6-2 Bio-Retexturing in the Upper Devonian Three Lick Bed, Ohio Shale, by the lingulid brachiopod Barroisella

Session: Advances in ichnology: walking in Memphis and other records of behavior

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Abstract:

Bio-retexturing (Pedley, 1992) refers to the process by which burrowing biota destroy original depositional textures by moving large amounts of unlithified sediment into or out of one or more sedimentary layers. In this case, the bioturbating organism is Barroisella, an elongate-oval, organic-shelled, lingulid brachiopod, which is a Late Devonian index fossil, common in the Upper Devonian Ohio, Chattanooga, and New Albany shales. We report here its occurrence in the Three Lick Bed of the Ohio Shale at two localities near Morehead and Berea in eastern Kentucky. In both occurrences, Barroisella occurs only in the second of the three blue-gray shale beds that comprise the Three Lick Bed and always occur in the lower parts of the shale bed just above the underlying black shale. Some of the brachiopods are still in vertical living position and show organic pedicle traces; others are disarticulated and moved. They always occur in heavily bioturbated areas and show the mixing of black muds from below with the blue-gray muds in which they were living. The brachiopods are the only macrofaunal elements present in the unit, although a mollusk-dominated, micromorph fauna of pyritized juveniles is relatively common. Previous work suggests water depth estimates of about 160 m for the unit.

            Our interpretations suggest that the brachiopods lived in a dysaerobic, deep-water setting and used their valves and pedicles to burrow and dislodge organic-rich muds from below, which were then kept in suspension for feeding by flapping valves or by waving valves on a moving stem-like pedicle. The thin, flat valves were apparently flexible and were easily inserted into soft sediment like a wedge-shaped blade. However, pedicle burrowing and waving appear to have been largely responsible for the intense bioturbation. Barroisella apparently used its pedicle, not only for attachment and burrowing, but as a food-generating implement. In the process, it completely transformed its environment by moving large amounts of anoxic, organic-rich mud upward into the organic-deficient layer in which it lived.

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