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Study modern analogs

‘I work on beaches,’ is always a good conversation starter, and for many people it conjures up images of relaxing in the tropics. Although that’s a pleasant thought, working in modern environments is rarely relaxing; rather it is hard work undertaken to bring clarity to sedimentary geology. Th rough modern research, geoscientists try to answer questions of what, where, why, and how and shed more light on the rock record. Modern research lets us access a wide range of depositional environments, and enables us to determine the conditions under which sediments are deposited and colonized by organisms. Th ese data provide the fundamental basis for interpreting sedimentary strata, and hence form the basis for seeking out new resources (e.g. hydrocarbons and water) contained within sedimentary rocks.

Consider Waterside Beach in New Brunswick, Canada, pictured here in 2011 with a sediment grain size map made in 2004. It is a good example of a beach with a large tidal range, which enables close examination of sedimentary structures and burrows at low tide.

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Waves breaking on the beach and shoreface produce a predictable set of sedimentary structures (sedimentology) that change as waves shoal onshore. As the sedimentary structures change, there is a corresponding change in the types of animals that colonize the sediment, leading to unique combinations of burrows (ichnology) constructed by those animals to cope with the environmental conditions. Depending upon the grain size of the sediments, the size of waves aff ecting the coastline, the sediment source, the geography of the basin with respect to its coastline, and the climate, astute geoscientists can determine the range of variability that can be found in the resulting depositional facies of beach–shoreface sediments. This integrated approach provides the basis for making effective rock-record interpretations, which enables us to better predict the architecture of sedimentary strata and determine the nature of the paleoenvironment. For petroleum geologists and hydrogeologists, such modern environment data constitute the analog models essential for exploring or exploiting resources contained in sedimentary rocks.

In addition to understanding the rock record, studying modern environments provides information on the plan view (lateral) distribution of sediments that cannot be accurately resolved from outcrop or subsurface geological studies. Walther’s Law, indeed, is founded upon the realization that knowing the spatial distribution of environments and their deposits is critical to understanding the vertical succession of facies we see preserved in the rock record. This is of fundamental importance to sedimentary geology because most new resources contained in sedimentary rocks reside in the subsurface and can only be exploited through drilling. Whether developing an exploration strategy for finding new resources, building a development strategy for a newly discovered oil pool or aquifer, or trying to predict the lateral extent of permeability barriers (e.g. mudstone beds in sandstone), data derived from modern environments serve as the starting point for understanding the depositional system.

Modern environments have been studied for nearly as long as the science of geology has existed. As elsewhere, technological advances have enabled us to push the limits of what we can do. Nowadays, modern research takes place in environments from the top of the Himalayas to the bottom of the Marianas Trench, and is heavily reliant on advanced technology. This has led to a plethora of information on nearly all depositional environments on the planet. Yet with the increased use of computer modelling there is a need for more quantified data. Now instead of asking, ‘Where is mud being deposited in estuaries?’, the question has become, ‘How thick and how laterally continuous are mud beds deposited at the bottom, in the middle, and at the top of an estuarine succession, and how does this change along its depositional profile?’.

Although new research questions are more tightly constrained, the fundamentals of modern environment research remain the same — to continue to build an understanding of the rock record. Modern analogs have been and remain a cornerstone of sedimentary geology.

The scale of a wavelet

The magic of Fourier

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