2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 299-6
Presentation Time: 10:15 AM


TESTA, Maurice P.1, KIRKLAND, Brenda L.2, POUNDERS, Deborah3 and QUALLS, Kevin1, (1)Mississippi State University, 108 Hilbun Hall, Mississippi State, MS 39762, (2)Department of Geosciences, Mississippi State University, P.O. Box 5448, Mississippi State, MS 39762, (3)Columbus Middle School, 175 HW 373, Columbus, MS 39705

The objective of this project is to test the hypothesis that micritic, microbial, dendritic shrub structures transition into aragonite botryoids, by serving as an organic substrate that promotes the initiation of aragonite crystal precipitation. Samples for this study were taken from three sources 1) a submerged Holocene stalactite found in the Lighthouse Reef Blue Hole, Belize; 2) aragonite botryoids filling pore space in the reef framework of the Permian Capitan Formation in the Guadalupe Mountains of west Texas and southeast New Mexico and 3) samples associated with large oncoids in the Lower Permian Laborcita Formation found in the Sacramento Mountains in south-central New Mexico. Each sample collected was studied in thin section and scanning electron microscopy (SEM). Thin sections of the Laborcita and the Capitan formations reveal ghost-like, micritic, branching structures within neomorphosed botryoidal aragonite splays. SEM images of the stalactite found in the Lighthouse Reef Blue Hole were collected under high magnification (up to 100,000X) and reveal abundant evidence of microbial debris and organic molecules both at the base of and within the botryoidal crystal splays. Organic material or anhedral protocrystals with no true crystal face are found at the base of the aragonite botryoids and extend into the aragonite crystal splays. This study is significant because it explores the idea that the transition from microbial shrub structures to aragonite botryoids could occur as a multistep process, which may lead to discrepancies in understanding of diagenetic history or age dating.