Subaqueous Deposits Research Articles

Late Carboniferous–Early Permian sedimentary–tectonic evolution in the eastern Qaidam Basin, Western China: Insight into the zircon U–Pb geochronology of ash-fall tuffs and sandstones

The Late Carboniferous–Early Permian period is a significant transitional phase within the late Paleozoic ice age and to investigate the sedimentary–tectonic evolution of the Qaidam Basin in this period is crucial for comprehensively understanding the tectonic history of the northeastern Paleo-Tethys Ocean and the related response to energy and mineral resources. This paper focuses on the Carboniferous–Permian strata of the Wanggaxiu-Dongdagou outcrop that was taken to represent the southern Oulongbruk terrane in the eastern Qaidam Basin. We determined the ages of tuff interbeds within the Zhabusagaxiu Formation originally identified as the upper Carboniferous and obtained the crystallization age spectra of detrital zircon grains from Carboniferous to lower Permian sandstones using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) isotope geochemical techniques. The origin of the volcanic ash and the sedimentary–tectonic evolution in this period were analyzed. The results indicate that the original Zhabusagaxiu Formation can be divided into two chronostratigraphic units: the upper Carboniferous Zhabusagaxiu Formation and the lower Permian. The earliest age obtained from tuffaceous layers within the dark shale interval is 297.8 ± 3.0 Ma (mean square weighted deviation (MSWD) = 0.87), which suggests a stratigraphic boundary between the Carboniferous and Permian periods. Detrital zircons from Carboniferous–Permian samples in the southern Oulongbruk terrane predominantly originated from the Qaidam block-North Qaidam ultrahigh-pressure belt continental island arc to the south. The ultrahigh-pressure belt had a significantly increased contribution to the detrital source supply system from the Late Carboniferous to Early Permian, while the Qaidam block experienced frequent volcanic eruptions from 298 to 293 Ma, dispersing volcanic ash only northward to the Oulongbruk back-arc basin and the Zongwulong Trough. The upper Carboniferous Zhabusagaxiu Formation was marked by siliceous clastic rock–carbonate rock interbedding in an epicontinental sea, while the lower Permian was characterized by shallow to bathyal marine shelf to subaqueous sedimentation. The Early Permian transgression potentially represents the largest transgression during the late Paleozoic ice age, indicating an enriched hydrocarbon-generating interval.

Nikolaevo-Otradnoye II—A New Early and Middle Paleolithic Site in the Northeastern Azov Region

We describe materials from a new Paleolithic site, discovered in 2020 on the right bank of Mius estuary, near its confl uence with the Taganrog Bay of the Sea of Azov, in the southern outskirts of the village of Nikolaevo-Otradnoye, which is in the Neklinovksky District of the Rostov Region. The clearing of a 10-meter-high river-bluff revealed a complex stratigraphy of subaqueous and subaerial Late and Middle Pleistocene rocks. Horizons with lithics and faunal remains were identifi ed. Cultural remains found in the coastal exposure and in the stratigraphic section belong to the Early and Middle Paleolithic. The early stage in the peopling of the Northeastern Azov and the Lower Don regions is documented by Early Paleolithic artifacts found in the subaqueous deposits of layers 5 and 6 (MIS 9–11, ~420– 270 ka BP). Heavil y waterworn patinated lithics include a core-shaped artifact, variou s types of side-scrapers, a scaled piece, fl akes, and chips. This complex is an informative addition to known complexes from the region, including contemporaneous ones. The most interesting is the Middle Paleolithic industry of layer 4 under the Kamenka (?) soil— layer 3, MIS 7. The toolkit consists of a diagonal side-scraper and a chip found in the section, as well as radial and Levallois cores, various side-scrapers, a par tly bifacial tool, spalls , and chips found in the denudation. Technological and typological criteria (primarily the Levallois technology) and the tentative date of non-waterworn patinated lithics make it possible to attribute them to the Early Middle Paleolithic of the southern Russian Plain. It is concluded that cultural remains of the Early Middle Paleolithic, dating to ~243–191 ka BP, have been found in the region for the fi rst time, fi lling the gap in the local Early Middle Paleolithic sequence. In adjacent regions, similar industries have been known since the late 1900s.

New data on the Late Paleozoic Ice Age glaciomarine successions from Tasmania (SE Australia)

The Late Paleozoic Ice Age (LPIA) is one of the coldest periods in Earth history, and led to the diachronous development of widespread ice centers across Gondwana in the Carboniferous and Permian. In Tasmanian Basin, located between northern Victoria Land (Antarctica) and Australia, the lowermost part of the Parmeener Supergroup (Late Carboniferous to Triassic), consisting of the Wynyard Tillite and its correlatives (Truro and Stockers tillites), recorded LPIA glacial sedimentation linked with ice covers that developed in the region. We carried out a detailed facies analysis of two drillcores which recovered glaciogenic sequences deposited in the Tasmanian Basin. Facies associations vary from possibly sub-glacial or ice-contact to ice-distal. Diamictite is the most common facies and its deposition is driven both by gravity and sediment remobilization processes and suspension settling with ice rafted debris accumulation. Mudstone layers, with and without dropstones, are interposed between diamictite intervals, recording ice-distal to non-glacial conditions respectively. Facies associations are indicative of subaqueous deposition in glaciomarine environment. The glacial sequence stratigraphy approach was applied and glacial system tracts and bounding surfaces, which define glacial sequences, were identified. The stacking pattern of the facies associations allow us to demonstrate that the glacial sequences in the Tasmanian Basin recorded different phases of advance and retreat of the glacial front into the basin, at about the end of the main glacial phase.

Subaqueous plopstone deposits: a unique product of sinkhole development in eogenetic carbonates

Subaqueous plopstone deposits: a unique product of sinkhole development in eogenetic carbonates

Multi-proxy investigation of the post-evaporitic succession of the Piedmont Basin (Pollenzo section, NW Italy): A new piece in the Stage 3 puzzle of the Messinian Salinity Crisis

Paleoenvironmental reconstruction of the Mediterranean Basin at the end of the Messinian Salinity Crisis is contentious. One section that records this final phase (Stage 3) is the Pollenzo Section in the Piedmont Basin (NW Italy). Here, we present new stratigraphic, sedimentological, petrographic, micropaleontological (ostracods, calcareous nannofossils, foraminifera, dinoflagellates) and geochemical ( 87 Sr/ 86 Sr ratios) data from the Cassano Spinola Conglomerates (CSC) and interpret the paleoenvironment of this northernmost tip of the Mediterranean Basin. The CSC comprise three depositional units: members A and C, which were deposited subaqueously, and the intervening member B, which is continental. The CSC is topped by a ~ 50 cm-thick black layer, which is directly overlain by the open marine Argille Azzurre Formation of early Zanclean age. Our investigation reveals that member A is largely barren of autochtonous microfossils, except for an almost monospecific ostracod assemblage of Cyprideis torosa at the top, which indicates shallow-water (<30 m) conditions. Paratethyan ostracods and, possibly, taxa of calcareous nannofossils adapted to low-salinity water first occur in member C. 87 Sr/ 86 Sr ratios measured on ostracod valves from the member A/B transition (0.708871–0.708870) and member C (0.708834–0.708746) are lower than the coeval Messinian seawater values (~0.709024) and the 87 Sr/ 86 Sr ratios of a hypothetical lake filling Piedmont (>0.7090) estimated by means of the present-day 87 Sr/ 86 Sr signature of the Po river, the main drainage system of Northern Italy that receives the weathering products (including ions) of the Alps and Apennines. These values are likely to reflect the mixing of local high 87 Sr/ 86 Sr river water with low 87 Sr/ 86 Sr from the Mediterranean, which at the time was dominated by inputs from Eastern Paratethys, circum-Mediterranean rivers and Atlantic Ocean. Our results suggest that, at times during the final stage of the Messinian Salinity Crisis, the Piedmont Basin was hydrologically connected with the main Mediterranean Basin. At regional scale, this implies that the water level in the Mediterranean Basin was relatively high. • Piedmont Basin alternated subaqueous and continental conditions during MSC Stage 3. • 87 Sr/ 86 Sr values are inconsistent with subaqueous sedimentation in a local river-fed endorheic lake • Piedmont Basin-Mediterranean connection during times of Paratethyan ostracods spreading. • The Mediterranean water-level was occasionally relatively high during Stage 3.

Ancient Winds, Waves, and Atmosphere in Gale Crater, Mars, Inferred From Sedimentary Structures and Wave Modeling

AbstractWave modeling and analysis of sedimentary structures were used to evaluate whether four examples of symmetrical, reversing, or straight‐crested bedforms in Gale crater sandstones are preserved wave ripples; deposition by waves would demonstrate that the lake was not covered by ice at that time. Wave modeling indicates that regardless of atmospheric density, winds that exceeded the threshold of aeolian sand transport could have generated waves capable of producing nearshore wave ripples in most grain sizes of sand. Reversing 3‐m‐wavelength bedforms in the Kimberley formation are interpreted not as wave ripples but rather as large aeolian ripples that formed in an atmosphere approximately as thin as at present. These exhumed bedforms define many of the ridges at outcrops that appear striated in satellite images. At Kimberley these bedforms demonstrably underlie and therefore predate subaqueous beds, suggesting that a thin atmosphere existed at least temporarily before subaqueous deposition ceased in the crater. The other three candidate wave ripples (Square Top, Hunda, and Voe) are consistent with modeled waves, but other origins cannot be excluded. The predominance of flat‐laminated (non‐rippled) beds in the lacustrine Murray formation suggests that some aspect of the lake was not conducive to formation or preservation of recognizable wave ripples. Water depths may generally have been too deep, lakebed sediment may have been too fine‐grained, the lake may have been smaller than modeled, or the lake may have been covered by ice.

Characterization of large tsunamigenic landslides and their effects using digital surface models: A case study from Taan Fiord, Alaska

On 17 October 2015, a large landslide entered the marine waters of Taan Fiord, Alaska, and generated a displacement wave with a 193 m runup. The wave scoured the surrounding hillslopes of soil and vegetation and deposited significant volumes of material into the fjord, onto hillslopes on the opposite side of the fjord, and on top of Tyndall Glacier. For this study, we generated six, 2-m posting Digital Surface Models (DSMs) using DigitalGlobe/Maxar satellite imagery acquired near-annually between 2012 and 2019, and the Surface Extraction with TIN-based Search-space Minimization (SETSM) high-performance computing algorithm. We aligned the DSMs to exposed bedrock in the 01 March 2014 DSM acquisition, and then used them to characterize topographic and volumetric changes from before and after the 2015 Taan Fiord rock avalanche. We find that the landslide mobilized roughly 77. 0 ± 0.9 Mm3 of material, of which approximately 56.3 Mm3 were deposited in the fjord waters. Furthermore, we quantified an additional 27.2 ± 3.8 Mm3 of material scoured from fjord-adjacent hillslopes and deposited in the fjord waters, providing new constraints on the subaqueous deposition. This is the first time that DSMs have been used to estimate the volume of scour caused by a tsunami and the subsequent changes in extent and volume with time. Our results for the landslide and runout are consistent with field measurements published previously. This study offers improved estimates of both subaerial and subaqueous deposition for the 2015 Taan Fiord landslide and describes additional regional environmental conditions. We identify precursory motion prior to the 2015 landslide, characterize several smaller-scale landslides in the larger Taan Fiord region, delineate terminus positions and associated ice dynamics of the Tyndall Glacier, and detail seasonal changes in vegetation growth and snow melt/accumulation. This work provides important new insights into the geomorphic features and dynamics of this landslide and subsequent tsunami. The interdisciplinary applications associated with DSMs and the accuracy of the measurements presented here demonstrate that these methods are an effective tool to improve our understanding of the pre- and post-landslide processes, for monitoring areas at risk for landslides and other natural hazards, and for rapid response to catastrophic events.

A 4000-year debris flow record based on amphibious investigations of fan delta activity in Plansee (Austria, Eastern Alps)

Abstract. The frequency of debris flows is hypothesized to have increased in recent decades with enhanced rainstorm activity. Geological evidence to test the relationship between climate and debris flow activity for prehistoric times is scarce due to incomplete sediment records, complex stratigraphy, and insufficient age control, especially in Alpine environments. In lacustrine archives, the link between onshore debris flow processes and the sedimentary record in lakes is poorly investigated. We present an amphibious characterization of alluvial fan deltas and a continuous 4000-year debris flow record from Plansee (Tyrol, Austria), combining light detection and ranging (lidar) data, swath bathymetry, and sediment core analyses. The geomorphic investigation of two fan deltas in different developmental stages revealed an evolutionary pattern of backfilling and new channel formation onshore, together with active subaqueous progradation on a juvenile fan delta, major onshore sediment deposition, and only few, but larger, subaqueous deposits on a mature fan delta. Geomorphic evidence for stacked and braided debris flow lobes, subaquatic landslide deposits, and different types of turbidites in sediment cores facilitated a process-based event identification, i.e. distinguishing between debris-flow-induced or earthquake-induced turbidites throughout the 4000-year sedimentary record. We directly correlate subaqueous lobe-shaped deposits with high backscatter signals to terrestrial debris flow activity of the last century. Moreover, turbidite thickness distribution along a transect of four cores allows us to pinpoint numerous events as being related to debris flow activity on a juvenile fan delta. In the sediment core, debris-flow-induced turbidites feature a more gradual fining upward grain size trend and higher TOC (total organic carbon) and δ13C values compared to earthquake-induced turbidites. The 4000-year event record contains 138 debris-flow-induced turbidites separated into four phases of similar debris flow activity (df phases). df phase 1 (∼2120 to ∼2040 before the common era – BCE) reflects the second-highest observed event frequencies and is interpreted as being a postseismic landscape response. After a long period of long recurrence intervals without any outstanding increases in debris flow activity during df phase 2 (∼2040 BCE to ∼1520 common era – CE), there are slightly increased event frequencies in df phase 3 (∼1520 to ∼1920 CE). df phase 4 (∼1920 to 2018 CE) exhibits a drastic increase in debris flow activity, followed by the overall highest debris flow frequency of the whole record, which is about 7 times higher than during df phase 3. We show that the frequency increase in the debris-flow-induced turbidite record matches a previously postulated increase in debris flow events derived from aerial photography at Plansee in the last century. The triggering of debris flows is more controlled by short, intense precipitation than any other mass movement process, and we demonstrate that lacustrine debris flow records provide a unique inventory of hazard-relevant rainstorm frequencies over decades, centuries, and millennia. The presented increase in debris flow frequency since the start of the 20th century coincides with a twofold enhanced rainstorm activity in the Northern European Alps and, therefore, provides a novel technique for the systematic understanding of non-stationary debris flow frequencies in a changing climate.

Seiches and the slide/seiche dynamics; subcritical and supercritical subaquous mass flows and their deposits. Examples from Swiss Lakes

Four historically documented large and potentially dangerous lacustrine waves in Swiss lakes show that these waves have been seiches (standing waves) triggered by sublacustrine slides; a statement which is in accordance with the experience of seismologists who see earthquakes triggering seiches in lakes. Nevertheless, large historical waves in Switzerland have recently been modeled as progressive shallow water waves (tsunamis), probably because the slide/seiche dynamics are not known, and experiments with subaquatic slides fail to generate seiches in test–flumes. It appears that these tests exhibit a small shear–energy/slide–energy ratio ε, if compared with the situation in lakes. These facts incite a shear–stress lemma that states that ε is the constituent factor for the slide/seiche coupling. The structure of the subaqueous mass flow deposit (MFD) in lakes Lucerne and Geneva suggests the occurrence of subcritical and of supercritical slide flows. The former would generate a contortite, a MFD with contorted bedding, the latter a debrite (mudclast conglomerate). Potential slide energy considerations are used for an estimation of the amplitudes of large seiches produced by subaquatic slides, a proceeding that yields partly similar and partly very different results, as compared with numerical tsunami simulations.

Lithofacies and Fauna of the Loyalhanna Limestone (Chesterian, Upper Mississippian) and Their Implications for its Origin in the Appalachian Basin

The Loyalhanna Limestone is one of the most recognizable rock units in the Appalachian Basin. Differential weathering of its large-scale cross-bedding and massive character make this unit a widely used dimension and quarry stone. Diverging thoughts on the origin of the iconic cross-bedding have led to a long-standing debate over whether the genesis of the Loyalhanna is eolian or marine. Diagnostic bedding characters exhibited by the Loyalhanna are equivocal with most features possible in environments of both subaerial or subaqueous dune formation. Other diagnostic subaerial textures such as exposure surfaces, translatent ripple laminates, tracks, and trails are unknown in the unit. However, the Loyalhanna does contain a number of features that can be attributed to subaqueous deposition. For example, endolithic algal borings and coatings are ubiquitous. The Loyalhanna Limestone also displays a north-to-south change in lithofacies characteristics. Along its northern and eastern boundaries, the typically massive Loyalhanna is interbedded with rippled sandstone and red to variegated shale. Near its southern geographic limits, the Loyalhanna is interbedded with nodular, argillaceous, fossiliferous limestone intervals. Between these two interbedded lithofacies, the unit consists of the typical massive, cross-bedded, sandy limestone. Petrographically, the Loyalhanna contains a common microfauna of endothyrid foraminifers, and fragmented brachiopods, bryozoans, and echinoderms. A macrofauna was noted at eight locations. This fauna consists of articulated brachiopods, gastropods, bivalves, and trilobites. At other locations, comminuted megafauna assemblages are widespread. These fragmental faunas are known even in north-central and northeastern Pennsylvania. The presence of marine micro- and megafossils from throughout the Loyalhanna depositional basin and the equivocal nature of the eolian features indicate that this unit is largely if not completely marine in origin.

New data on geology of the Rybalsky Quarry, unique object of geological heritage of Global Significance

&#x0D; &#x0D; &#x0D; Among the great variety of geological relics of Ukraine, one of the most attractive is the Rybalsky Quarry, located in the city of Dnipro, and well known outside Ukraine. First of all, it is famous for the Mandrykivski Layers exposed in one of the ridges of the Quarry back in the 1970s, although there are many other important peculiarities of the geological structure of the Quarry which attract scientists from Ukraine, Germany, France, Netherlands, Russia and other countries. There are full data on the history of discovery and survey of the Mandrykivski Layers from their discovery by Valerian Domger in 1882 to current studies that reveal various aspects of geological structure of the Quarry, the results of study of different groups of fossil fauna, compare them with the fauna of the Paris Upper Eocene basin and other well- known locations. Particularly in the Rybalsky Quarry, thanks to the author`s efforts, the Layers received the status of “layers with geographic name”, as confirmed by the decision of Cenozoic Commission of the National Stratigraphic Committee of Ukraine in 2001. New fragments of the section of subaerial and subaqueous deposits of the Quaternary deposits were found and their composition, structure and complete stratigraphic content were studied. The research allows us to consider it typical for the Middle Prydniprovia. Fluvioglacial and lake-glacial deposits of the Dnipro glaciations in the Quarry exposed for the second time in 25 years, but this is the first time when their genetic origin, position in the section and lithological-facies peculiarities were determined. Thick layer of sands embedded on the roof of the Mandrykivski Layers were identified to the fifth or Hadzhybeiska terrace of the Dnipro, in the upper part of which there were notable siliceous-clayey-ferruginous formations or lateral crust (ferruginous crusts). The studies of the layer of brown-green and red-brown clays in the roof of the Mandrykivski layers allows us to presume their marine origin. In this case, they are underwater weathering crust (terra rossa) developed in the process of halmyrolysis or are the product of dissolution of carbonate silt enriched with detritus of mollusks, corals and other inhabitants of the warm Mandrykivske Sea.&#x0D; &#x0D; &#x0D;

Similarities and contrasts between the subaerial and subaqueous deposits of subaerially triggered debris flows: An analogue experimental study

ABSTRACT Debris flows and lahars are dense masses of water and sediment which are common phenomena in mountainous and volcanic regions, respectively. Where these flows debouch into water bodies they can trigger impulse waves (tsunamis) and form subaqueous deposits. Such deposits are important indicators for areas at risk from debris flows, lahars, and tsunamis and form archives of past environmental conditions. Correctly interpreting this archive, however, depends on our understanding of the sedimentology and architecture of the deposits. While subaerial debris-flow deposits have been extensively studied, there is a comparative lack of understanding of the deposits of subaerial debris flows that debouch into a water body. We experimentally investigate the similarities and contrasts between subaerial and subaqueous debris-flow deposits for flows of various magnitudes and compositions initiated in a subaerial environment. We show that flows depositing on a subaqueous plane generally have a deposit area similar to flows forming in a subaerial setting. Deposits forming on a subaqueous plane, however, are typically shorter and wider with similar thickness, as a result of interactions between the flow and the reservoir water body. Both in subaerial and subaqueous environments the deposits form coarse-grained lateral levees and frontal snout margins. However, where the levees are able to laterally confine the subaerial flows leading to deposits with constant to tapering width, the subaqueous deposits widen with distance offshore because of flow fluidization. Moreover, the frontal snout is often very dispersed, a sharp frontal margin is absent, and many isolated particles are deposited in front of the main deposit margin as a result of interactions between the debris flow and the reservoir water body. These results largely agree with observations of subaqueous pyroclastic-flow deposits. The similarity in area of subaerial and subaqueous deposits suggests that we can apply empirical relations based on subaerial flows to estimate the inundation area and flow volume of subaerial–subaqueous flows.

Field‐Based Estimate of the Sediment Deficit in Coastal Louisiana

AbstractCoastal and deltaic sediment balances are crucial for a region's sustainability. However, such balances remain difficult to quantify accurately, particularly for large regions. We calculate organic and mineral sediment mass and volume balances using field measurements from 273 Coastwide Reference Monitoring System sites across the Louisiana Coast between 2006 and 2015. The rapid relative sea level rise rate (average 13.4 mm/year) is offset by the small dry bulk densities observed (average 0.3 g/cm3) to produce a 16.2 ± 41.1% mass deficit and 24.1 ± 14.0% volume deficit, significantly smaller than recent predictions for 2000–2100 (73–79% mass deficit). Geostatisical estimates show that this deficit is primarily located in areas not directly nourished by major rivers, yet these regions still accumulate ~24 MT/year of mineral sediment. A fluvial sediment discharge of 113.8 MT/year suggests a coast‐wide trapping efficiency of 31.5 ± 15.8% of the riverine sediment, excluding subaqueous deposition. Organic accumulation accounts for 25% of all mass accumulation during our study period, and total organic mass accumulation per unit area is relatively constant in both directly and indirectly nourished regions. Sediment characteristics in the modern coastal wetlands differ from the Holocene deposit, suggesting secular changes within the system that will likely continue to influence coastal dynamics over the coming decades. Our results suggest that the gap between accommodation and accumulation (mass or volume) during this decade was not as large as the previously predicted century average.

Occurrence, Classification and Formation Mechanisms of the Organic-Rich Clasts in the Upper Paleozoic Coal-Bearing Tight Sandstone, Northeastern Margin of the Ordos Basin, China

The detailed characteristics and formation mechanisms of organic-rich clasts (ORCs) in the Upper Paleozoic tight sandstone in the northeastern margin of the Ordos Basin were analyzed through 818-m-long drilling cores and logging data from 28 wells. In general, compared with soft-sediment clasts documented in other sedimentary environments, organic-rich clasts in coal-bearing tight sandstone have not been adequately investigated in the literature. ORCs are widely developed in various sedimentary environments of coal-bearing sandstone, including fluvial channels, crevasse splays, tidal channels, sand flats, and subaqueous debris flow deposits. In addition to being controlled by the water flow energy and transportation processes, the fragmentation degree and morphology of ORCs are also related to their content of higher plants organic matter. The change in water flow energy during transportation makes the ORCs show obvious mechanical depositional differentiation. Four main types of ORC can be recognized in the deposits: diamictic organic-rich clasts, floating organic-rich clasts, loaded lamellar organic-rich clasts, and thin interlayer organic-rich clasts. The relationship between energy variation and ORCs deposition continuity is rarely studied so far. Based on the different handling processes under the control of water flow energy changes, we propose two ORCs formation mechanisms: the long-term altering of continuous water flow and the short-term water flow acting triggered by sudden events.

Clasts in Archean conglomerates and implications for uplift: Evidence from the 2.7 Ga Agnew Greenstone Belt (Western Australia)

Archean greenstone belts commonly consist of a stratigraphy that records subaqueous deposition capped by subaerial sedimentation, yet it remains unclear if the controls on this change were driven by horizontal or vertical processes. Clasts in conglomerates can provide important constraints on this question because they inform on the changing nature of sources. The 2.7 Ga Agnew Greenstone Belt, Yilgarn Craton, Australia, provides the ideal opportunity for such a study because it contains abundant and diverse conglomerate facies and its basal stratigraphy is well understood. This study focusses on the texture and composition of lithic clasts derived from three stratigraphic conglomerate units and their host successions. The lowermost conglomerate-bearing unit, hosted in the Vivien Formation, unconformably overlies the mafic-ultramafic lavas and intrusions of the Kalgoorlie Group (ca. 2720–2690 Ma) and is dominated by aphyric to porphyritic mafic and felsic volcanic clasts. The conformably overlying Maria Mine Formation conglomerates contain a higher proportion of felsic clasts with medium- and plutonic groundmass textures. The Vivien and Maria Mine Formations (ca. 2690–2670 Ma) are dominated by cherts, turbidites and conglomerates, and represent subaqueous sediments formed in the ring-plain surrounding an emergent volcanic island. The unconformably overlying Scotty Creek Formation (ca. 2665–2655 Ma) contains conglomerates with many plutonic felsic clasts, and is dominated by bedded and cross-bedded sandstones formed in a subaerial environment. Whole-rock geochemistry of mafic and ultramafic clasts matches the local Kalgoorlie Group rocks and indicates progressive erosion of the underlying supracrustal sequence. Undeformed conglomerates lack clasts with metamorphic foliations, indicating uplift by horizontal compression could not have been significant before ca. 2655 Ma, which is considered as the time of the first major compressional event in many published structural frameworks for the region. The systematic erosion of a felsic stratovolcano, its associated plumbing system, and any resultant upwarping of underlying sequences through vertically-driven diapirism, better explains the progressive changes observed in clast texture and composition, as opposed to horizontally-driven uplift, such as compression associated with subduction.

Timing of deposition in the Dengzhangzi and Guojiadian Basins of the Yanshan fold-thrust belt, North China

ABSTRACT The Triassic-Jurassic stratigraphy in the Yanshan fold-thrust belt is dominated by nonmarine deposits, and the division of this stratigraphy remains controversial among geologists. Age results from biostratigraphic and isotope chronological studies are inconsistent, especially for the Dengzhangzi and Guojiadian Basins in the eastern part of the Yanshan belt. We present four new detrital zircon U–Pb isotope datasets for the Triassic-Jurassic stratigraphic units and one for the Permian unit in the basins. The geochronological results show that the andesitic breccia in the Permian strata was deposited at ca. 273.78 ± 1.68 Ma, the Laohugou Formation was deposited in the Anisian-Ladinian Stage, the andesitic lava in the Shuiquangou Formation erupted at ca. 238.56 ± 0.91 Ma, and the conglomerate in the Guojiadian Formation was deposited from ca. 170 ± 5 to 163.0 ± 2.2 Ma. Field observations and facies analyses demonstrate that the Laohugou, Shuiquangou and Dengzhangzi Formations predominantly consist of subaqueous debris flow deposits, subaerial fluvial deposits, and fan delta deposits while the Guojiadian Formation is generally composed of fluvial and subaerial mass-flow deposits that formed in braided channels. Here, we propose a more precise and comprehensive Triassic-Jurassic stratigraphic division scheme based on age constraints and facies analysis. With this new stratigraphic sequence, we compare the Mesozoic stratigraphic units in the study area with those in other basins in the Yanshan fold-thrust belt in terms of the lithological associations, regional unconformities and zircon U-Pb dating results. This comparison indicates that the Indosinian and Yanshanian movements exerted a far-reaching influence on the development and evolution of the Dengzhangzi and Guojiadian Basins in the study area, forming several important regional unconformities and syntectonic conglomeratic units. These new age data on the stratigraphy are of fundamental significance for understanding the Mesozoic tectonic evolution of Yanshan.

Controls on deposition of shallow marine carbonates and evaporites – lower Permian Gipshuken Formation, central Spitsbergen, Arctic Norway

AbstractThe interbedded shallow marine carbonates and evaporites of the 95 to 105 m thick lower Permian Vengeberget member in central Spitsbergen form a lowstand to possibly early transgressive wedge sandwiched between open marine highstand carbonates along the northern margin of Pangea. Deposition took place on a wide (much greater than 40 000 km2) evaporitic platform separated from the open marine environments to the east by an inferred shelf margin barrier. Based on detailed description of facies in unique mountain‐scale outcrops, five CaSO4 and nine carbonate facies have been identified, all reflecting deposition in shallow evaporitic environments. The gypsum beds represent subaqueous deposition in broad hypersaline lagoons whereas the carbonates were deposited in protected shallow marine to peritidal environments and ooid‐dominated grainstone shoals. Cyclicity is expressed both as lithological shifts from carbonate to CaSO4 deposition and in the stacking of facies during CaSO4 and carbonate deposition. The number of carbonate–evaporite cycles varies from 12 to 28, but the overall thickness of the succession varies only slightly as a result of variations in cycle thickness, from 0·5 to 13·0 m. Two basic types of carbonate units can be recognized and reflect a combination of allocyclic and autocyclic controls. In addition, differential subsidence along older north–south orientated lineaments added to the complexity of cyclicity. The study provides insight into the complexity of the controls on deposition, architecture and dynamics of large‐scale mixed carbonate–evaporite successions formed in the shallow inner part of an epeiric sea or platform.

Subaerial and Subaqueous Investigations of Volcanic Debris Avalanche and Lahar Deposits on the Northern Coast of Ulleung Island, Korea

Chun, J.-H. and Lee, H.-J., 2019. Subaerial and subaqueous investigations of volcanic debris avalanche and lahar deposits on the northern coast of Ulleung Island, Korea. In: Jung, H.-S.; Lee, S.; Ryu, J.-H., and Cui, T. (eds.), Advances in Remote Sensing and Geoscience Information Systems of Coastal Environments. Journal of Coastal Research, Special Issue No. 90, pp. 369-376. Coconut Creek (Florida), ISSN 0749-0208.Volcanic debris avalanche and lahar deposits associated with small-scale lava dome collapse have been poorly documented in volcanic islands. The Chusan Formation was emplaced on the collapsed northern flank of Ulleung Island, Korea. Subaerial and subaqueous investigations of the collapsed northern part of Ulleung Island have been performed based on shaded relief images generated from a digital elevation model (DEM), a GeoEye satellite image, outcrop observations, and multi-beam echosounder and high-resolution Chirp sub-bottom profiling systems. The Chusan Formation is an elongated (length, 800 m; width, 250 m) system of valley-confined deposits connected to the Albong lava dome within the Nari caldera depression. A 40-m-thick outcrop of the Chusan Formation consists of three aggradational units that were emplaced by lahars, volcanic debris avalanches, and mixed deposition due to these processes. The peat layer between the overlying Chusan Formation and underlying reworked sediments was dated at 3,070–3,275 cal B.P., matching the emplacement of the Chusan Formation. Equivalent subaqueous deposits of the Chusan Formation were not detected in the northern shelf; thus, large-scale caldera collapse deposits covered the marine terrace before emplacement of the Chusan Formation. The valley-confined Chusan Formation is the result of an aggradational succession of lahar and volcanic debris avalanche deposits associated with the Albong lava dome collapse, corresponding to the most recent volcanic activity of Ulleung Island.

Lacustrine paleoshoreline determination under established sequence stratigraphic framework and its controls on sand bodies and hydrocarbon accumulations

Abstract The lacustrine palaeoshoreline is the intersection between lake level and ancient land in geological time, and it marks the boundary between onshore deposits and subaqueous deposits. Identifying lacustrine paleoshorelines is the process of reconstructing past depositional environments. The study establishes the sequence stratigraphic framework of the Ordos Yanchang Formation based on a comprehensive analysis of seismic and well log data. The hierarchical lithological cycles is determined through Fourier transform and band-pass filtering analysis of Gramma Ray data. Subsequently, the lacustrine paleoshoreline is determined using the shoreline hierarchical control method under the established sequence stratigraphic framework, with additional evidence from cores, well logs and cutting and seismic sections. Lacustrine paleoshorelines has controlling effects on the sand bodies and hydrocarbon accumulations. For one thing, different types of paleoshoreline control the genesis of sand bodies, and the location of paleoshoreline in sag basin controls sand-body distribution. Furthermore, the migration of lacustrine paleoshoreline in sag basin indicates stacking patterns of sand bodies, and hydrocarbon accumulations.

Variolites of the Paleoproterozoic Hekpoort Formation (Transvaal sub-basin, Kaapvaal craton): Multistage undercooling textures?

Globular structures in volcanic and hypabyssal rocks called varioles (or spherulites) have been described from a wide variety of places and rock types including komatiites, basalts, dacites, rhyolites as well as alkaline dykes, but the processes leading to their formation are still debated. Here, we present a field, petrological and geochemical study of variole-bearing lavas (variolites) in the Paleoproterozoic volcanic Hekpoort Formation in the southern part of the Transvaal sub-basin of South Africa. Variolites were only observed in a restricted area, corresponding to a ≥3.5 km long basin or depression. The variolites are locally up to 50 m thick and correspond to a succession of one-meter-thick lava flows. Most of the flows consist of two distinct layers, with an upper layer rich in spherical varioles (1–32 cm in diameter), overlying a layer generally devoid in varioles but often showing vertical jointing. Both layers show randomly oriented acicular textures of centimetre-sized skeletal clinopyroxene crystals (Al-rich augite) that precede the formation of varioles. The varioles themselves are mainly composed of radiating acicular augite (1 μm in diameter), the crystallization of which caused diffusion of incompatible elements, which became enriched in the groundmass around the varioles. The whole rock geochemistry of the Hekpoort variolites is indistinguishable from that of non-variolitic Hekpoort lavas with the same MgO content. This excludes liquid immiscibility as the origin of the varioles. The acicular texture (of Al-rich augite) in combination with the incompatible element enrichment around the varioles suggests that both skeletal and acicular augite are related to undercooling rather than devitrification. Sub-aqueous deposition is thought to be the cause of undercooling.