Provenance and cyclostratigraphy of Permo-Carboniferous dust delivered to northeastern Gondwana
Abstract
Atmospheric dust preserved in loess, marine sediments, and ice cores provides valuable insight to climate for the Cenozoic and especially Pleistocene, but remains underutilized for Earth's deep-time climate record. Dust and loess deposits are widespread and increasingly recognized and studied in the late Paleozoic record of equatorial Pangaea, but less so for extratropical regions. Here, we use the silicate mineral fraction of carbonate facies as a proxy for eolian dust contributions to the Central Persian Terrain (CPT) along the northeastern margin of Gondwana at ~30o S, and study aspects of this record to reconstruct atmospheric dust loading and dust provenance for parts of the Permo-Carboniferous of this region. The CPT hosted a cyclic succession of warm-water, shallow-marine carbonates from the Middle Pennsylvanian to the earliest Permian, and our dataset includes two ~25 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 - 5 m thick and are interpreted to record glacioeustatic variations. Time series analysis of the silicate mineral fraction through the studied interval supports a hypothesis of orbital forcing. The stratigraphic pattern of the dust flux indicates minimal flux during highstands (0.19-0.27 g/cm2/kyr), and peak flux during glacial lowstands (3.77-4.57 g/cm2/kyr). Grain size analysis of the dust for all samples (n=230) reveals a bimodal distribution with peaks at 15.5 mm and 65 mm, corresponding to two Weibull distributions (fine- and coarse-grained dust). Dust deposition increased during glacial to relative interglacial periods, with fine dust increasing ~9 fold and coarse dust increasing ~26 fold. This bimodal distribution may indicate multiple sources—an interpretation consistent with highly variable Sr isotope values. The most likely sources are within the Arabian-Nubian Shield, with sources shifting between Arabia and Ethiopia during different phases. Dust flux increases during glacials may reflect glacial gustiness, with provenance changes driven by glacial-interglacial shifts in circulation.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMPP21C1623A
- Keywords:
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- 1616 Climate variability;
- GLOBAL CHANGE;
- 1622 Earth system modeling;
- GLOBAL CHANGE;
- 1626 Global climate models;
- GLOBAL CHANGE;
- 4934 Insolation forcing;
- PALEOCEANOGRAPHY