Authigenic zeolites and their relation to silica diagenesis in ODP Site 661 sediments (Leg 108, Eastern Equatorial Atlantic)

Bohrmann, Gerhard; Stein, Rüdiger; Faugères, Jean-Claude

doi:10.1007/bf01829322

Cited by 18 publications

(6 citation statements)

References 11 publications

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“…Authigenic zeolite of the clinoptilolite/heulandite group is common in Cenozoic oceanic (hemi)pelagic sediments (e.g. Bohrmann et al ., ; Gingele & Schulz, ; Nähr et al ., ). This mineral is also common in Late Cretaceous chalk of north‐western Europe (Pomerol & Aubry, ; Louail, ; Deconinck & Chamley, ), and in some formations of the Upper Jurassic to Lower Cretaceous in southern England (Brown et al ., ), but this mineral has never been identified in Lower Jurassic sediments of north‐western Europe.…”

Section: Discussionmentioning

confidence: 99%

Climatic and sea‐level control of Jurassic (Pliensbachian) clay mineral sedimentation in the Cardigan Bay Basin, Llanbedr (Mochras Farm) borehole, Wales

2019

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Early Jurassic climate is characterized by alternating cold and warm periods highlighted by studies based notably on oxygen isotopes measured on belemnite guards and other marine invertebrate shells. These climatic changes include changes in the hydrological cycle, and consequently weathering and runoff conditions. In order to clarify the erosion and weathering conditions during the Pliensbachian, this study determined the mineralogical composition of the clay fraction of 132 samples taken from the entire stage drilled in the Llanbedr (Mochras Farm) borehole (Cardigan Bay Basin). The clay mineral assemblages are composed of various proportions of chlorite, illite, illite/smectite mixed-layers (R1 I-S), smectite and kaolinite, with possibly occasional traces of berthierine. The occurrence of abundant smectite indicates that the maximum burial temperature never exceeded 70°C. Consequently, clay minerals are considered mainly detrital, and their fluctuations likely reflect environmental changes. The variations in the proportions of smectite and kaolinite are opposite to each other. Kaolinite is particularly abundant at the base of the jamesoni Zone, in part coinciding with the d 13 C negative excursion corresponding to the Sinemurian/Pliensbachian Boundary Event, and through the davoei Zone, whilst smectite is abundant in the upper part of jamesoni and base of ibex zones and through the subnodosus/ gibbosus subzones of the margaritatus Zone. The kaolinite-rich intervals reflect an intensification of hydrolysis and an acceleration of the hydrological cycle, while the smectite-rich intervals indicate a more arid climate. The spinatum Zone is characterized by a distinct clay assemblage with abundant primary minerals, R1 I-S, kaolinite reworked from previously deposited sediments or from Palaeozoic rocks, and probably berthierine originating from contemporaneous ironstone-generating environments of shallower waters. This mineralogical change by the end of the Pliensbachian likely reflects a transition from a dominant chemical weathering to a deeper physical erosion of the continent, probably related to a significant sea-level fall consistent with a glacio-eustatic origin.

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Section: Discussionmentioning

confidence: 99%

Climatic and sea‐level control of Jurassic (Pliensbachian) clay mineral sedimentation in the Cardigan Bay Basin, Llanbedr (Mochras Farm) borehole, Wales

2019

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“…The diagenetic conditions for the zeolites formation seem to be controlled by the chemistry of the mineralogical precursor, the chemistry of interstitial water, the composition of the host sediments, and the temperature. Bohrmann et al . (1989) recognized two types of clinoptilolite, both in sediments containing high amounts of opal‐CT and in sediments where no opal‐CT was found.…”

Section: Discussionmentioning

confidence: 99%

Effects of biogenic silica on sediment compaction and slope stability on the Pacific margin of the Antarctic Peninsula

et al. 2003

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Analysis of physical properties measured on cores and on discrete samples collected by the Ocean Drilling Programme (ODP) Leg 178 on the Pacific margin of the Antarctic Peninsula reveals anomalous down‐hole curves of porosity, density, water content, and P‐wave velocity. These indicate an overall trend of increasing porosity with depth and suggest that the drifts are mostly undercompacted. In one of the two boreholes analysed, a sharp decrease in porosity, matching increasing bulk sediment density and increasing compressional velocity occurs towards the base of the hole, which corresponds to a bottom‐simulating reflector in the seismic section. Analysis of seismic reflection, down‐hole logging, geotechnical and mineralogical data from two drilling sites indicates that the observed anomalous consolidation trends are a consequence of the presence of biogenic silica (diatom and radiolarian skeletons) even with a small to moderate amount. Above the bottom‐simulating reflector, intergranular contacts among whole or broken siliceous microfossils prevent normal sediment consolidation. Diagenetic alteration of biogenic opal‐A to opal‐CT causes a dramatic reduction of intra‐ and interskeletal porosity allowing sediments to consolidate at depth. This results in overpressuring and a decrease in the effective stress. Excess fluids are expelled towards the sediment surface through near vertical, small throw normal faults extending from the diagenetic front to the seafloor and affecting the stability of the submarine slope in the form of gravitational creep along a weakened surface. This work shows how physical properties of shallow fine‐grained marine sediments can be analysed as basin‐wide indicators of biogenic silica abundance. The diagenetic alteration of siliceous microfossils is a possible cause of slope instability along world continental margins where bottom‐simulating reflectors related to silica diagenesis are present at a regional scale.

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“…The authigenic nature of the clinoptilolite is clearly demonstrated by the euhedral crystal shapes, an observation that was often documented (Bohrmann et al, 1989) and that was also demonstrated by various casts of sediment particles (mostly calcareous nannofossils) on clinoptilolite crystals from Leg 115 samples (Plate 3). In general, clinoptilolite was precipitated from silica-rich interstitial water if enough aluminium, alkali, and alkaline earth materials were available.…”

Section: Clinoptilolitementioning

confidence: 77%

Carbonate-Free Sediment Components and Aspects of Silica Diagenesis at Sites 707, 709, and 711(Leg 115, Western Indian Ocean)

Hempel¹,

Bohrmann²

1990

Proceedings of the Ocean Drilling Program, 115 Scientific Results

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From the equatorial Indian Ocean, carbonate-free portions of sediment samples of Paleocene to Miocene calcareous oozes and chalks from Sites 707, 709, and 711 were studied using X-ray diffraction measurements and the scanning electron microscope. Downhole variations in biogenic opal, quartz, barite, and clinoptilolite were investigated. The abundance patterns of these major mineral phases show several similarities and may be used for additional lithologic correlations.Variations in biogenic opal contents reflect biogenic silica productivity. Beside the general pattern, a succession in biogenic silica decrease through time is generally recorded since the Oligocene. This succession started earliest at northernmost Site 711 and latest at southernmost Site 707, including Site 709 within these two. Opal-A variations as well as the barite distribution may be influenced by the paleoposition of the sites in relation to the high-productivity zone, which today lies south of the equator. Authigenic clinoptilolite apparently formed in two different modes. In deeper sediment intervals, clinoptilolite was the last mineral phase formed associated with enhanced silica diagenesis. In late Oligocene to middle Miocene sediments, clinoptilolite was the only authigenic silica phase encountered where otherwise strong opal dissolution was observed. The sponge spicules showed special dissolution features probably related to microbiological activity. Silica concretions mainly composed of opal-CT and authigenic quartz occur in carbonate-rich environments and are formed during later diagenesis when burial depth causes the sediments to reach higher temperatures. Opal-CT concretions in carbonate-free siliceous oozes were found at Site 711 and are probably formed during an early stage of silica diagenesis.

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Authigenic zeolites and their relation to silica diagenesis in ODP Site 661 sediments (Leg 108, Eastern Equatorial Atlantic)

Cited by 18 publications

References 11 publications

Climatic and sea‐level control of Jurassic (Pliensbachian) clay mineral sedimentation in the Cardigan Bay Basin, Llanbedr (Mochras Farm) borehole, Wales

Climatic and sea‐level control of Jurassic (Pliensbachian) clay mineral sedimentation in the Cardigan Bay Basin, Llanbedr (Mochras Farm) borehole, Wales

Effects of biogenic silica on sediment compaction and slope stability on the Pacific margin of the Antarctic Peninsula

Carbonate-Free Sediment Components and Aspects of Silica Diagenesis at Sites 707, 709, and 711(Leg 115, Western Indian Ocean)

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