Phanerozoic

About: Phanerozoic is a research topic. Over the lifetime, 1177 publications have been published within this topic receiving 70553 citations. The topic is also known as: Phanerozoic eon.

The Phanerozoic Record of Global Sea-Level Change

Abstract: We review Phanerozoic sea-level changes [543 million years ago (Ma) to the present] on various time scales and present a new sea-level record for the past 100 million years (My). Long-term sea level peaked at 100 ± 50 meters during the Cretaceous, implying that ocean-crust production rates were much lower than previously inferred. Sea level mirrors oxygen isotope variations, reflecting ice-volume change on the 10 4 - to 10 6 -year scale, but a link between oxygen isotope and sea level on the 10 7 -year scale must be due to temperature changes that we attribute to tectonically controlled carbon dioxide variations. Sea-level change has influenced phytoplankton evolution, ocean chemistry, and the loci of carbonate, organic carbon, and siliciclastic sediment burial. Over the past 100 My, sea-level changes reflect global climate evolution from a time of ephemeral Antarctic ice sheets (100 to 33 Ma), through a time of large ice sheets primarily in Antarctica (33 to 2.5 Ma), to a world with large Antarctic and large, variable Northern Hemisphere ice sheets (2.5 Ma to the present).

On The Geologic Time Scale

Abstract: This report summarizes the international divisions and ages in the Geologic Time Scale, published in 2012 (GTS2012). Since 2004, when GTS2004 was detailed, major developments have taken place that directly bear and have considerable impact on the intricate science of geologic time scaling. Precam brian now has a detailed proposal for chronostratigraphic subdivision instead of an outdated and abstract chronometric one. Of 100 chronostratigraphic units in the Phanerozoic 63 now have formal definitions, but stable chronostratigraphy in part of upper Paleozoic, Triassic and Middle Jurassic/Lower Cretaceous is still wanting. Detailed age calibration now exist between radiometric methods and orbital tuning, making 40Ar-39Ar dates 0.64% older and more accurate. In general, numeric uncertainty in the time scale, although complex and not entirely amenable to objective analysis, is improved and reduced. Bases of Paleozoic, Mesozoic and Cenozoic are bracketed by analytically precise ages, respectively 541 0.63, 252.16 0.5, and 65.95 0.05 Ma. High-resolution, direct age-dates now exist for base-Carboniferous, base-Permian, base-Jurassic, base-Cenomanian and base-Eocene. Relative to GTS2004, 26 of 100 time scale boundaries have changed age, of which 14 have changed more than 4 Ma, and 4 (in Middle to Late Triassic) between 6 and 12 Ma. There is much higher stratigraphic resolution in Late Carboniferous, Jurassic, Cretaceous and Paleogene, and improved integration with stable isotopes stratigraphy. Cenozoic and Cretaceous have a refined magneto-biochronology. The spectacular outcrop sections for the Rosello Composite in Sicily, Italy and at Zumaia, Basque Province, Spain encompass the Global Boundary Stratotype Sections and Points for two Pliocene and two Paleocene stages. Since the cycle record indicates, to the best of our knowledge that the stages sediment fill is stratigraphically complete, these sections also may fulfill the important role of stage unit stratotypes for three of these stages, Piacenzian, Zanclean and Danian

Variation of seawater 87Sr/86Sr throughout Phanerozoic time

Abstract: Precise measurements of 786 marine carbonate, evaporite, and phosphate samples of known age provide a curve of seawater 87Sr/86Sr versus geologic time through the Phanerozoic. Many episodes of increasing and decreasing values of 87Sr/86Sr of seawater have occurred through the Phanerozoic. The Late Cambrian–Early Ordovician seawater ratios are approximately equal to the modern ratio of 0.70907. The lowest ratios, ∼0.7068, occurred during the Jurassic and Late Permian. The configuration of the curve appears to be strongly influenced by the history of both plate interactions and seafloor spreading throughout the Phanerozoic. The curve provides a basis for dating many marine carbonate, evaporite, and phosphate samples. Furthermore, diagenetic modifications of original marine 87Sr/86Sr values are often interpretable. Analysis of 87Sr/86Sr data, therefore, may provide useful information on regional diagenetic patterns and processes. All of the Cenozoic samples and some of the Cretaceous samples are from Deep Sea Drilling Project (DSDP) cores. With the exception of the DSDP samples, the curve was constructed only from samples containing at least 200 ppm Sr and not more than 10% dilute acid insoluble material. All measurements are made by comparison with standard SrCO3 (NBS SRM 987) for which a 87Sr/86Sr of 0.71014 is assumed. Precision is estimated to be ± 0.00005 at the 95% confidence level. Measured ratios of 42 modern marine samples average 0.70907, with a standard deviation of 0.00004.

Regional stratigraphy of the Zagros fold-thrust belt of Iran and its proforeland evolution

Abstract: The latest Neoproterozoic through Phanerozoic stratigraphy of the Zagros fold-thrust belt of Iran has been revised in the light of recent investigations. The revised stratigraphy consists of four groups of rocks, each composed of a number of unconformity-bounded megasequences representing various tectonosedimentary settings. In the lowest group, ranging in age from latest Precambrian to Devonian(?), the uppermost Neoproterozoic to middle Cambrian rocks constitute a megasequence of evaporites, siliciclastic deposits, and interlayered carbonates, which were deposited in pull-apart basins that developed by the Najd strike-slip fault system. This megasequence is overlain by a second one, Middle to Late Cambrian in age, which consists of shallow, marine siliciclastic and carbonate rocks representing deposition in an epicontinental platform. The overlying shales, siltstones, and partly volcanogenic sandstones of Ordovician, Silurian, and Devonian(?) age are local remnants of stratigraphic units that were extensively eroded during development of several major unconformities. The second group consists of two megasequences, one Permian and the other Triassic, composed of widespread, transgressive basal siliciclastic rocks and overlying evaporitic carbonates of an equatorial, epi-Pangean, very shallow platformal sea. The third group is composed of four megasequences formed of shallow- and deep-water carbonates with some siliciclastic and evaporite deposits, which accumulated on a Neo-Tethyan continental shelf during earliest Jurassic through late Turonian time. The fourth group comprises siliciclastic and carbonate deposits of a largely underfilled, NW- to SE-trending, forward and backward migrating, late Cretaceous to Recent proforeland basin, which has evolved as an integral part of the Zagros orogen. This last group consists of three megasequences (IX, X, and XI) with distinctive lateral and vertical facies variations, which reflect specific tectonic events. Megasequence IX comprises uppermost Turonian to middle Maastrichtian prograding and retrograding siliciclastic and carbonate deposits, whose accumulations reflect emplacement (“obduction”) of ophiolite slivers and subsequent collisional events in the Zagros orogen. Megasequence X consists of uppermost Maastrichtian to upper Eocene siliciclastic and carbonate rocks, which deposited first progradationally in front of the Zagros orogenic wedge with reduced contractional tectonic activity, and then retrogradationally due to intensified thrust stacking in the interior parts of the orogen. Megasequence XI consists of Oligocene and lower Miocene carbonate strata deposited retrogradationally shortly after a period of intensified late Eocene thrust faulting in the deformational wedge, and an overlying succession of upward-coarsening, northeasterly-derived siliciclastic deposits of lower Miocene to Recent age which are composed of erosional byproducts of the southwest-vergent Zagros thrust sheets.

The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary

Abstract: The Cretaceous-Paleogene boundary similar to 65.5 million years ago marks one of the three largest mass extinctions in the past 500 million years. The extinction event coincided with a large asteroid impact at Chicxulub, Mexico, and occurred within the time of Deccan flood basalt volcanism in India. Here, we synthesize records of the global stratigraphy across this boundary to assess the proposed causes of the mass extinction. Notably, a single ejecta-rich deposit compositionally linked to the Chicxulub impact is globally distributed at the Cretaceous-Paleogene boundary. The temporal match between the ejecta layer and the onset of the extinctions and the agreement of ecological patterns in the fossil record with modeled environmental perturbations (for example, darkness and cooling) lead us to conclude that the Chicxulub impact triggered the mass extinction.