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Using modern versus ancient analogues

Depositional analogues are a valuable tool for predicting subsurface stratigraphic architecture, particularly when data are limited. They offer plausible architectural scenarios that support decision-making and help capture an appropriate range of depositional uncertainty.

The two main sources of depositional analogue information are interpreted geomorphological maps from Holocene (modern) systems and outcrop-based case studies.

It is important to consider the strengths and limitations of each analogue data source.

Advantages of Holocene (modern) data​

Clearly shows planview architecture
Satellite imagery and aerial photos allow detailed mapping of depositional features in plan-view such as beach ridges, distributary channels, and mouth bars.

Has better chronostratigraphic resolution
Precise dating methods (e.g., radiocarbon) provide time resolution from years to millennia, helping distinguish short-term versus long-term depositional events and thus better understanding the processes that control stratigraphic architecture.

Has better data continuity at different scales
Many modern systems form continuous datasets from local to regional scales, allowing full contextual analysis of depositional architecture.

Allows determining relationships between process and architecture
Modern environments allow direct observation of sedimentary processes and their influence on architectural outcomes, minimizing interpretive uncertainty.

Advantages of ancient outcrop and subsurface data​

Vertical stacking can be readily determined
Ancient datasets provide detailed insight into the vertical stacking of facies and bounding surfaces, allowing clear interpretation of how stratigraphy evolves through geological time.

Shows complete regressive-transgressive cycles
Ancient case studies preserve full RT cycles, enabling the mapping of system tracts and stratigraphic sequences—unlike modern datasets which often capture only part of these cycles.

Shows preserved stratigraphy
Outcrop-based analogues reveal stratigraphy that has survived erosional processes during and after deposition and thus show what tends to be preserved in the stratigraphic record.

Is easily relatable to subsurface data
Vertical facies descriptions and grain-size trends from ancient cores and outcrops closely match the type of data used in subsurface exploration.

Issues of preservation of modern systems​

It is important to recognize that not all architectural elements visible in modern systems will be preserved in the rock record. Nevertheless, such data remain highly valuable

  • Modern data are particularly useful for understanding the shapes, lateral distributions and dimensions of depositional units, even when these units are partially eroded.
  • Much of what we observe in the Holocene regressive reposits has already begun to enter the rock record, unless it is removed by subsequent transgressive ravinement. Not all deposits are removed by ravinement.
  • Many subsurface intervals will preserve only remnants of deposits observed in modern settings (e.g., amalgamated channel belt intervals). These deposits can still be modeled effectively using appropriate channel belt geometries and levels of amalgamation.
  • Depositional scale is important: modern systems are generally more useful for making predictions at the intra-parasequence scale, rather than for entire parasequences or parasequence sets.

Combined approach​

Stratigraphic prediction in the subsurface is a three-dimensional problem, so consulting both modern and ancient analogues often yields the best results.

This approach enables the use of the most suitable analogue type, depending on the specific depositional question being addressed.