7-16 Investigating The Signal Preserved in Growth Bands of Tabulate Coral and Stromatoporoids: New Results from The Khavtgai Section, Dundgovi Province, Mongolia

Session: Undergraduate Research, Part I (Posters)

Poster Booth No.: 16

Presenting Author:

Gabriel Wheaton

Authors:

Wheaton, Gabriel Jacob¹, Boyer, Diana², Munkjargal, Ariuntogos ³, Waters, Johnny⁴, Carmichael, Sarah K.⁵, Blood, David R.⁶, Javzankhuu, Togtokh⁷, Gonchigdorj, Sersmaa⁸, Waters, Will⁹, Dill, Vanya¹⁰

(1) Department of Geological and Environmental Sciences, Appalachian State University, Boone, North Carolina, USA, (2) Department of Chemistry, Physics, Geology & the Environment, Winthrop University, Rock Hill, South Carolina, USA, (3) Department of Geology and Hydrogeology, Mongolian University of Science and Technology, Ulaanbaatar, N/A, Mongolia; Palaeontology & Historical Geology, Senckenberg Research Institute and Natural History Museum, Frankfurt, N/A, Germany, (4) Department of Geological and Environmental Sciences, Appalachian State University, Boone, North Carolina, USA, (5) Department of Geological and Environmental Sciences, Appalachian State University, Boone, NC, USA, (6) N/A, DRB Geological Consulting LLC, New Brighton, PA, USA, (7) N/A, Unimin, LLC, Ulaanbaatar, N/A, Mongolia, (8) Department of Geology and Hydrogeology, Mongolian University of Science and Technology, Ulaanbataar, N/A, Mongolia, (9) Independent Researcher, USA, (10) Department of Geological and Environmental Sciences, Appalachian State University, Morrisville, NC, USA,

Abstract:

     The Middle Devonian (393.3-382.7 Ma) is marked by the Phanerozoic reef maximum: defined by periods of extensive, high-diversity reef building. As part of the Central Asian Orogenic Belt, Mongolia provides valuable insight into these events through successions of shallow-marine carbonates and volcanic units.

     Fieldwork in 2025 at the Khavtgai section, south of Mandalgovi, Mongolia, produced new geologic maps, stratigraphic columns delineating rock type and faunal diversity, and preliminary geochemical data. A Bruker Tracer Five X-ray Fluorescence instrument was used for in-field geochemical and lithological analysis. The section contains vesicular and andesitic pillow basalts overlain by multiple biohermal and biostromal successions, including a reef complex interrupted by volcanic ash beds, indicating volcanic activity concurrent with reef development. Reef accretion distinctively occurred under sustained island-arc volcaniclastic and siliciclastic influence, affecting reef growth and preservation. Mapped units included a series of sandstones, siltstones, volcaniclastic rocks and tuffs, limestones and calcareous sandstones/siltstones. Stromatoporoid and tabulate coral were the dominant faunal groups, although diversity and abundance varied through the succession.

     Specimens were collected throughout the section to evaluate whether observed growth banding reflects seasonal variations. Samples will be cut along primary growth axes, polished, and characterized by primary fabric including density as well as thickness of bands. Each distinct, identifiable band will be analyzed for carbon and oxygen stable isotopes using an IsoFLOW analyzer coupled with an Elementar PrecisION isotope ratio mass spectrometer. Growth band thickness and spacing will be measured to identify patterns within and between specimens and correlated with isotopic variability.

     Band density, thickness, and isotopic composition within growth band layers will be compared between the coral and stromatoporoids to test if fluctuations in environmental conditions are recorded in either or both faunal groups. A couplet of high-density, dark bands and low-density light bands generally record annual growth reflecting seasonal temperature differences. Density, color banding, and stable isotope data will be analyzed to determine whether growth-band variations, constrained by growth rate, record original annual-scale environmental signals such as changes in light availability, temperature, salinity, and clastic input, and to evaluate whether stromatoporoids and corals record similar or distinct environmental responses

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