Refine
Has Fulltext
- no (43) (remove)
Year of publication
Document Type
- Article (43) (remove)
Language
- English (43)
Is part of the Bibliography
- yes (43)
Keywords
- Chile (4)
- Marine terraces (3)
- Maule earthquake (3)
- TerraceM (3)
- African Humid Period (2)
- Central Chile (2)
- Coastal uplift (2)
- GPS (2)
- LiDAR (2)
- Maule (2)
Institute
Newly acquired high-resolution bathymetric data (with 5 m and 2 m grid sizes) from the continental shelf off Concepcion (Chile), in combination with seismic reflection profiles, reveal a distinctly different evolution for the Biobio submarine canyon compared to that of one of its tributaries. Both canyons are incised into the shelf of the active margin. Whereas the inner shelf appears to be mantled with unconsolidated sediment, the outer shelf shows the influence of strong bottom currents that form drifts of loose sediment and transport -material into the Biobio submarine canyon and onto the continental slope.
The main stem of the Biobio Canyon is connected to the mouth of the Biobio River and currently provides a conduit for terrestrial sediment from the continental shelf to the deep seafloor. In contrast, the head of its tributary closest to the coast is located similar to 24 km offshore of the present-day coastline at 120 m water depth, and it is subject to passive sedimentation. However, canyon activity within the study area is interpreted to be controlled not only by the direct input of fluvial sediments into the canyon head facilitated by the river-mouth to canyon-head connection, but also by input from southward-directed bottom currents and possibly longshore drift. In addition, about 24 km offshore of the present-day coastline, the main stem of the Biobio Canyon has steep canyon walls next to sites of active tectonic deformation that are prone to wall failure. Mass-failure events may also foster turbidity currents and contribute to canyon feeding. In contrast, the tributary has less steep canyon walls with limited evidence of canyon-wall failure and is located down-system of bottom currents from the Biobio Canyon. It consequently receives neither fluvial nor longshore sediments. Therefore, the canyon's connectivity to fluvial or longshore sediment delivery pathways is affected by the distance of the canyon head from the coastline and the orientation of the canyon axis relative to the direction of bottom currents.
The ability of a submarine canyon to act as an active conduit for large quantities of terrestrial sediment toward the deep sea during sea-level highstands may be controlled by several different conditions simultaneously. These include bottom current direction, structural deformation of the seafloor affecting canyon location and orientation as well as canyon-wall failure, shelf gradient and associated distance from the canyon head to the coast, and fluvial networks. The complex interplay between these factors may vary even within an individual canyon system, resulting in distinct levels of canyon activity on a regional scale.
Major earthquakes ( M > 8) have repeatedly ruptured the Nazca-South America plate interface of south-central Chile involving meter scale land-level changes. Earthquake recurrence intervals, however, extending beyond limited historical records are virtually unknown, but would provide crucial data on the tectonic behavior of forearcs. We analyzed the spatiotemporal pattern of Holocene earthquakes on Santa Maria Island (SMI; 37 degrees S), located 20 km off the Chilean coast and approximately 70 km east of the trench. SMI hosts a minimum of 21 uplifted beach berms, of which a subset were dated to calculate a mean uplift rate of 2.3 +/- 0.2 m/ky and a tilting rate of 0.022 +/- 0.002 degrees/ky. The inferred recurrence interval of strandline-forming earthquakes is similar to 180 years. Combining coseismic uplift and aseismic subsidence during an earthquake cycle, the net gain in strandline elevation in this environment is similar to 0.4 m per event
Geomorphic strain markers accumulating the effects of many earthquake cycles help to constrain the mechanical behaviour of continental rift systems as well as the related seismic hazards. In the Corinth Rift (Greece), the unique record of onshore and offshore markers of Pleistocene similar to 100-ka climate cycles provides an outstanding possibility to constrain rift mechanics over a range of timescales. Here we use high-resolution topography to analyse the 3D geometry of a sequence of Pleistocene emerged marine terraces associated with flexural rift-flank uplift. We integrate this onshore dataset with offshore seismic data to provide a synoptic view of the flexural deformation across the rift. This allows us to derive an average slip rate of 4.5-9.0 mm.yr(-1) on the master fault over the past similar to 610 ka and an uplift/ subsidence ratio of 1:1.1-2.4. We reproduce the observed flexure patterns, using 3 and 5-layered lithospheric scale finite element models. Modelling results imply that the observed elastic flexure is produced by coseismic slip along 40-60 degrees planar normal faults in the elastic upper crust, followed by postseismic viscous relaxation occurring within the basal lower crust or upper mantle. We suggest that such a mechanism may typify rapid localised extension of continental lithosphere.
The Gofa Province and the Chew Bahir Basin of southern Ethiopia constitute tectonically active regions, where the Southern Main Ethiopian Rift converges with the Northern Kenya Rift through a wide zone of extensional deformation with several north to northeast-trending, left-stepping en-e & PRIME;chelon basins. This sector of the Southern Main Ethiopian Rift is characterized by a semi-arid climate and a largely uniform lithology, and thus provides ideal conditions for studying the different parameters that define the tectonic and geomorphic features of this complex kinematic transfer zone. In this study, the degree of tectonic activity, spatiotemporal variations in extension, and the nature of kinematic linkage between different fault systems of the transfer zone are constrained by detailed quantitative geomorphic analysis of river catchments and focused field work. We analyzed fluvial and landscape morphometric characteristics in combination with structural, seismicity, and climatic data to better evaluate the tectono-geomorphic history of this transfer zone. Our data reveal significant north-south variations in the degree of extension from the Sawula Basin in the north (mature) to the Chew Bahir Basin in the south (juvenile). First, normalized channel-steepness indices and the spatial arrangement of knickpoints in footwall-draining streams suggest a gradual, southward shift in extensional deformation and recent tectonic activity. Second, based on 1-k(m) radius local relief and mean-hillslope maximum values that are consistent with ksn anomalies, we confirm strain localization within zones of fault interaction. Third, morphometric indices such as hypsometry, basin asymmetry factor, and valley floor width to valley height ratio also indicate a north to south gradient in tectonic activity, highlighting the importance of such a wide transfer zone with diffuse extension linking different rift segments during the break-up of continental crust.
We observed vertically displaced coastal and river markers after the 27 February 2010 Chilean earthquake [moment magnitude (Mw) 8.8]. Land-level changes range between 2.5 and -1 meters, evident along an ~500-kilometers- long segment identified here as the maximum length of coseismic rupture. A hinge line located 120 kilometers from the trench separates uplifted areas, to the west, from subsided regions. A simple elastic dislocation model fits these observations well; model parameters give a similar seismic moment to seismological estimates and suggest that most of the plate convergence since the 1835 great earthquake was elastically stored and then released during this event.
Tectonically active coasts are dynamic environments characterized by the presence of multiple marine terraces formed by the combined effects of wave erosion, tectonic uplift, and sea-level oscillations at glacialcycle timescales. Well-preserved erosional terraces from the last interglacial sea-level highstand are ideal marker horizons for reconstructing past sea-level positions and calculating vertical displacement rates. We carried out an almost continuous mapping of the last interglacial marine terrace along similar to 5000 km of the western coast of South America between 1 degrees N and 40 degrees S. We used quantitatively replicable approaches constrained by published terrace-age estimates to ultimately compare elevations and patterns of uplifted terraces with tectonic and climatic parameters in order to evaluate the controlling mechanisms for the formation and preservation of marine terraces and crustal deformation. Uncertainties were estimated on the basis of measurement errors and the distance from referencing points. Overall, our results indicate a median elevation of 30.1 m, which would imply a median uplift rate of 0.22 m kyr(-1) averaged over the past similar to 125 kyr. The patterns of terrace elevation and uplift rate display high-amplitude (similar to 100-200 m) and long-wavelength (similar to 10(2) km) structures at the Manta Peninsula (Ecuador), the San Juan de Marcona area (central Peru), and the Arauco Peninsula (south-central Chile). Medium-wavelength structures occur at the Mejillones Peninsula and Topocalma in Chile, while short-wavelength (< 10 km) features are for instance located near Los Vilos, Valparaiso, and Carranza, Chile. We interpret the long-wavelength deformation to be controlled by deep-seated processes at the plate interface such as the subduction of major bathymetric anomalies like the Nazca and Carnegie ridges. In contrast, short-wavelength deformation may be primarily controlled by sources in the upper plate such as crustal faulting, which, however, may also be associated with the subduction of topographically less pronounced bathymetric anomalies. Latitudinal differences in climate additionally control the formation and preservation of marine terraces. Based on our synopsis we propose that increasing wave height and tidal range result in enhanced erosion and morphologically well-defined marine terraces in south-central Chile. Our study emphasizes the importance of using systematic measurements and uniform, quantitative methodologies to characterize and correctly interpret marine terraces at regional scales, especially if they are used to unravel the tectonic and climatic forcing mechanisms of their formation. This database is an integral part of the World Atlas of Last Interglacial Shorelines (WALIS), published online at https://doi.org/10.5281/zenodo.4309748 (Freisleben et al., 2020).
The 'wet' early to mid-Holocene of tropical Africa, with its enhanced monsoon, ended with an abrupt shift toward drier conditions and was ultimately replaced by a drier climate that has persisted until the present day. The forcing mechanisms, the timing, and the spatial extent of this major climatic transition are not well understood and remain the subject of ongoing research. We have used a detailed palaeo-shoreline record from Lake Turkana (Kenya) to decipher and characterise this marked climatic transition in East Africa. We present a high-precision survey of well-preserved palaeo-shorelines, new radiocarbon ages from shoreline deposits, and oxygen-isotope measurements on freshwater mollusk shells to elucidate the Holocene moisture history from former lake water-levels in this climatically sensitive region. In combination with previously published data our study shows that during the early Holocene the water-level in Lake Turkana was high and the lake overflowed temporarily into the White Nile drainage system. During the mid-Holocene (similar to 5270 +/- 300 cal. yr BP), however, the lake water-level fell by similar to 50 m, coeval with major episodes of aridity on the African continent. A comparison between palaeo-hydrological and archaeological data from the Turkana Basin suggests that the mid-Holocene climatic transition was associated with fundamental changes in prehistoric cultures, highlighting the significance of natural climate variability and associated periods of protracted drought as major environmental stress factors affecting human occupation in the East African Rift System. (
The African Humid Period (AHP) between similar to 15 and 5.5 cal. kyr BP caused major environmental change in East Africa, including filling of the Suguta Valley in the northern Kenya Rift with an extensive (similar to 2150 km(2)), deep (similar to 300 m) lake. Interfingering fluvio-lacustrine deposits of the Baragoi paleo-delta provide insights into the lake-level history and how erosion rates changed during this time, as revealed by delta-volume estimates and the concentration of cosmogenic Be-10 in fluvial sand. Erosion rates derived from delta-volume estimates range from 0.019 to 0.03 mm yr(-1). Be-10-derived paleo-erosion rates at similar to 11.8 cal. kyr BP ranged from 0.035 to 0.086 mm yr(-1), and were 2.7 to 6.6 times faster than at present. In contrast, at similar to 8.7 cal. kyr BP, erosion rates were only 1.8 times faster than at present. Because Be-10-derived erosion rates integrate over several millennia; we modeled the erosion-rate history that best explains the 10Be data using established non-linear equations that describe in situ cosmogenic isotope production and decay. Two models with different temporal constraints (15-6.7 and 12-6.7 kyr) suggest erosion rates that were 25 to 300 times higher than the initial erosion rate (pre-delta formation). That pulse of high erosion rates was short (similar to 4 kyr or less) and must have been followed by a rapid decrease in rates while climate remained humid to reach the modern Be-10-based erosion rate of,similar to 0.013 mm yr(-1). Our simulations also flag the two highest Be-10-derived erosion rates at 11.8 kyr BP related to nonuniform catchment erosion. These changes in erosion rates and processes during the AHP may reflect a strong increase in precipitation, runoff, and erosivity at the arid-to-humid transition either at 15 or similar to 12 cal. kyr BP, before the landscape stabilized again, possibly due to increased soil production and denser vegetation.
The subduction of bathymetric anomalies at convergent margins can profoundly affect subduction dynamics, magmatism, and the structural and geomorphic evolution of the overriding plate. The Northern Patagonian Icefield (NPI) is located east of the Chile Triple Junction at similar to 47 degrees S, where the Chile Rise spreading center collides with South America. This region is characterized by an abrupt increase in summit elevations and relief that has been controversially debated in the context of geodynamic versus glacial erosion effects on topography. Here we present geomorphic, thermochronological, and structural data that document neotectonic activity along hitherto unrecognized faults along the flanks of the NPI. New apatite (U-Th)/He bedrock cooling ages suggest faulting since 2-3 Ma. We infer the northward translation of an similar to 140 km long fore-arc sliver-the NPI block-results from enhanced partitioning of oblique plate convergence due to the closely spaced collision of three successive segments of the Chile Rise. In this model, greater uplift occurs in the hanging wall of the Exploradores thrust at the northern leading edge of the NPI block, whereas the Cachet and Liquine-Ofqui dextral faults decouple the NPI block along its eastern and western flanks, respectively. Localized extension possibly occurs at its southern trailing edge along normal faults associated with margin-parallel extension, tectonic subsidence, and lower elevations along the Andean crest line. Our neotectonic model provides a novel explanation for the abrupt topographic variations inland of the Chile Triple Junction and emphasizes the fundamental effects of local tectonics on exhumation and topographic patterns in this glaciated landscape.