The introduction of the European Caucasotachea vindobonensis (Gastropoda: Helicidae) in North America, its origin and its potential range

We report the introduction of the central and eastern European helicid land snail Caucasotachea vindobonensis in North America. It was first recorded from Rensselaer County in the state of New York in 2015 by a community scientist. From 2016 to 2020, 14 additional occurrences in Rensselaer County, neighbouring Albany County and an imprecisely localized site in the Adirondack Mountains were recorded by community scientists. In 2020, the species was newly recorded at two sites in Schoharie County, NY, and at three sites in Québec, one of them approximately 700 km to the north of the initial record. Partial mitochondrial cox1 sequences from Rensselaer differ from an eastern Ukrainian haplotype only in a single substitution. Therefore, a Ukrainian origin for this introduction is likely, although not certain: the Rensselaer haplotype also differs in only two substitutions from a more widespread haplotype known from Ukraine, Hungary, Slovakia, Czechia, Serbia, and Bulgaria. An environmental niche model of the species based on occurrence data from central and eastern Europe indicated that a large region from the northern east coast to the midwestern United States is suitable for C. vindobonensis. The Canadian occurrences may indicate that the North American lineage is able to survive colder winters than predicted by the environmental niche model. Caucasotachea vindobonensis is not listed as a pest in Europe and it is unlikely to become an agricultural pest in North America as it prefers rotting plant material over living parts of plants, but its impact on native organisms can hardly be predicted.

Reconsidering initial Pb in titanite in the context of in situ dating

In situ U-Pb dating of titanite, which can preserve trace-element records of various petrologic processes but also incorporates significant initial Pb, has proliferated in recent years. The widespread use of titanite data to construct tectonic P-T-t paths warrants careful assessment of the available dating techniques, as well as attention to the assumptions that underpin the U-Pb data analysis. This contribution provides the first direct comparison of the two major analytical methods [SHRIMP (SIMS) and LA-ICP-MS] for in situ U-Pb titanite dating. A set of well-characterized titanite grains from Harrisville, New York, in the Adirondack Mountains were analyzed for U-Th-Pb isotopes along the same cross-grain traverses by Sensitive High Resolution Ion Microprobe (SHRIMP) and LA-ICP-MS. Both LA-ICP-MS and SHRIMP data sets define approximately linear arrays on the Tera-Wasserburg Concordia (semi-total Pb/U) diagram and would commonly be interpreted as representing a single date population with minor scatter. However, previous studies have suggested that Adirondack titanite actually records two regionally well-defined thermal events, ~50–100 m.y. apart. When titanite data arrays are treated in detail, attempts to determine concordia-intercept ages by robust three-dimensional linear regression produce large uncertainties and/or poor fit statistics that suggest that the data are not, in fact, isochronous. Grain-by-grain analysis of U-Pb titanite data shows that different subsets of titanite (determined by additional geochemical and microstructural data) show different patterns of U-Pb data. By comparing predictions for Pb-ingrowth evolution paths in Tera-Wasserburg diagrams with observed data, it is possible to recognize both a change in initial Pb composition and Pb loss in the Adirondack titanite U-Pb data set. This study provides an example of how greater geochronologic detail can be extracted from large in situ U-Pb titanite data sets. Even when precise dates are not recovered, geological processes and events that cause data scatter can be recognized through analysis of U-Pb data patterns using the Tera-Wasserburg diagram.