Stratigraphy and Sedimentology of Lower Permian Carbonates from Low-Latitude Tethys and Panthalassa Oceans
Date
2023-12-20
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Abstract
The Early Permian (Asselian–Kungurian) witnessed the peak and demise of the main phase of the late Paleozoic ice age (LPIA). This icehouse-greenhouse transition was concomitant to rising pCO2atm from pre-industrial levels in the earliest Asselian to modern-day values in the Sakmarian–Artinskian boundary before doubling today’s concentrations at the end of the Kungurian. This icehouse-greenhouse transition, considered one of the critical transitions affecting Earth prior to the latest Permian extinction, is viewed as a potential analogue to the icehouse-greenhouse shift predicted to occur if current pCO2atm continues to increase. Thus, the overarching goal of this study is to analyze the end of the LPIA as a potential analogue to an ever more likely future icehouse to greenhouse transition. In particular, this project is focussed on how low-latitude carbonate systems were impacted by the end of the LPIA. The Lower Permian carbonate-dominated successions in New Mexico, Austria, and South China record the peak and demise of the main phase of the LPIA. Asselian strata are arranged in transgressive-regressive sequences known as parasequences or cyclothems formed during this glacial interval. Sakmarian-Kungurian strata comprise non-cyclic deposits formed after glaciation. Cyclothems are widely interpreted as far-field records of glacioeustatic sea-level fluctuations mirroring the waxing and waning of ice sheets. However, the amplitude of glacioeustatic fluctuations represented in Paleozoic cyclothems remains unclear. Chapter 2 clarifies the amplitude of eustatic fluctuations represented in coeval cyclothems of the Robledo Mountains (New Mexico) and Carnic Alps (Austria) and proposes a stepwise demise of the main phase of the LPIA using microfacies analysis. Additionally, based on foraminifer and conodont biostratigraphy, the end of cyclic deposition is dated as Asselian–Sakmarian. Lastly, a sequence stratigraphic framework for the studied interval is established based on microfacies analysis and field observations. Contemporaneous to this glacial phase, an aridification and seasonality trend associated with intensifying low-latitude monsoonal circulation began across Pangea. In South China, a shift towards warm and humid conditions, known as the Artinskian Warming Event (AWE), had a profound impact on sedimentation of carbonate platforms adjacent to emerged areas. Enhanced coastal upwelling driven by intensified monsoonal circulation affected sedimentation of platforms outboard. Based on microfacies analysis, Chapter 3 investigates how shelf carbonates in South China were affected by AWE and enhanced coastal upwelling and provides an updated age interpretation of the upper Maping and lower Chihsia formations in Laibin and Dahua (South China) combining foraminifer and conodont biostratigraphy. Additionally, a sequence stratigraphic framework was suggested for the studied interval based on microfacies analysis and field observations. Enhancement of coastal upwelling may have been common across low-latitude carbonate systems as monsoonal circulation intensified. Analyzed Artinskian successions in this study are dominated by photozoan assemblages punctuated by recurrent interbeds with a heterozoan assemblage. The abundance and frequency of these interbeds may indicate the effect of Milankovitch cycles (i.e., precession) in the intensification of coastal upwelling. Chapter 4 explains the occurrence of these high-frequency shifts in carbonate assemblages observed in coeval Artinskian successions of New Mexico, Austria, and South China.
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Keywords
Early Permian, Carbonates, LPIA, Icehouse-greenhouse, CO2, Conodonts
Citation
Calvo Gonzalez, D. (2023). Stratigraphy and sedimentology of Lower Permian carbonates from low-latitude Tethys and Panthalassa Oceans (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.