[1] We discuss the detection of cyclic signals in stratigraphic 'time series' using spectral methods. The dominant source of variance in the stratigraphic record is red noise, which greatly complicates the process of searching for weak periodic signals. We highlight two issues that are more significant than generally appreciated. The first is the lack of a correction for 'multiple tests' -many independent frequencies are examined for periods but using a significance test appropriate for examination of a single frequency. The second problem is the poor choice of null hypothesis used to model the spectrum of non-periodic variations. Stratigraphers commonly assume the noise is a first-order autoregressive process -the AR(1) model -which in practice often gives a very poor match to real data; a fact that goes largely unnoticed because model checking is rarely performed. These problems have the effect of raising the number of false positives far above the expected rate, to the extent that the literature on spatial stratigraphic cycles is dominated by false positives. In turn these will distort the construction of astronomically calibrated timescales, lead to inflated estimates of the physical significance of deterministic forcing of the climate and depositional processes in the pre-Neogene, and may even bias models of solar system dynamics on very long timescales. We make suggestions for controlling the false positive rate, and emphasize the value of Monte Carlo simulations to validate and calibrate analysis methods.

The closure of the Uralian Ocean occurred in Early Permian-Early Triassic time. In the northern Ural fold belt, overthrusting to the west produced a major foreland basin to the west of the mountain chain. In contrast, in the northern extension of the Ural Orogen, the Taymyr fold belt, thrusting was directed to the SE. It is proposed that Novaya Zemlya, at the interface of these two zones, acted as a thin-skinned allochthonous nappe emplaced by gravity tectonics into a basin produced by rapid Permo-Triassic rifting in the eastern Barents Sea.

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Sedimentary strata are the paramount source of geohistorical information. The 'frozen accidents' of individual deposits preserve evidence of past physical, chemical and biological processes at the Earth's surface, while the spatial relationships between strata (especially superposition) yield successions of events through time. There is, however, no one-to-one relationship between strata and time, and the interpretation of the stratigraphic record depends on an understanding of its limitations. Stratigraphic continuity and completeness are unattainable ideals, and it is the departures from those ideals -the often cryptic gaps in the record -that provide both its characteristic texture and the principal challenge to its analysis. The existence of gaps is clearly demonstrated by consideration of accumulation rates, but identifying and quantifying them in the field is far more difficult, as is assessing their impact on the degree to which the stratigraphic record represents the environments and processes of the past. These issues can be tackled in a variety of ways, from empirical considerations based on classical field observations, to new ways of analysing data, to the generation and analysis of very large numbers of synthetic datasets. The range of approaches to the fundamental questions of the relationship between strata and time continues to expand and to challenge long-established practices and conventions.Superposed sedimentary strata are the most accessible routes into deep time, and acceptance of their historical significance was a major scientific breakthrough. Given that the study of strata has been undertaken in something like its modern form for over two centuries, stratigraphy as a scientific discipline might be expected to have stabilized, as perhaps is indicated by stratigraphy textbooks suggesting that the subject is widely regarded as boring. Yet if there is a problem with stratigraphy, it is the converse: its development is increasingly punctuated by paradigm shifts triggered by new theories (evolution; global tectonics; eustasy; orbital forcing of climate change) and technological breakthroughs (digital computing; continuous seismic profiling; isotopic methods in chronology and palaeoclimatology). With this accelerating progress, it has become increasingly clear that the stratigraphic record yields only snapshots of Earth's past surface processes -the 'frozen accidents' that give the record its character and its enduring fascination. 'Time is missing from sedimentary sequences on all scales . . . This discontinuity gives recorded planetary (geological) time a different architecture to human time' (Paola, C. 2003. Floods of record. Nature, 425, 459).Strata and Time: Probing the Gaps in our Understanding was the title of the Geological Society's William Smith Meeting for 2012. Its aim was to explore the relationship between the preserved sedimentary rock record and the passage of geological time, identifying, evaluating and updating the models that lie behind current stratigraphic method...