137-10 Seafloor through time: A quantitative assessment of the composition of sedimentary carbonates across the Phanerozoic

Session: Joint SGD-SEPM-IAS Focus on the Sedimentary Record of Climate Change

Presenting Author:

Pulkit Singh

Authors:

Singh, Pulkit¹, Ferre, Jordan², Thrasher, Bridget³, Monarrez, Pedro⁴, Al-Ramadan, Khalid⁵, Cantrell, Dave⁶, Lehrmann, Daniel⁷, Payne, Jonathan⁸

Abstract:

The composition of Earth’s sedimentary carbonates has evolved substantially over geologic time. Precambrian carbonates are dominated by abiotic and microbial components, whereas Phanerozoic carbonates increasingly reflect contributions from skeleton-forming organisms. While the geochemical properties of carbonates have been extensively studied for paleoclimate reconstructions, the relative contributions of abiotic and biotic allochems to carbonate sedimentation remain poorly quantified—largely due to the absence of systematic, time-resolved compositional datasets.

We address this gap by presenting a new dataset of petrographic point counts from 7,749 carbonate thin sections spanning the past 550 million years. These data, compiled from 111 sources including published literature, unpublished theses, and geological survey reports, allow us to quantify long-term trends in carbonate sediment composition at unprecedented resolution.

Our analysis reveals that carbonate cements and micrite combined are the dominant (mean>70%) components of carbonate sediments throughout the Phanerozoic, followed by skeletal material from metazoans. Calcareous algae and foraminifera are rare in Paleozoic carbonates but show a marked increase from the mid-Mesozoic onward. Among animals, echinoderms are the most abundant skeletal contributors across the Paleozoic, though their relative dominance declines after the Paleozoic–Mesozoic transition. On an average, the Paleozoic skeletal assemblages are dominated by echinoderms (45%), bryozoans (15%), brachiopods (10%), and calcifying sponges (30%), while mollusks (30%), foraminifera (~42%), and calcareous algae (~12%) emerge as major contributors in the Mesozoic and Cenozoic. In reef settings, micrite and cement dominate Paleozoic and Mesozoic examples, with biotic components becoming dominant only in the Cenozoic, particularly calcareous algae and foraminifera.

These compositional patterns underscore two key features of the Phanerozoic carbonate record: (1) the persistent dominance of micrite and cement in carbonate sedimentation across geologic time, and (2) the emergence of calcareous algae (chlorophytes and rhodophytes) and foraminifera as the primary biotic contributors to carbonate production in the Cenozoic. Together, these findings provide a quantitative framework for understanding the evolution of shallow marine carbonate factories in response to biological innovation and environmental change.

 

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

doi: 10.1130/abs/2025AM-10561

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