The evolution of the passive Armorican margin (Western France) during the Neogene and Quaternary was analyzed using field data. The morphology of the margin attests to a late Hercynian shaping, ...further deformation during the Mesozoic mid-Atlantic opening, during the Alpine Orogeny, and ultimately, a Late Cenozoic uplift, mostly related to an onshore isostatic accommodation in response to erosion and limited tectonic activity. A very limited strike–slip dynamic, with very low seismicity, accommodated the Neogene–Pleistocene N170 strains around the rigid Armorican terrane. The South Armorican domain and English Channel floor include shear zones that adjusted the Alpine convergence, facilitating its transpressive slip to the west. The Permo-Triassic N150 faults were reactivated during the inversion phases that began after the Bartonian under the distal control of the Alpine convergence and the decrease in the Atlantic spreading rate after 34 Ma. The Armorican marine platforms were stable after the late Eocene and slightly subsident, experiencing pulsed episodes of transient lithospheric doming during the Neogene and Quaternary. Co-seismic activity onshore without surface rupture was recorded around ∼5.3 Ma, ∼3.7 Ma, ∼2.4–1.2 Ma, and ∼400–250 ka, in tandem with an inland exhumation driven by isostatic adjustment due to an intensification of periglacial erosion at the onset of the early interstadials or by agriculture. Low-magnitude and ubiquitous shallow seismic activities seem to be related today to an isostatic uplifted old brittle–ductile transition due to the accumulation of shearing strain.
Abstract
The history of sea level across the Quaternary is essential for assessing past and future climate. Global sea-level reconstructions are typically derived from oxygen isotope curves, but ...require calibration with geological constraints that are scarce prior to the last glacial cycle (>130 thousand years ago). Here we show that the coral reef terrace sequence at the Huon Peninsula (Papua New Guinea) provides such constraints up to ∼420 thousand years ago, through a geometric analysis of high-resolution topographic data. We derive a northward tectonic tilt as regional deformation pattern, and estimate relative sea level for 31 Quaternary periods, including several periods for which no relative sea level data exists elsewhere. Supported by numerical reef models, these estimates suggest that oxygen isotope-based global mean sea-level curves systematically underestimate interstadial sea-level elevations, by up to ∼20 m. Compared to those curves, our results imply a stronger degree of non-linearity between ice-sheet volumes and global temperatures within Quaternary glacial cycles.
The NW trending Zagros fold‐and‐thrust belt is affected by two major dextral faults: (1) the NW trending Main Recent Fault that accommodates partitioning of oblique convergence at the rear of the ...western Zagros and (2) the north trending Kazerun Fault located in the central Zagros. Combined structural and fault kinematics studies and SPOT images analysis have shown a Pliocene kinematic change accompanied by a fault pattern reorganization, which has led to a modification in the accommodation of oblique convergence. Since the late Pliocene, the distributed transpressional deformation operating at the rear of the belt has become partitioned along the newly formed Main Recent Fault. This fault cuts through early Pliocene nappes and transpressional structures by right‐laterally reactivating high‐angle thrusts. The southeastern termination of the Main Recent Fault connects to the northern termination of Kazerun Fault that consists of three fault zones that end in bent, orogen‐parallel splay thrust faults. The Kazerun Fault, together with a series of north to NNW trending inherited basement strike‐slip faults, define an orogen‐scale fan‐shaped fault pattern pointing toward the Main Recent Fault–Kazerun Fault junction. This structural pattern allows slip from along the Main Recent Fault to become distributed by transfer to the longitudinal thrust faults and folds of the Zagros belt, with the fan‐shaped fault pattern acting as a horse‐tail termination of the Main Recent Fault.
In this study, we applied the environmental seismic intensity (ESI-2007) scale to a major recent Algerian earthquake. The ESI-2007 scale is an effective tool to assess the seismic hazard and has been ...applied to onshore earthquakes. Here we applied the scale to a recent earthquake (Mw 6.8, 2003) that took place offshore in the province of Boumerdès in the north of Algeria along the boundary between African and Eurasian plates. The main shock was associated to an unknown submarine structure. No surface ruptures were observed on the onshore domain, but many earthquake environmental effects (EEEs) were reported during several field investigations. In addition to onshore ground effects, this event triggered turbidity currents responsible for 29 submarine cable breaks. Mapping and describing coseismic ground effects allowed us to distinguish primary and secondary effects like coastal uplifts, liquefaction phenomena, tsunami waves, turbidity currents, cracks, rock falls, slope movements and hydrological anomalies. Considering the total area affected and the distribution of ground effects, we suggest intensity X that appears in agreement with intensity calculated in previous study with the EMS-98 scale. Thus, this method is validated even in the case of a coastal earthquake, and could be applied in the future to Algerian historical earthquakes that have affected scarcely inhabited zones but where EEEs were listed and located.
Deeply incised river networks are generally regarded as robust features that are not easily modified by erosion or tectonics. Although the reorganization of deeply incised drainage systems has been ...documented, the corresponding importance with regard to the overall landscape evolution of mountain ranges and the factors that permit such reorganizations are poorly understood. To address this problem, we have explored the rapid drainage reorganization that affected the Cahabon River in Guatemala during the Quaternary. Sediment-provenance analysis, field mapping, and electrical resistivity tomography (ERT) imaging are used to reconstruct the geometry of the valley before the river was captured. Dating of the abandoned valley sediments by the ...Be-...Al burial method and geomagnetic polarity analysis allow us to determine the age of the capture events and then to quantify several processes, such as the rate of tectonic deformation of the paleovalley, the rate of propagation of post-capture drainage reversal, and the rate at which canyons that formed at the capture sites have propagated along the paleovalley. Transtensional faulting started 1 to 3 million years ago, produced ground tilting and ground faulting along the Cahabon River, and thus generated differential uplift rate of 0.3 ± 0.1 up to 0.7 ±0.4 mm - y... along the river's course. The river responded to faulting by incising the areas of relative uplift and depositing a few tens of meters of sediment above the areas of relative subsidence. Then, the river experienced two captures and one avulsion between 700 ky and 100 ky. The captures breached high-standing ridges that separate the Cahabon River from its captors. Captures occurred at specific points where ridges are made permeable by fault damage zones and/or soluble rocks. Groundwater flow from the Cahabon River down to its captors likely increased the erosive power of the captors thus promoting focused erosion of the ridges. Valley-fill formation and capture occurred in close temporal succession, suggesting a genetic link between the two. We suggest that the aquifers accumulated within the valley-fills, increased the head along the subterraneous system connecting the Cahabon River to its captors, and promoted their development. Upon capture, the breached valley experienced widespread drainage reversal toward the capture sites. We attribute the generalized reversal to combined effects of groundwater sapping in the valley-fill, axial drainage obstruction by lateral fans, and tectonic tilting. Drainage reversal increased the size of the captured areas by a factor of 4 to 6. At the capture sites, 500 m deep canyons have been incised into the bedrock and are propagating upstream at a rate of 3 to 11 mm - y... while deepening at a rate of 0.7 to 1.5 mm - y... At this rate, 1 to 2 million years will be necessary for headward erosion to completely erase the topographic expression of the paleovalley. It is concluded that the rapid reorganization of this drainage system was made possible by the way the river adjusted to the new tectonic strain field, which involved transient sedimentation along the river's course. If the river had escaped its early reorganization and had been given the time necessary to reach a new dynamic equilibrium, then the transient conditions that promoted capture would have vanished and its vulnerability to capture would have been strongly reduced. (ProQuest: ... denotes formulae/symbols omitted.)
How can the sluggish, long‐wavelength mantle convection be expressed by so many time and space scales of morphotectonic activity? To investigate these relationships, we explore the Java‐Banda ...subduction zone, where geodynamic records cluster. In the far‐East Tethys, the exceptionally arcuate Banda subduction zone circumscribes the deepest oceanic basin on Earth, seismotectonic activity slices the upper plate more efficiently than anywhere else, and uncommonly vast expanses of continents are flooded in Sundaland and Northern Australia. By comparing numerical simulations of subduction dynamics to a set of independent observations, we reveal the many facets of tectonic and physiographic changes that the sole docking of the Australian continent onto the subduction zone triggered. While mantle flow remains slow and long‐wavelength at depth, intense tectonic activity, and dynamic uplift and subsidence profoundly rework the physiography at many spatial scales. These results demonstrate that a modest disruption in the slow geodynamic tempo may trigger manifold morphotectonic disturbances.
Key Points
Fast and short‐lived disruption in surface morphotectonics occur at all spatial scales during transient phases of mantle flow
Uncommon SE Asia seismotectonic activity, dynamic topography, and vertical land motion all triggered by the transience of mantle flow
Depiction of the intricate relationships between mantle dynamics and surface morphotectonics
During the Carboniferous collision stage, the West European Variscan orogen was affected by oblique convergence, wrenching, plate‐scale oroclinal bending, and widespread exhumation of the deep crust. ...One of these exhumed units forms the Léon dome located on the northern flank of the Ibero‐Armorican Arc in the western part of the Armorican massif. Structural field data from the Ouessant Island reveal kinematic changes between 330 and 300 Ma that affected the northwestern margin of the Léon dome. This margin underwent two ductile deformation phases with opposite strike‐slip shear senses. Dextral strike‐slip wrenching combined with orogen‐normal shortening, orogen‐parallel stretching, and local top‐to‐the‐NE shearing occurred during the Léon dome formation and exhumation of its gneissic core at 330–310 Ma. During tightening of the Ibero‐Armorican Arc at ~300 Ma, more localized sinistral wrenching reactivated the northwestern boundary of the Léon dome. The resulting N70°E trending sinistral Porspoder‐Ouessant shear zone together with its conjugate dextral South Armorican shear zone controlled the lateral escape of the Léon‐North‐Central Armorican rigid tectonic wedge triggered by indentation of the Cantabrian orocline at the core of the Ibero‐Armorican Arc.
Key Points
Dextral strike‐slip wrenching combined with orogen‐normal shortening, orogen‐parallel stretching, and local top‐to‐the‐NE shearing accommodate synconvergence Leon dome formation during the Variscan orogeny
A major sinistral Variscan shear zone accommodate the tightening of an orogenic syntax after the dome formation
The island of Borneo is enveloped by tropical rainforests and hostile terrain characterized by high denudation rates. Owing to such conditions, studies pertaining to neotectonics and consequent ...geomorphic expressions with regard to surface processes and landscape evolution are inadequately constrained. Here we demonstrate the first systematic tectono-geomorphic evaluation of north Borneo through quantitative and qualitative morphotectonic analysis at sub-catchment scale, for two large drainage basins located in Sarawak: the Rajang and Baram basins. The extraction of morphometric parameters utilizing digital elevation models arranged within a GIS environment focuses on hypsometric curve analysis, distribution of hypsometric integrals through spatial autocorrelation statistics, relative uplift values, the asymmetry factor and the normalized channel steepness index. Hypsometric analysis suggests a young topography adjusting to changes in tectonic boundary conditions. Autocorrelation statistics show clusters of high values of hypsometric integrals as prominent hotspots that are associated with less eroded, young topography situated in the fold and thrust belts of the Interior Highlands of Borneo. High channel steepness and gradients (>200m0.9) are observed in zones corresponding to the hotspots. Relative uplift values reveal the presence of tectonically uplifted blocks together with relatively subsided or lesser uplifted zones along known faults. Sub-catchments of both basins display asymmetry indicating tectonic tilting. Stream longitudinal profiles demonstrate the presence of anomalies in the form of knickzones without apparent lithological controls along their channel reaches. Surfaces represented by cold spots of low HI values and low channel gradients observed in the high elevation headwaters of both basins are linked to isolated erosional planation surfaces that could be remnants of piracy processes. The implication of our results is that Borneo experiences active folding of the Rajang Group fold–thrust belt to present and these events reactivated old major faults and minor related dislocations. From geomorphic analysis associated with sedimentary record, we posit that the terrain could have undergone high uplift rates since 5Ma or multi-phased uplift with periodic intermittent pulses of high and low uplift rates.
•First systematic morphotectonic evaluation of northern Borneo through quantitative and qualitative geomorphic analysis.•Hypsometry shows rejuvenated landscape with parts of less eroded, young topography of Rajang Group fold-thrust belts.•The young topography demonstrates high channel steepness (ksn) associated with relatively high uplift rates.•Stream longitudinal profiles reveals anomalies manifested as knickzones along channel reaches.•North Borneo experienced rapid uplift since 5 Ma and deformation continues hitherto leading to reactivation of faults.
The morphology of coastal sequences provides fundamental observations to unravel past sea level (SL) variations. For that purpose, converting morphometric observations into a SL datum requires ...understanding their morphogenesis. The long‐lasting sequence of coral reef terraces (CRTs) at Cape Laundi (Sumba Island, Indonesia) could serve as a benchmark. Yet, it epitomizes a pitfall that challenges the ultimate goal: the overall chronology of its development remains poorly constrained. The polycyclic nature of the terraces, involving marine erosion and reoccupation of old coral colonies by more recent ones hinders any clear assignment of Marine Isotope Stages (MIS) to specific terraces, in particular the reference datum corresponding to the last Interglacial maximum (i.e., MIS 5e). Thus, to overcome these obstacles, we numerically model the genesis of the sequence, testing a range of eustatic SL (ESL) reconstructions and uplift rates, as well as exploring the parameter space to address reef growth, erosion and sedimentation. A total of 625 model runs allowed us to improve the morpho‐chronological constraints of the coastal sequence and, more particularly, to explain the morphogenesis of the several CRTs associated with MIS 5e. Our results suggest that the lowermost main terrace was first constructed during the marine transgression of MIS 5e and was later reshaped during the marine regression of MIS 5e, as well as during the MIS 5c and MIS 5a highstands. Finally, we discuss the general morphology of the sequence and the implications it may have on SL reconstructions. At Cape Laundi, as elsewhere, we emphasize the necessity of addressing the development of CRT sequences with a dynamic approach, that is, considering that a CRT is a landform built continuously throughout the history of SL oscillations, and not simply during a singular SL maximum.
Careful modelling the morphology of a coral reef terrace (CRT) sequence permits to unravel the past sea level (SL) variations, to better understand the reef bioconstruction formed during transgressions, highstands and regressions, and thus potentially improve SL reconstructions. This article explains the presence of Marine Isotopic Stage (MIS) 5e ages of corals sampled on multiple distinct terraces by retracing the eustatic history of this MIS and by demonstrating that it is not necessary to invoke a double SL peak.
Abstract
The fossil record of Quaternary reef systems, as expressed in uplifted regions by sequences of stacked terraces, has been extensively used either to understand their morphodynamics or to ...unravel sea level variations. Yet, because these two aspects are intimately linked, Quaternary reef analysis is often underdetermined because the analysis often focuses on single sequences, along one‐dimensional profiles. Here, we take advantage of the lateral variations of coral reef sequences by documenting the morphological variations of the reef sequence on Sumba Island. Near Tambolaka, northwest Sumba, we analysed a reef transect, topography, and associated sedimentological record to obtain a precise coral reef stratigraphy and geomorphic patterns that can be compared with the well‐documented eastern counterpart. In Tambolaka, the reef sequence displays four lower layers of bedded chalky limestone units with a weakly cemented sandy matrix, which we attribute to the Middle Miocene to Pliocene Wakabukak formation based on calcareous nannofossils and planktonic foraminifers. The uppermost layer is a calcretized reefal limestone unit with a well‐lithified sandy matrix, which we attribute to the Plio–Pleistocene reef sequence of the Kalianga formation. Seven marine terraces imprint the regional morphology, four of which we correlate with Marine Isotope Stage (MIS) 5e, MIS 7e, MIS 9e, and MIS 11c terraces of Cape Laundi, northeast Sumba. When scrutinized at the light of numerical models of reef development, these results indicate that the morphodynamics of reefal sequences is strongly impacted by the tectonic evolution. The geodynamic context sets both the extrinsic conditions of reef development, such as the morphology of the basement and hydrodynamics, and the intrinsic properties, in particular reef growth rate. While the morphodynamic evolution of the sequence is at first‐order representative of the interplay between uplift rates and sea level oscillations, the detailed assemblage of the reef units drastically varies along the coastline.
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