The enigma of rare Quaternary oolites in the Indian and Pacific Oceans: A result of global oceanographic physicochemical conditions or a sampling bias?

Gallagher, Stephen; Reuning, Lars; Himmler, Tobias; Henderiks, Jorijntje; Vleeschouwer, David De; Groeneveld, Jeroen; Lari, A. Rastegar; Fulthorpe, Craig S.; Bogus, Kara; Renema, Willem; McGregor, Helen; Kominz, Michelle A.; Auer, Gerald; Baranwal, Soma; Castañeda, S.; Christensen, Beth A; Franco, Diogo; Gurnis, Michael; Haller, Christian; He, Yuxin; Ishiwa, Takeshige; Iwatani, Hokuto; Jatiningrum, R.S.; Korpanty, Chelsea; Lee, E. Y.; Levin, E.; Mamo, Briony; McHugh, C. M.; Petrick, Benjamin; Potts, D. C.; Takayanagi, Hideko; Zhang, W.

doi:10.1016/j.quascirev.2018.09.028

Cited by 24 publications

(21 citation statements)

References 36 publications

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“…This faunal assemblage indicates original deposition on a shallow-water inner shelf, followed by reworking, winnowing, and sediment starvation during the Holocene transgression [8]. The general lack of Indian Ocean sites in which ooids are forming at present [95,96] confirms the relict character of these palimpsest outer-shelf deposits [97].…”

Section: Fossil Faunasmentioning

confidence: 80%

Provenance of Bengal Shelf Sediments: 1. Mineralogy and Geochemistry of Silt

et al. 2019

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This article illustrates a multi-technique frontier approach for the provenance study of silt-size sediments. The mineralogical composition of low-density and heavy-mineral fractions of four samples of fine to very coarse silt deposited on the Bengal shelf was analyzed separately for six different grain-size classes by combining grain counting under an optical microscope, Raman spectroscopy, and X-ray diffraction. The geochemical composition was determined on both bulk-sediment samples and on their <5-μm classes. Such a “multiple-window” approach allowed capturing the full mineralogical information contained in each sample, as well as the size-dependent intra-sample variability of all compositional parameters. The comparison between grain-size distributions obtained by different methods highlighted a notable fallacy of laser granulometry, which markedly overestimated the size of the finest mode represented by fine silt and clay. As a test case, we chose to investigate sediments of the Bengal shelf, where detritus is fed from the Meghna estuary, formed by the joint Ganga and Brahmaputra Rivers and representing the largest single entry point of sediment in the world’s oceans. The studied samples show the typical fingerprint of orogenic detritus produced by focused erosion of collision orogens. Bengal shelf silt is characterized by a feldspatho-quartzose (F-Q) composition with a Q/F ratio decreasing from 3.0 to 1.7 with increasing grain size, plagioclase prevailing over K-feldspar, and rich transparent-heavy-mineral assemblages including mainly amphibole with epidote, and minor garnet and pyroxene. Such a detrital signature compares very closely with Brahmaputra suspended load, but mineralogical and geochemical parameters, including the anomalous decrease of the Q/F ratio with increasing grain size, consistently indicate more significant Ganga contribution for cohesive fine silt. The accurate quantitative characterization of different size fractions of Bengal shelf sediments represents an essential step to allow comparison of compositional signatures characterizing different segments of this huge source-to-sink system, from fluvial and deltaic sediments of the Himalayan foreland basin and Bengal shelf to the Bengal Fan.

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Section: Fossil Faunasmentioning

confidence: 80%

Provenance of Bengal Shelf Sediments: 1. Mineralogy and Geochemistry of Silt

et al. 2019

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“…Besides abundant Ca associated with ooids and bioclasts ( Figure 2I), the outer shelf sample SO347 displays the lowest concentration in heavy metals, relatively high Zr, and low Al ( Figure 4B), suggesting effective winnowing of clay by storm-generated bottom currents. Palimpsest sand including ooids and bioclasts represents drowned beach barriers deposited during the last lowstand stage around 20 ka ( [119,120]), followed by reworking and sediment starvation during the Holocene transgression, as also indicated by growth of glaucony within foraminiferal chambers and lack of reported sites where ooids are forming at present in the Indian Ocean ( [121,122]). Protracted sediment starvation just in front of the largest deltaic sediment system on Earth indicates that throughout the Holocene sea-level rise sediment was systematically swept by tropical cyclones toward the Swatch of No Ground, and from there funneled toward the Bengal Fan ( [7]), thus systematically bypassing the outer shelf.…”

Section: Bengal Shelfmentioning

confidence: 99%

Provenance of Bengal Shelf Sediments: 2. Petrology and Geochemistry of Sand

et al. 2019

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The Bangladesh lowlands are traversed by the largest sediment flux on the planet. Detritus generated mostly in Himalayan highlands and conveyed through the Ganga–Brahmaputra rivers and Meghna estuary reaches the Bay of Bengal, where it forms a composite deltaic system. This study integrates the vast existing database on Ganga–Brahmaputra sediments of all grain sizes from clay to sand with new petrographic, mineralogical, and geochemical data on estuarine and shallow-marine sands. A large spectrum of compositional signatures was used to: (i) assess the relative supply of the Ganga and Brahmaputra rivers to estuarine and shelfal sediments; (ii) define the compositional variability of estuarine sediments and the impact exerted by hydraulic sorting and climate-related chemical weathering on provenance signals; (iii) define the compositional variability of shelf sediments and the potential hydrodynamic segregation of fast-settling heavy minerals in coastal environments and of slow-settling platy micas on low-energy outer-shelf floors; (iv) consider the potential additional mud supply from the western subaerial part of the delta formerly built by the Ganga River; and (v) draw a preliminary mineralogical comparison between fluvio-deltaic sediments and turbidites of the Bengal–Nicobar deep-sea fan, thus tracing sediment dispersal across the huge sedimentary system extending from Tibet to the equatorial Indian Ocean. All investigated mineralogical and geochemical parameters, as well as Sr and Nd isotope ratios and clay–mineral assemblages, showed a clear prevalence in sediment supply from the Brahmaputra (60–70%) over the Ganga (30–40%). Heavy-mineral suites and Sr and Nd isotope fingerprints of Bengal shelf sediments are nearly identical to those of the Brahmaputra River and Meghna estuary, also because the Brahmaputra carries almost twice as many Ca-plagioclase grains and heavy minerals including epidote than the Ganga, and these minerals control the large majority of the Sr and Nd budgets. The experience gained in modern settings can be directly extrapolated only to the recent past, because sediments older than the late Pleistocene and buried more than a few hundred meters begin to lose less durable ferromagnesian minerals by selective chemical dissolution, which makes quantitative estimates progressively less robust in more deeply buried older strata.

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“…Cementation of pellets in shallow, tropical settings is controlled by elevated alkalinity and temperature, such as found on the Bahama Banks (Bathurst, 1975;Harris, 1979;Lees, 1975;Rankey & Reeder, 2010), north-western Arabian-Persian Gulf (Gischler & Lomando, 2005), Shark Bay (Logan, 1970;Read, 1974) and on the north-western shelf of Australia (Gallagher et al, 2018;James et al, 2004) and Bora Bora (Gischler, 2011). In the studied interval, the observation of framboidal pyrite and aragonite dissolution at the shallowest occurrence of pellets (1.15 m CSF-A) indicates BSR in the near sea floor environment (Figures 6 & 7).…”

Section: Lithification Of Pelletsmentioning

confidence: 99%

“…in the shallow water lagoon of Bora Bora, in areas of elevated alkalinity and pH (Gischler, ). Ooids and peloids on the Northwest Shelf of Australia formed in shallow water under arid conditions during the mid to late Pleistocene (Christensen et al., ; Gallagher et al., ; James, Bone, Kyser, Dix, & Collins, ). In contrast to tropical settings, peloids formed as faecal pellets are the only non‐skeletal carbonate grains which occur in subtropical to cool‐water carbonate settings.…”

Section: Introductionmentioning

confidence: 99%

“…Consequently, hardened faecal pellets were described only as a very minor component from cool‐water carbonate settings, such as the Great Australian Bight and Spencer Gulf (Betzler, Saxena, Swart, Isern, & James, ; O'Connell & James, ). Peloids have been recently reported from IODP site U1460 on the subtropical Southwest Shelf of Australia (Gallagher et al., , ). The aim of this study was to analyse the origin of these peloids using modal analysis and scanning electron microscopy (SEM) equipped with an energy‐dispersive X‐ray spectrometer (SEM‐EDX).…”

Section: Introductionmentioning

confidence: 99%

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Hardened faecal pellets as a significant component in deep water, subtropical marine environments

Deik

Reuning

Petrick

et al. 2019

The Depositional Record

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Non‐skeletal carbonate grains are classically interpreted to form in shallow, tropical environments. Peloids deposited in deep, subtropical marine conditions are poorly studied. IODP site U1460 on the subtropical Carnarvon Ramp (Southwest Shelf of Australia) recovered a nearly continuous Pliocene to Recent record of outer shelf and slope sediments. The relative abundance of peloids varies between 0% and 67% of the fine to medium sand fraction, and contributes on average ~4% of all grains. The origin and composition of these peloids were investigated using scanning electron microscopy equipped with an energy‐dispersive X‐ray spectrometer, light microscopy, X‐ray diffraction and stable isotope analysis. The peloids have a uniform size and shape and are interpreted as faecal pellets. They are mainly composed of skeletal fragments such as ascidian spicules, planktic foraminifera and sponge spicules in a mud‐sized matrix containing abundant coccolith plates. Mineralogical analysis show that the pellets consist of aragonite, calcite and dolomite. The pellets have an identical mineralogical composition and skeletal assemblage as the surrounding matrix, indicating that they have formed in situ. They occur more abundantly during interglacials when the site was situated in deeper waters below the swell wave base, presumably because the pellets were protected from disintegration and therefore available for cementation. The presence of framboidal pyrite within the pellets indicates bacterial sulphate reduction (BSR). The reduction of iron by hydrogen sulphide produced during BSR decreases the pH and likely explains the observed aragonite dissolution. Aragonite dissolution likely increases the alkalinity, and in consequence causes the precipitation of calcite and dolomite cements. It is suggested here that pellets are hardened due to this early cementation close to the sea floor increasing the potential for preservation in the fossil record.

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The enigma of rare Quaternary oolites in the Indian and Pacific Oceans: A result of global oceanographic physicochemical conditions or a sampling bias?

Cited by 24 publications

References 36 publications

Provenance of Bengal Shelf Sediments: 1. Mineralogy and Geochemistry of Silt

Provenance of Bengal Shelf Sediments: 1. Mineralogy and Geochemistry of Silt

Provenance of Bengal Shelf Sediments: 2. Petrology and Geochemistry of Sand

Hardened faecal pellets as a significant component in deep water, subtropical marine environments

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