Porosity reduction and burial history of siliceous rocks from the Monterey and Sisquoc Formations, Point Pedernales area, California

Research Article| May 01, 1991 Porosity reduction and burial history of siliceous rocks from the Monterey and Sisquoc Formations, Point Pedernales area, California JOHN S. COMPTON JOHN S. COMPTON 1Department of Marine Science, University of South Florida, St. Petersburg, Florida 33701 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1991) 103 (5): 625–636. https://doi.org/10.1130/0016-7606(1991)103<0625:PRABHO>2.3.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation JOHN S. COMPTON; Porosity reduction and burial history of siliceous rocks from the Monterey and Sisquoc Formations, Point Pedernales area, California. GSA Bulletin 1991;; 103 (5): 625–636. doi: https://doi.org/10.1130/0016-7606(1991)103<0625:PRABHO>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Porosity, grain density, and composition were determined for different rock types from a 1.2-km-thick Neogene section of the Monterey and Sisquoc Formations in the Point Pedernales area, California. Porosity decreases and dry bulk density increases with burial depth in these predominantly siliceous rocks. Porosity reduction is controlled largely by initial composition and silica diagenesis. There is a positive correlation between porosity and biogenic silica (diatom) content of diatomaceous shales. The porous, incompressible diatom frustule maintains a high porosity relative to detrital, organic, and calcareous components of the rock. Porosity reduction by physical compaction from increasing overburden pressure is much slower at burial depths greater than 0.5 km. Solution of the porous diatom frustule and precipitation of cryptocrystalline opal-CT resulted in a highly variable porosity reduction. Porosity reduction during the opal-A to opal-CT transformation depends on the amount, composition, and texture of the nonsilica grains. A large porosity reduction occurred locally in nodules and beds of pore-filling dolomite and silica.The porosity-depth relation of siliceous sediments and rocks from this and previous studies is used with biostratigraphic age data and estimated paleobathymetry to reconstruct the burial history of the Point Pedernales area. The sedimentation rate, corrected for compaction, quadrupled during deposition of the Sisquoc Formation. Using the constant water depth proposed for the Monterey Formation, and assuming that basin filling occurred during rapid deposition of the Sisquoc Formation, results in a tectonic subsidence curve similar to that observed for cooling oceanic lithosphere. Upwelling of asthenosphere near the surface would have produced a significantly higher paleogeothermal gradient, and the opal-A to opal-CT transformation is predicted to have occurred 3 m.y. earlier than if a constant, presentday geothermal gradient is assumed. Basin subsidence by faulting or flexure, without upwelling of asthenosphere, does not significantly alter the thermal history. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.