Title of article :
Millennial-scale climate origins for stratification in Cambrian and Devonian deep-water rhythmites, western USA
Author/Authors :
Elrick، نويسنده , , Maya and Hinnov، نويسنده , , Linda A.، نويسنده ,
Issue Information :
روزنامه با شماره پیاپی سال 1996
Pages :
20
From page :
353
To page :
372
Abstract :
Basinal facies of the Middle Cambrian Marjum Formation (western Utah) and Middle Devonian Denay Limestone (central Nevada) are characterized by thin, rhythmically interbedded limestone and marl layers (deep-water rhythmites). Limestone layers (average thickness range of 4.3–5.5 cm) are composed of laminated to massive pelleted lime mudstone; marl layers (average thickness range of 0.7–1.7 cm) are characterized by laminated, argillaceous, dolomitic mudstone. The absence of current- or wave-reworked features, paucity of bioturbation and skeletal fossils, stratigraphic relationships with adjacent facies, and the dark color indicate that limestone and marl layers in both rhythmite successions were deposited in quiet, dysaerobic waters below storm-wave base. Both limestone and marl layers are composed of submillimeter-thick graded laminae which represent discrete depositional events from dilute density currents generated by high-frequency storms or distal turbidity currents. Fluctuations in primary pelagic productivity cannot account for variations in carbonate influx because calcareous microfossils did not evolve until the Mesozoic. Instead, the rhythmic interbedding is interpreted to reflect climatically controlled variations in fluvial and/or eolian influx, or changes in marine currents (storm or distal turbidity currents) which transported shallow platform-derived carbonate material into the deep-water region. al analysis of carbonate time series were compared to lithologic rank series and, particularly for the Middle Cambrian rhythmites, were found to be statistically indistinguishable. The durations of significant spectral peaks were estimated from calculating the average sedimentation rates from the two biostratigraphically controlled stratigraphic sections; these rates range between 4.3 ± 4.1 cm/k.y. and 21.2 ± 29.2 cm/k.y. for the Cambrian, and 3.6 ± 1.8 cm/k.y. to 5.1 ± 7.4 cm/k.y. for the Middle Devonian. Application of these sedimentation rates to the Marjum couplets suggests that individual couplets represent between ∼190–2100 years of time. The Denay couplets represent ∼800–1900 years. The good agreement between empirical Holocene hemipelagic sedimentation rates and the sedimentologic evidence of relatively high depositional rates for the Paleozoic rhythmites supports this millennial-scale interpretation. results, combined with that from previous work in Paleozoic evaporite and carbonate successions, suggest that millennial-scale paleoclimatic variations affected marine and marginal-marine sedimentation as far back in time as the Cambrian. Millennial-scale climatic change appears to be a permanent feature affecting the oceans and atmosphere, and is apparently largely unaffected by major changes in Phanerozoic paleogeography, tectonics and atmospheric composition.
Journal title :
Palaeogeography, Palaeoclimatology, Palaeoecology
Serial Year :
1996
Journal title :
Palaeogeography, Palaeoclimatology, Palaeoecology
Record number :
2288177
Link To Document :
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