Differential response of a Devonian‐Carboniferous platform‐deeper basin system to sea‐level change and tectonics, N. Chilean Andes

Abstract

AbstractDeposition of a 2700‐m‐thick clastic platform succession in a N‐S striking basin in northern Chile began in the Early Devonian during a global sea‐level rise. A transition to terrestrial facies took place at the Early‐Late Carboniferous boundary when the Gondwana glaciation began and global sea‐level dropped. On the platform, interbedded cross‐bedded or bioturbated sandstones, offshore tidal dunes and sand waves, and mudstones and tempestites suggest switching intertidal and shallow or deep subtidal environments. However, evidence for subaerial erosion indicates a significant regression during the Early Devonian.In an adjacent and deeper N‐S striking sub‐basin to the W, up to 3600 m of turbidites were deposited from the Late Devonian to the Late Carboniferous by mainly southerly palaeocurrents. Turbidites accumulated in coarse‐grained proximal sand lobes in the N, and in fine‐grained lobe fringe and basin plain environments in the S, with alternating upward‐thinning and upward‐thickening cycles typical of tectonically controlled aggradational turbidite systems.The sedimentological data indicate that the deeper basin depositional system evolved to a large extent independently from the platform system. Sediment in the deeper basin is less mature and more poorly sorted than that on the platform, suggesting that detritus bypassed the platform and was shed directly from the source areas into the western basin. The only depositional link between the platform and deeper basin systems seems to be longshore platform currents which may have funnelled minor quantities of mature sand into the deeper basin via bypass canyons. Although platform and deeper basin evolved in a common extensional tectonic setting, the platform reflects eustatic changes of sea‐level whereas deposition in the deeper basin records syndepositional tectonics.