Mixed Siliciclastic/Carbonate Systems - Trace Fossils as Indicators of Sedimentary Environments - page 794

FIGURE 6 Trace fossils in the Hoyle Bay Formation (Middle Triassic), northwest Melville Island,
Canada, Sandy Point L46 core 1, 2526-2557 0 (769.3-780.2 m). Wavy lines denote erosional forma-
tion contacts. Wentworth size-classification acronyms include vf (very fine), f (fine), m (medium), c
(coarse), and vc (very coarse). Note that all photographs are core slabs shown in vertical orientation
except the bottom photograph in (C), which is shown in horizontal (bedding-plane) orientation. (A)
Strip log showing the distribution of facies in the Gore Point, Hoyle Bay, and Barrow Formations.
(B) Gryphaea sp. shells in a transgressive sandstone unit in the lowermost beds of the Hoyle Bay
Formation are commonly bored and are clearly reworked from their original site of emplacement.
(C) Glossifungites -demarcated discontinuity surface at the Hoyle Bay/Barrow contact. (D) Coplanar
Glossifungites and Trypanites trace-fossil assemblages at the top Gore Point contact ( ¼ the Roche
Point/Hoyle Bay contact).
pits (cf. Gastrochaenolites isp.) characterize this contact. The pits are infilled with
silty to muddy sandstone. Skolithos burrows pipe clean sandstone from the over-
lying units into the glauconitic/sideritic sandstone. The sharp-walled nature of the
burrows indicates that the sand was firm prior to penetration by the Skolithos con-
structors, supporting the assignment of this trace-fossil assemblage to the Glossi-
fungites Ichnofacies. The co-occurrence of two distinct substrate-controlled
ichnofacies at this contact underscores that this lithostratigraphic boundary repre-
sents a significant temporal break. Overlying this surface, within a transgressive
silty to muddy sandstone unit, occur numerous bored Gryphaea ( Fig. 6 D). These
ostreids occur primarily in convex-up position, indicating current mediation in
their emplacement ( Fig. 6 D). It is believed that these bored bivalves may have
been reworked either from the top Gore Point contact or from a unit that has been
erosionally removed from the study area.