Tectonic Forcing Research Articles

Tectonics and drainage development in central Amazonia: The Juruá River

Understanding the factors that controlled the development of large rivers lacks information from modern and ancient analogues. The Amazonian basin contains several of the largest rivers on Earth, with many having tectonic control. The study of these rivers can contribute to test the claim that large rivers have a tectonic forcing. Addressing the evolution of the Juruá River is relevant, since this is the longest Amazonian river that parallels the Solimões Megashear Zone, a major NE-striking structure with a long history of reactivation of faults and folds even in the Cenozoic. This work discusses the geological evolution of the Juruá River along the Pleistocene-Holocene based on digital elevation models, integrated with subsurface data (well log and seismic reflection). The goal was to characterize some ancient large river valleys in forested areas of Amazonia and to analyze whether they might be related to previous paths of the Juruá River. A physical connection was found between this river and three elongated belts (i.e., PV1, PV2, and PV3) with low topographic and dissection values and surfaces marked by sinuous to meandering strings or curved lines. These characteristics led to relate the belts to ancient Juruá River valleys, an interpretation also suggested by the correspondence between paleovalley morphologies and subsurface Pleistocene-Holocene deposits with concave-up erosional bases. A tectonic hypothesis could explain the development of these paleovalleys around drainage basins with an annular pattern associated with a large convex-up relief, which we relate to rock upwarping by folding. Reconstructing the geological evolution of the Juruá River can introduce new data in discussions focused on the origin of large tropical rivers and on the neotectonic history of the South American intraplate.

Scale‐Dependent Contributors to River Profile Geometry

AbstractA range of complex hydraulic and geomorphic processes shape terrestrial landscapes. It remains unclear how these processes act to generate observed drainage networks across scales of interest. To address this issue, we transform observed and synthetic longitudinal river profiles into the spectral domain with a view to interrogating the different scales at which fluvial landscapes are generated. North American river profiles are characterized by red noise (i.e., spectral power, ϕ ∝ k−2, where k is wave number) at wavelengths >100 km and pink noise (ϕ ∝ k−1) at shorter wavelengths. This observation suggests that river profile geometries are scale‐dependent and using small‐scale observations to develop a general understanding of large‐scale landscape evolution is not straightforward. At wavelengths >100 km, river profile geometries appear to be controlled by smoothly varying patterns of regional uplift and slope‐dependent incision. Landscape simulations, based upon stream power that are externally forced by regional uplift do not exhibit a spectral transition from red to pink noise because these simulations do not incorporate heterogeneous erodibility. Spectral analysis of erodibility extracted from patterns of lithologic variation along river profiles suggests that the missing spectral transition is accounted for by heterogeneous substrates, which are characterized by white or blue noise (ϕ ∝ k0 or k1). Our results have implications for the way by which rivers record large‐scale tectonic forcing while incising through complex lithologic patterns.

Morphometric properties of river basins as indicators of relative tectonic activity – Problems of data handling and interpretation

Morphometric properties of drainage basins, expressed as indices related to their shapes, altitude variability, river networks and stream profiles, are frequently used as proxy information concerning the relative intensity of uplift. Research procedures lead towards division of an area into classes of relative tectonic activity (various rates of surface uplift) and are typically based on compound indices that jointly consider various individual parameters. Given that index approaches are quantitative in nature and comprise large sets of data, their statistical treatment should become an inherent component of the workflow, whereby the results of the statistical analyses should guide the conclusions. However, various data handling issues seem to be seldom addressed or are given inadequate attention. They include selection of variables, correlation analysis, principles of classification in terms of relative tectonic activity, validity of classifications, and criteria for using specific statistical procedures. In this paper we demonstrate the need for rigorous statistical data analysis in a morphometric study, focused on an intraplate mountainous terrain in Central Europe (Orlickie-Bystrzyckie Mountains Block), subject to low or moderate uplift. We analysed 56 drainage basins within the footwall blocks of several prominent fault-generated escarpments. Following literature guidance, the hypsometric and shape characteristics of the drainage basins were considered, whereas clustering and pure-rank based approaches were tested to distinguish classes of relative tectonic activity. The results were compared with indicators of tectonic activity calculated for the escarpments themselves and using DEM-derived terrain attributes indicating enhanced erosion. In addition, we used statistical tests to identify possible lithological influence on the variability of morphometric parameters, which in this study was found to be of secondary importance. Statistical considerations neither allowed for unequivocal classification of drainage basins in terms of relative tectonic activity, nor did they reveal a clear spatial distribution pattern of drainage basins with different morphometric characteristics, typically considered to reflect tectonic forcing. Thus, statistics-based analysis is recommended to avoid the risk of over-interpretation. It is also possible that the likely morphometric signature of tectonically less active settings comprises spatially inconsistent information rather than it is typified by consistently low values of various morphometric parameters.

Quaternary landscape evolution of patagonia at the Chilean Triple Junction: Climate and tectonic forcings

Glacial and fluvial landforms record the recent history of the Earth surface and have the potential to provide information about uplift and climate changes during Quaternary times. Patagonia hosts uniquely well-preserved moraine deposits, along with outwash and fluvial terraces. This offers the possibility of determining the timing of glacier advances since the Great Patagonian Glaciation (ca. 1.2 Ma) and allows us to investigate landscape response to climate and tectonic forcing.In this study, we present twenty-eight new in situ 10Be exposure ages for glacial deposits, outwash sediments, and fluvial terraces at the latitude of the Chile Triple Junction (∼46°30′S). We combine this database with a detailed mapping and a morphological analysis of the Deseado River terrace system. The glacial and outwash deposits document at least five major glacial advances in the Lago Buenos Aires valley before the deposition of the Moreno system during Marine Isotope Stage (MIS) 8. Key advances occurred during MIS 12 and MIS 16. Further ice expansions that resulted in Telken V and VI/VII outwash surfaces date to 780 ka and ca. 1.2 Ma respectively. Overall, our data show the difficulty of dating pre-LGM glacial deposits using surface exposure methods and reinforce the idea that outwash surfaces are better targets to determine the age of glacial sequences in the region.The Deseado River terrace system yields stratigraphically consistent ages that range from 1167 to 447 ka, which indicate that these terraces formed during Pleistocene times. Our analysis suggests that terraces T3, T7 and T8 may have been formed during cold stages, close to the glacial-interglacial transitions. We also calculated incision rates that reveal a strong initial pulse, from ca. 1200 to 900 ka, which was followed by significantly weaker river incision pulses.Finally, our geomorphological analysis confirms that the oldest fluvial terraces of the Deseado River system exhibit a NE-SW tilting through a broad area, next to the Atlantic Ocean. This was previously interpreted as the surface response to a long-wavelength dynamic uplift, a phenomenon that should be reassigned to the early Pleistocene.

Deformation–sedimentation feedback and the development of anomalously thick aggradational turbidite lobes: Outcrop and subsurface examples from the Hikurangi Margin, New Zealand

ABSTRACT Concepts of the interaction between autogenic (e.g., flow process) and allogenic (e.g., tectonics) controls on sedimentation have advanced to a state that allows the controlling forces to be distinguished. Here we examine outcropping and subsurface Neogene deep-marine clastic systems that traversed the Hikurangi subduction margin via thrust-bounded trench-slope basins, providing an opportunity to examine the interplay of structural deformation and deep-marine sedimentation. Sedimentary logging and mapping of Miocene outcrops from the exhumed portion of the subduction wedge record heavily amalgamated, sand-rich lobe complexes, up to 200 m thick, which accumulated behind NE–SW-oriented growth structures. There was no significant deposition from low-density parts of the gravity flows in the basin center, although lateral fringes demonstrate fining and thinning indicative of deposits from low-density flows. Seismic data from the offshore portion of the margin show analogous lobate reflector geometries. These deposits accumulate into complexes up to 5 km wide, 8 km long, and 300 m thick, comparable in scale with the outcropping lobes on this margin. Mapping reveals lobe complexes that are vertically stacked behind thrusts. These results illustrate repeated trapping of the sandier parts of turbidity currents to form aggradational lobe complexes, with the finer-grained suspended load bypassing to areas downstream. However, the repeated development of lobes characterized by partial bypass implies that a feedback mechanism operates to perpetuate a partial confinement condition, via rejuvenation of accommodation. The mechanism proposed is a coupling of sediment loading and deformation rate, such that load-driven subsidence focuses stress on basin-bounding faults and perpetuates generation of accommodation in the basin, hence modulating tectonic forcing. Recognition of such a mechanism has implications for understanding the tectono-stratigraphic evolution of deep-marine fold and thrust belts and the distribution of resources within them.

New models for submarine channel deposits on structurally complex slopes: Examples from the Niger delta system

Submarine channel complexes are often described as having a two-phase stratigraphic evolution where an initial phase of migration is followed by aggradation, generating a ‘hockey-stick shaped’ channel trajectory. However, the role of tectonic forcing in modifying time-integrated sedimentary architectures remains poorly understood. Here, we evaluate how tectonically driven changes in slope modify the evolution—both in terms of morphology and stratigraphic architecture—of submarine channels across a range of spatial scales from the fundamental architectural unit, a channel element, to the scale of a channel complex set, using examples from the Niger Delta system. From a 3D, time-migrated seismic reflection volume, we use amplitude extractions, frequency decomposition and RGB blending to determine channel stratigraphic architectures. These observations are used systematically to evaluate the development of cross-sectional and planform architectures as the channel systems interact with a range of active and pre-existing structural bathymetry. Our results indicate that while a channel complex's stratigraphic architecture may be captured by a two-phase evolution on unstructured slopes, this model fails on structurally complex slopes. Unstructured slope channel complexes display a repeated arrangement of migration dominating the early stratigraphic record and subsequent aggradation. The late aggradational phase signals a decrease in the rate of growth in channel complex width and the rate of change in sinuosity relative to aggradation throughout the complex's development. However, tectonically driven changes in sinuosity and the relative rates of channel migration and aggradation modify complex development significantly. We identify three end-member styles of channel-structure interaction, determined by the timing of bathymetry development and its associated style: (1) pre-channel structural bathymetry; (2) coeval positive relief, and (3) coeval negative relief. Where structural relief pre-dates channel inception, a principal adjustment is in the initial channel course with early channel elements being forced around positive relief of the structure, generating long-wavelength bends in the complex's course. Where structure continues to modify slope creating positive and negative bathymetry during complex development, migration and bend development continue with complex width and channel element sinuosity increasing until abandonment. These observations demonstrate that submarine channel architecture and planform are highly sensitive to tectonic perturbation and we use these results to generate graphical models that show predicted architectural evolution of submarine channels on structurally complex slopes in general.

Drainage basin dynamics during the transition from early to mature orogeny in Southern Taiwan

The southern Central Range of Taiwan is in an early stage of orogeny and the landscape has not yet reached a steady state. To reveal the nature of the transient landscape and its evolution towards a steady state during orogeny, we conducted an in-situ 10Be cosmogenic nuclide study together with geomorphic analyses to characterize the spatial pattern of erosion rate at the scale of individual catchments. Sediment samples were collected at outlets of major basins, and within nested sub-basins. Basin-wide erosion rates were estimated from 10Be concentrations and basin mean 10Be production rates. The erosion rates of major basins show a northward increasing trend, which is consistent with the pattern of mean basin channel steepness, reflecting the early stage of orogeny and indicating that the landscape is evolving in response to tectonic forcing. However, nested samples reveal significant spatial variability in erosion rate at the sub-basin scale. These spatial variations are consistent with predictions of divide motion from χ analysis and other geomorphic metrics including cross-divide asymmetry. These suggest that the main divide is moving towards the west in southernmost Taiwan. We also found evidence of internal basin reorganization with several cases of growing basins at the expense of neighboring basins. These findings imply that even though tectonic forcing dominates the large-scale patterns, basin reorganization is a significant process affecting spatial patterns of erosion rate at the smaller scale, so that topographic steady state is likely to be found only for the largest characteristics of the landscape.

Climatic and Tectonic Control on the Bengal Fan Sedimentation Since the Pliocene

AbstractStrontium and Neodymium isotopic analysis of the lithogenic fractions of the hole U1445A (International Ocean Discovery Program‐353) collected from the deep‐water end of the Mahanadi basin (western Bay of Bengal) was carried out to evaluate the sediment sources as well as to understand the link between the temporal variations in the Sr‐Nd isotope ratios and climatic and tectonic forcings during the last 6 Ma. The Sr‐Nd isotopic compositions along with Fe/Al ratios and clay mineralogy show tell‐tale signature of Ganga‐Brahmaputra sedimentation (Bengal fan) in the study area. The significant temporal fluctuations observed in the Sr‐Nd isotopic compositions suggest variation in the relative sediment contribution by the Ganga and Brahmaputra river systems, which in turn are controlled by monsoon intensity variations coupled with orographic effect, glaciation, and multiple tectonic activities. The results show the marked influence of glacial‐interglacials on the relative sediment contribution by Ganga and Brahmaputra rivers during 0–1.8 Ma, while the sedimentation during the 1.8–6 Ma time window was likely influenced by both climatic and tectonic forcings such as uplift of the Shillong plateau, eastern syntaxis development of Indo‐Burma wedge, reorganization of Brahmaputra river system. The present study is the first high resolution (122 samples within 6 Ma) Sr‐Nd isotope ratio analysis from the Bengal Fan. The study has brought to light multiple isotope fluctuations linked to climatic and tectonic forcings. The work also establishes dominant control of Ganga‐Brahmaputra sedimentation along the deep waters of the Indian east coast.

Late Cretaceous aeolian desert system within the Mesozoic fold belt of South China: Palaeoclimatic changes and tectonic forcing of East Asian erg development and preservation

This study recognises and identifies the Late Cretaceous aeolian desert system from the Jianshi Basin, located in the intra-continental orogen within the Yangtze Block, South China. Erg deposits comprise aeolian dunes and dry aeolian sandsheets with alluvial facies associations at the margin and show an alluvial-aeolian depositional system. Palaeowind reconstruction of aeolian dune foresets showed that the dominant prevailing winds were westerlies, followed by northeasterlies and subordinate northwesterlies and southeasterlies. It is possible that monsoon rains recharged the water inflow system and caused the development of fluvial sand bodies at the margin of the Jianshi desert during the early deposition stage. The alluvial deposits in the study area were related to regional tectonism, while the dry aeolian system was dominated by mid- and low-latitudinal subtropical highs and the monsoonal climate. Orogenic topography, combined with planetary-scale subtropical high-pressure systems, blocked the transport of moisture, enclosed the low-lying land, and led to the aridification and development of desert depositional systems in the East Asian interior. Moreover, fault-controlled subsidence provided accommodation space in desert basins for alluvial and aeolian deposits. Based on the results obtained from palaeowind reconstructions, the divergent axis of subtropical highs during the Late Cretaceous was located in mid- and low-latitude areas of the Jianshi, Jianghan, Xinjiang, and Hengyang basins in South China. The relatively scattered nature of palaeowinds in the Jianshi Basin and adjacent deserts may indicate a seasonal drift in the divergent axis under the influence of a monsoonal climate.

Fault kinematics: A record of tectono-climatically controlled sedimentation along passive margins, an example from the U.S. Gulf of Mexico

Abstract Faults offsetting sedimentary strata can record changes in sedimentation driven by tectonic and climatic forcing. Fault kinematic analysis is effective at evaluating changes in sediment volumes at salt/shale-bearing passive margins where sediment loading drives faulting. We explore these processes along the northern Gulf of Mexico. Incremental throw along 146 buried faults studied across onshore Louisiana revealed continual Cenozoic fault reactivation punctuated by inactive periods along a few faults. Fault scarp heights measured from light detection and ranging (LiDAR) data are interpreted to show that Cenozoic fault reactivation continued through the Pleistocene. The areas of highest fault throw and maximum sediment deposition shifted from southwest Louisiana in the early Miocene to southeast Louisiana in the middle–late Miocene. These changes in the locus of maximum fault reactivation and sediment deposition were controlled by changing tectonics and climate in the source areas. Early Miocene fault throw estimates indicate a depocenter farther east than previously mapped and support the idea that early Miocene Appalachian Mountain uplift and erosion routed sediment to southeast Louisiana. By correlating changes in fault throw with changes in sediment deposition, we suggest that (1) fault kinematic analysis can be used to evaluate missing sediment volumes because fault offsets can be preserved despite partial erosion, (2) fault throw estimates can be used to infer changes in past tectonic and climate-related processes driving sedimentation, and (3) these observations are applicable to other passive margins with mobile substrates and faulted strata within overfilled sedimentary basins.

Geometry of glaciofluvial deposits and dynamics of the Lyonnais lobe ice front during the last glacial period (France, Northern Alps)

Previous studies in the foreland of the French Western Alps, based on the analysis of geomorphological criteria for the internal moraine complex, show several stages of retreat or stagnation of the Lyonnais ice lobe during marine isotopic stages 4 and 2. Based on chronological data of the literature, the age of the Würmian maximum extension of the Lyon ice lobe must have occurred during MIS 4 but this result is still debated. At the Last Glacial Maximum, in the western part of the Lyonnais ice lobe, glaciofluvial corridors were active during flash floods draining glacial meltwater. Today, these corridors are dead valleys and display a series of terraces. In this paper, we analyse the sedimentary geometries and dynamics of three glaciofluvial corridors (Moidieu, Septeme and Heyrieux) located at the front of the internal moraine complex of the Lyonnais ice lobe. Upstream, the Moidieu corridor splits into three branches called North Moidieu, Central Moidieu and South Moidieu. Glaciofluvial deposits in the corridors are composed of pebbles and gravels in a sandy matrix. Sedimentary structures show mass flow events and the migration of river bars in braided channels which are characteristic of proximal glaciofluvial rivers in a proglacial environment. According to a new geomorphological map built using a high-resolution digital elevation model and an isopach map of the Quaternary deposits created from a compilation of the borehole data, we suggest that these corridors correspond to “tunnel valleys” built during the most extensive Riss glaciation. Then during the Würm maximum glacial extension, these “tunnel valleys” show complex infilling by glacio-fluvial sediments during the Würmian maximal extent. In the three corridors, the number of river terraces can be better defined by using new geomorphological analyses. A total of three Würm terraces can be observed: two in the north and three in the south. This difference between the south and north is probably a result of climatic and tectonic forcing.

Improved Modelling of Soil Loss in El Badalah Basin: Comparing the Performance of the Universal Soil Loss Equation, Revised Universal Soil Loss Equation and Modified Universal Soil Loss Equation Models by Using the Magnetic and Gravimetric Prospection Outcomes

Water erosion is a natural fact in the cycle of shaping the earth’s landforms and the most evident form of land degradation on a planetary scale (Roose & De Noni, 2004; Dautrebande & Sohier, 2006; Toumi et al., 2013; Azaiez, 2020a). Its effects have largely affected the rural landscape. Although it is the result of an ancient and primeval climatic and tectonic forcing, man’s footprint in its intensification remains a reality. A real awareness of this problem on the part of scientists is reflected in the many studies on understanding the risks. Experiments have been carried out, equations and models have been developed with the aim of preserving the soil. The watershed of wadi El Badalah, the subject of this study, is not excluded from this risk. The present research is a new comparative contribution to the quantification of soil loss based on four empirical models (Universal Soil Loss Equation USLE, Revised Universal Soil Loss Equation RUSLE, Modified Universal Soil Loss Equation MUSLE and the adjusted model). The main objective of this research project is to test several empirical models of quantification of soil loss, extensively tested on a global scale, to discuss the potential of each model in order to choose the most appropriate for the El Badalah basin. The method is based on geotechnical and geophysical investigations. It consists of determining the anomalies of the subsoil based on the difference in density and the resistivity of the heterogeneous constituents of the subsoil. This is in order to look for sectors potentially favorable to infiltration at the expense of runoff.

Control of inherited accreted lithospheric heterogeneity on the architecture and the low, long-term subsidence rate of intracratonic basins

Intracratonic basins tend to subside much longer than the timescale predicted by thermal relaxation of the lithosphere. Many hypotheses have been suggested to explain their longevity, yet few have been tested using quantitative thermo-mechanical numerical models, which capture the dynamic of the lithosphere. Lithospheric-scale geodynamic modelling preserving the tectono-stratigraphic architecture of these basins is challenging because they display only few kilometres of subsidence over 1000 of km during time periods exceeding 250 Myr. Here we present simulations that are designed to examine the relative role of thermal anomaly, tectonics and heterogeneity of the lithosphere on the dynamics of intracratonic basins. Our results demonstrate that initial heterogeneity of accretionary continental lithosphere explains long-term subsidence and the arches-basins architecture of Saharan type intracratonic basins at first order. The simulations show that initially heterogeneous lithospheres inherited from accretion are strong enough to resist local isostatic re-equilibration for very long period of time. Indeed, the lateral density variations store potential gravitational energy that is then slowly dissipated by differential erosion and slow vertical movements. For relatively well-accepted coefficient of erosion of 10−6 m2/s, the subsidence last longer than 250 Myr. Extensional tectonic forcing and thermal anomalies both result in an effective strength drop of the lithosphere, which allows a temporal acceleration of local isostatic re-equilibration. Periodic changes in far field tectonic forcing from extension to compression complicate the tectono-stratigraphic architecture (intra-basin arches, sub-basins) introducing stratigraphic unconformities between different neighbouring basins such as the ones observed in North Africa.

Seismic characterization of carbonate platforms and reservoirs: an introduction and review

Abstract Improved seismic data quality in the last 10–15 years, innovative use of seismic attribute combinations, extraction of geomorphological data and new quantitative techniques have significantly enhanced understanding of ancient carbonate platforms and processes. 3D data have become a fundamental toolkit for mapping carbonate depositional and diagenetic facies, and associated flow units and barriers, giving a unique perspective on how their relationships changed through time in response to tectonic, oceanographic and climatic forcing. Sophisticated predictions of lithology and porosity are being made from seismic data in reservoirs with good borehole log and core calibration for detailed integration with structural, palaeoenvironmental and sequence stratigraphic interpretations. Geologists can now characterize entire carbonate platform systems and their large-scale evolution in time and space, including systems with few outcrop analogues such as the Lower Cretaceous Central Atlantic ‘pre-salt’ carbonates. The papers introduced in this review illustrate opportunities, workflows and potential pitfalls of modern carbonate seismic interpretation. They demonstrate advances in knowledge of carbonate systems achieved when geologists and geophysicists collaborate and innovate to maximize the value of seismic data from acquisition, through processing to interpretation. Future trends and developments, including machine learning and the significance of the energy transition, are briefly discussed.

Channel Profile Response to Abrupt Increases in Mountain Uplift Rates: Implications for Late Miocene to Pliocene Acceleration of Intracontinental Extension in the Northern Qinling Range-Weihe Graben, Central China

Abstract Cenozoic extension of the Qinling range-Weihe Graben system has occurred in response to the uplift and growth of the Tibetan Plateau. Rapid exhumation of the northern Qinling range since the late Miocene is also regarded as resulting from the eastward expansion of the northeast part of Tibet. Tectonic evidence of this in the landscape remains unclear, but the fluvial system can provide a sensitive proxy record of tectonic forcing through space and over time scales of 105–107 a. Here, we present a study of channel profiles in the northern Qinling range, which forms a footwall highland separated from the southern Weihe Graben by active normal faults. We identify a population of knickpoints that separate river profiles with a gentle upstream gradient from steeper downstream reaches. Above the knickpoints, steepness indices increase from the central part towards the west and east, whereas channel steepness shows its highest values in the Huaxian-Huayin section. We observed no systematic changes of channel steepness pattern as a function of rock resistance, drainage area, or channel concavity. Correlation analysis between channel steepness and basin elevation and relief documents the control of tectonic forcing on regional topography. While bearing no relation to geological outcrop boundaries, the knickpoints show a strong correlation between retreat distance, catchment area, and river length. We infer that the knickpoints formed in response to an increase in mountain uplift rates and retreated as a kinematic wave. Under linear slope exponent n, we calibrated channel erodibility K~1.00±0.44×10−6 m0.1/a and derived knickpoint ages of 5.59±1.80 Ma. Combining the ages of onset of active faulting and mountain growth in the NE Tibetan Plateau (8–10 Ma, e.g., Liupan Shan, Jishi Shan, and eastern segments of the Haiyuan and Kunlun faults) and in the southwest Qinling range (9–4 Ma), we conclude that growth of the NE Tibetan Plateau began in the mid-Miocene time and expanded eastwards to the Qinling range-Weihe Graben during the late Miocene and early Pliocene.

Reconstructing the incision of the Lancang River (Upper Mekong) in southeastern Tibet below its prominent knickzone using fluvial terraces and transient tributary profiles

The Lancang River (Upper Mekong) is a key large river in Asia with a prominent knickzone over 500 km distance (27.5‐30.7°N), as it descends the southeastern margin of the Tibetan Plateau. To explore the role of tectonics in regulating the river downcutting at regional and local scales, we reconstructed the rate and spatial pattern of incision within and below the knickzone. We combined the investigation of fluvial terraces with tributary river profile analysis for a 300-km reach near Yunlong below the knickzone (25–27.5°N). We conducted field mapping and dating of strath terraces at the heights of 60–380 m above the trunk river. The overlying terrace deposits comprise fluvial conglomerates and overbank sands as well as tributary alluvial fan conglomerates. K-feldspar post-infrared infrared stimulated luminescence (pIRIR) dating results suggest terrace formation during the Middle Pleistocene and the incision rate varying at <0.59–0.22 mm/yr. The river profiles of most tributaries in the study area are in a transient state with a knickpoint separating an upstream relict graded profile and a downstream steepened reach. These tributary profiles suggest river incision of ~50–1800 m, showing a spatial trend of increase towards the north. Knickpoint elevation and channel steepness of tributaries show a similar spatial pattern of northward increase. We suggest that the spatial variation in river incision along the Lancang River near Yunlong is likely to have been regulated by differential rock uplift in southeastern Tibet. Using the K-feldspar pIRIR dating method, we rectified the incision rate within the knickzone to vary at <0.63–0.28 mm/yr. New dating results thus suggest that terrace-derived incision rates along the Lancang River are similar to regional erosion rates on million-year and millennial time scales in terms of magnitude and spatial pattern. Coupled erosion rates on various time scales along the Lancang River and spatial pattern of river incision near Yunlong supports a primary role of tectonic forcing in shaping the southeastern Tibetan landscape.

Geomorphic assessment of the factors contributing to the evolution of landforms in Ukhaldhunga area, Kosi River valley, Kumaun Himalaya, Uttarakhand

This paper documents the various factors contributing to the evolution of landforms in the Kosi River valley, Ukhaldhunga area of the Kumaun Himalaya, Uttarakhand. The area falls in the major tectonic boundary between the Lesser Himalaya and the sub-Himalaya. Passing through the Parewa-Ukhaldhunga-Dabara area, this tectonic contact is known as the Main Boundary Thrust (MBT), which is characterized by presence of varied landforms. Study of the development of geomorphology, particularly those evolved in the MBT zone, suggests that the morphological features are intimately associated with the tectonic activities related to the movement of rocks along the MBT and the surface processes such as fluvial and mass movement. The various landforms observed in the MBT zone include strath terraces, fill terraces, paleochannels and V-shaped valley that pertain to fluvial genesis; gravity induced landforms such as landslide debris and colluvial fans; and tectonic landforms such as linear fault traces, swerving/swing of river course and linear depressions. Signature of recent tectonic activity along the MBT is observed between Dabara and Khakrakot. The activity is evident in the form of 8-km-long active fault trace trending NW-SE. Normal fault related landforms are observed in the hanging wall block of the MBT. Neotectonic strath terraces and fill terraces are well developed in the MBT zone. Multiple events of recurrence of landslides are evident from exposed section of landslide debris fans. The bedrocks are highly sheared, suggesting successive tectonic movements along the MBT. As a consequence, tectonic wedges have developed in the bedrocks. These wedges have facilitated for the recurrence of a number of landslides. The anthropogenic activities have also aggravated the slope stability. Truncation of older debris fan surfaces by an erosional/fault scarp is observed and the scarp separates the older fans from the youngest debris fan deposit. The scarp runs parallel to the MBT and Kosi River. Swerving of the Kosi River is as a result of the tectonic forcing along active lineaments/faults. The trend of lineaments of the maximum and high density is NE-SW, which is transverse to the trend of the NW-SE trending Himalayan fold-thrust belt.

Topographic controls on divide migration, stream capture, and diversification in riverine life

Abstract. Drainages reorganise in landscapes under diverse conditions and process dynamics that impact biotic distributions and evolution. We first investigated the relative control that Earth surface process parameters have on divide migration and stream capture in scenarios of base-level fall and heterogeneous uplift. A model built with the Landlab toolkit was run 51 200 times in sensitivity analyses that used globally observed values. Large-scale drainage reorganisation occurred only in the model runs within a limited combination of parameters and conditions. Uplift rate, rock erodibility, and the magnitude of perturbation (base-level fall or fault displacement) had the greatest influence on drainage reorganisation. The relative magnitudes of perturbation and topographic relief limited landscape susceptibility to reorganisation. Stream captures occurred more often when the channel head distance to divide was low. Stream topology set by initial conditions strongly affected capture occurrence when the imposed uplift was spatially heterogeneous. We also integrated simulations of geomorphic and biologic processes to investigate relationships among topographic relief, drainage reorganisation, and riverine species diversification in the two scenarios described above. We used a new Landlab component called SpeciesEvolver that models species at landscape scale following macroevolutionary process rules. More frequent stream capture and less frequent stream network disappearance due to divide migration increased speciation and decreased extinction, respectively, especially in the heterogeneous uplift scenario in which final species diversity was often greater than the base-level fall scenario. Under both scenarios, the landscape conditions that led to drainage reorganisation also controlled diversification. Across the model trials, the climatic or tectonic perturbation was more likely in low-relief landscapes to drive more extensive drainage reorganisation that in turn increased the diversity of riverine species lineages, especially for the species that evolved more rapidly. This model result supports recent research on natural systems that implicates drainage reorganisation as a mechanism of riverine species diversification in lowland basins. Future research applications of SpeciesEvolver software can incorporate complex climatic and tectonic forcings as they relate to macroevolution and surface processes, as well as region- and taxon-specific organisms based in rivers and those on continents at large.

Pliocene and Pleistocene stratigraphic evolution of the western Niger Delta intraslope basins: A record of glacio-eustatic sea-level and basin tectonic forcings

Although climate proxy (δ18O) across the world ocean basins reveals that orbital forcing significantly controlled the Pliocene and the Pleistocene sediment deposition, and has been demonstrated in seismic and outcrop studies on the continental shelves of many margins, few or no seismic stratigraphic studies have investigated orbital forcing on deep-water sediment records. In this study, we combined detailed seismic stratigraphy and 3D geomorphological analysis of a high-resolution 3D seismic block in a detailed study of the stratigraphic evolution of the western Niger Delta intraslope basins over the last 5.5 Ma. Two mega seismic units named MSU 1 and MSU 2 were identified. The change in sedimentary architecture from (i) mass flows and turbidite sequences to (ii) hemipelagic and turbidite sequences at the MSU 1/MSU 2 transition coincides with a significant (x3) increase in sedimentation rates and a transition from dominant 400 ka eccentricity cycles (from 5.3 Ma-0.8 Ma) to dominant 100 ka eccentricity cycles, at the Middle Pleistocene Transition (MPT) (circa 0.8‐–0 Ma). The timing of these changes was estimated based on a detailed analysis of seismic facies succession, correlation of seismic markers with high-resolution sea-level and oxygen isotope curves, and estimation of sequence duration. Further changes in the sedimentary record, characterised by turbidite-dominated sequences at the lower part of MSU 1 to mixed mass flows and turbidite sequences at the upper part of MSU 1, were respectively correlated with changes that occurred in the early Pliocene (circa 4.9 Ma) and in the early Pleistocene (circa 2.6 Ma). The depositional sequence on the western Niger Delta intraslope basin is usually characterised by a falling stage erosional surface (FSES) at its base and top (sequence boundary), and by (i) basal MTDs/bypass facies (where preserved), (ii) turbidite feeder channels/aggrading or meandering channel levee complexes and/or MTDs (slides/slumps) and (iii) hemipelagic drapes that successively document the falling stage, lowstand to early transgressive and late transgressive to highstand transits of the shoreline. The Pliocene and Pleistocene sedimentary records of the western Niger Delta intraslope basins were controlled by interplay between allocyclic forcing linked to glacio-eustatic sea-level oscillations and basin tectonics associated with mobile shale movements. .

Tectonic forcing of environmental transition in Central Asia at ~11–9 Ma

A comprehensive understanding of the Neogene paleoenvironmental evolution of Central Asia is important for predicting the future climatic and environmental conditions within the region. However, our understanding of the relative roles of Tibetan Plateau (TP) uplift and global cooling in driving its paleoenvironmental evolution remain elusive. Here we present two well-dated (~16–5 Ma) independent environmental magnetic records from the northern TP, together with a comprehensive analysis of other well-dated Neogene environmental magnetic datasets for ten other sites from the northern TP. The results indicate synchronous changes in magnetic parameters which we interpret as reflecting a major environmental transition in Central Asia at ~11–9 Ma, which is supported by evidence from multiple independent paleoecological and paleoclimatic studies. A major environmental transition at 11–9 Ma is also supported by the results of linear and non-linear analyses of the magnetic records of the two studied sections. Our analyses reveal that prior to ~11 Ma, the environmental fluctuations within the QB were primarily driven by insolation variations modulated by Earth orbital parameters; however, after ~11 Ma this influence faded and there was a shift from a stable environmental system, characterized by periodic fluctuations, to an unstable system with erratic fluctuations. The timing of this phase shift in the paleoenvironment of Central Asia was not related to global cooling but it coincided with extensive tectonic activity in the TP. Together with conceptual models and previous numerical simulations results, we conclude that a major shift of the dominant driver of Central Asia paleoenvironment occurred at ~11–9 Ma and that uplift of the TP, rather than global cooling, was responsible.