Time-series analysis in cyclic stratigraphy: An example from the Cretaceous of the Southern Alps, Italy

The importance of time-series analysis in cyclic stratigraphy is evaluated by comparing three different methods (adaptive multiple taper spectral analysis, auto-/cross-correlation analysis, cova functions) applied to stratigraphic time series from the Early Cretaceous Cismon section in northern Italy. Carbonate content and magnetic susceptibility vary in a quasi-cyclic fashion in this pelagic limestone section and are almost perfectly negatively correlated. The spectral technique requires a high degree of preprocessing of the original data (interpolation and resampling at a regular interval, filtering, inversion) which introduces smoothing and rounding errors. The statistical correlation analysis also requires evenly and (for cross-correlation) correspondingly spaced series. The geostatistical cova functions (a generalization of the cross-variogram) prove to be the most versatile and robust of the methods compared. Cova functions can be calculated from unevenly and noncor-respondingly spaced time series without any preprocessing. This method also retains relatively more of the signal if noise and extreme outliers obscure the picture. The periodicities detected in the Cismon time series fall in the range of Milankovitch cycles. Cycle periods of 45 cm and 80 cm likely correspond to dominant precession and obliquity cycles. Due to the inaccuracy of the Cretaceous time scale periods cannot be matched exactly yet, but cycle ratios are close to expected ratios so that there is great potential for future cyclostratigraphic work to contribute to a substantial improvement of the geologic time scale.     

Quaternary Fourier stratigraphy: Orbital templates and Milankovitch anomalies

A simple template-generating algorithm using summer insolation at 65°N as input provides a timeseries for the last 2 million years that can be compared directly with the oxygen isotope record in deep-sea sediments. Discrepancies between template and record are diminished by representing both series as Fourier expansions, and importing the power spectrum of the record to the template, without changing phase. The remaining differences between the hybrid template and the record contain messages about time spans of unusual behavior of the system. The most striking anomalies in the Quaternary are the unusually cold period following the mid-Pleistocene climate shift at 900 ka (Stage 22) and much of Stage 11 near 400 ka, representing excess warming. The present interglacial also is too warm, compared with expectations. Anomalies are thought to be the result of stabilization of unusually cold periods (by albedo feedback) and unusually warm periods (by carbon dioxide feedback). It is proposed that there is a connection between surplus ice buildup (after the mid-Pleistocene climate shifi at 900 ka) on marine shelves and subsequent extra-large transgressions, which stabilize warm periods by shallow-water carbonate production (coral reef hypothesis).     

Climate Changes and Cyclic Sedimentation in the Mid-Late Permian: Kennedy Group, Carnarvon Basin, Western Australia

Climate has an important direct and indirect influence of sedimentation, and especially on the development of cyclic sedimentation. Climate influences both accommodation and supply, the major controls on the architecture of sedimentary sequences. The Permian paleoclimate is the subject of increasing controversy, giving rise to numerous differing models developed and an expanding database of fossil evidence for climatic conditions.Western Australian basins, in particular the Carnarvon Basin, are unique among nearby Gondwanan basins in that they do not have extensive coal measures within their Permian successions. The Kennedy Group, the uppermost unit in the onshore Carnarvon Basin Permian succession, has a detrital composition indicative of arid weathering conditions. Within the Kennedy Group, even lagoonal and very nearshore sediments are devoid of plant debris or indications of the nearby presence of extensive flora. Presumed surfaces of subaerial exposure do not show paleosol development or root-traces. There has been little development of clay and chemical grain degradation is almost entirely related to diagenetic cementation and dissolution phases, rather than transport and source weathering. Nearby basins, at similar latitudes, in India and East Australia contain coal measures, consistent with the humid climates that are predicted for this latitude. It is suggested therefore that the inferred aridity in the climate of the Carnarvon Basin and other Western Australian Basins is due to local climatic effects, probably related to an interruption in atmospheric circulation caused by tectonic rifting and uplift to the west.Cyclicity in the Kennedy Group indicates regular Late Permian, Milankovitch scale eustatic sea-level change, and may signify the presence of some ice at the poles. The development of cycles may have been enhanced by shifting climate belts controlled by Milankovitch cyclicity.     

Griesbachian Cyclostratigraphy at MajiashanSection, Anhui Province, China

INTRODUCTIONAs a large regression continued over the world at the endof the Paleozoic, a new remarkable transgression was intrudinginto the Lower Yangtze located in the eastern Tethys duringthe Late Permian, resulting in many excellent continuous marine Permian-Triassic sequences in this region. But the middleTriassic indosinian movement transformed this region from marine to continental factes, resulting in the deposition of theLower Triassic in the marked regression setting prior to …     

Origin of cyclicity in Triassic-Jurassic radiolarian bedded cherts of the Mino accretionary complex from Japan

Abstract The abundance of magnetic microspherules in a Triassic-Jurassic continuous sequence of alternating chert and shale beds in the Mino accretionary complex, central Japan, was measured systematically. Depending on time, the magnetic microspherules extracted from shale beds change in abundance considerably from the minimum 0.9ppm/cm³ at latest Triassic ( ca 208Ma) and the maximum 75ppm/cm³ at late Early Jurassic ( ca 187Ma); however, the abundance is always higher approximately 10–100 (average 70) times than those from adjacent chert bed at any stratigraphic horizon. Such systematic difference reveals the origin of radiolarian bedded chert as cyclic-rapid accumulation of biogenic SiO₂ under extremely slow accumulative environments of shale with probable aeolian dust in origin. The accumulation data for individual shale and chert beds were obtained based on the microspherule abundance and radiolarian biostratigraphy, i.e., ca 0.018g/cm²Ka for lower Jurassic shale beds and ca 1.9g/cm²Ka for adjacent chert beds.
Duration time to make a chert-shale couplet corresponds to a dominantly 15–20Ka interval (average 23 Ka) in Upper Triassic bedded cherts with a low paleolatitude, whereas a 40–45 Ka interval (average 42 Ka) in Lower Jurassic ones which may been formed in higher latitude than Triassics before the final accretion to the Asian continental margin. Depending on paleolatitude, the cyclicity of 23 and 42 Ka may correspond to Milankovitch cycles which have been well documented in deep-sea sediments.     

Orbitally induced cycles in the chalk facies of the United Kingdom

The characteristic rhythmic bedding of the Upper Cretaceous pelagic carbonate sequences of the United Kingdom is interpreted as the result of orbital variations. A 23,000 year and a 41.500 year cycle have been recognised and can be used to confirm the dating of late Cretaceous events, especially in the Cenomanian.     

Investigating the sensitivity of the Atmospheric General Circulation Model ECHAM 3 to paleoclimatic boundary conditions

We present atmospheric simulations of three different time slices of the late Quaternary using the ECHAM 3 general circulation model in T42 resolution. In this work we describe the results of model runs for the time slices 6000 years BP (last climate optimum), 21 000 BP (last glacial maximum) and 115 000 years BP (glacial inception). Although the solar insolation is known for all time slices, a complete data set of the other boundary conditions which are necessary for running the atmospheric model exists only for the last glacial maximum in the form of the CLIMAP reconstruction. For the other two time slices, which are interglacial states like the modern climate, sea surface temperatures, land albedo and ice sheet topography are kept at modern values and only the solar insolation is changed appropriately. The response of the model to solar insolation changes is quite reasonable. The modelled anomalies are small and roughly opposite in sign for 6000 BP and 115 000 BP, respectively. In the case of last glacial maximum, the glacial ice sheet topography and ice albedo produce a much larger climate anomaly in the model. However, to enable a real test of model performance under glacial boundary conditions, the CLIMAP sea surface temperatures, which are now known to be partly inaccurate, should be replaced by an updated “state-of-the-art” reconstruction.     

测井曲线Milankovitch周期分析与应用

利用沿井剖面滑动时窗内的ＦＦＴ和最大熵谱估计算法，选择合适的滤波器、窗长和步长，从测井曲线中分析出了Ｍｉｌａｎｋｏｖｉｔｃｈ周期．研究了波长比，谱峰等特征与周期的关系，确定出沉积速率的渐变与突变，求出了沉积速率，经分析，与岩性结果相符合．     

Carbonate platform growth and cyclicity at a terminal Proterozoic passive margin, Infra Krol Formation and Krol Group, Lesser Himalaya, India

Abstract The Infra Krol Formation and overlying Krol Group constitute a thick (< 2 km), carbonate-rich succession of terminal Proterozoic age that crops out in a series of doubly plunging synclines in the Lesser Himalaya of northern India. The rocks include 18 carbonate and siliciclastic facies, which are grouped into eight facies associations: (1) deep subtidal; (2) shallow subtidal; (3) sand shoal; (4) peritidal carbonate complex; (5) lagoonal; (6) peritidal siliciclastic–carbonate; (7) incised valley fill; and (8) karstic fill. The stromatolite-rich, peritidal complex appears to have occupied a location seaward of a broad lagoon, an arrangement reminiscent of many Phanerozoic and Proterozoic platforms. Growth of this complex was accretionary to progradational, in response to changes in siliciclastic influx from the south-eastern side of the lagoon. Metre-scale cycles tend to be laterally discontinuous, and are interpreted as mainly autogenic. Variations in the number of both sets of cycles and component metre-scale cycles across the platform may result from differential subsidence of the interpreted passive margin. Apparently non-cyclic intervals with shallow-water features may indicate facies migration that was limited compared with the dimensions of facies belts. Correlation of these facies associations in a sequence stratigraphic framework suggests that the Infra Krol Formation and Krol Group represent a north- to north-west-facing platform with a morphology that evolved from a siliciclastic ramp, to carbonate ramp, to peritidal rimmed shelf and, finally, to open shelf. This interpretation differs significantly from the published scheme of a basin centred on the Lesser Himalaya, with virtually the entire Infra Krol–Krol succession representing sedimentation in a persistent tidal-flat environment. This study provides a detailed Neoproterozoic depositional history of northern India from rift basin to passive margin, and predicts that genetically related Neoproterozoic deposits, if they are present in the High Himalaya, are composed mainly of slope/basinal facies characterized by fine-grained siliciclastic and detrital carbonate rocks, lithologically different from those of the Lesser Himalaya.