The problem of inherited radiogenic strontium in sedimentary age determinations

Whitney, P.E; Hurley, Patrick

doi:10.1016/0016-7037(64)90116-4

Cited by 46 publications

(8 citation statements)

References 31 publications

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“…Most radiogenic isotope studies of low-grade petites have revealed younger Rb-Sr and K-Ar ages in finer grain size fractions. The problem of discordant ages related to Ar and Sr inherited from detrital contamination in coarse size fractions was recognized early on [27,28]. However, even for pure authigenic separates, the presence and variable proportions of multiple generations of authigenic clay and micas can present additional uncertainties and this is a particular problem for evaluating protracted clay growth or progressive recrystallization of phyllosilicates in a prograde environment.…”

Section: Dating Clay Diagenesismentioning

confidence: 99%

Sr and Nd isotopic evidence for punctuated clay diagenesis, Texas Gulf Coast

Ohr

Halliday

Peacor

1991

Earth and Planetary Science Letters

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We report Rb-Sr, Sm-Nd and mineralogical data for leached whole rock, < 2 btm and < 0.1 #m clay size fractions of lower-to mid-Tertiary shales spanning the smectite/illite transition, from a single deep well in the Texas Gulf Coast. The abrupt transition at 2400 m, from smectite-to illite-dominated assemblages is accompanied by a marked increase in 87Sr/S6Sr from 0.708 to 0.711 in exchangeable sites. Leached authigenic illite from the < 0.1 /~m fraction, sampled from below the smectite/illite transition, defines a Rb-Sr isochron age of 34.8 _+ 2.0 Ma. These data are consistent with a single episode of authigenic illite precipitation over a depth range of > 1200 m, independent of the duration of burial. The exchangeable Sr in the clay has remained an open system and has undergone isotopic exchange since that time. Minimum fluid/rock ratios of 0.2 to 2 are modeled from Sr isotopic data, consistent with rock-dominated, open system diagenesis. Leachates and residues of the < 0.1/zm fraction, below the smectite/illite transition appear to have achieved Nd isotopic equilibrium during clay diagenesis, and show no signs of subsequent exchange. The clay residues have low 147Sm/144Nd (< 0.085), indicating that authigenic illite has a lower Sm/Nd ratio than its bulk rock protolith. Conversely the coexisting exchangeable REE inventory has elevated Sm/Nd, as reflected by leachate 14VSm/144Nd as high as 0.188. This Sm/Nd fractionation, in conjunction with the preserved isotopic equilibrium may be useful for dating diagenesis and associated fluid-rock interaction in older rocks.

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Section: Dating Clay Diagenesismentioning

confidence: 99%

Sr and Nd isotopic evidence for punctuated clay diagenesis, Texas Gulf Coast

Ohr

Halliday

Peacor

1991

Earth and Planetary Science Letters

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“…The use of total-rock samples of shale for age determination by the rubidium-strontium method has been described by Compston & Pidgeon (1962) and independently by Whitney & Hurley (1964). Successful measurements of age were observed for Palaeozoic argillaceous samples of low detrital content and high in authigenically-fixed rubidium.…”

Section: Shales From the Adelaide System And From Overlying Lower Cammentioning

confidence: 99%

A radiometric estimate of the duration of sedimentation in the Adelaide geosyncline, south Australia

Compston

Crawford

Bofinger

1966

Journal of the Geological Society of Australia

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“…Good agreement was obtained in some cases for stratigraphically well-defined Palaeozoic sediments between the measured Rb-Sr age and the independently calibrated age for the relevant part of the Phanerozoic time-scale (Compston & Pidgeon 1962;Whitney & Hurley 1964;Bofinger & Compston 1967;Bofinger et al 1970). Good agreement was obtained in some cases for stratigraphically well-defined Palaeozoic sediments between the measured Rb-Sr age and the independently calibrated age for the relevant part of the Phanerozoic time-scale (Compston & Pidgeon 1962;Whitney & Hurley 1964;Bofinger & Compston 1967;Bofinger et al 1970).…”

Section: Direct Dating Of Sedimentary Rocksmentioning

confidence: 71%

Precambrian geochronology and the geological record

Moorbath¹,

Taylor²

1985

Memoirs

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SummaryRb-Sr, Sm-Nd and Pb/Pb whole-rock isochron methods and the U-Pb zircon method have been widely applied to dating Precambrian igneous and meta-igneous rocks. Application of these methods in regional geochronological studies provides reliable constraints on the age and temporal evolution of rock units, even when some parent-daughter systems have suffered disturbance in metamorphic and/or metasomatic events which significantly post-date primary rock formation. Initial isotopic compositions of Sr, Nd and Pb aid geological interpretation of isochron age data, constrain crustal residence time of the protoliths and can be used to assess the relative contributions of mantle and crust in magma genesis.Precambrian sediments can be indirectly dated by reference to age data on interbedded volcanics, or by age-bracketing between dated basement rocks and dated cross-cutting intrusives. Significant progress has also been made in the direct dating of sedimentary rocks. Published isotopic age determinations on early Precambrian sediments containing biogenic remains are briefly reviewed. Provided that stratigraphical and geochronological correlations are correct, it appears that stromatohtic limestones were being deposited by c.3400 - 3300 Ma ago, and that true microfossils occur in rocks dated at c.3200 - 3000 Ma. Evidence relating to possible biogenic markers in sediments reliably dated at c.3800 - 3700 Ma is not yet definitive.

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The problem of inherited radiogenic strontium in sedimentary age determinations

Cited by 46 publications

References 31 publications

Sr and Nd isotopic evidence for punctuated clay diagenesis, Texas Gulf Coast

Sr and Nd isotopic evidence for punctuated clay diagenesis, Texas Gulf Coast

A radiometric estimate of the duration of sedimentation in the Adelaide geosyncline, south Australia

Precambrian geochronology and the geological record

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