Long-distance correlation between tectonic-controlled, isolated carbonate platforms by cyclostratigraphy and sequence stratigraphy in the Devonian ofSouth China

During the early Middle Devonian in South China, an extensive carbonate pla tform was broken up through extension to create a complex pattern of platfo rms, and interplatform basins. In Givetian and Frasnian carbonate successio ns, five depositional facies, including peritidal, restricted shallow subti dal, semi-restricted subtidal, intermediate subtidal and deep subtidal faci es, and 18 lithofacies units are recognized from measured sections on three isolated platforms. These deposits are arranged into metre-scale, upward-s hallowing peritidal and subtidal cycles. Nine third-order sequences are ide ntified from changes in cycle stacking patterns, vertical facies changes an d the stratigraphic distribution of subaerial exposure indicators. These se quences mostly consist of a lower transgressive part and an upper regressiv e part. Transgressive packages are dominated by thicker-than-average subtid al cycles, and regressive packages by thinner-than-average peritidal cycles . Sequence boundaries are transitional zones composed of stacked, high-freq uency, thinner-than-average cycles with upward-increasing intensity of suba erial exposure, rather than individual, laterally traceable surfaces. These sequences can be further grouped into catch-up and keep-up sequence sets f rom the longterm (second-order) changes in accommodation and vertical facie s changes. Catch-up sequences are characterized by relatively thick cycle p ackages with a high percentage of intermediate to shallow subtidal facies, and even deep subtidal facies locally within some individual sequences, rec ording long-term accommodation gain. Keep-up sequences are characterized by relatively thin cycle packages with a high percentage of peritidal facies within sequences, recording long-term accommodation loss. Correlation of lo ng-term accommodation changes expressed by Fischer plots reveals that durin g the late Givetian to early Frasnian increased accommodation loss on platf orms coincided with increased accommodation gain in interplatform basins. T his suggests that movement on faults resulted in the relative uplift of pla tforms and subsidence of interplatform basins. In the early Frasnian, exten sive siliceous deposits in most interplatform basins and megabreccias at ba sin margins correspond to exposure disconformities on platforms.