The mid-Cretaceous was marked by emplacement of large igneous provinces (LIPs) that formed gigantic oceanic plateaus, affecting ecosystems on a global scale, with biota forced to face excess CO 2 resulting in climate and ocean perturbations. Volcanic phases of the Ontong Java Plateau (OJP) and the southern Kerguelen Plateau (SKP) are radiometrically dated and correlate with paleoenvironmental changes, suggesting causal links between LIPs and ecosystem responses. Aptian biocalcification crises and recoveries are broadly coeval with C, Pb, and Os isotopic anomalies, trace metal influxes, global anoxia, and climate changes. Early Aptian greenhouse or super-greenhouse conditions were followed by prolonged cooling during the late Aptian, when OJP and SKP developed, respectively. Massive volcanism occurring at equatorial versus high paleolatitudes and submarine versus subaerial settings triggered very different climate responses but similar disruptions in the marine carbonate system. Excess CO 2 arguably induced episodic ocean acidification that was detrimental to marine calcifiers, regardless of hot or cool conditions. Global anoxia was reached only under extreme warming, whereas cold conditions kept the oceans well oxygenated even at times of intensified fertility. The environmental disruptions attributed to the OJP did not trigger a mass extinction: rock-forming nannoconids and benthic communities underwent a significant decline during Oceanic Anoxic Event (OAE) 1a, but recovered when paroxysmal volcanism finished. Extinction of many planktonic foraminiferal and nannoplankton taxa, including most nannoconids, and most aragonitic rudists in latest Aptian time was likely triggered by severe ocean acidification. Upgraded dating of paleoceanographic events, improved radiometric ages of the OJP and SKP, and time-scale revision are needed to substantiate the links between magmatism and paleoenvironmental perturbations.

Abstract This volume is derived from an SEPM international workshop entitled Multidisciplinary Approach to Cyclostratigraphy, organized by the editors in May 2001 and held in Sorrento (Naples, Italy). In the Introduction we offer a brief history of how concepts of orbital cyclicity and its effects on the Earth evolved, an appraisal of the present state of research, and an overview of the papers in this volume. The main body of the volume consists of the contributed studies. These include a paper on conceptual and pragmatic approaches to stratification cycles by one of the pioneers of cyclostratigraphy, Walther Schwarzacher, who, in the 1940s, discovered the hierarchical expression of orbital cycles in rocks. The other contributions are specific studies of cyclic sequences, extending from the Quaternary back to the Triassic, covering the range from continental deposits to the deep sea, and employing a wide variety of techniques for extracting and processing the information.

Abstract Zircon dates and orbital interpretation of bedding rhythms have yielded very different estimates on the duration of Middle Triassi stages. Recently, a core was drilled in Middle Triassic basin sediments at Seceda (western Dolomites) to directly compare cyclostratigraphy with geochronologic data. Detailed study of facies, sediment sources, and transport mechanisms formed the basis of the statistical analysis of bedding rhythms that are based on a grayscale scan and a gamma-ray well log. Amplitude spectrograms reveal strong frequency components at f = 0.025 cycles/cm in the main nodular limestone interval (92–64 m core depth), corresponding to the dominant 40 cm bedding thickness. Significant spectral differences were found between the grayscale and gamma-ray bedding proxies, placing doubt on the appropriateness of the use of the latter as an effective tool in cyclostratigraphy. In the uppermost part of the succession (59–45 m core depth) calciturbidites constitute more than 50% of the rock volume. If turbidites and tuffs are removed from the rock column, the spectrogram in this interval becomes much smoother and significant peaks appear at higher frequencies. The signals of this pelagic background sedimentation were extracted by bandpass filtering and show strong similarities to Milankovitch cycles in the Quaternary. According to this cyclostrati-graphic interpretation, the dominant 40 cm bedding rhythm was produced by eccentricity, and the average sedimentation rate results in ~3.6 mm/ky. This estimate is in contrast to zircon data from volcaniclastic layers that bracket this core interval and suggest a sedimentation rate of 13.5 mm/ky. As it currently stands, neither of the two interpretations is yet fully satisfactory. Although the presence of orbital variations in the Triassic analogous to those predicted for the last 20 My remains questionable owing the presumed chaotic behavior of the planets, the zircon age data have uncertainties related to their origin that remain unaccounted for and require further investigation.

Abstract Detailed sedimentological and carbon-isotope data have allowed us to propose a high-resolution regional correlation between four Lower Cretaceous carbonate-platform successions, Early Aptian to Early Albian in age, cropping out in the southern Apennines. These successions, formed in open to restricted lagoonal and peritidal-supratidal settings, reveal a high-frequency cyclic recurrence of depositional and early meteoric (karstic and/or pedogenetic) features. The latter are normally superimposed on subtidal deposits, suggesting that the above cyclicity may be linked to sea-level changes. In the studied sections, elementary cycles are grouped into bundles, which in turn are grouped into superbundles. Although bundles and superbundles appear to be related to the Earth’s orbital short-eccentricity and long-eccentricity signal, respectively, elementary cycles seem to record either the precession or a combination of the precession and obliquity periodicity. Moreover, the stacking pattern of the orbitally controlled cycles suggests that they are superimposed on lower-frequency sea-level fluctuations (transgressive-regressive facies trends). The δC curves, established throughout the sections, show the same carbon-isotope pattern as the time-equivalent pelagic strata (two positive carbon-isotope episodes separated by an interval with lower carbon-isotope values). On the basis of this correspondence, and integrating the cyclostratigraphy and the carbon-isotope stratigraphy with the sequence stratigraphy, we propose a high-precision regional correlation and a chronostratigraphic chart and suggest a duration of 7.8 My for the studied interval. Moreover, on the basis of sequence stratigraphy and isotope geochemical criteria, and using our orbital chronostratigraphy as a reference frame, a correlation with current global scales is here proposed.

Abstract A detailed carbon-isotope stratigraphy has been generated from Barremian to Lower Aptian shallow-water carbonate sections in the Campania Apennines (Monte Raggeto, southern Italy). The new isotope curve is correlated with the magnetostratigraphically and biostratigraphically dated pelagic carbon-isotope stratigraphy from the Cismon locality (Southern Alps, northern Italy). All the major positive and negative carbon-isotope excursions that characterize the Barremian and Early Aptian carbon-isotope stratigraphy can be recognized in the shallow-water curve. Cyclostratigraphy, which was established earlier at the Monte Raggeto section, is used as an age calibration tool for the Barremian and Early Aptian isotope stratigraphy. The duration of the isotopically calibrated stratigraphic interval between the top of Chron M3 and the base of Chron M0 is estimated as 4 My. These time calculations are in good agreement with cyclostratigraphic data from the Cismon locality but differ from estimates based on a magnetic anomaly block model for the interval between M3 and M0 that yield only 3 My. We have also calculated that the Selli Level Equivalent (SLE) at the Monte Raggetto locality was deposited within 1.2 My. Our results demonstrate that the combination of chemostratigraphic and cyclostratigraphic studies can contribute significantly to the calibration of the Mesozoic time scale.

Abstract The Berriasian Pierre-Châtel Formation in the Swiss and French Jura Mountains is dominated by shallow-marine carbonates tha overlie lacustrine and marginal-marine sediments with a major transgressive surface. Detailed facies analysis of five sections allows the definition of elementary and small-scale depositional sequences, which commonlexhibit deepening-shallowing trends. Benthic foraminifera and rare ammonites on the platform, as well as a sequence-stratigraphic correlation with a well-dated deeper-water section,furnish the biostratigraphic framework. Thus, the large-scale sequence boundaries below and at the top of the Pierre-Châtel Formation can be correlated with dated boundaries in other European basins. This time constraint and the hie archical stacking pattern on the platform as well as in thebasin suggest that the sea-level fluctuations influencing the formation of the depositional sequences were controlled,at least partly, by Milankovitch cycles. The elementary sequences correspond to the 20 ky precession cycle, and the small-scale sequences to the 100 ky eccentricity cycle. Uncertainties in the definition of sequences exist if facies contrasts are too low to develop clearly marked sequence boundaries or maximum-flooding intervals. Nevertheless, a best-fit solution for the correlation of the small-scale sequences between the studied sections can be proposed. Thelowermost three small-scale sequences of the Pierre-Châtel Formation are analyzed in detail. They are decompacted and correlated on the level of the elementary sequences. Within this relatively precise time frame, the flooding of the Jura platform (following the early Berriasian sea-level lowstand) can be monitored. It is seen that the transgression occurred stepwise: every 20 ky, atransgressive pulse established marine facies farther towards the platform interior. This study demonstrates that the cyclostratigraphical approach makes it possible to construct a narrow time frame, within which the rates of sedimentary, ecological, and diagenetic processes can be evaluated, phases of differential subsidence identified, and the durations of stratigraphic gaps estimated. The complex and dynamic evolution of an ancient carbonate platform can thus be studied with a time resolution of 20 to 100 ky.

Abstract On the basis of cyclostratigraphy and sequence stratigraphy criteria, an orbital chronostratigraphy is hereproposed for the Upper Valanginian-Lower Hauterivian (Lower Cretaceous) stratigraphic interval. For such a purpose two biostratigraphically constrainedcarbonate platform section were measured and sampled at centimeter scale in southern Italy: (1) San Lorenzello, Matese Mountains in theCampania Apennines, and (2) Sferracavallo, Palermo Mountains in northwestern Sicily. The former has a thickness of about 87 m,and thelatter totals about 40 m. Analysis of depositional and early diagenetic features has shown that both the successions are characterized byinternal cyclicity, consistent with orbital (Milankovitch) forcing. This high-frequency cyclicity, in which the elementary cycles areorganized in bundles and in groups of bundles (superbundles), appears to be superimposed on three longer (from ~ 800 ky to ~ 1200 km transgressive-regressive facies trends (T∕RFTs). Whereas the elementary cycles record the precession and∕or the obliquity signal (or a combination of them), the bundles and the superbundles correspond to the short- and long - eccentricity signals (~ 100 ky and 400 ky cycles), respectively. Sequencestratigraphic criteria, used to interpret the superbundles and the T∕RFTs in terms of depositional-sequence equivalents, allowed us to propose chronostratigraphic diagrams of the studied intervals and to attempt regional- to global-scale physical correlations. At regional scale, the Sferracavallo section was correlated, bundle by bundle, with the time-correspondent segment of the San Lorenzello section. The chronostrat igraphic correlation shows that only one main gap, calculated as about 200 ky, occurs in the studied intervals. This allows us to assume that the sedimentary record can be considered quasi -continuous, at least at the superbundle scale (~ 400 ky).The assembled orbital chronostratigraphy suggests that the time recorded in the San Lorenzello and in the Sferracavallo sections is 2.9 and 1.9 My, respectively. At global scale, a physical correlation is proposed with the time-equivalent third-order sequences of Haq et al. 1987 and Jacquin et al. (1998) , taking into account the stratigraphic position of the Valanginian-Hauterivian (Early Cretaceous) boundary in the standard time scales, as well as in our orbital chronostratigraphy. This correlation shows that there is a good agreement between the 2.6 My time duration of the stratigraphic interval spanning from the Valanginian 4 to the Hauterivian 1 sequence boundaries (Jacquin et al., 1998) and the 2.8 My interval estimated on the basis of our orbital chronostratigraphy.

Abstract A 160-m-long section measured in the lagoonal facies of the Middle Triassic Latemar platform (Dolomites, Italy) reveals a set of frequency components that we interpret as a strong Milankovitch signal. In this interpretation, all principal frequencies associated with the theoretical Middle Triassic precession index, P1 = 1/(21.7 ky), P2 = 1/(17.6 ky), and its modulations, E1 = 1/(400 ky), E2 = 1/(95 ky),and E3 = 1/(125 ky), were detected in a time-frequency evaluation of the cycles. A weak obliquity signal is also present in part ofthe section.Thus, the Latemar cycles appear to have recorded the clearest orbital forcing signal yet found in a carbonate platform. This astronomical calibration indicates that the section was deposited in ca. 3.1 My and therefore that the entire Latemar cyclic succession (~470 m) took at least 9 My to form. However, the calibration also leads to serious conflicts with other interpreted geological data: U/Pb radiometric ages of zircons collected from tuffites within theLatemar lagoon and in coeval basinal sediments point to a timescale that is five times shorter than this astronomically calibrated estimate; similar discrepancies arise when the average duration of Triassic ammonoid biozones or the sedimentation rates of coeval basinal series are considered. Nonetheless,all of the methods that have been used to estimate the time of formation of the Latemar platform continue to have shortcomings, and the contradictions among these different geologicalcalibrations remain unresolved.

Abstract An integrated cyclostratigraphic approach was applied to the 460-m-thick succession in the Latemar platform interior. The approach uses new high-resolution cyclostratigraphic data from vertical sections, lateral tracing of physical surfaces over the platform top, new and existing biostratigraphic data, existing isotopic ages from volcanic ash layers, and new spectral analyses in order to develop a genetic cyclostratigraphic model. Hierarchical cycles include meter-scale shallowing-upward microcycles and 2–6 bundled thinning-upward macrocycles. Lateral tracing and correlation of microcycles and macrocycles provides a high-resolution 2D architectural model of the platform interior. The large majority of microcycles and macrocycles is physically persistent over the platform top with only moderate changes in thickness and internal facies. The platform top showed simultaneous vertical aggradation controlled by low-amplitude, high-frequency sea-level changes. Tied-in cyclostratigraphic and biochronostratigraphic data indicate that the 619–701 microcycles in the platform interior include little more than a single ammonoid biozone ( Secedensis Zone), that the total time interval is shorter than 4.10 Ma(average total time interval =1.88 My), and that the interpolated microcycle period is shorter than 5.85 ky (average interpolated microcycle period = 2.68 ky). Microcycles cannot be reconciled with precession forcing but reflect sub-Milankovitch forcing. Spectral analysis is based exclusively on accommodation cycles, which represent the only direct indication of external control on cyclic deposition. Blackman-Tukey spectral, multi-taper spectral, and harmonic analyses indicate highly similar and significant frequencies and amplitudes which are largely stationary over all subsets applied to the cyclic series. Ratios and periods indicative of orbital forcing in the Milankovitch band potentially exist at (very) high significance points with Δ t = 4.2 ky. In the Latemar cyclic succession, basic microcycles represent sub-Milankovitch forcing (4.2 ky), thinning-upward, 2–6 bundled macrocycles short- and long-precession forcing (18, 21 ky), and higher-order cycle bundles short and long obliquity (35, 45 ky) as well as short-eccentricity forcing (95–105 ky). Because of significant latitudinal temperature gradient and seasonal climate differences, the Triassic period held a significant potential for sub-Milankovitch fluctuations in coupled ocean-atmosphere circulation. They probably triggered low-amplitude, high-frequency changes in sea level and controlled the deposition of sub-Milankovitch microcycles. Previous studies of the Latemar carbonate platform favored a model-dependent approach based on smaller cyclostratigraphic datasets from single sections and spectral analyses. The resulting orbital-forcing models could not be reconciled with the existing biochronostratigraphic framework for the Triassic and the Anisian to Ladinian stages. They left a widely noted deep disagreement between biochronostratigraphic and cyclostratigraphic time scales. In contrast, the new forcing model of this study is based on a complete 2D cyclostratigraphic dataset, considers all biochronostratigraphic constraints, and includes time-calibrated spectral analyses. The model reconciles biochronostratigraphic and cyclostratigraphic time scales. The Latemar cyclic series includes the oldest explicit sub-Milankovitch signal and the oldest set of both sub-Milankovitch and Milankovitch signals yet observed in the geologic record.

Abstract The Salento continental shelf of Apulia (southern Adriatic) shows a complex stratigraphic architecture of Pleistocene prograding wedges that records the effects of the interplay of sediment accumulation, glacio-eustatic sea level changes, and regional tectonics. The interpretation of high-resolution seismic reflection profiles reveals three ravinement surfaces, extending landwards from the shelf break and showing low gradients. They have been considered to be stratigraphic markers and tentatively correlated to the oxygen curves of the isotopic stratigraphy. Even if direct dating of seismic sequences and corresponding unconformities is lacking, this correlation is well supported by the lateral extent and continuity of the ravinement surfaces, recognized in the whole investigated area. Similar qualitative correlation of unconformities with the curves of oxygen-isotope stratigraphy has been already used by other authors in different case histories of continental shelves of both active and passive margins. Moreover, in the study area the regional geological framework suggests that during the Middle Pleistocene the rate of tectonic uplift interacted with the rateof glacio-eustatic fluctuations, producing the deposition of forced-regression systems tracts. The forced-regression prograding wedge that enlarged the shelf by about fifteen kilometers is here dated as Middle Pleistocene. Starting fromthe upper part of the Middle Pleistocene, the stratigraphic architecture of the prograding wedges was controlled mainly by glacio-eustatic sea-level changes forced by short-eccentricity cycles. This is suggested by the stratigraphic architecture of the last two prograding wedges, interpreted as incomplete fourth-order depositional sequences and consisting of forced-regression, lowstand, and transgressive systems tracts. The eustatic signal as an expression of the Earth’s orbital cyclicity (short eccentricity) appears over whelming with respect to the tectonic one, and its prominence suggests a decrease in the rate of uplift of the Apulian foreland during the last 250 ky.

Abstract Petrophysical datasets and related spectral analysis from Plio-Pleistocene sediments cored on the Western Antarctic continental rise during the Ocean Drilling Program, Leg 178, are discussed. It is shown that in different cores, nonharmonic wavelength peaks, when normalized, exhibit a very high correlation factor with predicted Earth’s orbital variations. It is also found that both short (~ 95–125 ky)and long (~ 400 ky) eccentricity periodicities emerge clearly from the signal during the whole Pleistocene, without an evident switch to obliquity at mid-Pleistocene (~ 0.9 Ma), as reported in the literature. This suggests that the lithological parameters, a proxy for glacial cycles, are controlled, directly or indirectly, by astronomically forced processes (Milankovitch cycles). Moreover, the good correlatability among distant coring sites, based on systematic sedimentological variations at intervals of about 140 and 370 ky, allows extension of the results to regional scale.