Monterey Formation

California contains the largest formation of diatomite in the United States the Monterey Formation extends from Point Arena in Mendocino County in the north to San Onofre in the south (7). The most extensive deposit is near Lompoc, Santa Barbara County, and is of marine origin. A freshwater deposit is being mined near Burney, Shasta County. Other important deposits (not mined as of this writing) are located in Monterey, Fresno, Inyo, Kem, Orange, San Bemadino, San Joaquin, Sonoma, and San Luis Obispo counties. 

A. Soutar, S. R. Johnson, and T. R. Baumgartner, in C. Isaacs and J. Garison, eds.. The Monterey Formation and Related Siliceous Rocks of California, Society of Economic Paleontologists and Mineralogists, 1981, p. 123. 

Zaback DA, Pratt LM (1992) Isotopic composition and speciation of sulfur in the Miocene Monterey Formation reevaluation of sulfur reactions during early diagenesis in marine environments. Geochim Cosmochim Acta 56 763-774... 

Figure 5. Mass chromatogram of m/z 217 of the desulfurised polar fraction of the bitumen of an outcrop section at Naples Beach (California, U.S.A.) of the Monterey Formation.

Monterey-25 This sample is from the Upper Miocene Monterey Formation (California, U.S.A), a phosphatic-siliceous-carbonate rock sequence, and was collected from an outcrop near Vandenberg Air Force Base (Santa Barbara County). This Formation and similar samples have been described by Isaacs (53) and Orr (19). This sample (TOC = 17.3%) also contains immature (R0 = ca. 0.30%), sulfur-rich (atomic Sorg/C = 0.054) kerogen. 

Sulfur, carbon and hydrogen stable isotope ratios of pyrite, kerogens, and bitumens of two high-sulfur Monterey formation samples from the onshore Santa Maria Basin in California were determined. Kerogens from these were pyrolyzed at 300°C for periods of 2, 10 and 100 hours in closed systems and the yields and isotopic compositions of S-containing fractions (residual kerogens, bitumens and hydrogen sulfide) were determined. 

Two Type II-S kerogens (as defined by Orr (i)) from the onshore Santa Maria Basin Monterey formation were pyrolyzed in this study to determine (a) the distribution of sulfur and its isotopic composition among the various products formed during artificial maturation, and (b) maturation trends reflected in the sulfur isotopic and elemental S/C ratios of kerogens, and in the variation of C and H isotopes. In addition, S isotopes in pyrites, kerogens and bitumens from the two Monterey shale samples were examined to speculate on the mode of S incorporation into Santa Maria Basin sediments. 

Two Monterey Formation samples (M4110 and M4140) were obtained as drill cuttings from a well in the Santa Maria Valley West field. The pertinent characteristics of these samples are listed in Table I. 

Table I. Characteristic of Two Monterey Formation Shale Samples Used in the Pyrolysis Experiments...

Burns S.J. and Baker P.A. (1987) A geochemical study of dolomite in the Monterey Formation, California. J. Sediment. Petrol. 57, 126-139. 

Compton J.S. and Siever R. (1984) Stratigraphy and dolostone occurrence in the Miocene Monterey Formation, Santa Maria Basin area, California. In Dolomites of the Monterey Formation and Other Organic-Rich Units (eds. R.E. Garrison, M. Kastner and D.H. Zenger), pp. 141-153. Society Economic Paleontologists and Mineralogists Pacific Section 41. 

Compton J.S. and Siever R. (1986) Diffusion and mass balance of magnesium during early dolomite formation, Monterey Formation. Geochim. Cosmochim. Acta 50, 125-135. 

Garrison R.E., Kastner M. and Zenger D.H. (1984) Dolomites of the Monterey Formation and other organic-rich units. Soc. Econ. Paleontologists and Mineralogists Pacific Section Special Publication 41, 215 pp. 

The transformation of opal-A to opal-CT generally begins at 35-50 °C, corresponding to burial depths of hundred of meters. In some environments this temperature may be as low as 17-21 °C (Matheney and Knauth, 1993 Monterey Formation) or even 0-4 °C (Botz and Bohrmann, 1991 Antarctic deep sea). The acoustic properties of the sediment are altered during the transformation to opal-CT, typically providing an acoustic reflector of the diagenetic front (Calvert, 1983 Tribble et al., 1992). Opal-CT, also known as porcelanite, exhibits X-ray characteristics of low cristobalite and tridymite (Figure 4). This mineral exists as... 

Fichhubl P. and Boles J. R. (2000) Focused fluid flow along faults in the Monterey Formation, coastal California. Geol. Soc. Am. Bull. 112, 1667-1679. 

Baskin D. K. and Jones R. W. (1993) Prediction of oil gravity prior to drill stem testing in Monterey Formation reservoirs. Offshore California. Am. Assoc. Petrol. Geol. Bull. 77, 1479-1487. 

Schouten S., De Loureiro M. R. B., Sinninghe Damste J. S., and de Leeuw J. W. (2001a) Molecular biogeochemistry of Monterey sediments, Naples Beach, California I. Distributions of hydrocarbons and organic sulfur compounds. In The Monterey Formation from Rocks to Molecules (eds. C. M. Isaacs and J. Rullkotter). Columbia University Press, New York, pp. 150-174. 

Oehler, J.H., 1975. Origin and distribution of silica lepispheres in porcelanite from the Monterey Formation of California. J. Sediment. Petrol., 45 252—257. 

Malone, M.J., Baker, P.A. Burns, S.J. (1994) Recrystallization of dolomite evidence from the Monterey Formation (Miocene), California. Sedimentology, 41, 1223-1239. 

In marine turbidite sandstones of the central basin, following minor siderite precipitation, dolomites formed early in the zone of methanogenesis. These have Ca-rich compositions similar to dolomites reported from contemporaneous fine-grained rocks of the Monterey Formation, coastal California. The dolomites are an example of young (< 6 Ma) dolomite formation at shallow burial depth in marine pore water, and they may have undergone some recrystallization during shallow burial without resetting their initial Sr/ Sr values. 

Hennessy, j. Knauth, L.P. (1985) Isotopic variations in dolomite concretions from the Monterey Formation, California. J. sediment. Petrol, 55, 120-130. 

Pisciorro, K.A. (1981) Review of secondary carbonates in the Monterey Formation, California. In The Monterey... 

Bodnar, R. J. 1990. Petroleum migration in the Miocene Monterey Formation, California, USA. Constraints from fluid-inclusion studies. Minera-logical Magazine, 54, 295 304. 

Filippelli GM, Delaney ML, Garrison RE, Omarzai SK, Behl RJ (1994) Phosphoras accumulation rates in a Miocene low oxygen basin The Monterey Formation (Pismo Basin), California. Mar Geol 116 419-430... 

Inlet, Santa Barbara Basin, and the Miocene Monterey Formation. Mar Geol 174 159-176 Jnrinak JJ, Dndley LM, Allen MF, Knight WG (1986) The role of calcium oxalate in the availability of phosphoras in soils of semiarid regions A thermodynamic study. Soil Sci 142 255-261 Kaz ov AV (1937) The phosphorite facies and the genesis of phosphorites. Soviet Geol 8 33-47 Kemp AES, Baldanf JG (1993) Vast Neogene laminated diatom mat deposits from the eastern equatorial Pacific Ocean. Natnre 362 141-144... 

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