Characterization of Carbonate Crust from a Recently Discovered Methane Seep on the North Atlantic Continental Margin of the USA
Department of Geosciences, Mississippi State University, Mississippi State, MS 39762, USA
Department Earth & Environmental Sciences, University of Rochester, Rochester, NY 14627, USA
Rensselaer Polytechnic Institute, Troy, NY 12180, USA
Institute of Solid State Physics, RAS, Chernogolovla 142432, Russia
Center for Arctic Gas Hydrate, Environment and Climate, The Arctic University of Norway in Tromsø (UiT), 9037 Tromsø, Norway
Department of Earth Sciences, Syracuse University, Syracuse, NY 13210, USA
Department of Physical and Life Sciences, Chadron State College, Chadron, NE 69337, USA
Author to whom correspondence should be addressed.
Minerals 2019, 9(3), 138; https://doi.org/10.3390/min9030138
Received: 11 January 2019 / Revised: 18 February 2019 / Accepted: 21 February 2019 / Published: 26 February 2019
(This article belongs to the Special Issue Mineralogy, Petrology, Geochemistry and Diagenesis of Carbonate Minerals and Rocks)
This study is focused on mineralogical and chemical characterization of an authigenic carbonate rock (crust) collected at a recently discovered cold seep on the US North Atlantic continental margin. X-ray diffraction (XRD) and scanning electron microscopy (SEM) indicate that the carbonate rock is composed of microcrystalline aragonite cement, white acicular aragonite crystals (AcAr), equant quartz crystals, small microcrystalline aluminosilicates, and trace amounts of iron sulfide microcrystals. Element/calcium ratios were measured with laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) using a calcite standard, which was prepared by annealing USGS certified carbonate powder (MACS-3). The occurrence of microscopic, non-carbonate inclusions precluded evaluation of trace elements in the aragonite cement, but allowed for in situ analysis of AcAr crystals. Carbon and oxygen isotopes were analyzed via isotope ratio mass spectrometry (IRMS) and expressed as δ13C and δ18O. Low δ13C values suggest that aragonite grew as a result of anaerobic oxidation of methane and observed δ18O values indicate that the temperature of aragonite crystallization was 1.7–1.9 °C.