麻豆传媒

The lead-zinc deposit at Gays River, N. S. has been interpreted by previous studies as a Mississippi Valley type deposit hosted by an ecologic reef complex. Evidence now indicates that the host carbonate complex developed as a lime mud dominated mound without major frame-building organisms. This study presents a stratigraphic succession and depositional environment of an area of the complex.

Through detailed petrographic study of drill core three lithic units occur: a thin, basal carbonate cemented paraconglomerate, a siliceous carbonate unit, and a non-siliceous carbonate unit. Seven microfacies are evident in the two carbonate units. These microfacies define six biofacies assemblage zones: the siliceous cryptalgal, the coral, the dishmop algal, the bryozoan, the knobby cryptalgal, and the mixed skeletal zones. These assemblages are traceable with only minor variations throughout the entire area.

The carbonate succession records a single transgression with shoaling upward growth and isolated periods of subaerial emergence. The siliceous content of the sections decreases upward indicating progressive submergence of the source, the Meguma paleotopographic high. The siliceous cryptalgal, the coral, the dishmop, and the bryozoan assemblage zones record the deeper water of the rapid submergence, and subsequent shoaling upward growth. The knobby cryptalgal zone indicates very shallow water. Fenestre present in the zone are interpreted to be largely subaqueous in origin. Isolated periods of subaerial emergence are indicated by solution compaction, erosional contacts, and hardgrounds. The mixed skeletal zone probably records a return to deeper water.

Organisms are controlled by water depth, salinity, and substrate consistency. General ecology of the organisms indicates shallow to very shallow water with normal to slightly saline conditions.

An interesting Recent analogue to the Gays River sections is Rodriguez Bank in the Florida Reef Tract.

Keywords:
Pages: 97
Supervisors: Paul schenk