Formation of barite nodules in dysaerobic and anaerobic zones of stratified basins

Conference · Fri May 01 04:00:00 EDT 1987 · AAPG Bull.; (United States)

OSTI ID:6184416

Clark, S H.B.

Barite nodules occur at numerous localities in black and gray shale sequences of Ordovician and Devonian age in the Appalachian basin. The nodules occur generally in rocks deposited in oxygen-deficient marine environments: (a) in stratigraphic positions recording dysaerobic bottom conditions and (b) in association with layers containing calcareous and pyritic nodules that formed in anaerobic to dysaerobic zones. The barite nodules do not generally occur in shales representing aerobic environments, and the nodules generally occur in anaerobic shales only in association with carbonate. The barite nodules are in units that probably represent sedimentation during a shallowing pulse following times of maximum transgression. Characteristics of the barite nodules and the surrounding rocks, such as the deformation of laminae in enclosing shales around nodules and the alternation of layers of calcite and barite in some nodules, suggest that the nodules formed during diagenesis when the surrounding rocks were still uncompacted and that they formed in response to fluctuations in chemical conditions. Sulfur and oxygen isotope values for barite nodules have a large range and are considerably heavier than values of coeval seawater. The enrichment of heavy isotopes may have occurred as the result of nodule formation at interfaces where rates of sedimentation were slow relative to the rates of sulfate reduction. Although the amount of barium in normal seawater is very small, barium is soluble in anoxic seawater where sulfur is present mainly as hydrogen sulfide. Barite could be concentrated at interfaces having more oxygenated sulfate-bearing waters of the dysaerobic zones during early diagenesis, possibly with microbes serving as a catalyst. Barite could also be concentrated in areas of locally increased pH where calcium carbonate was forming in anaerobic environments.

• Research Organization: Geological Survey, Reston, VA
• OSTI ID: 6184416
• Report Number(s): CONF-870606-
• Conference Information: Journal Name: AAPG Bull.; (United States) Journal Volume: 71:5
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020200* -- Petroleum-- Reserves
Geology
& Exploration
ALKALINE EARTH METAL COMPOUNDS
APPALACHIAN MOUNTAINS
BARITE
BARIUM COMPOUNDS
BARIUM SULFATES
BITUMINOUS MATERIALS
BLACK SHALES
CARBONACEOUS MATERIALS
CHATTANOOGA FORMATION
DIAGENESIS
ENERGY SOURCES
FOSSIL FUELS
FUELS
GEOLOGIC FORMATIONS
GEOLOGIC STRUCTURES
GEOLOGY
MATERIALS
MINERALS
MOUNTAINS
OIL SHALES
OXYGEN COMPOUNDS
SEDIMENTARY BASINS
STRATIGRAPHY
SULFATE MINERALS
SULFATES
SULFUR COMPOUNDS