Planetary chaos and inverted climate phasing in the Late Triassic of Greenland.

Sedimentological records provide the only accessible archive for unraveling Earth's orbital variations in the remote geological past. These variations modulate Earth's climate system and provide essential constraints on gravitational parameters used in solar system modeling. However, geologic documentation of midlatitude response to orbital climate forcing remains poorly resolved compared to that of the low-latitude tropics, especially before 50 Mya, the limit of reliable extrapolation from the present. Here, we compare the climate response to orbital variations in a Late Triassic midlatitude temperate setting in Jameson Land, East Greenland (∼43°N paleolatitude) and the tropical low paleolatitude setting of the Newark Basin, with independent time horizons provided by common magnetostratigraphic boundaries whose timing has been corroborated by uranium-lead (U-Pb) zircon dating in correlative strata on the Colorado Plateau. An integrated cyclostratigraphic and magnetostratigraphic age model revealed long-term climate cycles with periods of 850,000 and 1,700,000 y ascribed to the Mars­Earth grand orbital cycles. This indicates a 2:1 resonance between modulation of orbital obliquity and eccentricity variations more than 200 Mya and whose periodicities are inconsistent with astronomical solutions and indicate chaotic diffusion of the solar system. Our findings also demonstrate antiphasing in climate response between low and midlatitudes that has implications for precise global correlation of geological records.

Influence of late Pleistocene sea-level variations on midocean ridge spacing in faulting simulations and a global analysis of bathymetry.

It is established that changes in sea level influence melt production at midocean ridges, but whether changes in melt production influence the pattern of bathymetry flanking midocean ridges has been debated on both theoretical and empirical grounds. To explore the dynamics that may give rise to a sea-level influence on bathymetry, we simulate abyssal hills using a faulting model with periodic variations in melt supply. For 100-ky melt-supply cycles, model results show that faults initiate during periods of amagmatic spreading at half-rates >2.3 cm/y and for 41-ky melt-supply cycles at half-rates >3.8 cm/y. Analysis of bathymetry across 17 midocean ridge regions shows characteristic wavelengths that closely align with the predictions from the faulting model. At intermediate-spreading ridges (half-rates >2.3 cm/y and [Formula: see text]3.8 cm/y) abyssal hill spacing increases with spreading rate at 0.99 km/(cm/y) or 99 ky (n [Formula: see text] 12; 95% CI, 87 to 110 ky), and at fast-spreading ridges (half-rates >3.8 cm/y) spacing increases at 38 ky (n [Formula: see text] 5; 95% CI, 29 to 47 ky). Including previously published analyses of abyssal-hill spacing gives a more precise alignment with the primary periods of Pleistocene sea-level variability. Furthermore, analysis of bathymetry from fast-spreading ridges shows a highly statistically significant spectral peak (P < 0.01) at the 1/(41-ky) period of Earth's variations in axial tilt. Faulting models and observations both support a linkage between glacially induced sea-level change and the fabric of the sea floor over the late Pleistocene.

Milankovitch cycles in banded iron formations constrain the Earth-Moon system 2.46 billion years ago.

The long-term history of the Earth-Moon system as reconstructed from the geological record remains unclear when based on fossil growth bands and tidal laminations. A possibly more robust method is provided by the sedimentary record of Milankovitch cycles (climatic precession, obliquity, and orbital eccentricity), whose relative ratios in periodicity change over time as a function of a decreasing Earth spin rate and increasing lunar distance. However, for the critical older portion of Earth's history where information on Earth-Moon dynamics is sparse, suitable sedimentary successions in which these cycles are recorded remain largely unknown, leaving this method unexplored. Here we present results of cyclostratigraphic analysis and high-precision U-Pb zircon dating of the lower Paleoproterozoic Joffre Member of the Brockman Iron Formation, NW Australia, providing evidence for Milankovitch forcing of regular lithological alternations related to Earth's climatic precession and orbital eccentricity cycles. Combining visual and statistical tools to determine their hierarchical relation, we estimate an astronomical precession frequency of 108.6 ± 8.5 arcsec/y, corresponding to an Earth-Moon distance of 321,800 ± 6,500 km and a daylength of 16.9 ± 0.2 h at 2.46 Ga. With this robust cyclostratigraphic approach, we extend the oldest reliable datum for the lunar recession history by more than 1 billion years and provide a critical reference point for future modeling and geological investigation of Precambrian Earth-Moon system evolution.

Mapping Solar System chaos with the Geological Orrery.

The Geological Orrery is a network of geological records of orbitally paced climate designed to address the inherent limitations of solutions for planetary orbits beyond 60 million years ago due to the chaotic nature of Solar System motion. We use results from two scientific coring experiments in Early Mesozoic continental strata: the Newark Basin Coring Project and the Colorado Plateau Coring Project. We precisely and accurately resolve the secular fundamental frequencies of precession of perihelion of the inner planets and Jupiter for the Late Triassic and Early Jurassic epochs (223-199 million years ago) using the lacustrine record of orbital pacing tuned only to one frequency (1/405,000 years) as a geological interferometer. Excepting Jupiter's, these frequencies differ significantly from present values as determined using three independent techniques yielding practically the same results. Estimates for the precession of perihelion of the inner planets are robust, reflecting a zircon U-Pb-based age model and internal checks based on the overdetermined origins of the geologically measured frequencies. Furthermore, although not indicative of a correct solution, one numerical solution closely matches the Geological Orrery, with a very low probability of being due to chance. To determine the secular fundamental frequencies of the precession of the nodes of the planets and the important secular resonances with the precession of perihelion, a contemporaneous high-latitude geological archive recording obliquity pacing of climate is needed. These results form a proof of concept of the Geological Orrery and lay out an empirical framework to map the chaotic evolution of the Solar System.

Empirical evidence for stability of the 405-kiloyear Jupiter-Venus eccentricity cycle over hundreds of millions of years.

The Newark-Hartford astrochronostratigraphic polarity timescale (APTS) was developed using a theoretically constant 405-kiloyear eccentricity cycle linked to gravitational interactions with Jupiter-Venus as a tuning target and provides a major timing calibration for about 30 million years of Late Triassic and earliest Jurassic time. While the 405-ky cycle is both unimodal and the most metronomic of the major orbital cycles thought to pace Earth's climate in numerical solutions, there has been little empirical confirmation of that behavior, especially back before the limits of orbital solutions at about 50 million years before present. Moreover, the APTS is anchored only at its younger end by U-Pb zircon dates at 201.6 million years before present and could even be missing a number of 405-ky cycles. To test the validity of the dangling APTS and orbital periodicities, we recovered a diagnostic magnetic polarity sequence in the volcaniclastic-bearing Chinle Formation in a scientific drill core from Petrified Forest National Park (Arizona) that provides an unambiguous correlation to the APTS. New high precision U-Pb detrital zircon dates from the core are indistinguishable from ages predicted by the APTS back to 215 million years before present. The agreement shows that the APTS is continuous and supports a stable 405-kiloyear cycle well beyond theoretical solutions. The validated Newark-Hartford APTS can be used as a robust framework to help differentiate provinciality from global temporal patterns in the ecological rise of early dinosaurs in the Late Triassic, amongst other problems.

Pacing of Paleozoic macroevolutionary rates by Milankovitch grand cycles.

Periodic fluctuations in past biodiversity, speciation, and extinction have been proposed, with extremely long periods ranging from 26 to 62 million years, although forcing mechanisms remain speculative. In contrast, well-understood periodic Milankovitch climate forcing represents a viable driver for macroevolutionary fluctuations, although little evidence for such fluctuation exists except during the Late Cenozoic. The reality, magnitude, and drivers of periodic fluctuations in macroevolutionary rates are of interest given long-standing debate surrounding the relative roles of intrinsic biotic interactions vs. extrinsic environmental factors as drivers of biodiversity change. Here, we show that, over a time span of 60 million years, between 9 and 16% of the variance in biological turnover (i.e., speciation probability plus species extinction probability) in a major Early Paleozoic zooplankton group, the graptoloids, can be explained by long-period astronomical cycles (Milankovitch "grand cycles") associated with Earth's orbital eccentricity (2.6 million years) and obliquity (1.3 million years). These grand cycles modulate climate variability, alternating times of relative stability in the environment with times of maximum volatility. We infer that these cycles influenced graptolite speciation and extinction through climate-driven changes to oceanic circulation and structure. Our results confirm the existence of Milankovitch grand cycles in the Early Paleozoic Era and show that known processes related to the mechanics of the Solar System were shaping marine macroevolutionary rates comparatively early in the history of complex life. We present an application of hidden Markov models to macroevolutionary time series and protocols for the evaluation of statistical significance in spectral analysis.

Proterozoic Milankovitch cycles and the history of the solar system.

The geologic record of Milankovitch climate cycles provides a rich conceptual and temporal framework for evaluating Earth system evolution, bestowing a sharp lens through which to view our planet's history. However, the utility of these cycles for constraining the early Earth system is hindered by seemingly insurmountable uncertainties in our knowledge of solar system behavior (including Earth-Moon history), and poor temporal control for validation of cycle periods (e.g., from radioisotopic dates). Here we address these problems using a Bayesian inversion approach to quantitatively link astronomical theory with geologic observation, allowing a reconstruction of Proterozoic astronomical cycles, fundamental frequencies of the solar system, the precession constant, and the underlying geologic timescale, directly from stratigraphic data. Application of the approach to 1.4-billion-year-old rhythmites indicates a precession constant of 85.79 ± 2.72 arcsec/year (2σ), an Earth-Moon distance of 340,900 ± 2,600 km (2σ), and length of day of 18.68 ± 0.25 hours (2σ), with dominant climatic precession cycles of ∼14 ky and eccentricity cycles of ∼131 ky. The results confirm reduced tidal dissipation in the Proterozoic. A complementary analysis of Eocene rhythmites (∼55 Ma) illustrates how the approach offers a means to map out ancient solar system behavior and Earth-Moon history using the geologic archive. The method also provides robust quantitative uncertainties on the eccentricity and climatic precession periods, and derived astronomical timescales. As a consequence, the temporal resolution of ancient Earth system processes is enhanced, and our knowledge of early solar system dynamics is greatly improved.

Cyclostratigraphy and astrochronology: Case studies from China.

A high-precision geologic time scale is the essential key for understanding the Earth's evolutionary history and geologic processes. Astronomical tuning of orbitally forced stratigraphic records to construct high-resolution Astronomical Time Scales (ATS) has led to a progressive refinement of the geologic time scale over the past two decades. In turn, these studies provide new insights regarding the durations and rates of major Earth events, evolutionary processes, and climate changes, all of which provide a scientific basis for contextualizing and predicting future global change trends. South China hosts some of the best-exposed and well-dated Neoproterozoic through Mesozoic stratigraphic sections in the world; many of which are suitable for cyclostratigraphy and calibrating the geologic time scale. In North China, several Cenozoic oil-bearing basins have deep boreholes with continuous sampling and/or well logging that enable derivation of astronomically tuned time scales for an improved understanding of basin evolution and hydrocarbon generation. This Special Issue focuses on case studies of astrochronology and applied cyclostratigraphy research using reference sections within China. In this introductory overview, we: (1) summarize all existing astrochronology studies of the Neoproterozoic through Cenozoic sections within China that have been used to enhance the international geologic time scale, (2) examine briefly the astronomically forced paleoclimate information recorded in various depositional systems and the modern techniques employed to analyze the periodicity of these signals encoded within the sedimentary record, and (3) summarize the 20 contributions to this Special Issue of Palaeogeography, Palaeoclimatology, Palaeoecology on 'Cyclostratigraphy and Astrochronology: Case studies from China'.

Orbital forcing of climate 1.4 billion years ago.

Fluctuating climate is a hallmark of Earth. As one transcends deep into Earth time, however, both the evidence for and the causes of climate change become difficult to establish. We report geochemical and sedimentological evidence for repeated, short-term climate fluctuations from the exceptionally well-preserved ∼1.4-billion-year-old Xiamaling Formation of the North China Craton. We observe two patterns of climate fluctuations: On long time scales, over what amounts to tens of millions of years, sediments of the Xiamaling Formation record changes in geochemistry consistent with long-term changes in the location of the Xiamaling relative to the position of the Intertropical Convergence Zone. On shorter time scales, and within a precisely calibrated stratigraphic framework, cyclicity in sediment geochemical dynamics is consistent with orbital control. In particular, sediment geochemical fluctuations reflect what appear to be orbitally forced changes in wind patterns and ocean circulation as they influenced rates of organic carbon flux, trace metal accumulation, and the source of detrital particles to the sediment.

Late Miocene episodic lakes in the arid Tarim Basin, western China.

The Tibetan Plateau uplift and Cenozoic global cooling are thought to induce enhanced aridification in the Asian interior. Although the onset of Asian desertification is proposed to have started in the earliest Miocene, prevailing desert environment in the Tarim Basin, currently providing much of the Asian eolian dust sources, is only a geologically recent phenomenon. Here we report episodic occurrences of lacustrine environments during the Late Miocene and investigate how the episodic lakes vanished in the basin. Our oxygen isotopic (δ(18)O) record demonstrates that before the prevailing desert environment, episodic changes frequently alternating between lacustrine and fluvial-eolian environments can be linked to orbital variations. Wetter lacustrine phases generally corresponded to periods of high eccentricity and possibly high obliquity, and vice versa, suggesting a temperature control on the regional moisture level on orbital timescales. Boron isotopic (δ(11)B) and δ(18)O records, together with other geochemical indicators, consistently show that the episodic lakes finally dried up at ∼4.9 million years ago (Ma), permanently and irreversibly. Although the episodic occurrences of lakes appear to be linked to orbitally induced global climatic changes, the plateau (Tibetan, Pamir, and Tianshan) uplift was primarily responsible for the final vanishing of the episodic lakes in the Tarim Basin, occurring at a relatively warm, stable climate period.

Pliocene-Pleistocene lineage diversifications in the Eastern Indigo Snake (Drymarchon couperi) in the Southeastern United States.

Indigo Snakes (Drymarchon; with five currently recognized species) occur from northern Argentina, northward to the United States in southern Texas and eastward in disjunct populations in Florida and Georgia. Based on this known allopatry and a difference in supralabial morphology the two United States taxa previously considered as subspecies within D. corais (Boie 1827), the Western Indigo Snake, D. melanurus erebennus (Cope 1860), and Eastern Indigo Snake, D. couperi (Holbrook 1842), are currently recognized as separate species. Drymarchon couperi is a Federally-designated Threatened species by the United States Fish and Wildlife Service under the Endangered Species Act, and currently being incorporated into a translocation program. This, combined with its disjunct distribution makes it a prime candidate for studying speciation and genetic divergence. In this study, we (1) test the hypothesis that D. m. erebennus and D. couperi are distinct lineages by analyzing 2411 base pairs (bp) of two mitochondrial (mtDNA) loci and one single copy nuclear (scnDNA) locus; (2) estimate the timing of speciation using a relaxed phylogenetics method to determine if Milankovitch cycles during the Pleistocene might have had an influence on lineage diversifications; (3) examine historical population demography to determine if identified lineages have undergone population declines, expansions, or remained stable during the most recent Milankovitch cycles; and (4) use this information to assist in an effective and scientifically sound translocation program. Our molecular data support the initial hypothesis that D. melanurus and D. couperi should be recognized as distinct species, but further illustrate that D. couperi is split into two distinct genetic lineages that correspond to historical biogeography and sea level changes in peninsular Florida. These two well-supported genetic lineages (herein termed Atlantic and Gulf lineages) illustrate a common biogeographic distributional break previously identified for other plants and animals, suggesting that these organisms might have shared a common evolutionary history related to historic sea level changes caused by Milankovitch cycles. Our estimated divergence times suggest that the most recent common ancestor (MRCA) between D. melanurus and southeastern United States Drymarchon occurred ca. 5.9Ma (95% HPD=2.5-9.8Ma; during the late Blancan of the Pleistocene through the Hemphillian of the Miocene), whereas the MRCA between the Atlantic and Gulf lineages in the southeastern United States occurred ca. 2.0Ma (95% HPD=0.7-3.7Ma; during the Irvingtonian of the Pleistocene through the Blancan of the Pliocene). During one or more glacial intervals within these times, these two lineages must have become separated and evolved independently. Despite numerous Milankovitch cycles along with associated forming of physical barriers (i.e., sea level fluctuations, high elevation sand ridges, clayey soils, and/or insufficient habitats) since their initial lineage diversification, these two lineages have likely come in and out of contact with each other many times, yet today they still illustrate near discrete geographic distributions. Although the Atlantic and Gulf lineages appear to be cryptic, a thorough study examining morphological characters should be conducted. We believe that our molecular data is crucial and should be incorporated in making conscious decisions in the management of a translocation program. We suggest that source populations for translocations include maintaining the integrity of the known genetic lineages found herein, as well as those coming from the closest areas that currently support sizable Drymarchon populations.

Synchronous interhemispheric Holocene climate trends in the tropical Andes.

Holocene variations of tropical moisture balance have been ascribed to orbitally forced changes in solar insolation. If this model is correct, millennial-scale climate evolution should be antiphased between the northern and southern hemispheres, producing humid intervals in one hemisphere matched to aridity in the other. Here we show that Holocene climate trends were largely synchronous and in the same direction in the northern and southern hemisphere outer-tropical Andes, providing little support for the dominant role of insolation forcing in these regions. Today, sea-surface temperatures in the equatorial Pacific Ocean modulate rainfall variability in the outer tropical Andes of both hemispheres, and we suggest that this mechanism was pervasive throughout the Holocene. Our findings imply that oceanic forcing plays a larger role in regional South American climate than previously suspected, and that Pacific sea-surface temperatures have the capacity to induce abrupt and sustained shifts in Andean climate.