Systematically variable geometry and architecture of incised‐valley fills controlled by orbital forcing: A conceptual model from the Pennsylvanian Breathitt Group (Kentucky, USA)

Abstract

Incised-valley fills preserved within ancient coastal to shallow-marine successions represent important archives of environmental and sea-level change.Most current knowledge about the origin of incised valleys stems from Quaternary case studies; however, research on pre-Quaternary examples can shed light on valley formation and evolution across longer timespans. This article describes different types of incised-valley fills from Lower to Middle Pennsylvanian fluvio-deltaic successions of the Breathitt Group (eastern Kentucky), accumulated in the Central Appalachian Foreland under prevalent glacioeustatic forcing driven by Gondwanan glaciations. Based on well-established criteria for their recognition, numerous incised-valley fills were identified from outcrop and subsurface data through more than 300 m of clastic successions consisting of fourth-order stratigraphic sequences stacked into third-order composite sequences. Incised-valley fills were categorized into three archetypes based on lateral extent and aspect ratio (relatively wide versus narrow valley fills), nature of infill (fully continental versus mixed marine and continental facies associations) and relationships to underlying coal zones (truncating versus non-truncating). The systematic occurrence of each incised-valley fill type at specific stratigraphic positions within every thirdorder sequence suggests control by a periodic allogenic factor. Valley-fill archetypes are interpreted in terms of variable accommodation-supply ratios driven by variable duration of formative base-level cycles. For example, relatively wide incised-valley fills with alluvial infill evolved during long-lived cycles whose prolonged base-level drawdown maintained low accommodation/supply ratios. Deeper valleys with low aspect ratios and mixed marinecontinental infills were generated by short-lived base-level drawdown that forced higher accommodation/supply ratios. Available chronological data for the studied successions consent to estimate base-level cycles spanning 10 4-5 years that were likely modulated by interference patterns of orbital parameters (obliquity and eccentricity) via global climate and glacioeustatic fluctuations. This conceptual model, relating incised-valley fill morphometry and internal architecture to orbital forcing patterns, provides a possible approach to predicting and interpreting incised-valley fill variability through successions accumulated during icehouse conditions. 2149

A cyclostratigraphic framework of the Upper Carboniferous Westoe and Cleaver formations in the southern North Sea Basin as a methodology for stratigraphic reservoir characterisation

“…Basin-wide forcing implies a more significant probability of the occurrence of sandstones within these stratigraphic intervals in the otherwise overall low net-to-gross Westoe and Cleaver Formations. Similar variations in net-to-gross ratios associated with long-eccentricity climate control are suggested for the Upper Carboniferous Upper Silesian (Opluštil et al, 2022) and Appalachian Basins (Le Cotonnec et al, 2020).…”

“…In the Dutch onshore, van der Belt et al (2015) identified cyclothems paced at a sub-eccentricity periodicity with dominant ∼21 kyr precession and interference of an obliquity component. For the central Appalachian Basin, Le Cotonnec et al (2020) suggested cyclothem forcing by the interference of ∼34 kyr obliquity and ∼100 and ∼400 kyr eccentricity, while for Eastern European Basins a ∼100 kyr short-eccentricity is proposed (e.g. Davydov et al, 2010; Jirásek et al, 2018; Opluštil et al, 2022).…”

Distinguishing mid‐channel and bank‐attached fluvial bars by flow divergence: Implications for the interpretation of stratigraphic records

“…For example, when evaluating possible fluvial responses to base-level changes (e.g. Yoshida, 2000;Li et al, 2010;Hampson et al, 2013;Le Cotonnec et al, 2020).…”

Arquitectura estratigráfica, ambientes de depósito y geocronología de la Formación Olinalá (Pérmico tardío), noreste de Guerrero, México

“…Adicionalmente, el carácter estrato-y granodecreciente de esta asociación de facies es típico de un proceso de relleno de canal fluvial, el cual tiene un significado geológico importante si consideramos que las barras fluviales son una guía aproximada de la profundidad mínima del canal contenedor (Miall, 2006). A partir de esto, se interpreta que los depósitos fluviales en la base de la Formación Olinalá representan un ilustrativo ejemplo de un relleno de valle de incisión fluvial, cuya profundidad fue de al menos 130 m. El reconocimiento de este elemento permite además deducir importantes variaciones en el nivel del mar (Le Cotonnec et al, 2020). De acuerdo con lo anterior inferimos que los depósitos marinos en la parte inferior de la Formación Olinalá fueron erosionados por sistemas fluviales regionales cuando el nivel del mar bajó y dejó expuesta parte de la plataforma (Figura 10a).…”