HYDROTHERMAL DOLOSTONES IN LOWER SILURIAN CARBONATES OF THE GASP

1
HYDROTHERMAL DOLOSTONES IN LOWER SILURIAN
CARBONATES OF THE GASPÉ BELT RELATIVE TIMING AND
HYDROCARBON CHARGE
DENIS LAVOIE Natural Resources Canada and CLAUDE
MORIN Hydro-Quebec Oil and Gas exploration
2
SIMPLIFIED GEOLOGICAL MAP OF GASPÉ AND LOCATION
OF STUDIED SECTIONS
St-Lawrence Gulf
Lac Matapedia Syncline
St-Lawrence R.
Isabelle Creek
Humber Zone
Chaleurs Bay
Miramichi Terrane
Bourque et al. (2000)
3
Stratigraphy of the Gaspé Belt
Ma
Pragian
DEV.
400
Transgression 2
Lochkov.
West Point
Pridolian
Regressive phase 2
Ludlovian
420
SILURIAN
Transgression 1
Wenlock.
Sayabec
Llandov.
Regressive phase 1
440
Ashgill.
Source rocks
Reservoirs
Production
4
PALEOGEOGRAPHIC MODEL OF THE SAYABEC CARBONATE
RAMP
Synsedimentary collapse
Taconian unconformity
Cambrian-Ordovician
5
FIELD OCCURRENCE OF MASSIVE DOLOSTONES
Lac Matapédia Syncline
Massive dolostone breccia
6
PETROGRAPHY OF SAYABEC DOLOSTONES
7
Sea- water
4
STABLE ISOTOPES
Matrix dolomite
2
-12
-14
-18
-2
-4
-6
-2
HTD
Meteoric calcite
-4
-6
8
FLUID INCLUSIONS
30
HTD
20
Salinity wt NaCl
Other calcite cements
10
Meteoric calcite
0
50
100
150
200
Homogenization Temperatures
(Lavoie and Chi, 2001)
9
HTD Model and Hydrocarbon charge
St-Léon
SAYABEC
300 m
Val-Brillant
UM
HTD
25 m
1 cm
VUG
Hydrocarbon charge
Meteoric calcite cement
10
CONCLUSIONS

• The Lower Silurian Sayavbec Formation is the
  oldest
• shallow marine carbonates in the Gaspé Belt
• Massive dolostones and breccias are currently
  known
• at two localities in northern Gaspé
• Field occurrence, petrography, stable isotope
• geochemistry and fluid inclusions point to
• fault-controlled pulses of Mg2, saline and high
• temperature fluids for dolomitization

Hydrothermal dolomitization of the Sayabec
limestone facies is currently an under-evaluated
play in the Gaspé belt