Simplified cross section of the evolution of the Tolstoj basin stratigraphy (not to scale). (A) Secondary volcanic crust buried the primary graphite flotation crust prior to Tolstoj basin formation. (B) The basin-forming impact excavated the primary crust and emplaced it as LRM around the basin. The impact likely also uplifted a central peak ring and generated LRM-rich impact melt that would have ponded in the basin interior. (C) Impact bombardment and tectonism modified the basin and surrounding terrain prior to infilling by volcanism. (D) After effusive and explosive volcanism resurfaced the basin interior, impact bombardment continued to mix LRM-rich impact melt and ejecta with the underlying secondary volcanic crust. Profiles X and Y are analogous to those in Figure 13: Mixing by bombardment reduces the reflectance and spectral contrast of LRM over time.