Horizontal or slightly inclined, rectilinear to slightly curved burrows of flattened to cylindrical section. No branching is observed and overlapping is rare. Burrow with smooth margins, without lining. Burrow fill differs from the host rock by having coarser grains and, apparently, being devoided of organic matter. Average burrow diameter 3.2 mm, the smallest measuring 1.18 mm and the biggest 7.41 mm. Preservation in positive hyporelief.
Description.—Subcylindrical to cylindrical, horizontal to inclined vermiform structures with smooth surface, predominantly preserved as full-reliefs within heterolithic facies (Fig. 7.8). Burrow width is 1 to 8 mm but is most commonly 3 to 5 mm. Overlap among specimens is common. Fill differs from host rockin being typically finer-grained.
Remarks.—Planolites montanus is distinguished from other ichnospecies of Planolites by its tortuous course with horizontal and inclined segments, penetrative nature, and lack of ornametation (Pemberton and Frey, 1982).
Diagnosis. Relatively small, curved to contorted Planolites, less than 5 mm in diameter (Pember ton and Frey, 1982; Fillion and
Horizontal burrows, straight or gently curved, with smooth walls, oval in cross section, diameter from 1 to 5 mm. They were produced close to the surface of the clay and follow very complex surfaces modelled by other burrowers. The burrow was apparently open to the surface along its whole length and is completely filled with sand from the overlying bed. Convex epireliefs.
Remark.P. beverleyensis a relatively large unornamented form, while P. montanus is relatively small (less than 5 mm in diameter) and unornamented (Pemberton and Frey, 1982; Fillion and Pickerill, 1990).
Irregularly cylindrical, sinuous, undulose and meandrous small burrows exibiting no obvious pattern other than a general dendency toward horizontal development. Burrow diameters may remain more or less constant but typically exhibit slight to pronounced small-scale variations. True branching is relatively rare, crossovers, interpenetrations and reburrowed segments may be abundant to profuse. Many specimens are highly undullose; inthese only short segments coincide with any given plane. Horizontal erosional truncation of vertically or obliquely oriented segments may give the appearance of knobby or "punctate" bedding surfaces. Burrow fills tend to consist of cleaner, better sorted sediments than the host matrix. Preserved an endichna, hypichnal ridges and epichnal grooves.