The Ediacaran-aged Shuram excursion was the last and largest of the Neoproterozoic negative carbon isotope anomalies. Recognized in stratigraphic successions around the globe, it precedes diverse evidence for macroscopic, multicellular life, and follows the Cryogenian global glaciations and Ediacaran Gaskiers glaciation. Hypotheses for the cause of the Shuram excursion can be broadly grouped into those that argue for post-depositional diagenetic alteration of the carbon isotope record and those that argue the extremely low δ13C values reflect a primary perturbation to the carbon cycle. Given the timing and magnitude of this event, distinguishing between these disparate hypotheses, or combining them, is critical for reconstructing the environmental conditions under which complex life evolved on Earth. We test specific predictions of each model using a range of stratigraphic observations and micro- and macro-analytical techniques. We find that the type sections in Oman where the Shuram excursion was first described are well preserved and contain a range of features difficult to reconcile with a post-depositional origin. However, many salient features are consistent with an extreme warming event coupled to a carbon cycle perturbation, analogous to the Paleocene-Eocene Thermal Maximum (PETM), and increased middle Ediacaran volcanism. We propose that cooling associated with the recovery was critical for origination rates of macroscopic soft-bodied organisms.

The habitability and ecology of Earth is fundamentally shaped by surface temperature, but the temperature history of our planet is not easily reconstructed, especially before the evolution of early biomineralizing animals. This work presents a billion-year-long, high-resolution, mineral-specific record of oxygen isotope measurements in shallow marine rocks. Clumped isotope paleothermometry results from four minerals resolves previous ambiguity in seawater oxygen isotope composition and confirms that long-term cooling punctuated by short-lived temperature extremes are dominant components of this record. We consider post-depositional effects by comparing Phanerozoic rock and fossil records, and identify temporal and spatial controls on alteration. Furthermore, this record is suggestive of key differences in dolomite (CaMg(CO3)2) formation processes between the Neoproterozoic (1000–538.8 Ma) and Phanerozoic (538.8–0 Ma), consistent with previous suggestions based on petrographic and sedimentological observations. This record, when viewed alongside the fossil record, suggests temperature change is tightly coupled to extinction and origination in the history of life and carbon cycle perturbations over the last billion years.

Quantitative scanning electron microscopy (SEM) quartz microtextural analysis can reveal the transport histories of modern and ancient sediments. However, because workers identify and count microtextures differently, it is difficult to directly compare quantitative microtextural data analyzed by different workers. As a result, the defining microtextures of certain transport modes and their probabilities of occurrence are not well constrained. We used principal component analysis (PCA) to directly compare modern and ancient aeolian, fluvial, and glacial samples from the literature with 9 new samples from active aeolian and glacial environments. Our results demonstrate that PCA can group microtextural samples by transport mode and differentiate between aeolian and fluvial/glacial transport modes across studies. The PCA ordination indicates that aeolian samples are distinct from fluvial and glacial samples, which are in turn difficult to disambiguate from each other. Ancient and modern sediments are also shown to have quantitatively similar microtextural relationships. Therefore, PCA may be a useful tool to constrain the ambiguous transport histories of some ancient sediment grains. As a case study, we analyzed two samples with ambiguous transport histories from the Cryogenian Bråvika Member (Svalbard). Integrating PCA with field observations, we find evidence that the Bråvika Member facies investigated here includes aeolian deposition and may be analogous to syn-glacial Marinoan aeolian units including the Bakoye Formation in Mali and the Whyalla Sandstone in South Australia.

Carbonate rocks on continental crust are one of Earth’s largest reservoirs of CO2 and yet the controls on their volume through time are poorly understood. Here we quantify temporal changes in preserved continental carbonate rocks over the last billion years in both global and North America-specific datasets within paleogeographic context. We find the preserved area of continental carbonate rocks increases by ~175% across the Neoproterozoic-Phanerozoic boundary ca. 539 million years ago, coincident with the rise of macroscopic, multicellular life and the evolutionary innovation of carbonate biomineralization in shallow water reefs. We demonstrate that crustal loading from carbonate sediments on one tropical paleo-continent (North America) contributes to an increase in continent-scale accommodation in the early Phanerozoic, expanding shallow marine environments. We predict this feedback between enhanced carbonate accumulation and subsidence was an important component of the termination of the Great Unconformity. These results are combined into a new conceptual model that links the changes in preserved carbonate rock volumes to the evolutionary innovation of carbonate biomineralization in a range of complex organisms. Our model implies evolutionary controls on the carbonate rock reservoir enhanced CO2 sequestration at the beginning of the Phanerozoic, with consequences for Earth’s carbon cycle, climate and habitability.

Detrital zircon records of provenance are used to reconstruct paleogeography, sediment sources, and tectonic configuration. Recognition of the biases in detrital zircon records that result from hydraulic sorting of sediment and the initial characteristics of zircons in source regions (e.g., size and abundance) has added new complexity and caution in the interpretation of these records. In this study, we examine the role of transport process and sediment sorting in these records. We begin our analysis by investigating the influence of grain size and transport process in biasing detrital zircon provenance records in an idealized sedimentary system. Our modeling results show that settling and selective entrainment can leave distinct, process-dependent fingerprints in detrital zircon spectra if initial size variation between source zircon populations exists. We then consider a case study: a detrital zircon record from Ediacaran to Terreneuvian Death Valley. We focus on the Rainstorm Member, which is geochemically, mineralogically, and sedimentologically unusual. In addition to Earth’s largest negative carbon isotope excursion (the Shuram excursion), the Rainstorm Member also contains anachronistic carbonate structures and a detrital mineral suite enriched in heavy minerals. We evaluate the detrital zircon provenance record of the Rainstorm Member, and find that, despite its unusual character, the provenance of the unit is similar to other units in the succession, with substantial input from Yavapai-Matzatzal provinces. Size and density measurements of heavy and light density components of the deposit suggest that its enriched heavy mineral suite is best explained through concentration by selective entrainment and winnowing. We find that our detrital zircon dataset is susceptible to hydrodynamic fractionation, so that grain size exerts influence on its provenance record, in particular for large Grenville-aged (1.0-1.2 Ga) grains.