Maxwell Alexander Lechte

McGill University | McGill · Department of Earth and Planetary Sciences

The Earth’s most severe ice ages interrupted a crucial interval in eukaryotic evolution with widespread ice coverage during the Cryogenian Period (720 to 635 Ma). Aerobic eukaryotes must have survived the “Snowball Earth” glaciations, requiring the persistence of oxygenated marine habitats, yet evidence for these environments is lacking. We examine...

The Neoproterozoic Sturtian glaciation is considered to be among the most severe glaciations in Earth history, possibly encompassing the entire planet and lasting for more than 50 m.y. Iron formations are globally associated with Sturtian glacial successions, although the influence of glaciation on the genesis of these iron formations remains conte...

The Kingston Peak Formation records glacial sedimentation during the Cryogenian in Death Valley, California, and contains iron formation horizons. These iron formations are part of a thick sedimentary succession containing glaciogenic diamictites, together with mass flow breccias, conglomerates, sandstones and siltstones. The Kingston Peak iron for...

The Chuos Formation of Namibia is the sedimentary product of the Neoproterozoic Sturtian (c. 720–660 Ma) glaciation and contains massive diamictites intercalated with finely laminated iron formation. Similar Sturtian glacially associated iron formations are found globally. The iron formations are laminated and generally very pure. The diamictites a...

Banded iron formations (BIFs) are iron-rich marine chemical sedimentary rocks, and their mineralogy and geochemistry can be used to gain insights into ancient ocean chemistry and biospheric evolution. Magnetite is the major iron-bearing mineral in many BIFs (particularly in the Archean) and is variably interpreted to be of primary, early diagenetic...

Earth’s surface has undergone a protracted oxygenation, which is commonly assumed to have profoundly affected the biosphere. However, basic aspects of this history are still debated—foremost oxygen (O2) levels in the oceans and atmosphere during the billion years leading up to the rise of algae and animals. Here we use isotope ratios of iron (Fe) i...

The Neoproterozoic ‘snowball Earth’ hypothesis suggests that a runaway ice–albedo feedback led to two intense glaciations around 717–635 million years ago, and this global ice cover would have drastically impacted biogeochemical cycles. Testing the predictions of this hypothesis against the rock record is key to understanding Earth’s surface evolut...

The mid-Proterozoic (ca. 1.8–0.8 Ga) witnessed a period of stable carbon cycling and long stasis in eukaryotic evolution, which was commonly ascribed to the persistently low oxygen levels in the atmosphere-ocean system. Recently, several pulsed marine oxygenations were identified from different continents, and presumed to have facilitated the short...

Molecular phylogenetic data suggest that photosynthetic eukaryotes first evolved in freshwater environments in the early Proterozoic and diversified into marine environments by the Tonian Period, but early algal evolution is poorly reflected in the fossil record. Here, we report newly discovered, millimeter- to centimeter-scale macrofossils from ou...

ORGANIC-WALLED MICROFOSSILS OF THE PALEOPROTEROZOIC AND MESOPROTEROZOIC MCARTHUR AND BIRRINDUDU BASINS, NORTHERN TERRITORY, AUSTRALIA (Invited Presentation) RIEDMAN, Leigh Anne, Department of Earth Science, University of California, Santa Barbara, Santa Barbara, CA 93106, PORTER, Susannah, Department of Earth Science, University of California, San...

The redox state of the surface ocean–atmosphere system has long been considered to have been remarkably stable during the mid-Proterozoic (ca. 1800–800 Ma); however, there is a growing body of evidence that supports dynamic redox fluctuations during this time. Sedimentary Mn enrichment in the Gaoyuzhuang Formation (North China) may represent an imp...

Marine red beds (MRBs) are common in sedimentary records, but their genesis and environmental implications remain controversial. Genetic models proposed for MRBs variably invoke diagenetic or primary enrichments of iron, with vastly different implications for the redox state of the contemporaneous water column. The Xiamaling Formation (ca. 1.4 Ga)...

The Tonian (1000 to 720 Ma) represents a critical transition in Earth history between the Mesoproterozoic (1600 to 1000 Ma) and the low-latitude glaciations of the Cryogenian (720 to 635 Ma). However, the early Tonian period is notoriously poorly understood and well-preserved exposures are rare in the stratigraphic record. The Proterozoic inliers o...

We present a new sequence stratigraphic and facies architectural model for the ca. 900–850 Ma Hematite Creek and Katherine groups (lower and middle Mackenzie Mountains Supergroup, respectively) in the Wernecke Mountains of east-central Yukon, Canada. This ~3-km-thick internally conformable succession provides a virtually continuous tectono-sediment...

In the Neoproterozoic Era there was widespread deposition of iron formations in close association with global or near glaciations. These 'snowball Earth’ glaciations likely played a key role in iron formation distribution and deposition. However, the environmental conditions, Fe sources, and formation mechanisms remain debated. Here we present the...

The Holowilena Ironstone is a Neoproterozoic iron formation in South Australia associated with glacial deposits of the Sturtian glaciation. Through a comprehensive field study coupled with optical and scanning electron microscopy, X-ray fluorescence, and X-ray diffraction, a detailed description of the stratigraphy, sedimentology, mineralogy, and s...