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

[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.

/pdf/high-precision-u-pb-zircon-age-calibration-of-the-global-192s61zdkd.pdf

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

The supercontinent Pangea completes its assembly and moves north during the Permian. The 47-million-year-long period begins with a great ice age and ends with the Earth’s greatest extinction. The interval is characterized by icehouse to greenhouse climate transition, major evaporites, changes in internal and external carbonate invertebrate skeletons, major diversification of fusulinacean foraminifers, ammonoids, bryozoans, and brachiopods. It concludes with the major end-Permian extinction of fusulinacean foraminifers, trilobites, rugose and tabulate corals, blastoids, acanthodians, placoderms, and pelycosaurs and dramatic reduction of bryozoans, brachiopods, ammonoids, sharks, bony fish, crinoids, and land vertebrates.

The Permian 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)

Cyclothem [sequence stratigraphic] correlation and biostratigraphy across the Moscovian-Kasimovian and Kasimovian-Gzhelian Stage boundaries (Upper Pennsylvanian Series) in North America and Eurasia

H.C. Forke

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)

Cyclothem [sequence stratigraphic] correlation and biostratigraphy across the Moscovian-Kasimovian and Kasimovian-Gzhelian Stage boundaries (Upper Pennsylvanian Series) in North America and Eurasia