Part 4 - Berg - Hughes Center

northwest. These sandstones accumulated on the shelf where they were subsequently
reworked. Kornfeld (1985) stated that proximal destructive delta systems existed in
northern Louisiana and northeastern Texas and that another system consisting of barrier
beaches and bars was located centrally between them.
Environments of deposition located landward from the open Gulf to the south and
paralleling the late Jurassic Gulf of Mexico coastline included a longshore barrier island
in northern Louisiana and a coastal lagoon in southern Arkansas. Sands to the barrier
island were supplied by a delta that was formed by the ancestral Mississippi River in
northeastern Louisiana and adjacent Mississippi (Thomas and Mann, 1966). The
description by these authors and others of the open and shallow marine systems together
with the nearshore coastal features typify the lithofacies of the formations within the
Cotton Valley Group. Updip in southern Arkansas, the uppermost Schuler Formation
pinches out. Of interest are the thick downdip marine deposits in northern Louisiana that
include the following formations: Bossier Shale, Terryville Sandstone, Hicos Shale,
Knowles Limestone, and Schuler Formation. The sedimentary characteristics of the
formations that comprise the group in northern Louisiana are summarized below.
Bossier Shale (Millerton Formation)
The open marine basin deposits of the Bossier Shale are found in northern Louisiana
and consist of dark-gray, fossiliferous, calcareous shale. A wedge of this marine shale
pinches out updip in southernmost Arkansas. It attains a maximum thickness of 2,000 ft
(610 m). The marine shale grades eastward into red shale and sandstone in northeastern
Louisiana (Swain, 1944; Forgotson, 1954). The Haynesville Formation conformably
underlies the Bossier; and where the Haynesville is absent, the Bossier rests on the
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