Tectonic Forcing Research Articles

Morphostructural evidence of crustal-scale, active along-strike segmentation of the Umbria-Marche Apennines, Italy

This paper discusses the response of topography and river networks to non-uniform lithology and tectonic forcing in the Umbria-Marche sector of the Apennines fold and thrust belt. We ruled out the role of variable erosion of rock types and interpret channel steepness data in terms of rock uplift, discovering a southward increase in the total amount of uplift. Such a trend appears as the large-scale response to uneven vertical motions of different sectors of the mountain ridge and foothills. The general coincidence between sector boundaries and transversal, NE-SW striking faults mapped by seismic interpretation in the outer zone of the fold and thrust belt, suggests that such faults extend to the SW, beneath the allochthonous thrust sheets of the mountainous area. Therefore, it may be inferred that such transversal faults represent long-lived, deeply rooted basement structures compartmentalizing both the axial and the outer zones of the fold and thrust belt. We suggest that differential uplift was essentially controlled by variable amounts of basement thrust displacement characterizing the compartmentalized belt. This interpretation deviates from a more conventional view that uplift of the central Apennines, particularly prominent in the south, is dynamically supported. Our results, besides shedding new light into the active tectonic behavior of a large portion of the Italian peninsula, also provide general insights into the surface response to the differential behavior of crustal blocks produced by along-strike segmentation of active mountain belts.

When did the Dead Sea fault become a transform?

This study re-evaluates the ~20 Myr development of the Dead Sea Fault System (DSFS) and its tectonic definition as a transform plate boundary. The DSFS conveys sinistral displacement between the Arabian-Sinai plates: ~105 km along its ~400 km-long southern segment (Gulf of Aqaba-Eilat to the Hula basin); ~90 km and 4–16 km along the central and northern segments (~190 km long each, across Lebanon, western Syria, and southern Turkey). A review of previous studies, combined with new seismological data analysis, associates the northward displacement decline with obstacles along the DSFS propagation path. During the Miocene, DSFS propagated up to the NW-trending Irbid rift (1st obstacle) and splayed NW towards the Mediterranean and NE along the Late Cretaceous Palmyra fold-thrust belt (2nd obstacle). Its reactivation uplifted the Hermon and the Anti-Lebanon mountain ranges. Northward DSFS propagation into the cold and rigid Aleppo plateau lithosphere (3rd obstacle) was stalled until the early Pliocene (~5 Ma), when volcanism and ongoing regional tectonic forcing enabled the DSFS to shift to the Yammouneh fault and rupture through the Missyaf-Ghab branch farther north (central and northern segments, respectively). During the Pleistocene-recent, connection of the DSFS with the ophiolite belt and East Anatolian Fault System (EAFS) along the Bitlis suture zone (4th obstacle) has not yet been established. Seismological data show a clear separation between the EAFS and the DSFS, while seismicity is scattered across the Aleppo plateau and the central and northern DSFS segments. In contrast, seismicity is localized along the southern DSFS segment. Our findings suggest that, at present, the DSFS has still not made a structural, seismologic, and tectonic connection with the EAFS. Hence, we redefine the DSFS as a pre-transform and suggest its interaction with the EAFS is a world-class example of a fault-fault-fault triple junction in the making.

Role of coseismic bedrock landslides in the landscape evolution of high-relief mountainous terrain: Insights from detrital 10Be dilution modeling

Episodic landslides supply vast quantities of debris from hillslopes to channels, resulting in the dilution of cosmogenic nuclides in fluvial sediment. This study revisited the nuclide dilution concept and proposed a novel model framework to quantify landslide-derived sediment yields to interpret the responses of entire landscape systems to tectonic forcing in an active orogen. The model was applied to datasets of detrital 10Be concentrations obtained from the Minjiang catchment in the eastern margin of the Tibetan Plateau, where the impacts of coseismic landslides were documented during the 2008 Wenchuan earthquake. Presumable model parameters were evaluated through multifaceted geospatial analyses by adopting the normalized channel steepness index as a proxy for background denudation rate, which was then converted to the corresponding nuclide concentration; the fluvial channel geometry was adopted for evaluating pre-event fluvial sediment storage. The scaling factors for quantifying the landslide debris influx were obtained via inversion of the diluted 10Be concentrations and corresponding landslide inventory to verify the feasibility of the model. The calibrated model was then applied at the regional scale to evaluate the long-term net denudation of the hillslopes with a certain earthquake recurrence interval. The resulting spatial distribution of increased denudation is consistent with very-long-term exhumation rates derived from low-temperature thermochronology, implying the critical role of coseismic landslides in mass removal from hillslopes to counterbalance long-term tectonic uplift.

Terrace formation linked to outburst floods at the Diexi palaeo-landslide dam, upper Minjiang River, eastern Tibetan Plateau

Abstract. River terraces are frequently investigated with the aim of extracting information regarding tectonic or climate forcing on the evolution of landscapes. Terraces formed following the blockage of valleys by large-scale landsliding have received limited attention despite the high likelihood of their prevalence in landslide-dominated mountain belts. Here, we investigate the geomorphology, sedimentology, and chronology of two outstanding sets of terraces upstream of the giant river-blocking Diexi palaeo-landslide on the upper Minjiang River, eastern Tibetan Plateau. The first set occurs at Tuanjie village and has seven levels (T1–T7); the second set, at Taiping village, has three levels (T1–T3). All the terraces display a consistent sedimentary sequence comprising lacustrine muds topped by fluvial gravel sometimes capped by loess and a palaeosol. Based on field examination, lithofacies analysis, elevation data, and chronometric data (optically stimulated luminescence and radiocarbon dating), we correlate T1, T2, and T3 at Taiping with T5, T6, and T7 at Tuanjie. Our analysis suggests that two damming and three outburst events have occurred at the Diexi palaeo-landslide over the past 35 000 years. A giant landslide (> 300 m high) blocked the river before 35 ka, followed by the first outburst flood at ∼ 27 ka; the river was blocked again between 27 and 17 ka, followed by a second outburst at ∼ 17 ka. A third outburst at ∼ 12 ka was followed by gradual fluvial incision of the palaeo-dam crest to its current level. We attribute the terraces at Diexi to the recurrent blockage and outburst events, which reflect the shifting sediment transport capacity and incision at the palaeo-dam crest. Here, climatic fluctuations play a minor role in terrace formation, and tectonism plays no role at all.

Analyzing Volcanic, Tectonic, and Environmental Influences on the Seismic Velocity from 25 Years of Data at Mount St. Helens

Abstract We estimate changes in the seismic velocity (dv/v) from 25 years of ambient seismic noise recorded at Mount St. Helens (MSH). At MSH, the availability of seismic stations changes frequently due to station failure and the installation of new stations. Therefore, it is difficult to combine relative measurements that do not span the same time and space. We tackle this challenge by developing a spatial imaging algorithm to normalize all ∼1400 dv/v time series onto one spatial grid. Thereby, we obtain time-dependent velocity change maps of the MSH region, which we analyze with the help of auxiliary observations, such as ground position (i.e., Global Navigation Satellite System [GNSS]), weather data, environmental observations, and regional seismicity. In the dv/v time series, we find a variety of dynamics caused by volcanic, tectonic, and environmental forcing. With the initiation of MSH’s 2004–2008 volcanic crisis, dv/v exhibits a significant increase, which we link to the deflation of the volcanic plumbing system, also observed on GNSS data. Between 2013 and 2018, when seismicity levels are elevated, we find lower velocities at depth. This phase is followed by an episode of relative quiescence, accompanied by significant dv/v increases close to the St. Helens seismic zone. We suggest a reinflation of the magmatic plumbing system after MSH’s 2004–2008 eruption lasting until about 2017. Afterward, the magmatic activity in the subsurface reduces, thereby decreasing pressure and increasing the seismic velocity. Fluctuating groundwater levels may dominate the seasonal cycles in the dv/v time series. A contrasting seasonal response between the high-elevation edifice and foothill valleys may indicate that surface freezing inhibits subsurface groundwater infiltration at higher altitudes.

Unraveling the sediment routing systems evolution of the south Pyrenean foreland basin during the lower to middle Paleogene period

Orogenesis plays a crucial role in creating, modifying, and disrupting sediment routing fairways. Reconstructing past source to sink systems is a critical step to unravel the geological history, mandatory to disentangle tectonic and climatic forcings, and to understand the perturbations that affected the overall system. The Paleocene-Eocene period is a debated early stage of the early Pyrenean orogeny, characterized by the piggy-back style tectonic partitioning of sub-basins as the deformation front propagates towards the southern foreland. An important issue is to understand how sedimentary systems reacted and reorganized in response to this dynamic scenario. and whether the stratigraphic and sediment provenance results align with the envisioned scenario.In this paper we aim at contributing to the paleogeographic, sedimentologic and tectono-sedimentary evolution of the South-Pyrenean foreland basin by reviewing the chronostratigraphic framework of the basin infill in its south-central sector (the Ager sub-basin in the Serres Marginals thrust sheet). We built five new magnetostratigraphic sections, which together encompass most of the Paleogene record, aimed to best reconcile magnetostratigraphic data with the defined biostratigraphic framework of the region including marine Shallow Benthic Zones (SBZ biozones) and continental mammalian localities (MP levels). Detailed trends in subsidence show the development and evolution of the foreland depozones, from forebulge to foredeep and wedge-top setting, relative to the successive emplacement of the Montsec and Serres Marginals thrust sheets.A correlation with the eastern portion of the foreland basin (Lower-Middle Pedraforca and Cadí Thrust Sheets) and adjacent northern Graus-Tremp basin (Montsec Thrust Sheet) was feasible and seeks to contribute to the tectono-sedimentary evolution of the South-Pyrenean foreland in the light of a source to sink approach. Our proposal includes a new paleogeographic evolution of the area in a series of paleogeographic maps from Late Thanetian to Late Cuisian times.

The Significance of Ancient Buried Landscapes as Natural Geomorphic Experiments

AbstractThere is considerable interest in developing quantitative methods for analyzing present‐day fluvial landscapes with a view to extracting information about tectonic forcing and drainage evolution, together with the influence of lithologic substrates and of paleoclimatic variations. In view of the multifactorial nature of this complex problem, it has previously been proposed that natural geomorphic experiments could play a significant role in developing a quantitative understanding of landscape growth and decay. Here, we describe and analyze a stacked sequence of five buried transient landscapes that punctuate marine strata along the fringes of the North Atlantic Ocean. We propose that these landscapes constitute a suite of natural experiments, which illuminate significant aspects of quantitative fluvial geomorphology. Our preliminary analysis of four of these buried landscapes suggests that the amplitude of external tectonic forcing plays a significant role in fluvial landscape evolution. In future, we hope that this suite of natural experiments will be further exploited by the fluvial community with a view to identifying the most appropriate analytical techniques.

Late Miocene tectonic forcing of climate transition in the northeastern Tibetan Plateau

Interactions among late Cenozoic global cooling, tectonic activity and regional climate evolution of the northeastern Tibetan Plateau remain elusive. To further understand the relative contributions of global climate change and tectonism, we conducted a comprehensive study of heavy minerals, rock magnetism, and branched glycerol dialkyl glycerol tetraethers (brGDGTs) in late Cenozoic sediments of the Laojunmiao section (ca. 12.7 Ma to 5 Ma) in the Jiuxi Basin. Our results reveal a notable increase in magnetic susceptibility (χ) and saturation isothermal remanent magnetization (SIRM) at 8.5 Ma, aligning with an accelerated decrease in temperature captured by brGDGTs. Combined with heavy mineral analysis, we propose that the profound changes in magnetic parameters and temperature are closely linked to the intensive uplift of the northern Qilian Shan since 8.5 Ma. Furthermore, this ongoing uplift has occurred simultaneously with persistent aridification in the Jiuxi Basin and its adjacent regions. The Qilian Shan might have reached a threshold elevation and began to act as a moisture barrier to northwestward moisture since 8.5 Ma. By synthesizing hydroclimate evolution records from the northeastern Tibetan Plateau, we deduce that changing topography resulting from tectonic uplift may have exerted a significant influence on regulating the moisture distribution in this region during the mid- to late Miocene.

Readjustment of fluvial systems to Quaternary tectonic disruption in the Central Afar (Ethiopia)

The Afar region constitutes the diffuse triple junction adjoining the Red Sea, Gulf of Aden, and Main Ethiopian Rifts. Extension in the Afar is distributed between on-axis, magmatic crustal spreading, and off-axis, amagmatic extension, such as in Dobe graben. The timing of initiation and development of these amagmatic grabens is key to understanding the final stages of continental extension/breakup in central Afar. All major graben-bounding faults in central Afar cut through the Quaternary Afar Stratoid Series, constraining the ages of initiation to younger than approximately 1 million years. The Afar Stratoid Series presents a widespread thick lava unit that smoothed and infilled the topography created by the prior 30 Ma of deformation. The ∼1 Ma top surface of the Afar Stratoid Series serves as a regional marker predating most Quaternary deformation. The initiation of a particular fault (or location along a graben-bounding fault) begins a process of local lowering of base level – this is recorded in the landscape as a knickpoint that incises the paleo drainage in the footwalls of the grabens, connecting it to the basin floor with a deep canyon. The rate at which knickpoints retreat upstream permits a space-for-time approach to assessing initiation. This study develops and applies a landscape evolution model to estimate relative maturity and age of drainage basins by measuring the long profile response to tectonic forcings over intermediate timescales in central Afar. This is applied under the assumption that faulting postdates Afar Stratoid Series emplacement. The model is calibrated by analysis of stream longitudinal profiles and terrestrial cosmogenic nuclide (TCN) analysis of samples collected in the field. Longitudinal stream valley profiles are mapped through remote sensing and photogrammetry, and TCN concentrations are assessed to calculate the uplift rate along the graben-bounding faults. Results indicate that faulting of Dobe Graben in the central Afar initiated in the southeast and propagated to the northwest. Along the southern margin of Dobe Graben, ages of 503 ± 116 ka were calculated for fault initiation at Hann Canyon in the southeast, and 339 ± 80 ka at Ishyilu Canyon to the northwest. These timing constraints have implications for competing tectonics models for central Afar. The general approach developed for modeling knickpoint retreat has broader utility beyond Afar, allowing for application to extensional tectonic regimes elsewhere where similar geological and surface constraints exist.

Deep-sea hiatus record reveals orbital pacing by 2.4 Myr eccentricity grand cycles

Astronomical forcing of Earth’s climate is embedded in the rhythms of stratigraphic records, most famously as short-period (104–105 year) Milankovitch cycles. Astronomical grand cycles with periods of millions of years also modulate climate variability but have been detected in relatively few proxy records. Here, we apply spectral analysis to a dataset of Cenozoic deep-sea hiatuses to reveal a ~2.4 Myr eccentricity signal, disrupted by episodes of major tectonic forcing. We propose that maxima in the hiatus cycles correspond to orbitally-forced intensification of deep-water circulation and erosive bottom current activity, linked to eccentricity maxima and peaks in insolation and seasonality. A prominent episode of cyclicity disturbance coincides with the Paleocene-Eocene Thermal Maximum (PETM) at ~56 Myr ago, and correlates with a chaotic orbital transition in the Solar System evident in several astronomical solutions. This hints at a potential intriguing coupling between the PETM and Solar System chaos.

Influence of Late Carboniferous–Early Permian climate change on the sedimentary evolution – a case study of the lacustrine Lower Anthracosia Shales (Intra-Sudetic Basin, SW Poland)

The Anthracosia Shales are lacustrine deposits within the volcano-sedimentary Pennsylvanian– Lower Permian succession of the Intra-Sudetic Basin. Core from the Rybnica Leśna PIG 1 borehole, which penetrated the Lower Anthracosia Shales, was analysed to explore the influence of climate on the evolution of the palaeolake, as distinct from tectonic and volcanic forcing. This reconstruction was made using mineralogical and geochemical proxies (elemental and mineralogical composition, TOC values, presence of framboidal pyrite and siderite). Based on the results, three chemically different intervals previously introduced by Wójcik-Tabol et al. (2021) are described. They represent the following stages of lake evolution: transgression (interval I), open lake (interval IIA and IIB), and termination (interval IIC and III). The initial stage of the lake (interval I) was probably related to a rise in humidity in the Late Pennsylvanian, linked to a southern Gondwana interglacial episode. Interval IIA represents the deepest facies of the Anthracosia Basin, where lake-floor anoxia prevailed. This stage was followed by a gradual lake-level fall recorded in interval IIB, with documented seasonality in humid and warm conditions. Interval IIC represents a stepwise lake regression attributed to aridification, as indicated by proxies showing a decrease in chemical weathering. Turbiditic sandy laminae in interval III reflect the terminal stage of lake infill.

Holocene climatic and tectonic forcing of decadal hydroclimate variation on the north-eastern Tibetan Plateau

A better understanding of past climate and landscape variability in high resolution on the Tibetan Plateau is of critical importance for the understanding of fundamental mechanisms and interactions in the global climate system. However, due to relatively few datasets in decadal-resolution available for analyzing possible seasonal effects and seismic activity on the northeastern Tibetan Plateau, further high-resolution lake records as an integration need to be explored to test the significance of the seasonal variations of surface processes and climatic phenomena as well as tectonic impact on a decadal scale. The rhomb-shaped pull-apart Lake Donggi Cona along the modern monsoon marginal zone on the north-eastern TP is considered an excellent archive that monitors neotectonic and climatic changes through time. We obtained new high-resolution (mean 20 yr) proxy records from a 488 cm-long sediment core from the lake and compare them directly with paleoclimate records from nearby lakes. A decadal-resolution oxygen stable isotope (δ18O) record co-varies positively with carbonate content and demonstrates the profound and varying contribution of glacier/snow melt (winter/spring moisture) to lake hydrology at different lake evolution stages. This is also indicated by the grain size composition and related endmember modelling (EMMA) results. During 11.8–9.4 cal Ka BP, the lake experienced a swamp status, apart from the major lake body followed by water rise towards the littoral zone until 7.5 cal Ka BP. Glacier melt water supply started to be active since the late Younger Dryas and led to the strong excursions of carbonate contents and δ18O values according to insolation increase. This phase was dominated by the westerlies and characterized as low seasonality with long winter duration. Water rose to its highest level during 7.5–6.5 cal Ka BP and fluctuated with deep water phases until 4.7 cal Ka BP, due to glacier melt maxima and potential increase of summer (convective) moisture preserved in the oxygen isotopic signals. Water cover dropped and remained low until 2.9 cal Ka BP due to the reduced glacier melt and colder climate. However, the low δ18O values at a reduced water budget points to the still active contribution of spring glacier/snow melt that kept the lake not dry-up unlike other lakes with no glacier melt water supply. After 2.9 cal Ka BP water level dropped towards a pond/lagoon situation until 2.0 cal Ka BP, albeit temperature rise after a long cold climatic interlude. It might be caused by another phase of lake deepening triggered by subsidence and related sediment relocation from the shore, rather than by climatic factors. However, water level increased again afterwards and fluctuated towards the present level due to non-summer moisture supply in long freezing winters. We assume profound signatures of high seasonality in climate after 7.5 cal Ka BP and the lake became open since1.3 cal Ka BP. We suggest that combined thermal forcing by glacier/snow melt and tectonics play a significant role together with solar forcing, governing hydroclimate changes on the north-eastern Tibetan Plateau with decadal to millennial cycles.

Tracing earthquakes through lake sediments for better prediction

<p>Intensive climatic extremes and frequent earthquakes, both in China and other regions, have captured public attention recently. The Tibetan Plateau at middle northern latitudes boasts large glacier and snow coverage, coupled with frequent tectonic activities, exerting profound yet poorly understood influences on zonal atmospheric motion and energy flux during interhemispheric coupling. This study proposes a comprehensive process-based approach involving multi-proxies focused on alpine lakes to illuminate the intricate interactions among tectonics, glacial processes and hydro-climatic variations. This perspective can enhance our understanding of the spatiotemporal diversity of the local-to-global hydro-climatic change pattern, particularly forced by Tibetan Plateau, and suggests to consider its combined summer thermal and tectonic forcing. Additionally, the approach provides unbiased geological data extracted from lakes, contributing to the optimization of hazard and climate models for better predictions of tectonics, abrupt and irreversible climate tipping points with confidence.</p>

Integrated uplift, subsidence, erosion and deposition in a tightly coupled source‐to‐sink system, Pagliara basin, northeastern Sicily, Italy

AbstractHow tectonic forcing, expressed as base level change, is encoded in the stratigraphic and geomorphic records of coupled source‐to‐sink systems remains uncertain. Using sedimentological, geochronological and geomorphic approaches, we describe the relationship between transient topographic change and sediment deposition for a low‐storage system forced by rapid rock uplift. We present five new luminescence ages and two terrestrial cosmogenic nuclide paleo‐erosion rates for the late Pleistocene Pagliara fan‐delta complex and we model corresponding base level fall history and erosion of the source catchment located on the Ionian flank of the Peloritani Mountains (NE‐Sicily, Italy). The Pagliara delta complex is part of the broader Messina Gravel‐and‐Sands lithostratigraphic unit that outcrops along the Peloritani coastal belt as extensional basins have been recently inverted by both normal faults and regional uplift at the Messina Straits. The deltas exposed at the mouth of the Pagliara River have constructional tops at ca. 300 m a.s.l. and onlap steeply east‐dipping bedrock at the coast to thickness between ca. 100 and 200 m. Five infrared‐stimulated luminescence (IRSL) ages collected from the delta range in age from ca. 327 to 208 ka and indicate a vertical long‐term sediment accumulation rate as rapid as ca. 2.2 cm/yr during MIS 7. Two cosmogenic 10Be concentrations measured in samples of delta sediment indicate paleo‐erosion rates during MIS 8–7 near or slightly higher than the modern rates of ca. 1 mm/yr. Linear inversion of Pagliara fluvial topography indicates an unsteady base level fall history in phase with eustasy that is superimposed on a longer, tectonically driven trend that doubled in rate from ca. 0.95 to 1.8 mm/yr in the past 150 ky. The combination of footwall uplift rate and eustasy determines the accommodation space history to trap the fan‐deltas at the Peloritani coast in hanging wall basins, which are now inverted, uplifted and exposed hundreds of metres above the sea level.

Dating the late Miocene marine sediments around the southern middle Durance valley (Provence, SE France): new evidences for a Tortonian age

The present study aims dating the topmost 50 m of a 115 m-long core retrieved from a valley located in the Cadarache Area (Upper Provence, South East France). Based on burial dating by in situ produced cosmogenic nuclides (10Be, 26Al and 21Ne), and paleomagnetic analyses, a Tortonian age was determined for the sedimentary succession exhibited in the core. In addition, thin sections, grain size analyses and quartz morphoscopy were used to characterize a shallow marine environment and to correlate the sediment core to the surrounding exposed sections. When comparing the studied sedimentary record to global sea level estimates, we establish that the local Tortonian transgression was not synchronous with the global scale sea level high-stand, but happened more likely later, during a global regressive trend. The timing of the Tortonian flooding in Upper Provence was therefore most probably driven by regional tectonic forcing. Finally, the Tortonian shallow marine sediments are topped by lacustrine tight carbonates. These carbonates protect the marine sediments from the following major erosional events resulting from the Messinian sea level drop and from interglacial-glacial fluctuations that both yielded to the present-day valley topography.

Controls on long-term denudation rate of carbonate terrains in the Eastern Mediterranean

Quantifying denudation rates under different climatic and tectonic settings is fundamental to understanding landscape evolution. Carbonate rocks may respond differently to climatic and tectonic forcings than other rock types because of their tendency to dissolve congruently. Yet, there is little information on the long-term denudation rate of carbonates and their controlling factors in different settings. Here, we present the first long-term denudation rates for carbonates in the south of the Central Anatolian Plateau. We quantified the outcrop denudation rates using in-situ cosmogenic 36Cl measured in 13 rock samples to evaluate spatial variations and potential controls on the style and rate of denudation. 36Cl-derived denudation rates range from 1.92 ± 0.31 to 45.77 ± 3.91 mm/ka. On the plateau, denudation rates are strongly correlated with precipitation and are lower than the theoretical maximum dissolution rates predicted assuming zero evaporation, implying that climate exerts the major control on carbonate denudation. These results indicate that chemical weathering is the prevalent denudation style. The denudation pattern shows spatial variability with a decreasing trend from SW to NE consistent with climate zones. High-to-moderate denudation rates occur in the continental climate, while the lowest denudation rates occur in the arid plateau interior. In the Mediterranean coastal region, measured denudation rates are higher than the predicted maximum dissolution rates, reflecting the mechanical removal of overlying rock or soil. The low denudation rates in the plateau interior indicate a slowly evolving landscape with an arid climate. The physical properties of rocks showed the weakest control on carbonate denudation.In the Central Taurides, significant infiltration of surface runoff resulted in strong subsurface karstification at the expense of surface drainage. This process caused disequilibrium between uplift and denudation and resulted in the preservation of high-elevation topography. Therefore, in the actively uplifting plateau margin, the influence of tectonics on carbonate denudation has been interfered with the impact of precipitation and subsurface karstification.

Decoupling external forcings during the development of Miocene fluvial stratigraphy of the North Patagonian Foreland

AbstractThe Patagonian Andean foreland system includes several intermountain basins filled with a Miocene non‐marine record deposited under syn‐tectonic conditions related to the Andean uplift and a regional climate change triggered by a rain shadow effect. Many of those basins, such as the Collón Cura basin in Neuquén Province, Argentina, present a well‐preserved fluvial record (i.e. the Limay Chico Member of the Caleufú Formation). Sedimentological and palaeomagnetic studies have allowed the interpretation of coeval transverse distributary fan and axial mixed‐load fluvial systems deposited between 10.6 ± 0.2 and 12.8 Ma. The basin infill arrangement shows that, while the axial mixed‐load fluvial system exhibits an aggradational stacking pattern, the transverse distributary fluvial fan system denotes three different orders of stratigraphic patterns: (i) large‐scale progradation of the transverse fluvial fan system over a time scale of 106 year; (ii) intermediate‐scale progradational–retrogradational transverse intra‐basinal fluvial fan episodes over a time scale of 105 year; and (iii) small‐scale transverse lobe progradation over a time scale of 105–104 year. These patterns were interpreted as transverse sediment flux variations triggered by variable external forcings. To decouple those forcings, we estimated the Collón Cura basin equilibrium time at 3–5 × 105 year and compared it with the time scale over which different external forcings varied in the Patagonian Andean and foreland regions during Miocene times. Large‐scale progradation is linked to an increase in sediment flux triggered by a long‐term tectonically driven exhumation forcing associated with the Miocene Patagonian Andean contractional phase. Intermediate‐scale progradational–retrogradational episodes are linked to variations in sediment flux due to a mid‐term tectonic forcing associated with the western fault system activity. The small‐scale fan lobe progradation is related to increases in sediment flux triggered by indistinguishable short‐term autogenic processes and/or high‐frequency tectonic and climatic forcings. This contribution shows the applicability and limitations of the basin equilibrium time concept to decouple external forcings from the geological record, considering their magnitude, nature and time scale, as well as the basin characteristics.

Erosion rate maps highlight spatio-temporal patterns of uplift and quantify sediment export of the Northern Andes

Erosion rates are widely used to assess tectonic uplift and sediment export from mountain ranges. However, the scarcity of erosion rate measurements often hinders detailed tectonic interpretations. Here, we present 25 new cosmogenic nuclide-derived erosion rates from the Northern Andes of Colombia to study spatio-temporal patterns of uplift along the Central and Eastern Cordillera. Specifically, we combine new and published erosion rate data with precipitation-corrected normalized channel steepness measurements to construct high-resolution erosion rate maps. We find that erosion rates in the southern Central Cordillera are relatively uniform and average ∼0.3 mm/a. In the northern Central Cordillera rapidly eroding canyons dissect slowly eroding, low-relief surfaces uplifting since 8.3−2.6+3.7 Ma, based on a block uplift model. We interpret that persistent steep slab subduction has led to an erosional steady-state in the southern Central Cordillera, whereas in the northern Central Cordillera, Late Miocene slab flattening caused an acceleration in uplift, to which the landscape has not yet equilibrated. The Eastern Cordillera also displays pronounced erosional disequilibrium, with a slowly eroding central plateau rimmed by faster eroding western and eastern flanks. Our maps suggest Late Miocene topographic growth of the Eastern Cordillera, with deformation focused along the eastern flank, which is also supported by balanced cross-sections and thermochronologic data. Spatial gradients in predicted erosion rates along the eastern flank of the Eastern Cordillera suggest transient basin-ward migration of thrusts. Finally, sediment fluxes based on our erosion maps, suggest that the Eastern Cordillera exports nearly four times more sediment than the Central Cordillera. Our analysis shows that accounting for spatial variations in erosion parameters and climate reveals important variations in tectonic forcing that would otherwise be obscured in traditional river profile analyses. Moreover, given relationships between tectonic and topographic evolution, we hypothesize that spatio-temporal variations in slab dip are the primary driver of the dynamic landscape evolution of the Northern Andes, with potentially superposed effects from inherited Mesozoic rift structures.

Examining the influence of disequilibrium landscape on millennial-scale erosion rates in the San Bernardino Mountains, California, USA

Temporal and spatial variations of tectonic rock uplift are generally thought to be the main controls on long-term erosion rates in various landscapes. However, rivers continuously lengthen and capture drainages in strike-slip fault systems due to ongoing motion across the fault, which can induce changes in landscape forms, drainage networks, and local erosion rates. Located along the restraining bend of the San Andreas Fault, the San Bernardino Mountains provide a suitable location for assessing the influence of topographic disequilibrium from perturbations by tectonic forcing and channel reorganization on measured erosion rates. In this study, we measured 17 new basin-averaged erosion rates using cosmogenic 10Be in river sands (hereafter, 10Be-derived erosion rates) and compiled 31 10Be-derived erosion rates from previous work. We quantify the degree of topographic disequilibrium using topographic analysis by examining hillslope and channel decoupling, the areal extent of pre-uplift surface, and drainage divide asymmetry across various landscapes. Similar to previous work, we find that erosion rates generally increase from north to south across the San Bernardino Mountains, reflecting a southward increase in tectonic activity. However, a comparison between 10Be-derived erosion rates and various topographic metrics in the southern San Bernardino Mountains suggests that the presence of transient landscape features such as relict topography and drainage-divide migration may explain local variations in 10Be-derived erosion rates. Our work shows that coupled analysis of erosion rates and topographic metrics provides tools for assessing the influence of tectonic uplift and channel reorganization on landscape evolution and 10Be-derived erosion rates in an evolving strike-slip restraining bend.

Surface deformation of northeastern Taiwan revealed by geomorphic indices

In northeast Taiwan, many areas are affected by various tectonic forcings. Some areas appear to have a subsidence tendency, whereas others reflect uplift activities on the surface, due to tectonic northward compressive forcing growth and decline. Owing to the presence of widespread mountain areas, limited geodetic surveys in the field have made data scarce in the study area in the past decades. The distribution of the geomorphic indices, which were calculated along the river channels, were used to analyze the activities on a regional scale in this study. The long-term landscape evolution of drainage basins can record topographic changes through the river channels. By calculating the location and drop height of knickpoint in the river longitudinal profile, as well as the spatial distribution of the normalized steepness index ({K}_{sn}) value, it is possible to comprehensively discuss the perturbations that were caused by possible factors in river channels. Our results from the geomorphic indices synthetically suggest that the river channel of drainage basins is mainly influenced by the perturbations such as geological structures, tectonic activity, various lithologies, potential ruptures. In the study area, tectonic forcing act on a large area from north to south, which is reflected in the long-term incision of the river into the bedrock. Moreover, the potential ruptures on the surface may also induce displacement in the local area.