Graptolite Biozones Research Articles

Stratigraphic framework of the Wufeng-Longmaxi shale in and around the Sichuan Basin, China: Implications for targeting shale gas

Stratigraphic division and correlation are crucial for the identification of sweet spots and drilling design of shale gas. In this study, a stratigraphic division and correlation was carried out for the Wufeng-Longmaxi Formations in southern China from the prospective of lithostratigraphy, sea level changes, and biostratigraphy using data from seismic investigation, wells, and outcrops. The Wufeng and Longmaxi Formations were respectively divided into four members, Wu 1 and Wu2 for the former and Long 1 and Long 2 for the latter. Of the members, Long 1 was subdivided and its first subdivision (Long 11) was further divided into 4 layers (Long 111, Long 112, Long 113, and Long 114). Three eustatic cycles were recognized in the Wufeng-Longmaxi Formations. Cycle I corresponds to the Wufeng Formation with the maximum flooding surface at the top of Wu 1. Cycle II corresponds to Long 1, with the maximum flooding surface at the top of Long 113. Cycle III corresponds to Long 2. Furthermore, 4 graptolite biozones (WF1 to WF4) were identified in the Wufeng Formation and 9 graptolite biozones (LM1 to LM9) in the Longmaxi Formation. WF1-2 and WF3-4 correspond to Wu 1 and Wu 2, respectively; and LM1, LM2-4, LM5, LM6, and LM7-9 correspond to Long 111, Long 112, Long 113, Long 114, and Long 12 and Long 2, respectively. High-quality shales mainly occur in the Wufeng Formation and Long 11. The major intervals that should be investigated with regards to shale gas production include LM1–LM5 (10 m thick) in the Weiyuan Block and WF1–LM5 (20–35 m thick) in the Changning Block. Long 111 is believed to be an optimal target for drilling due to its high TOC content, siliceous content, porosity, microfracture density, and horizontal/vertical permeability ratio.

Upper Silurian (Gorstian, Ludfordian, PŘÍDOLÍ) Graptolite Biozonation in the Muhurr area (Albania)

Three stratigraphical sections and several outcrops through the upper Silurian graptolite shales of the Muhurr area, Albania have been revised. Based on a new detailed re-examination and re-evaluation of graptolite collections and previously unpublished and published studies, a biozonal scheme with much new biostratigraphical data is established. The graptolite assemblages are dominated by Monograptidae: Neodiversograptus, Saetograptus, Bohemograptus, Colonograptus, Pseudomonoclimacis and Lobograptus which are associated with several Retiolitidae. A total of 37 graptolite species has been identified; selected important species are illustrated. The present study recognized and defined the following seven upper Silurian graptolite biozones: nilssoni and scanicus-chimaera in the Gorstian Stage, leintwardinensis, tenuis and formosus in the Ludfordian Stage and parultimus-ultimus and perneri in the Přídolí Series.

An integrated assessment system for shale gas resources associated with graptolites and its application

Shale gas exploration or development has been carried out in many countries, and gas shales have become one of the major sources of future natural gas production worldwide. However, many differences of gas shales in China with those in other regions make shale gas development in China exceptionally challenging. Fortunately, the Wufeng-Longmaxi gas shales in China contain abundant graptolites, providing a potential method for evaluating the quality of these gas shale reservoirs in South China. Numerous exploration studies have shown that the shale gas sweet-spot intervals in the Wufeng-Longmaxi Shale coincide with graptolite biozones WF2-LM5, providing new insight for evaluating shale gas sweet-spot intervals. This paper, for the first time, proposes a new integrated method using graptolite zones to identify shale gas sweet-spot intervals. Once the sweet-spot interval of shale gas is determined quickly by using this method in an explored block, it can provide an important reference for well design and hydraulically fracturing treatments within short time, significantly enhancing the efficiency of shale gas exploration. More importantly, this new integrated assessment system can be utilized to quickly judge the potential of shale gas development for new shale gas blocks or poorly explored blocks.

Revision of the Middle–Upper Ordovician acritarch genus Orthosphaeridium Eisenack 1968 nov. emend

The acritarch genus Orthosphaeridium Eisenack 1968 is one of the most frequently recorded acritarch taxa in the Ordovician. The taxonomy of this easily recognizable genus is revised herein based on a detailed literature review and on new investigations of palynological material from northeastern Iran and South China. The review confirms that Baltisphaera Burmann 1970 is a junior synonym of Orthosphaeridium of which the diagnosis is here emended. Over 20 species have been described in the literature, but many of them are apparently synonyms. The review indicates that the following four species can be easily differentiated: Orthosphaeridium bispinosum Turner 1984, Orthosphaeridium ternatum (Burmann 1970) Eisenack et al. 1976, Orthosphaeridium rectangulare (Eisenack 1963) Eisenack 1968 (type species) and Orthosphaeridium octospinosum Eisenack 1968. The taxonomical ranks of Orthosphaeridium rectangulare var. quadricornis Burmann 1970 and Orthosphaeridium octospinosum var. insculptum Loeblich 1970 are changed from the species to the varietas level. The review indicates that Orthosphaeridium first appeared in South China in the Expansograptus hirundo graptolite Biozone, i.e. in the early Dapingian (stage slice Dp1 and time slice 3a of the Middle Ordovician) and that it reached a global distribution during the Middle and Late Ordovician. The genus disappeared at the end of the Ordovician and has never been recorded from the Silurian. The genus is thus a stratigraphical index fossil for the Middle and Late Ordovician. Orthosphaeridium has been recorded from the margins of all paleocontinents and paleoecologically seems to be an eurythermic taxon.

A high-precision global biostratigraphy of myodocope ostracods for the Silurian upper Wenlock Series and Ludlow Series

The wide, trans-oceanic geographical distribution of myodocope ostracods during the Silurian (especially during the Ludlow and Pridoli epochs), and their widespread preservation in rocks of that age, permits the establishment of a transcontinental biostratigraphy of comparable resolution to coeval graptolite/chitinozoan/conodont biozones. Seven myodocope biozones, extending from the Homerian Stage, upper Wenlock Series Cyrtograptus lundgreni graptolite biozone to the middle part of the Ludfordian Stage of the Ludlow Series, enable a time-resolution for each biozone of circa 1 million years. These biozones can provide high-resolution correlation across Europe into Arctic Russia and Central Asia. There is also the potential for a myodocope biostratigraphy applicable from the uppermost Silurian (Pridoli) to the Carboniferous.

Age constraints of the Hungshihyen Formation (Early to Middle Ordovician) on the western margin of the Yangtze Platform, South China: New insights from chitinozoans

The Hungshihyen Formation represents the Lower to Middle Ordovician near-shore siliciclastic deposits on the western margin of the Yangtze Platform, South China. However, its age is still debated, largely because of insufficient studies. Here we documented the Bursachitina maotaiensis–B. qianbeiensis chitinozoan assemblage from the lower part of the Hungshihyen Formation at Songliang, Qiaojia County, eastern Yunnan Province. This assemblage is remarkably similar to an assemblage that roughly correlates to the middle part of the Corymobograptus deflexus graptolite Biozone in northern Guizhou Province, indicating that the Hungshihyen Formation at Songliang is probably of late Floian age and may extend into the early Dapingian. Additionally, a revision on the chitinozoans previously documented from the strata assigned to the same formation in the Wuding area was made according to the latest classification. The revision allows the recognition of the Euconochitina symmetrica–Eremochitina brevis assemblage, and therefore suggests a late Tremadocian age for this interval based on regional and global chitinozoan biostratigraphic correlations. Considering also its lithologic succession, we argue that the chitinozoan-bearing strata in the Wuding area previously assigned to the Hungshihyen Formation correspond most likely to the uppermost part of the underlying Tangchi Formation or the lowermost part of the Hungshihyen Formation. The base of the Hungshihyen Formation appears therefore to be diachronous in eastern Yunnan Province.

Graptolite turnover and δ13Corg excursion in the upper Wenlock shales (Silurian) of the Holy Cross Mountains (Poland)

Abstract The mid–late Homerian Age of the Silurian Period was a time of intense changes in biota, oceanic chemistry, and sea level and is known as the lundgreni extinction (for the graptolite extinctions), the Mulde bioevent (for the conodont turnover event) or the Homerian carbon isotope excursion (CIE) probably related to glacially influenced climate perturbation. New information on this interval from the deep water sedimentary and graptolite succession of the Kielce Region (Holy Cross Mountains, Poland) of the northern margin of the Małopolska Block is presented here based on analysis of the Prągowiec Ravine section. The lundgreni–nilssoni graptolite biozones interval have been recognized there. This interval is composed by dark shales with very rare benthic fauna, which indicate the deep open-marine (pelagic) paleoenvironment. Ten samples were taken for the δ13Corg analysis from the lundgreni (2 samples), parvus (2 samples), praedeubeli (2 samples), praedeubeli–deubeli (1 sample), ludensis (2 samples) and nilssoni (1 sample) biozones. According to the δ13Corg results, the first positive δ13Corg excursion of the Mulde Bioevent is well recognized. The δ13Corg values rise from −30.7 – −30.1 ‰ in the lundgreni Biozone to −29.3 – −28.7 ‰ in the parvus Biozone and fall below −30 ‰ in the praedeubeli–deubeli interval. The second positive δ13Corg peak of the Mulde Event was not recognized in the Prągowiec Ravine. Based on the numerical comparisons using Raup-Crick metric of co-occurrences of graptolite species, the upper Homerian was characterized by significant between-biozone turnover of these taxa at the given locality.

Duration, evolution, and implications of volcanic activity across the Ordovician–Silurian transition in the Lower Yangtze region, South China

Volcanism provides a reliable record of local and global tectonic events and substantially influences both modern and ancient environments, climates, and the evolution of life. The Ordovician–Silurian (O–S) transition is a special period because intensive volcanism occurred globally, including in the Yangtze region of South China. Volcanic events during this period are a symptom of plate tectonic behaviour and are thought to be responsible for the remarkable changes in climate in the early Palaeozoic, though the relationships between these events remain unclear and controversial. Coeval igneous rocks and volcanic sediments (VS) are primarily used to resolve this issue. However, limited studies have been performed on VS from the O–S transition in South China. Recently, a typical VS-bearing section was found in the Lower Yangtze region, which contains ∼100 thin, interbedded volcanic ash layers across the O–S transition. Detailed petrographic and geochemical analyses of the volcanic ashes were conducted to determine their isotopic ages, magma sources, evolutionary processes, and tectonic settings. Our preliminary results suggest that volcanic eruptions in South China lasted for more than 22 Ma across the O–S boundary, from ∼449.3 ± 3.6 to 427.6 ± 4.1 Ma, where 445.14 Ma is the lowermost graptolite biozone for Metabolograptus extraordinarius, as well as the initiation of the Late Ordovician mass extinction (LOME) event in the Yangtze region. The evolutionary history of the parental magma was constructed from a depleted mantle source in the early stage and from a crustal source in the late stage, with several transitional features in the middle. The mantle source and arc-related geochemical indicators for the volcanic ashes support the disputed “subduction-collision orogeny” model. We propose that the strong volcanism in South China, accompanied by volcanism in numerous other regions worldwide, was an important trigger for the LOME and was likely responsible for oceanic 87Sr/ 86Sr fractionation and other climatic changes during the O–S transition.

Darriwilian (Middle Ordovician) chitinozoans from the Qaidam Paleoplate, northwest China

The Qaidam Paleoplate is a microcontinent that is currently part of central Asia. Its position during the Ordovician is uncertain, with paleogeographic reconstructions placing it either near South China or near North China. Ordovician microfossils such as chitinozoans have not previously been reported from the Qaidam Paleoplate. In this paper, a chitinozoan microfauna from the middle part of the Shihuigou Formation in the Dameigou section, South Qilian Mountains, Qinghai Province, northwest China is documented. The assemblage is dated as Darriwilian (Undulograptus austrodentatus and Archiclimacograptus confertus graptolite biozones) on the basis of associated graptolites. The chitinozoan fauna is well-preserved and includes several biostratigraphically and paleogeographically important chitinozoan species, such as Lagenochitina langei, L. pirum, Rhabdochitina magna, R. usitata, Conochitina turgida, C. subcylindrica, C. decipiens, Clavachitina poumoti, Belonechitina nevillensis, B. cf. uniformipunctata and B. chydaea. The assemblage contains a specimen in which the collarette of a specimen of Desmochitina sp. is attached to the aboral pole of a specimen of Lagenochitina sp., possibly indicating that a single organism could produce more than one chitinozoan morphospecies. The Conochitina turgida–C. subcylindrica Biozone is indicated by the recovered chitinozoan assemblage. Biostratigraphically important species from the Qaidam microfauna suggest faunal affinities with Laurentia (North America), eastern Gondwana (Australia) and the peri-Gondwana area (southeast China). The chitinozoan paleogeographic data indicate that the Qaidam region was at low latitude during the Middle Ordovician, and that the area was near South China. The paleogeographic information deduced from chitinozoans is consistent with that obtained from graptolites and paleomagnetic analysis in previous studies.

Integrated Lower–Middle Ordovician graptolite and chitinozoan biostratigraphy of the Jiangnan Slope Region, South China

An integrated Early–Middle Ordovician graptolite and chitinozoan biostratigraphical study was carried out to improve the correlations between the two fossil groups in two sections in the Jiangnan Slope Region (deeper outer-shelf mud–sand–carbonate belt), South China. Six graptolite biozones and two chitinozoan biozones (including an undefined interval) were recognized. The chitinozoan Lagenochitina praepirum appears to be a stratigraphically useful species, despite being geographically restricted to South China, appearing at a level coincident with the first appearance of the index graptolite Levisograptus austrodentatus. Thus, the base of the Lagenochitina praepirum Biozone can also be regarded as the base of the Darriwilian Stage. The chitinozoan abundance in both sections is exceptionally low, and the assemblages do not contain the biostratigraphically important Belonechitina species. The distributions of both chitinozoans and graptolites are eco-dependent but show different onshore–offshore diversity trends. Chitinozoans are more diverse nearer to shore whereas graptolites are more diverse offshore, preferring slope facies. This may be caused by the different ecological preferences of chitinozoans and graptolites.

Lower and Middle Ordovician chitinozoans from Honghuayuan, South China: Biodiversity patterns and response to environmental changes

A complete chitinozoan succession through the uppermost Tremadocian to lower Darriwilian (Lower and Middle Ordovician) at Honghuayuan, northern Guizhou Province in South China, was systematically studied and 47 species of 14 genera were identified. Two chitinozoan biodiversity acmes were recognized, which occur in the lower part of the Acrograptus filiformis (uppermost Hunghuayuan Formation) and middle part of the Azygograptus suecicus (middle member of the Meitan Formation) graptolite biozones. In the upper Dapingian and lower Darriwilian (uppermost part of the Meitan Formation), chitinozoan diversity was relatively high after a less conspicuous peak in the upper Dapingian. Comparisons between diversity trends of chitinozoans, acritarchs and brachiopods, and the environmental changes revealed both similarities and differences. In the Floian, the chitinozoan biodiversity curve at Honghuayuan shows good correlation with sea-level changes. The group temporarily disappeared when the sea level was at the highest, then reappeared and reached a biodiversity acme when sea level was low. Furthermore, a large organic carbon isotope excursion is coincident with the absence of chitinozoans and a highstand period after the sea-level rise in the lower and middle Floian. Diversity curves show fewer connections with the sea-level and organic C-isotope undulations during the Dapingian and early Darriwilian. New data suggest that the environmental changes played a significant role in the early stage of Ordovician chitinozoan radiation, roughly corresponding to the Floian at the Honghuayuan section. In the Dapingian and early Darriwilian, the intrinsic factors seem to have played a more important role in shaping biodiversity patterns of chitinozoans in South China.

Source analysis of quartz from the Upper Ordovician and Lower Silurian black shale and its effects on shale gas reservoir in the southern Sichuan Basin and its periphery, China

A major breakthrough in shale gas exploration and development has been made concerning the black shale of the Upper Ordovician and Lower Silurian. In recent years, significant progresses have been made regarding the exploration and development of shale gas in the black shale of the Upper Ordovician and Lower Silurian. Accordingly, we investigated the petrological and geochemical characteristics of the black shale from WF2‐LM5 graptolite biozones and performed a source analysis of quartz as well as evaluated its effect on shale gas reservoirs. The black shale mainly contains clay, carbonate, and quartz with the average TOC of 2.21%. Three quartz types, Q1, Q2, and Q3, were identified via petrological and cathodoluminescence (CL) analysis. Q1 of detrital origin as suggested by its typical morphology with monocrystal structure, large grain‐size, subrounded to angular outlines, and clear edges. This is further supported by the occurrence of medium luminescence under cathodoluminescence and medium intensity of P1 and P2 and high intensity P3 according to CL images. Q2 accounts for more than 90% of quartz and exhibits cryptocrystalline texture, an irregular shape, blurring edges, and low luminescence, and its CL images show low intensity P1, low intensity P2, and high intensity P3. Q3 have the morphologies of siliceous organisms, for example, sponge spicules, radiolaria, and foraminifera. Q2 and Q3 belong to authigenic quartz derived from siliceous organisms. Th/U and V/Cr indicate black shale from LM1–3 mainly deposited in the dysoxic‐anoxic environment while black shale from LM4–5 deposited in the oxic environment. Authigenic quartz‐rich shales from LM1–3 were speculated to be the best shale gas reservoirs characterized by high TOC content, high gas content, and with negligible amount of detrital quartz. Compared with shale from LM1–3, black shale from LM4–5 usually have relatively high detrital quartz content and low TOC content and gas content. Considering the abundant interparticle pore space, the detrital quartz‐rich shale interbedded within the black shale from LM4–5, could also become good shale gas reservoirs if sufficient gas supply is guaranteed.

A record of Late Ordovician to Silurian oceanographic events on the margin of Baltica based on new carbon isotope data, elemental geochemistry, and biostratigraphy from two boreholes in central Poland

New stable isotope data from organic carbon (δ13Corg) and inorganic elemental geochemistry data have been generated from Upper Ordovician to Silurian strata in two boreholes in the Lublin Basin of Poland: Grabowiec-6 and Zwierzyniec-1. They have been integrated here with biostratigraphical data from graptolites, acritarchs, and chitinozoans. Faunal assemblages from Grabowiec-6 indicate that it spans from the Katian (clingani graptolite Biozone) to the Gorstian (scanicus graptolite Biozone); δ13Corg values from this section record the Sheinwoodian Ireviken Excursion, the Homerian Mulde Excursion, and a minor positive shift associated with the lower Ludfordian leintwardinensis Biozone. The second section, Zwierzyniec-1, spans the Sandbian through Gorstian (nilssoni Biozone); δ13Corg values record the Hirnantian carbon isotope excursion (HICE) and the Ireviken Excursion as well.Elemental geochemistry data is used to recognize subtle changes in provenance and lithology. Significant increases in the abundance of V and Mo are recognized in strata deposited above the Ireviken Excursion. The enrichment of these redox sensitive elements suggests that persistent regional anoxia and euxinia may be associated with the aftermath of these oceanographic disturbances. Some of these same trace elements, along with Fe2O3, and Pb are also abundant in strata coeval with, or just below the Ireviken and HICE excursions. This may have a causal link with malformed palynomorphs observed at these intervals by some workers, which are thought to reflect toxic levels of dissolved heavy metals in the world's oceans.

A proposed new global stratotype for Aeronian Stage of the Silurian System: Hlásná Třebaň section, Czech Republic

The current Global Stratotype Section and Point (GSSP) for the Aeronian Stage (Llandovery Series, Silurian System), on Trefawr track in the Llandovery area of Wales, is an inadequate marker for precise, global, correlation. The International Subcommission on Silurian Stratigraphy has, therefore, undertaken the selection of a new GSSP for this level. The lowest occurrence of the graptolite Demirastrites triangulatus, 1.38 m above the base of the black-shale succession of the Želkovice Formation at the Hlasna Třebaň section in Central Bohemia, is proposed to mark the base of the Aeronian Stage. The section, which fulfils all formal requirements for stratotype of a chronostratigraphical unit, should be considered as a candidate for the new GSSP. An abundant, well-preserved, diverse graptolite fauna occurs through the section along with common chitinozoans, which indicate that the Spinachitina maennili Biozone spans the boundary interval. The section comprises the lower–middle Aeronian (D. triangulatus–Lituigraptus convolutus graptolite biozones) along with underlying Rhuddanian (Akidograptus ascensus–Coronograptus cyphus biozones) and Hirnantian strata. Several graptolite genera of primary importance in global correlation (Demirastrites, Petalolithus, Rastrites and Campograptus) first appear in the lower part of the triangulatus Biozone. The structurally simple section is somewhat condensed, but there is a uniform succession of black shale without any evidence of disconformity in the broad boundary interval. The Corg isotope record exhibits a minor positive excursion just above the base of the triangulatus Biozone, whereas TOC and N isotope and elemental geochemical records provide evidence for uninterrupted sedimentation under stable, anoxic conditions.

The Homerian carbon isotope excursion (Silurian) within graptolitic successions on the Midland Platform (Avalonia), UK: implications for regional and global comparisons and correlations

New δ13Ccarb data from the most stratigraphically extensive graptolitic sections of Homerian age in the study area are reported from Wenlock Edge and the Ludlow Anticline (UK). These sections, situated upon the Midland Platform (Avalonia), were key in establishing the Homerian graptolite biozonation used within the type Wenlock Series, and are consequently of international importance. Based upon 162 δ13Ccarb samples from four outcrops (Eaton Track, Longville–Stanway Road Cutting, Burrington Section and Mortimer Forest Stop 1), new graptolite collections and a re-evaluation of the original graptolite collections, the onset of both lower (older) and upper (younger) peaks of the Homerian Carbon Isotope Excursion have been calibrated to a revised graptolite biozonation (lundgreni – nassa – praedeubeli-deubeli – ludensis biozones). In addition, high-resolution correlation between the Ludlow Anticline and Wenlock Edge has been achieved by bio-, chemo- and sequence stratigraphic techniques. These correlations suggest a uniformity of depositional rates across the study area and indicate minor diachroneity at the base of the Much Wenlock Limestone Formation. Finally, correlations of the Midland Platform Homerian Carbon Isotope Excursion have allowed for better comparisons with other sections from which high-resolution graptolite and carbon isotope data are available. Such comparisons highlight the pan-regional synchronicity of the Homerian Carbon Isotope Excursion.

Hirnantian (Ordovician) through Wenlock (Silurian) conodont biostratigraphy, bioevents, and integration with graptolite biozones, Cape Phillips Formation slope facies, Cornwallis Island, Canadian Arctic Islands

Cornwallis Island in the Canadian Arctic Archipelago provides one of the world’s best areas for establishing an integrated graptolite–conodont biozonation for the Late Ordovician – Silurian given the well-exposed interfingering relationship of the basinal shale and carbonate platform facies. Building on earlier graptolite work, 180 samples were collected from nine sections of the Cape Phillips Formation, of which 118 yielded approximately 7600 conodont elements representing 54 species in 25 genera, including one new genus and species, Mayrodus melchini; the conodonts are well preserved, with minimal thermal alteration (colour alteration index, CAI 1). Nine conodont zones are recognized and defined for this region, namely the Amorphognathus ordovicicus, Distomodus kentuckyensis, Aspelundia expansa, As. fluegeli, and Pterospathodus celloni Interval zones, Pt. a. amorphognathoides Taxon-range Zone, Pt. pennatus procerus and Kockelella ranuliformis Highest-occurrence zones, and K. ortus absidata Taxon-range Zone. An integration of graptolite and conodont zones is documented. Earlier paleontological and isotope geochemical studies have demonstrated the dynamic nature of the Silurian ocean–climate system and identified major faunal turnovers or events. Five of these are recognized in the Cornwallis fauna and related to oceanographic and climate changes, in part referring to recent oxygen isotope data from conodonts from the Cornwallis collections: Hirnantian extinction event, Sandvika Event (late Aeronian, Llandovery), Snipklint Primo Episode (early Telychian, Llandovery), Ireviken Event (late Telychian, Llandovery–Sheinwoodian, Wenlock), and Mulde Event (early Homerian, Wenlock).

Upper Homerian (Silurian) high-resolution correlation using cyclostratigraphy: an example from western Lithuania

AbstractThe Gėluva regional stage stratigraphically corresponds to the late Wenlock. This time interval witnessed significant graptolite extinctions and turnovers of conodont faunas, as well as a large positive Mulde carbon isotopic excursion. Thus, the development of a detailed stratigraphy is a necessary step in understanding the complex patterns of regional and global variations in the sediments accumulating during the time interval studied. Therefore, in this contribution we present a cyclostratigraphic analysis of gamma ray (GR) logs from four wells, which are located in the deep water facies belt of the Lithuanian part of the Silurian Baltic Basin of the Gėluva regional stage. The analysis was performed using REDFIT spectral estimation, continuous wavelet transform and signal filtering techniques. As a result two 4thorder and five 5thorder cycles were distinguished and named in all sections. The correlation of cycles between sections was calibrated with the graptolite biozones. The comparative analysis revealed that intra-basinal cyclostratigraphic correlation could achieve resolution of the order of several tens of thousands of years.

Recurrence and Cross Recurrence Plots Reveal the Onset of the Mulde Event (Silurian) in the Abundance Data for Baltic Conodonts

AbstractOne of the severest perturbations of the Silurian marine environment is the mid-Homerian Mulde bioevent. This event proceeded in several temporal steps, which, according to some authors, implies possible globally synchronous perturbation. The dynamic pace and consequences of these perturbations, as well as their effects on conodont community dynamics, are largely unknown. Here I used so-called recurrence and cross recurrence plots to test the hypothesis of common forcing of the Mulde event on conodont abundance dynamics at the regional scale. The results of the analysis of two Lithuanian sections from the Baltic basin revealed that in the uppermost part of the lundgreni graptolite biozone there was sharp transition in the recurrence patterns. Pre-Mulde Homerian time was characterized by high-amplitude fluctuations and a low recurrence rate. On the other hand, the Mulde interval state was characterized by low abundance and a high recurrence rate with longer horizontal, vertical, and diagonal lines ...

Temporal and spatial distribution of Ordovician–Silurian boundary black graptolitic shales on the Lower Yangtze Platform

During the end-Ordovician–early Silurian interval, two sequences of dark shales and cherts, the Wufeng and Kaochiapien formations, were deposited in Jiangsu and Anhui provinces on the Lower Yangtze Platform. Both sequences have great potential as petroleum source beds. Using previous biostratigraphic schemes for the area, combined with new material from outcrops and a borehole in the Nanjing Hills, this study recognized 11 graptolite biozones over four stages from the Dicellograptus complexus Biozone (Katian, Upper Ordovician) to the Coronograptus gregarius Biozone (early Aeronian, Silurian). Our comprehensive study of both the graptolite biostratigraphy and hydrocarbon source-bed features of a borehole in the Nanjing Hills showed that the Rhuddanian Parakidograptus acuminatus and Cystograptus vesiculosus biozones are the favorable intervals for shale gas occurrence.

Conodonts and tabulate corals from the Upper Ordovician Angullong Formation of central New South Wales, Australia

Zhen, Y.Y., Wang, G.X. & Percival, I.G., August 2016. Conodonts and tabulate corals from the Upper Ordovician Angullong Formation of central New South Wales, Australia. Alcheringa 41, xxx–xxx. ISSN 0311-5518.The Angullong Formation is the youngest Ordovician unit exposed in the Cliefden Caves area of central New South Wales. Its maximum age is constrained by a Styracograptus uncinatus graptolite Biozone fauna at the very top of the underlying Malongulli Formation, but the few fossils previously reported from higher in the Angullong Formation are either long-ranging or poorly known. From allochthonous limestone clasts in the middle part of the formation, we document a conodont fauna comprising Aphelognathus grandis, A. solidum, Aphelognathus sp., Aphelognathus? sp., Belodina confluens, Drepanoistodus suberectus, Panderodus gracilis, Panderodus sp., Phragmodus undatus, Pseudobelodina inclinata and Pseudobelodina? sp. aff. P. obtusa, which supports correlation with the Aphelognathus grandis Biozone (late Katian) of the North American Midcontinent succession. The species concepts of Aphelognathus and Pseudobelodina are reviewed in detail. Associated corals are exclusively tabulates, dominated by agetolitids, including Agetolites angullongensis sp. nov., Heliolites orientalis, Hemiagetolites breviseptatus, Hemiagetolites sp. cf. H. spinimarginatus, Navoites sp. cf. N. circumflexa, Plasmoporella bacilliforma, P. marginata, Quepora sp. cf. Q. calamus and Sarcinula sp. Affinities of the coral fauna from the Angullong Formation are closer to faunas from northern NSW and northern Queensland than to the locally recognized Fauna III of late Eastonian age in central NSW. We propose a subdivision of Fauna III to account for this difference, with the late Katian Fauna IIIB characterized by the incoming of agetolitid corals. The currently known distribution of representatives of this group with adequate age constraints suggests that agetolitids possibly originated in North China, subsequently migrating to Tarim, South China and adjacent peri-Gondwanan terranes while also spreading eastward to northern Gondwana, where they progressively moved through eastern Australia to reach the central NSW region by the early Bolindian.Yong Yi Zhen* (yong-yi.zhen@industry.nsw.gov.au) and Ian G. Percival (ian.percival@industry.nsw.gov.au), Geological Survey of New South Wales, W.B. Clarke Geoscience Centre, 947–953 Londonderry Road, Londonderry, NSW 2753, Australia; Guangxu Wang (gxwang@nigpas.ac.cn), State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, 39 East Beijing Road Nanjing 210008 PR China.