TIME AND PROCESS RATES OVER THE PAST 100 MY - A CASE FOR DRAMATICALLY INCREASED LANDSCAPE DENUDATION RATES DURING THE LATE QUATERNARY IN NORTHERN AUSTRALIA

摘要

A central question in the earth sciences is how rates and styles of landscape evolution have varied over time in response to climate and sea-level change, tectonic and isostatic uplift, and human disturbance, The Quaternary has been a period of major landscape evolution in many glaciated regions of the world, but few data sets of sufficient length are available to assess its significance to the long-term development of landscapes in nonglaciated regions, Analysis of denudation rates over the past 0.5 m.y. and 100 m.y. for upland and lowland surfaces in western Arnhem Land, tropical northern Australia, shows that denudation rates have increased by at least an order of magnitude in the late Quaternary compared to the previous 100 m.y., despite tectonic stability and the absence of glaciation in this region over the past 120 m.y. The lowlands have undergone denudation rates up to an order of magnitude higher than the uplands, so that the landscape has increased in relief independently of the absolute rate of denudation. This result is counter to several prominent theories of landscape development that postulate relief reduction over millions of years. At least 3%-7% of the post-Cretaceous denudation of this landscape occurred during the most recent 0.5 m.y. We suggest that the Quaternary here was a period of greatly accelerated erosion resulting from changes in climate and sea level accompanying glacial-interglacial cycles, General sea-level regression since the mid Cretaceous also likely initiated substantial lowland erosion in this region, It appears, therefore, that the past 100 m.y. have been punctuated by at least two episodes of accelerated landscape denudation. [References: 30]