61st Annual Report on Research 2016

The past year of this project produced some significant new findings, a massive amount of new information about the chemostratigraphy and biostratigraphy of the Appalachian Basin, and also included the first publications from this grant. The first major result of this project is the revised correlation of the basal Silurian units in the Appalachian Basin. The Whirlpool and Power Glen formations, both of which were previously considered to belong to the basal Silurian transgression above the Hirnantian glaciation, are actually Ordovician in age. The limited carbon isotope data produced suggests that perhaps these units are Hirnantian in age, whereas the biostratigraphic data, which includes chitinozoans and scolecodonts, suggests they belong to the Katian. Either way, all of the evidence is consistent in suggesting that these units certainly do not belong to the Silurian. This is a considerable change in the correlation of ‘basal Silurian’ units of the Appalachian Basin. This information was part of a student research project with our collaborators in Belgium and was published in 2016 in the Canadian Journal of Earth Science and the financial support of the ACS was acknowledged.

The second major finding this year concerned the top of the Silurian and our ability to calibrate the numerical age of the Silurian-Devonian boundary. The date from the ‘Kalkberg Bentonite’ remains the primary age control for the calibration of the Silurian-Devonian boundary, but new biostratigraphic information provided by this project provides important new chronostratigraphic correlation of the bentonite within the Silurian-Devonian boundary interval. The new conodont and chitinozoan information demonstrate that the ‘Kalkberg Bentonite’ is undoubtedly within Devonian strata and occurs at a position that can only be constrained as somewhere between the middle part of the lower Lochkovian to the middle part of the middle Lochkovian. The bentonite is not at the boundary itself and can only provide a date that the S-D boundary can be no younger than. The net result of these findings to the Silurian and Devonian time scales is that the early Lochkovian will likely have to be reduced in duration and the duration of the Pridoli will also likely be reduced by a minor amount. These results were included in Neo McAdams’ PhD dissertation (University of Iowa, 2016) and have been submitted to the journal Lethaia. The manuscript has been reviewed and is currently under revision for final editorial approval. ACS support for this project was acknowledged in the manuscript.

Data from the deep drill core in Ohio that was sampled in 2015 were finally returned in September of 2016. The data show a very clear indication of the Ireviken and Mulde positive carbon isotope excursions in addition to several other intriguing new details about the Silurian stratigraphy of the Appalachian Basin. For example, the middle Wenlock appears to be missing or extremely condensed in the core. Further work elsewhere throughout the Appalachian Basin will be required to determine if this is a consistent feature throughout the basin, or only within a specific area of the basin. Higher in the core we did not recover any obvious record of either the Lau Excursion or the Klonk Excursion. At the moment it remains unclear, based on these findings alone, to what part of the Ludlow and/or Pridoli the remainder of the core should be assigned.

Field work to the Virginia/West Virginia area was undertaken in summer of 2016 and samples are already being processed for conodont biostratigraphy and carbon isotope chemostratigraphy. These samples are part of the PhD work of Stephan Oborny here at the University of Iowa and he is on track to graduate in Spring of 2019. More than 350 carbon isotope samples have already been analyzed in the laboratory and if we are correct, we may have found the first clear record of the Mulde Excursion in this part of the Appalachian Basin. The conodonts are still being processed and we will have to wait until we can confirm these interpretations with biostratigraphy from the same outcrop. More than 100 conodont samples were taken and more than 50 of them have already been processed through formic acid. We are now in the process of heavy liquid separation and are beginning the process of picking the samples. Much of this part of the project was targeted as a result of the work my former Post-Doc Alyssa Bancroft did on the Charles Helfrich conodont collection.

The work on the Helfrich conodont collection is nearing completion. The scope of this undertaking was not clear until this past year when the reality of reassessing >3,000 slides that contain >50,000 specimens sunk in. All slides have been restudied and all taxonomy updated. Project Post-Doc Alyssa Bancroft has now moved on to a position at the Indiana Geological Survey, but we continue to work on the Helfrich material and the first publication from that work is due to be submitted in early 2017. This work will provide a new and detailed conodont biostratigraphy for the central Appalachian Basin, and combined with the work of PhD student, Stephan Oborny, will considerably improve the global chronostratigraphic correlation of the Silurian succession in the basin. The Helfrich collection, although immense, has generally been ignored in global studies due to several rare co-occurrences and overlapping ranges that are generally not seen elsewhere. We are struggling with how to parse out these co-occurrences and what they mean stratigraphically, biologically, and with respect to global correlation. These revisions will be published in two parts: The Llandovery-Ludlow interval, and the Pridoli-Devonian interval.

One paper is published and another in review. In total I now anticipate no fewer than five manuscripts to result from this project overall. The remaining balance of all funds will be spent this upcoming year.