Mesozoic cyclostratigraphy is being assembled into a continuous Astronomical Time Scale (ATS) tie... more Mesozoic cyclostratigraphy is being assembled into a continuous Astronomical Time Scale (ATS) tied to the Earth's cyclic orbital parameters. Recognition of a nearly ubiquitous, dominant ~400-kyr cycling in formations throughout the era has been particularly striking. Composite formations spanning contiguous intervals up to 50 myr clearly express these long-eccentricity cycles, and in some cases, this cycling is defined by third- or fourth-order sea-level sequences. This frequency is associated with the 405-kyr orbital eccentricity cycle, which provides a basic metronome and enables the extension of the well-defined Cenozoic ATS to scale the majority of the Mesozoic Era. This astronomical calibration has a resolution comparable to the 1% to 0.1% precision for radioisotope dating of Mesozoic ash beds, but with the added benefit of providing continuous stratigraphic coverage between dated beds. Extended portions of the Mesozoic ATS provide solutions to long-standing geologic problems of tectonics, eustasy, paleoclimate change, and rates of seafloor spreading.
ABSTRACT Thick successions from the margins of the Triassic Yangtze Platform of the South China B... more ABSTRACT Thick successions from the margins of the Triassic Yangtze Platform of the South China Block record a transition from carbonate-rich facies (Zhuganpo Formation and equivalents) to clastic-rich facies (Xiaowa Formation and equivalents) during the Carnian (early Late Triassic) that mark the final phase of termination of this long-lived platform. Cyclostratigraphy derived from spectral gamma-ray (SGR) intensity curves was combined with magnetostratigraphy of two sections in Guizhou Province (Wayao transect and its upward extension into the Geopark Wayao in Guanling county and the Laishike section in Zhenfeng county) and one location in Sichuan Province (Hanwang section). The cyclostratigraphy from all the Guizhou sections indicate a persistent suite of ca. 34 m, 9 m and 1.8 m cycles, which are consistent with the ratios of orbital-climate oscillations caused by long-eccentricity (405 kyr), short-eccentricity (~ 100 kyr) and precession (20 kyr). The magnetostratigraphy of all sections are consistent with the cyclicity and characteristic SGR features, thereby enabling a cycle-tuned magnetic polarity scale spanning ~ 2.4 myr. The main feature is a 1.3-myr interval of reversed polarity containing brief normal-polarity subchrons, and this reversed-polarity chron appears to correspond to the significant reversed-polarity-dominated interval spanning the upper half of the Trachyceras aonoides through lower half of the Austrotrachyceras austriacum ammonoid zones of the upper Julian (the lower substage of Carnian). This magnetostratigraphic correlation implies that the termination of the Yangtze Platform is coeval with the beginning of the mid-Carnian episode of climatic disruption in Europe, which is locally called the “Carnian Pluvial Event” or “Wet Intermezzo”, and with the temporary cessation of the platform carbonates in the Dolomites. The cycle-scaled magnetic-polarity time scale supports the “Short-Tuvalian/Long-Norian” age model of the Late Triassic in which the base of the cycle-tuned polarity pattern from the Newark Group of eastern North America is younger than the end of the Julian substage.
ABSTRACT Mesozoic cyclostratigraphy is being assembled into a continuous Astronomical Time Scale ... more ABSTRACT Mesozoic cyclostratigraphy is being assembled into a continuous Astronomical Time Scale (ATS) tied to the Earth's cyclic orbital parameters. Recognition of a nearly ubiquitous, dominant ~400-kyr cycling in formations throughout the era has been particularly striking. Composite formations spanning contiguous intervals up to 50 myr clearly express these long-eccentricity cycles, and in some cases, this cycling is defined by third- or fourth-order sea-level sequences. This frequency is associated with the 405-kyr orbital eccentricity cycle, which provides a basic metronome and enables the extension of the well-defined Cenozoic ATS to scale the majority of the Mesozoic Era. This astronomical calibration has a resolution comparable to the 1% to 0.1% precision for radioisotope dating of Mesozoic ash beds, but with the added benefit of providing continuous stratigraphic coverage between dated beds. Extended portions of the Mesozoic ATS provide solutions to long-standing geologic problems of tectonics, eustasy, paleoclimate change, and rates of seafloor spreading.
ABSTRACT In his remarkable theory, M. Milankovitch showed how cycles in some of the Earth&#39... more ABSTRACT In his remarkable theory, M. Milankovitch showed how cycles in some of the Earth's astronomical parameters---axial precession, obliquity, and orbital eccentricity---cause variation in insolation on the Earth. Today, the Milankovitch cycles are well documented in paleoclimate time series throughout the Cenozoic Era (0-66 Ma), and are calibrated to the La2004 solar system model. Additionally, there is secular resonance between Earth and Mars, which is expressed as long-period amplitude modulations in Earth's obliquity and eccentricity cycles. A 1.2 myr modulation affects the 41 kyr obliquity cycle, and a variable 2.35 to 2.45 myr modulation appears in the primary 405 kyr eccentricity cycle. These modulations have persisted over at least the past 40 Ma, originating from the secular frequencies of Earth and Mars, s4-s3 and g4-g3, and they have been detected in very long Cenozoic paleoclimate time series. For times prior to the Cenozoic, modeling suggests that chaotic motions in the Earth and Mars orbits involved changes to the secular frequencies of the two planets, and consequently, to the fore-mentioned modulations. Unfortunately, modeling cannot specifically predict when these changes occurred, or the precise changes to the modulations. Sensitivity tests on La2004 suggest that a significant chaotic transition occurred during the Late Cretaceous Period. Evidence for this chaotic behavior should be present in the long-term modulations of obliquity and eccentricity variations captured in the sedimentary record. Here we report on such evidence from a 25 myr long, continuous paleoclimate series recently constructed from the Aptian-Albian pelagic sedimentary record in the Piobbico drillcore (central Italy). The data is in the form of a time series of grayscale intensity versus age, the latter estimated through identification of 405 kyr cycles in the series and anchored to absolute time by geochronology. Time-frequency analysis of the Piobbico time series was accomplished by wavelet transformation, and plotting measured power against period of variation against elapsed time (age). Wavelet transformation was applied, because wavelets are very sensitive to local differences; transient variations are not forced into (nonexistent) global differences. We optimized the wavelet for frequency sensitivity; cycle modulations occur as transient variability in a carrier wave. Modulations related to g4-g3 were detected in the 300-500 kyr eccentricity band at a ~1.6-1.8 myr periodicity, shorter than the Mesozoic model prediction of 2.05 myr. Modulations related to s4-s3 were detected in the 32-50 kyr obliquity band at a ~1.6 myr periodicity, compared with the model prediction of 1.2 myr. The ~1:1 ratio of the observed modulation periods is consistent with the expectation of the Earth-Mars resonance state prior to the Cretaceous chaotic transition. Besides the secular frequencies, mostly in the Aptian an unknown power feature appears at ~ 200 kyr. It does not correspond to a Milankovitch cycle or La2004 term. The Aptian is known for unusual environmental variability and the occurrence of rare events, but it is difficult to see how such phenomena could impose this periodic 200 kyr power feature.
ABSTRACT The early Eocene climatic optimum ended with a long interval of global cooling that bega... more ABSTRACT The early Eocene climatic optimum ended with a long interval of global cooling that began in the early Middle Eocene and ended at the Eocene-Oligocene transition. During this long-term cooling, a series of short-term warming reversals occurred in the marine realm. Here, we investigate corresponding continental climate conditions as revealed in the Qianjiang Formation of the Jianghan Basin in central China, which consists of more than 4000 m of saline lake sediments. The Qianjiang Formation includes, in its deepest sections, a halite-rich rhythmic sediment succession with dark mudstone, brownish-white siltstone and sandstone, and greyish-white halite. Alternating fresh water (humid/cool)---saline water (dry/hot) deposits reflect climate cycles driven by orbital forcing. High-resolution gamma ray (GR) logging from the basin center captures these pronounced lithological rhythms throughout the formation. Several halite-rich intervals are interpreted as short-term warming events within the middle Eocene to early Oligocene, and could be expressions of coeval warming events in the global marine oxygen isotope record, for example, the middle Eocene climate optimum (MECO) event around 41 Ma. The Eocene-Oligocene boundary is distinguished by a radical change from halite-rich to clastic sediments, indicating a dramatic climate change from warm to cool conditions. Power spectral analysis of the GR series indicates strong short (~100 kyr) eccentricity cycling during the warm/hot episodes. Amplitude modulation of the short eccentricity in the GR series occurs with a strong 405 kyr periodicity. This cycling is calibrated to the La2004 orbital eccentricity model. A climate reversal occurs at 36.5 Ma within the long-term marine cooling trend following MECO, which is reflected also in the Qianjiang GR series, with the latter indicating several brief warm/dry reversals within the trend. A ~2.6 Myr halite-rich warm interval occurs in the latest Eocene in the continental record; both marine and continental records show continued warmth up to the Eocene-Oligocene boundary. This is followed at 33.96 Ma in both records by a shift to cooler climates, and in the continental record, more humid conditions.
Mesozoic cyclostratigraphy is being assembled into a continuous Astronomical Time Scale (ATS) tie... more Mesozoic cyclostratigraphy is being assembled into a continuous Astronomical Time Scale (ATS) tied to the Earth's cyclic orbital parameters. Recognition of a nearly ubiquitous, dominant ~400-kyr cycling in formations throughout the era has been particularly striking. Composite formations spanning contiguous intervals up to 50 myr clearly express these long-eccentricity cycles, and in some cases, this cycling is defined by third- or fourth-order sea-level sequences. This frequency is associated with the 405-kyr orbital eccentricity cycle, which provides a basic metronome and enables the extension of the well-defined Cenozoic ATS to scale the majority of the Mesozoic Era. This astronomical calibration has a resolution comparable to the 1% to 0.1% precision for radioisotope dating of Mesozoic ash beds, but with the added benefit of providing continuous stratigraphic coverage between dated beds. Extended portions of the Mesozoic ATS provide solutions to long-standing geologic problems of tectonics, eustasy, paleoclimate change, and rates of seafloor spreading.
ABSTRACT Thick successions from the margins of the Triassic Yangtze Platform of the South China B... more ABSTRACT Thick successions from the margins of the Triassic Yangtze Platform of the South China Block record a transition from carbonate-rich facies (Zhuganpo Formation and equivalents) to clastic-rich facies (Xiaowa Formation and equivalents) during the Carnian (early Late Triassic) that mark the final phase of termination of this long-lived platform. Cyclostratigraphy derived from spectral gamma-ray (SGR) intensity curves was combined with magnetostratigraphy of two sections in Guizhou Province (Wayao transect and its upward extension into the Geopark Wayao in Guanling county and the Laishike section in Zhenfeng county) and one location in Sichuan Province (Hanwang section). The cyclostratigraphy from all the Guizhou sections indicate a persistent suite of ca. 34 m, 9 m and 1.8 m cycles, which are consistent with the ratios of orbital-climate oscillations caused by long-eccentricity (405 kyr), short-eccentricity (~ 100 kyr) and precession (20 kyr). The magnetostratigraphy of all sections are consistent with the cyclicity and characteristic SGR features, thereby enabling a cycle-tuned magnetic polarity scale spanning ~ 2.4 myr. The main feature is a 1.3-myr interval of reversed polarity containing brief normal-polarity subchrons, and this reversed-polarity chron appears to correspond to the significant reversed-polarity-dominated interval spanning the upper half of the Trachyceras aonoides through lower half of the Austrotrachyceras austriacum ammonoid zones of the upper Julian (the lower substage of Carnian). This magnetostratigraphic correlation implies that the termination of the Yangtze Platform is coeval with the beginning of the mid-Carnian episode of climatic disruption in Europe, which is locally called the “Carnian Pluvial Event” or “Wet Intermezzo”, and with the temporary cessation of the platform carbonates in the Dolomites. The cycle-scaled magnetic-polarity time scale supports the “Short-Tuvalian/Long-Norian” age model of the Late Triassic in which the base of the cycle-tuned polarity pattern from the Newark Group of eastern North America is younger than the end of the Julian substage.
ABSTRACT Mesozoic cyclostratigraphy is being assembled into a continuous Astronomical Time Scale ... more ABSTRACT Mesozoic cyclostratigraphy is being assembled into a continuous Astronomical Time Scale (ATS) tied to the Earth's cyclic orbital parameters. Recognition of a nearly ubiquitous, dominant ~400-kyr cycling in formations throughout the era has been particularly striking. Composite formations spanning contiguous intervals up to 50 myr clearly express these long-eccentricity cycles, and in some cases, this cycling is defined by third- or fourth-order sea-level sequences. This frequency is associated with the 405-kyr orbital eccentricity cycle, which provides a basic metronome and enables the extension of the well-defined Cenozoic ATS to scale the majority of the Mesozoic Era. This astronomical calibration has a resolution comparable to the 1% to 0.1% precision for radioisotope dating of Mesozoic ash beds, but with the added benefit of providing continuous stratigraphic coverage between dated beds. Extended portions of the Mesozoic ATS provide solutions to long-standing geologic problems of tectonics, eustasy, paleoclimate change, and rates of seafloor spreading.
ABSTRACT In his remarkable theory, M. Milankovitch showed how cycles in some of the Earth&#39... more ABSTRACT In his remarkable theory, M. Milankovitch showed how cycles in some of the Earth's astronomical parameters---axial precession, obliquity, and orbital eccentricity---cause variation in insolation on the Earth. Today, the Milankovitch cycles are well documented in paleoclimate time series throughout the Cenozoic Era (0-66 Ma), and are calibrated to the La2004 solar system model. Additionally, there is secular resonance between Earth and Mars, which is expressed as long-period amplitude modulations in Earth's obliquity and eccentricity cycles. A 1.2 myr modulation affects the 41 kyr obliquity cycle, and a variable 2.35 to 2.45 myr modulation appears in the primary 405 kyr eccentricity cycle. These modulations have persisted over at least the past 40 Ma, originating from the secular frequencies of Earth and Mars, s4-s3 and g4-g3, and they have been detected in very long Cenozoic paleoclimate time series. For times prior to the Cenozoic, modeling suggests that chaotic motions in the Earth and Mars orbits involved changes to the secular frequencies of the two planets, and consequently, to the fore-mentioned modulations. Unfortunately, modeling cannot specifically predict when these changes occurred, or the precise changes to the modulations. Sensitivity tests on La2004 suggest that a significant chaotic transition occurred during the Late Cretaceous Period. Evidence for this chaotic behavior should be present in the long-term modulations of obliquity and eccentricity variations captured in the sedimentary record. Here we report on such evidence from a 25 myr long, continuous paleoclimate series recently constructed from the Aptian-Albian pelagic sedimentary record in the Piobbico drillcore (central Italy). The data is in the form of a time series of grayscale intensity versus age, the latter estimated through identification of 405 kyr cycles in the series and anchored to absolute time by geochronology. Time-frequency analysis of the Piobbico time series was accomplished by wavelet transformation, and plotting measured power against period of variation against elapsed time (age). Wavelet transformation was applied, because wavelets are very sensitive to local differences; transient variations are not forced into (nonexistent) global differences. We optimized the wavelet for frequency sensitivity; cycle modulations occur as transient variability in a carrier wave. Modulations related to g4-g3 were detected in the 300-500 kyr eccentricity band at a ~1.6-1.8 myr periodicity, shorter than the Mesozoic model prediction of 2.05 myr. Modulations related to s4-s3 were detected in the 32-50 kyr obliquity band at a ~1.6 myr periodicity, compared with the model prediction of 1.2 myr. The ~1:1 ratio of the observed modulation periods is consistent with the expectation of the Earth-Mars resonance state prior to the Cretaceous chaotic transition. Besides the secular frequencies, mostly in the Aptian an unknown power feature appears at ~ 200 kyr. It does not correspond to a Milankovitch cycle or La2004 term. The Aptian is known for unusual environmental variability and the occurrence of rare events, but it is difficult to see how such phenomena could impose this periodic 200 kyr power feature.
ABSTRACT The early Eocene climatic optimum ended with a long interval of global cooling that bega... more ABSTRACT The early Eocene climatic optimum ended with a long interval of global cooling that began in the early Middle Eocene and ended at the Eocene-Oligocene transition. During this long-term cooling, a series of short-term warming reversals occurred in the marine realm. Here, we investigate corresponding continental climate conditions as revealed in the Qianjiang Formation of the Jianghan Basin in central China, which consists of more than 4000 m of saline lake sediments. The Qianjiang Formation includes, in its deepest sections, a halite-rich rhythmic sediment succession with dark mudstone, brownish-white siltstone and sandstone, and greyish-white halite. Alternating fresh water (humid/cool)---saline water (dry/hot) deposits reflect climate cycles driven by orbital forcing. High-resolution gamma ray (GR) logging from the basin center captures these pronounced lithological rhythms throughout the formation. Several halite-rich intervals are interpreted as short-term warming events within the middle Eocene to early Oligocene, and could be expressions of coeval warming events in the global marine oxygen isotope record, for example, the middle Eocene climate optimum (MECO) event around 41 Ma. The Eocene-Oligocene boundary is distinguished by a radical change from halite-rich to clastic sediments, indicating a dramatic climate change from warm to cool conditions. Power spectral analysis of the GR series indicates strong short (~100 kyr) eccentricity cycling during the warm/hot episodes. Amplitude modulation of the short eccentricity in the GR series occurs with a strong 405 kyr periodicity. This cycling is calibrated to the La2004 orbital eccentricity model. A climate reversal occurs at 36.5 Ma within the long-term marine cooling trend following MECO, which is reflected also in the Qianjiang GR series, with the latter indicating several brief warm/dry reversals within the trend. A ~2.6 Myr halite-rich warm interval occurs in the latest Eocene in the continental record; both marine and continental records show continued warmth up to the Eocene-Oligocene boundary. This is followed at 33.96 Ma in both records by a shift to cooler climates, and in the continental record, more humid conditions.
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