ELONGATED STROMATOLITE-LIKE STRUCTURES IN THE UPPER CAMBRIAN HELLNMARIA MEMBER, NOTCH PEAK FORMATION, UTAH

The Upper Cambrian/ Ordovician Notch Peak Formation in west-central Utah is composed of limestone and dolomitic lithologies. It is well exposed in the House Range and the Wah Wah Mountains in Millard County. There has been extensive study of its stratigraphy, fossil content and biozonation. At several levels in the Notch Peak Formation there are features described as microbial stromatolites and stromatolite reefs.

In the course of study of these features, an unusual type of structure was found to be widespread in the upper part of the Hellnmaria Member. These structures resemble the stromatolites, but are elongated. They are from 15 to 35 cm wide and most commonly 1-3 m long, but some are up to 5 m in length. Where seen in vertical section they are 0.7-2.1 m high. These elongated structures occur in extensive fields, closely packed together, all oriented in the same direction. The orientation remains the same wherever we have observed this interval of the Hellnmaria in the House Range, over a distance of several kilometers. The origin of these structures is currently unknown but at present does not appear to be biogenic.

We have found similar structures in the Hellnmaria Member in the Wah Wah Mountains and in the Drum Mountains. At each of these locations there is also a consistent orientation, but the orientation is different at each location, and different from the orientation in the House Range.