Print this pageAbstract: Sedimentology and Paleoecology of Type Location of Kincaid Formation (Lower Midway Group, Paleocene), South-Central Texas
The type section of the Kincaid Formation, the lower unit of the Paleocene Midway Group, is exposed along the Frio River in Uvalde County, Texas. This formation unconformably overlies the Upper Cretaceous Escondido Formation and is overlain by the Wills Point Formation. Approximately 30 ft (9 m) of massive very fine-grained sandstone is present. Clay, abundant in the lower part of the sandstone, decreases upward, whereas the carbonate content increases. A few feet of arenaceous limestone are present at the top.
Well developed tidal channels from 10 to 30 ft (3 to 27 m) wide and from 8 to 54 in. (20 to 135 cm) deep are numerous in the middle of the section. The sediment filling these channels is lithologically the same as the material into which the channels are cut. Phosphatic pebbles are present in the channel bottoms. The sandstone is bioturbated intensely from bottom to top with both horizontal and vertical burrows. The size of the burrows decreases upward. Primary sedimentary structures are uncommon. Few whole macrofossils but many fragments are present, most of which are echinoid. The size and amount of shell material increase upward; the upper limestone units are very fossiliferous with mostly whole fossils of Paleocene species of the genera Nucula, Venericardia, and Turritella. Microfossils are common, and of particular importance is the planktonic Globigerina daubjergensis, an early Paleocene foraminifer. The planktonic forms make up a significant proportion of the foraminifers in the lower part, but decrease upward.
These early Paleocene sediments are interpreted as upper shoreface in origin. The lower half of the sandstone was deposited in the shallow sublittoral, and the middle, with many tidal channels, represents a littoral facies. The upper limestone units most likely were formed from shell debris deposited at, or slightly above, high tide. This contrasts greatly with most other exposures of the earliest Paleocene rocks which are of deeper water origin.
AAPG Search and Discovery Article #90972©1976 AAPG-SEPM Annual Convention and Exhibition, New Orleans, LA