About 80% of the southern part of the North American Cordillera within the Republic of Mexico is made up of suspect terranes. These terranes are suspect because their paleogeographic setting with respect to cratonic North America at various times through much of Phanerozoic time is uncertain. Much of northeastern and southeastern Mexico is underlain by basement accreted during late Paleozoic time, an extension of the Appalachian–Ouachita orogeny. This orogen has been considerably modified by Jurassic strike-slip translations related to the opening of the Gulf of Mexico. Western and southwestern Mexico is largely made up of several distinct but coeval latest Jurassic to Late Cretaceous submarine magmatic arc terranes with unknown basement that appear to have accreted against the disrupted North American margin by early Tertiary time. Only northeastern Sonora and the State of Chihuahua appear to be floored by unmoved North American cratonic basement. The combined effect of Mesozoic accretions and translations essentially eliminates the overlap of South America upon Mexico that is drived from late Paleozoic – early Mesozoic reconstructions of the closed Atlantic Ocean. This new vision of accretionary and translational tectonics in Mexico has profound implications for the study of tectogenesis in the southern Cordillera as well as for the interpretation of Mexico's vast natural resources. Preliminary analysis indicates that Mexico's gold–silver and lead–zinc deposits are directly or indirectly related to the terrane distributions discussed.

The environmental impacts of hydraulic fracturing, particularly those of surface spills in aquatic ecosystems, are not fully understood. The goals of this study were to (1) understand the effect of previous exposure to hydraulic fracturing fluids on aquatic microbial community structure and (2) examine the impacts exposure has on biodegradation potential of the biocide glutaraldehyde. Microcosms were constructed from hydraulic fracturing-impacted and nonhydraulic fracturing-impacted streamwater within the Marcellus shale region in Pennsylvania. Microcosms were amended with glutaraldehyde and incubated aerobically for 56 days. Microbial community adaptation to glutaraldehyde was monitored using 16S rRNA gene amplicon sequencing and quantification by qPCR. Abiotic and biotic glutaraldehyde degradation was measured using ultra-performance liquid chromatography--high resolution mass spectrometry and total organic carbon. It was found that nonhydraulic fracturing-impacted microcosms biodegraded glutaraldehyde faster than the hydraulic fracturing-impacted microcosms, showing a decrease in degradation potential after exposure to hydraulic fracturing activity. Hydraulic fracturing-impacted microcosms showed higher richness after glutaraldehyde exposure compared to unimpacted streams, indicating an increased tolerance to glutaraldehyde in hydraulic fracturing impacted streams. Beta diversity and differential abundance analysis of sequence count data showed different bacterial enrichment for hydraulic fracturing-impacted and nonhydraulic fracturing-impacted microcosms after glutaraldehyde addition. These findings demonstrated a lasting effect on microbial community structure and glutaraldehyde degradation potential in streams impacted by hydraulic fracturing operations.

Microorganisms play vital roles in Earth's biogeochemical cycles. Identifying disturbances in microbial communities due to anthropogenic contamination can provide insights into the health of ecosystems. Picher, Oklahoma, was the site of large-scale mining operations for Pb, Zn, and other heavy metals until the mid-1950s, operating within the Tri-State Mining District (TSMD) of Missouri, Kansas and Oklahoma. Although mining ceased decades ago, high concentrations of heavy metals (>1000 ppm) remain in area soil and water systems. Previously, we mapped metal concentrations on samples collected from mine tailings in Picher and along cardinal-direction transects within an 8.05-km radius of the town. To elucidate changes in microbial community structure due to regional metal contamination, 16S rRNA gene sequences and qPCR calculations of total Bacteria and Archaea were analyzed against these metal concentrations. Bacteria were negatively and significantly correlated with Pb, Cd, Zn, and Mg; however, Archaea was only significantly and positively correlated with pH. Illumina sequencing of 16S rRNA genes showed significant differences in microbial communities of chat and west transect samples. Comparison of soil chemistrywith community structure indicated that Al, Pb, Cd, and Zn significantly impacted community composition and distribution of individual OTUs. Mapping the distribution of heavy-metal contamination and microbial communities in these soils represents the first step in understanding effects of long-term, heavy-metal contamination at a basic trophic level.

Horizontal drilling and hydraulic fracturing extraction procedures have become increasingly present in Pennsylvania where the Marcellus Shale play is largely located. The potential for long-term environmental impacts to nearby headwater stream ecosystems and aquatic bacterial assemblages is still incompletely understood. Here, we perform high-throughput sequencing of the 16 S rRNA gene to characterize the bacterial community structure of water, sediment, and other environmental samples (n = 189) from 31 headwater stream sites exhibiting different histories of fracking activity in northwestern Pennsylvania over five years (2012–2016). Stream pH was identified as a main driver of bacterial changes within the streams and fracking activity acted as an environmental selector for certain members at lower taxonomic levels within stream sediment. Methanotrophic and methanogenic bacteria (i.e. Methylocystaceae, Beijerinckiaceae, and Methanobacterium) were significantly enriched in sites exhibiting Marcellus shale activity (MSA+) compared to MSA− streams. This study highlighted potential sentinel taxa associated with nascent Marcellus shale activity and some of these taxa remained as stable biomarkers across this five-year study. Identifying the presence and functionality of specific microbial consortia within fracking-impacted streams will provide a clearer understanding of the natural microbial community’s response to fracking and inform in situ remediation strategies.