Lower Part Of Unit Research Articles

Organic matter accumulation mechanisms and source rock potential of the Mesoproterozoic Xiamaling Formation, Yanliao Basin, North China

The Mesoproterozoic Xiamaling Formation (∼1.4 Ga) is considered to be a set of promising strata for shale oil and gas exploration and production in the Yanliao Basin, North China Craton. This study aimed to investigate the organic matter accumulation mechanism, and hydrocarbon generation and expulsion characteristics of the Xiamaling Formation, using various methods, including scanning electron microscopy, rock-eval pyrolysis, and elemental geochemistry. Multiple geochemical proxies indicate that Unit 3—Unit 1 of the Xiamaling Formation was deposited in a climate that alternated between highly humid and semiarid conditions, with the strong-to-weak terrigenous influx. The redox conditions of bottom water were undulatory oxic in Unit 3 and the upper part of Unit 1, but anoxic in Unit 2 and the lower part of Unit 1. Sulfurization of organic matter was the main reason for the high TOC content in Unit 3. However, the high TOC content in Unit 2 and the lower part of Unit 1 was caused by an oxygen-deficient water column. Unit 2 and the lower part of Unit 1 exhibit a significant shale oil potential owing to low maturity, high hydrogen index (HI) values, and prevalence of type Ⅰ, II1, and II2 kerogens.

The dinosaur tracks of Tyrants Aisle: An Upper Cretaceous ichnofauna from Unit 4 of the Wapiti Formation (upper Campanian), Alberta, Canada.

The Wapiti Formation of northwest Alberta and northeast British Columbia, Canada, preserves an Upper Cretaceous terrestrial vertebrate fauna that is latitudinally situated between those documented further north in Alaska and those from southern Alberta and the contiguous U.S.A. Therefore, the Wapiti Formation is important for identifying broad patterns in vertebrate ecology, diversity, and distribution across Laramidia during the latest Cretaceous. Tracksites are especially useful as they provide a range of palaeoecological, palaeoenvironmental, and behavioural data that are complementary to the skeletal record. Here, we describe the Tyrants Aisle locality, the largest in-situ tracksite known from the Wapiti Formation. The site occurs in the lower part of Unit 4 of the formation (~72.5 Ma, upper Campanian), exposed along the southern bank of the Redwillow River. More than 100 tracks are documented across at least three distinct track-bearing layers, which were deposited on an alluvial floodplain. Hadrosaurid tracks are most abundant, and are referable to Hadrosauropodus based on track width exceeding track length, broad digits, and rounded or bilobed heel margins. We suggest the hadrosaurid trackmaker was Edmontosaurus regalis based on stratigraphic context. Tyrannosaurids, probable troodontids, possible ornithomimids, and possible azhdarchid pterosaurs represent minor but notable elements of the ichnofauna, as the latter is unknown from skeletal remains within the Wapiti Formation, and all others are poorly represented. Possible social behaviour is inferred for some of the hadrosaurid and small theropod-like trackmakers based on trackway alignment, suitable spacing and consistent preservation. On a broad taxonomic level (i.e., family or above), ichnofaunal compositions indicate that hadrosaurids were palaeoecologically dominant across Laramidia during the late Campanian within both high-and low-latitude deposits, although the role of depositional environment requires further testing.

Multiple controls on the organic matter accumulation in early Cambrian marine black shales, middle Yangtze Block, South China

This study aims to investigate paleoenvironments, hydrothermal activity, and seawater restriction of the lower Cambrian Shuijingtuo Formation in the Three Gorges area and clarify the dominating factors on organic matter (OM) accumulation. In the studied SL well in western Hubei Province, the Shuijingtuo Formation was divided into three intervals based on geological and geochemical characteristics. Total organic carbon (TOC) contents were variable, averaging 0.69% in Unit 1, 5.40% in Unit 2, and 1.12% in Unit 3. Enrichment factors (EF) of Cu and Ni indicated higher paleoproductivity in Unit 2. Unit 1 and the lower part of Unit 2 were affected by hydrothermal activity, whereas hydrothermal events receded in Unit 3. Hydrothermal activities could provide nutrients and may also facilitate the reducing water condition. Redox proxies (Corg/P, EF(Mo)-EF(U)) suggested that Unit 1, Unit 2, and Unit 3 were deposited in oxic-suboxic, euxinic, and suboxic environments, respectively. Upwelling/restriction proxies (EF(Co)*EF(Mn), Co (ppm)*Mn (%), Mo/TOC, and Cd/Mo) implied that Unit 1, Unit 2, and Unit 3 were deposited in upwelling, semi-restricted, strong restricted conditions, respectively. In summary, an anoxic environment, semi-restricted water conditions, and hydrothermal events are beneficial for OM enrichment during the early Cambrian.

Integrated environmental records in Late Pleistocene Poland: The paleofluvial regime and paleoclimate inferred from Krosinko site

Multiproxy analyses performed at the Krosinko site in the Warsaw–Berlin ice marginal valley have provided data that characterize the depositional conditions, the paleofluvial regime, and the paleoclimate and help reconstruct the paleo-environment at a time of significant sediment (alluvium) accumulation (starting in central Poland ca. 45 ka BP). The sedimentological study, including sand-grain morphology and micromorphology analyses, reveals the presence at Krosinko of a meandering river and of a braided river during the Eemian (MIS 5e) and Upper Pleniweichselian (MIS 2), respectively. The fluvial regime changed over time, from low-energy, through high-energy, to low-energy, as documented by the differently formed sedimentary units A–D (vertical sedimentary succession from base to top: sandy silt, sand, gravelly sand, and sand). Sedimentary unit A and the lower part of unit B were accumulated in the Eemian interglacial (MIS 5e) by the low-energy meandering river. The high-energy fluvial environment during the Weichselian is associated with long, intense sediment transport, organic remains, and flints, as confirmed by taphonomic studies on conifer cones (Picea cf. abies) and wood remains (Juniperus). The river operated under distinct environmental conditions. First, during the accumulation of the upper part of unit B and unit C, there was a strong influence of freezing and aeolian weathering, which weakened significantly over time (unit D). This in turn indicates a change in climate from periglacial (upper part of unit B and unit C), when we also document the presence of permafrost in the subsurface or relatively deep seasonal frost, to temperate (unit D). With warming in the Holocene (MIS 1), an oxbow lake developed in Krosinko, the presence of which is recorded by peat.

A multiproxy reconstruction of the Late Pleistocene-Holocene paleoenvironment: New insights from the NW Black Sea

We provide new data on the Black Sea evolution during the preconnection and reconnection stages with the Mediterranean, based on sedimentology, geochemistry, calcareous nannoplankton and ostracods analysis, in 13 cores placed between 141 m and 1315 m water depths. Unit 1 – The Coccolith Mud, Unit 2 - The Sapropel Mud and Unit 3 – The Lacustrine Lutite, including red-brownish depositional intervals, were identified in all studied deep-water cores. These units are not present in a shallow setting, i.e., above 166.7 m water depth, being replaced by sandy levels and shell debris. The red-brownish layers are interpreted as hyperpycnites, but some of the red successions show turbidite features, especially the ones situated on canyon sides, at a water depth below 600 m. In the oldest intercepted Unit 3 of the Neoeuxinian lake, CaCO3 values are constantly low, but towards the top of this unit they show two distinct peaks, interpreted as signals of Bølling–Allerød and Preboreal interstadials. In between, a significant decrease in CaCO3 values, linked to the setting of the Younger Dryas, is coincident in the deep cores with diatom blooms and high frequency of ostracods related to cooler waters. The scarce but continuous occurrence of Emiliania huxleyi nannoplankton species from the top of Unit 3 indicates that the salinity was at least 10–11‰ prior the Sapropel Mud deposition and increase at a least 17‰ within the lower part of Unit. 2. In the same interval, the Ponto-Caspian ostracods are still present. The Mediterranean ostracods consistently occur from the top of Unit 2, when bottom water salinity reached values for allowing their survival. The first bloom of E. huxleyi is placed at the base of Unit 2, where coccolith laminae occur, while the second bloom is placed in Unit 1 that contains exclusively Mediterranean ostracods and consistent assemblages of benthonic foraminifers, similar with the ones present today.

The Chefar El Ahmar Formation (late Emsian-Frasnian Ib) in the Marhouma section (Saoura, Algerian Sahara): insights from ichnology and sedimentology

This contribution reports an ichnological study of the well-exposed strata belonging to the Chefar El Ahmar Formation, located in the Saoura Valley (Ougarta Range, Northwestern Algerian Sahara). This unit consists mainly of irregularly alternating shale and limestone with some intercalated sandstone. The data reflect hemipelagic to pelagic carbonate ramp character, episodically interrupted by internal waves in an extra-tempestite context. The ichnological analysis suggests a low bioturbation intensity. Eight ichnotaxa documented represent the Cruziana ichnofacies: Alcyonidiopsis, ?Balanoglossites, Chondrites, Nereites missouriensis, Neonereites biserialis, Palaeophycus, Thalassinoides and Zoophycos, distributed in an irregularly manner dominated by a Zoophycos-Chondrites assemblage in the lower part (units “a”, “b”, “c” and bottom part of unit “d”), a Zoophycos-Chondrites-Alcyonidiopsis-?Balanoglossites-Nereites missouriensis-Thalassinoides assemblage in the middle part (unit “d” and lower part of unit “e”) and a Chondrites-Alcyonidiopsis-Nereites missouriensis-Neonereites biserialis-Palaeophycus assemblage in the upper part (major part of unit “e” and unit “g”). The distribution of these trace fossils frame the major bioevents represented in this section. They are more frequent above and below the bioevent levels while rare to absent in the crisis beds themselves. The control was evidently provided by palaeoenvironmental conditions (including bathymetry, oxygenation and nutrient supply), as a result of the general deepening of the northern Gondwana carbonate platform from the late Emsian to the early Frasnian, due to the major transgression during the Middle Devonian.

Isotopic chemostratigraphy and biostratigraphy of Lower Cretaceous Alisitos Formation (Punta China section), Baja California, Mexico

Nine units of carbonate rocks are recognized, of which the highest five units are examined here under biostratigraphical and chemostratigraphical aspects in order to infer mid‐Cretaceous OAE intervals in Punta China section, Baja California. The biota in Units 5, 6, 7, and 8 show low diversity, while Unit 9 is characterized by a high diversity of microfossils. Benthic foraminiferal assemblage and rudist genera identified in Unit 9 indicate a lower Albian age. Lithofacies and fossil assemblages suggest that the depositional environment was a shallow marine shelf or platform adjacent to caprinid buildups. The limestones of the Alisitos Formation show both negative and positive δ13C values that range between −0.9 and + 7.5‰. Large variations in δ18O values are noticed in the limestone units (−7.9 to −2.2‰). The 87Sr/86Sr ratios of the bulk limestone samples vary between 0.706662 and 0.707305. Most of the limestones have lower 87Sr/86Sr ratios that may be the result of inclusion of less radiogenic strontium from the volcanic rocks. One limestone sample from Unit 7 has a relatively pristine 87Sr/86Sr ratio (0.707305) whose numerical age is 111.61 Ma. The carbon‐isotope curve reveals the presence of two episodes of oceanic anoxic subevents in the studied section. The lower part of Unit 9 has significant negative carbon isotope excursion (CIE) that correlated with the Paquier subevent. Similarly, another negative CIE is also observed in the upper part of Unit 9, which suggests a correlation with Leenhardt subevent.

Occurrence of high-diversity metazoan- to microbial-dominated bioconstructions in a shallow Kimmeridgian carbonate ramp (Jabaloyas, Spain)

The horizontal and vertical transitions of a wide range of bioconstructions are documented from the shallow domains of a Kimmeridgian carbonate ramp (Upper Jurassic) in the Jabaloyas area of NE Spain. The bioconstructions include microbial buildups, coral-bearing thrombolite buildups, coral-microbial buildups, branching coral patches, oyster patches, and stromatoporoid carpets. Buildups form stacked pinnacles up to 19 m thick, within a broad spectrum of coeval inter-buildup carbonate facies. Coral-bearing thrombolites are coincident with shallow-marine oolitic sands, indicating development during the initial platform flooding (unit 1). During the continued sea-level rise (units 2 and 3), coral-microbial buildups [encrusted by Crescentiella (Tubiphytes) and serpulids] were established from proximal to distal mid-ramp domains, and these showed an increasing proportion of microbial crust in distal domains. Inter-buildup oolitic facies sharply grade down-dip to hummocky cross-stratified intraclastic, peloidal, and skeletal deposits, mostly sourced from the coral-microbial buildups. The lower part of unit 4 was dominated by microbialites in the proximal areas, related to local fresh-water input causing seawater stratification and oxygen depletion. The upper part of unit 4 indicates an initial recovery of metazoan frame builders, with abundant branching corals. During the late regression (units 5 and 6), Marinella lugeoni red algae, oyster patches, and stromatoporoid boulders developed close to the shoreline in well-oxygenated waters with high nutrient content. The reported data contribute to the discussion of the optimal environmental conditions for each “bioconstruction window” in Jabaloyas, namely sediment and nutrient supply, water depth, water oxygenation, wave energy and light availability.

FORAMINIFERAL BIOSTRATIGRAPHY ACROSS THE VISEAN/SERPUKHOVIAN BOUNDARY IN THE VEGAS DE SOTRES SECTION (CANTABRIAN MOUNTAINS, SPAIN)

A continuous succession of the upper part of the Alba Formation is recorded in the Vegas de Sotres section in the Cantabrian Mountains, northern Spain. This section contains slightly shallower-water facies than elsewhere and as a result is particularly rich in foraminifers. Characterization of the late Visean to Serpukhovian interval in coeval deeper water settings is accomplished by means of integrating conodont, ammonoid and foraminiferal data. The foraminiferal assemblages recorded in units 1–4 of the Alba Formation enabled correlation with the Russian substages in the Moscow Basin, Urals and Donets Basin. The upper part of the Canalon Member (unit 1) is correlated with the Venevian, the lower part of unit 2 is correlated with the Tarusian, and the Steshevian is recognized in the middle and upper part of unit 2. Most of unit 3 is correlated with the Protvian and is equivalent to the E2a ammonoid zone. The youngest Millaro Member (unit 4) contains undiagnostic foraminifers and lies within the Gnathodus truyolsi Conodont Zone equivalent to the E2b/E2c ammonoid zones. The base of the Serpukhovian is defined on the first occurrence of the conodont Lochriea ziegleri . Slightly below this horizon are recorded Neoarchaediscus parvus, N . aff. N . postrugosus, Biseriella paramoderata, Asteroarchaediscus rugosus, Howchinia hemisphaerica and Rectoendothyra latiformis . At the Visean/Serpukhovian (V/S) boundary, species of Tubispirodiscus are recorded and just above, the presence of Asteroarchaediscus baschkiricus is confirmed. The late Serpukhovian is characterized by the occurrence of diverse Eostaffella pseudostruvei, E . sp. cf. E. postmosquensis, Eostaffellina “ protvae ”, Eost. actuosa and Plectostaffella varvariensis . Two new genera and four new species are described: Janischewskina gibshmanae n. sp., Endostaffellopsis umbilicata n. gen. n. sp., Vachardites spinosus n. gen. n. sp., V. priscelloides n. gen. n. sp.

Fluvial response to sea-level changes since the latest Pleistocene in the near-coastal lowland, central Kanto Plain, Japan

This paper addresses the influence of sea level changes on the stratigraphy and basal topography of latest Pleistocene–Holocene incised valley fill of the Arakawa and Menuma Lowlands in central Japan by using sedimentary drill cores and columnar geologic sections. In the study area, four buried fluvial terrace surfaces (I to IV) formed in response to sea-level fall during the last glacial period. Surface III is covered with As-YP tephra (15–16.5ka) and extends at least 65km landward from the present mouth of the Arakawa River. A buried valley named surface V that extends from at least 85km upstream from the present river mouth to about 120m below present sea level on the continental slope was incised in response to the sea-level lowstand of the Last Glacial Maximum. The incised valley fill can be divided into three units: unit A (gravelly river channel sediments including valley-bottom gravels), unit B (fluvial sediments), and unit C (marine sediments), which intertongues within unit B and pinches out up to 60km upstream from the present river mouth. Unit C marks the landward limit of Holocene transgression. The lower part of unit B is a fining-upward succession formed during rising sea level and indicates retrogressive aggradation of floodplain sediments during transgression, whereas the upper part of unit B was formed during a sea-level highstand. The floodplain migrated more than 85km upstream from the modern shoreline in response to sea-level rise until the middle Holocene and extends over several tens of kilometers beyond the landward limit of the Holocene marine transgression.

Carbonate and organic matter sedimentation and isotopic signatures in Lake Chungará, Chilean Altiplano, during the last 12.3 kyr

Sediments in lakes in the Andean volcanic setting are often made up of diatomaceous ooze together with volcaniclastics and small amounts of carbonates. Despite their scarcity, carbonates along with organic matter provide significant paleoenvironmental information about lake systems. This study focuses on the carbonates in Lake Chungará, their morphologies, distribution and origin deduced from the isotopic markers. These markers reflected changes in the water and the biomass between the onset of the Holocene and around 9.6 cal kyr BP. These changes are marked by general increases in TOC, TN, and TN-δ 15N AIR, and by fluctuating values of TOC-δ 13C VPDB in its sediments and are probably related to major shifts in the lake surface/volume associated with rises in lake level. An increase in salinity around 10 cal kyr BP is thought to be linked to a short dry period, giving rise to the onset of carbonate production. The mid-Holocene arid period between 7.3 and 3.5 cal ka BP, with a maximum of aridity around 6.0 cal kyr BP, was deduced from δ 18O VPDB values in the endogenic carbonates. These results match the reconstructions in Lake Titicaca based on benthic diatoms and paleoshore levels. Offshore sediments mainly consist of a diatomaceous ooze, laminated in the lower half (Unit 1), and banded-massive with tephra layers in the upper half of the sequence (Unit 2). TOC-δ 13C VPDB and the C/N ratio confirm that phytoplankton was the main source of organic matter in these sediments. Shallower sediments (units 3 to 5) developed in platform and littoral settings, providing evidence of subaqueous macrophytes and, to a lesser extent, land plants. Carbonate content ranges between 0.1 and 6 wt.% in offshore settings (30 to 40 m water depth) and reaches the maximum values in the lower part of Unit 2. Carbonate minerals (low magnesium calcite and minor amounts of high magnesium calcite and aragonite) are scarce and are arranged in mm-thick layers, commonly forming cm-thick levels or bioclasts. Carbonate layers are made up of euhedral-to-subhedral spindle-shaped calcite crystals and, to a lesser extent, aragonite needles, all in the μm range. Aragonite spheroids coexist in littoral sediments with other carbonate shapes and charophyte remains, where carbonate reaches locally up to 20 wt.%. CO 2 photosynthetic depletions related to seasonal phytoplankton blooms were responsible for the high frequency deposition of mm-thick carbonate layers. The average values for δ 13C VPDB in lake water, plankton and sediments of Lake Chungará (as organic matter or as carbonate) are around 15‰ higher than commonly reported values in other lakes. This 13C enrichment is attributed to carbon assimilation from a DIC affected by methanogenesis, in which HCO 3 − is the dominant species. The δ 13C VPDB and δ 18O VPDB variations and their covariation in endogenic carbonates suggest that lake water volume and lake level increased along the Holocene.

Palynostratigraphy of the Chapada Group and its significance in the Devonian stratigraphy of the Paraná Basin, south Brazil

The Alto Garcas Sub-basin in the northern part of the Parana Basin evolved differently from the Apucarana Sub-basin in the south. The marine environment was shallower in the Alto Garcas Sub-basin, which contains proportionately more silty and arenaceous rocks. The formations and members defined in the Apucarana Sub-basin are therefore difficult to apply in the Alto Garcas Sub-basin, where the Chapada Group (units 1–4) is more applicable. An integrated miospore and chitinozoan biozonation of the Chapada Group facilitates direct correlation between the Chapada Group’s units and the classical formations of the Parana Basin as defined in the Apucarana Sub-basin. The Furnas Formation and Chapada unit 1 constitute the same lithostratigraphic unit. Beds with rhyniophytes in the uppermost part of the Furnas Formation contain palynomorphs representative of the Si phylozone within the MN spore Zone (late Lochkovian), and the rhyniophyte beds occupy the same stratigraphic interval within Chapada unit 1 (the Lochkovian of the Parana Basin lacks chitinozoans). The lower part of Chapada unit 2 contains spores of the PoW Su spore Zone and chitinozoans of the Ramochitina magnifica and Ancyrochitina pachycerata zones, together indicating a late Pragian–early Emsian age-span. The upper part of Chapada unit 2 corresponds to the GS (AP) and Per (AD pre-Lem) spore Zones, and chitinozoans of the Ancyrochitina parisi, the informal Ancyrochitina varispinosa and Alpenachitina eisenacki chitinozoan zones, thus suggestive of a late Emsian – earliest Givetian age-span. Unit 3 is a proximal and lateral facies equivalent of the upper part of unit 2. The lower part of unit 4 includes spores typical of the early Givetian Lli (AD Lem) spore Zone and chitinozoans of the Ramochitina stiphrospinata chitinozoan Zone; the uppermost (early late Frasnian) part contains spores of the lower BMu (IV) spore Zone and chitinozoans of the Lagenochitina avelinoi chitinozoan Zone. The sandstones of unit 3 were inundated during the earliest Givetian, and the resultant flooding surface marks the base of unit 4 basin-wide. Clearly, the two sub-basins were distinct depositional centers during the Devonian.

Taxonomy of middle Eocene diatom resting spores and their allied taxa from the central Arctic Basin

In the late summer of 2004, Integrated Ocean Drilling Program (IODP) Expedition 302, also called the Arctic Coring Expedition (ACEX), successfully drilled the first deep boreholes on the Lomonosov Ridge in the central Arctic Ocean. The well preserved fossil diatoms used here are from biosiliceous Unit 2 inHoles 2A and 4Aof middle Eocene age. In the lower part ofUnit 2, resting spores occurred abundantly with other fossil diatoms. 25 diatom resting spore taxa and five allied vegetative cell taxa are described in this study of ACEX samples. Moreover 11 diatom taxa which did not occur in these sediments are also described for comparison with the Eocene Arctic resting spores. Their biostratigraphic ranges are also indicated. 10 of the resting spore species which occur in the ACEX samples had already appeared during the late Cretaceous while the rest of them appeared in Eocene. 21 of 25 (84%) resting spore taxa became extinct during the middle Eocene to early Oligocene. Most resting spore taxa described in this study do not belong to Chaetoceros resting spores because they lack a single ring of puncta on the hypovalvemantle that characterizes the resting spores of Chaetoceros and became extinct before Oligocene, therefore it is clear that Chaetoceros did not flourish in the middle Eocene in the Arctic Ocean. Other diatom genera that produced resting spores such as Pterotheca and Pseudopyxilla, might have prospered before the Eocene/Oligocene boundary, although their vegetative cells are unknown so far. Since some Chaetoceros resting spore taxa are reported in this study, most coastal regions experienced regular seasonal environmental change, which benefitted genera such as Pterotheca, Pseudopyxilla and Odontotropis, but also there might have been some patchy coastal upwelling regions with nutrient depletion and sporadic supplieswhere Chaetoceros may have survived. The abundant dinoflagellate cysts preserved in middle Eocene ACEX cores provide evidence of stable conditions before the Eocene/Oligocene boundary. The resting spore ecology of most resting spore taxa before the Eocene may have been similar to that of dinoflagellate cysts rather than that of Chaetoceros resting spores after the Oligocene.

End-Permian extinction and volcanism-induced environmental stress: The Permian–Triassic boundary interval of lower-slope facies at Chaotian, South China

In order to reveal environmental changes across the Permo-Triassic boundary (PTB), the detailed lithostratigraphy of the PTB interval is analyzed at Chaotian in northern Sichuan, China. The studied section is composed of the Changhsingian (Upper Permian) Dalong Formation and the Induan (Lower Triassic) Feixianguan Formation of a lower-slope facies deposited on the northwestern margin of the Yangtze carbonate platform. The 12-m-thick interval across the PTB consists mainly of bedded carbonates and mudstone, and is lithologically divided into 7 units, i.e., Units A to G, in ascending order. The main extinction horizon of Permian taxa is recognized at the Unit D/E boundary where various fossil metazoans and protists, such as ammonoids, brachiopods, bivalves, conodonts, and radiolarians, rapidly disappeared or became scarce. The complete disappearance of radiolarians at the Unit D/E boundary emphasizes that the PTB extinction affected not only various Late Permian benthic and free-swimming metazoans but also planktonic protozoans. The lowest Induan index conodont Hindeodus parvus first occurs at the base of Unit F, marking the biostratigraphically defined PTB horizon. Unit E composed of unique bedded marl between the main extinction horizon and the first occurrence of Triassic taxon represents a period of strong environmental stresses that suppressed productivity both of silica- and carbonate-secreting organisms. By changing their size, radiolarians reacted most sensitively to the environmental change that already started in the late Changhsingian, appreciably before the final extinction event. The frequent intercalation of rhyo-dacitic tuff beds, particularly in Unit D and the lower part of Unit E across the main extinction horizon, suggests that intermittent felsic volcanism and relevant environmental change may have been responsible for the mass extinction of the Permian taxa and for the prolonged post-extinction lag time before the initial recovery. The frequent ash falls during the late Changhsingian indicate that the volcanism-induced environmental change had already started earlier than the main extinction. All the biological production (carbonate, silica, and organic matter) collapsed at the Unit D/E boundary when the environmental stresses may have passed a critical threshold for maintaining ecological stability. The PTB interval between the extinction and the first appearance of Triassic taxon at Chaotian is ca. 1.4 m thick, apparently almost eight times thicker than that at the Global Stratotype Section and Point of PTB in Meishan (19 cm). The Chaotian section, as well as the neighboring Shangsi section in northern Sichuan, may provide a better chance for high-resolution chemostratigraphic analyses that may allow detection and correlation of subtle environmental changes across the PTB.

Geoarchaeology of the Kostenki–Borshchevo sites, Don River Valley, Russia

AbstractThe Kostenki–Borshchevo localities include 26 Upper Paleolithic sites on the first and second terraces along the west bank of the Don River, near Voronezh on the central East European Plain. Geoarchaeological research from 2001 through 2004 focused on sites Kostenki 1, 12, and 14, with additional work at Kostenki 11 and 16, and Borshchevo 5. The strata are grouped into three units (bottom up): Unit 1, > 50 ka, consists of coarse alluvium (representing upper terrace 2 deposits) and colluvium, overlain by fine‐grained sediments. Unit 2 includes archaeological horizons sealed within two sets of thin lenses of silt, carbonate, chalk fragments, and organic‐rich soils (termed the Lower Humic Bed and Upper Humic Bed) dating 50–30 ka. Separating the humic beds is a volcanic ash lens identified as the Campanian Ignimbrite Y5 tephra, dated elsewhere by Ar/Ar to ca. 40 ka. The humic beds appear to result from the complex interplay of soil formation, spring deposition, slope action, and other processes. Several horizons buried in the lower part of Unit 2 contain Upper Paleolithic assemblages. The springs and seeps, which are still present in the area today, emanated from the bedrock valley wall. Their presence may account for the unusually high concentration of Upper Paleolithic sites in this part of the central East European Plain. Unit 3, < 30 ka, contains redeposited loess with a buried soil (Gmelin Soil) overlain by a primary full‐glacial loess with an associated Chernozem (Mollisol), forming the surface of the second terrace. © 2007 Wiley Periodicals, Inc.

Quaternary evolution of the coastal dunes between Lake Hlabane and Cape St Lucia, KwaZulu-Natal

Research Article| September 01, 2004 Quaternary evolution of the coastal dunes between Lake Hlabane and Cape St Lucia, KwaZulu-Natal P. Sudan; P. Sudan School of Geological and Computer Sciences, University of Natal, Durban 4041, South Africa, e-mail: whitmore@ukzn.ac.za; uken@ukzn.ac.za Search for other works by this author on: GSW Google Scholar G. Whitmore; G. Whitmore School of Geological and Computer Sciences, University of Natal, Durban 4041, South Africa, e-mail: whitmore@ukzn.ac.za; uken@ukzn.ac.za Search for other works by this author on: GSW Google Scholar R. Uken; R. Uken School of Geological and Computer Sciences, University of Natal, Durban 4041, South Africa, e-mail: whitmore@ukzn.ac.za; uken@ukzn.ac.za Search for other works by this author on: GSW Google Scholar S. Woodbourn S. Woodbourn Quaternary Dating Research Unit, Environmentek, Council for Scientific and Industrial Research, Pretoria, South Africa, e-mail: swoodbor@csir.co.za Search for other works by this author on: GSW Google Scholar Author and Article Information P. Sudan School of Geological and Computer Sciences, University of Natal, Durban 4041, South Africa, e-mail: whitmore@ukzn.ac.za; uken@ukzn.ac.za G. Whitmore School of Geological and Computer Sciences, University of Natal, Durban 4041, South Africa, e-mail: whitmore@ukzn.ac.za; uken@ukzn.ac.za R. Uken School of Geological and Computer Sciences, University of Natal, Durban 4041, South Africa, e-mail: whitmore@ukzn.ac.za; uken@ukzn.ac.za S. Woodbourn Quaternary Dating Research Unit, Environmentek, Council for Scientific and Industrial Research, Pretoria, South Africa, e-mail: swoodbor@csir.co.za Publisher: Geological Society of South Africa First Online: 07 Mar 2017 Online ISSN: 1996-8590 Print ISSN: 1012-0750 © 2004 Geological Society of South Africa South African Journal of Geology (2004) 107 (3): 355–376. https://doi.org/10.2113/107.3.355 Article history First Online: 07 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation P. Sudan, G. Whitmore, R. Uken, S. Woodbourn; Quaternary evolution of the coastal dunes between Lake Hlabane and Cape St Lucia, KwaZulu-Natal. South African Journal of Geology 2004;; 107 (3): 355–376. doi: https://doi.org/10.2113/107.3.355 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySouth African Journal of Geology Search Advanced Search Abstract The northern KwaZulu-Natal coastal dunes rise to a height of more than 100m and a width of 2km between Lake Nhlabane and Cape St.-Lucia. This work documents detailed study of two cross-sections through the dunes and correlation of identified dune units over a 20km coastal stretch using confidential data from 6500 boreholes. The results provide useful constraints on the identification of dune units, their age relationships and spatial distribution.Based on mineralogy, geochemistry and textural properties the sediment comprising the dunes can be grouped into 6 units (Units A to E and Unit K). Along the most inland part of the coastal dunes, the basal light grey Unit K presents similar characteristics to the Kosi Bay Formation. This is overlain by Unit A, comprising beach and dune systems, characterised by a very high heavy mineral content. Unit A also forms the basal unit of the central and coastal portions of the dune cordon. Unit B overlies Unit A and contains a mixture of sediments partly reworked from Unit A. Unit C is only found in the southern part of the study area. It has unique characteristics interpreted as an aeolian deposit reworked from local fluvial sediments. Luminescence dating indicates that the calcareous Unit D was derived from a nearby beach – foredune system between 15 000 and 11 000 BP, during the marine transgression following the last glaciation. The Holocene Unit E is also calcareous and is derived from the current beach – foredune system. All units, with the exception of Unit C, are interpreted to be derived from immature sediment from the Tugela River mixed with mature sediment from the continental shelf.With the aid of sea level curves and the two luminescence dates, dune units were attributed an approximate age. The oldest Unit K, interpreted as the Kosi Bay Formation, and the older dune cordon (Dune Class 1) must be older than 200 Ka. The three younger packages are attributed to the penultimate interglacial (lower part of Unit A), last interglacial (upper part of Unit A, Units B and C) and “Holocene” interglacial (Units D and E). The “Holocene” dunes (Units D and E) are correlated to the Sibayi Formation. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Magnetostratigraphy of the Sherwood Sandstone Group (Lower and Middle Triassic), south Devon, UK: detailed correlation of the marine and non-marine Anisian

The Sherwood Sandstone Group in south Devon consists of the Budleigh Salterton Pebble Beds and the Otter Sandstone Formation. The Otter Sandstone Formation comprises four lithostratigraphic sub-units, from the base labelled A–D, and contains tetrapods corresponding to the Perovkan land vertebrate faunachron, and is consequently a key European non-marine Anisian succession. A total of 181 palaeomagnetic specimens from 92 horizons were measured to determine the palaeomagnetic signal. The magnetic properties and characteristic remanence is predominantly carried by haematite, most of which probably formed early in the depositional and diagenetic history. The lower part of the Sherwood Sandstone Group (Budleigh Salterton Pebble Beds and Otter Sandstone Formation, unit A, lower part of unit B) has predominantly normal polarity (magnetozones BS1, BS2 and BS3n) with three thin reversed polarity magnetozones. The lower part of unit B to the lower part of unit C of the Otter Sandstone Formation is predominantly reverse polarity (magnetozones BS3r, BS4 and BS5), but includes three short normal polarity intervals. The upper ca. 50 m of unit C shows a mix of normal and reverse polarity (BS6, BS7) with normal dominating. The ca. 15-m-thick unit D is entirely of normal polarity (BS8n). The magnetostratigraphy allows unambiguous comparison with conodont and ammonite calibrated magnetostratigraphies from elsewhere in Europe. These show that the BS2 and BS3n magnetozones of the Otter Sandstone Formation are lower Aegean to middle Pelsonian (lower to middle Anisian). The BS3r to BS5r magnetozone interval, is middle Pelsonian to lower Illyrian (middle to upper Anisian), and the BS6 to BS8n magnetozone interval is middle Illyrian to lower Fassanian. The top of unit D is correlated to an interval in the middle of the Nevadites Zone (close to the Anisian–Ladinian boundary). Consequently, the Otter Sandstone Formation correlates with the Muschelkalk in the Polish Basin, but is equivalent to only part of the Germanic Basin Muschelkalk. The continuous magnetostratigraphy from the Sherwood Sandstone Group, provides additional details of the polarity pattern through the Pelsonian to Illyrian interval, which appears to be lacking in discontinuous marine sections. A synthesis of adjacent European sedimentary basins in combination with the magnetostratigraphy, suggests that the Budleigh Salterton Pebble Beds are probably Late Spathian to lower Aegean.

Correlation Of Fine Carbonaceous Bands Across A Precambrian Stagnant Basin

ABSTRACT A carbon-banded siltite interval within the Precambrian Prichard and Aldridge Formations of the Belt-Purcell Supergroup correlates across a 3,000 square mile area from northern Idaho and Montana into southeastern British Columbia. The banded interval consists of a 13-foot sequence of light and dark gray bands 1 mm to 2 cm thick which can be matched, band-for-band, from outcrop to outcrop throughout the entire area. A type section of the banded interval was cored and photographed to scale. The photo of a distinctive six-inch sequence of bands was then matched to outcrops of the banded interval from one location to another. Adjacent light and dark bands of the marker interval both consist of uniform, well-sorted quartz and feldspar silt, with disseminated biotite, muscovite, and pyrrhotite. Dark bands differ from the light ones in that they contain amorphous carbon particles and clusters of monazite grains. The uppermost 6,000 feet of the Prichard and Aldridge Formations can be subdivided into five informal units A, B, C, D, and E. Units A and D are thick, uniform turbidite quartzites, B is interlaminated quartzite and siltite, and C is even-bedded carbonaceous siltite. Within the lower part of unit C is the 13-foot banded sequence that can be correlated on a band-for-band scale. The uppermost unit E, is cross-bedded and rippled argillite. The banded interval and the rest of unit C probably represent subaqueous deposition below wave base in a stagnant basin. Fluctuating widespread surface blooms of primitive planktonic algae may have formed the carbon and monazite-rich bands of the marker interval. The well-sorted silt matrix was perhaps derived from dust storms settling out over the Precambrian basin.

Stratigraphy and Oil Possibilities of Mesozoic Rocks in Kandik Basin, East-Central Alaska: ABSTRACT

Mesozoic sedimentary rocks in the Kandik basin are subdivided provisionally into four units. The oldest, unit A, rests unconformably on the Tahkandit Limestone of Permian age. It consists mainly of carbonaceous argillite but includes some limestone, oil shale, and quartz arenite. This unit is about 5,000 ft. thick and ranges in age from Middle Triassic (Ladinian) at its base to Early Cretaceous (Valanginian) at its top. Conformably overlying unit A is unit B, a massive quartz arenite with minor interbeds of argillite and chert-pebble conglomerate. Unit B is less than 100 ft. thick south of the Yukon River but northward it thickens to about 1,000 ft. or more in the headwaters of the Black River. Pelecypods of Valanginian age have been found in the quartz arenite at several widely spaced localities. Unit B grades conformably upward into unit C, a rhythmically bedded quartz arenite and argillite, at least 5,000 ft. thick, that forms a substantial part of the Kandik Formation (Lower Cretaceous) at its type locality. Pelecypods of Valanginian age occur in the lower part of unit C. Unit D consists of chert-pebble conglomerate, sandstone, siltstone, and argillite, all of the graywacke type. It rests conformably on unit C in the vicinity of the Yukon End_Page 1757------------------------------ River, but apparently rests unconformably on units B and A and on rocks of Paleozoic age near Indian Grave Creek. Unit D is several thousand feet thick and is provisionally correlated with non-marine clastic rocks of Early Cretaceous (Albian) age near Eagle, Alaska. The oil shale within unit A is a potential source bed for petroleum, but none of the Mesozoic rocks cropping out in the Kandik basin seem to have enough porosity to make them potential reservoirs. Although the oil possibilities of the Mesozoic rocks are not encouraging, some of the Paleozoic rocks contain oil and therefore deserve further investigation. End_of_Article - Last_Page 1758------------