Browsing by Author "Reimer, PJ"

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    Deglacial mesophotic reef demise on the Great Barrier Reef
    (Elsevier Science BV, 2013-12-15) Abbey, E; Webster, JM; Braga, JC; Jacobsen, GE; Thorogood, GJ; Thomas, AL; Camoin, G; Reimer, PJ; Potts, DC
    Submerged reefs are important recorders of palaeo-environments and sea-level change, and provide a substrate for modem mesophotic (deep-water, light-dependent) coral communities. Mesophotic reefs are rarely, if ever, described from the fossil record and nothing is known of their long-term record on Great Barrier Reef (GBR). Sedimentological and palaeo-ecological analyses coupled with 67 C-14 AMS and U-Th radiometric dates from dredged coral, algae and btyozoan specimens, recovered from depths of 45 to 130 m, reveal two distinct generations of fossil mesophotic coral community development on the submerged shelf edge reefs of the GBR. They occurred from 13 to 10 ka and 8 ka to present. We identified eleven sedimentary fades representing both autochthonous (in situ) and allochthonous (detrital) genesis, and their palaeo-environmental settings have been interpreted based on their sedimentological characteristics, biological assemblages, and the distribution of similar modern biota within the dredges. Facies on the shelf edge represent deep sedimentary environments, primarily forereef slope and open platform settings in palaeo-water depths of 45-95 m. Two coral-algal assemblages and one non-coral encruster assemblage were identified: 1) Massive and tabular corals including Porites, Montipora and faviids associated with Lithophylloids and minor Mastophoroids, 2) platy and encrusting corals including Porites, Montipora and Pachyseris associated with melobesioids and Sporolithon, and 3) Melobesiods and Sporolithon with acervulinids (foraminifera) and bryozoans. Based on their modem occurrence on the GBR and Coral Sea and modem specimens collected in dredges, these are interpreted as representing palaeo-water depths of <60 m, <80-100 m and >100 m respectively. The first mesophotic generation developed at modern depths of 85-130 m from 13 to 10.2 ka and exhibit a deepening succession of <60 to >100 m palaeo-water depth through time. The second generation developed at depths of 45-70 m on the shelf edge from 7.8 ka to present and exhibit stable environmental conditions through time. The apparent hiatus that interrupted the mesophotic coral communities coincided with the timing of modem reef initiation on the GBR as well as a wide-spread flux of siliciclastic sediments from the shelf to the basin. For the first time we have observed the response of mesophotic reef communities to millennial scale environmental perturbations, within the context of global sea-level rise and environmental changes. © 2013, Elsevier Ltd.
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    Late holocene sea-level fall and turn-off of reef flat carbonate production: rethinking bucket fill and coral reef growth models
    (GeoScienceWorld, 2015-02-01) Harris, DL; Webster, JM; Vila-Concejo, A; Hua, Q; Yokoyama, Y; Reimer, PJ
    Relative sea-level rise has been a major factor driving the evolution of reef systems during the Holocene. Most models of reef evolution suggest that reefs preferentially grow vertically during rising sea level then laterally from windward to leeward, once the reef flat reaches sea level. Continuous lagoonal sedimentation (“bucket fill”) and sand apron progradation eventually lead to reef systems with totally filled lagoons. Lagoonal infilling of One Tree Reef (southern Great Barrier Reef) through sand apron accretion was examined in the context of late Holocene relative sea-level change. This analysis was conducted using sedimentological and digital terrain data supported by 50 radiocarbon ages from fossil microatolls, buried patch reefs, foraminifera and shells in sediment cores, and recalibrated previously published radiocarbon ages. This data set challenges the conceptual model of geologically continuous sediment infill during the Holocene through sand apron accretion. Rapid sand apron accretion occurred between 6000 and 3000 calibrated yr before present B.P. (cal. yr B.P.); followed by only small amounts of sedimentation between 3000 cal. yr B.P. and present, with no significant sand apron accretion in the past 2 k.y. This hiatus in sediment infill coincides with a sea-level fall of ∼1–1.3 m during the late Holocene (ca. 2000 cal. yr B.P.), which would have caused the turn-off of highly productive live coral growth on the reef flats currently dominated by less productive rubble and algal flats, resulting in a reduced sediment input to back-reef environments and the cessation in sand apron accretion. Given that relative sea-level variations of ∼1 m were common throughout the Holocene, we suggest that this mode of sand apron development and carbonate production is applicable to most reef systems. Copyright © 2020 Geological Society of America
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    Morphological variation, composition and age of submerged reefs on the Great Barrier Reef
    (Geological Society of Australia, 2010-07-04) Abbey, E; Webster, JM; Jacobsen, GE; Thomas, AL; Henderson, G; Reimer, PJ; Braga, JC; Tudhope, AW; Beaman, RJ; Bridge, T; George, N
    Coral reefs are powerful indicators of environmental changes, such as sea level, salinity and sea surface temperature fluctuations. Many sites within the Indo‐Pacific and the Caribbean have been investigated, yet the Great Barrier Reef (GBR) remains largely under‐represented in early deglacial, Late Pleistocene records. IODP Expedition 325 Site Survey (Proposal 519) returned with 4200 km2 of high‐resolution multibeam bathymetry of submerged reef features on the shelf edge, revealing extensive terraces, barrier reefs, lagoons, pinnacles and palaeo‐channels. Fossil coral reef specimens were collected from these features (in situ and loose) at depths ranging from 45–160 m and dated using 14C AMS and U‐Th. Preliminary results suggest the morphology of the features and the timing of drowning are influenced by a number of complex factors, possibly including, but not limited to variations in sea level, latitude, shelf width, local weather patterns and reef community composition.
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    SHCal13 Southern Hemisphere calibration, 0–50,000 years cal BP
    (University Arizona Department Geosciences, 2016-02-09) Hogg, AG; Hua, Q; Blackwell, PG; Niu, M; Buck, CE; Guilderson, TP; Heaton, TJ; Palmer, JG; Reimer, PJ; Reimer, RW; Turney, CSM; Zimmerman, SRH
    The Southern Hemisphere SHCal04 radiocarbon calibration curve has been updated with the addition of new data sets extending measurements to 2145 cal BP and including the ANSTO Younger Dryas Huon pine data set. Outside the range of measured data, the curve is based upon the ern Hemisphere data sets as presented in IntCal13, with an interhemispheric offset averaging 43 ± 23 yr modeled by an autoregressive process to represent the short-term correlations in the offset. © 2013, by the Arizona Board of Regents on behalf of the University of Arizona.