Cool-water carbonate sedimentology and eustasy; Pleistocene upper slope environments, Great Australian Bight (Site 1127, ODP LEG 182)

Betzler, Christian; Saxena, S.; Swart, Peter K.; Isern, Alexandra R; James, Noël P.

doi:10.1016/j.sedgeo.2004.11.008

Cited by 19 publications

(16 citation statements)

References 32 publications

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“…It was shown that Recent and Pleistocene cool‐water carbonates may have aragonite contents of 30 to 80% (Nelson & Hancock, 1984; Gillespie & Nelson, 1997; Betzler et al. , 2005; James et al.…”

Section: Discussionmentioning

confidence: 99%

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Late Pleistocene and Holocene cool‐water carbonates of the Western Mediterranean Sea

Betzler¹,

Braga

Jaramillo‐Vogel³

et al. 2011

Sedimentology

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Post-glacial, neritic cool-water carbonates of the Western Mediterranean Sea were examined by means of hydroacoustic data, sediment surface sampling and vibrocoring to unravel geometries and to reconstruct sedimentary evolution in response to the last sea-level rise. The analysed areas, located on the Alboran Ridge, in the Bay of Oran, and at the southern shelf of the island of Mallorca, are microtidal and bathed by oligotrophic to weakly mesotrophic waters. Seasonal water temperature varies between 13°C and 27°C. Echosounder profiles show that the Bay of Oran and the southern shelf of Mallorca are distally steepened ramps, while the Alboran Ridge forms a steep-flanked rugged plateau around the Alboran Island. In the three areas, an up to 10 m thick post-glacial sediment cover overlies an unconformity. In Oran and Mallorca, stacked lowstand wedges occur in water depths of 120 to 130 m. On the Alboran Ridge and in the Bay of Oran, highstand wedges occur at 35 to 40 m. Up to 5 m long cores of upper Pleistocene to Holocene successions were recovered in water depths between 40 and 81 m. Deposits contain more than 80% carbonate, with mixed carbonate-volcaniclastics in the lower part of some cores in Alboran. The carbonates consist of up to 53% of aragonite and up to 83% of high magnesium calcite. Radiocarbon dating of bivalve shells, coralline algae and serpulid tubes indicates that deposits are as old as 12 400 cal yr bp. The carbonate factories in the three areas are dominated mostly by red algae, but some intervals in the cores are richer in bivalves. A facies rich in the gastropod Turritella, reflecting elevated surface productivity, is restricted to the Mallorca Shelf. Rhodoliths occur at the sediment surface in most areas at water depths shallower than 70 m; they form a 10 to 20 cm thick veneer overlying rhodolith-poor bioclastic sediments which, nonetheless, contain abundant red algal debris. This rhodolith layer has been developing for the past 800 to 1000 years. Similar layers at different positions in the cores are interpreted as reflecting in situ growth of rhodoliths at times of reduced net sedimentation. Sedimentary successions in the cores record the post-glacial sea-level rise and the degree of sediment exposure to bottom currents. Deepening-upward trends in the successions are either reflected by shallow to deep facies transitions or by a corresponding change of depth-indicative red Sedimentology (2011) 58, 643-669 643 algae. There are only weak downcore variations of carbonate mineralogy, which indicate that no dissolution or high magnesium to low magnesium calcite neomorphism occurs in the shallow subsurface. These new data support the approach of using the Recent facies distribution for interpretation of past cool-water, low-energy, microtidal carbonate depositional systems. Hydroacoustic data show that previous Pleistocene transgressive and highstand inner ramp deposits and wedges were removed during sea-level lowstands and accumulated downslope as stacked lowstand wedges; this suggests that, under...

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Section: Discussionmentioning

confidence: 99%

“…Therefore, the diagenetic potential of these carbonates may be lower than that of the deposits accumulated in the sediment wedges of the shaved cool‐water carbonate shelf type (James et al. , 1994), which contain up to 36% of aragonite (Betzler et al. , 2005).…”

Section: Discussionmentioning

confidence: 99%

Late Pleistocene and Holocene cool‐water carbonates of the Western Mediterranean Sea

Betzler¹,

Braga

Jaramillo‐Vogel³

et al. 2011

Sedimentology

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“…This could result either from intense reworking of grains or be a primary feature. Tunicate spicules, for example, are abundant sediment constituents in some recent heterozoan settings Betzler et al 2005), forming up to 36% of the sediment volume. Tunicates possess small aragonitic spicules in their tissues, which disintegrate upon death.…”

Section: Origin Of the Aragonitementioning

confidence: 99%

Missing Aragonitic Biota and the Diagenetic Evolution of Heterozoan Carbonates: A Case Study from the Oligo-Miocene of the Central Mediterranean

Knoerich

Mutti

2006

Journal of Sedimentary Research

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Several previous studies have addressed the diagenetic evolution of heterozoan carbonate assemblages. Generally it is assumed that early diagenetic processes in heterozoan settings are mainly destructive, including abrasion and dissolution on the sea floor. Constructive diagenesis (cementation) is delayed to later stages in the burial environment, with pressure solution of calcitic grains acting as a cement source. This paper presents a study of Oligo-Miocene inner-to outer-ramp heterozoan carbonates from the Central Mediterranean (Maltese Islands and Sicily) indicating that early diagenetic processes are more important than previously assumed.Four to five different cement types, including fibrous, two types of epitaxial, bladed and blocky cement, are distinguished based on transmitted light microscopy. Cathodoluminescence microscopy allowed a differentiation between primary high-Mg calcitic (fibrous and epitaxial cement I) and primary low-Mg calcitic (epitaxial cement II, bladed and blocky) cements. Stableisotope data indicate cement precipitation from marine, marine-derived, and meteoric waters. Trace-element analyses point to cementation in an open system (Maltese Islands) and a closed system (Sicily).Our investigations show that the majority of constructive diagenetic processes in these rocks occurs rather early in the shallow, marine burial environment, which is transitional between the marine seafloor and the deep-burial diagenetic environment. The main cement source in this environment is assumed to be aragonite. We suggest careful consideration of the importance of aragonitic components in fossil heterozoan settings, which seem to be more abundant than previously assumed and can act as a major early cement source. Due to the low preservation potential of these components, detailed geochemical studies are necessary to detect aragonite as the cement source. Our findings also have implications when considering the reservoir qualities of these rocks, because primary porosity can be occluded early and secondary porosity is not preserved.

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“…However, under the influence of waves and currents, these faecal pellets typically disintegrate into mud‐sized particles and are therefore not preserved as grains (Farrow & Fyfe, ). 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., , ).…”

Section: Introductionmentioning

confidence: 99%

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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Cool-water carbonate sedimentology and eustasy; Pleistocene upper slope environments, Great Australian Bight (Site 1127, ODP LEG 182)

Cited by 19 publications

References 32 publications

Late Pleistocene and Holocene cool‐water carbonates of the Western Mediterranean Sea

Late Pleistocene and Holocene cool‐water carbonates of the Western Mediterranean Sea

Missing Aragonitic Biota and the Diagenetic Evolution of Heterozoan Carbonates: A Case Study from the Oligo-Miocene of the Central Mediterranean

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

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