Calcium pumping and anhydrite/halite relationships in Silurian A unit of Michigan basin

Conference · Wed Mar 01 00:00:00 EST 1989 · AAPG Bull.; (United States)

OSTI ID:5880483

Leibold, A W; Howell, P D

Observed relationships between anhydrite and halite in the A unit of the Michigan basin are not easily explained by classical evaporite depositional models. Within the Northern Reef trend, productive Niagaran pinnacle reefs are surrounded by A unit halite, which commonly exceeds 100 m in total thickness. However, A unit evaporites consist of thick anhydrite deposits on reef flanks and above reefs in the A-1 and A-2, respectively, Stratigraphic data suggest that the anhydrites surrounding reefs are contemporaneous with off-reef halite deposits. This reef-evaporite relationship poses three problems. (1) Why would gypsum precipitate from a halite-saturated brine (2) Why are anhydrites associated with the reefs (3) Why are anhydrites significantly thicker than predicted by evaporation models In a normal marine evaporation sequence (Hardie-Eugster model), gypsum is deposited from a brine until calcium is depleted. Upon further evaporation, the resultant halite-saturated brine would precipitate gypsum only in contact with a calcium source. The authors propose a calcium pumping mechanism whereby calcium-rich water associated with pinnacle reefs is responsible for gypsum precipitation around these reefs contemporaneous with off-reef halite. The additional supply of calcium also explains the anomalous thickness of these anhydrite deposits. Similar anhydrite halos around pinnacle reefs have been observed in the Devonian Elk Point basin.

• Research Organization: Univ. of Michigan, Ann Arbor (USA)
• OSTI ID: 5880483
• Report Number(s): CONF-890404-
• Journal Information: AAPG Bull.; (United States), Vol. 73:3; Conference: AAPG annual convention with DPA/EMD Divisions and SEPM, San Antonio, TX, USA, 23-26 Apr 1989
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
MICHIGAN
SEDIMENTARY BASINS
GEOLOGY
ANHYDRITE
BRINES
EVAPORITES
GYPSUM
SILURIAN PERIOD
STRATIGRAPHY
ALKALINE EARTH METAL COMPOUNDS
CALCIUM COMPOUNDS
CALCIUM SULFATES
FEDERAL REGION V
GEOLOGIC AGES
GEOLOGIC STRUCTURES
MINERALS
NORTH AMERICA
OXYGEN COMPOUNDS
PALEOZOIC ERA
ROCKS
SEDIMENTARY ROCKS
SULFATE MINERALS
SULFATES
SULFUR COMPOUNDS
USA
020200* - Petroleum- Reserves
Geology
& Exploration