Index Fossil Biozone Duration Formula
Computes the total temporal lifespan and stratigraphic resolution of an index fossil taxon from its First Appearance Datum (FAD) to its Last Appearance Datum (LAD).
\[ \Delta t_{biozone} = \text{FAD}_{\text{Ma}} - \text{LAD}_{\text{Ma}} \quad \text{where } \text{FAD} > \text{LAD} \]
Plain Text Formula:
Biozone_Duration = FAD_Ma - LAD_Ma (where FAD > LAD in millions of years ago)
📐 Variable Definitions & Parameters
| Symbol | Variable Name | Standard Unit | Physical Definition |
|---|---|---|---|
| \[ \Delta t_{biozone} \] | Temporal Range Duration | Million Years (Ma) | Total duration over which the species existed |
| \[ \text{FAD} \] | First Appearance Datum | Ma | Oldest verified stratigraphic entry (geological age in Ma) |
| \[ \text{LAD} \] | Last Appearance Datum | Ma | Youngest verified occurrence prior to extinction (Ma) |
💡 Worked Engineering Example
Problem Statement:
Paradoxides davidis (Cambrian trilobite) has FAD = 505.0 Ma and LAD = 500.5 Ma. Find its biozone duration.
Step-by-Step Solution:
- Biozone Duration = 505.0 Ma - 500.5 Ma = 4.5 Ma
🎯 Result: The Paradoxides biozone spans 4.5 million years, serving as a tight biostratigraphic marker for the Middle Cambrian.