100-7 Investigation of a Cryogenian Subglacial Environment using Quartz Micromorphology and Rare Earth Element Signatures of Tava Sand Injectites and Ridges, Colorado Front Range

Session: Snowballs, Unconformities, BIFs and Beyond: Navigating the Neoproterozoic Rock and Climate Records Using Geochronology

Presenting Author:

Christine Siddoway

Authors:

Siddoway, Christine S¹, Courtney-Davies, Liam², Flowers, Rebecca M³, Oppenheim, Harold Smith⁴, Hite, Charlie⁵, Lorenz, Lenny Smith⁶, Pohlmann, Anders⁷

(1) Geology, Colorado College, Colorado Springs, CO, USA, (2) University of Colorado Boulder, Boulder, CO, USA; San Diego State University, San Diego, CA, USA, (3) Geological Sciences, University of Colorado Boulder, Boulder, CO, USA, (4) Geology, Colorado College, Colorado Springs, Colorado, USA, (5) Geology, Colorado College, Colorado Springs, CO, USA, (6) Geology, Colorado College, Colorado Springs, Colorado, USA, (7) Geology, Colorado College, Colorado Springs, CO, USA,

Abstract:

Tavakaiv (Tava) sandstone of Colorado formed at low latitude (~690-660 Ma), and displays unusual sedimentary relationships indicative of Cryogenian Period climate dynamics. The sandstone is pebbly diamictite consisting of non-touching granules and pebbles supported by unsorted quartz sand within injectites (sedimentary dikes) hosted by Proterozoic crystalline and Tava host rocks. It also forms kms-scale ridges up to 250x750m in lateral dimension, proximal to the Ute Pass fault. The injectite arrays and the massive ‘structureless’ character of Tava sediments indicate rapid emplacement of overpressured fluidized sediment. The timing of Tava sedimentation was determined by in-situ LA-ICP-MS U-Pb hematite (see 10.1073/pnas.2410759121) and U-Pb detrital zircon (DZ)(10.1130/L390.1). Both methods also yield evidence pertaining to the Tava’s environment of formation and sediment provenance. The current hypothesis for Tava sand injection and ridge formation entails fluid overpressure beneath a continental ice sheet overriding crustal faults that introduced geothermal fluids,  causing basal melting and hematite-quartz mineralization. Prominent in DZ data is a voluminous 1.3-1.0 Ga Grenville Orogen age population, providing evidence of multicycle sediment from distant sources.

Sediment entrainment at the base of an ice sheet produces distinctive quartz microtextures, so we imaged quartz grains using scanning electron microscopy to determine whether Tava quartz displays effects of subglacial processes. Using samples from four representative sites, we evaluated grains using qualitative criteria and the SandAI automated machine-learning tool (see 10.1073/pnas.2407655121). The results indicate diverse transport processes spanning fluvial, aeolian, coastal, and glacial.

Rare earth element (REE) signatures of Fe-oxides in veins or cement may fingerprint hydrothermal fluids, so we employed LA-ICP-MS to acquire REE data for Tava Fe-oxides and cements. REE data for sandstone cements display similar trends both for injectites and sand ridges, suggesting a regional rather than site-specific fluid signature. Intra-sample REE concentrations are diverse, and in particular Eu, Ce and Y anomalies vary. When compared to REE reference datasets for hydrothermal fluids and glacial meltwater, Tava REEs are more similar to geothermal fluids than meltwater.  A negative Eu anomaly in two dark, ferruginous injectites is consistent with geothermal fluids but signals the presence of goethite cement. Ongoing work will extend the ‘continental paleoenvironment’ dataset by characterizing Tava injectites at 14 widely separated sites distant from the Ute Pass fault.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9626

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