Climate modes of the phanerozoic

As the chronicle of plate motions through time, paleogeography is fundamental to our understanding of plate tectonics and its role in shaping the geology of the present-day. To properly appreciate the history of tectonics—and its influence on the deep Earth and climate—it is imperative to seek an accurate and global model of paleogeography. However, owing to the incessant loss of oceanic lithosphere through subduction, the paleogeographic reconstruction of ‘full-plates’ (including oceanic lithosphere) becomes increasingly challenging with age. Prior to 150 Ma ∼60% of the lithosphere is missing and reconstructions are developed without explicit regard for oceanic lithosphere or plate tectonic principles; in effect, reflecting the earlier mobilistic paradigm of continental drift. Although these ‘continental’ reconstructions have been immensely useful, the next-generation of mantle models requires global plate kinematic descriptions with full-plate reconstructions. Moreover, in disregarding (or only loosely applying) plate tectonic rules, continental reconstructions fail to take advantage of a wealth of additional information in the form of practical constraints. Following a series of new developments, both in geodynamic theory and analytical tools, it is now feasible to construct full-plate models that lend themselves to testing by the wider Earth-science community. Such a model is presented here for the late Paleozoic (410–250 Ma) together with a review of the underlying data. Although we expect this model to be particularly useful for numerical mantle modeling, we hope that it will also serve as a general framework for understanding late Paleozoic tectonics, one on which future improvements can be built and further tested.

Plate Tectonics in the Late Paleozoic

Phanerozoic Paleotemperatures: The Earth’s Changing Climate during the Last 540 million years

Abstract The global Hangenberg Crisis near the Devonian–Carboniferous boundary (DCB) represents a mass extinction that is of the same scale as the so-called ‘Big Five’ first-order Phanerozoic events. It played an important role in the evolution of many faunal groups and destroyed complete ecosystems but affected marine and terrestrial environments at slightly different times within a short time span of c. 100–300 kyr. The lower crisis interval in the uppermost Famennian started as a prelude with a minor eustatic sea-level fall, followed rather abruptly by pantropically widespread black shale deposition (Hangenberg Black Shale and equivalents). This transgressive and hypoxic/anoxic phase coincided with a global carbonate crisis and perturbation of the global carbon cycle as evidenced by a distinctive positive carbon isotope excursion, probably as a consequence of climate/salinity-driven oceanic overturns and outer-shelf eutrophication. It is the main extinction level for marine biota, especially for ammonoids, trilobites, conodonts, stromatoporoids, corals, some sharks, and deeper-water ostracodes, but probably also for placoderms, chitinozoans and early tetrapods. Extinction rates were lower for brachiopods, neritic ostracodes, bryozoans and echinoderms. Extinction patterns were similar in widely separate basins of the western and eastern Prototethys, while a contemporaneous marine macrofauna record from high latitudes is missing altogether. The middle crisis interval is characterized by a gradual but major eustatic sea-level fall, probably in the scale of more than 100 m, that caused the progradation of shallow-water siliciclastics (Hangenberg Sandstone and equivalents) and produced widespread unconformities due to reworking and non-deposition. The glacio-eustatic origin of this global regression is proven by miospore correlation with widespread diamictites of South America and South and North Africa, and by the evidence for significant tropical mountain glaciers in eastern North America. This isolated and short-lived plunge from global greenhouse into icehouse conditions may follow the significant drawdown of atmospheric CO2 levels due to the prior massive burial of organic carbon during the global deposition of black shales. Increased carbon recycling by intensified terrestrial erosion in combination with the arrested burial of carbonates may have led to a gradual rise of CO2 levels, re-warming, and a parallel increase in the influx of land-derived nutrients. The upper crisis interval in the uppermost Famennian is characterized by initial post-glacial transgression and a second global carbon isotope spike, as well as by opportunistic faunal blooms and the early re-radiation of several fossil groups. Minor reworking events and unconformities give evidence for continuing smaller-scale oscillations of sea-level and palaeoclimate. These may explain the terrestrial floral change near the Famennian–Tournaisian boundary and contemporaneous, evolutionarily highly significant extinctions of survivors of the main crisis. Still poorly understood small-scale events wiped out the last clymeniid ammonoids, phacopid trilobites, placoderms and some widespread brachiopod and foraminiferan groups. The post-crisis interval in the lower Tournaisian is marked by continuing eustatic rise (e.g. flooding of the Old Red Continent), and significant radiations in a renewed greenhouse time. But the recovery had not yet reached the pre-crisis level when it was suddenly interrupted by the global, second-order Lower Alum Shale Event at the base of the middle Tournaisian.

The global Hangenberg Crisis (Devonian–Carboniferous transition): review of a first-order mass extinction

The Devonian Period

The Late Devonian biotic crisis has been studied for a long time mainly on the basis of its taxonomic severity, but with little attention paid on the relationship between biogeography and evolutionary dynamics. In this study, brachiopod faunas across the biotic crisis are surveyed based on revised data compiled from 15 sections in South China. Data of brachiopod faunas are plotted using a network method to detect biogeographic variation and dynamics through the upper Frasnian, lower and middle Famennian. In addition, frequency analysis is performed on the occurrence of brachiopod faunas within the different localities and depositional settings through time. These data show significant taxonomic loss in the five depositional zones in South China, particularly in the littoral clastic and restricted-platform facies. Refuges during the survival interval were probably located in deeper water zones, especially in the inter-platform basin, but also in the peritidal and the open carbonate platform. A decrease of biogeographic connections within the brachiopod occurrence network, accompanied with an increase of low frequency taxa in the survival and recovery intervals, supports biogeographic divergence of ecological preferences of survival and recovery faunas in South China, as well as a turnover of brachiopod faunas through the biotic crisis. Reasons for variation of biogeographic distribution and connections are less known, besides the faunal colonisation that facilitated by sea-level fluctuation through the biotic crisis.

Palaeobiogeographic dynamics of brachiopod faunas during the Frasnian-Famennian biotic crisis in South China

Biostromal unit from the Middle Devonian Jinbaoshi Formation, Sichuan, Southwest China: Implications for ecological structure of coeval reef communities

Silurian ostracods from the Nyalam region, southern Tibet, China and their implications on palaeoenvironment and palaeobiogeography

Editorial preface to special issue: From Prototethys to Neotethys: Deep time paleobiogeographic and paleogeographic evolution of blocks in the Qinghai-Tibet Plateau

Wenkun Qie

Papers

Palaeobiogeographic dynamics of brachiopod faunas during the Frasnian-Famennian biotic crisis in South China

Biostromal unit from the Middle Devonian Jinbaoshi Formation, Sichuan, Southwest China: Implications for ecological structure of coeval reef communities

Silurian ostracods from the Nyalam region, southern Tibet, China and their implications on palaeoenvironment and palaeobiogeography

Editorial preface to special issue: From Prototethys to Neotethys: Deep time paleobiogeographic and paleogeographic evolution of blocks in the Qinghai-Tibet Plateau

Late Devonian benthic ostracods from South China and their response to the Frasnian–Famennian event