Abstract:Some present-day eolian sand sheets have small and width dunes, called zibars, as common type of depositional morphology. Their formation is related to different stabilizing factors, which reduce the availability of clastic materials for eolian processes. In fact, zibars are dunes which do not have time to develop a larger dune with slipface (proto-dune). Dunes in sands sheet areas generally are constructed by wind ripple laminations and commonly generate sedimentary succession less than 20 m thick, which are … Show more
“…The facies association 3 is interpreted as aeolian sandsheet deposits. The laterally continuous, planar to lowangled inclined, and parallel laminations with inverse grading are consistent with subcritical climbing translatent strata which are caused by migration, climbing, and accumulation of wind ripples (Cao et al, 2023;Fryberger et al, 1979;Hunter, 1977;Kocurek & Dott Jr., 1981;Mountney, 2006;Simplicio & Basilici, 2015). The horizontal bounding surfaces between the aeolian dunes and overlying aeolian sandsheets deposits are assumed to be deflation surfaces (Figures 4c,d, 5a,b and 9e-h), while the horizontal bounding surfaces between the aeolian sandsheets and overlying fluvial deposits are interpreted as flooding surfaces (Figure 9e,f; Langford & Chan, 1989).…”
Section: Facies Association 1: Aeolian Dunesmentioning
Aridification of Central Asia in the Late Mesozoic led to drastic environmental changes characterized by widespread aeolian deposits. We systematically investigated fluvial‐aeolian deposits in the Middle Jurassic Toutunhe Formation, Upper Jurassic Kalazha Formation, and Lower Cretaceous Tugulu Group in the Junggar Basin to the north of the Tianshan Orogenic Belt via unmanned aerial vehicle‐based photogrammetry, scanning electron microscope, grain‐size analysis, and detrital zircon geochronology. Paludal and deltaic environments transitioned to a fluvial‐aeolian environment from the late Middle Jurassic to the Late Jurassic. Fan delta and incisive braided river deposits accumulated in the earliest Cretaceous and evolved into a lacustrine environment with aeolian deposits in the lakeshore. Aeolian deposits are characterized by moderate‐ to well‐sorted and subangular to subround sandstones with large‐scale, high‐dip cross‐bedding, inversely graded lamination, dominant saltation grains, crescent‐shaped, and dish‐shaped impact structures. Aeolian deposits contain heavy minerals including more ilmenite, zircon, garnet, and, tourmaline and less magnetite and epidote than the fluvial deposits. The preserved aeolian sediments of the Kalazha Formation extend west–east for more than 100 km, suggesting a wide desert area during the latest Jurassic. The detrital zircon age patterns indicate that the provenance of the aeolian deposits was similar to that of coeval fluvial deposits. The cooccurrence of fluvial and aeolian deposits and the similar provenances but orthogonal flow directions indicate that the aeolian deposits were mainly sourced from the nearby fluvial material within the basin. The evolution of the fluvial‐aeolian system responded to a complete base‐level cycle controlled by the aridification and tectonics. Due to decreased sediment supply caused by aridification, the base level rose, leading to the change from braided rivers to meandering rivers, along with the deposition of aeolian sediments. Due to the tectonic reactivation in the Late Jurassic, the base level fell, causing the occurrence of alluvial fans and the expansion of the aeolian sediments. Previous studies revealed that the Tianshan in the Jurassic exhibited low relief. The fluvial‐aeolian system played an important role in maintaining the limited relief in southern Central Asia.
“…The facies association 3 is interpreted as aeolian sandsheet deposits. The laterally continuous, planar to lowangled inclined, and parallel laminations with inverse grading are consistent with subcritical climbing translatent strata which are caused by migration, climbing, and accumulation of wind ripples (Cao et al, 2023;Fryberger et al, 1979;Hunter, 1977;Kocurek & Dott Jr., 1981;Mountney, 2006;Simplicio & Basilici, 2015). The horizontal bounding surfaces between the aeolian dunes and overlying aeolian sandsheets deposits are assumed to be deflation surfaces (Figures 4c,d, 5a,b and 9e-h), while the horizontal bounding surfaces between the aeolian sandsheets and overlying fluvial deposits are interpreted as flooding surfaces (Figure 9e,f; Langford & Chan, 1989).…”
Section: Facies Association 1: Aeolian Dunesmentioning
Aridification of Central Asia in the Late Mesozoic led to drastic environmental changes characterized by widespread aeolian deposits. We systematically investigated fluvial‐aeolian deposits in the Middle Jurassic Toutunhe Formation, Upper Jurassic Kalazha Formation, and Lower Cretaceous Tugulu Group in the Junggar Basin to the north of the Tianshan Orogenic Belt via unmanned aerial vehicle‐based photogrammetry, scanning electron microscope, grain‐size analysis, and detrital zircon geochronology. Paludal and deltaic environments transitioned to a fluvial‐aeolian environment from the late Middle Jurassic to the Late Jurassic. Fan delta and incisive braided river deposits accumulated in the earliest Cretaceous and evolved into a lacustrine environment with aeolian deposits in the lakeshore. Aeolian deposits are characterized by moderate‐ to well‐sorted and subangular to subround sandstones with large‐scale, high‐dip cross‐bedding, inversely graded lamination, dominant saltation grains, crescent‐shaped, and dish‐shaped impact structures. Aeolian deposits contain heavy minerals including more ilmenite, zircon, garnet, and, tourmaline and less magnetite and epidote than the fluvial deposits. The preserved aeolian sediments of the Kalazha Formation extend west–east for more than 100 km, suggesting a wide desert area during the latest Jurassic. The detrital zircon age patterns indicate that the provenance of the aeolian deposits was similar to that of coeval fluvial deposits. The cooccurrence of fluvial and aeolian deposits and the similar provenances but orthogonal flow directions indicate that the aeolian deposits were mainly sourced from the nearby fluvial material within the basin. The evolution of the fluvial‐aeolian system responded to a complete base‐level cycle controlled by the aridification and tectonics. Due to decreased sediment supply caused by aridification, the base level rose, leading to the change from braided rivers to meandering rivers, along with the deposition of aeolian sediments. Due to the tectonic reactivation in the Late Jurassic, the base level fell, causing the occurrence of alluvial fans and the expansion of the aeolian sediments. Previous studies revealed that the Tianshan in the Jurassic exhibited low relief. The fluvial‐aeolian system played an important role in maintaining the limited relief in southern Central Asia.
“…The units with grad ual upward-in crease in lamina dip an gle may rep re sent rem nants of "trail ing" fa cies of a mi grat ing sand sea, as sug gested by S. Fryberger (writ ten comm., 2016). The phe nom e non of stacked zibars, sand sheet com plexes that formed an un usu ally thick sed i men tary suc ces sion (Simplicio and Basilici, 2015), proves sig nif i cant and sug gests a se creted ae olian bedform.…”
Section: Depositional Cycles Palaeoclimatic Cycles and The Phenomenomentioning
confidence: 94%
“…These zibar dunes (Simplicio and Basilici, 2015), are prob a bly sep a rate from "clas sic" sand sheets; as sum ing both the sand sheet lam i na tion sed i men tary deep is be tween 0 (hor i zon tal) -5°, and the zibar (slop ing sand sheet) lam i na tion sed i men tary deep is be tween 5-10°. The limit of 10° should be ana lysed in terms of con di tions that are fa vour able for form ing lee slope on dune forms (Fig.…”
Section: Depositional Cycles Palaeoclimatic Cycles and The Phenomenomentioning
A., 2016. Sand sheets in ter ac tion with ae olian dune, al lu vial and mar ginal playa beds in Late Permian Up per Rotliegend set ting (west ern part of the Poznañ Ba sin, Po land). Geo log i cal Quar terly, 60 (4): 771-800, doi: 10.7306/gq.1336The Up per Rotliegend de pos its of the west ern part of the Poznañ Ba sin, Po land, rep re sent three main sed i men tary en vi ronments: ae olian desert (dunes and sand sheets), al lu vial plain (al lu vial cov ers with wadi de pos its) and mar ginal playa. In arid pe ri ods, dunes prograded into ar eas dom i nated by al lu vial sed i men ta tion. Dur ing wet pe ri ods, al lu vial de pos its eroded the ae olian de pos its and prograded onto dune fields. Playa sed i ments were de pos ited among ae olian or al lu vial sed i ments during pe ri odic ex pan sions of the playa. These aeolian, allu vial and playa de pos its are ar ranged in depositional se quences. Bound aries be tween se quences are marked by rapid changes in depositional fa cies; and by ero sional bound ing sur faces. Max i mum Wet ting Sur faces have been dis tin guished within some parts of the depositional se quences, which en able regional cor re la tions. The sec tions stud ied are com posed of thick se quences of sand and sand-gravel sheets. The sand sheets rep re sent pe ri ods of strati graphic con den sa tion. Sys tems of sand sheets are typ i cal of mar ginal ar eas of ergs. We dis tin guish nine depositional com plexes (units) num bered 1-9 from base to top, re spec tively. These sub di vi sions are based on the in ter pre ta tion of the sedimentological re cord in palaeoclimatic terms, and in terms of ma jor ero sional bound aries, which are prob a bly of re gional ex tent. In the ae olian de pos its, ma jor bound aries are as so ci ated with de fla tion sur faces related to the sta bi li za tion of ground wa ter lev els. In the mar ginal playa de pos its, the most im por tant bound aries are cor re lated to transgressive sur faces that de vel oped dur ing playa ex pan sion. Time gaps rep re sented by the bound aries and the scale of ero sion be low them, are dif fi cult to es ti mate. The depositional sys tem of the Up per Rotliegend was dom i nated by sand and sand-gravel sheets, and is ei ther a unique fea ture in the en tire South ern Perm ian Ba sin or, as we as sume, sand sheets oc cur more com monly in the Rotliegend than has been pre vi ously thought.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.