ELEMENTAL ANALYSIS OF THE UPPERMOST PERMIAN TO THE LOWERMOST TRIASSIC OF THE SHAHREZA SECTION, IRAN

An unresolved question is the cause of the great catastrophe at the end of the Permian Period that left the Earth nearly lifeless. Lithological descriptions, petrographical observations, and geochemical analyses (isotopes and trace elements) are used to decipher a killing mechanism.

The uppermost Permian of the Shahreza section consists of relatively pure limestone which is suddenly replaced by red shales at the End Permian Event Horizon (EPEH). Alternating red shale and limestone were deposited in the interval between the EPEH and Permian – Triassic Boundary (PTB). The lowermost Triassic also consists of pure limestone.

Previous investigations have revealed that carbon isotope compositions of bulk carbonates of the Shahreza section decline by more than 6‰ PDB from the uppermost Permian to the lowermost Triassic. Petrographic observations and Sr analyses suggested that originally calcitic limestone were deposited in the uppermost Permian and originally aragonitic limestone formed in the lowermost Triassic.

The present study measured bulk rock concentrations of major, trace, and rare earth elements to determine their variations in the uppermost Permian to the lowermost Triassic of the Shahreza section. In particular, concentrations of Mn, Fe, Zn, Cu, Pb, Zr, Si, Ga, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Nb, Y, Hf, Ta, V, Cs, Sc are determined. These elements show low values in the uppermost Permian and the lowermost Triassic limestones but very high signatures at the EPEH and the PTB transition interval. In addition, all elements show linear negative correlations with Ca. Therefore, the rapid increases in concentrations of these elements at the EPEH and the PTB transition interval appear to be related to lithologic variations from the Permian to the Triassic.