Use this geological calculation for a transparent first-pass interpretation of measured rock, soil, fluid, well, stratigraphic, isotopic, geophysical, or seismic data under an explicitly selected model.

Strata dip

Dip of the onlapping (younger) strata in degrees.

Substrate dip

Dip of the underlying surface being onlapped in degrees.

Angle between dipping strata and the inclined older surface they progressively onlap: |dip(strata) - dip(substrate)|, assuming comparable dip directions. The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

Onlap angle

Onlap angle between strata and substrate in degrees.

• Stratal terminations and systems tracts are interpretations sensitive to seismic resolution, datum, compaction, subsidence, sediment supply, chronology, and depositional model. A geometric angle or thickness alone does not identify sequence boundaries.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Compare independent measurements and models, retain units and analytical metadata, propagate uncertainty, and validate interpretations against logs, cores, maps, laboratory data, or field observations.

• Downlap Angle Calculator

  Angle between downsloping (progradational) strata and the older surface onto which they downlap: |dip(strata) - dip(basal surface)|, assuming comparable dip directions.

• Toplap Angle Calculator

  Angle between initially inclined strata and the nearly horizontal upper surface beneath which they toplap: |dip(strata) - dip(upper surface)|, assuming comparable dip directions.

• Unconformity Angle Calculator

  Angular discordance across an unconformity: the absolute difference between dip of beds above and dip of beds below, assuming comparable dip directions.