The effect of early diagenetic processes on the quantification of fossil micrometeorite abundance and flux in the geological recordOPEN ACCESS 

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Isabelle S. Mattia, Matthew J. Genge, Martin D. Suttle

MAPS, Version of Record online: 24 January 2026

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“Fossil micrometeorites (MMs) recovered from lithified sedimentary rocks, particularly iron-rich (I-type) cosmic spherules (CSs) provide valuable insights into past dust-forming events. Their abundances, when combined with estimates of local sedimentation rates can be used to reconstruct the flux of extraterrestrial dust. However, their preservation in the geological record is highly susceptible to postdepositional diagenetic processes, complicating their quantification and past flux calculations. This study investigated lenticular calcitic concretions as potential sites of enhanced preservation of fossil MMs. A total of 17–18 I-types (but no silicate dominated spherules, S-types) were recovered from Cenomanian sediments within the Cretaceous Chalk Supergroup at Lulworth Cove, England. The I-types, identified by optical and SEM–EDX analyses, exhibited typical dendritic textures and varying degrees of alteration, including mottled surfaces and loss of Ni and Cr by leaching. Calcitic concretions yielded a comparable concentration of I-types to the surrounding hosting marl, but due to the added carbonate cementation during their growth, preservation per original sediment volume was shown to be enhanced (potentially by up to ~60%). Calcitic concretions can therefore act as microenvironments that enhance fossil MM preservation by limiting complete dissolution and loss of I-types. To constrain possible diagenetic effects on fossil MM quantification, future studies should compare cosmic dust yields across multiple sites exposing the same targeted sedimentary horizon.”

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