Stevens sandstone

Fig. 2. West to east cross-section across San Joaquin basin. See Fig. 1 for location of the cross-section line. Most of basin-fill is marine, including the Stevens sandstone, and is at maximum burial depth. Non-marine strata are Chanac and Kem River Formations. Low lateral continuity of beds and abundant shales have prevented meteoric water from entering the deep central basin. Cross-section from California Division of Oil and Gas.

Fig. 3. Time-depth-temperature burial history plot at North Coles Levee. Modihed from Wood Boles (1991). Note the rapid burial of the Stevens sandstone (shaded) at North Coles Levee, which is also typical of Stevens sandstone s burial history throughout the central basin. Carbonate cements formed throughout the burial history of the Stevens.

Evidence supporting an early precipitation origin of dolomite is Sr/ Sr ratios similar to sea water. Dolomites in Stevens sandstones at North Coles Levee have Sr/ Sr ratios of about 0.70860-0.70865. This is slightly less than the 0.7090 value expected for uppermost Miocene-age sea water during deposition of the Stevens at 5-6 Ma (Hess et al., 1986). Subsequent calcite cements in the basin have distinctly lower Sr isotopic ratios (< 0.7083) than the dolomites (Schultz et al., 1989). 

Another similarity between Monterey and Stevens dolomites is their excess Ca, typical of Tertiary dolomite compositions. Apparently these non-stoichiometric compositions are retained in San Joaquin dolomites at temperatures at least as high as 100°C (their present burial condition). Stevens dolomites are generally much richer in Fe than Monterey dolomites, possibly owing to the alteration of Fe-bearing minerals in the Stevens sandstones. 

Boles, J.R. (1984) Secondary porosity reactions i n Stevens sandstone, San Joaquin Valley, California. In Clastic Diagenesis (Eds McDonald, D.A. Surdam, R.C.). Mem. Am. Ass. Petrol. Geol., Tulsa, 37, 217-224. 

Fischer, K.S. Surdam, R.C. (1988) Contrasting diagenetic styles in a shelf turbidite sandstone sequence the Santa Margarita and Stevens sandstones, San Joaquin Basin, California, USA. In Studies ofthe Geology of the San Joaquin Basin (Ed. Graham, S.A.). Soc. Econ. Paleont. Miner. Pacific Sec. Publ., 60, 233-247. 

Lagoe, M.B. (1987) The stratigraphic record of sea level and climatic flucuations in an active margin basin the Stevens Sandstones, Coles Levee area, California. Palaios, 2, 48-68. 

We briefly described the sandstone cores and sampled each lithology type. For each sample, routine X-ray diffraction analyses and thin sections were made. Thin sections were prepared from rock containing pressure impregnated, blue-dyed, epoxy resin so that pore space would be readily discernable. Thin sections were stained to facilitate recognition of carbonates and K-feldspar using the techniques of Dickson (1966) and Bailey and Stevens (1960), respectively. Point-count analyses were made using a voice recognition system described by Dunn et al. (1985). A minimum of 300 points was counted per thin section. 

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