In the general Velma district of Southern Oklahoma Springer sandstones occur in five moderately well defined zones in the upper half of a thick dark shale sequence. These sandstones are broadly similar in that they are very fine to fine grained, and the only abundant constituents are quartz and clay. In detail, however, they show a great deal of diversity.

Two end member types can be recognized. The first is massively bedded, highly quartzose, fine-grained, and commonly is fossiliferous or has calcite cement. The second is thin-bedded, shaley, very fine grained, non-fossiliferous, and commonly has siderite cement. The first type makes up the oil reservoirs of the area, and each oil field appears to be bounded by a transition from the first to the second type.

A striking correlation exists between the character of the sandstones and their structural position. The best development of the reservoir sandstones is on the larger uplifts, and on each local uplift the better reservoirs are characteristically in the structurally higher positions.

As an interpretation of these relationships it is suggested that appreciably topographic relief was present in the basin during sedimentation, and that the type 1 reservoir sandstones were deposited on the topographic highs, and the type 2 sandstones in the lows. Further, the systematic relationship of sandstone character to structure suggests that much of the basin-floor relief was caused by early structural growth.

L. C. JACOBSEN

L. C. Jacobsen joined Sohio Petroleum Co. in 1955 as Senior Research Geologist. Since 1960 he has been Assistant to the Senior Vice President in charge of Exploration and Production. Previous to 1955 he was Assistant Professor of Geology at the University of Kentucky.

His education was received at the University of Minnesota (B.A.), Oklahoma University (M.S.), and the Pennsylvania State University (Ph.D.). His professional interests include petroleum geology, sedimentation, statistics, and petroleum economics.

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