Provincial variations in cap rock source materials of Gulf Coast salt domes

Conference · Fri Feb 01 04:00:00 EST 1985 · Am. Assoc. Pet. Geol., Bull.; (United States)

OSTI ID:5848534

Posey, H H; Hurst, S D; Kyle, J R; Price, P E; Taylor, A R

Isotopes of strontium, carbon, and oxygen are used to model hydrocarbon, brine, and meteoric fluid interactions during cap rock evolution. Provincial isotopic variations occur between older salt domes of the east Texas (ETx) and northern Louisiana (NLa) basins and the younger domes of the Texas-Louisiana (Tx-La) coastal basin. ETx and NLa cap rocks exhibit normal, mid-Jurassic seawater values (/sup 87/Sr//sup 86/Sr = 0.7068 to 0.7076), very wide delta/sup 13/C ranges (-5 to -49 per mil PDB) and delta/sup 18/O values (-6 to -11 per mil PDB) that are slightly lighter than Tx-La (-4 to -10 per mil). Tx-La domes yield remarkably high /sup 87/Sr//sup 86/Sr ratios (0.7073 to 0.7100), and their delta/sup 13/C values (-8 to -41 per mil) have means which are 5 to 15 per mil heavier than ETx and NLa domes. Detailed studies of the Hockley dome (Tx-La basin) reveal chemical diversity not recognized in domes farther inland. Anhydrite from the salt stock (mid-Jurassic Louann evaporites) mixed with two separate strontium sources during calcite formation. Calcites near the dome's center formed from an intermediate Sr ratio fluid (/sup 87/Sr//sup 86/Sr congruent to 0.7090), which, based on heavier than average delta/sup 13/C values, was enriched in CO/sub 2/ relative to CH/sub 4/; peripheral calcites evolved from a high Sr ratio fluid (/sup 87/Sr//sup 86/Sr congruent to 0.7105) with a lower CO/sub 2//CH/sub 4/ ratio. High /sup 87/Sr//sup 86/Sr ratios in other Tx-La anhydrite cap rocks compared with normal mid-Jurassic type values in ETx and NLa cap rocks suggest that the Tx-La basin was periodically isolated from normal seawater during Louann deposition; radiogenic fluids, derived either from local red beds or from eoric waters, equilibrated with seawater prior to anhydrite precipitation.

• Research Organization: Univ. of North Carolina, Chapel Hill
• OSTI ID: 5848534
• Report Number(s): CONF-850322-
• Conference Information: Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Journal Volume: 69:2
• Country of Publication: United States
• Language: English

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