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Adobe buildings -a 'gina' (highouse) of the Dogon people of Mali (Sangha, Mali), built with Sahelian adobe
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In discussions on loess, two types are often demarcated: glacial loess and desert loess. The origin of the idea of desert loess appears to lie with V.A. Obruchev who observed wind-carried silt on the Potanin expedition to Central Asia in 1895. It might be considered that desert loess would be defined as loess associated with deserts but it came to...
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Context 1
... Krinsley, 1978); 5 -Ganges-Brahmaputra delta; 6 -North India alluvium; 7 -Indus alluvium; 8 -Irrawaddy delta; 9 -Mekong delta be is a desert fringe material and adobe buildings shelter people in desert fringe communities. The southern fringe of the Sahara desert is classic adobe country and the great adobe buildings are found in this region (see Fig. ...
Context 2
... Krinsley, 1978); 5 -Ganges-Brahmaputra delta; 6 -North India alluvium; 7 -Indus alluvium; 8 -Irrawaddy delta; 9 -Mekong delta be is a desert fringe material and adobe buildings shelter people in desert fringe communities. The southern fringe of the Sahara desert is classic adobe country and the great adobe buildings are found in this region (see Fig. ...
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This article establishes a linkage between the mineral dust cycle and loess deposits during the Last Glacial Maximum (LGM) in Europe. To this aim, we simulate the LGM dust cycle at high resolution using a regional climate–dust model. The model-simulated dust deposition rates are found to be comparable with the mass accumulation rates of the loess d...
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The results of grain size distribution of loess units are suitable for the study of past climate change. There are many methods for the analysis of the grain size, but clustering methods have not been used before. In this article, a new approach in the sediment research, the k-median method was used. This method separates the grain size classes of...
The Quaternary wind-blown Chinese loess-paleosol sequence, which developed as a product of the intensification of Northern Hemisphere glacial-interglacial cycles, is a major source of information on aridification of the Asian interior. In northeastern (NE) China, extensive loess deposits occur that have great potential for reconstructing the long-t...
Citations
... Loess is a deposit formed by aeolian accumulation of silt-sized particles in periglacial climate conditions (Muhs, 2013) or in close vicinity of deserts occurring in low to midlatitude arid and semiarid regions (Muhs, 2013;Smalley et al., 2019;Lancaster, 2020). Loess and loess-like deposits cover over 10% of the Earth's surface (Haase et al., 2007) and are the subject of many research studies in paleogeography, sedimentology, geomorphology, and pedology (e.g. ...
Loess in Europe is heterogeneous due to differences in paleoenvironmental conditions during sedimentation and pedogenesis. In many regions of Europe, including southern Poland, loess accumulation was followed by the leaching of carbonates followed by clay translocation, which is typical in silty soils in humid climates. Loess soils in the temperate climate zone are characterized by the presence of well-developed or well-preserved microfabrics of different origin but with similar morphology, among which lamellae can be distinguished. Lamellae commonly occur in loess soils; however, detailed studies focused on their origin and evolution are lacking. The main aim of the present study was to determine the origin and transformation of lamellae both in calcareous and non-calcareous loess soils in the Central European loess belt, using an example from southern Poland. The following three hypotheses were tested: (1) decalcification of the upper part of loess soils is a necessary condition for soil lamellae formation, while frost action is not a key factor shaping their morphology and properties in the Central European loess belt, (2) occurrence of carbonate in the lower part of calcareous loess soils inhibits lamellae formation, (3) soil lamellae are transformed due to bioturbation and shrinking-swelling processes in both calcareous and non-calcareous loess soils. The obtained results indicate that decalcification of the upper part of calcareous loess soils enables the translocation of clay particles and lamellae formation. Field observations and micromorphological analysis indicate that the presence of carbonate limits the development of soil lamellae and constitutes a barrier to deeper clay translocation in loess soils. This finding suggests a pedogenic origin of lamellae in the loess soils of southern Poland. Soil lamellae show a number of signs indicating their mechanical degradation due to swelling and shrinking, bioturbation, and dissolution driven by eluviation and redox processes. The progressive evolution of lamellae leads to an enhancement of their expression in the illuvial Bt and transitional BC horizons.
... In fact, as revealed by micromorphology and grain size distribution analysis, the fine-grained parent deposit appears to be of loessic origin (Yaalon, 1987). Further analyses shall be carried out in this respect, because this would represent a newly found sink location of peri-desert loess deposition (Crouvi et Lancaster, 2020;Li et al., 2020;Smalley et al., 2019;Tsoar and Pye, 1987;Whalley et al., 1982), adding context to a much debated phenomenon that only has few and spread-apart case studies for Northern Africa (Coudé- Gaussen, 1990;Coudé-Gaussen and Rognon, 1988;Stokes and Horrocks, 2020). Interestingly, case studies of great similarity are found at the same latitudes in the southern Arabian Peninsula, where desert loess has been documented at the northern slopes of the Dhofar Mountains in the Sultanate of Oman (Cremaschi and Negrino, 2005;Cremaschi et al., 2015), at Ras Al Khaimah in the United Arab Emirates (Goudie et al., 2000), and in the area of Sana'a in Yemen (Nettleton and Chadwick, 1996), where the loess sequence also promoted the formation of isohumic soil with a radiocarbon age very similar to the one measured for JM1 and then buried in the Late-Holocene. ...
Studies upon past climates, natural landscapes, and environments of archaeologically pivotal regions of northern Africa have been of paramount interest in the past decades. For some of those regions, the human-environmental nexus, intended as the biunivocal mutual agency between people and nature, has been a long-standing research question; yet, for other areas, the environmental record is a still unexplored archive. Here we present case studies discussing archaeo-environmental sites from the easternmost stretches of the Sahelian belt, in the Kassala region of Sudan. Therein, in a landscape that is currently characterized by granitoid rocky outcrops dotting a vast gravelly pediplain colonized by xerophytes and thin ephemeral grass, pedosedimentary features that encase the climatic history of the region are found. By means of field survey, physico-chemical laboratory analyses, micromorphological analyses, and radiometric dating, we investigated the uppermost portion of the Quaternary record to contextualize the Late-Holocene archaeological record. The main identified features include buried isohumic soil horizons in lower flat grounds, which are legacy of water-reliant prairie environments formed in the wetter Early to Middle Holocene, and later accretional dusty aeolian deposits intermingled with colluvial gravels close to the outcrops’ eroded foothills, testimony of a climatic deterioration towards aridity and erosion driven by hyper seasonality. Results are of great importance as a contribution to a more holistic understanding of past human economies of the region, as well as being a newly added tile to the reconstruction of surface processes dynamics over Africa and their response to global climate changes.
... One basic premise of most studies dealing with desert loess is that primary (hilltop) terrestrial sediments represent more or less directly the material that was moved through the atmosphere (e.g., Crouvi et al. 2008;2009;. Formation of desert loess was therefore mainly approached from the supply side, based on the assumption that its genesis depended primarily on generation and transport of sufficient silt through the atmosphere (see summary in Smalley et al. 2019). Considered siltgenerating processes were mainly collision of dune sand grains during aeolian transport ) as an origin from glacial grinding seems unlikely. ...
Archaeological structures are usually subject to sedimentation after their aban-donment. These sediments ("debris") come partly from collapse and are often removed as quickly as possible in order to study artifacts and the intact remains of the structures. However, in the semi-arid and arid climates of Jordan, sediments of the debris contain (or consist of) aeolian dust. Thus they represent a potential environmental archive comparable to the famous loess sequences of the Negev. The latter mostly lack Holocene layers, meaning that the debris preserved in archaeological sites might be suited to continue dust records through the Holocene. A systematic comparison of sediments preserved in different archaeological structures (hilltop ruins, cisterns, and terraces), actual dust storms, and natural sediments around Petra in southern Jordan is presented in this contribution. Results suggest that long-range deposition of silty, calcareous sediment continues until today and that the terrace sediments and the material culture associated with them allow for reconstructions of ancient land use patterns.
... A debate on the production mechanism and genesis of loess has long persisted in the literature, and resulted in the primary division of mechanisms into "glacial"/"cold" loess, and "desert"/"warm" loess (Crouvi et al., 2010;Lancaster, 2020;Muhs and Bettis, 2003;Obruchev, 1945;Smalley, 1966;Smalley and Vita-Finzi, 1968;Smith et al., 1991;Tsoar and Pye, 1987;Wright, 2001). Additionally terms such as "mountain" loess also appear in the literature (Jipa, 2014;Smalley, 2008;Smalley et al., 2019;Smalley and Derbyshire, 1990;Xia et al., 2020), especially in relation to desert loess. However, in many cases glacial loess is also ultimately sourced from mountain areas and when production mechanisms (rather than geomorphic areas) are scrutinised the divisions between these categories become rather blurred (Fig. 11). ...
With one of the largest watersheds in Europe draining complex geological terrains within the Alps, Bohemian Massif, Carpathians, Dinarides, and the Balkan Mountains, the Danube River valley has long been linked to the formation of thick loess deposits, particularly within the Middle and Lower Danube basins. However, uncertainty over the provenance of loess-palaeosol sequences along the Danube impacts our understanding of sediment generation mechanisms and hinders interpretation of paleoenvironmental proxies preserved in loess. To date, most of the studies investigating loess provenance in Europe have not attempted a standardised characterisation and synthesis of loess deposits with potential source rocks. Further, despite clear links identified between loess and rivers in Asia and Europe, detrital zircons have not yet been used systematically to investigate the relationship between loess and the fluvial sediments of the Danube and its tributaries. Finally, in European loess research, provenance fingerprinting has often been conducted using indirect approaches or bulk sample geochemical analyses, which have been shown to have a limited application in well mixed sedimentary bodies such as loess.
This provenance study of loess along the Danube River integrates existing zircon U-Pb ages and Hf datasets for loess, rivers, and bedrock, with new loess zircon U-Pb and Hf results from loess sequences in Croatia, Serbia and Bulgaria. The results show that all surrounding mountain belts drained by the Danube (i.e., the Alps, Bohemian Massif, Carpathians, Dinarides Alps, and Balkan Mountains) contribute primary sediment to loess deposits in the Danube valley via its modern tributary network. Critically sedimentary sources remain relatively homogenous along the river, with no apparent major change in source with tributary confluence, further highlighting the role of fluvial transport in homogenising sediment prior to final aeolian deposition. Whilst some small site variations can be observed, they are likely explained by contributions restricted to very local rock outcrops. Moreover, geomorphological results support floodplain sediments as the proximal sediment source and suggest that short-distance aeolian transport dominates sediment delivery to loess sequences, challenging distant sources hypotheses such as major Saharan sources. The identification of sediment sourced from lower elevation regions such as the Bohemian Massif, Dinarides, and Balkans, which did not support ice-caps, suggests that the role of glacial action in silt-size sediment production has been previously exaggerated. Therefore, the glacial and desert loess division inadequately separates and describes sediment generation processes. This research supports and furthers previous work, which suggests “mountain sourced and transported by-rivers” as a more appropriate term for the particles forming loess, at least in the Danube basin.
... The processes leading to loess formation in the Levant are still discussed. The genesis of loss-like soils in this region is often considered to be connected with enhanced dust supply (Smalley et al. 2019;Lancaster 2020), and the debate therefore focuses on potential dust sources. Pleistocene abrasion of silt-sized quartz from moving sand in the Sinai-Negev dune field has been brought forward as major dustgenerating process (Crouvi et al. 2008;Enzel et al. 2010;Amit et al. 2021), but ages of dune mobilization (Roskin 2021), quartz generation during wind tunnel experiments (Swet et al. 2019; Adams and Soreghan 2020), and regional soil distribution (Lucke 2021) are not in agreement with this hypothesis. ...
... One basic premise of most studies dealing with the loessial paleosols in the Negev is that primary (hilltop) terrestrial sediments represent more or less directly material from remote sources that was moved through the atmosphere (e.g., Crouvi et al. 2008Crouvi et al. , 2009). Formation of Negev loess has so far been approached from the supply side, based on the premise that its genesis depended primarily on generation and transport of sufficient silt through the atmosphere (Smalley et al. 2019;Lancaster 2020). With regard to the Negev, abrasion of silt-sized quartz grains from moving Sinai sand dunes has been proposed as main dust-producing process, leading to downwind formation of the loessial paleosols during periods of dune activity (Enzel et al. 2010). ...
Ruins of archaeological structures, mainly dating to the Bronze Age till Byzantine period, were investigated in a case study in the Petra region in southern Jordan and in the northern Negev desert in Israel. They are covered by post-abandonment debris sediments which provided the parent material of initial soils now developed on the ruins. Such debris sediments have so far rarely been studied although they likely contain a significant aeolian dust fraction because structures and wall remains may act as effective dust traps. We analyzed different types of archaeological structures: cult sites on hilltops, runoff-irrigated terraces on slopes, and cisterns including associated cleanout mounds. As well, we collected current aeolian sediments in nearby dry marble dust traps. It was expected that the various ruins and location types would matter for sediment properties, but substrate composition in all investigated structures was similar. This suggests that most of the fine fractions of the debris material were primarily supplied by wind whereas fluvial processes only re-distributed aeolian sediments. A major aeolian contribution from local weathered rocks could be observed in the Petra region, but not in the Negev, which seems connected with the geology. In situ pedogenesis in both investigation regions is negligible. The ruins seem to act as current dust collectors, but their sediments cannot directly be compared with the material collected in nearby dry marble dust traps. Analogies to different types of collectors for aeolian sediments can be made: depending on design, dust traps gather aeolian material differently. Standard dry marble dust collectors are characterized by similar size of settling dust samples as compared to average aeolian deposition in the ruins, but are of dissimilar substrate composition with regard to particle size distribution and contents of major and trace elements. Sediments in the archaeological structures in southern Jordan show finer textures and higher contents of most major and trace elements which may indicate preferential fixation of silt and clay against sand in the ruins, whereas sediments in dry marble dust collectors in Jordan are relatively depleted in silt and clay. This could be due to crusts and clast covers because the studied archaeological hilltop structures were found covered by surface crusts and pavements of stones and pottery sherds. These may mirror the effect of desert pavements. In addition, current dust samples suggest that precipitation during aeolian sedimentation, in particular in case of snow, is connected with enhanced deposition of (possibly clay-coated) silt. Sediments in the archaeological structures include material from remote and local sources as well as from “recycled” paleosols. Average hilltop dust accretion rates were calculated as ~ 0.14 mm/year, which is in good agreement with results from dry marble dust collectors. They exceed rates calculated for Pleistocene hilltop loess in the Negev. This seems due to enhanced dust fixation in the archaeological ruins as compared to natural Negev loess soils, underlining a so far rarely considered but important role of sediment fixation mechanisms.
... Identification of loessites requires knowledge that the materials consist of silt-sized grains deposited by wind [437,438]. The presence of loess or loessite does not require that the silt was produced by glacial processes [439], nor that they are composed of quartz. Duststone is a term coined specifically for Mars by Bridges and Muhs [440] that refers to knowledge that the material was deposited by settling out of suspension from the Martian atmosphere. ...
Sedimentary rocks provide records of past surface and subsurface processes and environments. The first step in the study of the sedimentary rock record of another world is to learn to recognize their occurrences in images from instruments aboard orbiting, flyby, or aerial platforms. For two decades, Mars has been known to have sedimentary rocks; however, planet-wide identification is incomplete. Global coverage at 0.25–6 m/pixel, and observations from the Curiosity rover in Gale crater, expand the ability to recognize Martian sedimentary rocks. No longer limited to cases that are light-toned, lightly cratered, and stratified—or mimic original depositional setting (e.g., lithified deltas)—Martian sedimentary rocks include dark-toned examples, as well as rocks that are erosion-resistant enough to retain small craters as well as do lava flows. Breakdown of conglomerates, breccias, and even some mudstones, can produce a pebbly regolith that imparts a “smooth” appearance in satellite and aerial images. Context is important; sedimentary rocks remain challenging to distinguish from primary igneous rocks in some cases. Detection of ultramafic, mafic, or andesitic compositions do not dictate that a rock is igneous, and clast genesis should be considered separately from the depositional record. Mars likely has much more sedimentary rock than previously recognized.
... Volcanic ash or loess, for example, could have been brought to the region by aeolian activity sufficient to form a thick surface to depth horizon or sets of horizons (e. g. Greeley and Williams, 1994;Bridges et al., 2010;Séjourné et al., 2012;Bridges and Muhs, 2012;Skinner et al., 2012;Soare et al., 2014;Smalley et al., 2019). ...
... Volcanic ash or loess, for example, could have been brought to the region by aeolian activity sufficient to form a thick surface to depth horizon or sets of horizons (e. g. Greeley and Williams, 1994;Bridges et al., 2010;Séjourné et al., 2012;Bridges and Muhs, 2012;Skinner et al., 2012;Soare et al., 2014;Smalley et al., 2019). ...
The cyclicity and temporal succession of glacial-periglacial periods or epochs are keynotes of cold-climate geology on Earth. Relatively recent work within the Mars community has begun to dissect the mid- to higher-latitudinal terrain of Mars for analogical evidence of similar cold-climate cyclicity and succession.
Here, we carry on with this work by focusing on the terrain immediately to the north of the Moreux impact-crater (40–44° N, 43–47° E). The crater is located in northern Arabia Terra, to the south of Protonilus Mensae. It lies astride of and postdates Mars' crustal-dichotomy. The latter is a global geological-boundary that separates the ancient southern-highlands from the relatively younger northern-lowland plains.
Using cross-cutting relationships, relative stratigraphy and crater-size frequency distributions (CSFDs) we identify three glacial and two periglacial periods that are temporally intertwined and differentiated by a suite of features unique to each of these periods. For example, we report and discuss clusters of pingo-like mounds amidst ridge and trough terrain or “brain terrain”. On Earth, the former are the work of freeze-thaw cycling; on Mars, the latter are thought to be glacial remnants. In turn, the brain terrain is underlain by small-sized polygons possibly formed by thermal contraction cracking and with margins underlain by degraded ice-wedges. Age estimates derived of CSFDs suggest that the polygonised terrain could as much as ~100 Ma, whereas the brain terrain and pingo-like mounds are thought to be ~1–~10 Ma. Possible terminal-moraines that intercept brain-terrain fragments point to an even more recent period of glaciation.
If the CSFD age-estimates are valid, then the polygons that underlie the brain terrain and incise the basin floors of our study zone could be an order of magnitude older than most of the age estimates associated with polygonised terrain at other locations on Mars. The fact that there are two distinct periods of polygonization and periglacial activity with a wide offset of time within one relatively small study zone also highlights the extent to which the freeze-thaw cycling of water might be rooted as iteratively and as deeply in Mars' geological history as is its glaciation.
... The importance of silt generation in the form of "desert" loess-quartz fragmentation resulting from saltation-induced intergranular collisions-remains disputed (e.g., Smalley, 1990;Wright, 2001;Smalley et al., 2019). For example, some suggest that the large accumulations in the Chinese Loess Plateau originated in proximal deserts (Liu et al., 1994;Porter, 2001), whereas others suggest a glacial origin in the mountains of high Asia, followed by desert "storage" and ultimate deflation (e.g., Assallay et al., 1998;Smalley et al., 2005;Stevens et al., 2013;Li et al., 2018;Smalley et al., 2019). ...
... The importance of silt generation in the form of "desert" loess-quartz fragmentation resulting from saltation-induced intergranular collisions-remains disputed (e.g., Smalley, 1990;Wright, 2001;Smalley et al., 2019). For example, some suggest that the large accumulations in the Chinese Loess Plateau originated in proximal deserts (Liu et al., 1994;Porter, 2001), whereas others suggest a glacial origin in the mountains of high Asia, followed by desert "storage" and ultimate deflation (e.g., Assallay et al., 1998;Smalley et al., 2005;Stevens et al., 2013;Li et al., 2018;Smalley et al., 2019). Formation of the silt in Permian-Pennsylvanian loessite in western Pangea was similarly linked initially to saltation abrasion in coeval sand dunes, owing primarily to the low-latitude setting (e.g., Johansen, 1988), but later work has called this into question. ...
... Finally, the volumetrics of the loessite significantly exceed those of (potential) coeval eolian sandstone (Soreghan et al., 2008a, and references within). There is very little loess-sized silt documented in association with erg systems (e.g., Smalley and Vita-Finzi, 1968;Smalley and Krinsley, 1978;Tsoar and Pye, 1987;Smalley, 1990;Assallay et al., 1998;Muhs and Bettis, 2003;Smalley et al., 2005;Muhs, 2013;Smalley et al., 2019), consistent with experimental stud-ies that call into question the efficacy of making significant volumes of loess-sized quartz silt from saltation abrasion of eolian sand (Kuenen, 1959;Bullard et al., 2004;Swet et al., 2019;Adams and Soreghan, 2020). In the case of the Salagou Formation, grain-size modes, feldsparrich compositions, and sheer volume are similarly incompatible with a desert loess origin, especially considering the lack of coeval eolian sandstone in the greater region. ...
Carboniferous−Permian strata in basins within the Central Pangean Mountains in France archive regional paleoequatorial climate during a unique interval in geological history (Pangea assembly, ice-age collapse, megamonsoon inception). The voluminous (∼1.5 km) succession of exclusively fine-grained red beds that comprises the Permian Salagou Formation (Lodève Basin, France) has long been interpreted to record either lacustrine or fluvial deposition, primarily based on a local emphasis of subaqueous features in the upper ∼25% of the section. In contrast, data presented here indicate that the lower-middle Salagou Formation is dominated by up to 15-m-thick beds of internally massive red mudstone with abundant pedogenic features (microscale) and no evidence of channeling. Up-section, limited occurrences of ripple and hummocky cross-stratification, and mudcracks record the intermittent influence of shallow water, but with no channeling nor units with grain sizes exceeding coarse silt. These data suggest that the most parsimonious interpretation for the Salagou Formation involves eolian transport of the sediment and ultimate deposition as loess in shallow, ephemeral lacustrine environments. Provenance analyses of the Salagou Formation indicate coarse-grained protoliths and, together with geochemical proxies (chemical index of alteration [CIA] and τNa) that correspond respectively to a low degree of chemical weathering and a mean annual temperature of ∼4 °C, suggest that silt generation in this case is most consistent with cold-weathering (glacial and associated periglacial) processes in the Variscan highlands. Together with previous studies that detailed voluminous Permian loess in western equatorial Pangea, this work shows a globally unique distribution of dust at low latitudes that can be linked either directly to glaciated alpine terranes or to reworked and deflated deposits of other types (e.g., fluvial outwash) where fine-grained material was originally generated from glacial grinding in alpine systems. These results further support a revised model for early Permian climate, in which extratropical ice sheets coexisted with a semiarid tropics that may have hosted significant ice at moderate elevation.
... However, all share a similar position for their inflexion point, which is located over Yellow River valley (Sites [33][34][35][36][37][38][39][40]. Wall samples along the well-preserved Shandan section are relatively poor in chlorite and less variable compared with their associated background samples (Figure 7c), which often comprise colluvial/alluvial material (e.g., Sites 49,54,and 55). ...
... In theory, a 2% lime application rate is sufficient to reach the "lime fixation point" where ions are absorbed by clay minerals, which increases the unconfined compressive strength of the earthen material [86]. After this point, alkali activation can cause the (re)precipitation of calcite as part of a pozzolanic type reaction [54]. However, nano-fibers of secondary calcite are also found in natural loess material [48] such that (re)crystalized calcite in the earthen wall material is not itself conclusive evidence for lime addition by the Ming. ...
The earthen border wall (Great Wall) built by the Ming is largely made of wind-blown loess. However, does the composition of this loess change along the length of the wall in response to variations in regional sediment transport pathways and impacting on the wall’s erosional durability? To date, defining these sediment transport pathways has been a challenge because of the paucity of spatially-comprehensive, compositional information. Here, we show that satellite ASTER mineral maps, combined with field sample measurements along a 1200 km section of the Ming’s earthen wall, reveal both the compositional heterogeneity of loess as well as the complexity of the sediment transport pathways of individual loess components, including: (i) quartz sand from Cretaceous sandstones in the Gobi Desert; (ii) gypsum from evaporative lakes in the Tengger Desert; (iii) kaolinite from Devonian Molasse in the Qilian Shan; and (iv) chlorite and muscovite from meta-volcanic rocks exposed across the Alashan Block. Sediment transport pathways involve a combination of colluvial, aeolian and fluvial (ephemeral and permanent) processes shaped by the topography. ASTER enabled mapping of compositional gradients related to two pathways, namely: (i) quartz sand driven by aeolian saltation in concert with the Yellow River; and (ii) clay and fine silt travelling large distances (>500 km) by long-term wind suspension. The most intact section of wall is found along the Hexi Corridor, which is poor in quartz sand and rich in (kaolinitic) clay and fine-silt, driven by wind-shielding by the Alashan Block. We also found evidence that the Ming: (i) mined loess from close by the wall (<1 km); (ii) targeted loess richer in finer fractions; and (iii) routinely applied a Ca-rich additive (probably lime).
