Biosignatures Link Microorganisms to Iron Mineralization in a Paleoaquifer

Transcription

1 GSA DATA REPOSITORY Biosignatures Link Microorganisms to Iron Mineralization in a Paleoaquifer Weber et al. MATERIALS AND METHODS Carbon, Nitrogen, and 13 C Analyses In an effort to minimize identification of contaminating microbial growth on the surface of concretions, samples were first washed in 0.5N HCl to remove surface-bound iron and carbonates and subsequently rinsed with acetone and air dried to remove surface bound organics. The Fe(III) oxide rind was physically separated from the interior by breaking a concretion open with physical force using an acid-washed (0.5N HCl) pestle. The bleached sandstone interior was scraped from the rind. The rind was ground into a powder in an acid washed mortar and pestle and stored in acid washed glass vials prior to analysis. Triplicate samples were placed into tin (C and N analyses) and silver capsules ( 13 C total carbon) for combustion at 1050 C in an elemental analyzer (EA) for measurement of carbon and nitrogen as CO 2 and N 2, respectively. Background nitrogen was minimized by placing samples in an autosampler under a helium atmosphere. Evolved gas as CO 2 was immediately measured for 13 C analyses of total oxidizable carbon (denoted as total carbon) with a GV Isoprime isotope ratio mass spectrometer. The 13 C values of C associated with organic carbon were obtained separately after inorganic carbonates including iron carbonates were removed from samples in silver capsules by daily additions of 100 L of 6N HCl every day at 50 C for a period of eight days as previously described by Larson and colleagues (Larson et al., 2008). The stable isotope data were calibrated against international reference standards and expressed as per mil ( ) deviation ( ) relative to VPDB per Equation (1). (1) External precision, determined from repeated analysis of a sucrose working standard, was 13 C = ± Field Emission Scanning Electron Microscopy Small (1cm) concretions were split in half in an acid-washed (0.5N HCl) diamonite mortar. The concretion half was placed on an SEM stub with the cross-section facing up, dehydrated, and sputter coated with chromium. Samples were stored in a dessicator prior to

2 imaging. Samples were imaged on a Hitachi S4700 Field-Emission SEM at 5kv and 10kv at the Morrison Microsocopy Core Research Facility. NanoSIMS NanoSIMS ion mapping was performed using a CAMECA NanoSIMS 50 in the Centre for Microscopy Characterization and Analysis at the University of Western Australia. Subsamples of concretions containing the interface between the Fe-poor center and Fe-rich rind were embedded in resin, mounted in 1 cm diameter aluminum rings, polished using colloidal silica and coated with 5 nm of gold. All measurements were obtained with a 100 nm Cs + primary ion beam, with a net impact energy of ~16 kv, and a beam current of ~2 pa. The NanoSIMS was operated in multi-collector mode, allowing 12 C -, 16 O -, 12 C 14 N -, 28 Si - and 56 Fe 16 O - to be collected simultaneously from the same scanned area, with a dwell-time of 20 ms/pixel. The sample surface was presputtered with the primary ion beam to > ions/cm 2 as previously described by Gnaser (Gnaser, 2003) in order to reach a steady-state of ion emission and to remove surface contamination. Charge compensation was achieved by use of the electron gun. Image sizes were pixels and fields of view varied from m (i.e., 47 nm per pixel) to m (i.e., 195 nm per pixel).

3 TABLE 1. Replicate 13 C data collected from the exterior rind of three Fe(III)-oxide concretions. Fe(III)-oxide concretion Sample ID Total Carbon 13 C ( VPBD) Organic Carbon 13 C ( VPBD) SF SF SF SF SF SF SF SF SF Mean ± SEM -7.05± ±2.69

4 A B Figure DR1. Spheroidal Fe(III)-oxide concretions collected from Spencer Flat south-central Utah. A, Spheroidal Fe(III) oxide concretions of various sizes remain buried until they weather out of the sandstone. Once the concretions have weathered out of the sandstone they roll loose on the surface. B, Many of the spheroidal Fe(III) oxide concretions are composed of an Fe(III)-rich rind with a bleached sandstone interior as depicted here.

5 Figure DR2. Geologic map of a portion of south-central Utah showing the location where Fe(III) oxide concretions were collected in this study (Modified from Loope et al. 2010). Star denotes sample collection site.

6 Figure DR3. Field emission scanning electron micrographs (FE-SEM) and energy dispersion spectroscopy (EDS) data were collected from a region in which microorganisms were identified within the Fe(III) oxide rich exterior of a spheroidal Fe oxide concretion. A, Baclli-like microorganisms commonly identified in the Fe(III) oxide. Red and white circles denote areas in which EDS data was collected. B, EDS data collected in the area denoted by the red circle (Figure a) identified Fe and C in association with the bacilli-like microstructures. C, EDS of a region not directly associated with microbial structures (white circle Figure a) resulted in a significant silica signal and decreased Fe and Ca relative to the microbial fossils.