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Paleozoic igneous rocks exposed in the northern Yili Block are thought to have resulted from the subduction of the North Tianshan oceanic crust. However, the exact timing of the transition of the northern margin of the Yili Block from a passive to an active continental margin remains unknown. In this paper, the petrological and geochemical features, zircon U-Pb chronology, Lu-Hf isotopes, and Sr-Nd isotopes of volcanic rocks in the Nailenggeledaban area on the northern margin of the Yili Block were studied. Zircon U-Pb dating results show that the crystallization ages of the volcanic rocks in the Nailenggeledaban area on the northern margin of the Yili Block are 491 ± 2 Ma and 500 ± 2 Ma, suggesting they were formed during the Late Cambrian. Geochemical features show that the volcanic rocks are alkaline basalts with rare earth and trace element distribution patterns similar to OIB, although they exhibit some degree of Zr and Hf depletion. The εHf(t) values of alkaline basalts in the Nailenggeledaban area at the northern Yili Block range from −3.48 to −1.00, with a TDM1 age of 1152 to 1263 Ma. The εNd(t) values range from −3.53 to −0.96, with a TDM1 age of 1471 to 2162 Ma. Combined with geochemical data, the alkaline basalt magma in the Nailenggeledaban area on the northern margin of the Yili Block may be derived from the Mesoproterozoic enriched lithospheric mantle. The composition of the mantle source area is potentially garnet lherzolite, and the magma appears to have been either unaffected or only minimally contaminated by crustal materials during the ascending process. On the basis of the research results of the Early Paleozoic tectonic evolution in the northern margin of the Yili Block, this paper proposes that the volcanic rocks in the Nailenggeledaban area, located on the northern margin of the Yili Block, were formed in a back-arc extensional environment resulting from the subduction of the North Tianshan Ocean (or Junggar Ocean) beneath the northern margin of the Yili Block during the Late Cambrian. [ABSTRACT FROM AUTHOR]

The Early Paleozoic paleolatitudinal position of the terranes in the northern Tibetan Plateau is the key to unraveling the evolution of the Proto‐Tethys Ocean. We present the first Late Cambrian paleomagnetic results from the Oulongbuluke terrane (OT), in the northern Tibetan Plateau. The mean paleomagnetic direction for 16 sites is Ds = 196.2°, Is = −36.9° with κs = 31.5, α95 = 6.7°, corresponding to a paleopole at 68.2°S/51.9°E with dp/dm = 4.6°/7.8°. Rock magnetic and petrologic analyses demonstrate the primary origin of the magnetic mineralogy. This paleomagnetic result defines the Late Cambrian paleolatitude of the OT as 20.6 ± 4.6°S (reference point: 37.2°N/96.6°E). Combined paleomagnetic and geological evidence suggests that the terranes in the northern Tibetan Plateau were located to the northwest of the Indian plate of Gondwana during the Late Cambrian. Plain Language Summary: The Proto‐Tethys Ocean underwent a complex process of collision and amalgamation of the terranes in the northern Tibetan Plateau during the Early Paleozoic. Unraveling the Early Paleozoic paleogeography of these terranes is important for understanding the evolution of the Proto‐Tethys Ocean and is critical for reconstructing the formation of East Asia. However, quantitative constraints on the Early Paleozoic paleogeographic position of the terranes in the northern Tibetan Plateau are limited. Paleomagnetism is the only effective approach for directly constraining the paleolatitude of terranes. We conducted a paleomagnetic study of the Late Cambrian strata in the Oulongbuluke terrane (OT), northern Tibetan Plateau. The results define the paleolatitude of 20.6 ± 4.6 °S for the OT during the Late Cambrian. Based on paleomagnetic data and geological evidence, we also present a tentative paleogeographic reconstruction of the terranes in the northern Tibetan Plateau and the Proto‐Tethys Ocean in a global setting during the Late Cambrian. Key Points: We report the first Late Cambrian paleomagnetic results for the Oulongbuluke terrane (OT)The OT was located at ∼20.6°S during the Late CambrianThe terranes in the northern Tibetan Plateau may have been located northwest of the Indian plate during the Late Cambrian [ABSTRACT FROM AUTHOR]

Antarcticocyathus webersi, reported from the upper Cambrian of central West Antarctica, was originally described as an archaeocyath. It was compared with the late Cambrian species Wilbernicyathus donegani, which was thought to be an archaeocyath. W. donegani was subsequently identified as a lithistid sponge belonging to the Family Anthaspidellidae. Examination of the type material reveals that A. webersi is also an anthaspidellid sponge. Until now, A. webersi was the only taxon generally regarded as a late Cambrian 'archaeocyath'. Recognition of A. webersi as an anthaspidellid sponge suggests that archaeocyaths did not continue beyond the middle Cambrian. [ABSTRACT FROM AUTHOR]

The paper presents petrographic, geochemical, and new U-Pb zircon (LA-ICP-MS) geochronological data on the Upper Lena Fm. sediments which make part of the Cambrian sedimentary cover of the Siberian craton. The composition of lithic fragments in these clastic sediments, including mafic and felsic volcanics and granitoids, along with the correlation of major element ratios and the values of trace-element ratios point to predominant igneous (mainly felsic) rocks in the provenance. The U-Pb ages of detrital zircons from the sampled Upper Lena Fm. sandstones are mostly Early Paleozoic (∼500 Ma), with very few Archean-Paleoproterozoic determinations and quite many Neoproterozoic zircons. Ediacaran and Earliest Cambrian clastic sediments bearing Early Precambrian and Neoproterozoic detrital zircons, as well as Neoproterozoic and Early Paleozoic complexes of the Central Asian Orogenic Belt, could provide material for the Upper Lena clastic deposition. The geochronological evidence shows that the Upper Lena Fm. sandstones were deposited over vast territories of the southern Siberian craton in the Late Cambrian, in a single sedimentary basin, and originated from the same provenance. The Upper Lena deposition event in the Late Cambrian, immediately before the Ordovician period, makes a key milestone in the geological history of Siberia: the end of a large-scale Early Cambrian transgression and the beginning of gradual uplift of the southern craton margin, at least till the Carboniferous, which was associated with the formation of the Central Asian Orogenic Belt, a major tectonic unit of Asia.

The paper provides an overview of the geological structure and presents new data on petrography and geochemistry of igneous rocks of the Tekturmas accretionary complex (TAC). Consideration is being given to the age, petrogenesis and probable tectonic settings of formation of igneous rocks. It is shown that the TAC and adjacent ophiolite belt are parts of the Late Cambrian – Ordovician Pacific-type orogenic belt formed at an active margin of the Paleo-Asian Ocean. The TAC is dominated mainly by tholeiitic mafic igneous rocks (basalt, dolerite, gabbro). There are recognized three groups of rocks: high-Ti, medium-Ti and low-Ti. Geological and geochemical features of TAC igneous rocks suggest their formation in three tectonic settings: mid-ocean ridge (medium-Ti), oceanic island/seamount (high-Ti) and over subduction zones (low-Ti).

The tectonic setting and subduction polarity of the early Paleozoic North Qilian Orogenic Belt (NQOB) in northwestern China is poorly constrained due to complex tectonic deformation. Mafic and ultramafic rocks in the South Ophiolite Belt of the NQOB are interpreted to be middle ocean ridge ophiolite or suprasubdcution zone ophiolite. To address this, we have conducted geochemical and geochronological investigations of the mafic rock sequence (cumulate gabbros, diabases, isotropic gabbros, and basalts) in Hongtugou in the South Ophiolite Belt. Trace element characteristics of the pillow basalts and the isotropic gabbros with enrichment of Th and La relative to Nb on the N-MORB normalized multi-element diagram are consistent with a suprasubduction setting, where similarities with the Panamanian proto-arc rocks suggest they formed shortly after subduction initiation. Major element modelling for cumulate gabbros and basalts indicates the hydrous condition of crystallization which further supports a suprasubduction setting. The Proterozoic zircon crystals captured in a cumulate gabbro and a diabase suggest this suprasubduction zone is a continental convergent margin. A weighted mean zircon SHRIMP age of 507 ± 6 Ma from an isotropic gabbro is consistent with crystallization ages of other mafic rocks in this belt. This suggests the North Qilian oceanic lithosphere subducted beneath the continent in the late Cambrian. Mafic rocks in this study along with the serpentinized peridotite do not fall into the category of ophiolite, despite displaying an ophiolite sequence. [ABSTRACT FROM AUTHOR]

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Abstract Well preserved and diverse organic-walled marine microphytoplankton cysts (acritarchs sensu lato) occur in Member 4 (comprising mostly of fine-grained clastics with thin carbonate intercalations) of the Mila Formation at the type section, southwestern Damghan. Based on the association of such index acritarch taxa as Timofeevia phosphoritica, Cristallinium cambriense, Ninadiacrodium dumontii, Vulcanisphaera africana, Ooidium rossicum, Cymatiogalea cuvillieri, Caldariola glabra, and Dasydiacrodium sp. in the material studied, an local biozone, namely Ooidium rossicum­-Vulcanisphaera africana assemblage biozone dated as Late Cambrian (Furongian), and a barren interval are introduced in the upper and lower parts, respectively, of the rock unit investigated. Occurrence in the examined assemblages of such middle latitude acritarchs as Ninadiacrodium indicates that the Alborz Ranges was located in southern mid-latitudes (30º–60º) during the Late Cambrian. Retrieved marine microphytoplankton cysts from Member 4 of the Mila Formation is comparable with the Late Cambrian assemblages recorded from elsewhere, this allows for the pertinent assemblages to be associated with peri-Gondwanan palynofloras. Keywords: Biostratigraphy, Palaeoecology, Acritarchs, Late Cambrian, Mila Formation. Introduction Biostratigraphic zonation of the Middle and Upper Cambrian strata is based mainly on trilobites, particularly planktonic agnostids and olenids. For example, in South China base of the Furongian Series is defined by Glyptagnostus reticulatus Zone (Peng et al. 2004). In the last decades, organic-walled microfossils (acritarchs) have been widely used for Palaeozoic stratigraphic subdivisions (Molyneux et al. 1996). The Acritarch group is defined as organic-walled microfossils of unknown biological affinities by Evitt (1963). They are a heterogeneous group of various microfossils and may include the remains of a wide range of different kinds of organisms, such as egg of small metazoans, spores of different algal classes, and resting cysts (Servais 1996). Recently, some of the acritarchs have been attributed to different groups of algae e.g. Prasinophytes or Chlorophytes (Colbath and Grenfell 1995). In the last decades, organic-walled microphytoplankton have been widely used for stratigraphic correlation both regionally and globally and their utility in dating Proterozoic and Palaeozoic marine sedimentary rocks is widely recognized (Playford 2003). Acritarchs feature a relatively rapid development of morphological innovations and a large number of new morphotypes appeared. Several palynological investigations have been undertaken on the Upper Cambrian strata across the world; e.g., Canada (Martin and Dean 1988; Palacios 2012), Russia (Raevskaya and Golubkova 2006), Germany (Montenari and Servais 2000), Iran (Ghavidel-Syooki 2006; Ghavidel-Syooki and Vecoli, 2008), North Africa (Vecoli 1999), England (Potter et al. 2012) and Spain (Albani et al. 2006). The Mila Formation is the first lithostratigraphic unit representing the Middle–Upper Cambrian strata in the Alborz Ranges and the other parts of Iran (Aghanabati 2004). Palaeontological and structural geological studies in the Alborz indicate that northern Iran, along with central Iran and Zagros located on the divergent margin of protopaleotethys and north of the Gondwana palaeocontinents. The Mila Formation at its type section measured 585 m (Stöcklin et al. 1964) and subdivided into five members: Member 1, dolostone–marl; Member 2, terrigenous – carbonate; Member 3 fossiliferous limestone; and mainly terrigenous members 4 and 5. According to palaeontological and stratigraphical studies the first 2 units attributed to the Middle Cambrian and members 3 and 4 to the Late Cambrian. The former Member 5 of this unit was later considered to be equivalent of the Lashkarak Formation (Early Ordovician). The Mila Formation at the its type section is underlain and overlain by the Lalun and Jeirud formations, respectively. The Mila Formation generally consists of dolostone, thin-bedded, crystalline, glauconitic limestone, marl, coloured shales and sandstones. Several palaeontological investigations have been conducted such as on trilobites (Kushan 1973; Peng et al. 1999), brachiopods (Popov et al. 2009, 2013), conodonts (Müller 1973; Fazli and Hamdi 2008; Jahangir et al. 2016) and palynomorphs (Ghavidel-Syooki 2006). Considering the stratigraphic significance of organic-walled marine microphytoplankton in the Lower Palaeozoic biostratigraphy, the aim of this study is to determine relative age and to derive palaeogeographic implications for the Member 4 at its type section. Material & Methods: To retrieve palynological content of the Member 4 of Mila Formation at the type section, 21 surface samples collected from this rock unit. All samples prepared in palynological laboratories at Kharazmi University, Tehran and University of Lille, France using standard palynological processing procedures, encompassing initial treatment with HCl 10-50% and HF 40% for dissolution of carbonates and silicates, respectively. Then the residues saturated with ZnCl2 solution (2.0 gr/cm3) for mineral separation. All residues are sieved with 15 and 20 µm mesh and three slides of each sample are made. Discussion of Results & Conclusions: Well-preserved and diverse palynomorphs occur in Member 4 of the Mila Formation at the Mila Kuh section. The assemblage contains 14 species assigned to 13 genera of acritarchs and one species of prasinophytes. Based on the occurrence and stratigraphic distribution of index acritarch taxa such as Timofeevia phosphoritica, Cristallinium cambriense, Ninadiacrodium dumontii, Vulcanisphaera africana, Ooidium rossicum, Cymatiogalea cuvillieri, Caldariola glabra, and Dasydiacrodium sp. one local assemblage biozone namely Ooidium rossicum-Vulcanisphaera africana assemblage biozone is introduced in 41 m of the Member 4 and assigned to the Late Cambrian (Furongian). Additionally, one barren interval zone at the base (45 m) of the rock unit is also identifiable. The biozone (Ooidium rossicum-Vulcanisphaera africana) introduced herein is comparable to microflora A2 (partial) – A6 of Martin and Dean (1981, 1988) and RA3–RA10 microflora of Parsons and Anderson (2000) as well as the upper part of VK2 to VK5 of Volkova (1990) at the East European Platform. Furthermore, it is equivalent with the Zone II to IV of Ghavidel-Syooki and Vecoli (2008) in the High Zagros Mountains, southern Iran. Occurrence of such mid-latitude taxa as Ninadiacrodium and comparison of the acritarch assemblages with those from elsewhere in the world indicates the peri-Gondawanan affinity; thus supporting a 30°-60°S palaeolatitude for the eastern Alborz in the Late Cambrian

The sub-class Nautiloidea is divided into two super-orders, Nautilosiphonata and Calciosiphonata, based on different structural types of the connecting rings. The late Cambrian order Plectronocerida has the calciosiphonate type of connecting ring similar to that in post-Cambrian orthocerids. It is structurally more complex than the nautilosiphonate connecting ring in late Cambrian ellesemerocerid-like nautiloids. The plectronocerid nautiloids, therefore, evolved from the ellesmerocerid-like nautiloids and not vice versa. As indicated by the complex siphuncular structure in plectronocerids, cephalopod evolution began earlier than previously estimated, probably in the early Cambrian. The siphuncle in cephalopods originated from a calcareous septum that became partially non-calcified and formed the connecting ring. [ABSTRACT FROM AUTHOR]

Although Late Cambrian microbial build‐ups were recognized in the Point Peak Member of the Wilberns Formation in Central Texas (USA) nearly 70 years ago, only a few studies focused specifically on the build‐ups themselves. This study focuses on the interpretation of the regional (15 measured sections described in literature representing an area of 8000 km2) and local (field and drone photogrammetry studies in a 25 km2 area from within south Mason County) microbial build‐up occurrence, describes their growth phases and details their interactions with the surrounding inter‐build‐up sediments. The study establishes the occurrence of microbial build‐ups in the lower and upper Point Peak members (the Point Peak Member is informally broken up into the lower Point Peak and the upper Point Peak members separated by Plectotrophia zone). The lower Point Peak Member consists of three <1 m thick microbial bioherms and biostrome units, in addition to heterolithic and skeletal/ooid grainstone and packstone beds. One, up to 14 m thick, microbial unit associated with inter‐build‐up skeletal and ooid grainstone and packstone beds, intercalated with mixed siliciclastic–carbonate silt beds, characterizes the upper Point Peak member. The microbial unit in the upper Point Peak member displays a three‐phase growth evolution, from an initial colonization phase on flat based, rip‐up clast lenses, to a second aggradation and lateral expansion phase, into a third well‐defined capping phase. The ultimate demise of the microbial build‐ups is interpreted to have been triggered by an increase of water turbidity caused by a sudden influx of fine siliciclastics. The lower Point Peak member represents inner ramp shallow subtidal and intertidal facies and the upper Point Peak member corresponds to mid‐outer ramp subtidal facies. Understanding the morphological architecture and depositional context of these features is of importance for identifying signatures of early life on Earth. [ABSTRACT FROM AUTHOR]

The late Cambrian Steptoean positive carbon isotope excursion (SPICE) is a distinct chemostratigraphic feature of the Paleozoic, marked by a 4–5‰ shift in carbonate δ13C that has been recognized across the globe during the Paibian Stage. The SPICE may be related to enhanced burial of organic matter and pyrite during the expansion of marine euxinia, which as a source of O 2 also results in a pulse of atmospheric oxygen. However, geochemical proxies have not clearly illustrated how the ocean redox evolved with atmospheric oxygen changes during the SPICE. This study presents new carbonate I/Ca data, a redox proxy for the upper ocean, from three basins. I/Ca values are low at Great Basin and South China from early into the peak of SPICE, indicating generally anoxic conditions in shallow waters. The overall increasing trend in I/Ca through the peak and recovery phase of the SPICE roughly correlates with the previously modeled rise in atmospheric oxygen. Spatially, the Georgina Basin (Mt. Whelan) might have recorded a relatively more oxic upper ocean compared to the Great Basin and South China. Earth system model simulations also demonstrate the importance of paleogeographic and oceanographic settings on local redox conditions, highlighting the redox heterogeneity during the SPICE. • I/Ca proxy was used for reconstructing redox condition during SPICE. • An oxygenation event in the upper ocean was found during the peak and recovery phase of SPICE. • The ocean redox changes varied in different paleogeographic settings. [ABSTRACT FROM AUTHOR]

Modeling of physical and geological properties of a study object is an integral part of geological surveys at each stage. Without a model of physical and geological properties (PhGM) it is impossible to obtain a complete set of reflection indicators of an object in physical fields. The models are useful in solving a wide range of tasks on substantiation of survey methods and routines for interpreting the field data. Generally, a mineral deposit FGM contains the main elements represented by structural–material complexes (SMC) characterized by specific values of geometrical and physical parameters. We attempted at developing an PhGM of the diamond deposits controlled by the Middle Paleozoic trappe magmatism zone of the Vilyui paleoaulacogen. With this goal, in the period from 2002 to 2016, we carried out petrographic, paleomagnetic and geochemical studies of the SMC of the Nyurbinskaya pipe of Nakyn kimberlite field located in the Middle Markha district, West Yakutia. We studied terrigenous–carbonate rocks of the Late Cambrian of the Morkokinskaya and Oldondinskaya suites (Є3mrk and Є3–O1ol, respectively), dolerites of the Vilyui–Markha intrusive complex (βPZ2vm), autolithic kimberlite breccias of the Nakyn intrusive complex (iPZ2nk), and sandstones of the Early Jurassic Ukugut suite (J1uk). Important information was obtained on a wide range of petromagnetic parameters and paleomagnetism of the deposit SMC, elemental chemical composition of ferromagnetic minerals, and other data that can prove useful in discovering promising kimberlite sites in the Vilyui–Markha dike belt. The position of the paleomagnetic pole for the Late Cambrian of the Siberian Platform was clarified: latitude Φ=–35°, longitude Λ=136°, and confidence intervals dp/dm=3.5/6.9°. The poles were estimated for kimberlites (Φ=–11.5°, Λ=111.2°, dp/dm=3.5/7.5°) and pre-pipe basites (Φ=–14.6°, Λ=117.4°, dp/dm=3.7/7.1°). According to the Nyurbinskaya deposit PhGM developed on the basis of the paleomagnetic data, there was the Late Silurian – Early Devonian (S2–D1) stage of kimberlite- and trappe formation. The results of our study can enhance the prospects for discovering new primary diamond deposits on the Siberian platform.

The recent discovery of a possible Late Cambrian true polar wander (TPW) from the Jiangshan section in eastern South China has intrigued us to test this TPW in other continuous, well‐dated Upper Cambrian successions. We have conducted a detailed paleomagnetic study of a continuous Upper Cambrian succession in Wa'ergang, Hunan Province, middle South China, that contains well‐defined trilobite zones correlative with those of the Jiangshan section. Three remanence components were isolated from the Upper Cambrian limestone. The low‐ and intermediate‐temperature components represent a recent viscous magnetization and a Cretaceous remagnetization, respectively. The high‐temperature component passes fold tests, but its pole lies close to the Middle Triassic pole of South China, indicating a Middle Triassic remagnetization. Rock magnetic analyses and petrographic observations indicate that the high‐temperature component resides in small framboidal magnetite aggregates that were formed via alteration and replacement of pyrite and represents a chemical remagnetization. This Middle Triassic remagnetization and previously recognized Triassic remagnetization exhibit a younging trend from the east to the west of South China. The widespread Triassic remagnetization was likely associated with the Indosinian orogeny during which the scissor‐like suturing processes between the South and North China Blocks and the accompanying so‐called squeegeed orogenic fluids led to progressively westward younging remagnetization in South China. Although the new paleomagnetic results do not allow us to effectively test the Late Cambrian TPW due to the thorough remagnetization, these data provide important insights into understanding the Early Mesozoic remagnetization and associated geological processes. Key Points: A prefolding, Middle Triassic chemical remagnetization is recognized in the well‐dated Upper Cambrian succession in South ChinaA younging trend of the Triassic remagnetization from the east to west is first identified in South ChinaThe remagnetization was likely related to orogenic fluids associated with the scissor‐like collision between South and North China Blocks [ABSTRACT FROM AUTHOR]

This paper presents results of mineralogical and geochemical study of TiO 2 polymorphs that occur within two hydrothermal stratiform zones of the Wiśniówka area (south-central Poland). These two mineralized zones consist primarily of alternating pyritiferous and REE-bearing sedimentary quartzites, quartzitic sandstones and silty-clayey shales. Of the TiO 2 phases, anatase is a predominant type (mean of 56%) with a lesser amount of rutile (30%) and mixed rutile-anatase phases (11%) as well as rare rutile-brookite (2%) and brookite (1%) as evidenced by laser Raman microspectrometry. TiO 2 polymorphs typically form interstitial euhedral to anhedral or skeleton-like grains and aggregations averaging 30–50 μm in diameter occasionally attaining 110 μm. Extremely scarce pyritiferous microfossils are infilled with needle- and lath-like anatase. Under backscattered electron microscope images, TiO 2 grains are generally homogenous, in places with tiny inclusions of zircon, monazite, niobium oxide and palladium telluride. In addition, some rutile grains show oscillatory zonation or zonal-brecciated and patchy patterns. Results derived from electron microprobe examinations show enrichments of most TiO 2 phases in niobium (up to 4.98 wt%), zirconium (up to 0.58 wt%) and tantalum (up to 0.57 wt%) substituting titanium in the TiO 2 crystal structure. The Ti Nb pair shows the highest correlation (r2 = 0.98). Concentrations of these and other elements vary substantially within individual anatase/rutile grains. The lack of other potential Ti-bearing rock-forming or oxide minerals (e.g., biotite, pyroxene, hornblende, titanite, ilmenite, titanomagnetite, titanohematite) in sedimentary siliciclastic rocks of the study area also indicates that anatase and rutile may have crystallized along with prevailing pyrite, xenotime, aluminum-phosphate-sulfate (APS) minerals and most monazite directly from hydrothermal fluids at relatively low temperatures, presumably around 200 °C (range of 150 to 300 °C). Among these ore minerals, only goyazite and mixed goyazite-gorceixite aggregations contain up to 20.07 wt% Ti and 24.09 wt% Ti, respectively. Mineral and microtextural relationships show that TiO 2 polymorphs may have formed in two phases under reducing and subsequently oxidizing conditions of the Wiśniówka Late Cambrian depositional basin. [ABSTRACT FROM AUTHOR]

Various authors have described and illustrated exceptionally large acritarchs from the Furongian (upper Cambrian) from different parts of the world. The different morphotypes clearly belong to the ‘diacromorph’ acritarchs, but have until now usually been attributed, tentatively or erroneously, to the genusVeryhachium. Based on new material from the Holy Cross Mountains (central Poland) and the literature, the new genusGigadiacrodiumis erected to include these stratigraphically diagnostic and easily distinguishable morphotypes. The new genus includes the following species:Gigadiacrodium martinae(Pittau 1985) comb. nov., emend. nov. (type species) andGigadiacrodium vidaliisp. nov. In addition, a new combination is proposed: ?Solisphaeridium mutabileDi Milia et al. 1989, comb. nov. [ABSTRACT FROM PUBLISHER]

The SPICE (Steptoean Positive Carbon Isotope Excursion) is a significant event in the Late Cambrian, recording global carbon cycle perturbations. Its driving mechanism is still controversial, but mainly believed to be related to an increase of organic carbon burial caused by ocean anoxia. The shallow-water platform carbonates of the Upper Cambrian Loushanguan Formation of Yankong outcrop (Upper Yangtze) spans the event interval. Their primary geochemical proxy signatures (trace elements, carbon and strontium isotopes), have been utilized to better understand the driving mechanism of the SPICE event. The variations of paleoenvironmental proxies in the upper Loushanguan Formation exhibit a rapid transformation of redox conditions similar to those of deep-water regions, thus reflecting an expansion of anoxic seawater to shallow-water column. The increase of 87Sr/86Sr, Al, and ∑REE during the SPICE suggests an enhancement in nutrient inputs from continental weathering that might have promoted primary productivity, which preferentially consumed light 12CO 2 of surface waters, resulting in 13C-enriched DIC. The occurrence of PGMEE (Paibian global marine euxinia event), immediately before the enhancement of continental weathering, suggests that it was the onset-driving mechanism of the SPICE event and the increase in continental weathering might have promoted primary productivity to further intensify carbon burial and play a superimposed effect on that of the SPICE event. • SPICE event is influenced by water depth. • Shoaling of anoxic seawater into shallow-water settings during the Late Cambrian. • Inputs from continental weathering during the SPICE event. [ABSTRACT FROM AUTHOR]

The Steptoean Positive Carbon Isotope Excursion (SPICE) event is extensively documented in globally distributed carbonate and organic-rich successions of slope and platform environments during the late Cambrian (ca. 497–494 Ma). Despite numerous studies, its regional manifestation remains controversial because of the major uncertainty of the redox conditions in sedimentary paleoenvironments and its effect on the changes in the biota. Biogeochemical processes that occurred during the SPICE event are important for assessing whether the excursion is associated with the co-evolution of organisms and environments. In this study, we investigated the changes in plankton and paleoenvironment at the molecular level by combining kerogen elemental analysis, catalytic hydropyrolysis (HyPy), and gas chromatography-mass spectrometry (GC-MS) analyses of saturates and aromatics with published carbon isotopic data. The three fluorene series, gammacerane/C 30 hopane (G/C 30 H) and pristine/phytane (Pr/Ph) ratios demonstrated that the shallow shelf seawater changed significantly from relatively reducing to oxidizing and back to reducing conditions during the SPICE interval coupled with a regression-transgression cycle. The phytoplankton during the rise of the SPICE were mainly organic-walled, such as cyanobacteria, various acritarchs, and algae, as evidenced by terpanes, hopanes, and steranes. Significant decreases in phytoplankton diversity and abundance coincided with the peak of the SPICE, corresponding to the most oxidized and hypersaline periods during the SPICE event in the eastern Tarim Basin. Plankton assemblages diversified significantly with increasing living space due to the rise of sea-level during the post-SPICE period. Therefore, this study supports the idea that plankton groups changed dramatically with the environment, and its revolution followed the SPICE into the Great Ordovician Biodiversification Event. • The biological and environmental changes associated with the SPICE event were investigated at the molecular level. • The kerogens were not only sourced from marine plankton but also considerable terrigenous organisms. • The SPICE interval was coupled with a regression-transgression cycle. • The peak of the SPICE corresponded to the lowest sea-level and relatively oxic period in the eastern Tarim Basin. • Plankton changed dramatically with the environments and the SPICE was coincident with the onset of plankton revolution. [ABSTRACT FROM AUTHOR]

The ‘Great Ordovician Biodiversification Event’ comprises the rapid diversification of marine organisms during the Ordovician Period. It is now clear that this adaptive radiation started for some organisms already in the Cambrian and continued for others beyond the end of the Ordovician, making the ‘Great Ordovician Biodiversification Event’ part of a long-term late Proterozoic and Early Palaeozoic radiation, that in part is expressed by the fossil record as the ‘Cambrian Explosion.’ A significant diversification of different groups of the plankton is observed in the late Cambrian–Early Ordovician interval, leading to the subsequent ‘Ordovician Plankton Revolution.’ The possible causes of this ‘plankton revolution’ are currently debated. They include changes in palaeoclimate, palaeogeography or tectonic and volcanic activity, as well as a modified nutrient supply. In this context, the Steptoean Positive Carbon Isotope Excursion δ 13 C carb (SPICE) event in the late Cambrian (Paibian Stage, Furongian Series) has been related to a major increase in atmospheric O 2 (from 10–18% to some 20 – 29%) and to increased oceanic nutrient availability. Here we analyze the diversification of the planktonic groups during the late Cambrian and Early Ordovician, in particular in relation to the SPICE event. Our analyses include the changing diversities of the phytoplankton (acritarchs), diverse groups of zooplankton (e.g., radiolarians, graptolites, chitinozoans) and the switch to a planktonic mode of life of fossil groups (e.g., arthropods, molluscs) that were part of the Cambrian benthos and that later occupied pelagic niches. In addition, we focus also on data indicating evidence for a late Cambrian to Ordovician origin of planktotrophy in invertebrate larvae. It can be concluded that none of the diversifications of the different planktonic organisms can be related directly to the SPICE event. However, a long term (10–20 million years) oxygenation pulse related to the SPICE event might have fuelled the explosion of phytoplankton diversity observed in the latest Cambrian–Early Ordovician that led to completely modified trophic structures permitting an increase in diversity and abundance of plankton-feeding groups during the Ordovician. [ABSTRACT FROM AUTHOR]

The Furongian Słowińska Formation in Poland yielded minute three-dimensionally preserved, phosphatic fossils. Based on shape and structure, two distinct types are identified. The first type comprises sinuously folded, coiled, or spiral string-shaped specimens, interpreted as faecal material, coprolites. The specimens measure between less than one and two mm, the strings being long and against their subcircular to circular cross-section (60–150 μm). Many strings are folded in few to more than 30 regular loops, in this exceptional complexity unknown from any comparable fossil or extant faeces. Fully stretched, such strings may have an estimated length of more than three cm, suggesting continuous production of such faeces and resistance very a longer period after defecation until fossilization. Modelling similar strings indicates that the loops were produced by sidewards swinging of the body end of the producer during forward move. EDS analysis of the strings revealed low silica content, but high amounts of phosphate pointing to a organic-rich muddy bottom, which the producers swallowed and eventually became phosphatized as faeces. The producers of this faeces might have been few millimeter long and benthic, not infaunal worms, yet, none of the putative coprolites can be unquestionably ascribed to a particular animal group. The second type of fossils comprises between 100 and 220 μm long ellipsoidal to spherical forms with a smooth but wrinkled surface. They are interpreted as collapsed and deformed eggs or embryos lacking the egg shell, rather than coprolites made of digested and squeezed remains of possibly phosphatocopid crustaceans, the most abundant component of the Polish and Baltoscandian Orsten-type fossil assemblages. The spheres also have a smooth surface, which in all cases is partly broken off, uncovering an internal mass. This ranges from a small hump of possibly embryonic material in a large void, to a completely round body possibly presenting a late shield-bearing embryo filling the entire space underneath the egg shell. We interpret this second type of fossils as the first evidence of eggs in Orsten-type preservation, most likely belonging to phosphatocopid crustaceans. • The Furongian Słowińska Formation in Poland yielded microscopic three-dimensionally preserved phosphatized fossils. • Two distinct types of microscopic fossils were identified: a) up to 2 mm long and ca. 90 μm wide, sinuously folded, coiled, or spiral strings b) ellipsoidal to spherical forms of secondarily phosphatized cuticular material. • The diversity of the bromalites is evidence of a larger number of benthic organisms than previously known. • At least three undeformed spherical specimens of the second type are broken open and expose embryos of a different stage. • The findings are a significant contribution to our understanding of the faunal composition in the late Cambrian Sea. [ABSTRACT FROM AUTHOR]

The globally recognized late Cambrian Steptoean Positive Carbon Isotope Excursion (SPICE; ca. 497–494 Ma) is one of the most prominent carbon isotope excursions during the Phanerozoic eon, yet its primary cause remains debatable. To provide new insights into this issue, here we investigate zinc stable isotopes (expressed as δ66Zn) on two coeval carbonate successions spanning the Miaolingian-Furongian transition in North China. Similar stratigraphic δ66Zn trends are observed in the two sections, indicating a widespread perturbation to the marine Zn cycling. An abrupt decline of δ66Zn values by up to 0.4‰ and a concomitant increase of Zn/Ca ratios are observed at the pre-SPICE to the early SPICE interval, which can be best explained by the enhanced influx of isotopically light Zn from continental weathering. Enhanced continental weathering increased the inputs of terrestrial-sourced nutrients to the oceans, promoting the primary productivity and burial fluxes of organically bound Zn. At the middle stage of the SPICE, the coupled positive shifts of δ66Zn and δ13C carb indicate a phase of marine Zn cycling fluctuations driven by massive organic matter burial. Enhanced sequestration of organic carbon caused a rise in atmospheric oxygen levels, favoring the remobilization of previously buried Zn at shallower marine settings. With the development of muted continental weathering during the falling limb of the SPICE, the return of δ66Zn to initial background values marks the reestablishment of the stable seawater chemistry condition. Our results constrain the important roles of enhanced continental weathering and organic matter burial in micronutrient fluctuations during the SPICE, which were most likely the primary trigger for the SPICE. • A combined δ13C carb and δ66Zn carb record for the SPICE interval in North China. • Initiation of enhanced continental weathering prior to the onset of the SPICE. • Continental weathering and organic matter burial affect the micronutrient cycling during the SPICE. • Enhanced continental weathering and organic carbon burial as the important drivers for the SPICE. [ABSTRACT FROM AUTHOR]

The Furongian (Upper Cambrian; Jiangshanian and Sunwaptan) Tunnel City Group (Lone Rock Formation and Mazomanie Formation), exposed in Wisconsin and Minnesota, represents a shallow-marine clastic environment during a time of exceptionally high sea level. Lithofacies from shoreface to transitional-offshore settings document deposition in a wave- and storm-dominated sea. Flooding of the cratonic interior was associated with formation of a condensed section and the extensive development of microbial mats. Biolamination, mat fragments, wrinkle structures, and syneresis cracks are preserved in various sandstone facies of the Lone Rock Formation, as is evidence for the cohesive behavior of sand. These microbial-induced sedimentary structures (MISS) provide unique signals of biological-physical processes that physical structures alone cannot mimic. The MISS are associated with a trilobite extinction event in the Steptoean-Sunwaptan boundary interval. This may support recent claims that Phanerozoic microbial mats were opportunistic disaster forms that flourished during periods of faunal turnover. Further investigation of stratigraphic, taphonomic, and other potential biases, however, is needed to fully test this hypothesis. [ABSTRACT FROM AUTHOR]

Abstract: New data from detailed measured sections permit a comprehensive revision of the sedimentary facies of the Furongian (upper Cambrian; Jiangshanian and Sunwaptan stages) Tunnel City Group (Lone Rock Formation and Mazomanie Formation) of Wisconsin and Minnesota. Heterogeneous sandstones, comprising seven lithofacies along a depositional transect from shoreface to transitional-offshore environments, record sedimentation in a storm-dominated, shallow-marine epicontinental sea. The origin of glauconite in the Birkmose Member and Reno Member of the Lone Rock Formation was unclear, but its formation and preserved distribution are linked to inferred depositional energy rather than just net sedimentation rate. Flat-pebble conglomerate, abundant in lower Paleozoic strata, was associated with the formation of a condensed section during cratonic flooding. Hummocky cross-stratification was a valuable tool used to infer depositional settings and relative paleobathymetry, and the model describing formation of this bedform is expanded to address flow types dominant during its genesis, in particular the importance of an early unidirectional component of combined flow. The depositional model developed here for the Lone Rock Formation and Mazomanie Formation is broadly applicable to other strata common to the early Paleozoic that document sedimentation along flooded cratonic interiors or shallow shelves. [Copyright &y& Elsevier]

Abstract: New data from detailed measured sections permit comprehensive analysis of the sequence framework of the Furongian (Upper Cambrian; Jiangshanian and Sunwaptan stages) Tunnel City Group (Lone Rock Formation and Mazomanie Formation) of Wisconsin and Minnesota. The sequence-stratigraphic architecture of the lower part of the Sunwaptan Stage at the base of the Tunnel City Group, at the contact between the Wonewoc Formation and Lone Rock Formation, records the first part of complex polyphase flooding (Sauk III) of the Laurentian craton, at a scale smaller than most events recorded by global sea-level curves. Flat-pebble conglomerate and glauconite document transgressive ravinement and development of a condensed section when creation of accommodation exceeded its consumption by sedimentation. Thinly-bedded, fossiliferous sandstone represents the most distal setting during earliest highstand. Subsequent deposition of sandstone characterized by hummocky or trough cross-stratification records progradational pulses of shallower, storm- and wave-dominated environments across the craton before final flooding of Sauk III commenced with carbonate deposition during the middle part of the Sunwaptan Stage. Comparison of early Sunwaptan flooding of the inner Laurentian craton to published interpretations from other parts of North America suggests that Sauk III was not a single, long-term accommodation event as previously proposed. [Copyright &y& Elsevier]

Numerous shallow-marine limestone layers of the Furongian (Late Cambrian) Chaomidian Formation in the Jiulongshan section (Shandong Province, China) are breccias. Some of these breccias show abundant vertical to sub-vertical clasts. Typically, these clasts end abruptly at the contact plane with the overlying deposit, either abutting the overlying sedimentary bed or via an erosional plane that truncates the clasts. A few exposures show concentrations of clasts that must have been uplifted to the extent that they transgressed the then sedimentary surface or (possibly) penetrated the overlying sediment which, in this case, consists of muds or marls. The clasts tend to show clusters with respect to the enclosing fabric. All clasts are parallel to each other in a specific cluster, while the various clusters may show different orientations of the clasts. It is deduced that both the exceptional position and the exceptional orientation of the clasts must be ascribed to the upward movement of the clasts under the influence of pore water escaping under high pressure through fluidized sediment. [ABSTRACT FROM AUTHOR]

New palynological investigations allowed a better definition of the age of terrigenous deposits of the Monte Fonnesu tectonic Unit, exposed in the Arburese area (SW Sardinia). The section investigated consists of a coarsening upwards positive sequence, up to 10 m thick, that is made up of quartz-arenitic sandstones and light gray quartzite beds (0.5 m thick), interbedded with thin beds of black shale. In the lower part of the section, two quartzitic levels are rich in lingulid (brachiopods) shell fragments. This is the first report of macrofossils from the Monte Fonnesu Unit. Samples collected for palynological analyses in the black shale at the base and at the top of the lowest quartzitic level yielded a Late Cambrian acritarch microflora that can be correlated with the Peltura trilobite Superzone. The Late Cambrian age assigned to the lower part of the sequence allows us to define more precisely the age of Mt. Fonnesu sandstone, which in consequence is bracketed between the Late Cambrian and the Early Ordovician.

A set of 14 abstracts and short papers (extended abstracts) of presentations given at a meeting organized by the NFSR Working Group, "Micropaléontologie végétale et Palynologie (MVP)", held on May 11, 2005 at the University of Liège, Belgium.

Trace fossils such as Climactichnites offer rare insights into the palaeobiology of Cambrian soft-bodied animals, especially those that inhabited emergent sand flats and are not known from body fossils. Analysis of field and museum Climactichnites, together with experiments on the preservation of similar modern trails, indicates that the tracemaker was an elongate, bilaterally symmetrical, dorsoventrally flattened, soft-bodied animal with a muscular foot. These characteristics are consistent with the tracemaker being a primitive mollusc or mollusc-like animal. Unlike most Neoproterozoic and Cambrian molluscs, the tracemaker could reach considerable size; at up to c. 69 cm long, it was one of the largest Cambrian animals of its time. When moving on the sediment surface, locomotion resulted from muscular waves generated along the sole of its flexible foot; the foot was extended and then clamped onto the substrate. Contraction of pedal muscles then pulled the body forward. Sedimentary structures associated with Climactichnites  wilsoni, such as polygonal desiccation cracks, raindrop impressions, adhesion structures and gas escape structures demonstrate that the animal inhabited intermittently subaerially exposed environments. The tracemaker’s method of locomotion is similar to that employed by modern intertidal gastropods, which make Climactichnites-like trails on exposed sand flats. However, these modern trails are not preserved because of erosion by wind, waves, tides and subsequent bioturbation. Abundant microbial sedimentary structures are associated with C. wilsoni, and together with low levels of vertical bioturbation, intimate that microbial binding may have mediated the preservation of these early mollusc trails. [ABSTRACT FROM AUTHOR]

The acritarch Ninadiacrodium gen. nov. is erected to include forms with a basically triangular outline,but with a clearly bipolar arrangement of processes. It belongs to the 'diacrodian' dade; these are morphotypes with ornament and/or processes at the two opposite poles of the central body. They were extremely abundant and highly diverse during the Late Cambrian and Early Ordovician. The new genus includes the two widely-cited species Ninadiacrodium caudatum (Vanguestaine 1973) comb. nov. and Ninadiacrodium dumontii (Vanguestaine 1973) comb. nov. Both taxa are emended here. Ninadiacrodium is easily recognizable due to its elongate triangular shape, but is clearly differentiated from Veryhachium Deunff 1954, which appears in the Ordovician. Ninadiacrodium is apparently confined to the Late Cambrian, and has a global distribution. It is therefore an index fossil for the Late Cambrian. [ABSTRACT FROM AUTHOR]

This paper focuses on the formative processes of limestone pseudoconglomerates in the Gushan and Chaomidian Formations (Late Cambrian) of the North China Platform, Shandong Province, China. The Gushan and Chaomidian Formations consist mainly of limestone and shale (marlstone) interlayers, wackestone to packstone, grainstone and microbialite as well as numerous limestone conglomerates. Seventy-three beds of limestone pseudoconglomerate in the Gushan and Chaomidian Formations were analysed based on clast and matrix compositions, internal fabric, sedimentary structures and bed geometry. These pseudoconglomerates are characterized by oligomictic to polymictic limestone clasts of various shapes (i.e. flat to undulatory disc, blade and sheet), marlstone and/or grainstone matrix and various internal fabrics (i.e. intact, thrusted, edgewise and disorganized), as well as transitional boundaries. Limestone pseudoconglomerates formed as a result of soft-sediment deformation of carbonate and argillaceous interlayers at a shallow burial depth. Differential early cementation of carbonate and argillaceous sediments provided the requisite conditions for the formation of pseudoconglomerates. Initial deformation (i.e. burial fragmentation, liquefaction and injection) and subsequent mobilization and disruption of fragmented clasts are two important processes for the formation of pseudoconglomerates. Burial fragmentation resulted from mechanical rupture of cohesive carbonate mud, whereas subsequent mobilization of fragmented clasts was due to the injection of fluid materials (liquefied carbonate sand and water-saturated argillaceous mud) under increased stress. Storm-wave loading was the most probable deformation mechanism, as an external triggering force. Subsequent re-orientation and rounding of clasts were probably prolonged under normal compactional stress. Eventually, disrupted clasts, along with matrix materials, were transformed into pseudoconglomerates by progressive lithification. Soft-sediment deformation is prevalent in alternate layers of limestone and mud(marl)stone and/or grainstone, regardless of their depositional environments. [ABSTRACT FROM AUTHOR]

Abstract: This article deals with the systematic description of polymerid trilobites from the Upper Cambrian Eochuangia hana, Agnostotes orientalis, and Pseudoyuepingia asaphoides Zones of the Machari Formation, Konggiri section, Yongwol, Korea. Agnostoid trilobites from the same locality were reported in 2004. Described are 20 polymerid trilobite taxa, including two new genera (Joshuaspis and Macharia) and four new species (Metachangshania brachypyga, Proceratopyge promisca, Joshuaspis parvus, and Macharia pengi). While agnostoid trilobite assemblages were used for correlation with distant regions such as South China, Australia, Kazakhstan, Siberia, and Laurentia, these polymerid trilobite assemblages provide valuable information for correlation of the Machari Formation with the Furongian (Upper Cambrian) strata of North China. [Copyright &y& Elsevier]

Abstract: The Cambrian–Ordovician transition of the western Mediterranean region (NW Gondwana) is characterized by the record of major erosive unconformities with gaps that range from a chronostratigraphic stage to a series. The hiatii are diachronous and involved progressively younger strata along the Gondwanan margin, from SW (Morocco) to NE (Montagne Noire). They can be related to development of a multi-stage rifting (further North), currently connected to the opening of the Rheic Ocean, and concomitant erosion on southern rift shoulders. The platforms of this margin of Gondwana occupied temperate-water, mid latitudes and were dominated by siliciclastic sedimentation, while carbonate factories were only episodically active in the Montagne-Noire platform. The Upper Cambrian is devoid of significant gaps in the southern Montagne Noire and the Iberian Chains. There, the sedimentation took place in a transgressive-dominated depositional system, with common offshore deposits and clayey substrates, and was bracketed by two major regressive trends. The Late Cambrian is also associated with the record of volcanic activity (e.g., in the Cantabrian and Ossa-Morena zones, and the northern Montagne Noire), and widespread development of a tectonic instability that led to the episodic establishment of palaeotopographies and record of slope-related facies associations. Several immigration events are recognized throughout the latest Middle Cambrian, Late Cambrian and Tremadocian. The trilobites show a stepwise replacement of Acado-Baltic-type families (e.g., the conocoryphid–paradoxidid–solenopleurid assemblage) characterized by: (i) a late Languedocian (latest Middle Cambrian) co-occurrence of Middle Cambrian trilobite families with the first anomocarid, dorypygid and proasaphiscid invaders; (ii) a Late Cambrian immigration replacing previous faunas, composed of trilobites (aphelaspidids, catillicephalids, ceratopygids, damesellids, eulomids, idahoiids, linchakephalids, lisariids, onchonotinids, and pagodiids), linguliformean brachiopods (acrotretids, obolids, scaphelasmatids, siphonotretids, and zhanatellids), echinoderms (mitrates, glyptocystitid cystoids, and stromatocystoids), and conodonts belonging to the lower Peltura Zone; and (iii) the subsequent input of new trilobites (asaphids, calymenids, catillicephalids, nileids and remopleurids), which marks the base of the Proteuloma geinitzi Zone, associated with pelmatozoan holdfasts (Oryctoconus), and a distinct input of late Tremadocian conodonts (Paltodus deltifer Zone). The biogeographic distribution of latest Middle and Late Cambrian trilobites supports brachiopod data indicating strong affinities between the western Mediterranean region, East Gondwana (North China/Korea, South China, Australia, and Antarctica) and Kazakhstania during the late Languedocian, which became significantly stronger during the Late Cambrian. This major shift may suggest modification in oceanic circulation patterns throughout Gondwana across the Middle–Late Cambrian transition. [Copyright &y& Elsevier]

Numerous plectronocerid nautiloids appear in the Upper Cambrian of China. We have restudied their siphuncular structure, first described some 20 years ago. The siphuncle is characterized by: (1) long and holochoanitic septal necks dorsally but short and recurved necks laterally and ventrally; (2) strongly expanded connecting rings laterally; (3) two calcified layers in each connecting ring, outer spherulitic-prismatic and inner compact, the latter perforated by numerous pore canals; and (4) highly oblique siphuncular segments. The strongly expanded lateral sides of the connecting rings, together with the highly oblique course of the siphuncular segments, considerably enlarged the surface area of the connecting rings in each chamber, thereby increasing the transport capacity of cameral liquid. Thus, from their first appearance, plectronocerid nautiloids had developed a siphuncle for the replacement of cameral liquid with gases, and this system had a better and a more sophisticated design than that seen in stratigraphically younger nautiloids. However, their small orthoconic or slightly cyrtoconic shells were not well adapted for jet-powered swimming. [ABSTRACT FROM AUTHOR]

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Abstract: A single sample from the La Matosa Member of the Barrios Formation, exposed during the excavation of the El Fabar Tunnel in Asturias, N Spain, yielded a rich and well-preserved Late Cambrian acritarch assemblage. The Middle? to Upper Cambrian La Matosa Member consists mainly of quartz sandstone and includes locally a thick fossiliferous intercalation of dark shale (“El Fabar beds”) from which the acritarch sample was collected. The latter shale levels yielded also some linguliform brachiopods, olenid trilobites and phyllocarid crustaceans. Characteristic genera of the study sample are Acanthodiacrodium, Lusatia and Cristallinium. Other significant components are Cymatiogalea, Timofeevia and Vulcanisphaera. Lusatia dendroidea Burmann 1970, recorded for the first time in Spain, is a characteristic element of this assemblage. In the study sample, the latter species is abundant, well-preserved and exhibits appreciable morphological variability. This acritarch assemblage is correlated with the lower part of microflora RA5 of Parsons and Anderson [Parsons, M.G., Anderson, M.M., 2000. Acritarch microfloral succession from the Late Cambrian and Ordovician (early Tremadoc) of Random Island, eastern Newfoundland, and its comparison to coeval microfloras, particularly those of the East European Platform. AASP Contr. Ser. 38, 129 pp.] corresponding to the Protopeltura praecursor trilobite Zone. [Copyright &y& Elsevier]

The histology of some euconodonts of Late Cambrian from Benxi and Fuxian County, Liaoning Province is studied by the oil-immersion technique. The histological characteristics of six primitive species of euconodonts - Proconodontus muelleri, Proconodontus tenuiserratus, Granatodontus ani, Rotundoconus tricarinatus, Teridontus nakamurai and Cordylodus proavus are described in detail. Tubular dentine and atubular (parallel- and wavy-lamellar) dentine are found in the basal bodies of the primitive euconodonts Proconodontus tenuiserratus and Proconodontus muelleri, respectively. The tubular dentine and spherulitic dentine are also recognized from the basal bodies of Granatodontus ani and Rotundoconus tricarinatus. Since the histological characteristics of the studied six species of euconodonts belonging to Proconodontus lineage and Teridontus lineage Sensu Miller (Univ Kansas Paleontol Contr, 1980, 99; 1-39) seems to be almost the same, euconodonts are proposed as possibly monophyletic herein. [ABSTRACT FROM AUTHOR]

This study deals with the heterochrony of two Late Cambrian olenid trilobites, Olenus asiaticus Kobayashi, 1944 from the Glyptagnostus reticulatus Zone and Hancrania brevilimbata Kobayashi, 1962 from the Hancrania brevilimbata Zone, recovered from the Machari Formation in Yeongwol, Korea. Comparison of ontogenetic developments of Olenus asiaticus and Hancrania brevilimbata led to consider that the two species are phylogenetically related: viz., Hanerania brevilimbata is a probable descendant of Olenus asiaticus. The ontogenetic trajectories of the two species are closely comparable in the protaspid and early meraspid stages, but deviate in the late meraspid and holaspid stages. The morphological changes with growth in the Olenus asiaticus-Hancrania brevilimbata lineage may have resulted from combined heterochronic processes: i.e., the reduction of preglabellar field in the descendant is attained by paedomorphic progenesis, whereas the expansion of glabella is a consequence of peramorphic acceleration. Of these, the progressive reduction of preglabellar field has been known to occur in other parts of the world and thus is assumed to be useful in improving the biostratigraphic correlation among widely separated paleogeographic provinces, such as Baltica and Avalonia. The Glyptagnostus reticulatus Zone of the Paleozoic Gondwana can be correlated with the Olenus gibbosus Subzone of Avalonia and Baltica, while the Hancrania brevilimbata Zone of Korea with the O. attenuatus and O. dentatus subzones of Baltica and the lower part of the O. cataractes Subzone of Avalonia. [ABSTRACT FROM AUTHOR]

The Middle to Upper Cambrian Machari Formation in Korea is well known for abundant and diverse trilobites along with other invertebrate fossils. Based on recent reappraisal on the trilobites of the Machari Formation, eight trilobite zones have been proposed for the Upper Cambrian sequence: i.e., in ascending order the Glyptagnostus stolidotus, Glyptagnostus reticulatus, Proceratopyge tenuis, Hancrania brevilimbata, Eugonocare longifrons, Eochuangia hana, Agnostotes orientalis and Pseudoyuepingia asaphoides zones. Trilobites from the lower five zones and part of the Pseudoyuepingia asaphoides Zone have been already published elsewhere. In this paper, we describe the agnostoid trilobites of the upper three zones, Eochuangia hana, Agnostotes orientalis and Pseudoyuepingia asaphoides zones, of the Machari Formation. These comprise 24 species belonging to 13 genera, including one new genus (Yongwolagnostus) and ten new species (Homagnostus? sulcatus, Ivshinagnostus alatus, Ivshinagnostus quadratus, Yongwolagnostus stenorhachis, Yongwolagnostus dubius, Nahannagnostus pratti, Pseudagnostus? dividuus, Pseudagnostus medius, Pseudorhaptagnostus? urceus and Ammagnostus serus). These biozones correlate well with middle Upper Cambrian zones established in South China, Australia, Kazakhstan, Siberia, and Canadian Rocky Mountains. [Copyright &y& Elsevier]

Ontogeny of the Late Cambrian trilobite Olenus asiaticus Kobayashi, 1944 was examined based on the material from the Glyptagnostus reticulatus Zone of the Machari Formation in Yongwol area, Korea. Protaspides are differentiated into anaprotaspid and metaprotaspid stages. Anaprotaspides are represented by circular dorsal shields with faintly segmented axis, while meta-protaspides have five axial rings, eye ridges, and a differentiated protopygidium. Most of meraspides, represented by disarticulated cranidia, are further divided into six morphological groups. The Group 1 is assumed to represent the meraspid degree 0, whereas the remaining groups are subdivided in convenience to describe the morphological development of cranidia. Morphological changes within the meraspid stages are gradual in general. The glabella is parallel-sided or tapers rearwards in the early meraspides, whereas it tapers forwards in the later forms. The preglabellar field appears in the Group 3 and becomes progressively longer in the later meraspid stages. The holaspid cranidia are distinct in having a subquadrate glabella with three pairs of lateral glabellar furrows. [ABSTRACT FROM AUTHOR]

The morphological architecture and distribution of modern and ancient carbonate systems has been shown to follow spatial-self-organization, however, limited studies describe the morphometrics of microbial carbonates. Upper Cambrian microbial-build-ups outcropping in Central Texas, are exposed laterally (plan view), enabling a study of their morphological architecture and spatial distribution. Drone imagery was acquired to capture the outcrop features and develop a digital terrain model (cm scale resolution) for a bedding plane outcrop (600 × 200 m in size). Four scales of microbial growth (S1- few dm, S2- few m, S3- few tens of m, and S4- few hundreds of m) were identified and mapped. A series of morphometric analysis including Ripley's k, univariate, multivariate, and grouping were conducted and results demonstrate that, the scales S1, S2, and S3 display clustering and the spatial organization of microbial-buildups is naturally organized and not random. Further, as the size of the build-ups increases (from S1–S4), the anisotropy (length/width) increases, their shape becomes oblong, and they become aligned (S2–S4) with the inferred regional winds and tide-associated currents (NE-SW according to the present geography). The S1 scale does not align itself with the regional currents; instead, the build-ups behaved as a baffle during growth, and modified the currents locally, leading to preferential alignment at the edges within S2. As the scales increases in sizes (S2, S3, S4), there is competition for space, and due to regional currents, the larger scales preferentially align parallel to high-energy currents. The trends and spatial relationships identified in this study are particularly relevant and provide a scenario for sub-seismic scale heterogeneities for subsurface microbial hydrocarbon reservoirs. • Exposures of carbonate build-ups along an isochronous surface are studied, which are relatively rare in the rock record. • Morphometric analysis of build-ups reveals multi-scale spatial relationships, utilizing high-reaolution drone imagery. • Larger scales (few m - 100's of m) architecture is controlled by external factors, whereas, smaller scale (few dm) by local. [ABSTRACT FROM AUTHOR]