1 In the Circum-Arctic Palynological Event Stratigraphy project (CAPE), specialists were asked to document selected palynological events (for example taxon originations and extinctions) with correlation potential from the Silurian to the Cenozoic in the present-day Arctic region (Fig. 1). The results have been compiled into a series of papers in Atlantic Geology. The aim of the compilation is to develop a scheme of events across the Arctic tied to chronostratigraphic units and thus indirectly to the absolute time scale (Gradstein et al. 2020). The compilation thus develops a platform for stratigraphic studies, with flexibility for refinement and augmentation as additional information becomes available. The composite event scheme will contribute a refined timeframe to constrain interpretations of the geological evolution of the Arctic, a necessary precursor to various types of applied basin-fill studies.

2 Palynology (or strictly paleopalynology) is the study of fossil organic-walled microfossils (palynomorphs), including pollen and spores, dinoflagellates, acritarchs, and chitinozoans. Due to their microscopic size, fossilizable walls and potential abundance in marine and nonmarine sedimentary rocks, palynomorphs are the single most effective group of fossils for correlation and environmental interpretations of Phanerozoic strata, especially for subsurface studies that involve small rock samples. The main groups of palynomorphs and their stratigraphic ranges are discussed in detail in Williams et al. (2018) (Fig. 2). In Neoproterozoic to Lower Devonian rocks, acritarchs (organic-walled, single-celled organisms of unknown affinity) are the primary biostratigraphic group, with chitinozoans also being a significant group for the Ordovician to Devonian interval. Acritarchs continue to be present through the Phanerozoic but are only occasionally important and of limited stratigraphic value after the Devonian. Spores, which first evolved in the Ordovician, are the foremost nonmarine group used in biostratigraphic studies of Upper Devonian to Permian rocks. Gymnosperm pollen (primarily conifers) became increasingly important from the Late Carboniferous to the Early Jurassic, whereas angiosperm (flowering plant) pollen did not enter the record, at least consistently, until the Early Cretaceous. Angiosperm pollen are generally more useful as paleoenvironmental rather than biostratigraphic indicators. Dinoflagellate cysts (dinocysts), which first occur in the latest Middle Triassic, are the most useful palynomorph group for biostratigraphy from the Middle Jurassic to the Holocene in marine sedimentary rocks. Hence the key palynomorph group(s) used to define events vary through geological time (Fig. 2).

3 Most papers in the CAPE series describe palynoevents for today’s circum-Arctic region (Fig. 1) which includes Alaska, Arctic Canada, Greenland, northern Europe and northern Russia. Both onshore and offshore areas are included where data are available. Events from related areas, including the Labrador Sea, are incorporated when the assemblages are considered to represent Arctic populations. The location and geography of the modern circum-Arctic region varied during the Phanerozoic as plate-tectonic processes rearranged continental and oceanic components through time (Blakey 2021).

4 Most biostratigraphic studies of palynomorphs provide zonation schemes as a tool for stratigraphic correlation. While we recognize the value and advantages of zonation schemes, especially where a single scheme has remained relatively stable for many years (for example the standard western European ammonite zonation for the Jurassic), an event-stratigraphic scheme offers an alternative approach. Event schemes are more easily integrated with other parameters such as well logs (e.g., gamma-ray spikes), seismic markers, chemostratigraphic events (e.g., anoxic episodes) and other paleontological events. The papers in the CAPE series therefore propose event schemes for the Silurian to Cenozoic. Cambrian and Ordovician events have not been included due to current lack of data, but may be integrated in the future.

5 In the CAPE series of papers, selected markers comprise taxon origination events (first occurrences or FOs) and taxon extinction events (last occurrences or LOs). Some abundance events are included where they are considered useful for correlation: for example the FO of abundant monosaccate pollen is documented as the base of the Asselian (Mangerud et al. 2021b). The event schemes published in the CAPE series reflect the current state of knowledge and can be modified as knowledge of ranges become refined.

6 To facilitate this ongoing process, we plan to record all events as a datapack in TimeScale Creator (TSC; Geologic TimeScale Foundation 2021) that will be freely available online. TSC is a JAVA package operated by the Geologic TimeScale Foundation (GTS Foundation) based at Purdue University in West Lafayette, Indiana. It was developed to record stratigraphic data (including biostratigraphy, lithostratigraphy, and chronostratigraphy) and to update absolute ages in the geological time scale. Data presented in TSC are based on the Geological Time Scale (GTS) series of publications (the latest being Gradstein et al. 2020, which is used in the CAPE series of papers). The GTS Foundation provides regular updates that incorporate refinements to the absolute-age calibrations of chronostratigraphic units which are reflected in charts generated from TSC. These updates, together with the public availability of software and data, make TSC the ideal platform to store palynological event (palynoevent) data. Further details of how to use TSC are provided in the TSC website and Bringué et al. (in press).

7 To accommodate CAPE palynoevent data in TSC, it is necessary to define events relative to previously established chronostratigraphic units rather than absolute ages. The Geological Time Scale (Gradstein et al. 2020) is anchored to the stratigraphic record through “golden spikes” and type and reference sections, and its calibration in absolute time is continually being refined. Ideally, palynoevents should be tied to documented datums of other fossils groups, for example ammonites or planktonic foraminifera. An example is the FO of Jerseyiaspora punctispinosa, which in Mangerud et al. (2021c) occurs at the base of the ammonoid Keyserlingites subrobustus Zone. Note that relationships to bases are used for consistency and ease of application in TSC. If the palynoevent does not equate exactly with an independent horizon, then it is calibrated as a percentage above the base of a stratigraphic unit (e.g., an ammonoid zone or stage) relative to the next overlying unit of the same type. Thus, the LO of the spore genus Vittatina is documented as 70% up from the base of the Griesbachian Stage in Mangerud et al. (2021c). If a relationship with an independent fossil horizon cannot be identified, then a similar relationship with the base of a chronostratigraphic unit is employed. Thus, in Mangerud et al. (2021a), the FO of the spore Columinisporites heyleri is documented as the base of the Moscovian Stage; and the LO of the spore Microreticulatisporites nobilis is documented as 80% above the base of the Moscovian.

8 The CAPE series will comprise articles on Silurian – Devonian, Carboniferous, Permian, Triassic, Jurassic and Cretaceous palynoevents, and one or more on Cenozoic palynoevents.. The series will also include an article detailing the paleogeography of the circum-Arctic region (Blakey 2021), and one documenting the effect of the Cenozoic greenhouse to icehouse climatic shift on Arctic palynological assemblages.

9 Each palynoevent paper has a section summarizing previous work, followed by documentation of the palynoevents, and how each event is tied to chronostratigraphy. Each contribution includes a present-day map of the circum-Arctic region showing locations cited in the paper, a stratigraphic chart generated by TSC showing the events, and a table summarizing the events as an appendix.