T104 Impacts of Volcanism on Global Climate and Oceans—Drivers of Mass Extinctions through the Phanerozoic II

Monday, 11 October 2021
1:30 PM - 5:30 PM
Portland Ballroom 255 (Hybrid Room)

CADMIUM AS A TRACER OF VOLCANIC ERUPTION INTENSITY IN THE KPG SECTION FROM ELLES (TUNISIA)

Paper number: T104-10
Program: Technical Sessions
Time: 3:45 PM – 4:00 PM

Authors

Abstract

Massive volcanic eruptions of the Deccan coincided with the end-Cretaceous extinction. Knowing precisely when the most intense eruptions occurred is challenging because the resolution of geochronological techniques does not yet resolveevents shorter than 40 kiloannum (ka). Volcanic eruptions outgas volatile metals, e.g., Cd, along with sulfur dioxide and other gases that may have contributed to a gradual extinction observed in foraminifera that preceded the end-Cretaceous by about 300 ka. Trace metals like cadmium accumulate in sediments by deposition of aerosols, where the excess Cd reflects a combination of volcanic intensity with dilution by sediment. The KPg section at Elles represents a middle neriticdepositional environment with a sedimentation rate of approximately 3 cm/1,000 years. A series of sediment samples (marly limestone to shale) were taken from about 1 meter above the boundary to about 15 meters below the boundary.Elemental compositions of sediments (50 elements) were obtained by solution ICP-MS. Cadmium was determined using multiple isotopes to avoid isobaric interferences. USGS standards MAG-1, SCo-1, SDO-1 and SGR-1 were used for external standardization. Cadmium abundances ranged from values close to upper continental crust (UCC) to values about eight times higher. Such high values were found in sediments from the 100 ka period preceding the boundary corresponding to the Poladpur phase of the Deccan eruption. Above the boundary, there is a 25 ka period of normal shale Cd values interpreted here to represent the period between the Ambenali and Poladpur phases. We have previously shown from the neighboring El Kef section, representing ~ 10 ka, that Cd and Re are correlated in proportions similar to those from intraplate volcanoes. The new data for Elles indicate the presence of volcanogenic trace metals over most of the period of the Poladpur phase of the Deccan eruption. Cadmium as a tracer enables better correlation between foram-based chronology and intense pulses of the Deccan eruption. The data obtained thus far confirm that the period prior to the extinction was dominated by intense volcanism followed by relative quiessence during the earliest Danian recovery with important implications for the cause of the extinction.

Geological Society of America Abstracts with Programs. Vol. 53, No. 6

doi: 10.1130/abs/2021AM-370363

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