Paleowind Directions Research Articles

Reconstructing Redox Landscape With Coupled Nitrogen‐Sulfur Isotopes: A Case Study From Middle‐Late Triassic Chang 7 Member of the Yanchang Formation in the Ordos Basin (North China)

AbstractEuxinia, a crucial geological condition, usually signifies more severe extinction events attributed to deoxygenation in Earth's history. Despite extensive exploration of various proxies in paleoredox studies, most are primarily utilized to reconstruct atmospheric pO2, the proportion of anoxic water relative to the entire basin, and broader trends in redox states. Few, however, hold the capacity to precisely delineate local euxinia within confined areas. To address this gap and gain insights into the temporal and spatial extent of benthic euxinia, we propose leveraging the synergistic analysis of total nitrogen isotopes (δ15NTN) and pyrite sulfur isotopes (δ34Spy). Our study focuses on the Triassic Chang 7 Member from the Yanchang Formation, Ordos Basin, North China. Through coupling the δ15NTN and δ34Spy systematics on 11 drill cores within the Ordos Basin, we reconstruct the temporal and spatial distribution of the benthic euxinia zone during the Chang‐7 period. Our results suggest strong spatial heterogeneity of benthic redox conditions, with the euxinia boundary shifting from the central lake to the southwestern sections. Moreover, we identify redox‐controlling factors, including organic carbon loading, water depth, and potential water circulation, and evaluate their interplay with benthic euxinia. Furthermore, the discernment of water circulation patterns may provide an innovative approach to restore the paleowind direction. These findings highlight the effectiveness of coupling δ15NTN and δ34Spy in reconstructing the local benthic redox landscape of benthic environments, and enrich our understanding of biogeochemical processes.

Reconstructions of Paleowind Directions in the Pleistocene: Evidence from the Anisotropy of Magnetic Susceptibility of the Loess–Paleosol Series of Tajikistan and the Azov Region

Reconstructions of Paleowind Directions in the Pleistocene: Evidence from the Anisotropy of Magnetic Susceptibility of the Loess–Paleosol Series of Tajikistan and the Azov Region

Reconstructions of Paleowind Directions in the Pleistocene: Evidence from the Anisotropy of Magnetic Susceptibility of the Loess–Paleosol Series of Tajikistan and the Azov Region

Abstract—The magnetic fabric of the reference Khonako-II (south Tajikistan), Beglitsa, and Chumbur-Kosa (Azov region) loess-paleosol sections was studied to reconstruct the paleowind directions during the Middle and Upper Pleistocene. The paleosols and loesses of the Khonako-II section represent a promising object for study of paleowinds. Our data indicate a prevailing ~ northwestward or ~northeastward wind directions during accumulation of the upper 40.8 m of the section. Thereby, a change from warm (pedocomplex 2) to cold (loess 2) epochs during the accumulation of the lower half of the studied sequence (end of the Middle Pleistocene) was accompanied by “switching” the predominant winds (from northwestern to northeastern ones), whereas accumulation of the upper part of the sequence was mainly controlled by winds of intermediate directions. The latter can be considered as evidence for the lesser contrast of wind rose during later epochs that were responsible for the formation of the upper part of the sequence. The study revealed that the magnetic fabric of loess and paleosol horizons of the Azov region sequences was deformed and cannot be used for paleowind reconstruction. It was demonstrated that sampling using plastic container technique widely applied in studying loess–paleosol deposits could led to the significant deformation of primary magnetic fabric.

Paleo-trade wind directions over the Yangtze Carbonate Platform during the Cambrian–Ordovician, Southern China

AbstractThe Sichuan Basin was a part of the Yangtze Carbonate Platform (YCP) during the Cambrian–Ordovician, and marine carbonates were deposited in the basin during this interval. Although previous studies have evaluated the paleogeography, paleoclimate and paleoecology of this basin, they have primarily focused on the paleoecology and biological evolution in the basin; however, analysis of paleogeography and paleoclimate is lacking. This study integrated outcrop sedimentological and magnetic fabric data to document sedimentary differentiation and anisotropy of magnetic susceptibility (AMS) within the YCP. The aims of this study were to infer paleowind directions during each epoch of the Cambrian–Ordovician and to constrain the paleogeographic location of the YCP. The northwestern, central and southeastern sides of the YCP were characterized by high-energy deposition (e.g. sub-angular to rounded intraclasts), medium-energy deposition (e.g. sub-angular to sub-rounded intraclasts) and low-energy deposition (e.g. angular to sub-angular intraclasts), respectively. The centroid D-Kmaxvalues for the Early, Middle and Late Cambrian were 116° ± 52°, 145° ± 57° and 159° ± 62° from the present north, respectively; corresponding values for the Early, Middle and Late Ordovician were 169° ± 70°, 139° ± 73° and 91° ± 68° from the present north, respectively. Sedimentary differentiation and AMS results indicated that the prevailing wind directions during the Early Cambrian, Middle Cambrian, Late Cambrian, Early Ordovician, Middle Ordovician and Late Ordovician were 296° ± 52°, 325° ± 57°, 339° ± 62°, 349° ± 70°, 319° ± 73° and 271° ± 68° from the present north, respectively. The present study provides evidence for the location of the YCP during the Cambrian–Ordovician via the correspondence between the paleowind directions over the YCP and the trade winds in the Northern and Southern hemispheres. The novelty of this study lies in the following aspects: (1) it integrates microfacies and AMS analyses to establish paleowind patterns; (2) it constrains the paleo-hemispheric location of the YCP during the Cambrian–Ordovician; and (3) it provides a reference for further studies of the paleoclimate and paleogeography of the YCP during the Cambrian–Ordovician.

Provenances of the Oldest Xiashu loess and Xuancheng loess in southern China: Implications for dust transport and dust proxies of the East Asian winter monsoon

The loess-paleosol sequences of southern China are valuable paleoclimatic archives since the Middle Pleistocene, on the regional and global scales. Knowledge of loess provenance can shed light on dust transport and the development of paleoclimatic proxies for loess deposits. However, there is a research gap regarding the provenance of the Oldest (∼0.9 Ma) Xiashu loess near the Yangtze River valley. The precise source area of the Xuancheng loess in southern China remains to be unidentified. In this study, we used elemental geochemistry and detrital zircon UPb ages to identify the sources of the Oldest Xiashu loess and Xuancheng loess in southern China. The Oldest Xiashu loess is dominantly derived from Yangtze River sediments, and part of its fine-grained dust component originates from the arid regions of Central Asia or northern China. The elemental compositions of the size-fractionated silicates and detrital zircon UPb ages of the Xuancheng loess are like those of the Shuiyang River sediments in the Xuancheng region. These results demonstrate that the Xuancheng loess is mainly the product of local dust activity in the Xuancheng regions, and thus that the Xiashu and Xuancheng loess are the products of independent dust transport processes. This spatial differentiation of loess provenance may be a widespread phenomenon in southern China, and consequently, the grain size compositions of the various loess sections in southern China cannot be used to recover paleo-wind directions on a regional scale. Overall, our study shows that when the grain size compositions from the southern China loess are used to reconstruct East Asian winter monsoon intensity, the signals from local wind fields should first be removed.

Holocene evolution of parabolic dunes, White River Badlands, South Dakota, USA, revealed by high-resolution mapping

AbstractThe White River Badlands (WRB) of South Dakota record eolian activity spanning the late Pleistocene through the latest Holocene (21 ka to modern), reflecting the effects of the last glacial period and Holocene climate fluctuations (Holocene Thermal Maximum, Medieval Climate Anomaly, and Little Ice Age). The WRB dune fields are important paleoclimate indicators in an area of the Great Plains with few climate proxies. The goal of this study is to use 1 m/pixel-resolution digital elevation models from drone imagery to distinguish Early to Middle Holocene parabolic dunes from Late Holocene parabolic dunes. Results indicate that relative ages of dunes are distinguished by slope and roughness (terrain ruggedness index). Morphological differences are attributed to postdepositional wind erosion, soil formation, and mass wasting. Early to Middle Holocene and Late Holocene paleowind directions, 324°± 13.1° (N = 7) and 323° ± 3.0° (N = 19), respectively, are similar to the modern wind regime. Results suggest significant landscape resilience to wind erosion, which resulted in preservation of a mosaic of Early and Late Holocene parabolic dunes. Quantification of dune characteristics will help refine the chronology of eolian activity in the WRB, provide insight into drought-driven landscape evolution, and integrate WRB eolian activity in a regional paleoenvironmental context.

Reconstruction of paleowind directions during the Cambrian-Ordovician in the Tarim Basin, Northwestern China

The Tarim Basin was in the lower latitudes during the Cambrian-Ordovician, during which it experienced marine carbonate platform deposition. Although the platform is in the Trade Winds belt, the specific prevailing quantitative paleowind direction remains uncertain. This study integrated drill core and outcrop sedimentological data with outcrop magnetic fabric data to document sedimentary differentiation and anisotropy of magnetic susceptibility (AMS) within the Tarim Carbonate Platform (TCP). The aims of this study were to infer paleowind directions during each epoch of the Cambrian-Ordovician and to constrain the paleogeographic location of the TCP. The characteristics of the south, central, and northern sides of the platform were indicative of high-energy deposition (e.g., sub-angular to sub-rounded intraclasts with sparite cements), medium-energy deposition (e.g., angular to sub-rounded intraclasts with microspar and sparite cements), and low-energy deposition (e.g., angular to sub-angular intraclasts with microspar cements), respectively. AMS measurements yielded mean paleocurrent directions for the Early, Middle, and Late Cambrian of 226° ± 42°, 207° ± 43°, and 193° ± 36° from present north, respectively, whereas those for the Early, Middle, and Late Ordovician were 178° ± 39°, 165° ± 43°, and 155° ± 52° from present north, respectively. The results of sedimentary differentiation and AMS indicated that the prevailing wind directions of the Early Cambrian, Middle Cambrian, Late Cambrian, Early Ordovician, Middle Ordovician, and Late Ordovician were 226° ± 42°, 207° ± 43°, 193° ± 36°, 178° ± 39°, 165° ± 43°, and 155° ± 52° from present north, respectively. Since the TCP has rotated clockwise by ∼90° since the Ordovician, the paleowind directions of the Early, Middle, and Late Cambrian were 146° ± 42°, 117° ± 43°, and 103° ± 36° from paleo-north, respectively. The paleowind directions of the Early, Middle, and Late Ordovician were 88° ± 39°, 75° ± 43°, and 65° ± 52° from paleo-north, respectively. The TCP shifted from Southern Hemisphere to the Northern Hemisphere from the Early Cambrian to the Late Ordovician. The TCP was close to the Equator during the Early Ordovician. The novelty of this study related to: (1) integrating microfacies and AMS analyses to establish paleowind patterns; (2) constraining the paleo-hemispheric location of the TCP during the Cambrian-Ordovician; (3) providing references for the further study of paleoclimate and paleogeography of the TCP during the Cambrian-Ordovician.

Paleowind Directions over the Tarim Block during the Mesoproterozoic, Northwestern China

The Tarim Block is an ancient plate with a basement of ancient continental crust, which has been separated from the Rodinia supercontinent since the Neoproterozoic. During the Neoproterozoic, which lasted nearly 500 Myr, this block experienced significant evolutionary processes, such as proliferation, radioactive decay of elements, and gradual cooling and solidification. The investigation of Neoproterozoic paleogeography may shed light on the evolution of these geological events. In order to realize this potential, this study aimed to infer paleowind directions over the Tarim Block during each epoch of the Cryogenian–Ediacaran and to constrain the paleogeographic location of the Tarim Block. To this end, outcrop magnetic fabric data were employed to analyze the anisotropy of magnetic susceptibility within the Tarim Block. The anisotropy of magnetic susceptibility measurements yielded mean paleowind directions of 308° ± 69°, 277° ± 78°, and 256° ± 76° from the present north for the Early, Middle, and Late Cryogenian, respectively; the corresponding values for the Early and Late Ediacaran were 237° ± 77° and 254° ± 73° from the present north, respectively. Considering the rotation relationship of the Tarim Block from the Neoproterozoic to the present, the paleowind directions during the Early, Middle, and Late Cryogenian were ~55°, ~35°, and ~35° from the paleo-north, respectively. The paleowind directions during the Early and Late Ediacaran were ~35° and ~60° from paleo-north, respectively. By referring to the correspondence between the paleowind directions over the Tarim Block and trade winds in the Northern Hemisphere, this study provides evidence for the location of the Tarim Block during the Cryogenian–Ediacaran. The main contributions of this study can be summarized as follows: (1) paleowind patterns are established through the analysis of the anisotropy of magnetic susceptibility; (2) the paleogeographic location of the Tarim Block during the Cryogenian–Ediacaran is constrained; and (3) a reference for further study of the paleogeography of the Tarim Block during the Cryogenian–Ediacaran is provided.

Late Triassic paleowinds from lacustrine wave ripple marks in the Fleming Fjord Group, central East Greenland

Geological evidence of paleoclimate conditions provide important constraints on paleoclimate models. Paleowinds are one of the central paleoclimate parameters in global circulation models used to reconstruct past climatic conditions. However, only a few climate proxies such as eolian dunes and shallow-water wave ripples provide information on paleowind directions. In this study, we present new paleoclimatic data based on lacustrine sediments with wave ripple marks in the Upper Triassic Fleming Fjord Group, central East Greenland deposited at very shallow water depth in the northern part of Pangaea in a mid-latitude, warm-temperate climate. Wave-ripple orientations are measured on 380 individual fossilized wave-rippled beds at four localities in the ~8500 km 2 lacustrine basin. These ripple data are used to establish a geologic wind proxy and are compared to previously published general circulation models. Two wave ripple orientations are observed: The dominant ripple orientation and wave ripple characteristics indicate paleowinds from the Late Triassic SSE and NNW (154.5° and 334.5°), while a subordinate orientation indicate paleowinds from W or E (270° or 90°). This paleowind regime remained stable for at least ~7.5 million years during the mid-late Norian (218.5-211 Ma). These results correspond very well with some general circulation model results that suggest summer winds from the NNW and winter winds from the SSE. Based on the great compatibility between empirical data and general circulation model results, the wind pattern seems to have been greatly influenced by regional, Late Triassic mountain topography in the present-day Greenland and Norway channeling the paleowind in the northernmost part of the pre-Atlantic rift basin (the mid-Norwegian-east Greenland rift system).

The lithified aeolian dune field adjacent to the Apollinaris Sulci, Mars: Geological history and paleo-wind record

A lithified aeolian dune field in the Apollinaris Sulci region of Mars presents a unique opportunity to study ancient aeolian processes and paleo-wind conditions during an earlier episode of martian climate history. The ancient dunes occur inside an eroded, partly-filled impact structure. The petrified dune field retains its original geomorphology and has south-, south-southeast-, and south-southwest-facing lee slopes, indicating dominance of a north-to-south paleo-wind direction. The preserved dunes have crescentic and marginal barchan morphologies with crestlines ranging from 100 m to 7 km in length. To the north of the preserved dunes, the yardangs of the Apollinaris Sulci, eroded into strata of the Medusae Fossae Formation, have an average orientation (azimuth) of 169°. The yardangs are interpreted to form from reversing winds along this orientation, in contrast with the northerly winds that formed the paleodunes. The observed paleodunes, yardangs, modern bedforms, and abundant dust cover collectively demonstrate that the climate has changed over time. Certain, heavily eroded, slopes on the paleodunes show crest-parallel lineations interpreted as exposed cross strata. Second-order bounding surfaces within the strata provide evidence that the meter-scale, superimposed bedforms migrated across some lee faces when the dunes were active. This potentially reflects preservation of ancient bedforms analogous to the “large martian ripples” commonly observed on active martian dunes today. In the paleo-interdune spaces, linear ridges and grooves are interpreted as preserved paleo-transverse aeolian ridges. The juxtaposition of these three common martian bedforms – dunes, transverse aeolian ridges, and large martian ripples – all preserved in close proximity, suggests Mars in the Hesperian epoch was subject to similar aeolian dynamics as are observed today.

Paleowind directions from the magnetic fabric of loess deposits in the western Chinese Loess Plateau and implications for dust provenance

AbstractThe aeolian loess-paleosol sequences in the Chinese Loess Plateau (CLP) are an excellent archive of variations in atmospheric circulation in the geological past. However, there is no consensus regarding the roles of the East Asian winter monsoon and westerly winds in transporting the dust responsible for loess deposition during glacial and interstadial periods. We conducted detailed measurements of the anisotropy of magnetic susceptibility (AMS) on two parallel loess profiles covering the most recent 130 ka in the western CLP to determine paleowind directions. Results show that the magnetic lineations of the loess and paleosol units in both sections are significantly clustered along the northwest to southeast direction. These observations demonstrate that the prevailing wind system responsible for dust transport in the western CLP was the northwesterly winter monsoon, rather than the westerly winds. The AMS-derived dust-bearing wind direction was relatively stable during the last glacial and interglacial cycle in the western CLP, consistent with sedimentary and AMS evidence from the eastern CLP. Accordingly, it is reasonable to conclude that large areas of deserts and Gobi deserts areas located in the upwind direction were the dominant sources for the aeolian deposits of the Loess Plateau.

An Attempt to Recover a Paleomonsoon Signal in the Chinese Loess Plateau Using Anisotropy of Magnetic Susceptibility

The paleowind direction in the Chinese Loess Plateau (CLP) was studied using anisotropy of magnetic susceptibility (AMS) data. Magnetic fabrics were examined for the last glacial loess (L1) and last inter-glacial paleosol (S1) in the southern and central CLP along a present day precipitation zone of 600 mm per year. Statistical analyses of the orientations of AMS ellipsoids indicate that strong rainwater events may cause random distributions for the AMS azimuth of maximum axis and no deviation from the vertical plane for the average minimum axis. As high rainfall can distort paleowind analyses, it is challenging to conduct paleowind studies on the southern CLP - a topography of high precipitation density. Future studies could focus on the western and northern CLP, where there is less rainfall, making it more suitable for paleowind analysis by AMS.

Loess-derived polygenetic soils of North-Western Italy: A deep characterization of particle size, shape and color to draw insights about the past

The multiplicity of units present in a single loess bed greatly complicates the reconstruction of the history of polycyclic loess-derived soils. The present study implemented a combination of techniques to characterize different depositional events in a pedogenized loess formation of North-Western Italy. Field morphological observations, laboratory Particle Size Distribution (PSD) analyses, and single-grain image processing techniques were applied.Five different loess depositions, or cycles, were distinguished in the field. Laser PSD curves highlighted the fine nature of the studied loess, which stood out even in comparison to similar Italian loess-derived soils. All PSD functions showed a tri/bimodal distribution with a dominant peak at 8–14 μm, wider in younger depositions. The second most relevant peak, at 0.5–4 μm, displayed a greater intensity in older cycles where it also fell in correspondence of slightly bigger particles. The fine-grained nature of the loess was read as a sign of its alluvial origin, therefore the Po plain has been addressed as the source of the material. This hypothesis was supported by evidence of a dominant SE-to-NW paleo-wind direction, proved by the spatial trends of the coarse and fine silt fractions. The typical aeolian size-dependant depositional trait of one of the cycles (IV) was however opposite to that of the other four loess depositions. Therefore, the source of this material was attributed to a site North of the study area where, right behind the Lanzo ultramafic massif, an ice lobe stretched during the Last Glacial Maximum (LGM). Image analysis supported this hypothesis: as the loess grains of cycle IV were significantly darker colored than the others, this would agree with the provenance from an ultramafic source. In conclusion, the variety of applied techniques allowed us to combine different pieces of information in order to assess the physical and morphological properties of the studied loess-derived soils, trying to determine the most probable sources of the material and the weathering pathways.

Early Pennsylvanian fluvial - Aeolian interplay in the Amazonas Basin (central-western Gondwana) and its relation to marine transgression

The Monte Alegre Formation corresponds to the main reservoir rock in the Amazonas Basin petroleum system in Brazil and is correlated with the Pennsylvanian rocks of the Parnaíba and Solimões basins. Previous outcrop and well-based studies are concentrated on the southern edge of the basin and show that the Monte Alegre Formation basically represents an aeolian, deltaic and transitional marine succession. However, there is no published research that demonstrates the depositional system in the northern edge of Amazonas Basin. In this sense, outcrop-based facies and stratigraphic analysis is carried-out to understand the distal influence of marine incursion into the basin and its relationship with paleogeography in the Upper Carboniferous. The data show that the aeolian Monte Alegre system is represented by a braided fluvial system formed by five architectural elements: (i) sandy bedform, (ii) downstream-accretion macroform, (iii) gravel bars and bedforms, (iv) channel and (v) laminated sand sheets, pointing to a braided depositional system. The aeolian succession overlies the fluvial system and is represented by medium-scale trough cross-bedding and large-scale planar cross-bedded sandstones resulting from the accumulation and migration of transverse dunes toward the northwest that grade upward to dry interdunes and aeolian sand sheet deposits that are interbedded, consisting basically of translatent ripple cross-lamination and low-angle cross-stratified lamination sandstones related to water table raises. The stratigraphic record defines a wetting-upward stacking pattern of Monte Alegre Formation resulting from local sea level rise as a result the advance of the marine incursion that settled in the central-western region of Gondwana during the Late Carboniferous. Thus, in addition to corroborating the paleo wind directions predicted for the region during the Late Carboniferous, these deposits help to understand the paleoenvironmental relations between the northern and southern edges of the Amazonas Basin.

Tectonic and paleogeographic controls on development of the Early–Middle Ordovician Shanganning carbonate platform, Ordos Basin, North China

Lower–Middle Ordovician platform carbonates are important oil and gas reservoir rocks in the Ordos Basin of the North China craton (NCC). In recent years, numerous cores have been recovered from these units, but the depositional environments and facies architecture of this large carbonate platform system have not yet been reported in detail. This study integrates sedimentological and magnetic fabric data collected from outcrops and cores to document variation in microfacies and facies associations within the Shanganning carbonate platform (SCP), infer paleowind directions and the paleogeographic location of the SCP, and evaluate tectonic and paleogeographic controls on platform development. This analysis documented 25 microfacies belonging to 7 microfacies fabric and sediment types: carbonate mudstone, wackestone, packstone–grainstone, evaporite, bindstone–framestone, siliciclastics, and dolostone. Microfacies can be grouped into facies associations that represent tidal-flat, open-platform, restricted-platform, evaporite-platform, platform-margin, slope, and deep-basinal depositional environments. These environments are mainly distributed zonally around the L-shaped Qingyang paleo-uplift on the western and southern margins of the SCP. Anisotropy of magnetic susceptibility measurements at five platform-margin locales yielded paleocurrent directions of (all approximately) 318°–348°, 51°–81°, 42°–72°, 80°–110°, and 54°–84° from paleo-north after correction for a 120°–150° clockwise rotation of the NCC since the Ordovician. The depositional architecture of the SCP depended on a combination of tectonic and paleogeographic (wind) influences. Local tectonic movements controlled the spatial distribution of facies associations around the Qingyang paleo-uplift, which was characterized by open, restricted, and evaporite-platform facies in the platform interior and mainly slope and basinal facies on the outer-platform margin (to the west and south of the Qingyang paleo-uplift). Vertical tectonic movements resulted in cyclic submergence and emergence of the platform over its approximately 20-m.y.-long formation history. Paleo–trade winds influenced aspects of facies zonation across the platform, including growth of metazoan reefs on the windward platform margin and formation of oolitic grainstone and microbial reefs on the leeward platform margin. The facies model for the SCP developed in this study should provide a useful reference framework for future carbonate oil and gas exploration in Lower–Middle Ordovician units of the Ordos Basin. Furthermore, this study makes innovative use of magnetic anisotropy data, in combination with standard petrographic, core, and field data, to discern facies patterns and controls on a paleo-carbonate platform, which is an integrated methodology that may serve as a model for future studies of other carbonate platforms.

Influence of paleo-Trade Winds on facies patterns of the Cambrian Shanganning Carbonate Platform, North China

The Shanganning Carbonate Platform (SCP) of the North China Craton (NCC) was located in the Trade Winds belt during the Cambrian, which influenced its facies development. In recent years, numerous drillcores have been recovered from these units, but the depositional environments and facies architecture of this large (~2.0 × 105 km2) carbonate platform system have not yet been reported in detail. In this study, we integrate sedimentological and magnetic fabric data collected from outcrops and drillcores in order to document variation in microfacies and facies associations within the SCP, to infer paleowind directions and constrain the paleogeographic location of the SCP, and to evaluate eolian controls on platform development. This analysis documented numerous carbonate microfacies belonging to six fabric types (mudstone, wackestone, packstone, grainstone, framestone, and dolostone) along with rarer siliciclastic sediments. These microfacies belong to facies associations representing tidal flat, open platform, platform margin, slope, and deep basinal depositional environments. Anisotropy of magnetic susceptibility (AMS) measurements yielded mean paleocurrent directions for the Early, Middle, and Late Cambrian of 114°, 63°, and 83° (± ~30°) from paleo-north, respectively, that were relatively consistent for 12 out of 13 platform-margin sites, all vectors being corrected for a post-Cambrian ~150° clockwise rotation of the NCC. These wind orientations are consistent with the SCP shifting from south of the paleo-Equator in the Early Cambrian to north of it by the Middle Cambrian. Paleo-Trade Winds influenced facies patterns across the platform, producing a distinct windward-leeward zonation. The windward margin is characterized by well-sorted oolitic grainstone, as well as (favositids) coral and (dasycladacean) algal-sponge framestone, and the leeward margin by poorly-sorted oolitic wackestone-grainstone and fine bioclastic sediments. The present study is innovative in 1) integrating microfacies and AMS analyses in order to establish paleowind patterns and influences on an ancient carbonate platform, 2) documenting windward-leeward variation in quantifiable sediment properties across the SCP, and 3) constraining the paleo-hemispheric location of the NCC during the Cambrian.

Pronounced changes in paleo-wind direction and dust sources during MIS3b recorded in the Tacheng loess, northwest China

Central Asia loess deposits can yield detailed records of aridification across the Asian interior, as well as the atmospheric circulation. In this study, we presented grain size, heavy mineral assemblage, rock magnetism and anisotropy of magnetic susceptibility of a loess section in the Tacheng Basin in Xinjiang region, NW China. The results of anisotropy of magnetic susceptibility indicated that a near-surface SE wind prevailed in the Tacheng area since Marine Isotope Stage (MIS) 3, while a near-surface SW prevailing wind developed during MIS3b. We inferred that the change of wind direction was due to glacial advance during MIS3b. Combining the result of anisotropy of magnetic susceptibility with grain size, heavy mineral assemblage data and previously published low-field mass susceptibility revealed that dust transported by the near-surface SW wind had a greater ability to enhance magnetic susceptibility and higher amphibole/epidote ratio. Additionally, a strong Siberian High during Heinrich Event (H)5 at ca. 48 ka blocked the advection of moisture into the region via mid-latitude westerlies, causing glacial recession and the weakening of the prevailing SW wind. Our study has implications for identifying changes in paleo-wind direction and dust source, which can aid understanding of the influence of westerlies and the Siberian High on dust accumulation, as well as their interactions.

Late Jurassic-Early Cretaceous Erg Deposits in the Mengyin Basin, Western Shandong Province, China: Inferences about the Wind Regime and Paleogeography

The Late Jurassic-Early Cretaceous Santai Formation, sporadically distributed in western Shandong Province, comprises terrestrial alluvial-eolian successions, which records regional wind patterns and paleogeography in eastern North China. This paper conducts an analysis of eolian stratification, bounding surfaces, facies architecture and paleowind direction of the Santai Formation in the east of the Mengyin Basin, western Shandong Province. Three basic types of eolian stratification are recognized in the Santai Formation, including grainflow strata, wind ripple strata and adhesion strata, and have been grouped into eolian dune and interdune facies associations. The occurrences of reactivation surfaces and superimposition surfaces within eolian dune deposits indicate active compound dunes or draas. The association of adhesion strata with grainflow or windripple strata is the development of a wet eolian system. Cross-strata dip direction indicates different paleowind directions from the lower to the upper part of the Santai paleoerg. The lower part of the paleoerg was characterized by paleowinds blowing from northwest to northeast, whereas the upper part was under the influence of paleowinds consistently towards east to northeast. The identified changes in wind directions possibly suggest wind regime shifts from monsoon circulation to westlies of planetary wind system, which may be related with the collapse of the East China Plateau during the Late Jurassic to Early Cretaceous.

Feasibility of applying viscous remanent magnetization (VRM) orientation in the study of palaeowind direction by loess magnetic fabric

AbstractThe loess formation sampling method on the Chinese Loess Plateau generally involves the acquisition of samples from the basset section and the drilling core. Constraints imposed by the precision of the drilling machine operation make it difficult to determine the orientation of the samples due to the rotation of the core.Although researchers have proposed solutions for reconstructing the north direction of the samples by adopting the viscous remanent magnetization (VRM) orientation, it remains uncertain whether this approach can be adopted in studies that use the magnetic fabric to trace the palaeomonsoonal direction, and the degree to which this approach will change the magnetic fabric results.Based on the achievements of other researchers, we adopted the VRM orientation of the basset section samples oriented in the field. By determining how the VRM orientation changes the magnetic fabric of loess over different demagnetization temperature ranges, we can draw the preliminary conclusion that there is no significant difference between the magnetic fabric information of the loess obtained at 100–150°C VRM orientation and that obtained from the field orientation (the statistical bin size is 22.5°, significance level α = 0.05). This indicates that the VRM orientation approach is feasible for studying non-oriented drilling core samples to determine the prevailing surface paleowind direction with appropriate precision.

Delineation of early Jurassic aged sand dunes and paleo-wind direction in southwestern Wyoming using seismic attributes, inversion, and petrophysical modeling

Moxa Arch is a potential site for carbon sequestration in the state of Wyoming, recognized by the US Department of Energy. In this paper, we primarily focus on improving our understanding of the geology, including lithofacies and depositional environment, of Nugget Sandstone-a potential carbon storage reservoir, by integrating results from three different techniques including seismic attributes, seismic inversion, and petrophysical modeling. The Nugget Sandstone formation is primarily an eolian sandstone, deposited in the early Jurassic and is present throughout southwestern Wyoming. Seismic attribute analysis indicates the presence of NW-SE trending elongated geological features in the Nugget Sandstone interval. Based on our seismic and well log analyses, we interpret these features to be eolian sand dunes, which is consistent with the previous publications indicating a general NE-SW paleo-wind direction at the time of the deposition of Nugget Sandstone and other equivalent formations in Wyoming and Utah. The petrophysical analysis indicates that the Nugget Formation is mostly composed of quartz; however, clay and evaporites such as anhydrite and halite are also present. The acoustic impedance, derived from well logs, indicates that high porosity dunal sandstones correspond to low impedance values whereas interdunal evaporites are characterized by high impedance values. Combined analysis of seismic attribute coherence and inverted P-impedance discriminates the dunal and interdunal deposits in 3D seismic data volume; the low coherence defines the extent of low impedance dunal deposits. Detailed analysis of the curvature attribute from the seismic data indicates a dominant paleo-wind direction of approximately N225°.