Chronostratigraphic Subdivision Research Articles

Lower Devonian conodonts from the Xainza area, central Tibet and the Lower Devonian stage boundaries in China

We report conodont assemblages from the Dardong Formation of the Xainza area, Lhasa Block, yielding several chronostratigraphically significant conodont elements discovered from the Lhasa Block for the first time, including Gondwania profunda, Polygnathus pannonicus, P. kitabicus, P. cf. sokolovi and P. excavatus excavatus. Two conodont zones are identified, namely, the middle Pragian profunda Zone and the lower Emsian excavatus Zone. The Pragian–Emsian boundary is presumably located within the interval between bioclastic limestone beds 4 and 6 with an interbed of siltstones. Although the sparse conodont occurrences in this study precludes more precise chronostratigraphic subdivision, the Xainza area of the Lhasa Block is potentially important for recognition of Lower Devonian stage boundaries in China and deserves further conodont investigations.

Upper Precambrian General Stratigraphic Scale of Russia: Main problems and proposals for improvement

Research subject. Main problems of the General Stratigraphic Scale (GSS) of the Upper Precambrian including uncertainties in the hierarchy of subdivisions are analyzed.Results.Prospects for detailing the Upper Precambrian GSS are discussed, along with questions of its correlation with International Chronostratigraphic Chart (ICSC) and establishing the lower boundaries of chronostratigraphic subdivisions. The importance of unifying the existing views is emphasized.Conclusions.It is proposed to carry out the following reforms of GSS: to abolish Acrothemes / Acrons; to approve the Proterozoic (as well as the Archean) as an Eonotheme / Eon; to minimize the use of terms “Upper Proterozoic” and “Lower Proterozoic”; to assign the Riphean and Vendian to the rank of Erathem / Era (while preserving the status of the Vendian as a System / Period); to consider Burzyanian, Yurmatinian, Karatavian and Arshinian as Systems / Periods of the Riphean. Attention is focused on the Upper Riphean-Vendian interval. The lower boundary of the Upper Riphean (Karatavian) was proposed to establish according to the first appearance of theTrachyhystrichosphaera sp.microfossils. Then, the Terminal Riphean (Arshinian) lower boundary should be traced to the base of the tillites formed during the global Sturtian glaciation (which approximately corresponds to the base of the Cryogenian in ICSC). Apparently, the Vendian lower boundary may be raised to the level of the top of the Gaskiers tillites, as the deposits of the last major glaciation in the Precambrian. The indicated proposals are substantiated. It is necessary to form work groups to develop solutions.

A template for an improved rock-based subdivision of the pre-Cryogenian timescale

The geological timescale before 720 Ma uses rounded absolute ages rather than specific events recorded in rocks to subdivide time. This has led increasingly to mismatches between subdivisions and the features for which they were named. Here we review the formal processes that led to the current timescale, outline rock-based concepts that could be used to subdivide pre-Cryogenian time and propose revisions. An appraisal of the Precambrian rock record confirms that purely chronostratigraphic subdivision would require only modest deviation from current chronometric boundaries, removal of which could be expedited by establishing event-based concepts and provisional, approximate ages for eon-, era- and period-level subdivisions. Our review leads to the following conclusions: (1) the current informal four-fold Archean subdivision should be simplified to a tripartite scheme, pending more detailed analysis, and (2) an improved rock-based Proterozoic Eon might comprise a Paleoproterozoic Era with three periods ( early Paleoproterozoic or Skourian , Rhyacian, Orosirian), Mesoproterozoic Era with four periods (Statherian, Calymmian, Ectasian, Stenian) and a Neoproterozoic Era with four periods (pre-Tonian or Kleisian , Tonian, Cryogenian and Ediacaran). These proposals stem from a wide community and could be used to guide future development of the pre-Cryogenian timescale by international bodies.

Proposed chronostratigraphic units for the Carboniferous and early Permian of the southwestern Gondwana margin

Abstract The western Andean belt of Argentina displays a comprehensive record of the Carboniferous and earliest Permian rocks so extensive that it allows an exceptional reconstruction of the Late Paleozoic Ice Age of the southwestern margin of the South American Gondwana area. Severe endemism of the Gondwana biota during this period makes it difficult to achieve a precise correlation of these glacially influenced deposits with the coeval sequences of the palaeoequatorial belt, where the subdivisions of the International Chronostratigraphic Chart (ICC) are currently defined. The abundant palaeontological record available from the Upper Paleozoic deposits of central-western Argentina, central Patagonia and eastern Argentina makes it possible to recognize five successive faunal stages that allow a proper ordering of the sequences of this period. The proposed regional stages, and their assumed chronological position regarding the standards of the current ICC, are: the Malimanian (late Tournaisian), Barrealian (Mid-Carboniferous or Serpukhovian–Bashkirian), Aguanegrian (Upper Pennsylvanian), Uspallatian (Asselian–Tastubian?) and Bonetian (Sakmarian). This paper aims to reiterate former recommendations about the convenience of having regional reference units and suggests the consideration of the available faunal stages as possible chronostratigraphic subdivisions for the Carboniferous–early Permian of the southeastern margin of Gondwana.

Early Pleistocene Tiglian sites in the Netherlands: A revised view on the significance for quaternary stratigraphy

The Tiglian-A, B and C form the main subdivision of the Early Pleistocene Tiglian Stage in Northwest European chronostratigraphy since the 1960’s. We re-evaluated the sedimentary context and new and legacy pollen assemblages of the classic type localities of these Tiglian pollen zones in the Dutch-German border area and Roer-Valley-Graben. Following recalculation of new upland pollen sums, we found that the three-fold subdivision of the Tiglian Stage is too simplistic and lacks a sound stratigraphic basis. The Tiglian-A is only found locally and cannot be positively identified in the RVG. The Tiglian-B in the Tegelen-Maalbeek area is not unique since similar occurrences are present at other depths in the RVG. Sedimentary and pollen analysis suggests Tiglian-C as defined in the Tegelen-Maalbeek type area could have been deposited in a very short amount of time, although this does contradict mammal data. The T-B/C cycle preserved in the type area likely represent a single example of multiple similar Early Pleistocene climate cycles. The sediments of the so-called cool or cold phase of pollen zone T-C 4c in the stratotype of the Tiglian C substage are interpreted as having formed during the onset of crevassing and therefore its significance as a regional climate indicator is discussed. We conclude that the extrapolation of the Tiglian pollen zones into chronostratigraphical substages is questioned and it is concluded that the chronostratigraphical subdivision of the Early Pleistocene, based on palynological characteristics and palaeobotanical analyses, requires reconsideration based on independent dating and land-sea record integration.

Integrating the palynostratigraphy, petrography, X-ray diffraction and scanning electron microscopy data for evaluating hydrocarbon reservoir potential of Jurassic rocks in the Kala Chitta Range, Northwest Pakistan

In this paper, we present the palynostratigraphy, petrography, scanning electron microscopy (SEM) and X-ray diffraction (XRD) investigations to evaluate hydrocarbon reservoir potential of the Jurassic clastic-carbonate mixed sequence of the Kala Chitta Range, northwest Pakistan. The chronostratigraphic sub-divisions of the diverse lithologies within the sequence were made by using palynostratigraphy. The clastic dominated sequence of Datta Formation was assigned Toarcian-Bajocian age, while the Shinawari Formation was deposited during the Bajocian-middle Bathonian. The carbonate shoal facies of the Samana Suk Formation showed late Bathonian-Tithonian time of deposition. The primary and secondary porosities augmented by the plug porosity and permeability data suggest that the sandstone of Datta Formation is an excellent reservoir. The dominance of diverse matrix within the Shinawari Formation occluded the primary porosity. However, based on dissolution and dolomitization, the Shinawari Formation is categorized as a moderate reservoir. The dominance of various types of matrix and cement with superimposed burial diagenesis has occluded the primary porosity within the Samana Suk Formation. However, the diagenetic dissolution and dolomitization during the telogenetic stage were supported by the SEM and bulk geochemical data. Such diagenetic overprinting has significantly enhanced the reservoir potential of the unit.

Regional chronostratigraphic framework of sediments build-up in the Benin Basin: a guide for hydrocarbon prospecting

An attempt to understand the structural and sedimentation framework in the Benin Basin is made herein. Unlike in its contiguous basins in the Gulf of Guinea Province, no significant oil and gas discovery has been reported in the basin. The aim here is to provide a chronostratigraphic framework of sediments build-up as a guide to hydrocarbon prospectivity in the basin. Existing biostratigraphic and sedimentologic data as well as few proprietary reports were integrated to establish a chronostratigraphic correlation in six directions within the Nigerian portion of the Benin Basin. Isopach maps of the chronostratigraphic subdivision of the sequences in the basin were also made. Sedimentation in restricted grabens started in the western part of the basin. Only Ise-2 well penetrated the oldest Cretaceous (Neocomian to Albian) sediments in the area of study with a thickness reaching up to 869 m. During the Miocene the focus of sedimentation predominantly shifted towards the offshore in the basin. Significantly a missing Eocene/Oligocene section was observed both on the seismic section and the stratigraphic record of the basin. Only Epiya-1 shows gas occurrence in the Miocene. Based on this work and locations of hydrocarbons recovery in the other part of the basin, exploration effort should target the Cretaceous sediments in the Nigerian portion of the basin.

An Integrated Stratigraphic and Paleoenvironmental Studies from Narmada-Tapti Block, South Cambay Basin, Western India

An inclusive illustrated report on microfauna and palynoflora from sub-surface Tertiary sediments in Narmada-Tapti block in the south Cambay basin is presented. Facies dependency exhibited by microfauna (foraminifera, ostracoda) necessitated a linking study to utilise potential of palynoflora in the studied well section not favourable for microfauna for paleoenvironmental analysis. The microfaunal distribution has enabled to distinguish a broad chronostratigraphic sub-division that can be tied to seismic and other markers focussed in this part of the basin. A brief account a probable exploration targets in this part of the basin is presented.

A multi-proxy study on polygenetic middle-to late pleistocene paleosols in the Hévízgyörk loess-paleosol sequence (Hungary)

A multi-proxy analysis, including grain size, magnetic susceptibility and the examination of stable isotopes of hypocoatings, was performed on the loess-paleosol succession at Hévízgyörk (Hungary). Field investigations suggested a continuous record of sedimentation and pedogenesis. However, after the identification of the Bag Tephra, it revealed that paleosols and loess units are missing from the section, despite no obvious signs of erosion. Fluctuations in the measured proxies indicate a polygenetic development of the upper paleosol.Paleogeomorphological processes are supposed to be responsible for the polygenesis of the paleosols, alongside of the differences in the paleoenvironment and the local geomorphological position. Erosional processes could be more intensive during the beginning of interglacials along the slope, when vegetation was sparse but precipitation increased. On the other hand, it is presumed that sedimentation decreased locally, during glacial periods, because the strong winds carried away the deposited dust. These paleoenvironmental features may well have led to the partial erosion of paleosol horizons and the lack of or entire alteration of thin loess formed during the glacials, therefore the successive paleosol formed on the previous one. The case study shows that although the polygenetic development of paleosols disrupts the clear chronostratigraphical subdivision of the section, it can nonetheless provide valuable information about the sequence evolution.

Global chronostratigraphical correlation table for the last 2.7 million years, version 2019 QI-500

A substantially updated version of the correlation table showing chronostratigraphical subdivisions of late Cenozoic geological time, spanning the last 2.7 million years is presented. It provides scientists, students, professionals and the general public with a ready reference to stratigraphical terms and schemes in use in different areas for similar periods. The updates comprised the status of Quaternary chronostratigraphic subdivision, the combined age-modelled geomagnetic and isotope records from ocean drilling records, and revised regional correlation schemes, notably for eastern Europe. The paper describes the chart in its 2019 QI-500 form and contains sections on its types of usage and formal subdivision status, besides reference and description of the contents of the various columns. The paper also describes and discusses the resolution of correlations in younger and older parts of the last 2.7 Ma.

Biostratigraphy of the Hareelv Formation (Upper Jurassic) in the Blokelv-1 core, Jameson Land, central East Greenland

The Hareelv Formation in the Blokelv-1 core is biostratigraphically subdivided by means of ammonite and dinoflagellate cyst stratigraphy. The succession ranges from the Oxfordian C. densiplicatum Chronozone to the Volgian P. elegans Chronozone. The mudstones of the Blokelv-1 core are characterised by large amounts of amorphous organic matter. This hampers the preparation and identification of dinoflagellate cysts, which are also commonly degraded and corroded. Ammonites, on the other hand, are common and well-preserved in the core, contrasting with that observed in the equivalent facies and stratigraphic interval at outcrop. Integration of the ammonite and dinoflagellate cyst biostratigraphical data yields a robust chronostratigraphic subdivision of the middle Oxfordian – lowermost Volgian cored section.

Revision of the Cambrian Agnostina (Trilobita?) from Russia

Cambrian genera and species of Agnostina (?Trilobita) found in Russia are revised. Agnostid trilobite species are used as index taxa in chronostratigraphic subdivisions of the traditional Middle and Upper Cambrian in both regional and global stratigraphic scales. The correlation of the regional and international stratigraphic schemes largely depends on the state of knowledge of the regional agnostid fauna. Therefore, an up-to-date revision of this group based on the Russian collections taking into account their global diversity is very timely. For this study we reexamined the type collections of agnostids, including the holotypes of species described by Russian authors. This paper contains new photographic images of the holotypes housed in Russian museums. The compiled data offered solutions for some difficult taxonomic problems of the families Agnostidae, Ptychagnostidae, Peronopsidae, and some genera of Pseudagnostidae, Diplagnostidae. Apart from listing the diversity, this paper serves as the basis for studying the biogeography and evolution of this interesting arthropod group.

Cambrian trilobite biostratigraphy and its role in developing an integrated history of the Earth system

One of the principal biostratigraphical tools used in the lower Palaeozoic, and especially the Cambrian System, is trilobites. Historically, both polymerids and agnostoids have commonly been included as 'trilobite' groups, although currently the question of whether they comprise a monophyletic group or are polyphyletic is unsettled. Beginning in the late 1800s, the base of the Cambrian System was marked by the lowest occurrence of olenelline trilobites. Discovery of a rich pre-trilobite metazoan record in the mid-1900s led to significant modification of that concept, but polymerids and especially agnostoids still rank among the leading biostratigraphical and chronostratigraphical guides through much of the Cambrian. Chronostratigraphical sub-division of the trilobite-bearing part of the Cambrian System derives largely from biostratigraphical, ecological and evolutionary concepts about agnostoids and polymerids introduced in the 1940s to 1970s by A.H. Westergard, A.R. Palmer and R.A. Robison. Westergard introduced a zonation for Scandinavia that was largely based on agnostoids. Palmer explained the distribution of Cambrian trilobite faunas in terms of restricted and unrestricted access to open oceans. Together, these ideas coalesced in Robison's recognition of separate zonation schemes for restricted-shelf polymerids, open-shelf polymerids and open-shelf (cosmopolitan) agnostoids. Palmer also introduced the concept of biomeres, which placed sharp limits on biostratigraphical intervals recognizable from trilobites. Global correlation in the upper half of the Cambrian today depends to a large extent on the ranges of agnostoids and some polymerids characteristic of open-shelf to slope areas, ones that facilitate identification of precise intercontinental tie points. Agnostoid and polymerid biostratigraphy is now being integrated with information about coastal onlap and eustatic sea-level history, geochemical cycling and other data to provide a more complete understanding of the early Palaeozoic biosphere and its complex physico-chemical context.

A Tonian age for the Visingsö Group in Sweden constrained by detrital zircon dating and biochronology: implications for evolutionary events

AbstractDetrital zircon U–Pb ages from samples of the Neoproterozoic Visingsö Group, Sweden, yield a maximum depositional age of ≤ 886±9 Ma (2σ). A minimum depositional age is established biochronologically using organic-walled and vase-shaped microfossils present in the upper formation of the Visingsö Group; the upper formation correlates with the Kwagunt Formation of the 780–740 Ma Chuar Group in Arizona, USA, and the lower Mount Harper Group, Yukon, Canada, that is older than 740 Ma. Mineralized scale microfossils of the type recorded from the upper Fifteenmile Group, Yukon, Canada, where they occur in a narrow stratigraphic range and are younger than 788 Ma, are recognized for the first time outside Laurentia. The mineralized scale microfossils in the upper formation of the Visingsö Group seem to have a wider stratigraphic range, and are older thanc. 740 Ma. The inferred age range of mineralized scale microfossils is 788–740 Ma. This time interval coincides with the vase-shaped microfossil range because both microfossil groups co-occur. The combined isotopic and biochronologic ages constrain the Visingsö Group to between ≤ 886 and 740 Ma, thus Tonian in age. This is the first robust age determination for the Visingsö Group, which preserves a rich microfossil assemblage of worldwide distribution. The organic and mineralized microorganisms preserved in the Visingsö Group and coeval successions elsewhere document global evolutionary events of auto- and heterotrophic protist radiations that are crucial to the reconstruction of eukaryotic phylogeny based on the fossil record and are useful for the Neoproterozoic chronostratigraphic subdivision.

THE STATUS OF STRATIGRAPHY IN THE 21ST CENTURY

The 21st century geological time scale (GTS) will comprise an internationally agreed chronologic hierarchy. Correlation of events into the GTS will be undertaken using a wide variety of methods, including numeric dating, fossil occurrence, physical and chemical properties, tephrochronology and astrochronologic retrodictions. Chronostratigraphic subdivision of the sedimentary rock record should proceed in a bottom up hierarchical manner with lower units defining the boundaries of stratigraphically higher units. A moderate amount of work is required to improve the basis of the hierarchical subdivision of some Cenozoic series boundary subdivisions and to bring them in line with recommendations by the Stratigraphic Guide and recommendations by the International Committee of Stratigraphy (ICS).

A new look at the Precambrian and Cambrian event chronostratigraphic correlation of Mongolia

The Mongolian Precambrian and Cambrian event chronostratigraphic classification of sedimentary, sedimentary—volcanogenic, volcanogenic, and metamorphic rock sediments spread over the territory of Mongolia according to the new chronostratigraphic classification approved by the International Stratigraphic Commission is discussed. These ancient rock units are readily divided into two independent complexes. The lower complex (1000–3500 m) is represented by the Archean and Early Proterozoic crystalline basement and the upper complex is the latest Precambrian–Cambrian sediments (220–7500 m). A detailed study of abundant Neoproterozoic and Early Cambrian faunal (ichnofossils, hexactinellid sponges, archaeocyaths, trilobites, etc.) and floral (stromatolites, microphytolites, cyanobacterial mats, microfossils, etc.) fossils provides the first regional chronostratigraphic subdivision of different facies sediments. Every stage is characterized by distinctive geohistorical and biological events.

Givetian (Middle Devonian) historical bio- and chronostratigraphical subdivision based on conodonts

The conodont record supports the intended threefold subdivision of the Givetian as envisaged by the International Subcommision on Devonian Stratigraphy into Lower, Middle and Upper Givetian substages. The lower boundary of the Lower Givetian Stage coincides with the lower boundary of the Givetian and it is recognized with the entry of Polygnathus hemiansatus. The lower boundary of the Middle Givetian is identified with the entry of either P. varcus or P. rhenanus. The base of the Upper Givetian is defined with the entry of Schmidtognathus hermanni. The historical review shows the conceptual evolution from a stage with just one and a half zones to one with ten zones that are the basis for the threefold Givetian subdivision. This zonation is mostly based on evolutionarily related conodont genera that are common in pelagic environments. An alternative conodont zonation for shallow-water facies for the Lower and Middle Givetian can also be widely applied. The proposal of subdividing the disparilis Zone into three subzones is not accepted.

The Dinantian (Mississippian) succession of southern Belgium and surrounding areas: stratigraphy improvement and inferred climate reconstruction

1. IntroductionAfter fundamental works such as those of de Dorlodot (1910) and Delepine (1911), the stratigraphy and the sedimentology of the Belgian Dinantian – a term better describing the Lower Carboniferous carbonate strata in western and central Europe than ‘Mississippian’ – were the subject of numerous papers during the 1960th and 1980th by various authors (Pirlet, Groessens, Bless, Bouckaert and others), mainly under the leadership of Raphael Conil. Especially the litho- and biostratigraphic work was summarized in two important synopses: Paproth et al. (1983) and Conil et al. (1991). In the first decade of this century, the older stratigraphic framework has been significantly revised and new basin-wide correlation schemes have been developed using bio-, chrono-, litho- and sequence stratigraphy – mainly in Hance et al. (2001, 2002, 2006), Poty et al. (2002a, 2006) and Devuyst (2006, for the Tournaisian – Visean boundary). These works led to a relatively coherent bio-, litho- and sequence stratigraphic model, which can be efficiently used in the Eurasia realm in shallow-water (e.g. Hance et al., 2011; Poty et al., 2007, 2014) and deeper water facies (e.g. Aretz, 2016, this volume; Herbig, 2016, this volume). This model also enabled the redefinition of the Belgian substages. Their boundaries can be correlated globally, which shows their high potential for further chronostratigraphic subdivision of the Carboniferous (Poty et al., 2014). Consequently, the Dinantian success

Ambiguities in conchostracan biostratigraphy: A case study of the Permian–Triassic boundary

In recent years, conchostracan biostratigraphy has become a popular tool for the recognition of the Permian–Triassic boundary and for the chronostratigraphic subdivision of the Triassic in intracontinental settings, including also the bone-bearing Keuper strata of Poland. The ambiguous nature of the new bio-chronostratigraphic approach was characterized in a case study of the Permian–Triassic boundary interval. The most important problems were: (1) the lack of documentation of the index species, (2) the indirect correlation with the conodont stratigraphy in marine reference sections through the sporomorph spectra, (3) the lack of definition and documen- tation of supporting palynologic zones, and (4) difficulties in reliable taxonomic determination of Conchostraca. Testing and, if necessary, revision of the zonation by several independent research groups is suggested.

Overview and biostratigraphy

Abstract Excellent coastal exposures of strongly folded and faulted Cambrian rocks occur around the St David's Peninsula of SW Wales. The best sections occur in the St David's Anticline, in the vicinity of St David's itself, and these have been the subject of scientific study since the mid-Nineteenth Century. Based on this early work, a quadripartite lithostratigraphical scheme emerged, comprising the Caerfai, Solva and Menevian groups and the Lingula Flags Formation. However, this scheme is unnecessarily complex, and sometimes unworkable in practice. The Caerfai Group is here redefined to embrace much of the Solva Group of earlier authors, while the upper part of the Solva Group, the Menevian Group and Lingula Flags are combined in the new Porth-y-rhaw Group. Traditionally, all these Cambrian rocks have been thought of as being deposited on a stable cratonic platform, but there is substantial evidence of tectonic influences on sedimentation, particularly in the older part of the succession. The Cambrian was originally recognized and defined in North Wales. There, as in many other areas, it became common practice to divide the period into three parts, but more recent work favours a four-fold chronostratigraphical subdivision. The oldest part of the Cambrian is missing in South Wales, but rocks of Terreneuvian, C2, C3 and Furongian age are all represented. Age-diagnostic fossils are few in the older part of the local succession. Trace fossils low in the Caerfai Group indicate the avalonensis Ichnozone or Teichichnus Interval of the Terreneuvian, while a radiometric date of early C2 (CS3) age has been obtained higher up. Trilobite faunas occur more commonly in the higher parts of the Caerfai Group and in the Porth-y-rhaw Group, and these facilitate international correlation of the C3 (CS5) to Furongian (Paibian) parts of the succession. Trilobites characteristic of the oelandicus Biosuperzone and the gibbus , fissus , parvifrons , punctuosus , pisiformis and Olenus biozones all occur.