shield suggests two Phanerozoic heating and cooling episodes indicating significant, previously unsuspected, Phanerozoic heat flow variations. Phanerozoic temperature and heat flow variations are temporally associated with burial and erosion of the Precambrian crystalline shield and its overlying Phanerozoic successions, which are now eroded completely. Maximum Phanerozoic temperatures occurred in the late Paleozoic when the geothermal gradient is estimated to have been ~ 40–50 °C/km (compared to a present day gradient of ~ 14 ± 2 °C/km) and the sedimentary cover was ~ 800–1100 m thick. Our thermal history models, confirm regional stratigraphic relationships that suggest that the Paleozoic succession was completely eroded prior to beginning of Mesozoic sedimentation. A second heating phase occurred during Late Cretaceous–Paleogene burial when the geothermal gradient is estimated to have been ~ 20–25 °C/km and the Mesozoic and Cenozoic succession was ~ 1200 to 1400 m thick. The Phanerozoic thermal history at the URL site shows a pattern similar to that inferred previously for the epicratonic Williston Basin, the centre of which lies several 100 km to the west. This implies a common regional thermal history for cratonic rocks underlying both the basin and the currently exposed shield. It is suggested that the morphotectonic differences between the Williston Basin and the exposed shield at the URL are due to a dissimilar thermomechanical response to a common, but more complicated than previously inferred, Phanerozoic geodynamic history. The two Phanerozoic periods of variations in geothermal gradient (heat flow) were coeval with epeirogenic movements related to the deposition and erosion of sediments. These paleogeodynamic variations are tentatively attributed to far-field effects of orogenic processes occurring at the plate margin (i.e. the Antler and the Cordilleran orogenies) and the associated accumulation of cratonic seaway sedimentary sequences (Kaskaskia and Zuni sequences).

The generalized eustatic and tectonoeustatic models developed by the author are tested on Lower Cretaceous deposits of the eastern part of the Russian Plate. The models are applicable to facies analysis of sections of epicontinental basins with mainly slope sedimentation. They demonstrate possible variations in section lithology depending on the rate of eustatic changes and the intensity and direction of epeirogenic movements. It has been revealed that the Lower Cretaceous sections in the east of the Russian Platform formed as a result of the synchronous global eustasy and regional epeirogeny. Superposition of the global eustatic curve onto the Lower Cretaceous chronostratigraphic chart of the eastern part of the platform showed that global eustasy, periodically concealed by regional epeirogeny, played a crucial role in the Early Cretaceous history of the study area. Regional epeirogenic and eustatic curves were constructed. The epeirogenic curve demonstrates the contribution of vertical tectonic movements to the overall eustatic-epeirogenic result recorded on a regional eustatic curve. The latter was constructed from the analysis of the spatial and temporal changes in the stratigraphic position of formations and strata and transgressive surfaces ranking. Eustatic cycles of different ranks, from elementary (systems tracts) to regional scale, have been recognized. In the rank of largest lithostratigraphic units, three sequences are revealed: Valanginian (RP-1K), Upper Hauterivian–Upper Aptian (RP-2K), and Albian (RP-3K), which reflect the crucial stages of the Early Cretaceous evolution of the eastern Russian Plate. The eustatic-epeirogenic processes during accumulation of formations and strata from Early Berriasian to Late Albian (145.5–99.6 Ma) are considered. It is shown that the division of the studied composite section into sequences permits precise prediction of diverse solid minerals.

Southern Africa's topography is distinctive. An inland plateau of low relief and high average elevation is separated from a coastal plane of high relief and low average elevation by a steeply dipping escarpment. The origin and evolution of this topography is poorly understood because, unlike high plateaus elsewhere, its development cannot be easily linked to present day compressional plate boundary processes. Understanding the development of this regional landscape since the break-up of Gondwana is a first order step towards resolving regional epeirogenesis. We present data that quantifies the timing and extent of exhumation across the southern Cape escarpment and coastal plane, using apatite fission track analysis (AFTA) of 25 outcrop samples and 31 samples from three deep boreholes (KW1/67, SA1/66, CR1/68). Outcrop fission track (AFT) ages are Cretaceous and are significantly younger than the stratigraphic ages of their host rocks, indicating that the samples have experienced elevated paleotemperatures. Mean track lengths vary from 11.86 to 14.23 μm. The lack of Cenozoic apatite ages suggests that major cooling was over by the end Cretaceous. The results for three boreholes, situated seaward (south) of the escarpment, indicate an episode of increased denudation in the mid-late Cretaceous (100–80 Ma). An earlier episode of increased denudation (140–120 Ma) is identified from a borehole north of the escarpment. Thermal modelling indicates a history involving 2.5–3.5 km of denudation in the mid-late Cretaceous (100–80 Ma) at a rate of 175 to 125 m/Ma. The AFT data suggest that less than 1 km of overburden has been eroded regionally since the late Cretaceous (< 80 Ma) at a rate of 10 to 15 m/Ma, but do not discount the possibility of minor (in relative amplitude) episodes of uplift and river incision through the Cenozoic. The reasons for rapid denudation in these early and mid-Cretaceous episodes are less clear, but may be related to epeirogenic uplift associated with an increase in mantle buoyancy as reflected in two punctuated episodes of alkaline intrusions (e.g. kimberlites) across southern Africa and contemporaneous formation of two large mafic igneous provinces (~ 130 and 90 Ma) flanking its continental margins. Because Cenozoic denudation rates are relatively minimal, epeirogenic uplift of southern Africa and its distinct topography cannot be primarily related to Cenozoic mantle processes, consistent with the lack of any significant igneous activity across this region during that time.

At least 12 km of strata ranging in age from the latest Precambrian to the Recent are exposed in the Zagros Mountains of Iran. This sedimentary cover is characterized by distinct stratal packages separated by major unconformities forming twelve supersequences. They are informally named as: (1) Late Precambrian – Cambrian Hakhamanesh Supersequence, (2) Ordovician Kourosh Supersequence, (3) Silurian Camboojiyeh Supersequence, (4) Devonian Darioush Supersequence, (5) Mississippian – Pennsylvanian Khashayar Supersequence, (6) Permian – Triassic Ashk Supersequence, (7) Jurassic Farhad Supersequence, (8) Early Cretaceous Mehrdad Supersequence, (9) Late Cretaceous Ardavan Supersequence, (10) Paleocene – Oligocene Sassan Supersequence, (11) Oligocene – Miocene Ardeshir Supersequence, and (12) Miocene – Pleistocene Shapour Supersequence. These supersequences and their correlatives in neighboring areas have been used to infer tectonic events. The dominant interpretation has been that local or regional epeirogenic movements were responsible for the formation of these supersequences. Unconformities are considered as indications that epeirogenic movements associated with tectonic events affected the area. The present investigation provides an alternative to the established view of the Phanerozoic supersequences of the Zagros Mountains. A good correlation exists between the lithofacies of supersequences in the Zagros Mountains and the second-order eustatic sea-level changes. Deposition of deep-water, marine shales occurred during periods of eustatic sea-level rise. Platform-wide unconformities coincided with eustatic sea-level lows. In fact, supersequences of the Zagros Mountains are nearly identical to those described from the North American Craton and the Russian Platform suggesting that these stratal packages are global. These observations suggest that supersequences of the Zagros Mountains formed by second order eustatic sea-level changes and not by local or regional epeirogenic movements. Although tectonic events did not produce supersequences of the Zagros Mountains, they influenced regional lithofacies patterns through the formation of intrashelf depressions such as the Hormoz Salt Basin during the Precambrian and the Dezful Embayment and the Lorestan Basin during the Mesozoic. Tectonic events also affected sedimentation during the Tertiary collision of Arabia and the Central Iran microplate through uplift, erosion, and the formation of the Zagros Foreland Basin. The results of this investigation necessitate a re-evaluation of the role and the significance of pre-Tertiary tectonic events commonly used to interpret the geological evolution of the Zagros Mountains.

A pronounced latitudinal asymmetry in the present-day morphology of the Australian continental shelf is reflected in Neogene stratigraphic relationships. The northern Australian margin has a broad shelf, typically 200–500 km wide and a Neogene record of stratal onlap. Relative to the continent, sea levels are currently as high as at any stage during the Neogene. In contrast, the southern shelf is typically less than 100 km wide and shows a record of progressive offlap with Neogene palaeo-shorelines commonly many hundreds of kilometres inland, at elevations up to ∼250 m above present-day sea level. This continental-scale ‘reciprocal’ stratigraphy implies 250–300 m N-down, SSW-up apparent vertical motion with respect to sea level since the mid-Miocene. The apparent vertical motion can be attributed to variations in dynamic topography and the geoid along Australia's NNE plate circuit; specifically, the movement of the southern margin off the dynamic topography low, geoid low presently centred on the Australian– Antarctic discordance, and the northern margin towards a dynamic topography low, geoid high associated with the subduction realm to the north. Variations in the geoid appear to account for about 10% of the total apparent motion, depending on assumptions about how the geoid field has evolved during Australia's northward motion. This inferred Neogene, continental-scale dynamic N–S tilting rate of ∼15–20 m/myr provides a compelling new constraint on the nature of the Earth's dynamic topographic field. © 2007 Elsevier B.V. All rights reserved.

Mountain ranges that are actively forming around the western and northern perimeter of the Indo-Eurasia collisional deformational field, such as the Mongolian Altai, comprise a unique class of intracontinental intraplate transpressional orogen with structural and basinal elements that are distinct from contractional and extensional orogens. Late Cenozoic uplift and mountain building in the Mongolian Altai is dominated by regional-scale dextral strike–slip faults that link with thrust and oblique–slip faults within a 300-km-wide deforming belt sandwiched between the more rigid Junggar Basin block and Hangay Precambrian craton. Dominant orogenic elements in the Mongolian Altai include double restraining bends, terminal restraining bends, partial restraining bends, single thrust ridges, thrust ridges linked by strike–slip faults, and triangular block uplifts in areas of conjugate strike–slip faults. The overall pattern is similar to a regional strike–slip duplex array; however, the significant amount of contractional and oblique–slip displacement within the range and large number of historical oblique–slip seismic events renders the term “transpressional duplex” more accurate. Intramontane and range flanking basins can be classified as ramp basins, half-ramp basins, open-sided thrust basins, pull-apart basins, and strike–slip basins. Neither a classic fold-and-thrust orogenic wedge geometry nor a bounding foredeep exists. The manner in which upper crustal transpressional deformation is balanced in the lower crust is unknown; however, crustal thickening by lower crustal inflation and northward outflow of lower crustal material are consistent with existing geological and geodetic data and could account for late Cenozoic regional epeirogenic uplift in the Russian Altai and Sayan regions.

The North Atlantic margins are archetypally passive, yet they have experienced post-rift vertical movements of up to kilometre scale. The Cenozoic history of such movements along the NW European margin, from Ireland to mid-Norway, is examined by integrating published analyses of uplift and subsidence with higher resolution tectono-stratigraphic indicators of relative movements (including results from the STRATAGEM project). Three episodes of epeirogenic movement are identified, in the early, mid- and late Cenozoic, distinct from at least one phase of compressive tectonism. Two forms of epeirogenic movement are recognised, referred to as tilting (coeval subsidence and uplift, rotations

We agree that there is now convincing evidence which favours the idea that a region encompassing the British Isles is dynamically supported by convective circulation beneath the lithospheric plate. For example, the coincidence of a long wavelength (>800 km) free-air gravity anomaly with anomalously slow velocities beneath the lithospheric plate suggests that regional elevation of Northern Britain is maintained by a tongue of hot asthenosphere protruding away from Iceland (Jones et al. 2002a; Arrowsmith et al. 2005). These observations are corroborated by the crustal thickness measurements of Davis et al. (2012). The Icelandic plume initiated 62 Ma and there is excellent evidence in the Irminger and Icelandic basins that this plume has waxed and waned with different periodicities (Jones et al. 2002b; Poore et al. 2009). This transient activity has manifest itself in geochemical and earthquake records along the Reykjanes Ridge (Poore et al. 2011; Parnell-Turner et al. 2013), in the Neogene record of deep-water overflow across the Greenland-Scotland Ridge (Poore et al. 2006), and along the fringing continental margins where spectacular buried ephemeral landscapes have been encountered (Shaw-Champion et al. 2008; Rudge et al. 2008; Hartley et al. 2011). Around the British Isles, there is considerable onshore and offshore evidence favouring a history of transient and/or permanent vertical motions which may reflect Palaeogene and Neogene plume activity (White & Lovell 1997; Jones et al. 2001; Jones et al. 2002a; Al-Kindi et al. 2003; Jones & White 2003; Mackay et al. 2005). This regional pattern of epeirogeny is locally complicated by faulting and folding, which is often difficult to date with precision.

Thick terminal Proterozoic–lowest Cambrian successions allow reference of the Saint John, New Brunswick, and MacCodrum Brook, southern Cape Breton Island, areas to the marginal platform of the Avalon microcontinent. Marginal-platform siliciclastic-dominated sequences form a cover on Late Precambrian arc successions from southern New Brunswick to North Wales. Their deposition in fault-bounded basins began with the origin of the Avalon microcontinent and development of a persistent transtensional regime in the latest Precambrian. The terminal Proterozoic–lowest Cambrian on the Avalonian marginal platform consists of three successive lithofacies associations: lower subaerial rift to marginal-marine facies; overlying cool-water, wave-influenced, marine platform sandstones and shales; and higher macrotidal quartz arenites (=Avalonian depositional sequences 1–2). Only the Lower Cambrian macrotidal quartz arenites onlap southeast, where they form the oldest Cambrian unit on the inner platform. These major lithofacies are the Rencontre, Chapel Island, and Random formations, respectively, in Avalonian North America. Southwest thinning of the Rencontre–Chapel Island–Random interval in southern New Brunswick reflects slower subsidence of a fault-bounded area in the city of Saint John. The depositional sequence 1–2 unconformity, which falls in the sub-trilobitic Lower Cambrian Watsonella crosbyi Zone of the Chapel Island Formation, persists for 650 km along the marginal platform from southeastern Newfoundland to southern New Brunswick and, potentially, appears in Cape Breton Island. Latest Precambrian-earliest Cambrian epeirogenic and depositional history was very uniform along the marginal platform, and a unified lithostratigraphic nomenclature is appropriate.

It is generally accepted that Cenozoic epeirogeny of the African continent is moderated by convective circulation of the mantle. Nevertheless, the spatial and temporal evolution of Africa's “basin-and-swell” physiography is not well known. Here we show how continental drainage networks can be used to place broad constraints on the pattern of uplift through space and time. First, we assemble an inventory of 710 longitudinal river profiles that includes major tributaries of the 10 largest catchments. River profiles have been jointly inverted to determine the pattern of uplift rate as a function of space and time. Our inverse model assumes that shapes of river profiles are controlled by uplift rate history and modulated by erosional processes, which can be calibrated using independent geologic evidence (e.g., marine terraces, volcanism and thermochronologic data). Our results suggest that modern African topography started to develop ∼30 Myr ago when volcanic swells appeared in North and East Africa. During the last 15–20 Myr, subequatorial Africa was rapidly elevated, culminating in the appearance of three large swells that straddle southern and western coasts. Our results enable patterns of sedimentary flux at major deltas to be predicted and tested. We suggest that the evolution of drainage networks is dominated by rapid upstream advection of signals produced by a changing pattern of regional uplift. An important corollary is that, with careful independent calibration, these networks might act as useful tape recorders of otherwise inaccessible mantle processes. Finally, we note that there are substantial discrepancies between our results and published dynamic topographic predictions.

The Angolan margin is the type area for raft tectonics. New seismic data reveal the contractional buffer for this thin-skinned extension. A 200-km-long composite section from the Lower Congo Basin and Kwanza Basin illustrates a complex history of superposed deformation caused by: (1) progradation of the margin; and (2) episodic Tertiary epeirogenic uplift. Late Cretaceous tectonics was driven by a gentle slope created by thermal subsidence; extensional rafting took place updip, contractional thrusting and buckling downdip; some distal folds were possibly unroofed to form massive salt walls. Oligocene deformation was triggered by gentle kinking of the Atlantic Hinge Zone as the shelf and coastal plain rose by 2 or 3 km; relative uplift stripped Paleogene cover off the shelf, provided space for Miocene progradation, and steepened the continental slope, triggering more extension and buckling. In the Neogene, a subsalt half graben was inverted or reactivated, creating keystone faults that may have controlled the Congo Canyon; a thrust duplex of seaward-displaced salt jacked up the former abyssal plain, creating a plateau of salt 3–4 km thick on the present lower slope. The Angola Escarpment may be the toe of the Angola thrust nappe, in which a largely Cretaceous roof of gently buckled strata, was transported seawards above the thickened salt by up to ∼20 km.

Rivers are extremely sensitive to subtle changes in their grade caused by tectonic tilting. As such, recognition of tectonic tilting effects on rivers, and their resultant sediments, can be a useful tool for identifying the often cryptic warping associated with incipient and smaller-scale epeirogenic deformation in both modern and ancient settings. Tectonic warping may result in either longitudinal (parallel to floodplain orientation) or lateral (normal to floodplain orientation) tilting of alluvial river profiles. Alluvial rivers may respond to deformation of longitudinal profile by: (1) deflection around zones of uplift and into zones of subsidence, (2) aggradation in backtilted and degradation in foretilted reaches, (3) compensation of slope alteration by shifts in channel pattern, (4) increase in frequency of overbank flooding for foretilted and decrease for backtilted reaches, and (5) increased bedload grain size in foretilted reaches and decreased bedload grain size in backtilted reaches. Lateral tilting causes down-tilt avulsion of streams where tilt rates are high, and steady down-tilt migration (combing) where tilt rates are lower. Each of the above effects may have profound impacts on lithofacies geometry and distribution that may potentially be preserved in the rock record. Fluvial sedimentary evidence for past tilting is traditionally based on the assumption that depositional features reminiscent of modern fluvial tectonic effects are evidence for past tectonic effects where it is closely associated with historically active structures, or where non-tectonic causes cannot be invoked; however, caution must be exercised when using these effects as criteria for past or current tectonic warping, as these effects may be caused by non-tectonic factors. These non-tectonic causes must be eliminated before tectonic interpretations are made.

The history of southern Israel during the ∼100 Myr period between the Cretaceous and the Eocene is an example of epeirogenic movements which were controlled by magmatism and heating. Initially this region was uplifted and became a local swell; then it subsided more than its surroundings and became a local basin. This study analyzes the subsidence history of the region during its cooling for two purposes: first, to understand the relations between the tectonic pattern of subsidence and the resulting stratal geometry, and second, to constrain the volume of magmatism that intruded the lithosphere and perturbed the isostatic equilibrium. Our results show that lateral changes in the intensity of the tectonically-driven subsidence are not always expressed by simple corresponding changes in the thickness of sedimentary units. The most prominent example of this was found in the Cenomanian section, which thickens northward in absolute contrast with the tectonic pattern of subsidence during its deposition. The reason for this discrepancy lies in lateral differences in the compactibility of the substrate upon which these sediments were deposited. The two most important factors controlling the compactibility of the substrate are the thickness of previously existing sediments and their history of uplift. Since sediments that are reburied after an uplifting phase do not compact significantly until they reach their previous maximal depth, we emphasize the need to reveal the amount of exhumation from the amount of erosion hidden in unconformities. Our second aim was achieved only in part because we cannot distinguish the subsidence caused by midlithospheric intrusions from secondary factors. One possible scenario that satisfies the observations is a combination of midlithospheric intrusions equivalent to a 15-km-thick sill, plus thermal thinning of the lithosphere of the same order.

Epeirogenic uplift and denudation are difficult to quantify because, unlike basin subsidence, they do not leave an unambiguous record. In recent years, much research has been focussed on calculating regional denudation from sonic velocity measurements, from vitrinite reflectance profiles, and from fission track analyses. Here we show that inverse modelling of the remnant stratigraphy within extensional sedimentary basins yields estimates of denudation within a corridor which crosses the British Isles. For a variety of reasons, these estimates are minima but they do broadly agree with those determined by inversion of vitrinite reflectance profiles. Our results also demonstrate that denudation estimates from fission track analyses are meaningful. A combined stratigraphic and thermal indicator approach should now be used to map denudation across different continents.

The magnitude and timing of synorogenic and postorogenic denudation along fold and thrust belts and their associated foreland basins, of interest because of both tectonic and economic implications, is generally poorly constrained. Along the late Paleozoic Ouachita trend, a thin veneer of Cretaceous strata is preserved above a low-relief erosional surface that beveled the Ouachita orogen and adjacent foreland areas. This regional erosion surface provides a valuable constraint for interpreting new and previously published apatite fission track (AFT) data obtained from exposed structural highs along the Ouachita trend (Marathon, Llano, Arbuckle, and Benton uplifts). AFT data from sampled localities within the deformation belt (Marathon and Benton uplifts) exhibit younger ages and, generally, longer mean lengths than data from localities on the foreland side of the deformation front (Llano and Arbuckle uplifts). This observation suggests that erosion of the orogen, rather than its extensional collapse, was the primary mechanism responsible for flexural isostatic unloading of the foreland crust. In addition, all samples show evidence for mild reheating following their pre-Cretaceous cooling history. Specifically, the lack of a significant population of >14.5-μm tracks in all samples appears to require residence at temperatures of ≥55°±5°C after development of the sub-Cretaceous erosional surface. This implies that ∼1000 m of Cretaceous-Paleogene (?) strata were deposited across the entire Ouachita frontal trend and subsequently removed during later Tertiary time. This Tertiary denudation is interpreted to reflect the interplay between regional denudation and isostatic compensation in response to slow (∼10 m/m.y.) epeirogenic uplift of the southern midcontinent and a long-term drop (∼200 m) in eustatic sealevel during this time.

North American Phanerozoic cratonic strata comprise six transgressive/regressive sequences separated by interregional unconformities. The mechanism of formation of the sequences and their bounding unconformities remain uncertain. Although eustasy probably contributed, it cannot have acted alone in their formation, as testified by syn-depositional faulting and post-depositional tilting of strata. We have developed a three-dimensional stratigraphic model which incorporates vertical motions from dynamic topography, background cratonic subsidence, eustasy, denudation, mixed carbonate and elastic deposition, Airy isostasy in response to loading and unloading, and mechanical compaction. The model has been used to test possible contributions of eustasy, epeirogeny and background subsidence to patterns of cratonic strata. The results demonstrate the potential of dynamic topography to account for observed long-wavelength tilting. They also demonstrate the importance of background subsidence on the craton in providing accommodation space to accumulate and preserve the observed thicknesses of stratigraphic sequences.

In the geological past when the Earth's decelerating rotation passed through the critical length of day of ∼ 22.2 h, the free nutation or ‘tipping’ of the fluid core (for a core shape in hydrostatic equilibrium) would have resonated precisely with the Earth's retrograde annual forced nutation caused by solar torques. This annual resonance may have caused orders-of-magnitude amplification of core rotation and velocity of core motions, leading to temperature increase and heat release near the core-mantle boundary, instability of the D″ thermal boundary layer at the base of the mantle, and the upwelling of deep mantle plumes. Neoproterozoic palaeotidal data indicate 21.9 ± 0.4 h/day at ∼ 620 Ma, thus placing the critical length of day of ∼ 22.2 h and core resonance at 530 ± 100 Ma. A core shape departing by ±5% from its equilibrium value places resonance in the interval 530 ± 250 Ma. The one distinctive, major tectonothermal event in the interval 530 ± 250 Ma was that of ‘late Pan-African’ age, which affected much of Gondwana during the late Neoproterozoic-early Palaeozoic. This tectonothermal activity, which peaked between ∼ 570 and ∼ 500 Ma, was marked by high temperatures at mid-crustal levels and elevated heat flow, widespread granulite facies metamorphism and crustal reworking and anatexis, commonly in the absence of obvious pervasive deformation, extensive epeirogenic uplift and extrusion of flood basalts; such features indicate an intense crustal heating event that may be ascribed to mantle plumes and hotspots. Furthermore, flood volcanism and rifting in Laurentia during the late Neoproterozoic-early Palaeozoic suggest the coeval upwelling of mantle plumes that led to continental breakup including the opening of the Iapetus Ocean. The apparent global peak in plume activity between ∼ 570 and ∼ 500 Ma may reflect an increase in core-mantle heat flux and instability of D″, caused by the annual resonance of the fluid core (for a core shape in or near hydrostatic equilibrium). The core evidently underwent stronger resonances with the semi-annual and 1/3-annual forced nutations at widely spaced times during the Archaean, when the length of day was approximately 17.7 ± 0.4 h and 15.4 ± 0.4 h, respectively; these two resonances probably caused much greater increases in the velocity and amplitude of core motions and in core-mantle heat flux than occurred during the annual resonance. Proterozoic palaeorotational data suggest that the very strong semi-annual resonance may correlate with the worldwide tectonothermal event at ∼ 2700 Ma; this event is marked by widespread mantle and crustal anatexis, granitoid intrusion and the extrusion of flood basalts and komatiites, and has been ascribed to the upwelling of high-temperature plumes from the core-mantle boundary. The hypothesis that major tectonothermal reworking events may have resulted from thermal plumes generated at the core-mantle boundary in response to resonances of the fluid core for a tidally decelerating Earth may be tested by the acquisition of high quality palaeorotational data for the early Palaeoproterozoic and Archaean.

Despite the century-long recognition of regional epeirogeny along the middle Atlantic passive margin, relatively few studies have focused on understanding postrift uplift mechanisms. Here, we demonstrate that epeirogenic uplift of the central Appalachian Piedmont and subsidence of the Salisbury Embayment represent first-order, flexural isostatic processes driven by continental denudation and offshore deposition. Our results show that regional epeirogenic processes, present on all Atlantic-type passive margins, are best resolved by specific stratigraphic and geomorphic relationships, rather than topography. A simple one-dimensional geodynamic model, constrained by well-dated Baltimore Canyon trough, Coastal Plain, and lower Susquehanna River (piedmont) stratigraphy, simulates flexural deforamtion of the U.S. Atlantic margin. The model represents the passive margin lithosphree as a uniformly thick elastic plate, without horizontal compressive stresses, that deforms flexurally under the stress of strike-averaged, vertically applied line loads. Model results illustrate a complex interaction among margin stratigraphy and geomorphology, the isostatic repsonse to denudational and depositional processes, and the modulating influence of exogenic forces such as eustasy. The current elevation, with respect to modern sea level, of fluvial terraces and correlateive Coastal Plain deposits or unconformities is successfully predicted through the synthesis of paleotopography, eustatic change, and margin flexure. Results suggest that the middle U.S. Atlantic margin landward of East Coast Magnetic Anomaly is underlain by lithoshpere with an average elastic thickness of 40 km (flexural rigidity, D = 4 X 10(exp 23) N m), the margin experience an average, long-term denudation rate of approximately 10m/m.y., and the Piedmont has been flexurally upwaped between 35 and 130 meters in the last 15 m.y. Long term isostatic continental uplift resulting rom denudation and basin subsidence resulting rom sediment loading are accomodated primately by a convex-up flexural hinge, physiographically represented by the Fall Zone. Our results elucidate an inherent danger in using topography alone to constrain late-stage passive margin deformation mechanisms. Only through careful synthesis of field stratigraphic and geomorphic elements such as fluvial terraces, Coastal Plain deposits, and offshore stratigraphy can age control be extended from the offshore depositional setting to the erosionally dominated continent. This sudy demonstrates that despite a relatively subdued topography, the middle U.S. Atlantic margin experiences progressive flexural isostatic deformation similar to that proposed for high-relief margins characterized by great escarpments. Thus margin topographic diversity remains a function of other factors, such as lithospheric composition and/or structure, supracrustal stratigraphy and structure, degree of drainage integration, drainage divide migration and climate.

29 pages; International audience; We analyse tectonic and sedimentary field and subsurface data for the Angola onshore margin together with free-air gravity anomaly data for the offshore margin. This enables us to characterize the mode of synrift tectonism inherited from the Precambrian and its impact on the segmentation of the Angola margin. We illustrate that segmentation by the progressive transition from the Benguela transform-rifted margin segment to the oblique-rifted South Kwanza and orthogonal-rifted North Kwanza margin segments. The spatial variation in the intensity of post-rift uplift is demonstrated by the study of a set of geomorphic markers detected in the post-rift succession of the coastal Benguela and Kwanza Basins: Upper Cretaceous to Cenozoic uplifted palaeodeltas, erosional unconformities, palaeovalleys, Quaternary marine terraces and perched Gilbert deltas. The onshore Benguela transform margin has a distinctive, mainly progradational stratigraphic architecture with long-term sedimentary gaps and high-elevation marine terraces resulting from moderate Upper Cretaceous–Cenozoic to major Quaternary uplifting (i.e. 775–1775 mm/ky or m/Ma). By contrast, repeated synchronous episodes of minor Cenozoic to Quaternary uplift occurred along the orthogonal-rifted North Kwanza segment with its Cenozoic aggradational architecture, shortterm sedimentary gaps and low-elevation Pleistocene terraces. Margin style likewise governs spatial variations in the volume of offshore sediment dispersed in the associated deep-sea fans. Along the lowlying North Kwanza margin, sedimentation of the broad Cenozoic to Pleistocene Kwanza submarine fan was probably governed by the width of the Kwanza interior palaeodrainage basin combined with the wet tropical Neogene climate. Along the high-rising Benguela margin, the small size of the Benguela deep-sea fan is related to the interplay between moderate continental sediment dispersal from long-lived small catchments and a warm, very arid Neogene climate. However, the driving forces behind the epeirogenic post-rift uplift of the Angola coastal bulge remain a matter of speculation.

Comparisons of MAGSAT magnetic contrasts and geology across the Mesozoic assembly of Africa and South America provide new insight into the interpretation of the long-wavelength magnetic anomalies near the present continental margins. Across continental Africa and South America, the MAGSAT magnetic contrasts can be correlated with geologic provinces formed before the Mesozoic separation of the continents. On the continents, areas affected by significant Mesozoic hotspot tectonism display negative magnetic contrasts suggesting a causative relationship between hotspot tectonism and the origin of the observed magnetic contrasts. The magnetic characteristics of a portion of the lower crust in these areas appear to have been significantly altered during the Mesozoic hotspot epeirogeny. By analogy with the processes of continental rifting, it is suggested that the magnetic mineralogy of the intruded lower crust may be dominated by weakly- to non-magnetic titanomagnetites. Oceanic magnetic contrast comparisons show that the positions of magnetic anomaly highs over the Rio Grande-Walvis Ridge System of the South Atlantic are consistent with the interpretation of their evolution over the Walvis Hotspot. However, only the parts of these ridges that were formed during the Cretaceous normal polarity geomagnetic epoch bear strong magnetic contrasts. Remanent magnetization thus appears to be an important contributor toward the MAGSAT magnetic anomalies of these features.

Amplitude spectra of fundamental-mode Rayleigh and Love waves are used to determine shear-wave Q ( Q β ) models for the upper crust of the Arabian peninsula. The observed spectra are compared to theoretical spectra computed for earthquakes with known fault-plane solutions. Shear-wave Q in the upper crust can be obtained by trial-and-error modeling to fit the the slope of the amplitude spectra at short periods (5–30 s), if the source time function is less than about 6 s and if the depth of the earthquake is known to within about 3 km. Shear-velocity Q values obtained in this way vary from about 60 along the margin of the Red Sea to 100–150 in the central part of the peninsula, to 65–80 in the eastern folded region. These values are unusually low for a stable region and suggest that observed anelasticity there is affected by tectonic and epeirogenic activity which has occurred over the past 30 m.y. The shear-wave Q models derived from surface waves at periods of 5–30 s closely predict reported values of Lg Q at 1 Hz; shear-wave Q , therefore, appears to be independent of frequency in this region at periods between about 1 and 30 s.

[1] Inversion is one of the most common modes of intraplate deformation and a primary mechanism of sedimentary basin exhumation. The key criterion for identification of basin inversion is the contractional reactivation of extensional faults. Reverse displacement associated with inversion is focused along the upper segments of faults, so the evidence for inversion may be removed in deeply exhumed basins. We believe this is the case in the Irish Sea, western British Isles. Previous authors have attributed the severe exhumation of this basin to plume-related uplift and have ruled out inversion as a cause of uplift. We present a method for identifying tectonic inversion in a basin where exhumation has removed evidence of reverse displacement on the upper segments of faults. We utilize compaction-based mapping of erosion patterns recorded by anomalously high sonic velocities in Upper Triassic shales. We show that the amount of section removed during exhumation in the Irish Sea varies between 1.3 and 3.3 km and that exhumation patterns are markedly heterogeneous. Neither the heterogeneity of exhumation nor its focusing over hanging wall blocks of major faults is consistent with solely plume-related uplift, and we believe that our results record cryptic basin inversion that is superimposed on epeirogenic exhumation (some of which may be plume related). The direct evidence for this inversion has been removed because erosion has proceeded beneath the null lines of reactivated faults, and we propose erosion of reactivated fault segments as one of the major reasons why shortening is frequently underestimated in inverted basins.

The stratigraphic record contains clear evidence that broad regions have experienced rapid changes in sea level unrelated to changes in glacial ice volume (e.g., third- and higher-order Vail sea level variations, continental foundering). We propose that many of these changes can be caused by stress-induced changes in plate density. Stress changes produce significant changes in the density of the crust and lithosphere (a point missed in previous investigations) and propagate across even the largest plates in less than 30,000 years. Lithospheric plates interacting at existing boundaries can produce stress-related density changes sufficient to cause several meters change in plate elevation; these may account for many of the regressions and transgressions seen in the stratigraphic record. The creation of new rifts could increase plate compression enough to cause ∼50 m of plate subsidence. Plate elevation changes of up to −200 m could result from increased plate compression during continental collisions. A particularly enigmatic kind of rapid nonglacial global (NGG) sea level change is a coupled ∼50 m sea level fall (regression) and roughly equal rise (transgression) occurring in less than 106 years. These couplets, associated with black shales and marine extinctions, can be explained by the elastic snapback attending the rapid formation of a new rift. Isostatic disequilibria along the new rift depresses the seafloor sufficiently to cause a ∼50 m fall in sea level. Mantle flow restores isostatic equilibrium along the rift axis and erases the fall in ∼60,000 years. Unusually intense hydrothermal circulation along the new rift during the snapback promotes anoxic bottom water conditions and deposition of black shales. A rapid drop in global sea levels reduces the area of ocean bottom within the photic zone, causing overpopulation, food exhaustion, and extinctions. The connections between changes in plate stress and density have many implications. Perhaps the most far reaching is that tectonic events on the 3/4 of the globe that is covered by oceans, as well as the 1/4 that is subaerial, are recorded in sedimentary strata.

We evaluate the sea level changes caused by changing the age/area relationship of the seafloor by altering the thermal structure and hence the elevation of the world seafloor. We do this by having a passive-margined (and therefore continuously aging) “Atlantic-type” ocean open at a uniform rate at the expense of an active-margined (and therefore constant age) “Pacific-type” ocean. This run of the model was specifically constructed to answer the question of how much sea level would change if the Atlantic opened at a uniform rate. Therefore it specifically excludes the other major processes that change sea level. These would include changes in ice volume, other changes in plate generation/consumption rates, continental orogeny and epeirogeny, lithospheric stretching, lithospheric flexure, and thermally induced subsidence at passive margins and amplification thereof caused by water and sediment loading. The isostatic effects of continental flooding and oceanic unloading are accommodated by application of balanced global isostasy to an Earth model consisting of 121 independent columns. The lithospheric portions of the columns are linked to the hypsographic curve. Sea level changes are viewed from two different observational positions: (1) geologically stable and continually emerged continental plateau and (2) geologically stable and continually submerged shelf break. The modeled sea level that results from changing the age/area relationship of the seafloor since 160 Ma peaks at ∼85 Ma and is ∼30% less for the emerged observer (34 m) than for the submerged observer (48 m). Furthermore, the peak is in phase with, but only ∼1/4; (48 m versus 200+ m) of that portrayed by either the “eustatic” curves inferred from seismic stratigraphy or the isostatically readjusted positions of marine strandlines of the stable platform of North America. We therefore conclude that the other 3/4 of sea level rise that accompanies the opening of the Atlantic must be partitioned among the other causes suggested above.

Sea-level data from eastern North America are analyzed for evidence of neotectonism, which is inferred from residual sea-level anomalies, after removal of glacial isostatic and eustatic components. The sea level is examined on two different time scales, using long-term Holocene paleosealevel indicators, and short term (≤ 100 yrs) tide-gauge records. The major process affecting Holocene sea levels in this region is the continuing response to glacial unloading. The northward migration of the collapsed bulge peripheral to the retreating ice sheets is clearly delineated by the displacement of the hingeline between glacioisostatic subsidence and uplift from around 43° to 48°N, over the last 14,000 years. Similarly, the zone of maximal subsidence (collapsed forebulge) has moved from ~ 36°–42°N prior to 11,000 years to 44°–46°N during the last 5000 years. Tide-gauge data for the East Coast covering the last 100 years indicate a sea-level rise of around 2–4 mm/yr. Subtraction of the late Holocene trend reduces the regional mean from 2.72 ± 0.71 mm/yr to 1.26 ± 0.78 mm/yr, which is close to the value (1.47 ± 0.68 mm/yr) obtained by using viscoelastic model corrections (after Peltier, 1986). Thus, nearly half of the recent regional sea level rise appears to be of glacioisostatic origin. The corrected mean regional trend lies within a few tenths of a mm/yr of the estimated mean global eustatic trend (~1.1 mm/yr; Gornitz and Lebedeff, 1987). Generally, the results show no evidence for major tectonic movements, especially for large fault offsets. Nevertheless, several anomalous areas persist, that are suggestive of gentle warping, after glacioisostatic and eustatic processes have been taken into account. These correspond to areas with known Neogene epeirogenic movements, and include the region between Savannah, Georgia-Charleston, South Carolina (subsidence), Cape Fear Arch (uplift), southern Chesapeake Bay (Late Pleistocene-Holocene uplift, succeeded by recent subsidence), Montauk and the Long Island platform (uplift?). Subsidence in the Charleston area and southern Chesapeake Bay may be in part caused by groundwater withdrawal.

While Davis et al. provide convincing evidence for dynamic support of modern topography in NW Scotland, we take issue with their claims that the spatial distribution of Cenozoic denudation correlates poorly with the pattern of upper crustal shortening, and that the magnitude of shortening is insufficient to cause the observed denudation. We disagree with Davis et al.'s map of denudation, which forms the basis of their claims, and believe that their conclusions seriously downplay the widely documented contribution of crustal shortening to Cenozoic denudation of many areas of the British Isles.

[1] We investigate under what conditions the present-day long wavelength anomalous elevation (∼500 m) of the southern African Plateau can be attributed to Mesozoic plume events. The anomalous, long wavelength topography of the southern African Plateau cannot be easily explained by recent heating of the upper mantle, as opposed to other areas of the African Superswell, and geomorphological studies provide few hard constraints on the timing of the uplift. A Mesozoic origin for the plateau uplift is attractive in that southern Africa experienced several large magmatic events in the Mesozoic. We formulate numerical and scaling models to investigate if plume material ponded beneath cratonic lithosphere in the Mesozoic could produce 500 m of present-day elevation. We find that starting plume heads are ineffective at producing much long lasting uplift because the material spreads into a thin layer, tens of km thick. The ponded plume material also suppresses secondary convection by having a stable boundary at its base. Over time, heat continues to flow out of the top of the lithosphere, and a net imbalance of heat flow in the lithosphere develops, resulting in subsidence. Even after the plume material has cooled to the temperature of the mantle adiabat, secondary convection supplies less heat to the lithosphere than is lost upward by conduction. The cratonic lithosphere returns to its original thermal structure on a timescale of less than 200 m.y. Even two mantle starting plume heads, one at the time of Karoo volcanism (ca.183 Ma) and the other at the time of kimberlite eruption (ca. 80–90 Ma) in our models, cannot produce much (

The flooding of continental platforms is controlled as much by global eustatic sea level fluctuations as by epeirogenic, vertical motions. This basic, but underappreciated, geologic observation is consistent with the simplest model of mande convection. Eustatic fluctuations are driven by changes in the top thermal boundary layer of convection (the lithosphere), while epeirogenic motions are driven by convective upwellings and downwellings (subduction). Continental platforms were exposed during the Triassic before Pangea broke apart and then became flooded during the Cretaceous when the continents were dispersing. This longest term cycle in global sea level is predicted by models of mantle convection where non-subducting continental plates dynamically interact with the mantle. These dynamic models predict that apparent eustatic sea level changes can be driven by long wavelength dynamic topography.

Evidence in the geological record shows that continental interiors periodically undergo enigmatic episodes of large-scale subsidence. We propose that mantle flow associated with the descent of cold plumes and slabs, and their interaction with the endothermic phase change at 660 km depth, may provide a plausible mechanism for these epeirogenic events. Simulations of mantle convection that incorporate the thermodynamic effects of the phase change and both depth- and temperature-dependent viscosity are used to model the descent of plumes and slabs through the 660 km boundary. We find that the plume-slab flow scenarios are capable of supporting topographic deflections of amplitudes of ∼1 km and horizontal wavelengths of ∼1000 km that persist over time scales of 100–150 m.y.

Epeirogenic movements of regional extent have been manifest and recorded in several parts of India from Late Proterozoic to present times through the Tertiary and Recent. The main features of these movements, especially Recent vertical movements, in typical areas in the platform and coastal areas of peninsular India are described and the salient results of the study, qualitative and quantitative, of these zones are outlined. Quantitative measurements of Recent vertical movements have been made largely by geodetic methods and precision levelling in the plateau areas as also in the mobile, orogen zones of the Himalayan and sub-Himalayan tracts and by sea-level measurements through an extensive network of coastal automatic tide-gauge stations. The annual variations of sea level have been studied for several Indian ports. The land uplift or subsidence in relation to mean sea level over the Indian coast has also been studied. The application of geophysical techniques in the identification and delineation of regions of epeirogenic movements has been discussed and illustrated by the results in two type areas, viz., the coastal sedimentary belt of Madras and the vast Deccan Trap territory in western India. In the latter area, blanketed by extensive basaltic lavas over a vast region, the gravity data have brought out a number of major zones of subsidence and uplift which have been corroborated by the results of refraction seismic soundings. One of these major zones of subsidence is in the Koyna region which witnessed a major disastrous earthquake a few years ago. The results of deep seismic sounding along a traverse across the southern part of the Indian peninsula now in progress have also been briefly mentioned. Five important areas have been selected for quantitative measurements of current epeirogenic movements, namely the Shillong Plateau in northeast India, the Chhotanagpur Plateau and Singhbhum region in Bihar, the Aravalli region of Rajasthan, the Narmada Sone Rift in central India and the Deccan Trap territory including the Koyna earthquake zone.

Epeirogenic motions can be quantified if paleodatum planes can be recognized. These motions have been determined for the time interval mid-Cretaceous (Cenomanian) to recent in continental Africa using the vertical displacement of ancient shoreline sediments and other nearshore or low-elevation deposits that are inferred to represent a Cenomanian sea level datum plane. The Cretaceous Trans-Saharan seaway brought shoreline sediments deep into the African continental interior, and additional data suggest that most of the remaining terrestrial regions were also low-lying during the Cenomanian. The present elevations of the sea level sediments indicate that large portions of Africa have undergone epeirogenic uplift since the Cenomanian. The character of the motions in north Africa can be described as small-scale high-amplitude (3 km) doming separated by relatively flat-lying areas of deposition. The largest single epeirogenic feature is the uplift associated with Red Sea and East African Rift development. The timing of post-Cenomanian epeirogenic motions can be further constrained using paleontologic, K-Ar, faulting, paleodrainage and sedimentary data. The most likely causal mechanism for African epeirogeny may be hot spot activity reflective of the mantle convection regime underlying the African lithosphere.

A mechanism is proposed to explain epeirogenic motions of craton interiors in terms of the response of the lithosphere to subduction. The effects of changes in sea level are distinguished from subsidence of the basement by analyzing the tilt of chronostratigraphic sequences in which the bounding horizons were deposited at approximately the same elevation with respect to sea level. As an example, the Late Cretaceous subsidence and Tertiary uplift of the western interior of North America is examined, and a maximum tilt amplitude of 3 km, with a horizontal deflection scale of approximately 1400 km, is inferred. The link between platform sedimentation and subduction is tested by using numerical models of mantle convection which mimic the subduction and by examining the horizontal scale of the deflections to the overlying lithosphere. It is found that this scale is relatively insensitive to the temperature contrast between the slab and the surrounding mantle, the flexural rigidity of the lithosphere, and even the physical process assumed to govern the subduction. The most important factor affecting the scale is the dip of the subduction zone, and shallower subduction angles (less than 45°) can produce horizontal deflections of the order of 1000 km or more. In contrast, the vertical scale of the deflection is sensitive to all the above parameters. Using these results, two subduction models are introduced which predict both the time and length scales of the North American tilt, and it is conjectured that the process may be responsible for other regions of platform subsidence where subducted lithosphere may have passed beneath the continent at a shallow angle.

An integrated geological analysis of the Himalaya and Indo-Gangetic Plains demonstrates that the Great Vindhyan Basin incorporating large parts of these morphotectonic units were uplifted into an uneven landmass due to the Pre-Mesozoic orogenic cycle. This uneven landmass was eroded off largely during a considerable part of the Devonian and Carboniferous thereby causing partial absence of sedimentary sequences of these periods except in parts of the Tethys Himalaya. The Late Paleozoic epeirogenic movements brought about renewed sedimentation in the Lesser and Tethys Himalayas in the Krol and Tethys Basins, respectively, which was terminated by the Himalayan Orogeny during Late Cretaceous—Early Eocene.