Examine the geologic cross section and describe the order of all the geologic events that can be depicted from this image

Question

Don't limit yourself to merely the lettered rock units; include episodes of folding and erosion, too. Use descriptive geologic verbs like "deposition" and "intrusion" rather than simply saying the "rock unit J was formed."
What will be an ideal response?

Answer 1

Answer: The blue rock units labeled C are the oldest. These strata would have originally been deposited horizontally and then were folded, presumably during a compressional episode of mountain building. A period of erosion followed, and the ancient mountain belt was ground down to its roots. Deposition of the strata of unit B followed next, so the contact between C and B is an angular unconformity. Sometime later, igneous unit A intruded into both C and B as magma. The aureole of contact metamorphism that surrounds A shows that A must be younger than the units it cuts across. The surface of B was subject to erosion, and unit D filled a large concave gouge that was cut downward into B, perhaps an ancient river channel? (Technically, we cannot tell whether unit D was incised into B first, or whether unit A intruded first, because they have no direct or indirect relationship to one another.) Unit igneous F then cut across all units on its way up to the surface as a dike. Note that dike F has baked the units it cuts across (A, B, and D) with contact metamorphism. When it got to the surface, it erupted as a volcano. This volcano, as well as units B and D, was eventually buried underneath another batch of strata. The various layers of E were deposited next, covering everything that came before. Finally, the fault marked "G" cut through, offsetting portions of B, D, and E with apparent normal dip-slip motion.