B1 · Publication Volume 6

Sedimentology and Stratigraphy

Develops process-based reasoning from sedimentary features, facies and stratigraphic relationships.

Purpose of this book

Sedimentary rocks are records of movement and interruption. A grain may be released by weathering, transported several times, stored on a floodplain, deposited in a basin, altered during burial, exposed by uplift and moved again. A bed may represent minutes of current activity, while the surface above it may represent a much longer interval of erosion or non-deposition. This book develops the reasoning needed to move from those incomplete records to testable histories of sediment production, transport, deposition, preservation and basin fill.

The organising question is not simply “what environment is this?” It is: which observations support which process, at what scale, and what alternative process could produce a similar record? Grain size, structures, fossils, mineral composition, bed geometry, vertical stacking and regional position become powerful only when their measurement, preservation and uncertainty are made explicit.

General and institution-neutral scope

This is a general tutorial with no affiliation to any company or individual. It does not depend on proprietary software, a commercial classification, a named mine, a private borehole database or a particular national workflow. Examples use schematic catchments, rivers, deserts, lakes, coasts, shelves and basins so that the method can be transferred to any region for which suitable evidence exists.

Named standards and public scientific agencies appear only in source notes. A classification is useful when its version and boundaries are declared; it is not a substitute for observations. Likewise, an environmental label is a hypothesis to be tested, not an intrinsic property hidden inside a rock name.

The website that hosts this material is only a delivery surface. It is not presented as the textbook's author, publisher, sponsor, scientific authority or curriculum subject.

What you should already know

You should be comfortable with geological observation, maps and sections; mineral and rock description; relative and numerical time; units, logarithms, graphs, vectors and uncertainty. You should be able to distinguish an observation from an inference and to record where a sample, image or measurement came from. Familiarity with basic fluid motion, density and chemical equilibrium is helpful, but the sedimentological meaning of each concept is developed here.

Learning outcomes

By the end of the book, you should be able to:

  • construct a sediment budget from source through temporary storage to final preservation;
  • describe grain size, sorting, shape, fabric and composition without prematurely assigning an environment;
  • measure sedimentary structures and combine directional data with an appropriate representation of spread;
  • compare continental, coastal, marine, carbonate and chemical sediment systems through processes rather than memorised pictures;
  • define facies and facies associations from stated criteria and test environmental interpretations;
  • establish stratigraphic order, identify hiatuses and correlate sections without forcing equivalence;
  • explain how accommodation and sediment supply influence shoreline trajectory and stacking pattern;
  • integrate outcrop, core, logs, maps and geophysical surfaces into a basin-fill model; and
  • present at least two viable interpretations and specify the observation that would best discriminate between them.

Evidence discipline

Every lesson uses a six-link chain:

  1. Material: what particles, precipitates or organic components are present?
  2. Texture and structure: what sizes, shapes, fabrics, surfaces and bed geometries were observed?
  3. Process: which transport, depositional, erosional or diagenetic mechanisms are consistent with them?
  4. Environment: which combination of processes and boundary conditions could persist in the inferred setting?
  5. Stratigraphic context: how does the unit relate laterally and vertically to neighbouring units and time surfaces?
  6. Uncertainty: what was not observed, what could have been removed, and what competing history remains possible?

The links are not reversible without qualification. A current can make cross-lamination, but cross-lamination alone does not identify a river. Mud can settle in quiet water, arrive in flocs during energetic conditions, or be introduced by later alteration. A sharp contact can record erosion, bypass, a rapid facies shift, compaction or an observational gap. Responsible interpretation preserves those alternatives until evidence reduces them.

How to use the figures

Each lesson contains one purpose-built schematic. The diagrams simplify geometry to expose relationships; they are not site maps, measured sections or universal templates. Scale bars are omitted where dimensions are conceptual. Arrows show proposed transfers or relative directions, not measured velocities. Recreate each diagram with observations from your own dataset, and change or remove any arrow that the evidence does not support.

Completion task: a two-hypothesis basin history

Assemble a small public or instructor-provided dataset containing at least three measured sections or logs, photographs or core descriptions, grain-size observations and a map or cross-section. Define units without environmental names. Build a correlation model with explicit confidence, then propose two depositional and stratigraphic histories that explain the data. For each history, state the sediment sources, transport processes, environments, important surfaces, likely preservation controls and unresolved age relationships. Finish with a ranked list of new observations that would distinguish the two histories.

The required product is an auditable argument, not a polished certainty. Every correlation must point to its evidence; every inferred absence must be distinguished from an unobserved interval; and every environment must be supported by an association rather than one supposedly diagnostic feature.

Core sources