Document Type : Original Research Paper
Authors
1 M.Sc., Faculty of Earth Sciences, Damghan University, Damghan, Iran
2 Assistant Professor, Faculty of Earth Sciences, Damghan University, Damghan, Iran
3 ] Associate Professor, Faculty of Earth Sciences, Damghan University, Damghan, Iran
Abstract
Due to some environmental variations such as sea level fluctuation and the Hangenberg mass extinction event, geochemical variations of elements have occurred in the Devonian-Carboniferous transition, which some of these elements are useful indicators to display the source of sediments and the sea level changes. In this transition, Sr is one of these elements has a reverse relation with sea level changing and a direct relation with amount of sediment deposition. Trace elements such as Sr, Fe, Mn, Mg, Al, and Ca display the depositional environment conditions and their changing is affected by indoor and outdoor environmental conditions such as pH, Eh, climate, etc. This study has focused on investigation of elemental changes at the Devonian-Carboniferous boundary in the Khoshyeilagh and Mobarak Formations in the Labnesar section, North of Damghan.
The elemental changing in Brachiopoda shells and its containing sediments has the same trend as they show the fossil samples are in situ. The environmental situation of fossil organisms and their involving sediments in the study section were semi close to open sea with anoxia conditions. The black shale at D-C boundary shows LREE richer than HREE that confirmed its continental source. The variation of some elements such as Mn, Fe, Na… at D-C boundary in the Labnesar section indicates of LMC (low magnesium calcite) in the Brachiopod shells and involving sediments. The quantity variations of Mn and Sr in D-C boundary are related to sea level fluctuations. These elements are influenced by the sea level changes and impress the amount of other elements such as Fe, Al, Ti, Mg, Ca, Na, and K. The median amount of Na at the boundary indicates a moderate salinity.
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