Thursday, January 22, 2015

Erosional Truncation & Toplap

Erosional truncation indicates that the sediment package formerly extended higher than it does today but that portions were removed by erosion,

whereas toplap indicates deposition near sea level and that the sediment package never extended significantly higher in the section.

With good seismic data quality, toplap sometimes can be distinguished from erosional truncation because there were changes in the depostional environment near toplap and consequently reflections are changeable in attitude and character, whereas no such changes occured at erosional truncation terminations.

Erosional truncation is the primary evidence for a sea-level fall. Where sediment packages are thick enough and noise sufficiently low, reflections showing these features can be seen in seismic data and used to determine the sea-level changes.

(Sherrif. 1995. Exploration Seismology)

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