COLOR PATTERN PRESERVATION IN DIAGENETICALLY ALTERED, EOCENE AGE CARICELLA GASTROPODS FROM NEW BERN, NORTH CAROLINA

Color and color patterns are rarely preserved in the fossil record, because original coloration naturally degrades over time. In addition, diagenetic processes further degrade possible preserved color and color patterns. In general, the older and/or more diagenetically altered a specimen, the less likely any original color or color pattern will be retained. In some cases, color patterns that are no longer visible in natural light may be revealed under UV lighting, dependent on the quality of the preservation of the original shell mineralogy. Examples of this type of color preservation include the gastropod Caricella from the Eocene Moodys Branch Formation of Mississippi and the Gosport Sand of Alabama, where both sites contained unaltered aragonitic shells. A study in 2015 also found that when aragonite recrystallizes to calcite, the UV responsive residual pigments in the specimens are destroyed and they no longer fluoresce, though some residual pigments may still be observed in natural light.

In 2018 and 2019, multiple specimens of Cariella were collected at a quarry near New Bern, NC, from the Spring Garden Member of the Castle Hayne Formation. This unit is Late Middle Eocene, similar in age to both the Moodys Branch and Gosport Sand localities. Despite clear diagenetic alteration from aragonite to calcite, many of these specimens still retain color patterns that are visible in natural light and/or fluoresce in UV light. Out of a total of 76 specimens, 51 show a typical Caricella dotted color pattern. Of these 51 specimens, 39 have patterns visible under natural light (though some are quite faint) and the pattern on all 39 fluoresces a pale brown. No pattern is visible under natural light for an additional 11 specimens, but the same dotted color pattern appears as a bright yellow in UV light. One specimen has visible spots (which fluoresce brown) on the third of the body whorl closest to the aperture, then transitions to spots that are no longer visible but fluoresce bright yellow for the rest of the body whorl. Geochemical analysis is needed to determine how these specimens are able to retain their color pattern despite diagenetic alteration.