Teepee structures

Fig. 11. (A) Type 1 tabular unit from the middle of the Unnamed Member. Note the good preservation of sedimentary structures. Units on the scale are in decimetres. (B) Type 2 tabular unit from the Piedra Parada Member. Note absence of sedimentary structures. Units on the scale are in decimetres. (C) Teepee structure from the middle of the Unnamed Member. Units on the scale are in centimetres. (D) Photomicrograph of fenestral/laminar microtextures common in tabular units with laminar, brecciated and teepee outcrop morphologies.

Irregular, unoriented and fenestral millimetresized calcite-filled fractures found in some units are interpreted as brecciation structures. Structures that resemble small folds are probably teepee structures because they are associated with rhizocretions and alveolar microtextures. There is not enough clay in these units to cause expansion, although expansive calcite growth cannot be ruled out. The laminar cemented units in the Zia Formation have abun-... 

Klappa, C.F. (1980a) Brecciation textures and teepee structures in Quaternary calcrete (caliche) profiles from eastern Spain the plant factor in their formation. Geol. J., 15(2), 81-89. 

A number of different X-ray structures of bacterial potassium channels reveal the detailed atomic picture of the pore-forming part, helices S5 and S6 [9]. KcsA, which is crystallized in the closed conformation, has an overall structure similar to an inverted teepee [9a], Four identical subunits surround the ion-conducting pathway (Figure 8.2). Each subunit contains two full transmembrane helices, S5 and S6, as well as the P loop. The S6 helices line the central cavity, whereas the S5 helices are involved in interactions with the lipid environment. In the closed channel conformation the transmembrane helices meet at the cytosolic side to block the ion conduction path. In the open conformation of the channel, the S6 helix kinks at a conserved glycine residue to open the ion conduction path, as shown in the structure of the bacterial channel MthK [10], The ion conduction path is formed by the selectivity filter and the large water-filled central cavity. 

---