Uplift Events Research Articles

Dynamics of the Earth's Surface in the Eastern Tibetan Plateau

River erosion increased rapidly following rock uplift events in the plateau approximately 11 million years ago.

Cretaceous–Cenozoic sedimentary budgets of the Southern Mozambique Basin: Implications for uplift history of the South African Plateau

In this study, data from 41 wells were used to quantify the evolution of the sedimentary budget in the Southern Mozambique passive margin basin, with a high temporal resolution for the Cenozoic period. We found that the drainage areas, which supplied sediments to the Southern Mozambique Basin, were eroded in two episodes. The first, of Mid–Late Cretaceous in age, is concordant with both thermochronological datation and sedimentary fluxes estimated by other studies in the Namibian and South African and Northern Mozambique margins. This erosion episode ended when the African surface, as defined by Burke and Gunnel (2008), had become flat and low-lying over most of the South African Plateau by ∼65Ma. Carbonate sediment deposition became more important in the shallow waters of the Mozambique basin after that time. The second erosion episode began at ∼23Ma and is likely due to an uplift event of the North-eastern part of the South African Plateau. It seems that the Limpopo catchment and the whole area sourcing the studied basin have inherited their present relief from two epeirogenic uplift pulses of Late Cretaceous and Miocene ages.

Beetles of Peru: Biogeography

Peru is the third largest country in South America, after Brazil and Argentina. Administratively, Peru is divided into 24 Regiones (formerly Departamentos) each with a regional government and capital. The two largest cities are Lima and Arequipa. Below is a broad outline of Peru’s geography, vegetation, and habitats. Peru’s 1.285 sq. km. lie entirely within the tropics from the equator to ,18uS latitude. This latitudinal position of Peru, along with changes in the strength of the coastal oceanic currents, fosters a zonation of climate from north to south. Peru’s topography is complex, due to the age and orogeny of the Andes Mountains (Antonelli et al., 2009; Hoorn et al., 2010) and the evolution of Amazonia (Hoorn and Wesselingh, 2010). The Peruvian Andes are relatively young mountains dating to the Cretaceous, with periodic uplifting events over the past 50 ma years (Hoorn et al. 2010) above the subduction zone where the Nazca plate slides beneath the South American plate. The Peruvian landscape has three broad geographic zones running longitudinally in a north to south axis—coastal desert (or Costa), central Andes (or Sierras), and eastern wet forest zone (or Selva) with the headwaters of the Amazon River and the Amazon basin. These broad zones roughly correspond to Peru’s climate regions. Brack (1986) recognized nine terrestrial ecoregions. Additionally, 83 of 104 life zones defined in the Holdridge system are

The sedimentary and tectonic evolution of the Amur River and North Sakhalin Basin: new evidence from seismic stratigraphy and Neogene–Recent sediment budgets

AbstractThe North Sakhalin Basin in the western Sea of Okhotsk has been the main site of sedimentation from the Amur River since the Early Miocene. In this article, we present regional seismic reflection data and a Neogene–Recent sediment budget to constrain the evolution of the basin and its sedimentary fill, and consider the implications for sediment flux from the Amur River, in particular testing models of continental‐scale Neogene drainage capture. The Amur‐derived basin‐fill history can be divided into five distinct stages: the first Amur‐derived sediments (>21–16.5 Ma) were deposited during a period of transtension along the Sakhalin‐Hokkaido Shear Zone, with moderately high sediment flux to the basin (71 Mt year−1). The second stage sequence (16.5–10.4 Ma) was deposited following the cessation of transtension, and was characterised by a significant reduction in sediment flux (24 Mt year−1) and widespread retrogradation of deltaic sediments. The third (10.4–5.3 Ma) and fourth (5.3–2.5 Ma) stages were characterised by progradation of deltaic sediments and an associated increase in sediment flux (48–60 Mt year−1) to the basin. Significant uplift associated with regional transpression started during this time in southeastern Sakhalin, but the north‐eastward propagating strain did not reach the NE shelf of Sakhalin until the Pleistocene (<2.5 Ma). This uplift event, still ongoing today, resulted in recycling of older deltaic sediments from the island of Sakhalin, and contributed to a substantially increased total sediment flux to the adjacent basinal areas (165 Mt year−1). Adjusted rates to discount these local erosional products (117 Mt year−1) imply an Amur catchment‐wide increase in denudation rates during the Late Pliocene–Pleistocene; however, this was likely a result of global climatic and eustatic effects, combined with tectonic processes within the Amur catchment and possibly a smaller drainage capture event by the Sungari tributary, rather than continental‐scale drainage capture involving the entire upper Amur catchment.

High-precision levelling, DInSAR and geomorphological effects in the Emilia 2012 epicentral area

In May 2012, two moderate earthquakes (Mw=6.1 and 5.9), associated with a noticeable aftershock sequence affected the eastern sector of the Po Plain, northern Italy. The co-seismic areal uplift events are crucial for a better understanding of the seismotectonics of the broader area and thus for a better assessment of the seismic hazard in the region. In the present study, we compared the results of analyses based on high precision levelling, the DInSAR technique, the distribution of liquefaction occurrences, the geomorphological map of the area and the structural model of the region. The DInSAR technique revealed a marked uplift of the ground (up to 17cm), which was confirmed by high precision levelling. The results of both techniques substantially agreed, although there were some considerable local discrepancies, due to well-documented and diffuse liquefaction phenomena. Some strategic precautions when planning high-precision levelling networks are suggested.

Geochemical Characteristics and Hydrocarbon Generation Processes of Cretaceous Source Rocks in the Songliao Basin

The Fulongquan Depression is a major production area for natural gas in the Songliao Basin. This study was based on geochemical analysis of source rocks. Our results indicate that the kerogen types are primarily type III. These rocks represent a source of gas in a highly mature stage. The basin was formed during two major events of tectonic subsidence and uplift between 144 and 95 Ma before present. These periods were followed by a stable sedimentary burial phase. In the Cretaceous fault period, processes of secondary hydrocarbon generation were present. Corresponding to the two major tectonic subsidence movements, there were two key hydrocarbon generation processes. Contingent on research on sedimentary facies, source rock thicknesses, and the distribution and intensity of hydrocarbon generation, the northern and southern parts of this depression represent favorable areas for the exploration and development of hydrocarbon extraction.

Post-Miocene landscape rejuvenation at the eastern end of the Alps

In the debate on the causes of uplift and landscape evolution of the Alps, most studies focus on regions that were glaciated at some stage during the last 2 m.y. In these areas, it is difficult to separate glacial-driven versus tectonically driven rates of erosion. Here, we present 10 Be-derived erosion rates from unglaciated catchments in the Koralpe range at the eastern end of the Alps. This region features strong geomorphologic evidence for landscape transience with young valleys incised into a smooth relict landscape. Erosion rates average 49 ± 8 mm/k.y. for catchments located on the relict landscape and 137 ± 15 mm/k.y. for catchments in the incised landscape. From these data, we estimate the onset of incision at 4 ± 1 Ma, the surface uplift at 350 ± 90 m, and a total relative base-level fall of 540 ± 140 m. Our results are in close agreement with both the magnitude and the age of onset of uplift of the Styrian Basin and the northern Molasse Basin, as well as the incision rate of the Mur River into the Styrian karst. The inferred timing of the onset of uplift around 4 Ma relates to interpreted basin inversion in the Pannonian Basin. Since this uplift event appears to have involved both the Pannonian Basin and the entire eastern end of the Alpine mountain range, we suggest that it may have occurred in response to a deep-seated process in the lithosphere. As such, we argue for tectonic drivers for the post-Miocene uplift in the eastern Alps.

Fission Track Thermochronology Evidence for the Cretaceous and Paleogene Tectonic Event of Nyainrong Microcontinent, Tibet

AbstractFission track dating was applied to analyze the 20 samples from Nyainrong microcontinent, and we obtained 20 apatite and 15 zircon fission track ages. The results show single population grain ages with a single mean age and associated central ages mainly ranging from 108±7Ma to 35±4Ma. Their mean track lengths are 12.2–13.9 μm with a single peak. Zircon fission track age range from 78±3 Ma to 117±4 Ma. The results represented the two tectonic uplift events in the study area, namely the Cretaceous and Paleogene periods. According to thermal history modeling results, uplifting rates of two tectonic events is 0.31–0.1 mm/a and 0.07–0.04 mm/a respectively. Combined with field condition and study results, it is suggested that the Cretaceous tectonic uplift event was related to the closure ocean basin caused by Qaingtang Lhasa collision, and the Paleogene tectonic uplift event was related to the south to thrust system caused by Indo‐Asian collision.

Marine vertebrates from the Santonian coastal carbonates ofnorthwestern Germany – a tool for the reconstruction of a Proto-North Sea Basin intertidal dinosaur-exchange bridge

AbstractA diverse vertebrate fauna, dominated by sharkteeth, is recorded from conglomerates within the limestonesof the Upper Cretaceous (Santonian) BurgsteinfurtFormation of northwestern Germany. The conglomeratebeds comprise carbonatic, glauconitic and phosphatenodules, as well as Triassic, Jurassic and Cretaceous extraclasts.The Burgsteinfurt Formation conglomerates containfining-upwards parasequences 2–20 cm in thickness,interpreted as tempestite layers within a unit formed bylarger-scale Milankovitch Cycles. The presence of the inoceramidSphenoceramus patootensis and belemnite Gonioteuthisgranulata indicate a late Santonian age for theunit. The studied vertebrate fauna from the Weiner Eschlocality consists of 20 selachian species (14 macroselachiansand 6 microselachians), a few teleosts, rare marinemosasaur remains, and one tooth from a theropod dinosaur.95% of the vertebrates in the assemblage are depositionallyautochthonous, with the remaining materialreworked from older underlying Cenomanian–Coniacian(lower Upper Cretaceous) limestones. On the basis of observedsedimentary structures, the scarcity of deep-seaselachians, and the dominance of the Mitsukurinidae(59% of the preserved shark fauna) in the fossil assemblage,the unit is interpreted as a shallow (0–3 metresdeep), subtidal, nearshore environment, or even subaerialcarbonate-sand islands, located on the southern marginof a submarine swell. The presence of a Santonian theropodin this deposit, and other dinosaur records in northernGermany, together support the interpretation of ashort-lived uplift event with strong upwelling influence forthe Northwestphalian-Lippe submarine swell north of theRhenish Massif in the southern Proto- North Sea Basin. Anew migration model for dinosaurs moving along carbonatecoasts or intertidal zones of shallow carbonate-sand islandsin Central Europe is presented, which may explainthe scattered distribution of dinosaur remains across Europein the Upper Cretaceous.

Thermal evolution and shale gas potential estimation of the Wealden and Posidonia Shale in NW‐Germany and the Netherlands: a 3D basin modelling study

AbstractSedimentary basins in NW‐Germany and the Netherlands represent potential targets for shale gas exploration in Europe due to the presence of Cretaceous (Wealden) and Jurassic (Posidonia) marlstones/shales as well as various Carboniferous black shales. In order to assess the regional shale gas prospectivity of this area, a 3D high‐resolution petroleum system model has been compiled and used to reconstruct the source‐rock maturation based on calibrated burial and thermal histories. Different basal heat flow scenarios and accordingly, different high‐resolution scenarios of erosional amount distribution were constructed, incorporating all major uplift events that affected the study area. The model delivers an independent 3D reappraisal of the tectonic and thermal history that controlled the differential geodynamic evolution and provides a high‐resolution image of the maturity distribution and evolution throughout the study area and the different basins. Pressure, temperature and TOC‐dependent gas storage capacity and gas contents of the Posidonia Shale and Wealden were calculated based on experimentally derived Langmuir sorption parameters and newly compiled source‐rock thickness maps indicating shale gas potential of the Lower Saxony Basin, southern Gifhorn Trough and West Netherlands Basin.

Patterns of diversification in small New World ground doves are consistent with major geologic events

South America has undergone many dramatic changes during the past 60 million years, which has had a major impact on the patterns of biological speciation and diversity in the region. Birds have been particularly affected, and major geologic events have been an important factor in generating avian diversity in the New World. Here we investigate the impact of two geologic events, Andean uplift and the Panamanian land bridge formation, on the speciation and diversification patterns of birds in the New World using a broadly dispersed clade, the small New World ground doves (Aves: Columbidae). Using complete species-level sampling for the clade (barring 2 possibly extinct species), we used sequences of 4 mitochondrial genes and 1 nuclear gene to infer a phylogenetic tree for the group. To address historical biogeographic questions, we estimated divergence times and reconstructed ancestral ranges. The phylogenetic analysis resulted in a well-supported tree. Divergence time estimates and historical biogeographic reconstruction indicated a South American origin for the clade, with several speciation events coinciding with either Andean uplift events or the land bridge formation. These results indicate how major geologic events affected the diversification of this group of birds, and lead to a broader understanding of the impact of these events on patterns of speciation in New World birds.

Neotectonics, flooding patterns and landscape evolution in southern Amazonia

Abstract. The paper examines the role of neotectonic activity in the evolution of the landscape in southern Amazonia during the Holocene. It uses both new and published data based on the analysis of remote sensing imagery and extensive field work in the Llanos de Moxos, Bolivian Amazon. The study of the region's modern and palaeorivers, ria lakes, palaeosols and topography provides a strong case in favour of the thesis that the northern part of the Llanos de Moxos constitutes the southern margin of the Fitzcarrald Arch and that it has experienced uplift during the Holocene. The paper assesses the extent and timing of the neotectonic activity in light of the new data and reconstructs the evolution of the landscape since the late Pleistocene. The evidence suggests that at least two uplift events took place: a first uplift in the late Pleistocene, which caused the formation of Lake Oceano, and a second uplift during the mid-Holocene, which formed Lake Rogaguado. These two uplifts appear to be linked to the knickpoints observed close to the towns of Guayaramerín and Puerto Siles respectively. The backwater effect due to these uplifts transformed the region's major rivers in seasonal ria lakes, causing the deposition of thick organic clay layers along the Beni, Mamoré and Madre de Dios river banks. I argue that neotectonic episodes could have dramatically changed the drainage of the Llanos de Moxos, determining its flooding regime, soil properties and forest–savannah ecotone. These results stress the need for geomorphologists, palaeo-ecologists and archaeologists to take into account neotectonics when reconstructing the region's past.

Iodine chemistry in the troposphere and its effect on ozone

Abstract. Despite the potential influence of iodine chemistry on the oxidizing capacity of the troposphere, reactive iodine distributions and their impact on tropospheric ozone remain almost unexplored aspects of the global atmosphere. Here we present a comprehensive global modelling experiment aimed at estimating lower and upper limits of the inorganic iodine burden and its impact on tropospheric ozone. Two sets of simulations without and with the photolysis of IxOy oxides (i.e. I2O2, I2O3 and I2O4) were conducted to define the range of inorganic iodine loading, partitioning and impact in the troposphere. Our results show that the most abundant daytime iodine species throughout the middle to upper troposphere is atomic iodine, with an annual average tropical abundance of (0.15–0.55) pptv. We propose the existence of a "tropical ring of atomic iodine" that peaks in the tropical upper troposphere (~11–14 km) at the equator and extends to the sub-tropics (30° N–30° S). Annual average daytime I / IO ratios larger than 3 are modelled within the tropics, reaching ratios up to ~20 during vigorous uplift events within strong convective regions. We calculate that the integrated contribution of catalytic iodine reactions to the total rate of tropospheric ozone loss (IOx Loss) is 2–5 times larger than the combined bromine and chlorine cycles. When IxOy photolysis is included, IOx Loss represents an upper limit of approximately 27, 14 and 27% of the tropical annual ozone loss for the marine boundary layer (MBL), free troposphere (FT) and upper troposphere (UT), respectively, while the lower limit throughout the tropical troposphere is ~9%. Our results indicate that iodine is the second strongest ozone-depleting family throughout the global marine UT and in the tropical MBL. We suggest that (i) iodine sources and its chemistry need to be included in global tropospheric chemistry models, (ii) experimental programs designed to quantify the iodine budget in the troposphere should include a strategy for the measurement of atomic I, and (iii) laboratory programs are needed to characterize the photochemistry of higher iodine oxides to determine their atmospheric fate since they can potentially dominate halogen-catalysed ozone destruction in the troposphere.

Slow and delayed deformation and uplift of the outermost subduction prism following ETS and seismogenic slip events beneath Nicoya Peninsula, Costa Rica

Two ODP CORK (Ocean Drilling Program circulation obviation retrofit kit) borehole hydrologic observatory sites deployed in 2002 at the toe of the subduction prism off Nicoya Peninsula, Costa Rica were visited in December 2013. The five years of seafloor and formation fluid pressure data collected since the previous visit include clear signals associated with an episodic tremor and slip (ETS) event off the coast of Nicoya Peninsula in 2009, and a Mw 7.6 subduction thrust earthquake beneath the Peninsula in 2012. Formation pressure anomalies associated with the ETS event are similar to ones observed following ETS events observed previously here, as well as ones following very low frequency earthquake swarms within the Nankai accretionary prism off southwestern Japan. Positive and negative impulsive transients in the hanging wall and foot wall of the subduction thrust, respectively, suggest contractional and dilatational strain generated by local slip propagating up the thrust fault beneath the outermost prism. In the case of the 2009 event, the transients occurred roughly two weeks after the initiation of slip observed at GPS sites along the adjacent coast. At the same time, a decrease in seafloor pressure at the prism site relative to the subducting plate was observed, indicating concurrent uplift of the prism of 1.2 cm. Other events at the prism toe following ETS events closer to the coast are seen in 2006, 2007, 2008, 2010, and 2011. The time between the initiation of ETS slip constrained by GPS and the onset of the prism toe transients suggest up-dip “rupture” propagation along the seaward part of the subduction thrust at rates of a few km/day. In the case of the 2009 event, the slip at the prism toe (c. 11 cm), estimated from the 1.2 cm uplift and the local dip on the decollement (6°), is roughly a factor of 5 greater than the slip further landward estimated from GPS data by Dixon et al. (in press). In other cases, slip at the toe is less or unresolvable. Similar uplift and formation fluid pressure transients occurred two days after the 2012 Nicoya thrust earthquake, then episodically (unrelated to aftershocks) every 1–3 weeks over the next few months. Slip rates at the prism toe, estimated from the magnitude and duration of these and ETS-related uplift events, are roughly 5 cm/day. Such rates are much too slow for tsunamigenesis or seismogenesis. Total slip of the outermost prism after the 2012 earthquake, determined from the uplift accumulated until the end of the observation period and the estimated local fault dip, is roughly 75 cm, a significant fraction of the seismogenic slip of the Mw 7.6 earthquake itself (a maximum of over 3 m). Negative steps in formation pressure are observed at both the prism and subducting plate sites simultaneous with the 2012 thrust earthquake. The sign of these steps is inconsistent with the contractional deformation predicted by an elastic fault-dislocation model with slip limited to the seismogenic zone. Highly compliant (low shear modulus) sediment below the decollement, or very low-stress deformation along splay faults, may be responsible for the co-seismic dilatation observed in the outermost prism and incoming plate.

The tectono-depositional evolution of the Syrian Euphrates Graben Area using the 3D seismic data

A detailed interpretation of seismic data in the Euphrates Graben Area (intra the northern margin of Arabian plate) has contributed to describe the tectono-depositional evolution. The stratigraphic sequences from the Paleozoic to recent time within the Euphrates Graben are composed of a number of discrete depositional cycles separated by nondeposition and/or erosional surfaces. This graben could be divided into several categories of structural units based on the degree of deformation and structural geometry. Intensive extensional tectonic activities have caused to create the NW–SE trending Euphrates Rift System in the Late Cretaceous and associated with volcanic intrusion which was distinguished by chaotic reflections on seismic profiles. Furthermore, it led to deposit of continental Derro Rocks. During this period, the Judea and Rutbah Formations exposed to erosion processes left behind unconformity surface at base of Upper Cretaceous is called BKU Unconformity. The Euphrates Graben Area had also exposed uplift events in Palaeozoic time in which volcanic intrusions played an essential role in uplift of some of the Euphrates Area parts as indicated restoration model.

Karst landscape evolution in the littoral area of the Bay of Biscay (north Iberian Peninsula)

The western Pyrenean area contains extensive karst areas, however, their genesis and development are still mostly unknown. In this work, we make a general description of the karst landscape in different karst areas: 1) Rasa type; 2) Cone-type karst; and 3) Alpine-type karst. The first two types are present in the littoral area, where geomorphological evolution mostly depends on sea level and climatic changes. We focused our study in two karst areas of the littoral cone-type karst. We correlate different caves created from different stable water table levels. Three representative caves are studied in detail, studying their stratigraphic record based on allostratigraphy. Finally we dated the different phases of speleothem formation in the three caves. Using all this information, we defined four stable paleowater table levels, at 50, 150, 220 and 350 m asl, controlled by sea level changes and isostatic uplift events. The lowest level is the youngest, with an age of c. 1 Ma. We discovered that the interior of the three caves display very similar endokarst allostratigraphic sequences, characterized firstly by an erosion phase, a fluvio-karst input, flowstone speleothem formation and finally dripping speleothem formation. The chronological data shows a correlation between these phases and Pleistocene climatic phases; the erosion phase is related to the falling sea level, fluviokarst detrital input is related to cold (glacial) stages and the formation of speleothems is related to the warmest (interglacial) moments and high sea level periods.

Magmatic development of the outer Vøring margin from seismic data

AbstractThe Vøring Plateau off mid‐Norway is a volcanic passive margin, located north of the East Jan Mayen Fracture Zone (EJMFZ). Large volumes of magmatic rocks were emplaced during Early Eocene margin formation. In 2003, an ocean bottom seismometer survey was acquired over the margin. One profile crosses from the Vøring Plateau to the Vøring Spur, a bathymetric high north of the EJMFZ. The P wave data were ray traced into a 2‐D crustal velocity model. The velocity structure of the Vøring Spur indicates up to 15 km igneous crustal thickness. Magmatic processes can be estimated by comparing seismic velocity (VP) with igneous thickness (H). This and two other profiles show a positive H‐VP correlation at the Vøring Plateau, consistent with elevated mantle temperature at breakup. However, during the first 2 Ma magma production was augmented by a secondary process, possibly small‐scale convection. From ∼51.5 Ma excess melting may be caused by elevated mantle temperature alone. Seismic stratigraphy around the Vøring Spur shows that it was created by at least two uplift events, with the main episode close to the Miocene/Pliocene boundary. Low H‐VP correlation of the spur is consistent with renewed igneous growth by constant, moderate‐degree mantle melting, not related to the breakup magmatism. The admittance function between bathymetry and free‐air gravity shows that the high is near local isostatic equilibrium, precluding that compressional flexure at the EJMFZ uplifted the high. We find a proposed Eocene triple junction model for the margin to be inconsistent with observations.

Post-rift geodynamics of the Songliao Basin, NE China: Origin and significance of T11 (Coniacian) unconformity

The T11 unconformity lies between the Qingshankou and Yaojia Formations in the post-rifting sequence of the Cretaceous Songliao Basin, NE China. It is intimately associated with petroleum reservoirs and considered to be a disconformity forming in the tectonic quiet stage. We present the interpretations from new seismic surveys and cored sections of the Cretaceous Continental Scientific Drilling borehole (CCSD-SK-1) in order to resolve the nature and origin of T11 unconformity. The T11 is often a low-angle unconformity with underlying Qingshankou Formation having been deformed and eroded prior to deposition of the Yaojia Formation. In the post-rift evolution of the basin it marks an abrupt change from a deep lake to shallow lake or subaerial environment, documented by reddening of the lacustrine mudstone, extinction of the ostracod assemblages and a great increase of coarse detrital inputs. The sharp change of depositional environment, the truncation of gentle folds and the cluster of volcanic and paleoearthquake activities, all happened simultaneously, immediately before the development of T11 unconformity, indicating a significant regional compressional uplift event in the basin. The timing of the T11 unconformity formation is within the interval 88–86.2Ma. Correlations with coeval unconformities in other Cretaceous sedimentary basins in eastern Asia indicate that this compressional uplift coincided with an episode of global plate reorganization between the Eurasian and Paleo-Pacific plates that culminated at 88–87Ma. During this short interval the northeast Asian margin, in eastern China, South Korea, Japan and Russian Far East experienced widespread violent volcanic and granite emplacement activity triggered by compression resulting from rapid and orthogonal slab subduction. The post-rift basin tectonic inversion occurred during T11 (Coniacian) time; thereafter the basin again evolved in an extension regime. Two subsidence phases in post-rift history took place as the direct consequence of Coniacian compression peak, which defined the distribution of oil sources and reservoirs.

Rapid South Atlantic spreading changes and coeval vertical motion in surrounding continents: Evidence for temporal changes of pressure-driven upper mantle flow

The South Atlantic region displays (1) a topographic gradient across the basin, with Africa elevated relative to South America, (2) a bimodal spreading history with fast spreading rates in Late Cretaceous and Eo-Oligocene, and (3) episodic regional uplift events in the adjacent continents concentrated in Late Cretaceous and Oligocene. Here we show that these observations can be linked by dynamic processes within Earth's mantle, through temporal changes in asthenosphere flow beneath the region. The topographic gradient implies westward, pressure-driven mantle flow beneath the basin, while the rapid spreading rate changes, on order 10 million years, require significant decoupling of regional plate motion from the large-scale mantle buoyancy distribution through a mechanically weak asthenosphere. Andean topographic growth in late Miocene can explain the most recent South Atlantic spreading velocity reduction, arising from increased plate boundary forcing associated with the newly elevated topography. But this mechanism is unlikely to explain the Late Cretaceous/Tertiary spreading variations, as changes in Andean paleoelevation at the time are small. We propose an unsteady pressure-driven flow component in the asthenosphere beneath the South Atlantic region to explain the Late Cretaceous/Tertiary spreading rate variations. Temporal changes in mantle flow due to temporal changes in regional mantle pressure gradients imply a correlation of horizontal and vertical motions: we find that this prediction from our models agrees with geologic and geophysical observations of the South Atlantic region, including episodes of passive margin uplift, regional basin reactivation, and magmatic activity.

Transient fluvial incision as an indicator of active faulting and Plio-Quaternary uplift of the Moroccan High Atlas

One of the challenges facing Earth Scientists is to determine the extent to which geomorphic features can be used to extract tectonic signals from landscapes. Here, we quantitatively analyse the long profiles of rivers that drain southwards across the South Atlas Fault (SAF), a thrust fault that forms the southern margin of the High Atlas Mountains in Morocco, to derive new data on the Late Cenozoic activity of this fault system. River long profiles were extracted for 32 major rivers flowing southwards into the Ouarzazate Basin. Of these, eleven exhibit concave-up river profiles with a mean concavity of 0.64 and normalized steepness indices in the range 47.5–219.0m0.9. By contrast, 21 rivers exhibit at least one knickpoint upstream of the thrust front. Knickpoint height varies from 100 to 1300m, with calculated incision at the range bounding fault ranging from 80 to 900m, despite the drainage areas upstream of the knickpoint ranging over several orders of magnitude. In map view, knickpoint locations generally plot along sub-parallel lines and there are no obvious relationships with lithological units for knickpoints exhibiting slope-break morphology. Channel reaches below slope-break knickpoints have higher mean concavities (0.76) than above the knickpoint indicative. This observation combined with a lithological or river-capture origin for the knickpoints having been ruled out suggests that an increase in uplift rate along a planar fault zone during the Plio-Quaternary caused the initiation of the transient response (i.e., knickpoint formation) to a change in base-level observed in the river profiles. This uplift event can be correlated to the convective removal of the lithospheric root to the Atlas Mountains resulting in the anomalously high topography at the present day.