Since 65 million years ago (Ma), Earth's climate has undergone a significant and complex evolution, the finer details of which are now coming to light through investigations of deep-sea sediment cores. This evolution includes gradual trends of warming and cooling driven by tectonic processes on time scales of 10(5) to 10(7) years, rhythmic or periodic cycles driven by orbital processes with 10(4)- to 10(6)-year cyclicity, and rare rapid aberrant shifts and extreme climate transients with durations of 10(3) to 10(5) years. Here, recent progress in defining the evolution of global climate over the Cenozoic Era is reviewed. We focus primarily on the periodic and anomalous components of variability over the early portion of this era, as constrained by the latest generation of deep-sea isotope records. We also consider how this improved perspective has led to the recognition of previously unforeseen mechanisms for altering climate.

/pdf/trends-rhythms-and-aberrations-in-global-climate-65-ma-to-cflhxkixnq.pdf

Trends, Rhythms, and Aberrations in Global Climate 65 Ma to Present

Advances in sequence stratigraphy and the development of depositional models have helped explain the origin of genetically related sedimentary packages during sea level cycles. These concepts have provided the basis for the recognition of sea level events in subsurface data and in outcrops of marine sediments around the world. Knowledge of these events has led to a new generation of Mesozoic and Cenozoic global cycle charts that chronicle the history of sea level fluctuations during the past 250 million years in greater detail than was possible from seismic-stratigraphic data alone. An effort has been made to develop a realistic and accurate time scale and widely applicable chronostratigraphy and to integrate depositional sequences documented in public domain outcrop sections from various basins with this chronostratigraphic framework. A description of this approach and an account of the results, illustrated by sea level cycle charts of the Cenozoic, Cretaceous, Jurassic, and Triassic intervals, are presented.

https://science.sciencemag.org/content/sci/235/4793/1156.full.pdf

Chronology of fluctuating sea levels since the triassic.

Direct physical evidence is presented for an unusual event at exactly the time of extinctions in the planktonic realm. Deep-sea limestones exposed in Italy, Denmark, and New Zealand indicate iridium increases of about 30, 160, and 20 times, respectively, above the background level at precisely the time of the Cretaceous-Tertiary extinctions, 65 million years ago. Reasons are given that this iridium is of extraterrestrial origin, but did not come from a nearby supernova. A hypothesis is set forth which accounts for the extinctions and the iridium observations. One prediction of this hypothesis is verified, that the chemical composition of the boundary clay, which is thought to come from the stratospheric dust, is markedly different from that of clay mixed with the chemically similar Cretaceous and Tertiary limestones.

/pdf/extraterrestrial-cause-for-the-cretaceous-tertiary-2yoc56x8wn.pdf

Extraterrestrial Cause for the Cretaceous-Tertiary Extinction

Knowledge of the evolution of atmospheric carbon dioxide concentrations throughout the Earth's history is important for a
reconstruction of the links between climate and radiative forcing of the Earth's surface temperatures. Although atmospheric
carbon dioxide concentrations in the early Cenozoic era (about 60Myr ago) are widely believed to have been higher than at present,
there is disagreement regarding the exact carbon dioxide levels, the timing of the decline and the mechanisms that are most
important for the control of CO2 concentrations over geological timescales. Here we use the boron-isotope ratios of ancient
planktonic foraminifer shells to estimate the pH of surface-layer sea water throughout the past 60 million years, which can be used
to reconstruct atmospheric CO2 concentrations. We estimate CO2 concentrations of more than 2,000 p.p.m. for the late Palaeocene
and earliest Eocene periods (from about 60 to 52 Myr ago), and ®nd an erratic decline between 55 and 40 Myr ago that may have
been caused by reduced CO2 outgassing from ocean ridges, volcanoes and metamorphic belts and increased carbon burial. Since
the early Miocene (about 24Myr ago), atmospheric CO2 concentrations appear to have remained below 500 p.p.m. and were more
stable than before, although transient intervals of CO2 reduction may have occurred during periods of rapid cooling approximately
15 and 3 Myr ago.

Atmospheric carbon dioxide concentrations over the past 60 million years

We have constructed a magnetic polarity time scale for the Late Cretaceous and Cenozoic based on an analysis of marine magnetic profiles from the world's ocean basins. This is the first time, since Heirtzler et al. (1968) published their time scale, that the relative widths of the magnetic polarity intervals for the entire Late Cretaceous and Cenozoic have been systematically determined from magnetic profiles. A composite geomagnetic polarity sequence was derived based primarily on data from the South Atlantic. Anomaly spacings in the South Atlantic were constrained by a combination of finite rotation poles and averages of stacked profiles. Fine-scale information was derived from magnetic profiles on faster spreading ridges in the Pacific and Indian Oceans and inserted into the South Ariantic sequence. Based on the assumption that spreading rates in the South Atlantic were smoothly varying but not necessarily constant, a time scale was generated by using a spline function to fit a set of nine age calibration points

/pdf/a-new-geomagnetic-polarity-time-scale-for-the-late-47c9jfk0ho.pdf

A new geomagnetic polarity time scale for the Late Cretaceous and Cenozoic

Cretaceous planktonic foraminiferal biostratigraphy and evolutionary trends from the Bottaccione Section, Gubbio, Italy

Cretaceous paleoceanography: Evidence from planktonic foraminiferal evolution

The planktonic foraminiferal generaMorozovellaandAcarininarapidly (in ;10 k.y.) diversified during the late Paleocene thermal maximum (LPTM), giving rise to such morphotypes asM. allisonensis(new species),M. africana, andA. sibaiyaensis. Single-specimen isotopicanalysisconfirmsthatM.allisonensisandA.sibaiyaensisarerestrictedtotheLPTM carbon isotope excursion recorded at Ocean Drilling Program Site 865 (equatorial Pacific Ocean). The short-lived (50 to several 100 k.y.) ‘‘excursion’’ taxa attest to the ephemeral effectsoftheLPTMonthecalcareousplankton.Single-specimenoxygenisotopedatashow that evolution of M. allisonensis and A. sibaiyaensis was accompanied by migration to deeper water depths. AncestralM. velascoensisandA. soldadoensiswere extremely rare or absent during the early stages of the LPTM, but immigrated back into the study area to coexist with their descendants in later LPTM horizons. Photosymbiosis may have facilitatedthemorozovellidandacarininiddiversificationsduringtheoligotrophicconditionsof the LPTM.

/pdf/rapid-diversification-of-planktonic-foraminifera-in-the-nf2un3lnjn.pdf

Rapid diversification of planktonic foraminifera in the tropical Pacific (ODP Site 865) during the late Paleocene thermal maximum

APTICORE at the Cismon Valley (Belluno Basin, Southern Alps) penetrated 131.8 m of pelagic limestones, marlstones and black shales. The cored interval extends from the upper Albian to the lower upper Hauterivian. Freshly cored material and logs from the Cismon drill site provide a very informative record. Detailed, multidisciplinary studies show high and low frequency changes in lithologic, paleontologic, paleomagnetic, and geochemical records. Moderate to good preservation of calcareous and siliceous plankton and palynomorphs allowed the identification of several calcareous nannofossil, planktonic foraminiferal, radiolarian and dinoflagellate events. Magnetostratigraphy is available for the entire interval and Chrons CM0 through CM9 were detected. Stable C and O, and Sr isotopes were analysed and chemostratigraphy of the Cismon core comprises both delta 13 C carb curve and the 87 Sr/ 86 Sr record. Integrated stratigraphy of the Cismon APTICORE resulted in the first coherent scheme derived from direct calibration of bio-, magneto-, and chemo-stratigraphy for the Upper Hauterivian-Aptian interval. In the upper portion of core, an unconformity removed part of the upper Aptian, the lower Albian and most of the middle Albian. The Upper Hauterivian is characterized by folding and some slumps resulting in high sedimentation rates. The uppermost Hauterivian consists of red pseudonodular limestone with low sedimentation rate. We propose the Cismon core as a "reference section" for the Barremian-Aptian at low latitudes, containing both a complete carbonate and organic carbon record through the critical black shale intervals.

Isabella Premoli Silva

Papers

Cretaceous planktonic foraminiferal biostratigraphy and evolutionary trends from the Bottaccione Section, Gubbio, Italy

Cretaceous paleoceanography: Evidence from planktonic foraminiferal evolution

Rapid diversification of planktonic foraminifera in the tropical Pacific (ODP Site 865) during the late Paleocene thermal maximum

Integrated stratigraphy of the Cismon Apticore (southern Alps, Italy); a reference section for the Barremian-Aptian interval at low latitudes

Similarities between planktonic and larger foraminiferal evolutionary trends through Paleogene paleoceanographic changes