Archives par mot-clé : Jurassic

climate and geology

Global-Scale Warming Events Of ‘Up To 15 °C Within A Few Decades’ Have Occurred Since The Jurassic

Boulila et al., 2022 in NoTricksZone

A new study (Boulila et al., 2022) suggests “abrupt and severe changes in Earth’s past climate” have been occurring at ~1,500-year periodicities since the iceless Jurassic period.

Warming events of degrees C per within decades or less were at one time thought to have occurred only at locations like Greenland and the North Atlantic during the last glacial period (70 to 12 thousand years ago).

But the evidence has been piling up from locations throughout the globe (e.g., on continents and tropical to high latitude oceans, lakes, and rivers) indicating these warming events have “a global interconnection between the two hemispheres.”

These “abrupt and severe” global warming events with ~1,500-year periodicities can even be traced back to the iceless Jurassic period when Antarctica was a rainforest and 38°C warmer than today. This suggests the driving force for these global warming periods were not dependent on ice sheet dynamics.

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Abstract

Earth’s past climate exhibits short-term (1500-year) pronounced fluctuations during the last glacial period, called Dansgaard–Oeschger (DO) glacial events, which have never been detected in pre-Quaternary times. The record of DO equivalent climate variability in Mesozoic strata can provide constraints on understanding these events. Here we highlight a prominent 1500-year cyclicity in a Jurassic (~ 155 Ma) ice-free sedimentary record from the Tethyan Basin. This Jurassic 1500-year cyclicity is encoded in high-resolution magnetic susceptibility (MS) proxy data reflecting detrital variations, and expressed as marl-limestone couplets. Additionally, MS data detect the modulation of these DO-scale couplets by supercouplet sets, reflecting the precession and its harmonics. We suggest that this Jurassic DO-like cyclicity may originate from paleo-monsoon-like system, analogous to the record of DO events in the Pleistocene East Asian monsoon archives. Paleogeographic reconstructions and atmosphere–ocean simulations further support the potential existence of strong, ancient monsoon circulations in the Tethyan Basin during the Jurassic.

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only geology

Fossils suggest flowers originated 50 million years earlier than thought

by eLife, December 18, 2018 in ScienceDaily

Scientists have described a fossil plant species that suggests flowers bloomed in the Early Jurassic, more than 174 million years ago, according to new research in the open-access journal eLife.

Before now, angiosperms (flowering plants) were thought to have a history of no more than 130 million years. The discovery of the novel flower species, which the study authors named Nanjinganthus dendrostyla, throws widely accepted theories of plant evolution into question, by suggesting that they existed around 50 million years earlier. Nanjinganthus also has a variety of ‘unexpected’ characteristics according to almost all of these theories.

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