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The AAPG/Datapages Combined Publications Database

GCAGS Transactions

Abstract


Gulf Coast Association of Geological Societies Transactions
Vol. 37 (1987), Pages 383-391

Ostracode Shells as Indicators of Thermal History

Mervin Kontrovitz (1)

ABSTRACT

Ostracode shells from 20 species were subjected to various temperatures and pressures (T-P) to mimic burial. For the first time with ostracodes, mineral mixtures, organic matter, and saline water were used to simulate sediments and pore fluids. Features developed that were diagnostic of narrow T-P ranges and sediment types .

Alteration in quartz was used as a standard for comparison. The shell features were, at increments of 30°C and 100 atm, as follows:

Tabulated data; refer to PDF file.

Except for the rosettes, all features are seen on fossil ostracodes, although rosettes also are common in sediments. For each 100 atm less, an additional 15 to 30°C was needed to achieve the alteration listed for a given temperature.

Seawater (35 ppt) retarded alteration and had to be 30°C warmer to produce features like those in distilled water. More saline water (70 ppt) enhanced alteration and had to be 60°C cooler to match results in pure water.

An additional 60°C was needed with one clay (61% silica) to equal the effect of quartz at a given T-P; in another clay (51% silica) and in calcite, 90 and 90 to 120°C were needed, respectively. The alteration in sediment mixtures was predictable, and depended upon the proportion of silica.

Temperature, sediment and pore water salinity were the major controls of alteration of ostracode shells. For interpretations, a resolution of about 15°C was possible, but smaller increments in experiments may give even better results.


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