The distinctive character of lumpy limestones (Early Jurassic, Lusitanian Basin, W Portugal)

Coimbra, Rute; Duarte, Luís V.

doi:10.1002/gj.3485

Cited by 3 publications

(1 citation statement)

References 63 publications

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“…This timescale of disintegration means they would not track the duration of longer, millennial‐scale hiatuses associated with skeletal lags or concentrations. The criteria for detecting millennial‐scale time averaging based on valves with cements and with composite alteration can be applied to Palaeozoic, Mesozoic and Cenozoic deposits in environments prone to subsurface cementation in the mixed layer (Zamora et al ., 2008; Vodrážka et al ., 2009; Fernández‐López, 2011; Wilson et al ., 2012; Coimbra & Duarte, 2020). For example, repeated exhumation of skeletal particles initially cemented in subsurface conditions is suggested by the encrustation and bioerosion of exhumed concretions (Kennedy & Garrison, 1975; Fürsich, 1978; Fürsich et al ., 1992; Hesselbo & Palmer, 1992).…”

Section: Discussionmentioning

confidence: 99%

Inferring time averaging and hiatus durations in the stratigraphic record of high‐frequency depositional sequences

et al. 2021

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A sequence stratigraphic framework predicts that time averaging and hiatus durations will be long at times of fastest sea-level rise. This prediction does not necessarily apply to environments where carbonate production keeps up with sea-level rise and where undetected hiatuses decouple short-term from long-term sedimentation rates. The taphonomic clock, however, which measures the residence time of skeletal particles in the mixed layer, can estimate the duration of hiatuses if the rate of skeletal alteration is slow and if skeletal particles endure long-term exposure in the mixed layer. Here, time averaging is calibrated by using evidence from alteration of bivalves in a metrescale Holocene sequence in the Adriatic Sea. In this sequence, transgressive molluscan lags, a maximum-flooding zone shell bed with bivalves, and highstand bryomol assemblages were all deposited under similar long-term sedimentation rates (ca 0.01 to 0.03 cm year À1 ) and exhibit millennial time averaging. Median ages of valves stained by pyrite and cemented by highmagnesium calcitic micritic envelopes exceeding ca 1000 years indicate that: (i) these authigenic processes are slow in subsurface zones with reducing conditions (with prolonged sulphate reduction and carbonate ions sourced from dissolved shells in the surface zones); and (ii) subsurface micrite precipitation prolongs the disintegration half-lives of valves exhumed to surface zones from decades to millennia. The high abundance of stained valves, valves with micrite envelopes, and valves with composite alteration (encrusters and borers colonizing stained and cemented grains) thus identifies hiatuses and skeletal concentrations time-averaged to >1000 years. The upcore decrease in abundance of valves with composite alteration, coupled with temporally-constant long-term sedimentation rates and time averaging, indicates that a temporal decline in sediment exhumation was compensated by a decline in burial of skeletal carbonate produced by molluscs.

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Section: Discussionmentioning

confidence: 99%

Inferring time averaging and hiatus durations in the stratigraphic record of high‐frequency depositional sequences

et al. 2021

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Facies types and depositional cyclicity of a Toarcian–Aalenian(?) carbonate-siliciclastic mixed succession (Cabo Carvoeiro Formation) in the Lusitanian Basin, Portugal

2021

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Sources of uncertainty in field gamma-ray spectrometry: Implications for exploration in the Lower-Middle Jurassic sedimentary succession of the Lusitanian Basin (Portugal)

Sêco

Pereira

Duarte

et al. 2021

Journal of Geochemical Exploration

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The distinctive character of lumpy limestones (Early Jurassic, Lusitanian Basin, W Portugal)

Abstract: Ephemeral carbonate facies presenting restricted geographical and temporal occurrence hold the key to complete the knowledge of past environmental conditions.

Cited by 3 publications

References 63 publications

Inferring time averaging and hiatus durations in the stratigraphic record of high‐frequency depositional sequences

Inferring time averaging and hiatus durations in the stratigraphic record of high‐frequency depositional sequences

Facies types and depositional cyclicity of a Toarcian–Aalenian(?) carbonate-siliciclastic mixed succession (Cabo Carvoeiro Formation) in the Lusitanian Basin, Portugal

Sources of uncertainty in field gamma-ray spectrometry: Implications for exploration in the Lower-Middle Jurassic sedimentary succession of the Lusitanian Basin (Portugal)

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