Late Precambrian through Early Paleozoic Stratigraphic and Tectonic Evolution of the Nanling Region, Hunan Province, South China

Publisher Website
Google Scholar
Abstract
The Late Precambrian through Silurian tectonic evolution of east-central South China is modeled in terms of a history of rift, drift, and collision during Late Proterozoic, Sinian, and Late Ordovician-Early Silurian times, respectively. We review the regional stratigraphie development of this area, focusing particularly on north-central Hunan province, and argue from our observations and those of others that the Jiangnan, Xuefeng, and Jiuling ranges of the Nanling realm approximately demarcate the paleogeographic transition in Sinian to Ordovician times of shelf to off-shelf environments developed along a passive-type continental margin that started rifting in the pre-Sinian Late Proterozoic. The rift sequence is recorded by the Penhsi (= Banxi) Group, which rests unconformably above an older-presumed Middle to early Late Proterozoic-low-grade metamorphic basement. The Penhsi varies markedly in thickness but is everywhere characterized by nonmarine to paralic clastic facies. The Penhsi conformably to disconformably underlies the Sinian through Lower Paleozoic sequence throughout central South China, which developed along an E-facing, passive-type continental margin. This passive-type margin was destroyed by the Guangxian Orogeny. The Guangxian Orogeny was marked initially by the northwestward progradation of deep-marine turbidites of Late Ordovician age in the most off-shelf regions, progressing to earliest Silurian age on the shelf to the northwest. Folding and concomitant thrusting in the off-shelf regions, and subsequent erosion beneath the unconformably overlying nonmarine Middle Devonian strata, truncate the stratigraphie record of the orogen within the Early Silurian. Farther northwest, in regions undisturbed by the Guangxian Orogeny, Silurian foreland-basin sedimentation included the entire Lower Silurian succession, which grades rapidly upward from basinal to inter-tonguing marine and nonmarine elastics. This reflects a change from flexurally induced subsidence first outpacing local sedimentation, followed by sedimentation outstripping and then keeping pace with subsidence.