Relict Surfaces Research Articles

Origin and characteristics of ancient organic matter from a high‐elevation Lateglacial Alpine Nunatak (NW Italy)

AbstractIn high‐mountain areas, Pleistocene glaciations and erosion‐related processes erased most of the pre‐existing landforms and soils. However, on scattered stable surfaces, ancient soils can be locally preserved for long periods, retaining valuable palaeoenvironmental information. Such relict surfaces survived during glaciations either through coverage by non‐erosive, cold‐based, ice or as nunataks. Thus, soils preserved on such surfaces retain an excellent pedo‐signature of different specific past climatic/environmental conditions. In this study, we performed a detailed chemical characterisation of the organic material found in palaeosols, discovered inside periglacial features on a high‐elevation Lateglacial Alpine Nunatak (Stolenberg Plateau), above 3000 m a.s.l. (NW Italian Alps). The soil organic matter (OM) was separated into different pools by means of density fractionation, in order to separate the more fresh/unaltered free and occluded organic material (Light Fraction) from the stable fraction chemically bound to the mineral phase (Mineral Organic Matter—MOM). To better characterise the MOM fraction, this was further subjected to chemical fractionation, in order to separate the alkali‐extractable OM (ext‐MOM) from the fraction intimately bound to minerals. The obtained fractions were then characterised by chemical and 13C nuclear magnetic resonance (NMR), and Fourier Transform Infrared (FT‐IR) spectroscopy. The results indicated that the largest part (>90%) of organic carbon was stored in the stable MOM pool, characterised by a high degree of decomposition and consisting mainly of paraffinic substances, such as lipids and waxes (37–50%), cellulose and hemicellulose (29–37%). The OM likely originated from autochthonous, well‐adapted, ancient alpine vegetation (alpine tundra) that grew on the Plateau during warm climatic phases since the end of the Last Glacial Maximum (LGM). These results further strengthen the palaeoenvironmental reconstruction at the Stolenberg Plateau, which represents a Lateglacial Alpine Nunatak, and has acted as biological refugia (at least) since the end of the LGM.Highlights The origin and composition of ancient organic matter from a high‐elevation Alpine Nunatak were uncovered. More than 90% of organic carbon was stored in the stable mineral organic matter (MOM) pool. Based on NMR and FT‐IR spectra the MOM fraction consisted of paraffinic substances (37–50%), cellulose and hemicellulose (29–37%). The organic matter originated from ancient alpine tundra that developed on the Nunatak since the end of the Last Glacial Maximum.

Stylolitization structures as possible migration routes of organic matter in microbial genesis sedimentary deposites

It was studied that the possibilities of preservation, migration and transformation of organic matter (OM) in rocks of Precambrian age, the textural and structural characteristics of which are inextricably linked with the physiological characteristics of microorganisms, and the role of stylolithization structures in these processes. The similarity of modern stromatolites with ancient ones in the mechanism of deposition of carbonate micrite and the formation of porous frameworks allowed us to establish that a significant amount OM of cyanobacterial lamins could be preserved after the buildings were immersed in the sedimentation basin and transformed into sedimentary strata. OM was concentrated on numerous relict surfaces between micrite carbonate secretions deposited by microorganisms during life. Subsequent transformations were expressed in the recrystallization of the carbonate substance, accompanied by a significant loss of primary voidness, oustion and redistribution of OM, as well as clay material deposited from the suspension. During detailed petrographic studies, it was observed how clay-organic material (COM), displaced by recrystallization, concentrated on the crystal faces and in intercrystalline pores in certain areas and composed numerous lenticular layers in contact with each other, forming surfaces of complex configurations - rudimentary microstylolites. According to the authors, recrystallization is one of the main catalysts of stillolithization processes, because it creates mineral aggregates in which the pressure on the COM enclosed between them varies greatly at different points. This contributes to the occurrence of the phenomenon of differentiated dissolution under pressure, more intensive transformation of OM in areas with maximum load and, as a consequence, excessive release of CO, which in turn leads to saturation of pore solutions with carbon dioxide and initiation of chemical dissolution. Probably, this is how stylolites and associated fractured voidness are formed in stromatolites, which is available for the migration of OM.

Inverted channel variations identified on a distal portion of a bajada in the central Atacama Desert, Chile

In deserts, the interplay between occasional fluvial events and persistent aeolian erosion can form composite modern and relict surfaces, especially on the distal portion of alluvial fans. There, relief inversion of alluvial deposits by differential erosion can form longitudinal ridges. We identified two distinct ridge types formed by relief inversion on converging alluvial fans in the hyperarid Chilean Atacama Desert. Although they are co-located and similar in scale, the ridge types have different ages and formation histories that apparently correspond to minor paleoclimate variations. Gravel-armored ridges are remnants of deflated alluvial deposits with a bimodal sediment distribution (gravel and sand) dated to a minor pluvial phase at the end of the Late Pleistocene (~12 kyr). In contrast, younger (~9 kyr) sulfate-capped ridges formed during a minor arid phase with evaporite deposition in a pre-existing channel that armored the underlying deposits. Collectively, inverted channels at Salar de Llamara resulted from multiple episodes of surface overland flow and standing water spanning several thousand years. Based on ridge relief and age, the minimum long-term deflation rate is 0.1–0.2 m/kyr, driven primarily by wind erosion. This case study is an example of the equifinality concept whereby different processes lead to similar landforms. The complex history of the two ridge types can only be generally constrained in remotely sensed data. In situ observations are required to discern the specifics of the aqueous history, including the flow type, magnitude, sequence, and paleoenvironment. These findings have relevance for interpreting similar landforms on Mars.

Contrasting exhumation histories and relief development within the Three Rivers Region (south-east Tibet)

Abstract. The Three Rivers Region in south-east Tibet represents a transition between the strongly deformed zone around the Eastern Himalayan Syntaxis (EHS) and the less deformed south-east Tibetan Plateau margin in Yunnan and Sichuan. In this study, we compile and model published thermochronometric ages for two massifs facing each other across the Mekong River in the core of the Three Rivers Region (TRR), using the thermo-kinematic code Pecube to constrain their exhumation and relief history. Modelling results for the low-relief (< 600 m), moderate-elevation (∼ 4500 m) Baima Xueshan massif, east of the Mekong River, suggest regional rock uplift at a rate of 0.25 km/Myr since ∼ 10 Ma, following slow exhumation at a rate of 0.01 km/Myr since at least 22 Ma. Estimated Mekong River incision accounts for 30 % of the total exhumation since 10 Ma. We interpret exhumation of the massif as a response to regional uplift around the EHS and conclude that the low relief of the massif was acquired at high elevation (> 4500 m), probably in part due to glacial “buzzsaw-like” processes active at such high elevation and particularly efficient during Quaternary glaciations. Exhumation of the Baima Xueshan is significantly higher (2.5 km since ∼ 10 Ma) than that estimated for the most emblematic low-relief “relict” surfaces of eastern Tibet, where apatite (U–Th) / He (AHe) ages > 50 Ma imply only a few hundreds of metres of exhumation since the onset of the India–Asia collision. The low-relief Baima Xueshan massif, with its younger AHe ages (< 50 Ma) that record significant rock uplift and exhumation, thus cannot be classified as a relict surface. Modelling results for the high-relief, high-elevation Kawagebo massif, to the west of the Mekong, imply a similar contribution of Mekong River incision (25 %) to exhumation but much stronger local rock uplift at a rate of 0.45 km/Myr since at least 10 Ma, accelerating to 1.86 km/Myr since 1.6 Ma. We show that the thermochronometric ages are best reproduced by a model of rock uplift on a kinked westward-dipping thrust striking roughly parallel to the Mekong River, with a steep shallow segment flattening out at depth. Thus, the strong differences in elevation and relief of two massifs are linked to variable exhumation histories due to strongly differing tectonic imprint.

Englacial drainage structures in an East Antarctic outlet glacier

AbstractGround-penetrating radar data acquired in the 2016/17 austral summer on Sørsdal Glacier, East Antarctica, provide evidence for meltwater lenses within porous surface ice that are conceptually similar to firn aquifers observed on the Greenland Ice Sheet and the Arctic and Alpine glaciers. These englacial water bodies are associated with a dry relict surface basin and consistent with perennial drainage into an interconnected englacial drainage system, which may explain a large englacial outburst flood observed in satellite imagery in the early 2016/17 melt season. Our observations indicate the rarely-documented presence of an englacial hydrological system in Antarctica, with implications for the storage and routing of surface meltwater. Future work should ascertain the spatial prevalence of such systems around the Antarctic coastline, and identify the degree of surface runoff redistribution and storage in the near surface, to quantify their impact on surface mass balance.

Arrested development: Erosional equilibrium in the southern Sierra Nevada, California, maintained by feedbacks between channel incision and hillslope sediment production

Tributary creeks of the southern Sierra Nevada have pronounced knickpoints that separate the landscape into an alternating sequence of gently sloped treads and steeply sloped risers. These knickpoints and the surrounding “stepped topography” suggest that the landscape is still responding to Pleistocene changes in base level on main-stem rivers. We tested this hypothesis using cosmogenic nuclides and uranium isotopes measured in stream sediment from widely distributed locations. Catchment-scale erosion rates from the cosmogenic nuclides suggest that the treads are relict surfaces that have adjusted to a previous base level. Nevertheless, erosion rates of relict interfluves are similar to canyon incision rates, implying that relief is unchanging in the lower Kings and San Joaquin Rivers. In addition, our results suggest that much of the southern Sierra Nevada is in a state of arrested development: the landscape is not fully adjusted to—and moreover is not responding to— changes in base-level lowering in the canyons. We propose that this can be explained by a paucity of coarse sediment supply, which fails to provide sufficient tools for bedrock channel incision at knickpoints. We hypothesize that the lack of coarse sediment in channels is driven by intense weathering of the local granitic bedrock, which reduces the size of sediment supplied from hillslopes to the channels. Our analysis highlights a feedback in which sediment size reduction due to weathering on hillslopes and transport in channels is both a key response to and control of bedrock channel incision and landscape adjustment to base-level change.

Geomorphological controls on soil fertility of semi-arid alluvial fans: A case study of the Joghatay Mountains, Northeast Iran

Alluvial fans are ideal locations to examine the effect of geomorphic processes and landforms on the soil characteristics. The rate of soil development and fertility differs between active surfaces, exposed to aggradation, and old or relict surfaces, subject to degradation. The aim of this research is to evaluate the effect of landforms and processes on soil fertility based on the studies on three alluvial fans of different ages (relict, old and young). A total of 36 soil samples were collected from these three alluvial fan surfaces. The samples were gathered from different locations of fans (apex and toe) and landforms (gully beds, interfluves, swales, and bars) and for each sample, nine variables including soil texture, acidity (pH), electrical conductivity (EC), total neutralizing value (TNV), available phosphorus (AP), available potassium (AK), total nitrogen (TN), total organic carbon (TOC), and hydraulic conductivity (K) were measured. The results show that the values of TNV, AP, AK, TN and TOC increase as clay% increases. In the relict and old fans, the values of TNV, TOC, TN, AP, AK, clay%, and silt% are higher in the interfluves than in the gully beds. Also, in the relict and old fans, the rates of clay%, silt%, TOC, TN, and AP are higher in the apexes than in the toes. In the young fan, the values of most variables are higher in the toe compared to the apex. The wide and relatively flat interfluves of the apex of old and relict fans have soils that are more fertile compared to the extensively entrenched surfaces of relict and old fan toes with relatively steep sloped interfluves. The less fertile soils in the apex of young fan can be attributed to its coarse-textured soils and also to repeated flooding and depositional processes. Overall, this study reveals that geomorphological landforms and processes such as aggradation and degradation play an important role in the spatial variation of soil fertility.

Pliocene –Pleistocene geomorphological evolution of the Adriatic side of Central Italy

Abstract This work is a significant contribution to knowledge of the Quaternary and pre-Quaternary morphogenesis of a wide sector of central Italy, from the Apennine chain to the Adriatic Sea. The goal is achieved through a careful analysis and interpretation of stratigraphic and tectonic data relating to marine and continental sediments and, mostly, through the study of relict limbs of ancient landscapes (erosional surfaces shaped by prevailing planation processes). The most important scientific datum is the definition of the time span in which the modelling of the oldest morphological element (the “summit relict surface”) occurred: it started during Messinian in the westernmost portion and after a significant phase during middle-late Pliocene, ended in the early Pleistocene. During the middle and late Pleistocene, the rapid tectonic uplift of the area and the climate fluctuations favoured the deepening of the hydrographic network and the genesis of three orders of fluvial terraces, thus completing the fundamental features of the landscape. The subsequent Holocene evolution reshaped the minor elements, but not the basic ones.

Geomorphology and topography of relict surfaces: the influence of inherited crustal structure in the northern Scandinavian Mountains

Low-relief surfaces in northern Norway are mapped and analysed to explore (1) whether surfaces were once continuous and possibly correlative, recording an ancient, relict landscape, (2) whether the distribution of (now disrupted) surfaces reveals a tectonic history related to rifting of the North Atlantic and (3) how topography changes across the transition between the North Atlantic and Barents Sea margins. Elevation contours on surfaces, a smoothed fit to mean elevations and histograms of elevation show three distinct, coast-parallel zones onshore northern Norway, and a different pattern in coastal Lofoten–Vesterålen. A sharp transition from continuous surfaces to lower, discretely stepped, discontinuous surfaces is located where the crust thins rapidly to the NW from >39 to <25 km. In margin-parallel transects, elevations remain high for >100 km north of the Senja Fracture Zone and then decrease gradually further NE. The spatial pattern suggests that a continuous, low-relief, relatively low-elevation surface formed in late Mesozoic time and was preserved despite modification by Cenozoic faulting, uplift and slow erosion. Scandinavia's present-day topographic envelope reflects a crustal strength profile set up during earlier hyperextension and maintained by slow Neogene erosion rather than resulting from opening of the North Atlantic or caused by glacial erosion. Supplementary material: A map of polygons of all surface heights within the study area and data on the location of median centres of polygons, assigned attributes and selected zonal statistics are available at https://doi.org/10.6084/m9.figshare.c.3312960

Pace of Landscape Change and Pediment Development in the Northeastern Sonoran Desert, United States

Pediments of the Sonoran Desert in the United States have intrigued physical geographers and geomorphologists for nearly a century. These gently sloping bedrock landforms are a staple of the desert landscape that millions visit each year. Despite the long-lived scientific curiosity, an understanding of the processes operating on the pediment has remained elusive. In this study we revisit the extensive history of pediment research. We then apply geospatial, field, and laboratory cosmogenic 10Be nuclide dating and back-scattered electron microscopy methods to assess the pace and processes of landscape change on pediment systems abutting the Salt River in Arizona. Our study focuses on the Usery pediments linked to base-level fluctuations (river terraces) of the Salt River. Relict pediment surfaces were reconstructed with dGPS data and kriging methodologies utilized in ArcGIS—based on preserved evidence of ancient pediment surfaces. 10Be ages of Salt River terraces established a chronology of incision events, where calculating the volume between the reconstructed relict pediment and modern surface topography established minimum erosion rates (∼41 mm/ka to ∼415 mm/ka). Pediment area and length appear to have a positive correlation to erosion rate and development of planar pediment surfaces. Field and laboratory observations reveal that pediment systems adjust and stabilize at each Salt River terrace. Relief reduction across the pediment begins with pediment channel incision via headward erosion. Next, tributary drainage capture begins and collapses interfluves. Lateral stream erosion promotes planation where the porosity of decayed granite along channel banks exceeds the bedrock underneath ephemeral channels.

Geomorphic analysis of transient landscapes in the Sierra Madre de Chiapas and Maya Mountains (northern Central America): implications for the North American–Caribbean–Cocos plate boundary

Abstract. We use a geomorphic approach in order to unravel the recent evolution of the diffuse triple junction between the North American, Caribbean, and Cocos plates in northern Central America. We intend to characterize and understand the complex tectonic setting that produced an intricate pattern of landscapes using tectonic geomorphology, as well as available geological and geophysical data. We classify regions with specific relief characteristics and highlight uplifted relict landscapes in northern Central America. We also analyze the drainage network from the Sierra Madre de Chiapas and Maya Mountains in order to extract information about potential vertical displacements. Our results suggest that most of the landscapes of the Sierra Madre de Chiapas and Maya Mountains are in a transient stage. Topographic profiles and morphometric maps highlight elevated relict surfaces that are characterized by a low-amplitude relief. The river longitudinal profiles display upper reaches witnessing these relict landscapes. Lower reaches adjust to new base-level conditions and are characterized by multiple knickpoints. These results backed by published GPS and seismotectonic data allow us to refine and extend existing geodynamic models of the triple junction. Relict landscapes are delimited by faults and thus result from a tectonic control. The topography of the Sierra Madre de Chiapas evolved as the result of (1) the inland migration of deformation related to the coupling between the Chiapas Massif and the Cocos forearc sliver and (2) the compression along the northern tip of the Central American volcanic arc. Although most of the shortening between the Cocos forearc sliver and the North American Plate is accommodated within the Sierra de Chiapas and Sierra de los Cuchumatanes, a small part may be still transmitted to the Maya Mountains and the Belize margin through a "rigid" Petén Basin.

Contrasting environmental memories in relict soils on different parent rocks in the south-western Italian Alps

Soils on the Alps are usually weakly developed, both because of the extensive Pleistocene glaciations, and because of slope steepness and climate enhancing erosion. However, on some stable, relict surfaces, particularly in the outermost sections of the Alpine range, some highly developed soils are apparently in contrast with Holocene soil forming conditions. In this work we assess the extent of pedogenesis in some of these soils, located under montane-level vegetation in the Ligurian Alps (SW Piemonte, Italy), and relate it to the effects of climate and parent material.The considered well developed profiles showed signs of extremely different pedogenetic processes on the different lithotypes. In particular, Podzols with extremely thick E horizons (up to more than 2 m thick) and very hard, thick ortstein or placic horizons were formed on quartzite. Reddish “terra rossa” Luvisols were formed on limestone. Red, extremely acidic Alisols were formed on shales. The chemical properties, the micromorphology and the clay mineralogy demonstrated high intensity pedogenic trends, and were characteristic of processes usually occurring under different climates.They may therefore represent excellent pedo-signatures of different specific past climatic/environmental conditions, as a response of different lithologies to specific soil-forming environments, which range from warm and humid climates typical of red Alisols and Luvisols, to cool and humid/wet climates leading to the formation of Podzols with ortstein/placic horizons.

The Qingzang movement: The major uplift of the Qinghai-Tibetan Plateau

Thirty-five years ago, the idea of a young Qinghai-Tibetan Plateau was proposed based on a comprehensive investigation on the Qinghai-Tibetan Plateau. This hypothesis suggested that the plateau began to rise from a planation surface (relict surface) that was less than 1000 m high formed during the Miocene to Pliocene. The fast uplift, i.e., the Qingzang Movement, began since ~3.6 Ma, evidenced by massive molasse deposits around the plateau margin and the synchronous occurrence of faulted basins within the plateau. However, later studies challenged this idea and suggested earlier (8, 14 or 35 Ma) formation of the huge plateau topography. Here we reevaluate the Qingzang Movement on the basis of our previous results and in light of new studies in the recent decades. The plateau margin has been subjected to intensive incision by very large drainages and shows the landscape characteristics of an “infant” stage of the geomorphological cycle. However, these drainages were not formed until 1.7–1.9 Ma; headwater erosion has not yet reached the hinterland of the plateau, so the interior of Tibet is free of significant erosion despite its lofty elevation, and remains an “old stage” landform. If the mean erosion rate is equivalent to the sum of clastic and soluble discharges of the modern rivers draining the Tibetan Plateau, it should have been worn down to a lowland within 8.6 Ma, ignoring tectonic uplift and isostasy. The massive conglomerate around the plateau margin began to deposit at about 3.6 Ma, indicating an increased relief after that time. Furthermore, the Hipparion fauna sites were widely distributed, and elephants, giraffes, and rhinos were abundant in the Qaidam Basin until the early Pliocene. Cenozoic climate change alone is not able to account for the dense occurrence of Hipparion fauna, unless the paleo-elevation of Tibet was lowered. The rise of Tibet since the Qingzang Movement has had a great influence on the Asian interior aridification.

Indications of an extreme event deposits along the west coast of India: evidences from GPR investigations

The ground-penetrating radar (GPR) was used to trace the subsurface details in the Palshet coastal zone (Maharashtra) as it exhibits an interesting array of geomorphological features. Furthermore, our main goal was to identify and locate features that might have formed during a reported extreme event and its effects on the flow of the nearby Sundri River. Two profiles (8 and 4 m depth) were collected across the beach and along the backshore, respectively. While the 8-m depth profile (west to east; across the beach) indicates a series of coastline regression in this area, the 4-m depth profile along the coastline (north to south) in the backshore zone reveals two significant incidents viz., (1) stages of development of the paleo-channels that indicate the migration of the Sundri River towards south and (2) huge sediment deposits up to 2.5-m thick in the backshore area. The erosional relict surface (~2.5 m depth) was traced along with various spells of sediments that perhaps occurred due to an extreme event. Sand samples were collected from two trial pits along the GPR profiles to understand the sedimentology and mineralogy in the backshore area. These data together with beach profiles and geomorphological maps suggest that the sands were deposited by an extreme event perhaps during the 1854 cyclonic storm. The sands were trapped in suitable geomorphological sites along the Palshet coast and these sand deposits of about 2.5 m thickness forced the River Sundri to shift its course towards the south. This new revelation facilitates a further study that could focus on the nearby coastal areas to document such extreme event deposits and their influence on the geomorphic set-up.

Constraining landscape history and glacial erosivity using paired cosmogenic nuclides in Upernavik, northwest Greenland

High-latitude landscape evolution processes have the potential to preserve old, relict surfaces through burial by cold-based, nonerosive glacial ice. To investigate landscape history and age in the high Arctic, we analyzed in situ cosmogenic Be(sup 10) and Al (sup 26) in 33 rocks from Upernavik, northwest Greenland. We sampled adjacent bedrock-boulder pairs along a 100 km transect at elevations up to 1000 m above sea level. Bedrock samples gave significantly older apparent exposure ages than corresponding boulder samples, and minimum limiting ages increased with elevation. Two-isotope calculations Al(sup26)/B(sup 10) on 20 of the 33 samples yielded minimum limiting exposure durations up to 112 k.y., minimum limiting burial durations up to 900 k.y., and minimum limiting total histories up to 990 k.y. The prevalence of BE(sup 10) and Al(sup 26) inherited from previous periods of exposure, especially in bedrock samples at high elevation, indicates that these areas record long and complex surface exposure histories, including significant periods of burial with little subglacial erosion. The long total histories suggest that these high elevation surfaces were largely preserved beneath cold-based, nonerosive ice or snowfields for at least the latter half of the Quaternary. Because of high concentrations of inherited nuclides, only the six youngest boulder samples appear to record the timing of ice retreat. These six samples suggest deglaciation of the Upernavik coast at 11.3 +/- 0.5 ka (average +/- 1 standard deviation). There is no difference in deglaciation age along the 100 km sample transect, indicating that the ice-marginal position retreated rapidly at rates of approx.120 m yr(sup−1).

Multiple cosmogenic nuclides document the stability of the East Antarctic Ice Sheet in northern Victoria Land since the Late Miocene (5–7 Ma)

The timing and amplitude of changes in the Antarctic ice level are relevant to understanding past climate fluctuations and ongoing changes in the global climate and sea levels. In this study, we present surface exposure ages based on in situ produced cosmogenic 10Be and 21Ne in the bedrock samples of glacially eroded relict surfaces from the Deep Freeze Range, northern Victoria Land. The proximity of this region to the East Antarctic Ice Sheet indicates that the area is sensitive to variations in inland ice volume, permitting the investigation of the behavioural relationship between the East Antarctic Ice Sheet and the alpine glacial system in northern Victoria Land. Dating erosional surfaces provides a precise chronology of northern Victoria Land paleoclimate evolution and allows us to correlate the East Antarctic Ice Sheet response to global climate events and local ice level variations. The 10Be and 21Ne concentrations from the highest peaks of the Deep Freeze Range strongly indicate that the relict landscape features were continuously exposed for 5–7 Ma. Denudation rates inferred from our data show that the erosion rate of the summits has been extremely low (∼5 cm/Ma) for at least 5–7 Ma. Along with evidence of persistent climate stability (cold and arid conditions) from other sectors of the Transantarctic Mountains, our results indicate that the transition from the wet-based to the cold-based glacial regime in northern Victoria Land occurred after the creation of the polar East Antarctic Ice Sheet in the Middle Miocene.

Stream capture as driver of transient landscape evolution in a tectonically quiescent setting

Research Article| September 01, 2011 Stream capture as driver of transient landscape evolution in a tectonically quiescent setting Philip S. Prince; Philip S. Prince Department of Geosciences, Virginia Polytechnic Institute and State University (0420), Blacksburg, Virginia 24061, USA Search for other works by this author on: GSW Google Scholar James A. Spotila; James A. Spotila Department of Geosciences, Virginia Polytechnic Institute and State University (0420), Blacksburg, Virginia 24061, USA Search for other works by this author on: GSW Google Scholar William S. Henika William S. Henika Department of Geosciences, Virginia Polytechnic Institute and State University (0420), Blacksburg, Virginia 24061, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Philip S. Prince Department of Geosciences, Virginia Polytechnic Institute and State University (0420), Blacksburg, Virginia 24061, USA James A. Spotila Department of Geosciences, Virginia Polytechnic Institute and State University (0420), Blacksburg, Virginia 24061, USA William S. Henika Department of Geosciences, Virginia Polytechnic Institute and State University (0420), Blacksburg, Virginia 24061, USA Publisher: Geological Society of America Received: 16 Dec 2010 Revision Received: 24 Mar 2011 Accepted: 03 Apr 2011 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2011 Geological Society of America Geology (2011) 39 (9): 823–826. https://doi.org/10.1130/G32008.1 Article history Received: 16 Dec 2010 Revision Received: 24 Mar 2011 Accepted: 03 Apr 2011 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Philip S. Prince, James A. Spotila, William S. Henika; Stream capture as driver of transient landscape evolution in a tectonically quiescent setting. Geology 2011;; 39 (9): 823–826. doi: https://doi.org/10.1130/G32008.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract We use unique fluvial gravel deposits preserved atop a regional drainage divide to confirm the role of stream capture in driving ∼250 m of incision in the transient Roanoke River basin of the Appalachian Mountains (United States). Gravel provenance constrains the pre-capture position of the divide, indicating that ∼225 km2 of basin area were abruptly connected to the base level of the capturing stream. The resulting wave of incision is currently manifest as major knickzones separating adjusting reaches from relict headwaters resembling streams of the New River basin, from which the Roanoke River was captured. The unusual preservation of the unconsolidated gravels on small relict surfaces adjacent to bedrock gorges indicates extreme spatial variability in erosion rates within the Roanoke basin, which is the first documented example of a transient passive margin basin connected to a capture event by stranded fluvial debris. Our results show the potential for stream capture across an asymmetric drainage divide to drive major transient incision independent of external forcings, such as climate change or tectonic uplift. A continuation of this process will lead to eventual capture of ∼7000 km2 of the New River basin in the relatively near geologic future. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Geomorphological response of fluvial and coastal terraces to Quaternary tectonics and climate as revealed by geostatistical topographic analysis

Geostatistical topographic analysis is widely recognized as a useful tool for the statistical reconstruction of planar geomorphic markers from relict surfaces. This work is aimed at improving the geostatistical approach used in previous works and developing a method for evaluating the incision rates of rivers in their lower catchments during the Late Quaternary. We chose the major valleys of the Adriatic foothills (central Italy), affected since Late Miocene by a differential tectonic uplift which is still active. In particular, (i) we applied the geostatistical analysis to reconstruct the original top-surfaces of fluvial-to-coastal terrace bodies at the Metauro River and Cesano River mouths; (ii) we performed correlations between the height distribution of the alluvial terrace sequences and the Quaternary climatic curve to estimate the average long-term fluvial incision rates in the lowermost reaches of the Metauro, Cesano, Misa and Esino Rivers. The obtained averaged incision rates have been interpreted also in the light of the Stream-Length Gradient Index (SL Index), Steepness Index (Ks), and Concavity Index (θ) as proxies of the stream-power per unit length. Results confirm that geostatistical and terrain analysis of topographic and geometric arrangements of fluvial and coastal terraces is an effective tool in detecting geomorphic and tectonic factors inducing perturbations on planar geomorphic markers. In particular, we better delineated the surface geometry and boundaries of well-developed coastal fans at the mouths of the Metauro and Cesano Rivers, already recognized in previous works through sedimentological, morphostratigraphic, and chronological data. Moreover, we found evidence for cut-and-fill phases that took place during and immediately after the river aggradation of the late Quaternary glacial periods. Despite the Slope–Area analysis evidenced a widespread influence of the regional differential uplift on single river basin configuration, we observed some space and time variability of averaged incision rates for adjacent valleys, mainly explained by physiographic configuration and dynamics of drainage network. Copyright © 2011 John Wiley & Sons, Ltd.

Chronology of late Cenozoic volcanic eruptions onto relict surfaces in the south-central Sierra Nevada, California

Early twentieth-century geologists ob-served extensive areas of subdued topography in the otherwise strongly dissected landscape of the southern Sierra Nevada that they ascribed to periods of stability following episodes of orogenic uplift. From this evidence, they developed an uplift history for the Sierra Nevada. This conceptual model for landscape evolution of the Sierra has largely been rejected or ignored since the middle of the twentieth century, based in considerable part on observations indicating that these surfaces can be explained as dynamic landforms actively developing in response to conditions of the relatively recent geological past and that long-term erosion rates are much too high to permit pre-Quaternary surfaces to be preserved. We investigated the chronology of basaltic flows and ejecta on several such apparent relict surfaces located west of Bishop, California. Most of the basalt cones and flows that were sampled are nearly concordant with the present topography, generally showing no more than 50 m of landscape inversion. The 40 Ar/ 39 Ar ages of the basalts fall into two groups: 11.76 ± 0.05 Ma and 3.40 ± 0.06 Ma. These ages demonstrate that paleosurfaces dating back to at least the Miocene can be preserved close to the summits of the Sierra Nevada with minimal erosion. The elevations and relative sequences of these surfaces do indeed appear to preserve a topographic history of the Sierra Nevada, encouraging continued investigation of their significance within the tectonic history of the Sierra Nevada.

Quantifying landscape differences across the Tibetan plateau: Implications for topographic relief evolution

We quantify the bulk topographic characteristics of the Tibet‐Qinghai plateau with specific focus on three representative regions: northern, central, and southeastern Tibet. Quantitative landscape information is extracted from Shuttle Radar Topography Mission digital elevation models. We find that the morphology of the Tibetan plateau is nonuniform with systematic regional differences. The northern and central parts of the plateau are characterized by what we suggest to call “positive topography,” i.e., a topography in which elevation is positively correlated with relief and mean slope. A major change from the internally drained central part of Tibet to the externally drained part of eastern Tibet is accompanied by a transition from low to high relief and from positive to “negative topography,” i.e., a topography where there is an inverse or negative correlation between elevation and relief and between elevation and mean slope. Relief in eastern Tibet is largest along rivers as they cross an ancient, eroded plateau margin at high angle to the major strike‐slip faults, the Yalong‐Yulong thrust belt, implying strong structural control of regional topography. We propose that the evolution of river systems and drainage efficiency, the ability of rivers to transport sediments out of the orogen, coupled with tectonic uplift, is the simplest mechanism to explain systematic regional differences in Tibetan landscapes. Basin filling due to inefficient drainage played a major role in smoothing out the tectonically generated structural relief. This mode of smoothing started concurrently with tectonic construction of the relief, as most clearly illustrated today in the Qilian Shan‐Qaidam region of the northeastern plateau. In the interior of Tibet, further “passive” filling, due to internal drainage only, continued to smooth the local relief millions of years after the cessation of major phases of surface uplift due to crustal shortening. Thus, diachronous beveling at high elevation produced the low‐relief surface of the high plateau. In southeast Tibet, headward retreat of external drainages brought back “in” the global ocean base level, first disrupting then interrupting the relief‐reduction process. It produced a transitional topography by dissecting the “old” remnant plateau surface, which introduced younger and steeper incision of this hitherto preserved high base level. This provides a unifying mechanism for the formation of the low‐relief plateau interior, and for the origin of the high‐elevation, low‐relief relict surface in southeastern Tibet. Our analysis brings forth the importance of surface processes, in particular drainage efficiency, in shaping plateau morphology and landscape relief. Such key processes appear to have been mostly ignored in numerical models of plateau deformation. Our results also cast doubt on and provide a more realistic alternative to the fashionable contention that a continuous preuplift, low‐relief surface first formed at low elevation, extending all the way to the South China Sea shore, before being warped upward in the late Miocene‐Pliocene by lower crustal channel flow.