Chapter 4 c0004 Cyclostratigraphy and Astrochronology L.A. Hinnov and F.J. Hilgen Chapter Outline 4.1. Introduction 63 4.2. Earth’s Astronomical Parameters 64 4.3. The 405-kyr Metronome 67 4.4. Astronomically Forced Insolation 67 4.5. Cyclostratigraphy through Geologic Time 67 4.6. Constructing Astrochronologies and the ATS 71 4.7. Precision and Accuracy of the ATS 72 4.7.1. Seasonal Phase Relations 72 4.7.2. Tidal Dissipation, Dynamical Ellipticity and Climate Friction 74 4.7.3. Solar System Diffusion 76 4.7.4. Summary of Uncertainties 76 4.8. Astrochronology-Geochronology Intercalibration 76 4.9. A New Astronomical Solution 78 References 78 s0010 4.1. INTRODUCTION p0015 Paleoclimatological research has led to wide acceptance that quasi-periodic oscillations in the Sun-Earth position, known as Milankovitch cycles, have induced significant variations in Earth’s past climate. These astronomically forced climate variations have in turn influenced climate-sensitive sedimentation, and thereby came to be fossilized in the Earth’s cyclic stratigraphic, or cyclostratigraphic record. The subdiscipline that has developed to study this record is known today as cyclostratigraphy. The detection of astronomical signals in cyclostratigraphy has been facilitated by impressive advancements in celestial mechanics, which have provided accurate models of Earth’s orbital-rotational behavior through geological time, and also by equally notable improvements in data collection and analysis. p0020 A principal outcome of these developments has been the recognition that the cyclostratigraphic record, when shown to carry a signal specific to Earth’s astronomical parameters, serves as a powerful chronometer. The astronomical calibration of these cycles leads to astrochronology and construction of the Astronomical Time Scale (ATS). High quality data from the Cenozoic Era have demonstratively preserved all of the astronomical cycles predicted by modern celestial mechanics; the Neogene and Paleogene periods are now almost completely astronomically calibrated, as reported in Chapters 28 and 29, although serious problems remain in the Paleogene. Cyclostratigraphy from more remote geological ages cannot be calibrated fully or directly to the astronomical variations, because of model limitations and uncertainties in determining stratigraphic age. Nonetheless, in numerous instances signals analogous to those of the modeled astronomical variations have been detected in cyclostratigraphy, prompting the development of “floating” astrochronologies over extended time intervals (multiple millions of years). Astronomically calibrated floating time scales have now been proposed for intervals that extend through entire stages in the Triassic, Jurassic and Cretaceous periods, and are presented in Chapters 25, 26 and 27. p0025This chapter provides an introduction to the Earth’s astronomical parameters, the nature of the astronomically forced incoming solar radiation (insolation), and the discovery of astronomically forced insolation signals in cyclostratigraphy. For remote geologic times, partial astronomical calibration with the modeled 405-kyr orbital eccentricity variation is allowable; the construction and application of the “405-kyr metronome” is explained. This is followed by a summary of the cyclostratigraphy that was used in the “absolute” and “floating” astrochronologies of A Geologic Time Scale 2012 (GTS2012). A discussion of the precision and accuracy that can be expected from astronomically calibrated cyclostratigraphy is also given. The chapter concludes with remarks on recent inter-calibration efforts between The Geologic Time Scale 2012. DOI: 10.1016/B978-0-444-59425-9.00004-4 Copyright Ó 2012 Elsevier B.V. All rights reserved. 63 To protect the rights of the author(s) and publisher we inform you that this PDF is an uncorrected proof for internal business use only by the author(s), editor(s), reviewer(s), Elsevier and typesetter TNQ Books and Journals Pvt Ltd. It is not allowed to publish this proof online or in print. This proof copy is the copyright property of the publisher and is confidential until formal publication. 10004-GRADSTEIN-9780444594259 astrochronology and geochronology e the key to future improvement in geologic time scale determination. s0015 4.2. EARTH’S ASTRONOMICAL PARAMETERS p0030 The Earth undergoes quasi-periodic changes in its orientation relative to the Sun, as a consequence of interactions between the Earth’s axial precession and variable orbit induced by motions of the other planets. These changes may be described in terms of the Earth’s astronomical parameters (Figure 4.1). Quantification of these parameters has been carried out numerous times in the past using analytical approximations of the planetary motions; a brief history of these computations is given in Laskar et al. (2004). Today, models of the astronomical parameters are based on computerized numerical integration, and include important new variables, e.g., relativistic effects, flattening of the Earth, Sun and Moon, Earth’s tidal deceleration, climate friction, and other factors. The nominal La2004 model includes all of the above-mentioned variables, and provides an accurate orbital eccentricity model back to 40 Ma (Laskar et al., 2004). A new La2010 solution extends accuracy back to 50 Ma (Section 4.9). Further back in time, however, modeling validity rapidly diminishes due to uncertainties in model initial conditions and numerical integration error. While the initial conditions can be improved, integration error ultimately limits the validity of the model to approximately 60 Ma (Laskar, 2006). p0035Over the past 10 million years the Earth’s orbital eccentricity has varied between 0e0.07 (Figure 4.2a) with principal periods at 95 kyr, 99 kyr, 124 kyr, 131 kyr, 405 kyr, and 2260 kyr (Figure 4.3a), caused by gravitational perturbations from the motions of the other planets acting on Earth’s orbital elements P and e (Figure 4.1). The obliquity variation changes the Earth’s axial tilt by between 22e24 (Figure 4.2b), with a principal period at 41 kyr, and lesser ones at 39 kyr, 54 kyr and 29 kyr (Figure 4.3b), due to planetary motions acting mainly on orbital elements I and U (Figure 4.1). The precession index represents the combined effects of orbital eccentricity and the Earth’s axial precession on the Sun-Earth distance (Figure 4.2c), and has principal periods at 24 kyr, 22 kyr, 19 kyr and 17 kyr (Figure 4.3c). p0040Long-term secular changes in geophysical and astrodynamical factors are expected to have influenced the frequencies and phasings of the astronomical parameters. These factors include chaotic diffusion of the Solar System, tidal dissipation of the Earth-Moon system, Earth’s dynamical ellipticity and climate friction (Section 4.7). At present ε ψ Earth NP ϕ n I b a Sun P γ f2 ω Ω R E F E R E N C E F I X E D E C L I P T I C line of intersection γο f1 N ECLIPTIC OF DATE ϖ Earth's path f0010 FIGURE 4.1 The Earth’s astronomical parameters viewed from above the Earth’s geographic North Pole (NP) in a configuration of northern summer solstice (NP pointed towards the Sun). The Earth’s orbit is elliptical with (invariant) semi-major axis a and semi-minor axis b defining eccentricity e. The Sun occupies one of the two foci (f1, f2). Variables e, P, I and U are “orbital elements,” where P ¼ U þ u. The plane of the Earth’s orbit (the “ecliptic of date”) is inclined at an angle I relative to the fixed reference ecliptic, and intersects this reference ecliptic at a longitude U at point N, the ascending node, relative to fixed vernal point go. (In this depiction, I is greatly exaggerated from its actual magnitude of 1 to 2.) The orbital perihelion point P is measured relative to go as the longitude of perihelion P, and moves slowly anticlockwise. The Earth’s figure is tilted with respect to the ecliptic of date normal n at obliquity angle ε. Earth’s rotation 4 is anticlockwise; gravitational forces along the ecliptic of date from the Moon and Sun act on the Earth’s equatorial bulge and cause a clockwise precession j of the rotation axis. This precession causes the vernal equinox point g to migrate clockwise along the Earth’s orbit, shifting the seasons relative to the orbit’s eccentric shape; this motion constitutes the “precession of the equinoxes.” The angle 6between g and P is the moving longitude of perihelion and is used in the precession index esin6 to track Earth-Sun distance. Variations of e, ε and esin6 are shown in Figure 4.2. 64 The Geologic Time Scale 2012 To protect the rights of the author(s) and publisher we inform you that this PDF is an uncorrected proof for internal business use only by the author(s), editor(s), reviewer(s), Elsevier and typesetter TNQ Books and Journals Pvt Ltd. It is not allowed to publish this proof online or in print. This proof copy is the copyright property of the publisher and is confidential until formal publication. 10004-GRADSTEIN-9780444594259 21 22 23 24 25 26 degrees 0 2 4 6 8 10 millions of years ago 0.00 0.02 0.04 0.06 0.08 0.10 0 2 4 6 8 10 millions of years ago -.1 -.05 0 .05 .1 0 2 4 6 8 10 millions of years ago dimensionlessdimensionless (a) (b) (c) f0015 FIGURE 4.2 Variations of the Earth’s astronomical parameters over the past 10 million years according to the nominal La2004 model sampled at 1-kyr intervals (Laskar et al., 2004). (a) Orbital eccentricity (dimensionless). (b) Obliquity variation, in degrees of axial tilt. (c) Precession index (dimensionless). All values may be downloaded from the website: http://www.imcce.fr/Equipes/ASD/insola/earth/earth.html. 65Chapter | 4 Cyclostratigraphy and Astrochronology To protect the rights of the author(s) and publisher we inform you that this PDF is an uncorrected proof for internal business use only by the author(s), editor(s), reviewer(s), Elsevier and typesetter TNQ Books and Journals Pvt Ltd. It is not allowed to publish this proof online or in print. This proof copy is the copyright property of the publisher and is confidential until formal publication. 10004-GRADSTEIN-9780444594259 0 .005 .010 .015 .020 .025 0.03 0.04 0.05 0.06 0.07 0.08 dimensionless cycles/kyr 23.607 22.326 23.079 19.073 19.124 16.439 0 0.2 0.4 0.6 0.8 0.015 0.02 0.025 0.03 0.035 0.04 cycles/kyr 55.04 40.8 40.11 39.45 29.75 28.83 degrees .004 .006 .008 .010 .012 .014 0.0 .002 0 0.005 0.01 0.015 0.02 cycles/kyr 667 488 405 345 220 202 179 131 124 99 95 88 83 77 63 56 2260 1000 dimensionless (a) (b) (c) f0020 FIGURE 4.3 Harmonic analysis using 4p multi-tapers (Thomson, 1982) of the Earth’s astronomical parameters depicted in Figure 4.2. Labels identify periodic components in thousands of years. (a) Orbital eccentricity. (b) Obliquity variation. (c) Precession index. Due to the quasi-periodic nature of the parameters and other factors (Section 4.7), the significance, periodicity and amplitude of the labeled components may change for analyses performed over other time segments. 66 The Geologic Time Scale 2012 To protect the rights of the author(s) and publisher we inform you that this PDF is an uncorrected proof for internal business use only by the author(s), editor(s), reviewer(s), Elsevier and typesetter TNQ Books and Journals Pvt Ltd. It is not allowed to publish this proof online or in print. This proof copy is the copyright property of the publisher and is confidential until formal publication. 10004-GRADSTEIN-9780444594259 the effects of these factors are in the main known only theoretically; the cyclostratigraphic record has yet to be analyzed for the magnitude and timing of these factors. s0020 4.3. THE 405-KYR METRONOME p0045 While chaotic behavior has in all liklelihood affected Earth’s ~100 kyr scale orbital eccentricity terms through geologic time, the 405 kyr eccentricity cycle has remained relatively stable overatleast the past 250 millionyears (Laskar etal.,2004). This high-amplitude cycle is the consequence of gravitational interactions between Jupiter and Venus, i.e. , motions of their orbital perihelia, g2eg5. The large mass of Jupiter is responsible for the stability of the 405-kyr cycle, which has an estimated uncertainty of ~500 kyr at 250 Ma. Thus, this cycle can be used asa basic calibration periodfor cyclostratigraphy; thisapproach has been advocated by Laskar et al. (2004), and many others. Today 405-kyr cyclicity has been recognized in many cyclostratigraphic sequences, as demonstrated in the astrochronologiespresentedinChapters25e29ofthisvolume.Itnow appears that many of the so-called “third order sequences” in Mesozoic stratigraphy are responses to the 405-kyr eccentricity cycle through climate forcing by precession index carriers (e.g., Gale et al., 2002; Boulila et al., 2010a). p0050 To obtain the 405-kyr metronome, Laskar et al. (2004) suggested using the simple formula: e405 ¼ 0.027558 À 0.010739 cos(2434” þ 3.200”t). However, this formula is valid only for 0e100 Ma. To provide an accurate metronome for the entire modeled 0e249 Ma, the nominal La2004 orbital eccentricity series was downsampled to an 8 kyr spacing (down from 1 kyr given by Laskar et al., 2004); bandpass filtering was applied to extract the 405-kyr cycle. The filtered signal (normalized to unity) is the 405-kyr metronome; four representative time slices are shown in Figure 4.4. The depicted single-frequency metronome has been included in TSCreator (Ogg, et al., 2011). The long-term goal of astrochronology is to assign (“tune”) cyclostratigraphy to the appropriate 405-kyr bins. p0055 A slightly wider passband surrounding the 405-kyr term includes the important g4eg3 modulation into the metronome (Laskar et al., 2011). Figure 4.4 also displays this wide-band metronome, which can vary significantly from the singlefrequency metronome. The wide-band metronome can be used to accurately tune cyclostratigraphy over 0e40 Ma using La2004, and over 0e50 Ma using La2010 (Section 4.9). Prior to 50 Ma, however, the g4eg3 modulation is inaccurately known (Section 4.7); for Mesozoic and older cyclostratigraphy the single-frequency metronome should be assumed. s0025 4.4. ASTRONOMICALLY FORCED INSOLATION p0060 The orbital parameters affect changes in the intensity and timing of the incoming solar radiation, or insolation, at all points on the Earth. When considered at interannual time scales, these insolation changes comprise the well-known Milankovitch cycles (Milankovitch, 1941; reissued in English in 1998). Figure 4.5 compares Milankovitch’s original calculation of northern summer insolation at 65N with a modern calculation based on La2004. Geographical location, time of year, and even the time of day all determine the relative contributions of the orbital parameters to the interannual insolation (e.g., Berger et al., 1993; Berger et al., 2010). For example, Figure 4.6 depicts the globally available spectral power of orbitally forced daily insolation at the top of the atmosphere on June 21 (solstice) and March 21 (equinox). These examples are idealized in the sense that it is unlikely that climate responds to insolation on only one day of the year, but rather integrates insolation over certain times of the year and collectively over specific geographic areas, possibly over different areas at different times. This “climatic filtering” alters the relative contributions of the orbital parameters to the total output climate response, this even prior to internal climate system responses to the insolation. Thus, it is left to the discretion of the paleoclimatologist to determine which time(s) of the year and at which location(s) a prevailing climate has responded to insolation; this can require considerable insight into the infinite number of ways that one can sample insolation in space-time (Rubincam, 1994). s00304.5. CYCLOSTRATIGRAPHY THROUGH GEOLOGIC TIME p0065The prospect that Earth’s astronomical variations have exerted large-scale climatic changes that could be detected in the geologic record was already being debated in the 19th century (e.g., Herschel, 1830; Adhe´mar, 1842; Lyell, 1867; Croll, 1875). Early attempts to link astronomical effects to paleoclimate are reviewed in Hilgen (2010). Gilbert (1895) was the first to attribute the origin of limestone/shale cyclic strata of the Cretaceous Niobrara chalks (Colorado, USA) to astronomical forcing. Bradley (1929) counted varves in the lacustrine oil shale/marl cycles of the Eocene Green River formation (Utah, USA) estimating an average 21,630-year time scale for the cycles, and pointing to the precession of the equinoxes as a potential cause. The first correlation between astronomically calculated insolation minima and Late Quaternary ice age deposits of the Alps was made by Ko¨ppen and Wegener (1924), who used insolation as calculated by Milankovitch for critical latitudes and seasons (i.e. , similar to 65N Summer); this correlation and tuning was also discussed at length in Milankovitch (1941). Milankovitch (1941) was the first to attempt a quantitative correlation between astronomically calculated insolation minima and Late Quaternary ice age deposits of the Alps. However, later radiocarbon studies of glaciation timings in North America did not clearly corroborate Milankovitch’s insolation 67Chapter | 4 Cyclostratigraphy and Astrochronology To protect the rights of the author(s) and publisher we inform you that this PDF is an uncorrected proof for internal business use only by the author(s), editor(s), reviewer(s), Elsevier and typesetter TNQ Books and Journals Pvt Ltd. It is not allowed to publish this proof online or in print. This proof copy is the copyright property of the publisher and is confidential until formal publication. 10004-GRADSTEIN-9780444594259 calculations, and the astronomical theory fell into disfavor (review in Imbrie and Imbrie, 1979; update in Broecker and Denton, 1989). p0070 At the same time, significant progress had been made in understanding the origins of the prevalent rhythmic stratification of Mesozoic Alpine limestones (e.g., Schwarzacher, 1947, 1954). This research culminated in the seminal work of Fischer (1964), who found that the meter-scale beds (the socalled Lofer cyclothems) of the Triassic Dachstein Limestone contained vertically repeating facies indicative of shallow marine environments exposed to oscillating sea levels, with a ca. 40 kyr timing. However, glaciations were unknown for the Triassic, raising doubts about the mechanisms by which such sea level oscillations could have occurred; the origin of the Lofer cyclothems continues to be debated today (e.g., Schwarzacher, 1993; Enos and Samankassou, 1998; Cozzi et al., 2005). p0075It was not until investigation of the Late Quaternary deepsea sedimentary record that Milankovitch’s theory of climate change was firmly validated. Emiliani (1955, 1966) explained oxygen isotope fractionation in marine calcareous microfauna as a function of ocean temperature and salinity; 0 0.02 0.04 0.06 0 0.02 0.04 0.06 0 1 2 3 4 5 EccentricityEccentricity 0 0.02 0.04 0.06 Eccentricity 0 0.02 0.04 0.06 Eccentricity time (Ma) metronomemetronomemetronomemetronome 0 1 100 101 102 103 104 105 time (Ma) 200 201 202 203 204 205 time (Ma) 245 246 247 248 249 250 time (Ma) (d) (a) (b) (c) 0 1 0 1 0 1 1 2 3 4 5 6 7 8 9 10 11 12 248 249 250 251 252 253 254 255 256 257 258 259 493 494 495 496 497 498 499 500 501 502 503 504 605 606 607 608 609 610 611 612 613 614 f0025 FIGURE 4.4 The 405-kyr eccentricity metronome. The nominal La2004 eccentricity series was subjected to Taner bandpass filtering (Taner, 2000) centered at 1/(405.091 kyr), with cutoff frequencies set at Æ0.000001 cycles/kyr on either side of this center frequency. The filtered output was normalized to unity; this constitutes the “single-frequency” 405-kyr metronome. Excerpts are displayed in (a)-(d) (red curve) and illustrate maintenance of phasing through the full La2004 eccentricity solution (black curve) back to 249 Ma (the La2004 model terminous). The number labels indicate 405-kyr cycle number relative to the present. This metronome may be accessed from TSCreator (Ogg et al., 2011), which can be downloaded from the website: http://www.tscreator.com/. Filtering with cutoff frequencies set at Æ0.001 cycles/kyr on either side of the center frequency provides a “wide-band” 405-kyr metronome (green curve) for tuning the cyclostratigraphic record from 0e40 Ma with La2004 (0e50 Ma with La2010). 68 The Geologic Time Scale 2012 To protect the rights of the author(s) and publisher we inform you that this PDF is an uncorrected proof for internal business use only by the author(s), editor(s), reviewer(s), Elsevier and typesetter TNQ Books and Journals Pvt Ltd. It is not allowed to publish this proof online or in print. This proof copy is the copyright property of the publisher and is confidential until formal publication. 10004-GRADSTEIN-9780444594259 subsequently, Shackleton (1967) demonstrated that the majority of change in the marine oxygen isotope fractionation was linked to ocean volume (see also Dansgaard and Tauber, 1969). This result was followed by the landmark study of Hays et al. (1976) in which the oxygen isotope record was quantitatively linked to the Milankovitch cycles. Bolstered by the advent of global paleomagnetic stratigraphy in combination with new radioisotopic dates, it was subsequently discovered that the same isotope signal, now encompassing the entire Brunhes chron (0 to 0.78 Ma), was present in all of the major oceans (Imbrie et al., 1984). Finally, calibration of this proxy for global ocean volume to geological evidence for large sea level changes (e.g., Chappell and Shackleton, 1986; Waelbroeck et al., 2002) established, albeit indirectly, the connection between the Quaternary ice ages and Milankovitch cycles. Later research into polar ice stratigraphy uncovered other isotope signals with strong orbital frequencies, providing additional, overwhelming support for the astronomical forcing theory (e.g., Petit et al., 1999; EPICA Community Members, 2004). p0080 Meanwhile, it was shown convincingly that the astronomical tuning approach, using both oxygen isotopes and sedimentary cycles, could be extended well beyond 800 ka, i.e. the time of the last major glaciations (Shackleton et al., 1990; Hilgen, 1991a, b). These milestone studies touched off multiple initiatives to search for astronomical cycles in stratigraphy back through geologic time, using isotopes as well as other climate proxies, including facies stratigraphy, percent carbonate, biogenic silica, magnetic susceptibility, wireline logs, and grayscale scans (Table 4.1). Continental PliocenePleistocene sediments recovered from Lake Baikal revealed a strong biogenic silica signal closely mimicking that of the marine isotope record (e.g., Williams et al., 1997; Prokopenko et al., 2006), as do the long Chinese loess sequences (e.g., Sun et al., 2006). Deep sea drilling yielded a continuous oxygen isotope signal spanning 0e6 Ma (Shackleton et al., 1995), and today, there is near-continuous Milankovitch cycle coverage back to the start of the Cenozoic Era from combinations of marine climate proxies from deep sea drilling and outcrop studies (Chapters 28 and 29 of this volume). The Cretaceous/Paleogene boundary was recently the subject of a rigorous intercalibration effort between astrochronology and geochronology (Section 4.8). p0085Strong evidence for astronomical forcing continues back into the Mesozoic Era. Multi-million year long cyclostratigraphic successions from all three periods have been tapped for astrochronology and are used in GTS2012 (Chapters 25, 26 and 27). The thick Upper Triassic continental lacustrine deposits of eastern North America contain a nearly perfect eccentricity signal that modulates facies successions linked to wetting-drying climate cycles at precessional time scales. Several of the Mesozoic successions which are now available provide records of continuous astronomical signals that are 20 million years long or more; these include the Aptian-Albian Piobbico core Tethyan sequence (Herbert et al., 1995) and the Carnian-Hettangian Pangean sequence from the Newark Basin Coring Project (Olsen and Kent, 1999), and most recently, the Smithian-Carnian Panthalassic chert sequences of Japan (Ikeda et al., 2010). For geologic times prior to the late Triassic, the evidence for astronomically forced stratigraphy is generally less clear. One reason is that pre-Jurassic oceanic sediments are not composed of the abundant, -500 0 500 350 375 400 0 100 200 300 400 500 600 Thousands of Years Before Present Milankovitch 1941 Laskar 2004 caloricunits Watts/m2 0 100 200 300 400 500 600 Millennia before the Year 1800 f0030 FIGURE 4.5 Milankovitch cycles for summer half-year mean insolation at 65 North, 0e600 ka, as originally calculated by Milankovitch (1941; table XXV, p. 513e519) compared with the same calculated with the La2004 nominal model (Analyseries 2.4.2). 69Chapter | 4 Cyclostratigraphy and Astrochronology To protect the rights of the author(s) and publisher we inform you that this PDF is an uncorrected proof for internal business use only by the author(s), editor(s), reviewer(s), Elsevier and typesetter TNQ Books and Journals Pvt Ltd. It is not allowed to publish this proof online or in print. This proof copy is the copyright property of the publisher and is confidential until formal publication. 10004-GRADSTEIN-9780444594259 continuous rain of pelagic oozes as are the post-Jurassic ones. Therefore, research is focused more on the prolific shallow marine record, for which the primary evidence of Milankovitch forcing is more a systematic “interruption” rather than a continuous recording (Fischer, 1995). p0090 Paleozoic formations show clear evidence for astronomical forcing, but none have been integrated into GTS2012. The Permian Castile Formation, a varved marine evaporite sequence, shows a strong, but short-lived Milankovitch signal (Anderson, 1982, 2010). The spectacular shelf carbonate cycles of the Pennsylvanian Paradox Basin (Utah, USA) indicate high-frequency sea level oscillations with some astronomical signal characteristics (Goldhammer et al., 1994). The classic transgressive-regressive cyclothems of the Pennsylvanian world (e.g., Heckel, 2008) and the rhythmic Mississippian hemipelagic limestones of Ireland 0.0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 90S 60S 30S 0 30N 60N 90N LATITUDE CYCLES/KYR 24 22 19 17 98 128 404 0 5 10 15 20 25 Watts/m2 0.0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 90S 60S 30S 0 30N 60N 90N LATITUDE CYCLES/KYR 24 22 19 17 41 39 5498 128 4042400 0 5 10 15 20 25 Watts/m2 (a) (b) f0035 FIGURE 4.6 Frequency distribution of interannual insolation over 0e5 million years ago, sampled at 1ekyr intervals (Analyseries; Paillard et al., 1996) and displayed as multi-tapered amplitude spectra with respect to geographic latitude. (a) Daily mean insolation on June 21 (solstice). Latitudes south of ca. 66S receive no insolation on this day. Maximum daily insolation occurs in the northern polar regions, which experiences 24-hour exposure. (b) Daily mean insolation on March 21 (equinox). Insolation strength is a function of local solar altitude, highest at the Equator on this day of equal-time exposure everywhere. Contributions from the obliquity variation are absent. [Additional notes: Insolation for the December 21 solstice similar to (a), but with reversed latitudes; and the September 21 equinox is practially identical to (b). Also, the precession component of variation in (a) is at all locations 90 out of phase with the precession component in (b). Additional examples are given in Berger et al., 1993.] 70 The Geologic Time Scale 2012 To protect the rights of the author(s) and publisher we inform you that this PDF is an uncorrected proof for internal business use only by the author(s), editor(s), reviewer(s), Elsevier and typesetter TNQ Books and Journals Pvt Ltd. It is not allowed to publish this proof online or in print. This proof copy is the copyright property of the publisher and is confidential until formal publication. 10004-GRADSTEIN-9780444594259 (Schwarzacher, 1993) appear to express the dominant 405-kyr eccentricity cycle, ½AU2Š conclusions that have recently been supported by high-precision geochronology and cyclostratigraphy of the Donets Basin, Ukraine (Davydov et al., 2010). There are reports of astronomical-scale cycles in Devonian formations (review in Tucker and Garland, 2010), and for the Silurian (e.g., Crick et al., 2001; Nestor et al., 2001, 2003). Stratigraphers have attempted to develop integrated stratigraphy and some astrochronology for the Ordovician (Kim and Lee, 1998; Gong and Droser, 2001; Rodionov et al., 2003) but these efforts remain uncoordinated and largely incomplete. The thick Cambrian-Ordovician cyclic carbonate banks found worldwide show abundant evidence of Milankovitch-scale forcing, although the origins of these high-frequency cyclic sequences remains unsettled (e.g., Osleger, 1995). Research on Cambrian cyclostratigraphy, although off to a productive start several decades ago (e.g., Read, 1995), is presently inactive. p0095 Precambrian cyclostratigraphy also has evidence for astronomical-like signals. Several shallow marine carbonate successions have been examined, including the meter-scale shallowing upward cycles of the Rocknest Formation, the relict of an early Proterozoic (1.89 Ga) passive margin carbonate platform in the Northwest Territories, Canada (Grotzinger, 1986), and the platform sequence of the late Archean (2.65 Ga) Cheshire Formation, Zimbabwe (Hofmann et al., 2004). However, these records have not been assessed with a specific astronomical model. It has also long been speculated that the banded iron formations (BIFs), with their strong, compound and sustained depositional cyclicity, might have recorded early Milankovitch cycles (e.g., Ito et al., 1993; Ha¨lbich et al., 1993; Simonson and Hassler, 1996). Thus far only one study has attempted to quantify BIF Milankovitch-band cyclicity (Franco and Hinnov, 2008). s00354.6. CONSTRUCTING ASTROCHRONOLOGIES AND THE ATS p0100The time predictability of the Earth’s astronomical parameters invites the practice of using cyclostratigraphy as a highresolution geochronometer. While this application was already considered by Croll (1867), it was Ko¨ppen and Wegener (1924), using insolation curves calculated by Milankovitch, who first calibrated theoretical astronomicalband insolation (“canon of insolation”) directly to the geologic record, adjusting approximately known ages of the Late Quaternary Alpine ice ages to the insolation minima of the calculated curves. Significant advances in astrochronology began during the latter half of the 20th century with the development of high-resolution global marine oxygen isotope stratigraphy and magnetostratigraphy for the Pleistocene epoch (review in Kent, 1999). p0105Absolute astrochronologies recovered from cyclostratigraphy are explicitly connected to the time scale of the astronomical model. For GTS2012, a composite, continuous cyclostratigraphy has provided an absolute astrochronology from the present day back to the Oligocene/Eocene transition (0e34 Ma). Calibration of a cyclostratigraphic sequence begins with the assumption of a target astronomical curve. This may take the form of an insolation signal that most likely affected the climate that influenced sedimentation (e.g., 65N summer insolation assumed for Pleistocene astrochronology, see Chapter 29), or it can be as simple as the sum of the standardized orbital parameters (e.g., the ETP curve of Imbrie et al., 1984). This assumption introduces a basic uncertainty, because the true nature of the astronomical forcing of the sediment is not known exactly. Hilgen et al. (2000), for example, calibrated Miocene marl-clay deep sea cycles to two possible target curves, 65N summer insolation and the t0010 TABLE 4.1 Sedimentary Parameter Associated Climate Conditions EXTRINSIC (independent of sedimentation rate) Oxygen isotopes Carbon isotopes Clay assemblages Microfossil assemblages Temperature/salinity/precipitation/eustasy Productivity/C-sequestration/redox conditions Surface hydrology Salinity/temperature INTRINSIC (directly related to and/or influenced by sedimentation rate) Percent CaCO3, Si, Corg Magnetic susceptibility Microfossil abundance Clay/dust abundance Lithofacies Sediment color Grain size Productivity Sedimentation rate Productivity Surface hydrology/atmospheric circulation Depositional environment Productivity/redox conditions Erosion intensity/hydrodynamics Commonly measured sedimentary parameters that have been linked to orbitally forced climate change, and the inferred climate conditions. Extrinsic parameters vary independently from sediment supply; intrinsic parameters are directly related to sediment supply, and their signals tend to be more dramatically influenced (distorted) by changes in sedimentation rate (Herbert, 1994). Hinnov & Hilgen 71Chapter | 4 Cyclostratigraphy and Astrochronology To protect the rights of the author(s) and publisher we inform you that this PDF is an uncorrected proof for internal business use only by the author(s), editor(s), reviewer(s), Elsevier and typesetter TNQ Books and Journals Pvt Ltd. It is not allowed to publish this proof online or in print. This proof copy is the copyright property of the publisher and is confidential until formal publication. 10004-GRADSTEIN-9780444594259 precession index, correlating the mid-points of the marls to the centers of the insolation maxima and precession minima. These two calibrations produced chronologies that differ by several thousand years for any given cycle; this was taken as a fair representation of astrochronologic uncertainty. Other questions persist about which model produces the most accurate astrochronologies back through time related to Earth’s tidal dissipation and dynamical ellipticity, which to date have been assessed only in Neogene data (Section 4.7). p0110 Floating astrochronologies are disconnected from absolute time but are anchored to an independent geochronometer (e.g., a radioisotope-dated horizon, magnetic reversal, or biozone boundary). The astronomical calibration is based upon the assumption that the signal frequencies observed in cyclostratigraphy can be related to one or several frequencies predicted by astronomical modeling, for example, the 405kyr eccentricity cycle. It is assumed that planetary motions are stable enough to be recognizable back to the geological age represented by the data. This assumption holds reasonably well at least as far back as the Cretaceous/Paleogene boundary (Westerhold et al., 2008, 2009), and there are numerous key similarities between the cyclostratigraphic record and astronomical modeling at times as remote as Triassic (examples in Hinnov and Ogg, 2007). p0115 The stratigraphic coverage of the ATS that has been assembled for GTS2012 is summarized in Figure 4.7. Considerable progress has been made in the Cenozoic ATS since GTS2004. Astrochronology for the interval between 10e12 Ma that had been based on the continental Orera section in Spain is now replaced by the deep marine Monte dei Corvi section (Hu¨sing et al., 2007). The downward extension of Monte dei Corvi near La Vedova is used for the interval between 13.5e14.3 Ma (Hu¨sing et al., 2010; Mourik et al., 2010). Unfortunately, magnetization in the interval between 12e13.5 Ma is too weak, and reversal ages still have to be calculated from marine anomaly profiles. The same is true for the interval 16e23 Ma, but high-resolution studies of ODP sites from Leg 208 (Walvis Ridge; Liebrand et al., 2011) and IODP Leg 320 (equatorial Pacific) offer bright prospects for solving the remaining problems in the Early Miocene ATS, including that of the Oligocene-Miocene boundary, because the cores have reliable magnetostratigraphic records. p0120 The tuning of the Eocene-Oligocene boundary interval has also improved, in large part from analysis of the EoceneOligocene boundary section at Massignano in Italy (e.g., Brown et al., 2009). Part of the Middle Eocene has also been tuned using the classical Contessa section (Jovane et al., 2010). Finally, much progress has been made in constructing an ATS for the entire Paleocene and Early Eocene (Lourens et al., 2005; Westerhold et al., 2007, 2008; Westerhold and Ro¨hl, 2009; Hilgen et al., 2010). This has used the intercalibration of 40 Ar/39 Ar radioisotope dating and astronomical tuning to constrain a first-order tuning (Kuiper et al., 2008). In principle, astronomical tuning prior to 40e50 Ma can only be carried out at the 405-kyr eccentricity scale in view of limitations in the accuracy of the astronomical solution (Section 4.7). Uncertainties still exist in the number of 405-kyr eccentricity-related cycles in the Paleocene, and several tuning options have been presented that reflect the uncertainty (Westerhold et al., 2008; Hilgen et al., 2010). These problems will likely be resolved in the coming years when highprecision state-of-the-art single crystal 40 Ar/39 Ar sanidine and U-Pb zircon ages become available from key stratigraphic levels such as the Cretaceous-Paleogene, PaleogeneEocene and Eocene-Oligocene boundaries. p0125The ATS has been extended, in “floating” form, into the Mesozoic Era, spanning more than 75 percent of the Mesozoic time scale (Figure 4.7). The entire Maastrichtian has now been tuned (Husson et al., 2011); two options are presented, reflecting the ongoing uncertainty in the initial tuning to the orbital eccentricity. Aside from longstanding gaps in the lower Campanian and Turonian, there is continuous stratigraphic coverage to the base of the Oxfordian. BajocianBathonian cyclostratigraphic analysis is ongoing (Zio´1kowski and Hinnov, 2010); the Callovian and Sinemurian stages are the only gaps remaining in the Jurassic ATS. The Triassic ATS continues to be dominated by the continental Newark series record (Olsen and Kent, 1996). The Lower Triassic of the Germanic Basin has now been analyzed by several groups (e.g., Bachmann and Kozur, 2004; Menning et al., 2005); the Middle Triassic remains unresolved, in part due to the “Latemar controversy” (Tanner, 2010). s00404.7. PRECISION AND ACCURACY OF THE ATS p0130A number of significant factors have been identified that limit the precision and accuracy of the ATS. There are uncertainties in the climatic forcing leading to any given cyclostratigraphic record, and of the geophysical effects on the past precession of the Earth, and in modeling Solar System diffusion prior to 40e50 Ma, as follows. s00454.7.1. Seasonal Phase Relations p0135Tuning to the wrong insolation target curve can result in tuning errors of up to 10e12 kyr (half a precession cycle). For example, consider a marine sedimentary system that experiences depositional cyclicity as the result of dilution of pelagic carbonate from terrestrial run-off that peaks annually in early spring (month of March) (Figure 4.8a); when insolation is low, terrestrial run-off is correspondingly low, and pelagic carbonate deposition is relatively high (Figure 4.8b). Thus, tuning should match insolation minima with carbonate maxima. Suppose that in error it is assumed that peak summer-time ocean productivity was the cause of the pelagic carbonate cyclicity (Figure 4.8c), and that a mid-summer (month of July) insolation target is used to match carbonate 72 The Geologic Time Scale 2012 To protect the rights of the author(s) and publisher we inform you that this PDF is an uncorrected proof for internal business use only by the author(s), editor(s), reviewer(s), Elsevier and typesetter TNQ Books and Journals Pvt Ltd. It is not allowed to publish this proof online or in print. This proof copy is the copyright property of the publisher and is confidential until formal publication. 10004-GRADSTEIN-9780444594259 f0040FIGURE4.7StratigraphiccoverageoftheATSinGTS2012.1dLourensetal.(2004);2dHilgenetal.(2007);3dHu¨singetal.(2009);4dHilgenetal.(2003);5dHolburnetal.(2007);6dHu¨sing etal.(2010);7dBillupsetal.(2004);8dPa¨likeetal.(2006);9dPa¨likeetal.(2001);10dJovaneetal.(2010);11dWesterholdandRo¨hl(2009);12dLourensetal.(2005);13dWesterholdetal.(2007); 14dWesterholdetal.(2008);15dKuiperetal.(2008);16dHussonetal.(2011);17dLocklairandSageman(2008);18dSiewertetal.(2011);19dMeyersetal.(inpress);20dMeyersetal.(2001); 21dMitchelletal.(2008);22dLancietal.(2010);23dGaleetal.(1999);24dGaleetal.(2011);25dGrippoetal.(2004);26dHuangetal.(2010a);27dFietandGorin(2000);28dSprovierietal. (2006);29dHuangetal.(1993);30dGiraudetal.(1995);31dSprengerandTenKate(1993);32dHuangetal.(2010b);33dWeedonetal.(2004);34dHuangetal.(2010c);35dStrasser(2007); 36dBoulilaetal.(2008a);37dBoulilaetal.(2008b);38dBoulilaetal.(2010a);39dBoulilaetal.(2010b);40dHinnovandPark(1999);41dSuanetal.(2008);42dHuret(2006);43dWeedonand Jenkyns(1999);44dWeedonetal.(1999);45dKentandOlsen(2008);46dRuhletal.(2010);47dWhitesideetal.(2010);48dOlsenandKent(1996);49dBachmannandKozur(2004);50dKozur andBachmann(2005);51dMenningetal.(2005);52dSzurlies(2004);53dSzurlies(2007). 73Chapter | 4 Cyclostratigraphy and Astrochronology To protect the rights of the author(s) and publisher we inform you that this PDF is an uncorrected proof for internal business use only by the author(s), editor(s), reviewer(s), Elsevier and typesetter TNQ Books and Journals Pvt Ltd. It is not allowed to publish this proof online or in print. This proof copy is the copyright property of the publisher and is confidential until formal publication. 10004-GRADSTEIN-9780444594259 maxima to insolation maxima (Figure 4.8d). This results in a systematic error in chronology that is on the order of ~3 kyr. In sum, if very little to nothing is understood about the conditions of sedimentary deposition relative to the local seasonal climate, the seasonal uncertainty can be as large as Æ 10e12 kyrs (half a precession cycle). s0050 4.7.2. Tidal Dissipation, Dynamical Ellipticity and Climate Friction p0140 Through geologic time, the Earth’s rotation rate has progressively decelerated as a result of tidal energy dissipation. Tidal dissipation results in an exchange of angular momentum between the Earth and Moon, a decreasing Earth rotation, increasing EartheMoon distance, and lunar recession (Figure 4.9a). Lunar laser ranging from August, 1969 e December, 1993 indicates a lunar recession rate of 3.82 cm/ yr, which corresponds to a change in length-of-day of 2.3 ms/ century. Geological data confirm that Earth’s rotation was faster in the geological past, with apparently a 19-hour length-of-day 1 billion years ago (Figure 4.9b). Changes in rotation rate have not been uniform through time, with greater deceleration occurring after 500 Ma. p0145 The rotational deceleration increases the Earth’s precession rate p, and in turn, the obliquity and precession periods (Berger et al., 1992; Laskar et al., 1993a; Ito et al., 1993; Berger and Loutre, 1994). Table 4.2 shows the principal obliquity and precession periods over the past 250 Ma according to the La2004 nominal model, which assumes a length-of-day evolution of 2.68 ms/century, close to the 2.3 ms/century measured by lunar laser ranging (Dickey et al., 1994). In addition, Earth’s shape, or dynamical ellipticity, also contributes to p. p0150Several pioneering studies have assessed Earth’s deceleration from the cyclostratigraphic record. Lourens et al. (1996) compared astronomical models with different tidal dissipation and dynamical ellipticity values to cyclostratigraphic (oxygen isotope) data from the Mediterranean, Atlantic and Pacific oceans, concluding that the best fit was to a model based on present-day values of dynamical ellipticity and tidal dissipation. Likewise, Pa¨like and Shackleton (2000) showed that present-day dynamical ellipticity and tidal dissipation applied to astronomical tuning target curves for the past 23 million years produced the best fit with ODP Leg 154 (Ceara Rise) cyclostratigraphy based on magnetic susceptibility. However, in a study of an extremely highresolution cyclostratigraphic series from 2.4e2.9 Ma, Lourens et al. (2001) found that half of present-day tidal dissipation produced an astronomical model with the best fit. As the global cyclostratigraphic database improves and extends further back in geologic time, renewed investigation 290 300 310 320 330 340 0 50 100 150 200 Watts/m2 kiloyears before present 420 440 460 480 500 520 540 0 50 100 150 200 Watts/m2 kiloyears before present ~3 kyr error March 40ºN July 40ºN Summer productivity Spring run-off This is correct phase for CaCO3 maxima... ...but this was used for CaCO3 maxima weak run-off (a) (b) (c) (d) f0045 FIGURE 4.8 Example of seasonal uncertainty in astrochronology. (a) A northern mid-latitude marine depositional system in which the source of sedimentary (carbonate-noncarbonate) cyclicity is dilution of pelagic carbonate by terrestrial-derived siliciclastics during early spring (month of March) melt season. (b) The spring run-off depicted in (a) varies with March insolation, such that low insolation corresponds to decreased run-off, hence to pelagic carbonate maxima in the interannual stratigraphic record. (c) An incorrect model in which marine productivity during the summer (month of July) is the source of sedimentary cyclicity. (d) The model in (c) would be assumed to vary with July insolation, such that high insolation corresponds to higher productivity, and to carbonate maxima in the stratigraphic record. In sum, assuming (a)e(b) would result in an accurate tuning of stratigraphy to a March insolation target curve; assuming (c)e(d) would introduce a systematic ~3 kyr error in the tuning, due to an incorrect description of the sedimentary system response to climate change. 74 The Geologic Time Scale 2012 To protect the rights of the author(s) and publisher we inform you that this PDF is an uncorrected proof for internal business use only by the author(s), editor(s), reviewer(s), Elsevier and typesetter TNQ Books and Journals Pvt Ltd. It is not allowed to publish this proof online or in print. This proof copy is the copyright property of the publisher and is confidential until formal publication. 10004-GRADSTEIN-9780444594259 should clarify the long-term evolution of Earth’s tidal dissipation and dynamical ellipticity, which are thought to change as a function of continent/ocean configuration, core-mantle processes and crustal loading (e.g., ice sheets). p0155 Glacial loading of the Earth’s crust, i.e., climate friction, is thought to engender “obliquity-oblateness feedback” and secular change in Earth’s obliquity (tilt) angle (Bills, 1994; Rubincam, 1995; Ito et al., 1995; Levrard and Laskar, 2003). Thomson (1990) noticed systematic differences between the spectral lines of the Pleistocene SPECMAP stack (Imbrie et al., 1984) and those of the astronomical parameters, suggesting that the recorded signal was perturbed as a result of the repeated massive ice sheet loading/unloading in the Northern Hemisphere. Thomson discovered a differential phasing in the obliquity and precession bands of SPECMAP that could be explained by varying the precession rate p by Æ 10% at 100,000-year timescales (the scale of the glaciations). Laskar et al. (1993a, b) point out that such a change could allow for passage of p into resonance with the s6 À g6þg5 precession term and induce a ~0.5 increase in maximum obliquity. Modeling shows that predicted longer length-of-day in the near future will force precession into this resonance (see Figure 14 in Laskar et al., 2004). However, thus far, no evidence has been presented that Earth’s EARTH from above North Pole spin direction MOON accelerates Earth's tidal bulge raised by Moon is delayed,so leads Earth-Moon axis Torque operates against spin recedes 20 22 24 2000 1500 1000 500 0 x Modern value Corals, mean Corals, maximum Bivalves, mean Stromatolites, mean Brachiopods, maximum Stromatolites, maximum Elatina-Reynella x Age (Ma) Hoursperday (a) (b) La2004 x f0050 FIGURE 4.9 Earth rotation deceleration from tidal energy dissipation. (a) The Moon raises a tidal bulge that is delayed due to friction between the oceans and crust, and within the solid Earth, by an angle d, which is 0.2 for the solid M2 tide and ~65 for the net ocean M2 tide (Munk, 1997; Ray et al., 2001). Gravitational force from the Moon acts on the offset bulge, producing a torque on the Earth in a direction opposite from the rotation, causing the Earth to decelerate. (b) Deceleration of the Earth over the past 2 billion years based on geological data. The data shown are from Williams (2000). Corals, bivalves and brachiopods secrete daily growth bands that modulate annually; fossils indicate more growth bands per year back in time. Stromatolite laminations have been interpreted similarly. Tidalites are an alternate, relatively rare source of information. The red dashed line indicates the length-of-day model used in the nominal La2004 solution of Laskar et al. (2004), which assumes present-day tidal dissipation and dynamical ellipticity. Table 4.2 lists obliquity and precession periodicities for key geological times. 75Chapter | 4 Cyclostratigraphy and Astrochronology To protect the rights of the author(s) and publisher we inform you that this PDF is an uncorrected proof for internal business use only by the author(s), editor(s), reviewer(s), Elsevier and typesetter TNQ Books and Journals Pvt Ltd. It is not allowed to publish this proof online or in print. This proof copy is the copyright property of the publisher and is confidential until formal publication. 10004-GRADSTEIN-9780444594259 precession ½AU3Š has undergone resonance as the result of climate friction. s0055 4.7.3. Solar System Diffusion p0160 Modeling experiments demonstrate that the inner planets of the Solar System experienced significant chaotic diffusion throughout the remote past (Laskar 1990; Laskar et al., 1992; Laskar, 1994). Over the past ~40 million years, the Earth and Mars orbits have been in 2:1 secular resonance, described by the argument q ¼ (s4es3) À 2(g4eg3), where s3 and s4 are secular frequencies defining the rotation of the ascending nodes of the orbits, and g3 and g4 are secular frequencies for the rotation of orbital perihelia of Earth and Mars (Matthews et al., 1997; Laskar, 1999; Laskar et al., 2004). Prior to 40 million years ago, modeling indicates that the two orbits experienced intermittent chaotic transitions, and 1:1 resonance states, i.e. , q ¼ (s4es3) À (g4eg3) (e.g., Figure 23 in Laskar et al., 2004). These resonance states may be observed indirectly in paleoclimate data in long-period modulations of Earth’s obliquity and precession index, in the beat frequencies produced by the terms pþs3 (1/41 kyr) and pþs4 (1/39 kyr) in the obliquity, and pþg3 (1/19.1 kyr) and pþg4 (1/18.9 kyr) in the precession index, where p ¼ 50.4467718”/yr is the Earth precession rate (variable through time due to tidal dissipation and dynamical ellipticity). The term g4eg3 is also present in Earth’s orbital eccentricity as a long-period modulation in the ~100 kyr variation, e.g., the beat frequency raised by g4eg5 (1/94.9 kyr) and g3eg5 (1/98.8 kyr). p0165Figure 4.10 shows s4es3 and g4eg3 in the modulation envelopes of the La2004 obliquity and eccentricity, for which the former has a ~1.2 myr periodicity, and the latter, a ~2.4 myr periodicity, over 0e10 Ma; also shown are the modulations over 85e95 Ma to illustrate transient shortening of the modulations from chaotic diffusion. These modulations have been confirmed in Cenozoic stratigraphy, notably across the Miocene-Oligocene transition in deep-sea sedimentary sequences recovered by the Ocean Drilling Program (Shackleton et al., 1999; Pa¨like et al., 2004). In the future, the documentation of Earth-Mars secular resonance states throughout the Mesozoic Era will provide key constraints on the gravitational parameters used in Solar System modeling (Laskar 2003; Laskar et al., 2004). s00604.7.4. Summary of Uncertainties p0170In Figure 4.11 the “tidal uncertainty” refers to lack of knowledge about Earth’s past tidal dissipation and its effect on the precession rate, which presents as an accumulating deficit of years in the recorded obliquity and precession cycles back through time (Figure 20.7 in Lourens et al., 2004). As this amount accumulates, at some point it becomes necessary to tune instead to the orbital eccentricity; this is depicted at 50 Ma. At times prior to 50 Ma, astronomical models diverge as the combined result of initial condition uncertainties and integration error, with close agreement only for the 405-kyr eccentricity cycle back to 250 Ma. Sometime between 50 and 100 Ma, modeling indicates that a “transition” occurred in the resonance state between the Earth and Mars orbits, which would have affected the 100-kyr eccentricity variation. This is shown by the shaded area labeled “transition”, at which point it becomes necessary to restrict tuning to the 405-kyr cycle only. The precise timing of the transition will be determined through future, detailed examination of the cyclostratigraphic record (Laskar et al., 2011). s00654.8. ASTROCHRONOLOGYGEOCHRONOLOGY INTERCALIBRATION p0175The extension of the astronomical dating method into the MiddleeEarly Pleistocene and Pliocene (Shackleton et al., 1990; Hilgen, 1991a, b) stimulated much research directed at the comparison of astronomical and radio-isotopic ages, especially because astronomical ages proved to be significantly older e by ~3 to 12% e than published K/Ar ages for the same magnetic reversal boundaries. This discrepancy was t0015 TABLE 4.2 (a) Time (Ma) 54 kyr 41 kyr 39 kyr 29 kyr 28 kyr 0e5 53562 40917 39510 29727 28852 50e55 50710 39185 37975 28877 28003 100e105 47847 38865 36324 27910 27137 150e155 45188 35852 34807 27027 26233 200e205 42680 34211 33300 26130 25374 244e249 40502 32830 31949 25272 24582 (b) Time (Ma) 24 kyr 22 kyr 19.0 kyr 18.9 kyr 16.5 kyr 0e5 23657 22336 19080 18947 16453 50e55 23052 21820 18716 18539 16168 100e105 22472 21304 18335 18090 15873 150e155 21863 20768 18077 17794 15574 200e205 21258 20206 17519 17391 15253 244e249 20691 19708 17129 17007 14968 Dissipation-induced changes in the main periods of the Earth’s obliquity variation (a) and precession index (b) from 0 to 250 million years ago. Periods are estimated over 5 million year intervals of the La2004 nominal solution (Laskar et al., 2004) with 4p multi-taper amplitude spectra using Analyseries (Paillard et al., 1996); values are in thousands of years. Hinnov & Hilgen 76 The Geologic Time Scale 2012 To protect the rights of the author(s) and publisher we inform you that this PDF is an uncorrected proof for internal business use only by the author(s), editor(s), reviewer(s), Elsevier and typesetter TNQ Books and Journals Pvt Ltd. It is not allowed to publish this proof online or in print. This proof copy is the copyright property of the publisher and is confidential until formal publication. 10004-GRADSTEIN-9780444594259 largely attributed to incomplete Ar degassing of basaltic bulk rock samples used for dating the reversals (Hilgen et al., 1991b). The switch to 40 Ar/39 Ar dating led to very accurate and precise ages, but only the analytical error, leading in K/Ar dating, was initially taken into account and not the full error of ~2.5% that included such factors as uncertainties in the decay constants and mineral dating standards (Min et al., 2000). This encouraged further research, as the error in astronomical dating is comparatively small once the tuning itself is correct (~0.1% between 5 and 10 Ma; e.g. Kuiper et al., 2008). p0180 Following earlier attempts (e.g., Renne et al., 1994; Hilgen et al., 1997), a direct½AU1Š intercalibration was achieved through a direct comparison of astronomical and Ar/Ar ages of ash beds intercalated in astronomically tuned marine sections in the Melilla Basin in Morocco (Kuiper et al., 2008). This study revealed a systematic offset with astronomical ages being ~0.7% older. This offset was removed by fitting the 40 Ar/39 Ar ages to the astronomical ages by adjusting the age of the Fish Canyon tuff sanidine (FCs) dating standard from 28.02 Æ 0.28 Ma (Renne et al., 1998) to 28.201 Æ 0.046 Ma. Consequently, the error in the astronomically calibrated FCs age is greatly reduced due to the fact that uncertainties related to decay constants and the age of the primary dating standard which together 0 0.005 0.01 9492908886 Eccentricity 0 0.005 0.01 0 1 1086420 Eccentricity Millions of years b.p. Millions of years b.p. 0 1 obliquity(º) obliquity(º) (a) (b) f0055 FIGURE 4.10 Amplitude modulations (AM) of the eccentricity (blue lines) and obliquity (green lines). The eccentricity modulations have a dominant ~2.45 myr periodicity, and the obliquity modulations have a 1.2 myr periodicity. These AM curves were estimated by applying Hilbert transforms to Taner bandpass filtered (Taner, 2000) La2004 eccentricity and obliquity series over 0e249 Ma with a passband of 0.01025 Æ 0.00075 cycles/kyr (short eccentricity) and a passband of 0.0275 Æ 0.0045 cycles/kyr (main obliquity). The filtered series were Hilbert-transformed (Taner et al., 1979) to obtain the amplitude modulations. The two excerpts illustrate (a) 2:1 secular resonance from 0e10 Ma, and (b) 1:1 resonance indicated by the frequency correspondence between eccentricity and obliquity from 87e90 Ma. 77Chapter | 4 Cyclostratigraphy and Astrochronology To protect the rights of the author(s) and publisher we inform you that this PDF is an uncorrected proof for internal business use only by the author(s), editor(s), reviewer(s), Elsevier and typesetter TNQ Books and Journals Pvt Ltd. It is not allowed to publish this proof online or in print. This proof copy is the copyright property of the publisher and is confidential until formal publication. 10004-GRADSTEIN-9780444594259 dominate the full error in 40 Ar/39 Ar dating are effectively eliminated. p0185 The 28.201 Æ 0.046 Ma FCs age has been independently confirmed by 40 Ar/39 Ar dating of the A1 ashbed in the astronomically tuned Faneromeni section, and U-Pb dating of single zircon crystals in the Fish Canyon tuff and in ash beds from the astronomically dated Monte dei Corvi section (Rivera et al., in press; Wotzlaw et al., 2010). These results suggest that the FCs age of 28.30 Ma based on 40 Ar/39 Ar-UPb pairs and neglecting astronomical dating (Renne et al., 2010) is too old, and that an FCs age of 27.93 Ma based on 40 Ar/39 Ar-astrochronologic intercalibration of the Matayuma/ Brunhes transition (Channell et al., 2010) is too young. The 28.201 Æ 0.046 Ma FCs standard is further supported by a three-way intercalibration of 40 Ar/39 Ar, U-Pb and astrochronology across the Cenomanian/Turonian boundary (Meyers et al., in press), and by a direct comparison of U/Pb and 40 Ar/39 Ar ages of two ash beds from the Eocene Green River Formation, allowing a direct comparison with the astronomical solution for the first time (Smith et al., 2010). The intercalibration guarantees that astronomical and 40 Ar/39 Ar dating will produce the same age when the same event in Earth history is dated. The astronomically calibrated FCs standard provides unprecedented tight constraints for the tuning of pre-Neogene successions. In this way, problems such as the existing Eocene gap in the ATS or the reduced reliability of the astronomical solution further back in time can be circumvented. s0070 4.9. A NEW ASTRONOMICAL SOLUTION p0190A new solution, La2010, has now been made available (Laskar et al., 2011). This solution is limited to the orbital eccentricity, and uses the new, highly accurate ephemeris solution INPOP10 over short time scales (Fienga et al., 2009, 2010). La2010 is reliable back to 50 Ma, as compared to 40 Ma for La2004. This is a major improvement, as the solution must be one order more accurate in order to extend its reliability by an additional 10 myr (Laskar et al., 2004). La2010 will play a major role in solving problems presently encountered in the tuning of the Paleocene and early Eocene (Westerhold et al., 2008; Hilgen et al., 2010). It will shed light on the possibility of long-period eccentricity forcing of Eocene hyperthermals (Lourens et al., 2005) and Mesozoic black shales (Mitchell et al., 2008). cesectitle00REFERENCES Adhe´mar, J., 1842. Les re´volutions de la mer, de´luges pe´riodiques. CarilianGouery et V. Dalmort, Paris, p. 184. Anderson, R.Y., 1982. A long geoclimatic record from the Permian. Journal of Geophysical Research 87, 7285e7294. 41 405 100 20 0.001 0.01 0.1 1 10 0 100 200 300 400 500 %ageuncertainty U-Pb, 40Ar/39Ar 30 kyr 150 kyr 350 kyr 500 kyr maximum uncertainty transition 60 kyr ~300 kyr tidal uncertainty (a) MILLIONS OF YEARS B.P. Anchored to La2004 Future Paleozoic ATS coverage 'Floating' ATS coverage (b) 0 100 200 300 400 500 f0060 FIGURE 4.11 Summary of current ATS uncertainty and stratigraphic coverage through the Phanerozoic Eon. (a) Lower limit of age uncertainty (in %) from high-precision geochronology (dash-dot line) and cyclostratigraphy (solid curves). Red lines indicate the geologic time intervals for which the different modeled astronomical parameters may be used with confidence. “Tidal uncertainty” refers to the uncertainty in knowledge of past tidal friction and its effect on the Earth’s rotation and precession rate p (Lourens et al., 2004). “Maximum uncertainty” on the 405-kyr term refers to uncertainty estimated from differences among six different astronomical models (Laskar et al., 2004). The shaded area labeled “transition” refers to the latest predicted Earth-Mars orbital resonance transition. The 405-kyr orbital eccentricity term prior to 250 Ma has not been modeled, and so maximum uncertainty has not been extended into the Paleozoic Era. (b) Stratigraphic coverage of the ATS in GTS2012 in solid red lines; future ATS coverage for the Paleozoic Era (potential candidates in Section 4.5) in dashed red lines. The Cenozoic ATS is anchored to the La2004 solution, although uncertainties persist in Paleogene tuning. The Mesozoic ATS is a “floating” timescale, anchored locally by radioisotope dating, but not to a specific astronomical solution. 78 The Geologic Time Scale 2012 To protect the rights of the author(s) and publisher we inform you that this PDF is an uncorrected proof for internal business use only by the author(s), editor(s), reviewer(s), Elsevier and typesetter TNQ Books and Journals Pvt Ltd. It is not allowed to publish this proof online or in print. This proof copy is the copyright property of the publisher and is confidential until formal publication. 10004-GRADSTEIN-9780444594259 Anderson, R.Y., 2010. Earth as diode: monsoon source of the orbital ~100 ka climate cycle. Climate of the Past Discussions 6, 1421e1452. Bachmann, G.H., Kozur, H.W., 2004. The Germanic Triassic: correlations with the international chronostratigraphic scale, numerical ages and Milankovitch cycliycity. Hallesches Jahrbuch fu¨r Geowissenschaften B26, 17e62. Berger, A., Loutre, M.-F., 1994. 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This proof copy is the copyright property of the publisher and is confidential until formal publication. 10004-GRADSTEIN-9780444594259 AUTHOR QUERY FORM Book: GRADSTEIN-9780444594259 Chapter: 04 Please e-mail your responses and any corrections to: E-mail: P.Wilkinson@Elsevier.com Dear Author, Any queries or remarks that have arisen during the processing of your manuscript are listed below and are highlighted by flags in the proof. (AU indicates author queries; ED indicates editor queries; and TS/TY indicates typesetter queries.) Please check your proof carefully and answer all AU queries. Mark all corrections and query answers at the appropriate place in the proof (e.g., by using on-screen annotation in the PDF file http://www.elsevier.com/framework_authors/ tutorials/ePDF_voice_skin.swf) or compile them in a separate list, and tick off below to indicate that you have answered the query. Please return your input as instructed by the project manager. Uncited reference: References that occur in the reference list but are not cited in the text. Please position each reference in the text or delete it from the reference list. The following are not cited Prokopenko et al., 2001 Missing reference: References listed below were noted in the text but are missing from the reference list. Please make the reference list complete or remove the references from the text. NIL Location in Chapter Query / Remark AU:1, page 77 Should these have 40 and 39 superscripts? , AU:2, page 71 Please insert table title? , AU:3, page 76 Please insert table title? , GRADSTEIN: 04 Non-Print Items Abstract: The Milankovitch theory that quasi-periodic oscillations in the Earth-Sun position have induced significant 104 -106 year variations in the Earth’s stratigraphic record of climate is widely acknowledged. This chapter summarizes the Earth’s astronomical parameters, the nature of astronomically forced solar radiation, fossil astronomical signals in the stratigraphic record, and the use of these signals in calibrating geologic time. Keywords: ---