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Frozen on the beach


Robin Bailey on uniformitarianism and the rare, untypical events that allow us to apply it…

Geoscientist 20.05 May 2010

Chris Garland, in a recent Soapbox (Geoscientist 19.7), suggests that the uniformitarian axiom implies that we can watch the processes that formed the Late Jurassic Piper Sand reservoir of the northern North Sea at work today on Worthing beach. Given that modern sandy beach accumulations feature low-angle cross-stratification and wave-rippled surfaces, it seems reasonable to assume that ancient sandstones showing similar features record beach sedimentation. But repeated visits to a sandy, tidally-influenced, Worthing-type, beach would show that the pattern of ripples is subject to twice-daily change and liable also to variation in response to monthly fluctuations in the tidal range and unpredictable, weather-related, variations in wave direction and power.

So, if millions of essentially similar, but individually unique, ripple patterns could be generated in a beach environment in 100kyr time-frames, then what circumstances could have led to any one particular pattern being preserved in the stratigraphical record? This might imply that the ripple-marked sand layer was atypical of the beach’s erosion-dominated sedimentary processes (which normally would have created a new and different set of ripples within hours). On the other hand, given the millions of opportunities to capture the sedimentary imprint of typical beach processes, under a variety of wave and tidal conditions, why not accept that this has occurred?

Net increase in coastal accommodation space1 increases the chances of such capture, but does not explain it. Sand can be added or removed from Worthing beach at rates of centimetres per day, whereas typical rates of increase in accommodation are less than a centimetre per year and would be completely overwhelmed by this sedimentary ‘noise’. Likewise, there is no way that sandstone packages with the typical low-angle cross-stratification could be the outcome of continuous accumulation at these slow net rates. It is easier to suppose that metre-scale units of beach facies, such as the Piper Sand, are the cumulative effect of very rare centimetre-scale sedimentary ‘frozen accidents’ 2 in an environment where the slow net rate of accumulation reflects the dominance of erosion.

Is the present the key to the past and the future? We certainly do not know whether sedimentary processes currently operating on Worthing beach will remain in the local record, 5000 or five million years hence. It seems unlikely, since they have low preservation potential. So is the uniformitarian axiom flawed? No: the processes encapsulated by the concept ‘beach’ are global and everywhere leave the same sort of sedimentary imprint; so, where we see analogous features in the record, it is safe to assume that we are looking at one of those rare series of ‘snapshots’ of beach sedimentation. But uniformitarianism, in this instance, may depend on ‘frozen accidents’.


  1. Neal, J and Abreu, V 2009. Sequence stratigraphy, hierarchy and the accommodation succession method. Geology 37, no. 9, 779-782.
  2. Gell-Mann, M 2002. Plectics: The study of simplicity and complexity. Europhysics News, Jan/Feb issue, 17-20.