Abstract
The silicate mineral fraction of shallow marine carbonates archives dust contributions to the Central Persian Terranes along the northeastern margin of Gondwana (∼30ºS paleolatitude), enabling reconstruction of atmospheric dust loading and circulation for intervals of the late Paleozoic ice age. The Central Persian Terranes hosted cyclic deposition of warm water carbonates from middle Pennsylvanian to earliest Permian time, and our data set includes two ∼28 m sections from the Moscovian and Asselian sampled at 20 cm intervals. Bounding surfaces between successive cycles (high-frequency sequences) are recognized by either abrupt basinward shifts in facies or subtle exposure features; these high-frequency sequences range from 1 m to 5 m thick and are interpreted to record glacioeustatic variations. Time series analysis of the dust fraction through the studied interval supports the hypothesis of orbital forcing for the dust signal. The stratigraphic pattern of the dust flux indicates minimal flux during interglacial highstands (0.19−0.27 g/cm2/kyr) and peak flux during glacial lowstands (3.77−4.57 g/cm2/kyr) after accounting for hiatal time at sequence boundaries. Grain size analysis of the dust for all samples (n = 230) reveals modal sizes (volume-based) of 1−15 µm through the Moscovian interval and 10−75 µm through the Asselian interval. Dust deposition increased during glacial times relative to interglacial times by a factor of 16 to 19. Additionally, the Asselian interval exhibits higher dust flux overall relative to the Moscovian interval, which is interpreted to reflect the more extreme icehouse conditions of the Asselian. Variation in the dust content through the studied sections provides an indicator of temporal changes in atmospheric loading that varied at both glacial−interglacial and higher-frequency (<104 yr) scales. Geochemical data reveal that the Arabian−Nubian Shield and southwestern Pangaea (South America) are the most likely sources of dust deposition in the Central Persian Terranes, with sources shifting during different phases. Increased dust flux during glacials likely reflects multiple factors, including enhanced aridity in the source region, exposure of shelf regions, and potential changes in winds. However, the discrepancy in model reconstructions of the amplitude of glacial−interglacial dust variations indicates that increased production of dust sourced by dynamic glaciation played a large role in enhancing dust flux during glacial phases.
Highlights
The late Paleozoic Earth is our most recent analog for the icehouse conditions that have existed during the late Cenozoic; both are distinguished by repeated, high-magnitude glacial– interglacial climate shifts
A growing data set indicates that the Permo-Carboniferous was marked by a dusty atmosphere that was recorded in the form of abundant and widely distributed loess deposits (e.g., Murphy, 1987; Johnson, 1989; Soreghan et al, 2008; Giles et al, 2013; Sweet et al, 2013; Foster et al, 2014; Pfeifer et al, 2020) and in shallow marine units with large eolian contributions (e.g., Carroll et al, 1998; Sur et al, 2010a,b), albeit most of the data supporting this come from low paleolatitudes
The carbonate strata of the Moscovian Absheni Formation and the Asselian Emarat Formation occur in repetitive successions relatively analogous to the cyclothems recorded in Pennsylvanian–Permian sections in paleo-equatorial regions (e.g., Heckel, 1986; Algeo and Heckel, 2008)
Summary
The late Paleozoic Earth is our most recent analog for the icehouse conditions that have existed during the late Cenozoic; both are distinguished by repeated, high-magnitude glacial– interglacial climate shifts. A growing data set indicates that the Permo-Carboniferous was marked by a dusty atmosphere that was recorded in the form of abundant and widely distributed loess deposits (e.g., Murphy, 1987; Johnson, 1989; Soreghan et al, 2008; Giles et al, 2013; Sweet et al, 2013; Foster et al, 2014; Pfeifer et al, 2020) and in shallow marine units with large eolian contributions (e.g., Carroll et al, 1998; Sur et al, 2010a,b), albeit most of the data supporting this come from low paleolatitudes (western equatorial Pangaea). Pennsylvanian–Permian strata are cyclic in many regions; within marine and paralic systems of the low–mid paleolatitudes, these cycles are commonly interpreted as glacioeustatic in origin (e.g., Heckel, 1986; Algeo and Heckel, 2008), reflecting repeated oscillations between glacial and interglacial climates. Given that nutrients carried by dust can potentially fertilize primary production (e.g., Boyd et al, 2004; Krishnamurthy et al, 2010; Kanakidou et al, 2012), such large shifts in dust flux might have had large repercussions for carbon cycling during this interval of Earth history (Soreghan et al, 2015; Sur et al, 2015; Sardar Abadi et al, 2020)
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