A NEW LOCALITY OF NEOPROTEROZOIC TUBE STRUCTURES IN NORTHERN UTAH: INSIGHT INTO GENESIS AND AGE OF A CAP CARBONATE

Tube structures in Neoproterozoic post-glacial cap carbonates are extremely rare, documented in only four localities worldwide: Death Valley, Brazil, and n. and s. Namibia. A new locality for these structures has recently been discovered in the cap-carbonate sequence that sharply overlies the Mineral Fork Formation in northern Utah. These tube structures appear similar to those in the Noonday Dolomite of Death Valley, with a few potentially important differences that may suggest an alternate mode of formation. The Utah tube structures may also be the first reported occurrence in a non-Marinoan post-glacial cap carbonate (Richey et al., this meeting).

To compare the Utah cap carbonate and tube structures with those reported from other locations -and to address the question of how they may have formed- we report primarily on detailed macroscopic and microscopic analyses similar to those used by previous workers. This includes 1) field measurements of size/type/spacing of tube structures in host rock, 2) hand-sample analysis of tube and host rock composition, texture, and structure 3) petrographic thin section and scanning-electron microscope (SEM) analysis of tube and host rock composition and texture.

Initial analyses indicate the Utah tube structures have an average width of 0.60 cm (varying from 0.2 – 2.0 cm dia.), are typically spaced 1.90 cm apart (varying from 1 – 4 cm spacing), and are mainly infilled with sparry cement, although micrite and “ghost” fill also occurs. Most tube structures are oriented perpendicular to bedding and some tubes change along their vertical length from one fill type to another, suggesting that the fill type may be the result of diagenesis rather than an original feature. The tube fill appears laminated in some tubes but not in others, and when laminae are present, they do not always display obvious concave-up geometry. Within the tube structure interval (~ 1.5 m thick), undulose lamination is common, some of which is locally disrupted. Tubes are clustered in m-scale, laterally discontinuous lengths and clusters are separated by areas of massive to laminated strata.

Continuing analyses will provide more information about tube structure and host rock composition and interactions, ultimately yielding clues about the origin and occurrences of these enigmatic structures.

Session No. 14

T4. Neoproterozoic–Early Paleozoic Tectonic and Climatic Evolution of the Cordilleran Margin

Thursday, 19 May 2011: 8:00 AM-12:00 PM

Cottonwood (Riverwoods Conference Center)

Geological Society of America Abstracts with Programs. Vol. 43, No. 4, p.56

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