The Paradox of Equivalence of the Davisian End-Peneplain and Penckian Primary Peneplain

The Davisian model elucidates landscape development through an orogeny by denudation processes, postulating prolonged still-stand of a landmass following rapid tectonic uplift, ultimately resulting in a peneplain. The Penckian model emphasizes that landscape is shaped by concurrent tectonics and denudation, and includes the primary peneplain as an antithesis against the Davisian end-peneplain by assuming a steady state between tectonic uplift and denudation from the beginning of orogenesis. Every ordinary landscape development through an orogeny has been expected to follow a course located between the two distinctive courses of landscape development. On the basis of the relationships between mountain altitude, local relief and denudation rate observed in Japan, denudation rate increases with local relief and the local relief increases with mountain altitude. A mountain range is considerably denuded even during the uplift phase. As denudation rate approaches tectonic uplift rate with an increase in mountain altitude by tectonic uplift, a steady state between denudation and uplift appears, and the mountain range attains a critical altitude that remains constant, in spite of continuous tectonic uplift. If tectonic uplift ceases, the mountain range is lowered by denudation, resulting in a subdued low relief landscape, ultimately a peneplain. The primary peneplain requires a low uplift rate to keep a balance with the low denudation rate due to its low altitude. Based on the observed data in Japan whose denudation rates are among the highest class in the world, the tectonic uplift rate must be 0.05 mm/yr or lower for a mountain range with an altitude of 100 m above sea level to maintain its low altitude. This low uplift rate should be classified not as an orogenic crustal movement but as crustal stability. Thus, the Penckian primary peneplain must be an irrelevance. A low relief landscape recognized as a primary peneplain must be formed originally as a Davisian endpeneplain. The sequence of ordinary landscape development is outside the two courses of the Davisian and Penckian models.