Geologische Untersuchungen an Sedimenten des indisch-pakistanischen Kontinentalrandes (Arabisches Meer)

Schott, W.; Stackelberg, Ulrich von; Eckhardt, F.-J.; Mattiat, B.; Peters, J.; Zobel, B

doi:10.1007/bf01820944

Cited by 14 publications

(8 citation statements)

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“…Where pyrite is found within the tests of planktonic and nonindigenous benthonic foraminifera, it could possibly be assigned to a source on the outer shelf or upper continental slope. This would be in accordance with the zone of low oxygenation and reduced bottom sediments in these depths today (Schott et al, 1970). Fleisher (personal communication) has pointed out that some interbeds contain rare shallow-water foraminifera represented by neritic benthics and juvenile planktonics.…”

Section: Provenance Of the Deep-sea Sand Particlessupporting

confidence: 70%

Sedimentation of Coarser Grained Interbeds in the Arabian Sea and Sedimentation Processes of the Indus Cone

Jipa¹,

Kidd²

1974

Initial Reports of the Deep Sea Drilling Project

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This sedimentologic study is based on material sampled during Leg 23 in the Arabian Sea. It has shown that, in the sedimentary history of the Indus Cone, the deposition of terrigenous fine silt and clay on a major scale has been an almost permanent feature of the environment. The classic concept of the development of submarine fans by spasmodic deposition from turbidity currents receives critical appraisal. The turbidity current mechanism alone is insufficient to explain the sedimentary sequences encountered. A variety of sedimentation mechanisms have combined in building up the great thickness of Indus Cone sediment. It appears that the major contribution of terrigenous material has been by the deposition of fine silt and clay from turbid flows originating in shelf areas. The possibilities of these flows being of the suspended type, entering the water column along water density interfaces, or of bottom-following type, are discussed. Other fine sediments from winds and surface currents combine with the flows to supply a continuous silty clayey suspension to the surface of the submarine fan. Graded interbeds of coarse silt and fine sand within the sedimentary sequence are probably the result of intermittent events involving turbidity current activity. Most of the sands have originated from the mouth of the Indus River, but others can be shown to have come from other sources, for example, farther south on the Indian Shelf and the Laccadive-Maldive Ridge. Evidence of more permanent bottom current activity is presented. This seems to most readily fit an overall Indus Cone development by a sedimentation process involving semipermanent bottom following turbid flows of fine sediment together with spasmodic turbidity current deposition of "coarse silt and fine sand. Minor intervals of pelagic sediments mixed with land-derived fine clastic material indicate long periods when the turbid flow mechanism was less active. This could have been due to restricted Indus River supply or to climatic changes.

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Section: Provenance Of the Deep-sea Sand Particlessupporting

confidence: 70%

Sedimentation of Coarser Grained Interbeds in the Arabian Sea and Sedimentation Processes of the Indus Cone

Jipa¹,

Kidd²

1974

Initial Reports of the Deep Sea Drilling Project

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“…However, at the Pakistan margin, benthic organic carbon content of surface sediments did not show a decreasing trend with water depth, but increased within the core OMZ. It has been suggested that downslope redistribution of shelf sediments and increased preservation of organic carbon under anoxic conditions have caused the high organic carbon content in the core OMZ (Schott et al, 1970). Indeed, the highest organic carbon content was found along with the highest C:N ratio at the bottom of the OMZ (station 16), which hints toward the assumption that the organic matter is more refractory.…”

Section: Discussionmentioning

confidence: 99%

Benthic Nitrogen Loss in the Arabian Sea Off Pakistan

et al. 2012

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A pronounced deficit of nitrogen (N) in the oxygen minimum zone (OMZ) of the Arabian Sea suggests the occurrence of heavy N-loss that is commonly attributed to pelagic processes. However, the OMZ water is in direct contact with sediments on three sides of the basin. Contribution from benthic N-loss to the total N-loss in the Arabian Sea remains largely unassessed. In October 2007, we sampled the water column and surface sediments along a transect cross-cutting the Arabian Sea OMZ at the Pakistan continental margin, covering a range of station depths from 360 to 1430 m. Benthic denitrification and anammox rates were determined by using 15N-stable isotope pairing experiments. Intact core incubations showed declining rates of total benthic N-loss with water depth from 0.55 to 0.18 mmol N m−2 day−1. While denitrification rates measured in slurry incubations decreased from 2.73 to 1.46 mmol N m−2 day−1 with water depth, anammox rates increased from 0.21 to 0.89 mmol N m−2 day−1. Hence, the contribution from anammox to total benthic N-loss increased from 7% at 360 m to 40% at 1430 m. This trend is further supported by the quantification of cd1-containing nitrite reductase (nirS), the biomarker functional gene encoding for cytochrome cd1-Nir of microorganisms involved in both N-loss processes. Anammox-like nirS genes within the sediments increased in proportion to total nirS gene copies with water depth. Moreover, phylogenetic analyses of NirS revealed different communities of both denitrifying and anammox bacteria between shallow and deep stations. Together, rate measurement and nirS analyses showed that anammox, determined for the first time in the Arabian Sea sediments, is an important benthic N-loss process at the continental margin off Pakistan, especially in the sediments at deeper water depths. Extrapolation from the measured benthic N-loss to all shelf sediments within the basin suggests that benthic N-loss may be responsible for about half of the overall N-loss in the Arabian Sea.

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“…The bulk of the sedimentary components are biogenic and pelagic in origin. Planktonic foraminifera are better preserved during upper Miocene and Pleistocene than during Pliocene suggesting, along with the preservation pattern of the siliceous fossils, that the reduced oxygen content in the northern Indian Ocean (Wyrtki, 1971) was subject to major fluctuations (Schott et al, 1970;Stackelberg, 1972). This might be correlated to the almost synchronous appearance or disappearance of burrowing/ mottling in the sediments (Figure 7, see Olausson and Olsson, 1969).…”

Section: Gulf Of Aden Sitesmentioning

confidence: 99%

Sediment Coarse Fractions from the Western Indian Ocean and the Gulf of Aden (Deep Sea Drilling Project, Leg 24)

Thiede¹

1974

Initial Reports of the Deep Sea Drilling Project

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Hemipelagic sediments in the Gulf of Aden, pelagic deep-water deposits in the Somali Basin and pelagic shallow-water sequences in the central Indian Ocean were penetrated and recovered during Leg 24 of the Deep Sea Drilling Project. The coarse fractions from these sediments have been studied. They have provided evidence that the Gulf of Aden has existed at least since middle Miocene as an ocean basin with typical hemipelagic sediments (high total sedimentation rates, high terrigenous input, high contents of organic carbon, high sedimentation rates of calcareous nannoplankton and planktonic foraminifera, high proportion of benthic fossils, abundant fish remains) suggesting its water masses to have been very fertile. The region had an arid climate during Miocene and Pleistocene times, while it seems to have been less dry during Pliocene (plant debris). An elevated ridge crest not accessible to coarse sediment components from both sides of the gulf had already been developed in the Miocene. The region now occupied by the >5000-meter-deep Alula-Fartak Trench which offsets Sheba Ridge seems to have been passable for sediment transport from the Arabian side of the gulf to the southeast during Pliocene. Upper Cretaceous deposits above the Somali Basin basement east of Chain Ridge are already true pelagic sediments. The preservation of calcareous sediment components of both deep Somali Basin sites suggests that a large portion has been replaced from areas of shallower water depths. Pliocene sediments east of Chain Ridge contain shallow-water-derived components which may have come either from the Gulf of Aden or from an area northeast of Carlsberg Ridge. The central Indian Ocean sites contain early Tertiary to Quaternary pelagic oozes and chalks. The sediments of all three sites are pertinent to the equatorial high production belt thus precluding major geographic readjustments of that piece of oceanic crust in a north-south direction since early Tertiary. The degree of fragmentation of planktonic foraminifera offers a useful tool for determining paleodepth although these sites were nearly always well above the calcium carbonate compensation depth. This is important for the interpretation of vertical sea-floor movements in connection with shifts of the spreading centers. The pattern of preservation of planktonic foraminifera also shows that a high proportion of the recovered sediments are displaced. This is substantiated by the joint occurrence of well-preserved planktonic foraminifera and true shallow-water-derived components in coarse-grained horizons in a matrix of poorly preserved calcareous oozes.

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Geologische Untersuchungen an Sedimenten des indisch-pakistanischen Kontinentalrandes (Arabisches Meer)

Cited by 14 publications

References 0 publications

Sedimentation of Coarser Grained Interbeds in the Arabian Sea and Sedimentation Processes of the Indus Cone

Sedimentation of Coarser Grained Interbeds in the Arabian Sea and Sedimentation Processes of the Indus Cone

Benthic Nitrogen Loss in the Arabian Sea Off Pakistan

Sediment Coarse Fractions from the Western Indian Ocean and the Gulf of Aden (Deep Sea Drilling Project, Leg 24)

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