Soil Chemistry and Clay Mineralogy of an Alluvial Chronosequence from the North Carolina Sandhills of the Upper Coastal Plain, USA

Temporal changes in soil development were assessed on fluvial terraces of the Little River in the upper Coastal Plain of North Carolina. We examined five profiles from each of six surfaces spanning about 100,000 years. Soil-age relationships were evaluated with inter-surface clay mineral comparisons and regression of chemical properties versus previously reported optically-stimulated luminescence ages using the most developed subsoil horizon per profile. Bases to alumina (Bases/Al2O3) ratios have negative correlations with age, whereas dithionite-Fe (FeD) concentrations are positively correlated with time and differentiate floodplain (<200 yr BP) from terrace (≥10 ± 2 ka) soils and T4 pedons (75 ± 10 ka) from younger (T1-T3b, 10 ± 2–55 ± 15 ka) and older (T5b, 94 ± 16 ka) profiles. Entisols develop into Ultisols with exponentially decreasing Bases/Al2O3 ratios, reflecting rapid weatherable mineral depletion and alumina enrichment during argillic horizon development in the first 13–21 kyr of pedogenesis. Increasing FeD represents transformation and illuviation of free Fe inherited from parent sediments. Within ~80–110 kyr, a mixed clay mineral assemblage becomes dominated by kaolinite and gibbsite. Argillic horizons form by illuviation, secondary mineral transformations, and potentially, a bioturbation-translocation mechanism, in which clays distributed within generally sandy deposits are transported to surface horizons by ants and termites and later illuviated to subsoils. T5b profiles have FeD concentrations similar to, and gibbsite abundances greater than, those of pedons on 0.6–1.6 Ma terraces along Coastal Plain rivers that also drain the Appalachian Piedmont. This is likely because the greater permeability and lower weatherable mineral contents of sandy, Coastal Plain-sourced Little River alluvium favor more rapid weathering, gibbsite formation, and Fe translocation than the finer-grained, mineralogically mixed sediments of Piedmont-draining rivers. Therefore, recognizing provenance-related textural and mineralogical distinctions is crucial for evaluating regional chronosequences.

Rapid response of silicate weathering rates to climate change in the Himalaya

Chemical weathering of continental rocks plays a central role in regulating the carbon cycle and the Earth’s climate (Walker et al., 1981; Berner et al., 1983), accounting for nearly half the consumption of atmospheric carbon dioxide globally (Beaulieu et al., 2012). However, the role of climate variability on chemical weathering is still strongly debated. Here we focus on the Himalayan range and use the lithium isotopic composition of clays in fluvial terraces to show a tight coupling between climate change and chemical weathering over the past 40 ka. Between 25 and 10 ka ago, weathering rates decrease despite temperature increase and monsoon intensification. This suggests that at this timescale, temperature plays a secondary role compared to runoff and physical erosion, which inhibit chemical weathering by accel-erating sediment transport and act as fundamental controls in determining the feedback between chemical weathering and atmospheric carbon dioxide.

Late Quaternary Tectonics along the Peri-Adriatic Sector of the Apenninic Chain (Central-Southern Italy): Inspecting Active Shortening through Topographic Relief and Fluvial Network Analyses

Active compressional tectonics along the outer front of the Apenninic-Maghrebian chain (Italy) is well documented along the northern and central segments and in Sicily. On the other hand, the Southern Apenninic Outer Front (SAOF) orogenic activity is well established only until the Lower-Middle Pleistocene. We address the hypothesis of its subsequent late Quaternary activity in central-southern Italy (Abruzzo and Molise regions). We integrated topographic and fluvial network analyses along with morphotectonic investigation of fluvial terraces to identify evidence of differential rock uplift. We compared the results with the main geolithological units, known structural elements, and long-term deformation history from seismic line interpretation. We found variable evidence suggesting localized rock uplift in the Abruzzo region along the SAOF (Abruzzo Citeriore Basal Thrust segment) and inward structures on its hanging wall (Casoli-Bomba high), as well as along part of the Struttura Costiera thrust. Middle-to-Late Pleistocene deformation is constrained by terrace tilting and disruption along the Pescara river. Localized shortening along segments of the Apenninic Outer Front could explain the observed pattern of anomalies which is difficult to explain with long-wavelength regional uplift alone. Our reconstruction is consistent with the long-term deformation of the area and agrees with its seismotectonic setting. Despite the low deformation rate context and the peculiar geological setting which challenges the interpretation of the topographic and geomorphic signals, this study compels reconsideration, in terms of seismic hazard assessment, of the existence of late Quaternary active thrusting in central-southern Italy.

Neotectonics and Paleoseismicity of a Major Junction Between Two Strands of the Awatere Fault, South Island, New Zealand

<p><b>In northeastern South Island, New Zealand, obliquely-convergent relativemotion between the Pacific and Australian plates is accommodated by slip acrossactive dextral-oblique faults in the Marlborough fault system. The Awatere Fault isone of four principal active strike-slip faults within this plate boundary zone, andincludes two sections (the eastern and Molesworth sections) that have differentstrikes and that join across a complex fault junction in the upper Awatere Valley.</b></p> <p>Detailed mapping of the fault traces and measurement of 97 geomorphicdisplacements along the Awatere Fault in the vicinity of the fault junction show thatthe eastern and Molesworth sections of the fault intersect one another at a low angle(10-15º), at the eastern end of an internally faulted, elongate, ~15 km long and up to3 km wide fault wedge or sliver. The region between the fault sections is split by aseries of discontinuous, en-echelon scarps that are oriented from ~10º to 20-30ºclockwise from the principal fault sections. Based on other observations ofdiscontinuities in strike-slip earthquake ruptures around the globe, this low-angleintersection geometry suggests that the junction between these fault sections may notact as a significant barrier to earthquake rupture propagation. This interpretation ofthe mechanical significance of the fault junction to earthquake ruptures is counter toprevious suggestions, but is supported by new paleoseismic data from fourpaleoseismic trenches excavated on each side of the junction. In a new paleoseismictrench on the Molesworth section at Saxton River, 18 km to the west of the junction,up to ten surface-rupturing events in the past ~15 ka are recognised from 12radiocarbon ages and 1 optically stimulated luminescence age. In two new trencheson the eastern section near to Upcot Saddle, 12 km northeast of the fault junction,five events took place in the past 5.5 ka, based on 21 radiocarbon ages. Thischronology from Upcot Saddle is combined with data from two previous trencheslocated ~55 km to the northeast at Lake Jasper, to infer nine events on the easternsection since 8330-8610 cal. years B.P. These well-dated events on the easternsection are compared to those on the Molesworth section to the west of the faultjunction. At 95% confidence, five events on both sections have occurred withstatistical contemporaneity since ~6 ka B.P. These five events may have rupturedboth the eastern and Molesworth sections simultaneously, in accordance with the interpretation that the fault section junction does not arrest rupture propagation.</p> <p>Alternatively, these events may have been separate earthquakes that occurred withinthe statistical resolution provided by radiocarbon dating.</p> <p>The most recent event to rupture the eastern section was the Mw ~7.5 1848Marlborough earthquake. The coseismic slip distribution and maximum traceablelength of this surface rupture are calculated from the magnitude and distribution ofsmall, metre-scale geomorphic displacements attributable to this earthquake. Thesedata suggest this event ruptured >100-110 km of the eastern section, with meansurface displacement of 5.3 ±1.6 m. Based on these parameters, the momentmagnitude of this earthquake would be Mw 7.4-7.7. This magnitude estimate isindistinguishable from previous calculations that were based on attenuation ofshaking intensity isoseismals that were assigned from contemporary historicalaccounts of that earthquake. On the basis of similar rupture lengths and coseismicdisplacements, it is inferred that the penultimate event had a similar momentmagnitude to the 1848 earthquake.</p> <p>Horizontal displacement of a flight of 6 fluvial terraces at Saxton River by theMolesworth section of the Awatere Fault is constrained to have occurred at a nearconstantrate of 5.5 ±1.5 mm/a since ~15 ka B.P. These rates are based on two newoptically stimulated luminescence ages for the highest terrace treads of 14.5 ±1.5 and6.69 ±0.74 ka B.P. These rates are indistinguishable from recent strike-slip rateestimates for the eastern section of 5.6 ±1.1 and 6 ±2 mm/a. Comparing themagnitudes and ages of the terrace riser displacements at Saxton River to the timingof paleoearthquakes on the Molesworth section implies a mean per-eventdisplacement of 4.4 ±0.2 m since ~15 ka. The new terrace ages also record twoperiods of aggradation that post-date the Last Glacial Maximum.</p>

Neotectonics and Paleoseismicity of a Major Junction Between Two Strands of the Awatere Fault, South Island, New Zealand

<p><b>In northeastern South Island, New Zealand, obliquely-convergent relativemotion between the Pacific and Australian plates is accommodated by slip acrossactive dextral-oblique faults in the Marlborough fault system. The Awatere Fault isone of four principal active strike-slip faults within this plate boundary zone, andincludes two sections (the eastern and Molesworth sections) that have differentstrikes and that join across a complex fault junction in the upper Awatere Valley.</b></p> <p>Detailed mapping of the fault traces and measurement of 97 geomorphicdisplacements along the Awatere Fault in the vicinity of the fault junction show thatthe eastern and Molesworth sections of the fault intersect one another at a low angle(10-15º), at the eastern end of an internally faulted, elongate, ~15 km long and up to3 km wide fault wedge or sliver. The region between the fault sections is split by aseries of discontinuous, en-echelon scarps that are oriented from ~10º to 20-30ºclockwise from the principal fault sections. Based on other observations ofdiscontinuities in strike-slip earthquake ruptures around the globe, this low-angleintersection geometry suggests that the junction between these fault sections may notact as a significant barrier to earthquake rupture propagation. This interpretation ofthe mechanical significance of the fault junction to earthquake ruptures is counter toprevious suggestions, but is supported by new paleoseismic data from fourpaleoseismic trenches excavated on each side of the junction. In a new paleoseismictrench on the Molesworth section at Saxton River, 18 km to the west of the junction,up to ten surface-rupturing events in the past ~15 ka are recognised from 12radiocarbon ages and 1 optically stimulated luminescence age. In two new trencheson the eastern section near to Upcot Saddle, 12 km northeast of the fault junction,five events took place in the past 5.5 ka, based on 21 radiocarbon ages. Thischronology from Upcot Saddle is combined with data from two previous trencheslocated ~55 km to the northeast at Lake Jasper, to infer nine events on the easternsection since 8330-8610 cal. years B.P. These well-dated events on the easternsection are compared to those on the Molesworth section to the west of the faultjunction. At 95% confidence, five events on both sections have occurred withstatistical contemporaneity since ~6 ka B.P. These five events may have rupturedboth the eastern and Molesworth sections simultaneously, in accordance with the interpretation that the fault section junction does not arrest rupture propagation.</p> <p>Alternatively, these events may have been separate earthquakes that occurred withinthe statistical resolution provided by radiocarbon dating.</p> <p>The most recent event to rupture the eastern section was the Mw ~7.5 1848Marlborough earthquake. The coseismic slip distribution and maximum traceablelength of this surface rupture are calculated from the magnitude and distribution ofsmall, metre-scale geomorphic displacements attributable to this earthquake. Thesedata suggest this event ruptured >100-110 km of the eastern section, with meansurface displacement of 5.3 ±1.6 m. Based on these parameters, the momentmagnitude of this earthquake would be Mw 7.4-7.7. This magnitude estimate isindistinguishable from previous calculations that were based on attenuation ofshaking intensity isoseismals that were assigned from contemporary historicalaccounts of that earthquake. On the basis of similar rupture lengths and coseismicdisplacements, it is inferred that the penultimate event had a similar momentmagnitude to the 1848 earthquake.</p> <p>Horizontal displacement of a flight of 6 fluvial terraces at Saxton River by theMolesworth section of the Awatere Fault is constrained to have occurred at a nearconstantrate of 5.5 ±1.5 mm/a since ~15 ka B.P. These rates are based on two newoptically stimulated luminescence ages for the highest terrace treads of 14.5 ±1.5 and6.69 ±0.74 ka B.P. These rates are indistinguishable from recent strike-slip rateestimates for the eastern section of 5.6 ±1.1 and 6 ±2 mm/a. Comparing themagnitudes and ages of the terrace riser displacements at Saxton River to the timingof paleoearthquakes on the Molesworth section implies a mean per-eventdisplacement of 4.4 ±0.2 m since ~15 ka. The new terrace ages also record twoperiods of aggradation that post-date the Last Glacial Maximum.</p>

Assessing the Prediction Accuracy of Geomorphon-Based Automated Landform Classification: An Example from the Ionian Coastal Belt of Southern Italy

Automatic procedures for landform extraction is a growing research field but extensive quantitative studies of the prediction accuracy of Automatic Landform Classification (ACL) based on a direct comparison with geomorphological maps are rather limited. In this work, we test the accuracy of an algorithm of automatic landform classification on a large sector of the Ionian coast of the southern Italian belt through a quantitative comparison with a detailed geomorphological map. Automatic landform classification was performed by using an algorithm based on the individuation of basic landform classes named geomorphons. Spatial overlay between the main mapped landforms deriving from traditional geomorphological analysis and the automatic landform classification results highlighted a satisfactory percentage of accuracy (higher than 70%) of the geomorphon-based method for the coastal plain area and drainage network. The percentage of accuracy decreased by about 20–30% for marine and fluvial terraces, while the overall accuracy of the ACL map is 69%. Our results suggest that geomorphon-based classification could represent a basic and robust tool to recognize the main geomorphological elements of landscape at a large scale, which can be useful for the advanced steps of geomorphological mapping such as genetic interpretation of landforms and detailed delineation of complex and composite geomorphic elements.

The Paleomorpholigic Conditions of the Formation of the Settlement of Shitkino (Northwest Russia)

Для многих раннесредневековых памятников Северо-Запада Европейской России палеогеографические условия реконструированы недостаточно. При этом географический контекст развития поселений играет важную роль в исторической и экономической жизни людей Средневековья на локальном уровне. Археологический памятник поселение Шниткино расположен в бассейне Западной Двины на западном макросклоне Валдайской возвышенности. Изучаемое поселение находится на берегу озера Шнидкино, через которое насквозь протекает река Торопа. Используя геолого-геоморфологические методы, авторы статьи описали строение озерной террасы и озерно-речной поймы, в которых был найден культурный слой IX–X веков и отдельные археологические артефакты. Седиментационные архивы торфа, озерных, аллювиальных и склоновых отложений, продатированные радиоуглеродным методом, позволили оценить, насколько рельеф раннего Средневековья отличался от современного, и определить возможную функциональность территории во время существования поселения. Выявленные стабильность берега и аккумулятивная динамика озерно-речной системы свидетельствуют о том, что за последние несколько тысяч лет форма берега почти не изменилась. Речные и озерные террасы с похожей динамикой, обнаруживаемые в бассейне реки Торопы, считаются наиболее привлекательными позициями для поселенцев раннего Средневековья. The palaeomorphology of many early medieval monuments in Northwest Russia has not been reconstructed yet. In historical and economic perspective, the geographical location has a great impact on settlement formation and affects people’s lives significantly. The settlement of Shitkino is an archaeological monument situated in the basin of the Western Dvina at the western slope of the Valdai Hills. The settlement of Shitkino is located at the shore of Shnidkino lake, which is traversed by the Toropa River. The authors of the article employ geological and geomorphological analyses to explore the floodplain and its fluvial terraces, to make archaeological finds and to gain evidence of the events of the 9th–10th centuries. The method of radiocarbon dating enabled the scientists to estimate the age of peat sediments, fluvial and slope deposits, to estimate the degree of relief transformation and to tentatively assess the extent of the functionality of the land in medieval times. The accumulated data, such as the structural stability of the shore and the dynamics of the river-lake system show that during the recent thousands of years the shores of the lake have been only insignificantly transformed. It is believed that in the early middle ages people preferred to settle in the basin of the Toropa River.

Morphoneotectonics of the Abruzzo Periadriatic Area (Central Italy): Morphometric Analysis and Morphological Evidence of Tectonics Features

Drainage basin-scale morphometric analysis and morphological evidence of tectonics represent helpful tools to evaluate and investigate morphoneotectonic processes in tectonically active regions. In this perspective, we applied an integrated analysis to the Abruzzo Periadriatic Area, between the Tronto and Sinello rivers (Central Italy). It involved morphometric analysis, structural geomorphological field mapping, and detailed analysis of fluvial terraces. Geomorphic indexes and markers (e.g., Irta, SL index, ksn, and knickpoints) were used in this study to detect the response of landscapes to drainage systems’ unsteadiness and tectonic deformation processes, possibly induced by the ongoing activity of the buried tectonic structures. Furthermore, the investigation of morphological field evidence of tectonics, integrated with the analysis of fluvial terraces’ spatial and temporal arrangement, was performed to assign relative, geomorphologically-based, age constraints of the landscape evolution. The resulting data allowed us to define domains affected by different morphostructural and morphoneotectonic processes, related to the impact and ongoing activity of the five detected families of structural elements (S1, F1, F2, F3, and F4), mainly characterized by compressive, extensional, and transtensive kinematics. Finally, this study could represent a scientific basis for integrating morphometric, fluvial, and tectonic geomorphology analysis to better define the main phases of the landscape evolution and the impact of morphoneotectonic processes on fluvial environments in uplifting piedmont areas.

Integrated geological and geophysical study of the Tagil river valley morphology in its middle course

Relevance. Integrated geological and geophysical studies of a bridge in the Makhnevo village area are considered in the frame of the Urals eastern slope geology. Research objective is to study the lithology of the underlying part of the valley floor, determine soil physical and mechanical characteristics, and study a complex of fluvial terraces. Results. Relief elevations across the river valley have been studied, and four main fluvial terrace levels typical of the Urals eastern slope have been identified. An unstable section of the streambed with a canyonshaped valley above the neotectonic unwarping zone has been identified. The geological section of the river’s floodplain and streambed were studied based on geological and geophysical data. A change in the physical properties of glauconite sandstones and clays of Paleogene age in the recent underlying part of the river valley has been established. Layers of sand and glauconite sandstone that can be developed have been found at the new bridge site near the existing sand and gravel deposit. Conclusions. A complex of terraces of the Tagil river valley in its middle course is typical for the Urals eastern slope. The paleovalley is cut into a Paleogene glauconite sandstone layer. In the underlying part of the valley floor, changes in sandstones and clays physical properties have been recorded, and the presence of hypogene minerals was revealed. These are the signs of possible neotectonic processes in the series of the Cenozoic and Quaternary deposits.