Acme and demise of the late Palaeozoic ice age: A view from the southeastern margin of Gondwana

摘要

Palaeoenvironmental reconstructions from across the globe indicate that the climatic and oceanographic changes that accompanied the Permian transition from deep icehouse to greenhouse conditions were uneven and asynchronous. Because of a paucity of well-constrained data, environmental changes in Gondwana remain poorly understood relative to tropical Pangaea. In this regard, the Permian System of eastern Australia provides a unique record of this transition along a high-latitude, open marine shelf. Not only was glaciation protracted here relative to other regions of Gondwana, but the record also spans temperate to polar palaeolatitudes, providing an opportunity to examine environmental changes along a latitudinal transect. We integrate proxies for delta O-18(seawater) palaeotemperature, pCO(2), and depositional environment to assess the evolution of nearshore conditions through the Permian. Glaciation was not continuous, but rather focused into four discrete, glacial epochs (P1-P4), each several million years in length, which alternated with nonglacial intervals of similar duration. During the Asselian-mid-Artinskian (P1-P2 time), uniform conditions along the full extent of the margin were maintained by a cold boundary current coupled with oceanic upwelling. Increased spatiotemporal variability is evident at the end of glacial P2 (mid-Artinskian), perhaps due to tectonic changes that impacted the palaeogeography of the margin. Although glaciers had disappeared by this time elsewhere in Gondwana, eastern Australia saw two additional periods of glaciation, P3 (Roadian-earliest Captianian) and P4 (early Wuchiagingian). Continued, albeit intermittent, glaciation was facilitated by drift toward higher palaeolatitudes, orogenic activity that led to the development of areas of high elevation that could serve as nucleation points for glaciers, and transient drops in atmospheric pCO(2). Variations in meltwater input exerted a strong effect on local delta O-18(seawater) values, complicating attempts to reconstruct latitudinal gradients in palaeotemperature.. Results point to atmospheric CO2 as the primary driver responsible for the dynamic climate variations evident in the record. (C) 2014 Elsevier B.V. All rights reserved.