Perturbations in the carbon cycle during the Carnian Humid Episode: carbonate carbon isotope records from southwestern China and northern Oman

Abstract

The Carnian Humid Episode is an interval of prominent climatic changes in the Late Triassic. We studied the carbon isotope (δ 13 C) geochemistry of carbonates from sections in southwestern China and northern Oman. δ 13 C records from the Yongyue section (western Guizhou, South China) show a progressive positive shift from 1.4 to 2.8‰ in the early to middle Julian 1 substage. This positive trend is followed by a swift negative shift of c. 4.2‰ from 2.8 to −1.4‰ in the Julian 2 substage. δ 13 C from the Wadi Mayhah section (northern Oman) shows a positive shift from 2.2 to 2.8‰ in the Julian 1 substage, followed by a negative shift of c. 3.2‰ from 2.8 to −0.3‰ in the Julian 2 substage. The δ 13 C records from the two study sections generally correlate well with each other as well as with published records, pointing to a considerable input of isotopically light carbon starting in the late Julian 1 substage. Such a large amount of light carbon probably derived from direct degassing and the sediment–sill contact metamorphism of the Panthalassan Wrangellia Large Igneous Province and contemporary Tethyan volcanism. The voluminous volcanogenic greenhouse gases probably contributed to the warming pulse in the middle Carnian. Thus the dry–wet climatic transition during the Carnian Humid Episode is best interpreted as a warm climate-driven intensification of the activities of the atmospheric circulation and hydrological cycle.

Mercury deposition in Western Tethys during the Carnian Pluvial Episode (Late Triassic)

“…Coeval volcanic activity has previously been invoked as a cause for the CPE’s NCIEs, both in terms of direct C emissions and as a trigger for positive C-cycle feedbacks (e.g., release of 13 C-depleted C from ocean floor clathrates) 6 , 13 , 17 . The emplacement of the Wrangellia oceanic plateau, a submarine large igneous province (LIP), has been the main candidate for this scenario 6 , 8 , 9 , 15 – 18 . However, besides age overlap 25 and Os isotope data from deep water successions of Panthalassa that show Wrangellia started in the Early Carnian Trachyceras ammonoid Zone, hereafter referred to as Julian 1 16 , further evidence for volcanic activity in the sedimentary record has been lacking.…”

Carnian (Late Triassic) C-isotope excursions, environmental changes, and biotic turnover: a global perturbation of the Earth's surface system

“…The temporal progression of the CPE is exemplified in this thematic set: bed by bed measurement of changes through the episode, matched to global chrono-and or biostratigraphy, are provided. A full understanding of the spatial variability of environmental change through the CPE is still lacking, but significant work has been made in China (Sun et al 2016, Shi et al 2018Jin et al 2018), Oman (Sun et al 2018), and the southern USA (Lucas & Tanner 2018) that reaffirms earlier work and extends the documentation of the CPE, further confirming that this is not only western Tethys change in biota and depositional environments, but a global event. Visscher et al (1994) proposed that the deposition of coal and plant debris in the Germanic Basin, attributed to the Carnian Pluvial Episode (CPE) by Simms & Ruffell (1989), was an artifact of preservation in locally damp environments.…”

“…This Middle-early Late Triassic isotopic trend seems a global signal and has been originally interpreted by Korte et al (2005) as the result of the enhancement of organic carbon burial in coal swamps after the early Triassic 'coal gap', but an increase in primary productivity in the ocean is also proposed (Sun et al 2018). The trend is interrupted by sharp negative δ 13 C excursions in the Julian 2 substage in both the records studied by Sun et al (2018). δ 13 C data from SW China (Yongyue section) show a negative excursion at the base of the Julian 2.…”

“…The new isotopic records presented in this thematic set strengthen the evidence that the onset of the CPE was marked by a major change in the carbon isotope composition of the reservoirs of the exogenic C-cycle. Sun et al (2018) present new carbonate carbon isotope data from Northern Oman and Southwest China. Both these records show a positive trend in the early Julian 1, which is a feature of many published carbonate and organic carbon isotope curves for the same interval (e.g.…”

“…Until a few years ago, little was known of the effects of the CPE in China. As of now, the recent works of Sun et al (2016Sun et al ( , 2018, Zhang et al (2018), Jin et al (2018) and Shi et al (2017Shi et al ( , 2018, the CPE in the South China Block became a hot research topic and shed a light on an area with its own special character and unique response to climate change, as compared with the better studied regions of continental Europe and western Tethys.…”