Richard Horne

Dartmouth, N.S.

B. Sc. Honours Thesis

Depositional Environments and Diagenesis of a Section of the Herbert River Limestone Member, Windsor Group, Upper Pleasant Valley, Nova Scotia

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A stratigraphic section of the Herbert River Limestone Member, Windsor Group, exposed on Pleasant Brook, Upper Pleasant Valley, N.S., consists of ten carbonate lithologies. From base to top of section (with their respective depositional environment), these are:

1. Calcareous siltstone (lagoonal)
2. algal bindstone (intertidal)
3. wackestone - packstone (shallow sub- littoral)
4. Palaeocrisidia priscilia - organic (algal?) Filament bindstone (shallow sub-littoral)
5. brecciated dolomitic wackestone (?)
6. bryozoan bafflestone*
7. bioclastic packstone*
8. mudstone - wackestone* (*deep sub-littoral)
9. stromatolites (intertidal)
10. crystalline carbonate (supratidal)

These ten lithologies have been placed into three stratigraphic zones on the bases of lateral distribution, gross terrigenous silt content and distinct changes in the lithologic nature of the rock.

The succession of interpreted environments indicates a transgressive stage followed by a regressive stage of sedimentation. Using the assumed depositional extent of the basin (after Moore, 1967) and the interpreted environments of deposition, geographic and stratigraphic relationships of the environments of deposition have been proposed (fig. 14).

Diagenesis has altered the limestone - dolostone unit during eight major events. In chronological order these are:

1. primary pyrite formation
2. neomorphism
3. dolomitization and associated leaching
4. ?iron oxide introduction
5. stylolitization
6. second stage leaching
7. quartz introduction
8. calcite spar and ?chalcopyrite introduction

Dolomitization occurred by the mixing of fresh and sea waters (Badiozamani 1973).

Keywords:
Pages: 114
Supervisor: Paul Schenk