Earth was very dynamic during the Carboniferous with major components of the Pangea supercontinent being assembled from late Famennian to latest Pennsylvanian times, although maximum consolidation occurred during Late Permian – Early Triassic time. During the Carboniferous Period, our planet also underwent at least three major icehouse periods. The first two, in late Famennian – early Tournaisian and late Visean – Bashkirian times, indicate the onset of the Late Palaeozoic Ice Age (LPIA) with ice sheets being confined to the alpine regions of southern Gondwana. The third icehouse regime during Gzhelian – Early Permian time represents the main episode of the LPIA when a continental ice sheet developed on the Australian, Antarctic and southern African components of southern Gondwana. During the Tournaisian equatorial areas in Euramerica were occupied by extensive arid belts, in which massive carbonate deposits formed on vast platforms in that time. From the late Tournaisian into the Visean and Serpukhovian much of the equatorial belt developed into a humid-tropical realm and the former arid belt split and shifted to higher latitudes. Shelf-carbonate deposition continued over extensive areas of the continental shelves and western Palaeo-Tethys but coal swamps were developing in the forelands of the rising Appalachian and Variscan orogens. The late Serpukhovian – early Bashkirian interval saw the closure of the Rheic Ocean and a continent–continent collision between Euramerica (Laurussia) and Gondwana to form Pangea. As a consequence, a marked transition from Visean carbonate deposition to the development of coal swamps and deposition of siliciclastics during the Serpukhovian Stage occurred in many regions.
Abstract The end‐Devonian mass extinction (~359 Ma) substantially impacted marine ecosystems and shaped the roots of modern vertebrate biodiversity. Although multiple hypotheses have been proposed, no consensus has been reached about the mechanism inducing this extinction event. In this study, I/Ca ratio of carbonate was used to unravel the changes in local oxygen content of the upper water column during this critical interval. The Devonian‐Carboniferous boundary was recorded in two shallow water carbonate sections in south China. I/Ca values at both locations show a clear decline in the Middle and Upper Siphonodella praesulcata conodont zones, which coincides with a positive shift in carbonate carbon isotope composition and a negative shift in nitrogen isotope composition. These results suggest that deoxygenation was intensified during this critical interval, which likely influenced shallow water habitats, lending support to the notion that oxygen deficiency likely was a direct mechanism impacting the end‐Devonian mass extinction.
The Late Ordovician mass extinction (LOME) constitutes the second largest of the “Big Five” extinctions of the Phanerozoic. The LOME comprised two extinction pulses associated with sea level changes linked to the Hirnantian glaciation. Although climate change has been implicated as a potential driver of the mass extinction, uncertainty remains as to its precise impact relative to the concurrent development of ocean anoxia. Here, we investigate the behavior of the oceanic cadmium (Cd) cycle, as a key element involved in a number of biological processes, across the LOME and into the Early Silurian. Our focus is on the Wangjiawan section in South China, which is the Global Stratotype Section and Point section marking the base of the Hirnantian Stage. We combine authigenic Cd isotope analyses (δ114Cdauth) with total organic carbon concentrations and isotopes, and major and trace element systematics, to determine the evolution of marine productivity across the LOME and to provide insight into the mass extinction and relationships between climatic and environmental change. Our δ114Cdauth data display a gradually decreasing trend from the late Katian to the Katian‒Hirnantian boundary, suggesting enhanced biological assimilation of isotopically light Cd followed by export to the sediments. This interpretation is supported by an increase in organic carbon isotope (δ13Corg) compositions, as well as a progressive decrease in P/Al ratios and increase in Corg/P ratios in the early part of the late Katian. A slight increase in Cd isotope values in the early Hirnantian was likely caused by drawdown of light Cd (as CdS) in euxinic shallower seawater settings. During glacial melting in the late Hirnantian, organic carbon burial declined, consistent with lower Cd/Al, Zn/Al, and Ni/Al ratios. However, δ114Cdauth values remain low across this interval, possibly due to an increase in the supply of isotopically light Cd from enhanced weathering and rising sea levels, as supported by elevated Al contents and chemical index of alteration (CIA) values. Elevated δ114Cdauth values subsequently occurred in the Early Silurian (Rhuddanian), alongside a decline in CIA and Al values, suggesting that the Cd sink was gradually balanced by a decline in the weathering input of Cd and lower rates of primary productivity. Our data provide new insight into the Cd cycle through the Late Ordovician to Early Silurian, and suggest that elevated marine productivity drove enhanced burial of organic matter, which likely contributed to CO2 drawdown and the initiation of the Hirnantian glaciation.
Hebei Province is rich in geological heritage resources due to its diverse landforms and unique natural conditions. However,detailed investigation and study of the resources are still limited,and a systematic survey conducted on a small scale has not been fully implemented. In this paper,the resource types and characteristics of the geological heritage in Shunping County are systematically discussed,on the basis of field investigation and scientific evaluation. With reference to the existing criteria for geological heritage resources survey,the heritage values and corresponding levels were assessed by using multi-factor quantitative evaluation approach. The results show that there are 33 geological heritage sites in Shunping County,which fall into 3 categories,10 classes and 17 subcategories. Among them,2 heritage sites are above the provincial level,14 heritage sites are at the provincial level and 17 ones are below the level. These heritage sites are not only natural resources with great tourism potential,but also valuable asset in geological research,human history,ecological conservation,scientific education and some other aspects. It is hence of great significance to conduct the scientific and reasonable appraisal for having a better understanding,good protection and development of the geological heritage resources in Hebei Province.
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