Climate and Sea-level changes since the last glacial maximum: Preliminary results from IODP Expedition 325 the Great Barrier Reef Environmental Change

2012 ◽  
Vol 279-280 ◽  
pp. 550
Author(s):  
Yusuke Yokoyama
Geology ◽  
2019 ◽  
Vol 48 (1) ◽  
pp. 39-43 ◽  
Author(s):  
Kazuhiko Fujita ◽  
Noriko Yagioka ◽  
Choko Nakada ◽  
Hironobu Kan ◽  
Yosuke Miyairi ◽  
...  

Abstract Reef growth patterns and the development of associated environments have been extensively studied from reef deposits from Holocene and previous interglacial highstands. However, reefs that grew during glacial lowstands are comparatively poorly understood. Here we show the formation of reef-flat and back-reef environments following rapid sea-level fall (15–20 mm yr−1 and 20–40 m in magnitude) during the Last Glacial Maximum (LGM) on the present shelf edge of the Great Barrier Reef. Sedimentological and foraminiferal analyses of unconsolidated reef sediments recovered in cores 111–140 m below sea level at Hydrographers Passage during Integrated Ocean Drilling Project (IODP) Expedition 325 reveal the occurrence of a benthic foraminiferal assemblage dominated by the genera Calcarina and Baculogypsina, which is common in modern reef-flat and back-reef environments in the Great Barrier Reef and elsewhere. This assemblage is associated with higher foraminiferal proportions in reef sediments and higher proportions of well-preserved Baculogypsina tests in the same intervals, which also characterize reef-flat environments. Radiocarbon (14C–accelerator mass spectrometry) ages of reef-flat dwelling foraminifers (n = 22), which indicate the time when these foraminifers were alive, are consistent with the timing of the two-step sea-level fall into the LGM as defined by the previously published well-dated coralgal record. This foraminiferal evidence suggests the development of geomorphically mature fringing reefs with shallow back-reef lagoons during the LGM. Our results also imply that back-reef sediment accumulation rates during the LGM lowstand were comparable to those during the Holocene highstand.


Water ◽  
2021 ◽  
Vol 13 (2) ◽  
pp. 155
Author(s):  
Giacomo Deiana ◽  
Luciano Lecca ◽  
Rita Teresa Melis ◽  
Mauro Soldati ◽  
Valentino Demurtas ◽  
...  

During the lowstand sea-level phase of the Last Glacial Maximum (LGM), a large part of the current Mediterranean continental shelf emerged. Erosional and depositional processes shaped the coastal strips, while inland areas were affected by aeolian and fluvial processes. Evidence of both the lowstand phase and the subsequent phases of eustatic sea level rise can be observed on the continental shelf of Sardinia (Italy), including submerged palaeo-shorelines and landforms, and indicators of relict coastal palaeo-environments. This paper shows the results of a high-resolution survey on the continental shelf off San Pietro Island (southwestern Sardinia). Multisensor and multiscale data—obtained by means of seismic sparker, sub-bottom profiler chirp, multibeam, side scan sonar, diving, and uncrewed aerial vehicles—made it possible to reconstruct the morphological features shaped during the LGM at depths between 125 and 135 m. In particular, tectonic controlled palaeo-cliffs affected by landslides, the mouth of a deep palaeo-valley fossilized by marine sediments and a palaeo-lagoon containing a peri-littoral thanatocenosis (18,983 ± 268 cal BP) were detected. The Younger Dryas palaeo-shorelines were reconstructed, highlighted by a very well preserved beachrock. The coastal paleo-landscape with lagoon-barrier systems and retro-littoral dunes frequented by the Mesolithic populations was reconstructed.


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