Petrology and Geochemistry of Silicified Upper Miocene Chalk, Costa Rica Rift, Deep Sea Drilling Project Leg 69

Hein, James R.; Sancetta, Constance; Morgenson, L.A.

doi:10.2973/dsdp.proc.69.116.1983

Cited by 15 publications

(12 citation statements)

References 23 publications

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“…Similar interpretations have been made from DSDP sediments (Heath 1973;Garrison et al 1975;Keene 1975;Hein et al 1983). The advanced stage of silicification in Zones I and II make inferences as to chertburrow relationships difficult.…”

Section: The Relationship Of Chert and Dolomite To Trace Fossilssupporting

confidence: 61%

“…Micrites that contain abundant silica, commonly indicated by a high degree of induration and a conchoidal fracture, are termed siliceous micrites. Chert is a dense, hard, vitreous rock, with a conchoidal fracture, which consists of one or several forms of microcrystalline or cryptocrystalline authigenic silica (Lancelot 1973;Hein et al 1983). Chert nodules are three-dimensional bodies of chert which are <l-2 m long, rounded or lensoid, and contained in carbonate or detrital sediments.…”

Section: Terminologymentioning

confidence: 99%

“…10A). Large rhombic or blocky crystals may also result from replacement of original void-filling sparry calcite cement or from pseudomorphic replacement of foraminiferal tests (see also Hein et al 1981Hein et al , 1983. The smaller size of pores and carbonate grains, and impedance of crystal growth by the presence of other crystals in the micrite matrix, appears to result in smaller authigenic quartz crystals.…”

Section: Semmentioning

confidence: 99%

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Sedimentology and petrography of early diagenetic chert and dolomite in the Late Cretaceous‐early Tertiary Amuri Limestone Group, eastern Marlborough, New Zealand

Lawrence

1993

New Zealand Journal of Geology and Geophysics

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The dominantly micritic Amuri Limestone Group of eastern Marlborough, New Zealand, consists of six regionally extensive units: the Mead Hill Formation, Teredo Limestone Formation, Lower Limestone Formation, Middle Limestone Formation, and the Lower and Upper Marl Formations, which were deposited in a northwest-trending trough. Six separate diagenetic zones (I-VI) are recognised, based on visually estimated proportions of chert, dolomite, or limestone. Zones I-V occur in the Mead Hill to Lower Limestone Formations, and Zone VI occurs in the Middle Limestone Formation. There is no chert or dolomite in the two Marl formations. The bulk of the chert and dolomite occurs in the basin centre (mainly in the Mead Hill Formation) where the limestone is thickest, but decreases in abundance stratigraphically upwards and towards the basin margins. Zone I consists almost entirely of chert which is either detrital rich or detrital poor. Zones II and IV consist of chert and dolomite in approximately equal proportions. Zones III and VI contain varying proportions of chert and limestone. Zone V is a thin, chertified, fine sandstone-mudstone of limited extent. Sulphide nodules, usually <10 mm in diameter, are common in all zones. Chert usually forms discontinuous nodular beds or nodules. Some elongated chert nodules which may be in excess of 2 m (chert bands) are found near the top of the chert sequence. Dolomite occurs as <1 mm diameter rhombohedra in discontinuous chert-cemented beds and lenses. The common pinch and swell morphology displayed throughout most zones results from differential compaction of relatively chert-free limestone, or dolomite, around chert nodules. Stylolites are generally absent, but where present they are deflected around chert nodules, indicating chert formation prior to stylolitisation.In thin section, Zone II dolomites contain inclusions arranged in cloudy-centre clear-rim patterns. Zone IV dolomite has inclusions arranged in diagonal planes. Both dolomite types are associated with abundant disseminated pyrite. All cherts consist of microcrystalline or cryptocrystalline quartz or chalcedony, with common disseminated pyrite. Petrographic evidence and δ 18 O data indicate that the Received 20 February 1992; accepted 19 November 1992 dolomite formed at temperatures <60°C, probably in the upper sediment column. The presence of pyrite suggests that dolomite formed in association with sulphate reduction. The δ 18 O composition of the chert is very similar to that of the dolomite, implying that chert formation may have occurred at similar depths and times in the sediment as the dolomite. The association of pyrite with chert suggests that sulphate reduction may also have promoted silica nucleation. Therefore, the sedimentological and petrographic evidence is consistent with the early nucleation of both chert and dolomite. G92009

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Section: The Relationship Of Chert and Dolomite To Trace Fossilssupporting

confidence: 61%

Section: Terminologymentioning

confidence: 99%

Section: Semmentioning

confidence: 99%

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Sedimentology and petrography of early diagenetic chert and dolomite in the Late Cretaceous‐early Tertiary Amuri Limestone Group, eastern Marlborough, New Zealand

Lawrence

1993

New Zealand Journal of Geology and Geophysics

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“…X-ray-diffraction measurements performed aboard ship identified the chert samples as composed of cryptocrystalline quartz. Quartz is the end product of the oceanic silica diagenesis series that starts with biogenic opal-A, converting to opal-CT, and eventually totally recrystallizing as quartz (Wise and Weaver, 1974;Hein et al, 1983).…”

Section: Laboratory Studies Samplesmentioning

confidence: 99%

Seismic Properties and Reflectivity of North Pacific Ocean Cherts

Wilkens¹,

Christensen²,

Collins³

1993

Proceedings of the Ocean Drilling Program

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Identification of a sediment/basement contact using seismic reflection recordings has proven to be extremely difficult in wide areas of the North Pacific Ocean owing to the presence of massive, highly reflective chert layers within the sediment column. Leg 136 of the Ocean Drilling Program recovered coherent pieces of chert of sufficient size for the first comprehensive laboratory measurements of the seismic properties of this material. Compressional-wave velocities of six samples at 40-MPa confining pressure averaged 5.33 km/s, whereas shear-wave velocities at the same pressure averaged 3.48 km/s. Velocities were independent of porosity, which ranged from 5% to 13%, suggesting that pores within the samples were mostly high aspect ratio vugs as opposed to low aspect ratio cracks. Back-scattered electron images made with a scanning electron microscope confirmed this observation. Acoustic impedances were calculated for the chert samples and from shipboard measurements of the red clay sediment overlying the chert layers. An extremely large compressional-wave reflection coefficient (0.73) characterized the interface between the two lithologies. A synthetic seismogram was calculated using chert and typical pelagic carbonate properties to illustrate the influence of chert layers on a marine seismic-reflection section. Compressional-wave to shear-wave velocity ratios of the chert samples (Vp/Vç =1.53) are close to that of single-crystal quartz in spite of variable porosity. Shear-wave reflection coefficients are estimated to be approximately 0.94. A compressional-wave reflection coefficient for a basement/sediment (carbonate) interface is estimated to be approximately 0.50, significantly less than that of sediment/chert. (Fig. 1). The major objective of Leg 136 was to establish a test site for the Ocean Seismic Network (OSN)-a reentry hole drilled into the oceanic basement for placement of a downhole seismometer . Previous attempts to reach basement during the Deep Sea Drilling Project had been frustrated by layers of chert in the sedimentary column that proved impenetrable with the technology available (Winterer, Riedel, et al., 1971). Leg 136 was able to reach basement at Site 843, although severe drilling problems (high torque on the drill string, poor recovery) were encountered owing to the cherts, and recovery was limited for most of the sedimentary section to cherts in wash cores. INTRODUCTIONChert layers within the sediments posed another problem familiar in the North Pacific Ocean. Reflection seismic records did not reveal two-way traveltime to the sediment/volcanic basement interface because of the extremely reflective nature of the chert-sediment layers (Collins et al., 1992). Reflections were seen as deep as 0.5 s below the sediment surface, although expanding-spread profile data collected earlier in the area suggested a basement depth of 0.26 s (Brocher and ten Brink, 1987;Lindwall, 1991). Data from site surveys illustrate the reverberant nature of the reflection records (Fig. 2).Cherts layers have...

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“…Boron is considered to be a biogenic indicator and is found mainly in sponge spicules, which are associated with shallow-water deposits (Hein et al, 1981(Hein et al, , 1982Truscott and Shaw, 1983). No shallow-water sediments were drilled on Leg 129, and sponge spicules are extremely rare, only observed in sandstone and chalk turbidites that were redeposited from shallow water.…”

Section: Boronmentioning

confidence: 99%

Sedimentological and Geochemical Characteristics of Leg 129 Siliceous Deposits

Karl¹,

Wandless²,

Karpoff³

1992

Proceedings of the Ocean Drilling Program

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Siliceous deposits drilled on Ocean Drilling Program Leg 129 accumulated within a few degrees of the equator during the Jurassic through early Tertiary, as constrained by paleomagnetic data. During the Jurassic and Early Cretaceous, radiolarian ooze, mixed with a minor amount of pelagic clay, was deposited near the equator, and overall accumulation rates were moderate to low. At a smaller scale, in more detail, periods of relatively higher accumulation rates alternated with periods of very low accumulation rates. Higher rates are represented by radiolarite and limestone; lower rates are represented by radiolarian claystone. Our limited data from Leg 129 suggests that accumulation of biogenic deposits was not symmetrical about the equator or consistent over time. In the Jurassic, sedimentation was siliceous; in the Cretaceous there was significant calcareous deposition; in the Tertiary claystone indicates significantly lower accumulation rates at least the northern part of the equatorial zone. Accumulation rates for Leg 129 deposits in the Cretaceous were higher in the southern part of the equatorial zone than in the northern part, and the southern side of this high productivity zone extended to approximately 15°S, while the northern side extended only to about 5°N.Accumulation rates are influenced by relative contributions from various sediment sources. Several elements and element ratios are useful for discriminating sedimentary sources for the equatorial depositional environments. Silica partitioning calculations indicate that silica is dominantly of biogenic origin, with a detrital component in the volcaniclastic turbidite units, and a small hydrothermal component in the basal sediments on spreading ridge basement of Jurassic age at Site 801. Iron in Leg 129 sediments is dominantly of detrital origin, highest in the volcaniclastic units, with a minor hydrothermal component in the basal sediments at Site 801. Manganese concentrations are highest in the units with the lowest accumulation rates. Fe/Mn ratios are >3 in all units, indicating negligible hydrothermal influence. Magnesium and aluminum concentrations are highest in the volcaniclastic units and in the basal sediments at Site 801. Phosphorous is very low in abundance and may be detrital, derived from fish parts. Boron is virtually absent, as is typical of deep-water deposits. Rare earth element concentrations are slightly higher in the volcaniclastic deposits, suggesting a detrital source, and lower in the rest of the lithologic units. Rare earth element abundances are also low relative to "average shale." Rare earth element patterns indicate all samples are light rare earth element enriched. Siliceous deposits in the volcaniclastic units have patterns which lack a cerium anomaly, suggesting some input of rare earth elements from a detrital source; most other units have a distinct negative Ce anomaly similar to seawater, suggesting a seawater source, through adsorption either onto biogenic tests or incorporation into authigenic minerals for Ce i...

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Petrology and Geochemistry of Silicified Upper Miocene Chalk, Costa Rica Rift, Deep Sea Drilling Project Leg 69

Cited by 15 publications

References 23 publications

Sedimentology and petrography of early diagenetic chert and dolomite in the Late Cretaceous‐early Tertiary Amuri Limestone Group, eastern Marlborough, New Zealand

Sedimentology and petrography of early diagenetic chert and dolomite in the Late Cretaceous‐early Tertiary Amuri Limestone Group, eastern Marlborough, New Zealand

Seismic Properties and Reflectivity of North Pacific Ocean Cherts

Sedimentological and Geochemical Characteristics of Leg 129 Siliceous Deposits

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