The recurrence of the same types of sequence stratigraphic surface through geologic time defines cycles of change in accommodation or sediment supply, which correspond to sequences in the rock record. These cycles may be symmetrical or asymmetrical, and may or may not include all types of systems tracts that may be expected within a fully developed sequence. Depending on the scale of observation, sequences and their bounding surfaces may be ascribed to different hierarchical orders. Stratal stacking patterns combine to define trends in geometric character that include upstepping, forestepping, backstepping and downstepping, expressing three types of shoreline shift: forced regression (forestepping and downstepping at the shoreline), normal regression (forestepping and upstepping at the shoreline) and transgression (backstepping at the shoreline). Stacking patterns that are independent of shoreline trajectories may also be defined on the basis of changes in depositional style that can be correlated regionally. All stratal stacking patterns reflect the interplay of the same two fundamental variables, namely accommodation (the space available for potential sediment accumulation) and sediment supply. Deposits defined by specific stratal stacking patterns form the basic constituents of any sequence stratigraphic unit, from sequence to systems tract and parasequence. Changes in stratal stacking patterns define the position and timing of key sequence stratigraphic surfaces. Precisely which surfaces are selected as sequence boundaries varies as a function of which surfaces are best expressed within the context of the depositional setting and the preservation of facies relationships and stratal stacking patterns in that succession. The high degree of variability in the expression of sequence stratigraphic units and bounding surfaces in the rock record means ideally that the methodology used to analyze their depositional setting should be flexible from one sequence stratigraphic approach to another. Construction of this framework ensures the success of the method in terms of its objectives to provide a process-based understanding of the stratigraphic architecture. The purpose of this paper is to emphasize a standard but flexible methodology that remains objective.

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Sequence stratigraphy: methodology and nomenclature

Geological Society Special Publications

Two mass extinctions brought the Paleozoic to a close: one at the end of the Guadalupian, or middle Permian (ca. 260 Ma), and a more severe, second event at the close of the Changhsingian Stage (ca. 251.6 Ma). Here we review work over the past decade that defines the probable causes of the mass extinction, and evaluate several extinction hypotheses. The marine extinctions were selective; epifaunal suspension feeders were more affected than other clades, although significant variations occurred even among the filter feeders. In southern China, the Changhsingian marine extinction was nearly catastrophic, occurring in 0.5 m.y. On land, vertebrates, plants, and insects all underwent major extinctions. The event coincides with (1) a drop of d 13 C in carbonates, from 2‰ to 2‰ in both marine and terrestrial sections; (2) the eruption of the massive Siberian continental flood basalts; and (3) evidence of shallow-water marine anoxia, and perhaps deep-water anoxia. Although the cause of the extinction remains unclear, a series of constraints on speculation have been established in the past few years. Leading contenders for the cause are the climatic effects, including acid rain and global warming, possibly induced by the eruption of the Siberian flood basalts; and marine anoxia. An extraterrestrial impact is consistent with the geochronological and paleontological data from southern China and elsewhere, and some possible evidence for impact has recently been advanced.

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End-Permian mass extinctions: A review

[1] High-precision ID-TIMS U-Pb zircon ages for 12 interstratified tuffs and tonsteins are used to radiometrically calibrate the detailed lithostratigraphic, cyclostratigraphic, and biostratigraphic framework of the Carboniferous Donets Basin of eastern Europe. Chemical abrasion of zircons, use of the internationally calibrated EARTHTIME mixed U-Pb isotope dilution tracer, and improved mass spectrometry guided by detailed error analysis have resulted in an age resolution of <0.05%, or ∼100 ka, for these Carboniferous volcanics. This precision allows the resolution of time in the Milankovitch band and confirms the long-standing hypothesis that individual high-frequency Pennsylvanian cyclothems and bundles of cyclothems into fourth-order sequences are the eustatic response to orbital eccentricity (∼100 and 400 ka) forcing. Tuning of the fourth-order sequences in the Donets Basin to the long-period eccentricity cycle results in a continuous age model for the Middle to Late Pennsylvanian (Moscovian-Kasimovian-Ghzelian) strata of the basin and their record of biological and climatic changes through the latter portion of the late Paleozoic Ice Age. Detailed fusulinid and conodont zonations allow the export of this age model to sections throughout Euramerica. Additional ages for Mississippian strata provide among the first robust radiometric calibration points within this subperiod and result in variable lowering of the base ages of its constituent stages compared to recent global time scale compilations.

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High‐precision U‐Pb zircon age calibration of the global Carboniferous time scale and Milankovitch band cyclicity in the Donets Basin, eastern Ukraine

Only the GSSPs for the Bashkirian (base of the Pennsylvanian), Visean and Tournaisian (base of the Mississippian) have been formalized, although the latter now has complications.

The Carboniferous Period

Global time scale and regional stratigraphic reference scales of Central and West Europe, East Europe, Tethys, South China, and North America as used in the Devonian-Carboniferous-Permian Correlation Chart 2003 (DCP 2003)

Embleton et al. (1996; hereafter referred to as EMMZL) EMMZL’s incorrect dating of the Illawarra Reversal resulted from a false correlation between the Upper Permian of Chinese detected the Late Permian Illawarra Reversal (IR: top of the Carboniferous–Permian reversed megazone, Kiaman, 265 Ma) chronostratigraphic schemes and that of Harland et al. (1990). The Upper Permian used in China is equivalent to the Lopingian in the lower Upper Shihezi (Shihhotse) Formation of North China. Series (Zhan, Zhaang & Li 1982; Sheng et al. 1982), while the Lower Permian is equivalent to the Chisian and the Maokouan In their stratigraphic scheme (Table 1 and Fig. 5, redrawn in our Fig. 1) the lower boundaries of the Upper Shihezi (Fig. 2). However, Harland et al.’s (1990) Upper Permian spans the Ufimian to the Changhsingian, and therefore closely Formation, Ufimian and Late Permian coincide. Consequently, EMMZL conclude that the Permo-Carboniferous reversed corresponds to the entire Permian succession that EMMZL identified in the Shanxi section. In the EMMZL scheme (Fig. 1) (Kiaman) superchron ends in mid-Ufimian time. This interpretation does not agree with the position of the IR in the the Lower Shihezi Formation corresponds to the entire Lower Permian, whereas in the Sheng & Jin (1994) scheme it is lower part of the type Tatarian on the East European Platform (Khramov 1963), which has been accepted for the last 30 years assigned to the upper Chihsian and the lower Maokouan and, combined with the Jin et al. (1994) scheme, corresponds to the and has been confirmed most recently by Gialanella et al. (1997). EMMZL do not mention this significant discrepancy middle part of the Permian (upper Kungurian plus Roadian plus Wordian; Fig. 2). (Fig. 1). We are certain that the difference can be explained better using a revised stratigraphic scheme than by suggesting EMMZL (p. 382) stated ‘The Shanxi Formation is rich in brachiopods, corals and fusulinids that date it as Late methodological insufficiencies or remagnetization. EMMZL use reliable palaeomagnetic equipment and Carboniferous’. This statement is untrue. In reality, the underlying Taiyuan Formation comprises normal marine sediments methodologies. Their magnetostratigraphic results are significant according to the sequences investigated, although no and contains fusulinids, corals and brachiopods, but the Shanxi (Shansi) Formation does not as it is of lacustrine origin fold test or conglomerate test is possible and mainly the red horizons of a grey/red Permian/Triassic succession yield (BGRM Shanxi 1989). The Shanxi (Shansi) Formation has never been assigned to the Late Carboniferous in the last stable remanent magnetizations. Plenty of facts support their magnetic zones. The Zijderfeld plots reflect continuous thermal decade. It is late Artinskian to post-Artinskian in age, because the upper part of the underlying Taiyuan Formation contains demagnetization and stable remanence (EMMZL, Fig. 2). Inclination and declination of the remanence are at the Artinskian conodonts such as Streptognathodus whitei (Wang et al. 1987) (Fig. 2). expected values; normal and reversed samples are grouped and bipolar (EMMZL, Fig. 3). A minimum of 13 polarity zones The plant fossils from the Upper Shihezi (Shihhotse) Formation and the Shiqianfeng (Shichienfeng) Formation are have been detected between the IR and the Permian/Triassic boundary. This number is in good agreement with data from referred to as the late stage of the Cathaysian flora (Li 1963). Indeed, the plant assemblage of the Shichienfeng (Shiqianfeng) the Salt Range (Haag & Heller 1991), Central Europe (Menning 1995) and Australia (Theveniaut et al. 1994). Formation contains some characteristic Zechstein species (Wang et al. 1989; also see Sheng & Jin 1994, p. 65). The different position of the IR within the Tatarian (Khramov 1963) and within the Ufimian (EMMZL) results Consequently, the Upper Shihhotse Formation (position of the IR of EMMZL) may correspond with part of the Upper from the stratigraphic schemes used by EMMZL (Table 1, Fig. 5). They refer their data to the ‘official Chinese stratiRotliegend (conformable below the Zechstein), where the IR is detected (Menning et al. 1988). graphic scheme’ (EMMZL, no details given) and the Harland et al. (1990) timescale (cf. Fig 1). On the other hand, the In the Sheng & Jin (1994) scheme the lower part of the Upper Shihhotse (Shihezi) Formation (position of the IR of magnetostratigraphic results of EMMZL and Khramov (1963) are consistent when referred to the correlation chart of Permian EMMZL) corresponds with the Upper Maokouan (Fig. 2). The IR has been expected within the Maokouan (Menning, deposits in China (Sheng et al. 1982; Sheng & Jin 1994) (Fig. 2).

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Comment on ‘Permo‐Triassic magnetostratigraphy in China: the type section near Taiyuan, Shanxi Province, North China’ by B.J.J. Embleton, M.W. McElhinny, X. Ma, Z. Zhang and Z.X. Li

Y.-G. Jin

Papers

Global time scale and regional stratigraphic reference scales of Central and West Europe, East Europe, Tethys, South China, and North America as used in the Devonian-Carboniferous-Permian Correlation Chart 2003 (DCP 2003)

Comment on ‘Permo‐Triassic magnetostratigraphy in China: the type section near Taiyuan, Shanxi Province, North China’ by B.J.J. Embleton, M.W. McElhinny, X. Ma, Z. Zhang and Z.X. Li