February Geology and GSA Today media highlights

Temperature proxy data and their significance for the understanding of pyroclastic density currents
Andrew C. Scott, Geology Department, Royal Holloway University of London, Egham, Surrey TW2O OEX, UK. Pages 143-146.

Scott et al. have shown that data from plants charred by contact with hot pyroclastic (ash) flows can be used to help in the modelling of pyroclastic density currents. Hot pyroclastic flows are one of the most dangerous volcanic phenomena and have been responsible for many fatalities. Famous examples include the eruption of Vesuvius with the destruction of Herculanium and Pompeii and the eruption of Mont Péle in Martinique that destroyed the town of St. Pierre, killing nearly all the inhabitants. Understanding how these flows behave is important in assessing volcanic hazards. One of the biggest problems has been obtaining temperature data from pyroclastic density currents. A major dome collapse of the Soufrière Hills volcano, Montserrat, on 26 December 1997, generated a devastating pyroclastic density current that destroyed vegetation and left a distinctive tar-like deposit on the surface that deposit included a range of charred, mainly herbaceous flowering plant axes and roots. Reflectance studies of these charcoalified plants provided minimum flow temperatures of 300-425 °C, providing an estimate of pyroclastic density current characteristics. Scott et al. estimate flow-front current densities near the ground of 1.8 to 3 kilograms per cubic meter, using constraints from a mean flow speed of 90 meters per second estimated from seismic data. The mean temperature of the ash component is estimated as 400-610 °C.

Caribbean chronostratigraphy refined with U-Pb dating of a Miocene coral
Rhawn Denniston et al., Department of Geology, Cornell College, Mount Vernon, Iowa 52314, USA. Pages 151-154.

Uplift of the Central American volcanic arc isolated the Caribbean and Pacific oceans approximately 3 million years ago, and changed the physiochemical characteristics of the Caribbean. In response, many shallow marine taxa experienced an increase in speciation. Quantifying these evolutionary rates requires having precise age constraints on the related sedimentary sequences, but such a well-defined chronology has been lacking. Denniston et al. refined the age of one sedimentary unit from the Dominican Republic that contains a diverse and well-preserved fossil taxa by obtaining a uranium-lead (U-Pb) age on the primary aragonite of a pristine Miocene age coral. The recognition that such ancient corals may be sufficiently well preserved to allow direct U-Pb dating opens doors for continued refinement of late Cenozoic sedimentary sequences.

Size of the earliest mollusks: Did small helcionellids grow to become large adults?
Mónica Martí Mus et al., Area de Paleontología, Facultad de Ciencias, Universidad de Extremadura, 06071 Badajoz, Spain. Pages 175-178.