Search Results (3)

The Upper Carboniferous strata in the eastern Qaidam Basin, comprising several hundred meters of thick, mixed clastic–carbonate successions that have been little reported or explained, provide an excellent geological record of paleoenvironmental and paleo-sea level changes during the Late Carboniferous icehouse period. This tropical carbonate–clastic system offers critical constraints for correlating equatorial sea level responses with high-latitude glacial cycles during the Late Paleozoic Ice Age. Based on detailed outcrop observations and interpretations, five facies assemblages, including fluvial channel, tide-dominated estuary, wave-dominated shoreface, tide-influenced delta, and carbonate-dominated marine, have been identified and organized into cyclical stacking patterns. Correspondingly, four third-order sequences were recognized, each composed of lowstand, transgressive, and highstand system tracts (LST, TST, and HST). LST is generally dominated by fluvial channels as a result of river juvenation when the sea level falls. The TST is characterized by tide-dominated estuaries, followed by retrogradational, carbonated-dominated marine deposits formed during a period of sea level rise. The HST is dominated by aggradational marine deposits, wave-dominated shoreface environments, or tide-influenced deltas, caused by subsequent sea level falls and increased debris supply. The sequence stratigraphic evolution and geochemical records, based on carbon and oxygen isotopes and trace elements, suggest that during the Late Carboniferous period, the eastern Qaidam Basin experienced at least four significant sea level fluctuation events, and an overall long-term sea level rise. These were primarily driven by the Gondwana glacio-eustasy and regionally ascribed to the Paleo-Tethys Ocean expansion induced by the late Hercynian movement. Assessing the history of glacio-eustasy-driven sea level changes in the eastern Qaidam Basin is useful for predicting the distribution and evolution of mixed cyclic succession in and around the Tibetan Plateau. Full article

The Ria de Coruña (NW Spain) is a wide estuary recently formed by the flooding of the Mero fluvial valley lowlands during the last postglacial transgression. During the last glacial episode, with the sea level located more than 100 m below the current one, the final section of the Mero river and lateral tributaries contributed numerous deposits that the postglacial rise in sea level has partially flooded. Until now, the presence of these alluvial deposits disconnected from the main network by the Holocene marine transgression had been misinterpreted, especially for lack of an absolute chronology that would place them in an adequate paleoclimatic context. For the first time, a deposition age was assessed in this work by optically stimulated luminescence (OSL) dating back from 128 ka to 51 ka. Full article

Numerous sandy deposits, interpreted as the remains of old climbing dunes, are preserved on the cliffy coast of Galicia (northwest Spain). These deposits can be found both in open coastal areas and in the interior of the Galician Rias. In this paper, a formation age is established for four aeolianite outcrops dating back to 166 ± 9 ka, 131 ± 6 ka, 128 ± 18 ka and 62 ± 3 ka, using the IRSL₂₉₀ signal of feldspars. These sands were mobilised by coastal winds from a sea level lower than the current one during MIS6 and MIS4. The sea level fall during these regressive episodes shifted the coastline several kilometres away from its current position. This favoured the action of the wind blowing over the emerged coastal strip, which acted as a source area for aeolian sands. During warmer episodes, such as the Eemian and the Holocene, the advance of the sands onto the coast was progressively reduced as the sea level rose and the oceanic waters flooded the continental shelf. Full article