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Frasnian Substages Working Group Progress Report - July 2000

The working Group on Frasnian Substages has added new members and currently stands at 24 individuals (Table 1). Communication with all members has been sent, but replies have not been complete. Three steps are in order for members to consider:

1) Substage divisions

A three-fold division is traditional and was favored by an initial vote. Proposals have suggested two-, three-, and five-fold divisions for the Frasnian. In summary these are:

a) The first appearance of Palmatolepis punctata, the nearly concurrent appearance of Ancyrodella gigas serves as a related indicator that corresponds to the base of TR cycle IIc of Johnson et al. (1985) and the Middlesex deepening in eastern North America. Palmatolepis punctata is a widely distributed and widely recognized taxon.

b) The base of TR IId(1) which is the Rhinestreet deepening in eastern North America. This is approximated by Ancyrognathus barba, a distinct taxon, and a dated ash horizon, the Belpre Ash at 381.1 +/- 1.3 Ma (Tucker et al., 1998).

c) The first occurrence of Palmatolepis semichatovae, a widely occurring and distinct taxon associated with a deepening event in the lower portion of MN Zone 11 (jamieae or Lower rhenana Zone).

d) The base of TR cycle IId(2) and the Lower Kellwasser event (Pipe Creek Shale in eastern North America). This is approximated by the first occurrence of Palmatolepis bogartensis.

Any, all, or other proposed boundaries would result in two, three, four, or five Frasnian substages. I am currently preparing a poll of the committee to reach a consensus and direction to take. The substage boundaries should reflect recognizable biotic, geochemical, and eustatic changes.

2) Substage definition

Conodonts are the logical choice for definition of Frasnian substage boundaries. Agreement must be reached in regard to the taxon and which, if any, morphotypic variations that may be present will be considered. The schemes already proposed have pointed to two taxa: Palmatolepis punctata and Palmatolepis semichatovae as middle and upper substage boundary indicators, respectively. These two taxa are associated with sea-level rises and have wide occurrences. A substage boundary associated with a global deepening event requires investigation and recognition of the first occurrence of a distinct taxon not associated with a facies change. I also hope that focused attention on Frasnian subdivisions will solve several questions on the correlation of eustatic sealevel changes (e.g., timing of the IId cycle).

3) Substage stratotypes

Stratigraphic sections that contain an unbroken conodont faunal sequence as well as a good representation of other taxonomic groups, geochemical, magnetosusceptability, and stratigraphic marker beds should be considered for reference and stratotype designation. A preliminary list of sections proposed as substage stratotypes and boundaries will be compiled. These will be posted and sent to all interested members.

At this time zircons recovered from two ash suites in Tennessee, USA, are under analysis by R. Tucker at Washington University. 1) The Center Hill Ash from the upper part of the Dowelltown Member of the Chattanooga Shale, which is close to the Frasnian-Famennian boundary in MN Zone 13. Palmatolepis linguiformis has not been found in the sections where the ash was sampled. 2) The upper two ashes in the Belpre Ash suite at Little War Gap, in the lower Dowelltown Member of the Chattanooga Shale, that bound a shale bed containing Ancyrognathus barba, are also being analyzed. Preliminary results indicate difficulty with dating; more zircons will be run.

Bardashev, Igor (Tajikistan) ibard@geol.tajik.net

Dastanpour, Mohammad (Iran) FAX 98-341-267681

Menner, Vladimer (Russia) amenner@glasnet.ru

Over, D. Jeffrey (United States) over@geneseo.edu

Streel, Maurice (Belgium) maurice.streel@ulg.ac.be

Wang Cheng-Yuan (China) FAX 025-3357026

Sincerely yours,

D. Jeffrey Over

Corresponding Member