Hardened faecal pellets as a significant component in deep water, subtropical marine environments
Abstract 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 Pl...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
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Wiley
2019-06-01
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| Series: | The Depositional Record |
| Subjects: | |
| Online Access: | https://doi.org/10.1002/dep2.64 |
| _version_ | 1818048353201553408 |
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| author | Hanaa Deik Lars Reuning Benjamin Petrick Hideko Takayanagi |
| author_facet | Hanaa Deik Lars Reuning Benjamin Petrick Hideko Takayanagi |
| author_sort | Hanaa Deik |
| collection | DOAJ |
| description | Abstract 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. |
| first_indexed | 2024-12-10T10:20:20Z |
| format | Article |
| id | doaj.art-864b467036e648df8a39b2217f78a9de |
| institution | Directory Open Access Journal |
| issn | 2055-4877 |
| language | English |
| last_indexed | 2024-12-10T10:20:20Z |
| publishDate | 2019-06-01 |
| publisher | Wiley |
| record_format | Article |
| series | The Depositional Record |
| spelling | doaj.art-864b467036e648df8a39b2217f78a9de2022-12-22T01:52:53ZengWileyThe Depositional Record2055-48772019-06-015234836110.1002/dep2.64Hardened faecal pellets as a significant component in deep water, subtropical marine environmentsHanaa Deik0Lars Reuning1Benjamin Petrick2Hideko Takayanagi3Energy and Mineral Resources Group Geological Institute, RWTH Aachen University Aachen GermanyEnergy and Mineral Resources Group Geological Institute, RWTH Aachen University Aachen GermanyMax‐Planck‐Institute for Chemistry Mainz GermanyInstitute of Geology and Paleontology, Graduate School of Science Tohoku University Sendai JapanAbstract 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.https://doi.org/10.1002/dep2.64Australian Shelfearly cementationIODPnon‐skeletal grainpeloidsubtropical carbonate |
| spellingShingle | Hanaa Deik Lars Reuning Benjamin Petrick Hideko Takayanagi Hardened faecal pellets as a significant component in deep water, subtropical marine environments The Depositional Record Australian Shelf early cementation IODP non‐skeletal grain peloid subtropical carbonate |
| title | Hardened faecal pellets as a significant component in deep water, subtropical marine environments |
| title_full | Hardened faecal pellets as a significant component in deep water, subtropical marine environments |
| title_fullStr | Hardened faecal pellets as a significant component in deep water, subtropical marine environments |
| title_full_unstemmed | Hardened faecal pellets as a significant component in deep water, subtropical marine environments |
| title_short | Hardened faecal pellets as a significant component in deep water, subtropical marine environments |
| title_sort | hardened faecal pellets as a significant component in deep water subtropical marine environments |
| topic | Australian Shelf early cementation IODP non‐skeletal grain peloid subtropical carbonate |
| url | https://doi.org/10.1002/dep2.64 |
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