International Geologic Time Scale Research Articles

Cyclostratigraphy and paleoclimate analysis of the Lingshui Formation in Changchang Sag, Qiongdongnan Basin, China

The Qiongdongnan Basin, located in the sea between Hainan Island and the Xisha Islands, is a faulted Cenozoic basin on the northern continental margin of the South China Sea. The Changchang Sag, situated in the eastern part of the central depressional zone in the deepwater area of the Qiongdongnan Basin, exhibits a near EW-striking morphology and represents an important potential target for oil/gas exploration. However, the age of the interface of the Lingshui Formation remains controversial, which hinders a comprehensive understanding of the tectonic evolution and hydrocarbon accumulation pattern in the Changchang Sag. This study focuses on well A, located in the depositional center of the Changchang Sag, and employs cyclostratigraphic analysis to identify cyclic signals of the Milankovitch cycles recorded in the sedimentary strata. Spectral analysis of natural gamma logging data from this well reveals the presence of 405 kyr long eccentricity cycles, 100 kyr short eccentricity cycles, 39.3 kyr obliquity cycles, and 20.58 kyr age precession cycles. By employing astronomical tuning, a “floating” astronomical time scale of the Lingshui Formation spanning 5.483 million years (Myr) is established. The top interface of the Oligocene in the International Geological Time Scale 2020 (GTS2020), with a geological age of 23.03 Ma, is used as the time anchor to establish a high-precision absolute astronomical age framework for the Lingshui Formation. The results indicate that the bottom interface of the first member of the Lingshui Formation is dated at 23.79 Ma, the bottom interface of the second member is dated at 25.08 Ma, and the bottom interface of the third member is dated at 28.51 Ma. Additionally, the average sedimentation rate during this period is estimated to be 9.261 cm/kyr. Furthermore, paleoclimate and paleoenvironmental reconstructions were carried out through quantitative analysis of spore and pollen assemblages, as well as foraminifera within the Lingshui Formation. These analyses suggest that the deposition of the Lingshui Formation occurred under warm and humid temperate climatic conditions. The results of paleoclimate proxy analysis and comparative fitting analysis of the astronomical time scale confirm that the climate evolution during this period was influenced by astronomical orbital forces, such as eccentricity and precession.

A knowledge graph and service for regional geologic time standards

Geologic time is an important dimension in geological research. Geologic time data are commonly collected from multiple sources in data-intensive studies of Earth’s history and raise an issue of data cleansing and integration. A knowledge graph of the international geological time scale has been established to harmonize heterogeneous data to facilitate effective and efficient data-driven discovery. Although many regional geologic time standards are also used in various databases and literature, there is limited discussion or development of knowledge graph for them. In this research, we construct a knowledge graph for the geologic time standards in 17 regions at the Epoch and Age levels. This regional geologic time knowledge graph is integrated with the international geologic time knowledge graph as a comprehensive deep-time knowledge base. A SPARQL endpoint has been established to provide open and free online service to the knowledge base. Several use cases are presented here to demonstrate the functionality of the knowledge graph we built as well as its application in open data exploration. Our work addresses the shortage of machine-readable knowledge graphs for regional geologic time standards and will help accelerate geologic data integration from multiple sources in data-intensive studies. All data and code in this paper are made open source and are accessible on GitHub and Zenodo.

Cyclostratigraphy and astrochronology: Case studies from China

A high-precision geologic time scale is the essential key for understanding the Earth’s evolutionary history and geologic processes. Astronomical tuning of orbitally forced stratigraphic records to construct high-resolution Astronomical Time Scales (ATS) has led to a progressive refinement of the geologic time scale over the past two decades. In turn, these studies provide new insights regarding the durations and rates of major Earth events, evolutionary processes, and climate changes, all of which provide a scientific basis for contextualizing and predicting future global change trends. South China hosts some of the best-exposed and well-dated Neoproterozoic through Mesozoic stratigraphic sections in the world; many of which are suitable for cyclostratigraphy and calibrating the geologic time scale. In North China, several Cenozoic oil-bearing basins have deep boreholes with continuous sampling and/or well logging that enable derivation of astronomically tuned time scales for an improved understanding of basin evolution and hydrocarbon generation. This Special Issue focuses on case studies of astrochronology and applied cyclostratigraphy research using reference sections within China. In this introductory overview, we: (1) summarize all existing astrochronology studies of the Neoproterozoic through Cenozoic sections within China that have been used to enhance the international geologic time scale, (2) examine briefly the astronomically forced paleoclimate information recorded in various depositional systems and the modern techniques employed to analyze the periodicity of these signals encoded within the sedimentary record, and (3) summarize the 20 contributions to this Special Issue of Palaeogeography, Palaeoclimatology, Palaeoecology on 'Cyclostratigraphy and Astrochronology: Case studies from China’.

Shift in the paradigm for GSSP boundary definition

For over 200 years the use of biotic events as the basis for the establishment of chronostratigraphic boundaries has been the only approach successfully utilized for international and national chronostratigraphy. The traditional biostratigraphic method provides relatively high resolution, averaging 1 Ma or sometimes less. This biochronological evolutionary approach to the Global Boundary Stratotype section and Point (GSSP) utilizes biotic Primary Markers (PM), with a few exceptions, encompasses the integrated PM and other non-PM markers as the general principles for defining GSSP boundaries and is a reasonably reliable mechanism for global correlation and a relatively stable International Geologic Time Scale (IGTS). The biotic PM's, however, possessed several serious restrictions: the nature of biological taxonomy, climatic, sedimentary, environmental - and directly applicable within the tropics-subtropics only. Biotic evolution and radiogenic isotopes are the only systems in geologic time that encompass the direction of time. The latter possessed less restrictions than the former. The recent tendency to define GSSP's utilizing magnetic chrons, climatic events and geochemistry may work in the Cenozoic, but is useless in the Mesozoic and older sediments because their cyclic nature (repeatedness) and the need for a second, directional in time index (biostratigraphic or radioisotopic) to place the PM in the right position within the scale. I propose here to utilize volcanic ash beds as the best Primary Marker in geologic chronostratigraphy. The U-Pb system is one of the most dependable of the geochronologic systems because it relies on a simple and non-interpretive radioisotopic decay constant. The ash-bed GSSP as a lithological horizon is universal for the GSSP definition and can be correlated as an age in any facies (marine, lagoon and continental), regardless of paleoclimatic zones, paleoceanographic, geochemical, and most other geological factors. Even moderate level metamorphism (>900 °С) does not affect the U-Pb dating of zircons. The GSSP at the base of a volcanic ash bed (Primary Marker) could be established in a short working time and these ash beds can be integrated with the existing as well as new biostratigraphic, geochemical, magnetostratigraphic and astronomical data (Secondary Markers) to create a robust, accurate and highly useable time scale. Several potential GSSP's that could be established with the volcanic ash beds close to the traditional and/or historical boundaries serve as examples for this approach and include Devonian-Carboniferous, Moscovian-Kasimovian, Kasimovian-Gzhelian, and Sakmarian-Artinskian boundaries.

Radioisotopic and biostratigraphic constraints on the classical Middle–Upper Permian succession and tetrapod fauna of the Moscow syneclise, Russia

Abstract The East European Platform and the PreUrals are the regions where the Permian System was first established, but the provincialism of fossils and lack of radioisotopic age control have prevented the use there of the regional Permian subdivisions used outside of the region. We report the first U-Pb zircon chemical abrasion–isotope dilution–thermal ionization mass spectrometry (CA-ID-TIMS) age of 253.95 ± 0.06 Ma for a volcanic tuff from the terrestrial upper part of the lower Vyatkian Regional Stage in the Moscow syneclise (Russia). This age greatly improves the correlation of the East European Platform and the PreUrals with the international geologic time scale, and contributes to our understanding of sedimentation within the Permian-Triassic transition in the studied region. The new radioisotopic age integrated within the regional chronostratigraphic framework reveals the synchrony in extinction of faunas of the Dinocephalian superassemblage in the studied region with that in South Africa.

New biostratigraphic framework for the Triassic–Paleogene in the Neo-Tethys realm of southern Xizang (Tibet), China

Abstract Multifaceted biostratigraphic work on Triassic to Paleogene strata in southern Xizang (Tibet), western China, in the last decades allows a new, refined biochronostratigraphic framework in the Qinghai–Xizang plateau region. Synthesis of the latest biostratigraphic progress is carried out in this paper to build a new integrated biostratigraphic scheme comparable to the international Geological Time Scale. The scheme incorporates key fossils as many of each system, such as ammonites, calcareous nannofossils, conodonts and foraminifers. Other fossil groups that are helpful for stratigraphic division and interregional correlation are also contained. These include bivalves, miospores and radiolarians, some of which, e.g. radiolarians and miospores, not previously well explored, are now utilised for new zones. Biostratigraphic zones of this new integrative system, especially the Lower Triassic conodonts and ammonites, uppermost Triassic–Lower Jurassic ammonites, Upper Cretaceous planktonic foraminifers and calcareous nannofossils, correlate well with the international standards. The results are tabulated as four new comprehensive biostratigraphic charts, which, we hope, will provide a new and more reliable chronostratigraphic foundation for study of Neo-Tethys.

High-precision radioisotopic ages for the lower Midian (upper Wordian) Stage of the Tethyan time scale, Shigeyasu Quarry, Yamaguchi Prefecture, Japan

Global correlation of strata to the Guadalupian Series (Permian Period) of the International Geologic Time Scale remains provisional due to a lack of the sufficient biostratigraphically constrained radioisotopic ages. Five new high-precision UPb radioisotopic ages were obtained from tuffs in the lower Midian (upper Wordian) volcano-siliciclastic succession of the Akiyoshi Plateau, southwestern Japan. Two undisturbed and continuous tuffs occur within fusulinid-bearing laminated limestone turbidites, with precise biostratigraphic control. The Colania douvillei and Lepidolina shiraiwensis fusulinid Zones in the Akiyoshi succession provide an early Midian age in the Tethyan provincial time scale. The range of ages (267.46 ± 0.04 Ma to 265.76 ± 0.03 Ma) over 25 m of section including the limestone turbiditic beds suggest that this lower Midian Stage of the Tethyan time scale is correlated with the upper Wordian Stage of the International Geologic Time Scale. The sedimentologic, bio- and geochronologic data affirm the effectively conformable nature of the siliciclastic‑carbonate succession of the Tsunemori Formation at the Shigeyasu Quarry, and the presence of acidic volcanic tuffs are consistent with a forearc basin or trench slope basin depocenter for the Tsunemori Formation.

Recalibrating Australian Triassic Palynostratigraphy to the International Geologic Timescale Using High Resolution CA-IDTIMS Dating

The Triassic is an important interval for Australian petroleum exploration, with Middle to Upper Triassic Mungaroo Formation reservoirs in the Northern Carnarvon Basin, and recent Lower Triassic discoveries in the Roebuck Basin. The chronostratigraphic understanding of Triassic petroleum systems is underpinned by biostratigraphic dating using palynological zonations. The numerical ages of these zones are usually assigned through inference and interpolation, often via tenuous correlations to the international geologic timescale using scattered marine biota, (primarily foraminifera, and rare ammonites, conodonts and/or dinoflagellates). In contrast, we tie Australian biozones to the timescale through Chemical Abrasion-Isotope Dilution Thermal Ionisation Mass Spectrometry (CA-IDTIMS) dating of interbedded volcanic tuffs. Such ashfalls are reasonably common in Australian basins, and can provide high-precision CA-IDTIMS ages if they contain magmatic zircons. We recently recalibrated Australian middle and late Permian palynozones using this approach and preliminary results suggest that Triassic biozone ages are likewise in need of considerable revision.We have targeted Triassic tuffs across Queensland, (Tarong beds, Brisbane Tuff, Moolayember Formation, Rewan Group), New South Wales (Garie Formation, Coal Cliff Sandstone, Milligan Road Formation), and Tasmania (upper Triassic coal measures) to provide numerical ages for palynozones. Additional dates in New Zealand (Murihiku Supergroup) and Timor-Leste (Wailuli Formation) will allow international correlation of dinocyst and spore-pollen zones. Numerical constraints for Triassic biozone boundaries facilitate correlation of Australian biozones with the international geologic timescale. This can impact burial history models used in petroleum exploration anywhere these biozones are used, often far beyond the basins from which the samples were collected.

Comment on “When did the Anthropocene begin? A mid-twentieth century boundary is stratigraphically optimal” by Jan Zalasiewicz et al. (2015), Quaternary International, 383, 196–203

We offer a comment on the paper: “When did the Anthropocene begin? A mid-twentieth century boundary is stratigraphically optimal” by Jan Zalasiewicz et al. (2015), Quaternary International, 383, 196–203. We consider this proposal in the context of the procedures and terminology employed by the International Union of Geological Sciences which underpin the formal designation of chronostratigraphic units. Our conclusion is that there is no practical value in establishing the lower boundary of a new interval of geological time in the mid-twentieth century; equally, there is no sound stratigraphical basis for designating an additional chronostratigraphic unit above the Holocene in the international Geological Time Scale.

Towards updated stratigraphic frameworks for Australia

A standardised and precise timescale is invaluable to geological research and crucial to meaningful correlation at local, regional and global scales for both researchers and industry. Modern techniques and instruments are delivering increasingly accurate ages, and biozonation schemes are continually refined and standardised on a global basis. Updates to the international geologic time scale occur regularly, and constant updates to stratigraphic schemes are required to ensure that major regional geological events can be correlated across the Australian margin. Several different sequence stratigraphic schemes have been developed for the basins of the North West Shelf. These range from basin-specific to margin-wide schemes. While these schemes have much in common, there are some significant differences. Understanding the nature and reasons for both the differences and commonalities is an essential step for improving understanding of the region’s evolution. The continuing improvements being made to biostratigraphic zonation schemes for the Triassic to Cenozoic will assist in better defining sequences and correlations, and allow geologists to better understand whether apparent differences in sequence definition across the margin are real, and therefore if they reflect different basin histories or are simply an artefact of biostratigraphic imprecision. Geoscience Australia endeavours to—in collaboration with industry—produce unified stratigraphic schemes for the various hydrocarbon provinces. This work will fundamentally support present and future acreage releases.

The times they are a-changin': Australian biozones, petroleum basins, and the international geologic time scale (GTS) 2012

The international Geologic Time Scale (GTS) continually evolves due to refinements in age dating and the addition of more defined stages. The GTS 2012 has replaced GTS 2004 as the global standard timescale, resulting in changes to the age and duration of most chronological stages. These revisions have implications for interpreted ages and durations of sedimentary rocks in Australian basins, with ramifications for petroleum systems modelling. Accurate stratigraphic ages are required to reliably model the burial history of a basin, hence kerogen maturation and hydrocarbon expulsion and migration. When the resolution of the time scale is increased, models that utilise updated ages will better reflect the true basin history. The international GTS is largely built around northern hemisphere datasets. At APPEA 2009, Laurie et al. announced a program to tie Australian biozones to GTS 2004. Now, with the implementation of GTS 2012, these ties are being updated and refined, requiring a comprehensive review of the correlations between Australian and International biozonation schemes. The use of Geoscience Australia’s Timescales Database and a customised ‘Australian Datapack’ for the visualisation software package TimeScale Creator has greatly facilitated the transition from GTS 2004 to GTS 2012, as anticipated in the design of the program in 2009. Geoscience Australia’s basin biozonation and stratigraphy charts (e.g. Northern Carnarvon and Browse basins) are being reproduced to reflect the GTS 2012 and modified stratigraphic ages. Additionally, new charts are being added to the series, including a set of onshore basin charts, such as the Georgina and Canning basins.

Reply to comment by P. Olivier on “Preorogenic exhumation of the North Pyrenean Agly Massif (Eastern Pyrenees, France)”

We make this reply to Philippe Oliver's comments on the deformation of the Mesozoic cover of the northern Agly massif.

LOWER PRECAMBRIAN SRATIGRAPHIC SHEME IN RUSSIA AND UKRAINE: COMPARISON, ANALYSIS OF DIFFERENCES, WAYS OF RAPPROCHEMENT

Official scheme (scale) of the general subdivision of Lower Precambrian in Russia and Ukraine are compared with each other and with the international Geological Time Scale. The authors concluded that historical and geological (event-stratigraphic) principle of constructing of Precambrian general scales takes precedence over chronometric principle and there is need to return to the practice of correlation Lower Precambrian sections by comparing major units on a range of structural and tectonic, geological and formational, petrological and geochemical characteristics. Geological interpretation, taking into account the multi-stage tectonic and thermal evolution of Early Precambrian area, should precede the use of isotope-geochronological data. The authors offered their own versions of Lower Precambrian Correlation Scheme of the Ukrainian Shield and Lower Precambrian Interregional Correlation Scheme of Russia and Ukraine. These schemes are based on the Russian national scale, including three categories of stratigraphic units: Acrothem, Eonothem, Erathem. The authors propose to divide Archean Acrothem into Lower Archean, Middle Archean and Upper Archean Eonotems, typal units of which are Aldanian, Stanovian, Lopian. The age of Stanovian lower boundary are defined greater than 3800, the top – equal to 3500 Ma.

The Geological Society of America Geologic Time Scale

The Geological Society of America has sponsored versions of the geologic time scale since 1983. Over the past 30 years, the Geological Society of America Geologic Time Scale has undergone substantial modifications, commensurate with major advances in our understanding of chronostratigraphy, geochronology, astrochronology, chemostratigraphy, and the geomagnetic polarity time scale. Today, many parts of the time scale can be calibrated with precisions approaching less than 0.05%. Some notable time intervals for which collaborative, multifaceted efforts have led to dramatic improvements in our understanding of the character and temporal resolution of key evolutionary events include the Triassic-Jurassic, Permian-Triassic, and Neoproterozoic-Phanerozoic boundaries (or transitions). In developing the current Geological Society of America Time Scale, we have strived to maintain a consistency with efforts by the International Commission on Stratigraphy to develop an international geologic time scale. Although current geologic time scales are vastly improved over the first geologic time scale, published by Arthur Holmes in 1913, we note that Holmes, using eight numerical ages to calibrate the Phanerozoic time scale, estimated the beginning of the Cambrian Period to within a few percent of the currently accepted value. Over the past 100 years, the confluence of process-based geological thought with observed and approximated geologic rates has led to coherent and quantitatively robust estimates of geologic time scales, reducing many uncertainties to the 0.1% level. (Less)

Late Cretaceous stratigraphy, Songliao Basin, NE China: SK1 cores

The Songliao Basin is the largest Cretaceous oil and gas-producing lacustrine basin in China, with its greatest aerial extent in the middle Cretaceous. A coring program (SK1) has to date yielded 2485.89m of continuous core (96.46% recovery) and provides significant material for Cretaceous research. The sequence of the core consists mainly of lacustrine sandstone, dark grey mudstone, shale and oil-shale. The Upper Cretaceous stratigraphic section has been subdivided into the Quantou, Qingshankou, Yaojia, Nenjiang, Sifangtai and Mingshui formations in ascending order. Late Cretaceous microfossils are diverse and abundant. A detailed biostratigraphic study has subdivided the sequence into high precision biozones: 21 ostracode assemblages, 10 phytoplankton assemblages, 7 palynological zones and 4 charophyta assemblages, respectively. In addition, marine foraminifera were first discovered from the basin. Three 206Pb/238U ages and one 40Ar/39Ar age were analysed. Ten local magnetozones have been recognised in the SK1 (North), and two magnetozones have been indicated in the SK1 (South). Based on biostratigraphy, high-resolution magnetostratigraphy and SIMS U–Pb zircon analyses, the SK1 stratigraphy is correlated with Upper Cretaceous stages in the International Geologic Time Scale. The upper part of the Quantou Formation is the lower Turonian; the Qingshankou Formation is the upper Turonian–lower Coniacian; the Yaojia Formation is from the upper Coniacian to middle Santonian; the Nenjiang Formation is the upper Santonian to middle Campanian; the Sifangtai Formation is limited to the upper Campanian; and the Mingshui Formation is the uppermost Campanian to Maastrichtian. It is likely that the upper part of the Mingshui Formation belongs to the Paleocene, and the K/Pg boundary is within the Member 2 of the Mingshui Formation around the depth of 328m by new micropalaeontologic and magnetostratigraphic data.

Milankovitch and sub‐Milankovitch forcing of the Oxfordian (Late Jurassic) Terres Noires Formation (SE France) and global implications

ABSTRACTHigh‐resolution analysis (2277 samples) of magnetic susceptibility (MS) was performed on ∼700‐m‐thick Early–Middle Oxfordian marine marls of the Terres Noires Formation, SE France. MS variations within these sediments record sub‐Milankovitch to Milankovitch frequencies with long‐term eccentricity (405 kyr and ∼2 Myr) being the most prominent. The 405 kyr cycle was used as a high‐resolution geochronometer for astronomical calibration of this poorly constrained interval of Late Jurassic time. The estimated duration of this Early–Middle Oxfordian interval concurs with the current International Geologic Time Scale GTS2004 (∼4 Myr), but the estimated durations of the corresponding ammonite zones are notably different. The calibration improves the resolution and accuracy of the M‐sequence magnetic anomaly block model that was previously used to establish the Oxfordian time scale. Additionally, the 405 kyr cyclicity is linked to third‐order sea‐level depositional sequences observed for Early–Middle Oxfordian time. Strong ∼2 Myr cycles are consistent with long‐term eccentricity modulation predicted for the Late Jurassic. These cycles do not match second‐order sequences that have been documented for European basins; this raises questions about the definition and hierarchy of depositional sequences in the Mesozoic eustatic chart. Our results require substantial revisions to the chart, which is frequently used as a reference for the correlation of widely separated palaeogeographic domains. Finally, a long‐term trend in the MS data reflects a progressive carbonate enrichment of the marls expressing an Early Oxfordian global cooling followed gradually by a warming in the Middle Oxfordian. This trend also records a major transgressive interval likely peaking at the Transversarium ammonite zone of the Middle Oxfordian.

Cyclostratigraphy and the Astronomical Time Scale

An important innovation in the International Geologic Time Scale 2004 is the use of astronomically forced stratigraphy, or cyclostratigraphy, to define geologic time over 0 to 23.03 Ma, much of it at an unprecedented resolution of 0.02 myr. In addition, ‘floating’ astronomical time scales with 0.10 to 0.40 myr resolution are defined for entire epochs and stages in the Paleogene and all three Mesozoic periods. Some of these calibrations use a new astronomical model with an hypothesized high accuracy over 0-250 Ma. These accomplishments have motivated the International Commission on Stratigraphy to complete a continuous Astronomical Time Scale (‘ATS’) for the past 250 Ma, and to initiate a coordinated prospecting for astronomical-like signals in Paleozoic cyclostratigraphy. Astronomically calibrated geologic time with a 0.02 to 0.40 myr resolution is a major breakthrough for the geosciences. Chronostratigraphy between widely spaced horizons dated with high-precision radioisotope geochronology suffers total loss in precision and accuracy; a continuous ATS between horizons can restore this hard-won precision and accuracy. Consequently, estimates of rates and magnitudes for a wide range of Earth system processes that can be examined only in the context of Earth history, e.g., paleoclimatology, geochronology, geodynamics, structural geology, geochemical cycles and biotic evolution, will be improved up to an order of magnitude over what is possible today.

Defining the Quaternary

The Quaternary System is under threat of extinction as a chronostratigraphic unit in the international Geological Time Scale. In its place, the Neogene System (previously comprising Miocene and Pliocene Series), is to be extended to include the Pleistocene and Holocene Series. It may be possible to “save” the Quaternary by defining it as a Subsystem of the Neogene. In doing so, it would be an opportune time to extend the base of the Quaternary to 2.6 Ma to encompass the time during which (1) Earth's climate has been strongly influenced by bi-polar glaciation, and (2) the genus Homo first appeared and evolved.

Status of Divisions of the International Geologic Time Scale

Each chronostratigraphic unit of the International Geologic Time Scale will be defined at its base by a Global Stratotype Section and Point (GSSP) or Global Standard Stratigraphic Age (GSSA). Nearly 50 GSSPs and 10 GSSAs have now been ratified. Ideally, the GSSP coincides with events having a global correlation potential. The international stage divisions of some systems, such as the Jurassic or Neogene, are similar to traditional usage in European geology. However, in order to utilize global correlation horizons, the international stage divisions of other systems, such as the Ordovician or Permian, have required assembling new stage nomenclatures or hybrids of different regional stages. A reference table by the International Commission on Stratigraphy itemizes the current or potential GSSP and GSSA definitions of all international geologic time units.

Revised correlations for Carboniferous marine invertebrate zones of eastern Australia

A review of the international significance of Carboniferous biostratigraphic units of eastern Australia, incorporating brachiopod, ammonoid, conodont and foraminiferal/algal evidence, is carried out in order that new ion microprobe ages can be used to calibrate the Australian units and to provide greater precision to the international geological timescale. The ages of brachiopod zones, which have been most used for regional correlation throughout eastern Australia, are revised using new conodont information from Jenkins et al. (1993), recent revisions of European ammonoid zones (Riley, 1990a, 1991), existing foraminiferal/algal data, and new internal evidence from brachiopods. Major changes include recognition that: the Tulcumbella tenuistriata Zone straddles the Devonian-Carboniferous boundary and extends into the mid-Hastarian (Tn1b-lowest Tn2b); the Schellwienella burlingtonensis Zone is late Hastarian to earliest Molinacian (Tn2c-Tn3c) in age; the Orthotetes australis Zone early Visean (Chadian to early Arundian; V1a-V1b) rather than late Visean in age based on new data from conodonts and reinterpretation of the ammonoid evidence; the Delepinea aspinosa Zone ranges in age from Arundian to early Holkerian (V1b to V2b), though the boundary with the succeeding Rhipidomella fortimuscula Zone cannot be well defined; the fortimuscula Zone is late Holkerian to Asbian (V3b), with the top of the zone being taken within the B2b ammonoid zone; and the Marginirugus barringtonensis Zone extends throughout the remainder of the Asbian and the Brigantian, to the end of the late Visean. Gondwanan assemblages succeeding the Early Carboniferous cosmopolitan faunas cannot be readily correlated with Northern Hemisphere biozones. The Levipustula levis Zone is Namurian in age at the base.