Page 443 - Carbonate Facies in Geologic History

432

Plate XI. Spongiostrome Structure in Pelleted Micrite
and Pelsparite

(A) Spongiostrome laminite, standard microfacies 21, composed of peloids origi-
nally bound together by filamentous blue-green algae existing on tidal flats. Note
the irregular anastomosing fabric between the grains. The laminae are caused by
micrograding or at least alternation of coarse and fine layers. The finer, dark
micrite layers are formed at times of minor marine flooding when only the most
minute particles can be carried across the algal mats. Sample SP-50, Hauptdo-
lomit (Upper Triassic-Norian) below the Steinplatte Haus, above Waidring, Aus-
tria. Thin section, x 18

(B) Pelsparite with three, centimeter-thick, micrograded laminae with small-
scale ripples, standard microfacies 16. Peloids are discrete and well-rounded,
shaped and deposited by moving water. Sample SJ-1 is from the San Juan Can-
yon, Utah. Middle Pennsylvanian sediment at the top of a sedimentary cycle. Just
above the thin micritic layers, large reworked lithoclasts and a few bioclasts occur
with the peloids. Thin section, x 11
See also Plate IX for higher magnification of standard microfacies 16. Also
Horowitz and Potter (1971), Plate 100 for pelsparite with lithoclasts from the
Palliser Formation, Devonian of Alberta, Canada