In the panhandles of Texas and Oklahoma, the Morrow Formation is the basal transgressive, predominantly clastic unit of the Pennsylvanian system unconformably overlying the Mississippian. The upper and lower boundaries are delineated by the base of the "Thirteen-Finger" limestone, an electric log marker, and by the Pennsylvanian-Mississippian contact. The panhandle area is bordered on the west by the Sierra Grande uplift and on the south by the Amarillo uplift. The major tectonic features within the area are the western Anadarko basin, southern Hugoton embayment, Cimarron arch-Keyes dome, Dalhart basin, and a number of smaller structures in the unstable belt marginal to the deeper Anadarko basin.

The Morrow Formation was subdivided into three lithologically distinct units recognizable on electrical and sample logs. The lower unit, a wedge of predominantly clastic material, is overlapped by the relatively calcareous middle unit. In the predominantly shaly upper Morrow, marine or lagoonal shales grade upward into nonmarine shales and coals near the top of the unit. This suggests filling of the basin which caused a temporary retreat of marine environments prior to renewed transgression in the post-Morrow units.

Regionally, Mississippian rocks are progressively truncated away from the basin axis. The absence of Chesterian beds over several structures suggests local pre-Pennsylvanian movement. Lower Morrow sand accumulations correlate strongly with the configuration of the pre-Pennsylvanian surface. Apparently, significant structure existed before, or developed during, deposition of the lower unit. Isopach and structure data indicate continued activity of these structures throughout Morrow deposition.

Distribution of coarse clastics within the predominantly fine clastic Morrow Formation suggests one source of sands west of the panhandle area and a second source to the northeast. In the lower unit widespread sheet sands and sands parallel with trends of early Morrow shorelines are interpreted as nearshore marine sediments deposited as the early Morrow sea overlapped onto the shelf area. The thin, lenticular upper Morrow sands are interpreted as having been deposited by a complex distributary system flowing southeastward toward the basin axis.

JAMES M. FORGOTSON

James M. Forgotson, Jr. is a graduate of the University of Texas, Washington University, and Northwestern University where he earned a Ph.D. in Geology in 1956. Since 1956 he has been in the Research Department of Pan American Petroleum corporation in Tulsa. He has published on the stratigraphy and depositional history of Jurassic and Lower Cretaceous rocks of the Gulf Coast, quantitative mapping techniques, stratigraphic nomenclature, and applications of electronic computers to exploration problems. He is President of the Tulsa Geological Society for 1963-64.

ANTHONY T. STATLER

Anthony T. Statler holds A.B. and M.S. degrees from Vanderbilt University and also did graduate work at Northwestern University. His professional career includes geologic mapping and economic work for the Tennessee Division of Geology and topographic surveying with the U.S. Army Corps of Engineers. In 1958 he joined the Research Department of Pan American Petroleum Corporation where he has worked largely in the fields of stratigraphy and sandstone petrology.

MARTHANN K. DAVID

Marthann K. David is a native of Tulsa, Oklahoma, and a graduate of the University of Texas. From 1943 to 1944 she was a geologist for Carter Oil Company in Tulsa and since 1944 she has been Research Geologist for Pan American Petroleum Corporation. Her field of interest is primarily subsurface correlations and interpretations.

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