Tectonic Implications of Stratigraphy Architecture in Distal Part of Foreland Basin, Southwestern Taiwan

Abstract

A foreland basin system with its asymmetric basin geometry extends from the frontal areas of a mountain-building belt to the margin of craton and includes, as defined by DeCelles and Giles [1], wedge-top, foreland basin, forebulge and backbulge. Foreland basins have been well modeled based on the concept of flexed lithosphere under tectonic loading of thrust sheets and sediments deposited into the basin [2, 3, 4]. Rapid subsidence in a ancient foreland basin and the uplifted forebulge at its distal part has been viewed as the result of tectonic loading due to active thrust sheet emplacement [5, 6, 7, 8]. Corresponding to each episodic thrust belt advancement, a coarsening-upward clastic wedge would form and prograde into the newly subsided foreland basin [9, 10, 11]. Characteristics of sedimentary sequences in a foreland basin are, thus, related to dynamic and kinematic modes of orogen-foreland basin evolution. Inversely, such characteristics can be used to investigate tectonic motion of the adjacent orogen [12, 13]. Different models for the development of a foreland basin predict distinct stratigraphy architecture across the basin. An elastic plate model predicts that the asymmetric foreland basin with the uplifted forebulge would migrate toward the craton as the rising orogen advances [14, 15, 16] and that the continuous migration of the orogen-foreland basin pair would leave a regional unconformity in the basin, which is younger toward the craton [17, 18]. The strata sequences overlying and onlapping at the unconformity have been viewed as the initial deposits of the foreland basin development [19, 20, 21, 22, 23]. The elastic model can be applied to infer the scale of erosion at the forebulge unconformity and the rate of strata onlapping across the unconformity under the conditions of variable crustal rigidity and variable migration rate of the orogenic wedge [22]. If a visco-elastic model is applied, the stress imposed on a loaded lithosphere would be relaxed and the foreland basin would become narrower and deeper with the forebulge migrating