15 Taphonomy: The Good, the Bad and the Ugly

Thursday, 12 April 2018
1:30 PM - 5:30 PM
Room 301 B

EXCEPTIONAL COLOR/COLOR PATTERN RETENTION IN THIRTY MILLION YEAR OLD OLIGOCENE, RIVER BEND FORMATION INVERTEBRATE SPECIMENS FROM NORTH TOPSAIL BEACH, NC

Paper number: 15-4
Program: Theme Sessions
Time: 2:30 PM – 2:50 PM

Authors

Abstract

The retention of color/color patterns is rare in the fossil record. Many factors, including color fragility and effects of the diagenetic process, impact preservation leaving most specimens monochromatic unless tinted by secondary mineral absorption during diagenesis. The prevailing concept: the older a specimen and/or the more diagenetically altered, the less likely any color or color pattern will be retained.

In direct contrast are the specimens from the 30 million year old Oligocene, River Bend Formation exposed on North Topsail Beach, NC. Many appear to retain trace color and/or color patterns, despite diagenetic alteration. This retention appears in more than one species, across multiple phyla and in multiple colors.

Hemipatagus carolinensis (sea urchin) presents multiple distinct, replicating color patterns in mauve to purple hues, over many hundreds of specimens, on both the aboral and adoral sides. Gagaria mossomi (sea urchin) shows dark pentagonal radiation around the peristome and several of the asteroids (brittle stars) display pink coloration. Most Balanus sp. (acorn barnacles) display red to rust colored hues similar to those found on modern acorn barnacles. Most Pycnodonte paroxis (extinct oyster genus) display a variety of tan lines radiating from their umbos to the outer margin of their shells, including being offset at injury points on the mantle similar to modern day oysters.

Fossils on North Topsail Beach are the result of a sand replenishment project accidentally dredging through offshore River Bend Limestone. The material was pumped several miles to shore as a slurry of rock, sand and water, effectively sand blasting the fossils free of matrix in route. Rapid, mass burial of this layer is suggested by larger chunks of matrix containing numerous echinoderms, randomly oriented, in close proximity to each other with their spines still attached and Aristotle’s lanterns intact. Most oysters are double valved and closed.

The combination of rapid burial and unorthodox matrix removal could have contributed to the color/color pattern retention. Further geochemical analysis is needed to determine if any original color remains.

Geological Society of America Abstracts with Programs. Vol. 50, No. 3

doi: 10.1130/abs/2018SE-311837

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