Chronostratigraphy Units defined based on time-equivalent stratal surfaces, natural stratigraphic subdivisions Chronozones vary in space but not time Correspond to physical boundaries, which can generate reflections SLIDE 9 When using a lithostratigraphic methodology: Units defined based on time-equivalent stratal surfaces, natural stratigraphic subdivisions Chronozones vary in space but not time Correspond to physical boundaries, which can generate reflections The diagrammatic cross section shows 3 time-units - one major episode or pulse of deposition color-coded yellow - a second episode shown in orange - a third erisode indicated by white How do we break the rock record into time units? - there may be index fossils - there may be beds that mark time – e.g., a volcanic ash layer - we can use a method we call sequence stratigraphic analysis – which is beyond the scope of this course Unit 3 Unit 2 Unit 1 Time Unit 1 Time Unit 2 Time Unit 3 Courtesy of ExxonMobil L 11 – Stratigraphic Analysis