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292-3 Uncovering the Cone-in-Cone Enigma: Integrated Sedimentological, Mineralogical, and Geochemical Evidence from the Cretaceous Kiowa Formation, Kansas

Session: New Advances in Mesozoic Paleontology, Stratigraphy, and Paleogeography of the Western Interior of North America (Part I)

Presenting Author:

Brayden Rowley

Authors:

Rowley, Brayden Scott¹, Suarez, Marina², El-Shenawy, Mohammed³, Kaufman, Alan Jay⁴, Wollney, Jenna C⁵, Liu, Xiao-Ming⁶, Cheng, Yanan⁷, Goderis, Steven⁸, Smith, Rachel⁹, Fang, Yihang¹⁰, Puthalath, Saranya¹¹, Nippert, Jesse¹², Lacroix, Brice¹³, Spencer, Joel Quintus Godfrey¹⁴, Cui, Huan¹⁵r> (1) School of Earth and Environment, Kansas State University, Manhattan, KS, USA, (2) Department of Geology, University of Kansas, Lawrence, KS, USA, (3) Department of Geology, University of Kansas, Lawrence, KS, USA, (4) Department of Geological, Environmental, and Planetary Sciences, University of Maryland, College Park, Maryland, USA; Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD, USA, (5) Department of Geological, Environmental, and Planetary Sciences, University of Maryland, College Park, MD, USA, (6) Department of Earth, Marine and Environmental Sciences, University of North Carolina, Chapel Hill, NC, USA, (7) Department of Earth, Marine and Environmental Sciences, University of North Carolina, Chapel Hill, NC, USA, (8) AMGC, Vrije Universiteit Brussel, Brussels, Belgium, (9) Kansas Geological Survey, Lawrence, KS, USA, (10) Earth and Environmental Sciences, Division of Natural and Built Environment, University of Missouri-Kansas City, Kansas City, MO, USA, (11) School of Earth and Environment, Kansas State University, Manhattan, KS, USA; Division of Biology, Kansas State University, Manhattan, KS, USA, (12) Division of Biology, Kansas State University, Manhattan, KS, USA, (13) School of Earth and Environment, Kansas State University, Manhattan, KS, USA, (14) School of Earth and Environment, Kansas State University, Manhattan, KS, USA, (15) School of Earth and Environment, Kansas State University, Manhattan, KS, USA,

Abstract:

Cone-in-cone (CIC) structures are enigmatic sedimentary features composed of nested, concentrically stacked cones of authigenic carbonates. Despite more than a century of discovery, the mechanisms responsible for CIC formation remain poorly understood due to the scarcity of modern analogues and limited geochemical investigation. Exceptionally well-developed CIC structures occur in the Cretaceous Kiowa Formation of Kansas, reaching lengths of up to 10 cm, representing some of the largest CIC examples reported globally. These structures were first described by H. J. Harnly in 1896, yet they have never been investigated using modern geochemical approaches.

Here we present an integrated sedimentological, mineralogical, and geochemical study of CIC structures within the Kiowa shales. Petrography and micro-XRF mapping reveal individual cones separated by thin clay films interpreted as resulting from early diagenesis. Carbonate carbon isotope compositions from 40 micro-drilled spots across 8 CIC samples show an average value of −26.75‰ (VPDB), with the lowest down to −33.21‰. Organic carbon isotope compositions of the Kiowa shale show consistent values of ~−25‰. These data indicate strong influence of anaerobic oxidation of methane during CIC precipitation. Strontium isotopic ratios (⁸⁷Sr/⁸⁶Sr ≈ 0.7073) match Cretaceous seawater signals, supporting early diagenetic formation. Trace element patterns show weak negative Ce anomalies (Ce/Ce* = 0.7), no Eu anomaly, and Y/Ho ratios ~31.8, consistent with porewater signals with partial seawater influence. The presence of Mn oxide (e.g., birnessite) within CICs and elevated Mn concentrations suggest Mn oxides may have acted as electron acceptors facilitating methane oxidation.

δ³⁴S values measured from sulfide crystals and thin gypsum layers closely associated with the CICs show distinct ranges. Sulfide δ³⁴S values of +12.9 to +16.4‰ (mean = +14.1‰, n = 12) approach or even slightly exceed those of coeval marine sulfate (~+15‰), indicating minimal fractionation and elevated rate of microbial sulfate reduction under relatively closed-system conditions. Thin gypsum layers yield broader δ³⁴S values from −1.7 to +10.5‰ (mean = +5.3‰, n = 17), suggesting mixing with sulfur derived from pyrite oxidation under shallow diagenetic or evaporative conditions.

Our results suggest that coupled methane oxidation with sulfate reduction and likely Mn⁴⁺ reduction during early diagenesis played a key role in CIC formation, revealing previously unrecognized links between carbonate growth and methane cycling in organic- and sulfate-rich marine environments during Cretaceous greenhouse conditions.

Uncovering the Cone-in-Cone Enigma: Integrated Sedimentological, Mineralogical, and Geochemical Evidence from the Cretaceous Kiowa Formation, Kansas

Description

Session Format: Oral

Presentation Date: 10/14/2026

Presentation Start Time: 08:30 AM

Presentation Room: CCC, Bluebird Ballroom 3A

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