Depositional environments beneath the shelf-edge slopes of the Great Barrier Reef, inferred from foraminiferal assemblages; IODP Expedition 325

Online Access: Get full text
doi: 10.1016/j.palaeo.2018.10.033
Author(s): Yagioka, Noriko; Nakada, Choko; Fujita, Kazuhiko; Kan, Hironobu; Yokoyama, Yusuke; Webster, Jody M.
Author Affiliation(s): Primary:
University of the Ryukyus, Graduate School of Engineering and Science, Nishihara, Japan
Kyushu University, Japan
University of Tokyo, Japan
University of Sydney, Australia
Volume Title: Palaeogeography, Palaeoclimatology, Palaeoecology
Source: Palaeogeography, Palaeoclimatology, Palaeoecology, Vol.514, p.386-397. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0031-0182 CODEN: PPPYAB
Note: In English. 69 refs.; illus., incl. 2 tables, sketch map
Summary: To understand sea-level changes since the Last Glacial Maximum (LGM) and their effects on coral reef systems, the shelf-edge slopes of the Great Barrier Reef (GBR) were cored during the Integrated Ocean Drilling Program (IODP) Expedition 325. Recovered unconsolidated sediments beneath the submerged shelf edge reefs contain abundant foraminiferal tests, which record changes in depositional environments and paleo-water depths. A total of 177 sediment samples were collected from 17 holes along three transects located within two geographical areas (Noggins Pass and Hydrographers Passage), and were analyzed to determine stratigraphic changes in foraminiferal assemblages (2-0.5 mm size fraction). Results show that four foraminiferal assemblages (A, B, C and D) are delineated by multivariate analyses (Q-mode cluster analysis and non-metric multidimensional scaling: NMDS), and these assemblages correspond to a back-reef to reef margin zone (0-10 m deep; Assemblage A), an upper photic zone (10-30 m deep) associated with hard substrates (Assemblage B), an intermediate to lower photic zone (30-90 m deep) characterized by soft substrates (Assemblage C), and a lower photic zone (90-130 m deep) only found in modern shelf slopes (Assemblage D). Gradual shifts in these four foraminiferal assemblages superimposed on a two-dimensional NMDS ordination mainly reflect water-depth gradients and the relative dominance of two substrate types (hard and soft substrates). Pre-LGM (older than Marine Isotope Stage 3: ≥MIS3) sediments along transects at Hydrographers Passage were deposited at intermediate to lower photic zones. In contrast, relatively shallow-water sequences found in ≥MIS3 deposits at Noggins Pass likely owe their origin to either turbidite and/or land slide processes. The lack of Assemblage D in ≥MIS3 deposits from all transects could be related to lowering temperature and/or increasing terrestrial influences (i.e. more light attenuation). Shallowing upward sequences found in LGM (MIS 2) deposits at Hydrographers Passage are likely related to stepwise sea-level falls to the full extent of the LGM. These foraminifer-based paleoenvironmental interpretations suggest that the GBR shelf edge slopes have changed their depositional environments continuously in response to sea-level fluctuations during the last glacial cycle.
Year of Publication: 2019
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 24 Surficial Geology, Quaternary Geology; Anthozoa; Assemblages; Cenozoic; Cluster analysis; Cnidaria; Coral Sea; Cores; Depositional environment; Expedition 325; Foraminifera; Geotraverses; Great Barrier Reef; Great Barrier Reef Environmental Changes; Holocene; Integrated Ocean Drilling Program; Last glacial maximum; Marine environment; Multivariate analysis; Pacific Ocean; Paleoenvironment; Quaternary; Reef environment; Shelf environment; Size; Slope environment; South Pacific; Southwest Pacific; Statistical analysis; West Pacific
Coordinates: S195100 S152800 E1502900 E1454900
Record ID: 2019026749
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands