Robyn E. Hannigan

Shaken and stirred: Seismites and tsunamites at the Permian-Triassic Boundary, Guryul Ravine, Kashmir, India

ABSTRACT The famous Permian-Triassic boundary section at Guryul Ravine in Kashmir shows repeated strong disturbances in the uppermost 3 m of the section below the main end-Permian mass extinction horizon. Two one-meter-thick disturbed beds, with convoluted bedding and fluid escape structures, are interpreted as seismites. Immediately above, three lenticular, fining-upward, bioclastic grainstone beds, interbedded with argillites, are interpreted as tsunamites. In these beds, hummocky cross-stratification and grading indicate deposition by waning irregular waves at a minimum water depth of 100 m based on physical processes and faunas. Bed grain sizes indicate that the waves needed to move even the coarse sand of the matrix, let alone associated large pebbles up to 20 cm in diameter, range from amplitudes of ∼40 m for wave periods of 10 s (the upper limit for storm waves) to amplitudes of ∼3 m for wave periods of 50 to 1000 s (typical of large open-ocean tsunamis). Fossil and sedimentary evidence suggests lengthy intervals between successive tsunami events, which, together with a lack of geochemical evidence for impact, favors terrestrial causes. Geochemical proxies show that the Guryul Ravine environment remained oxic or suboxic throughout the P–Tr transition, but that anoxia developed regionally at the time of the boundary crisis. This paper is the first to propose seismites and tsunamites at the P-Tr boundary, so the geographic extent of these deposits is unknown, although analogous deposits occur in many sections worldwide from published reports.

Elemental Fingerprints used to Identify Essential Habitats: Nantucket Bay Scallop

ABSTRACT Elemental fingerprinting of adult and juvenile Nantucket bay scallop shells, Argopecten irradians (Lamarck 1819) revealed distinct element/Ca ratios that can be used to distinguish provenance of bay scallops in Nantucket Harbor. Within this small harbor (∼ 10 km2), we identified 3 distinct habitat zones defined by the abundance of scallops at a location: zone 1 (barren), zone 2 (low abundance), and zone 3 (high abundance). Element/Ca ratios were associated with proximity to the harbor mouth, with elemental differences attributed to variation in salinity and pH. Using binary logistic regression, we identified the source zones based on shell elemental ratios (i.e., various elemental concentrations divided by [Ca]). We also identified boundary salinity and pH conditions that support large abundance of A. irradians within Nantucket Harbor. This information is crucial to seeding projects and the management of the Nantucket Harbor A. irradians population.

Metal Geochemistry of a Brackish Lake: Étang Saumâtre, Haiti

Etang Saumâtre (also known as Lac Azuei, Lago del Fondo, or Yainagua) is a brackish lake located in eastern Haiti. Sources of irrigation and drinking water for the surrounding communities in Thomazeau, Ganthier, and Fond Parisien are freshwater springs and shallow wells tapping the complex fractured aquifer system surrounding Etang Saumâtre. In some groundwater samples, we found concentrations of trace metals exceeding World Health Organization guideline values. Lake sediment trace metal concentrations were also high. For example, chromium (Cr) ranged from 26.24 to 198.44 mg/kg, exceeding the USEPA sediment quality guideline value for heavily polluted. High concentrations of potentially toxic trace metals in both lake sediments and groundwater suggest that the population relying on this lake for drinking water, irrigation, and subsistence fishing may be at risk for metal-induced health effects. By understanding the geochemical behavior of redox-sensitive trace metals such as Cr, in the context of limnology and long-term fate and transport within the system, our results provide unique insights into the geochemical controls on remobilization of redox metals from the sediments and the potential impact of future environmental change on the sediment and water quality in this system.