FOSSIL PEARLS FROM THE UPPER CRETACEOUS OF TEXAS

Pearls are natural gems that have excited the imagination of mankind since ancient times. Many cultures have treasured them throughout history and today they remain a sign of elegance and unsurpassed beauty.

Fossil pearls are rare in the fossil record. Their oldest record goes back to the Triassic. In this work, we report the occurrence of fossil pearls of the Upper Cretaceous (Gulfian Series) (Cenomanian and Turonian) of the Eagle Ford Group of North Central Texas. Inoceramid bivalves are very abundant throughout the Britton and Arcadia Park Formations and Kamp Ranch Member, where twenty four fossil pearls have been collected. The shape of the pearls ranges from a perfect sphere to irregular shapes. Their sizes range from micropearls of mere1mm in diameter to megapearls of 3 cm in diameter. Their color is tan, grayish to black. Mineralogical studies (XRD analyses) show a calcitic composition, secondary to an aragonitic/prismatic calcite original composition. Some of the pearls show a visible onion ring layer arrangement characteristic also of modern pearls. Some pearls present a secondary radial symmetry, due to recrystallization.

Regarding their origin, the Cretaceous pearls studied herein are attributed to inoceramid pelecypods due to the fact that most pearls were found in association with them and others were found still attached to inoceramid shells. Inoceramid bivalves were abundant epifaunal bivalves in the benthic dysoxic environments of the eaglefordian Cretaceous seas. They declined in diversity towards the late Maastrichtian becoming extinct worldwide towards the end of the Cretaceous, just prior to the K/Pg boundary.

Fossil pearls have a potential application in paleoecological reconstruction of the benthic marine environments of the Late Cretaceous.