Daniel O. Breecker

Loess plateau storage of northeastern Tibetan plateau-derived Yellow River sediment

Marine accumulations of terrigenous sediment are widely assumed to accurately record climatic- and tectonic-controlled mountain denudation and play an important role in understanding late Cenozoic mountain uplift and global cooling. Underpinning this is the assumption that the majority of sediment eroded from hinterland orogenic belts is transported to and ultimately stored in marine basins with little lag between erosion and deposition. Here we use a detailed and multi-technique sedimentary provenance dataset from the Yellow River to show that substantial amounts of sediment eroded from Northeast Tibet and carried by the rivers upper reach are stored in the Chinese Loess Plateau and the western Mu Us desert. This finding revises our understanding of the origin of the Chinese Loess Plateau and provides a potential solution for mismatches between late Cenozoic terrestrial sedimentation and marine geochemistry records, as well as between global CO2 and erosion records.

Profile of a paleo-orogen: High topography across the present-day Basin and Range from 40 to 23 Ma

Records of past topography connect Earth’s deep interior to the surface, reflecting the distribution of heat and mass, past crustal structure, and plate interactions. Many tectonic reconstructions of the North American Cordillera suggest the presence of an Altiplano-like plateau in the location of the modern Basin and Range, with conflicting timing and mechanisms for the onset of surface-lowering extension and orogen collapse. Here we show, through a paleotopographic profile, that from the Eocene to the Oligocene a high, broad orogen stretched across Nevada, with a distinct crest that divided a continuous westward-draining slope extending to central California from an internally drained eastern Nevada plateau. This paleo-orogen maintained demonstrably higher-than-modern elevations, reaching 3500 m in the late Oligocene. Despite the long-term high gravitational potential energy of the crust supporting this topography, surface-lowering extension did not occur until the transition to a transform margin changed the external kinematic framework of the system. Maximum surface lowering was spatially decoupled from brittle upper crustal extension, requiring a large component of mid-crustal flow.

Characterization of Microbial Mat Microbiomes in the Modern Thrombolite Ecosystem of Lake Clifton, Western Australia Using Shotgun Metagenomics

Microbialite-forming communities interact with the environment and influence the precipitation of calcium carbonate through their metabolic activity. The functional genes associated with these metabolic processes and their environmental interactions are therefore critical to microbialite formation. The microbiomes associated with microbialite-forming ecosystems are just now being elucidated and the extent of shared pathways and taxa across different environments is not fully known. In this study, we profiled the microbiome of microbial communities associated with lacustrine thrombolites located in Lake Clifton, Western Australia using metagenomic sequencing and compared it to the non-lithifying mats associated with surrounding sediments to determine whether differences in the mat microbiomes, particularly with respect to metabolic pathways and environmental interactions, may potentially contribute to thrombolite formation. Additionally, we used stable isotope biosignatures to delineate the dominant metabolism associated with calcium carbonate precipitation in the thrombolite build-ups. Results indicated that the microbial community associated with the Lake Clifton thrombolites was predominantly bacterial (98.4%) with Proteobacteria, Cyanobacteria, Bacteroidetes, and Actinobacteria comprising the majority of annotated reads. Thrombolite-associated mats were enriched in photoautotrophic taxa and functional genes associated with photosynthesis. Observed δ13C values of thrombolite CaCO3 were enriched by at least 3.5‰ compared to theoretical values in equilibrium with lake water DIC, which is consistent with the occurrence of photoautotrophic activity in thrombolite-associated microbial mats. In contrast, the microbiomes of microbial communities found on the sandy non-lithifying sediments of Lake Clifton represented distinct microbial communities that varied in taxa and functional capability and were enriched in heterotrophic taxa compared to the thrombolite-associated mats. This study provides new insight into the taxa and functional capabilities that differentiate potentially lithifying mats from other non-lithifying types and suggests that thrombolites are actively accreting and growing in limited areas of Lake Clifton.

Andean topographic growth and basement uplift in southern Colombia: Implications for the evolution of the Magdalena, Orinoco, and Amazon river systems

Surface uplift of the Garzon Massif in the northern Andes formed a critical orographic barrier (2500–3000 m elevation) that generated a deep rain shadow and strongly influenced the evolution of the largest river systems draining northern South America. This basement massif and its corresponding foreland basement high define the headwaters and drainage divides of the Amazon, Orinoco, and Magdalena Rivers. Despite its pivotal role, the exhumation history of the Garzon Massif and its relationships to the structural evolution of the broader Eastern Cordillera fold-thrust belt remain unclear. The northern Andes underwent major Cenozoic shortening, with considerable thin-skinned and thick-skinned deformation and topographic development in the Eastern Cordillera focused during late Miocene time. On the basis of widespread coarse-grained nonmarine sedimentation, previous studies have inferred that uplift of the Garzon Massif began during the late Miocene, coincident with rapid elevation gain elsewhere in the Eastern Cordillera. We take an integrated, multiproxy approach to better reconstruct Andean topographic growth and distinguish between exhumation and surface uplift of the Garzon Massif. We present new U-Pb detrital zircon provenance data, sandstone petrographic data, and paleoprecipitation data from upper Miocene clastic fill of the Neiva Basin within the adjacent Upper Magdalena Valley of the modern hinterland. In addition, six new apatite fission track (AFT) ages from the central segment of the northeast-trending Garzon Massif (Jurassic granite and Proterozoic gneiss and schist) directly constrain its Neogene exhumation history. The results indicate that early exhumation may have initiated by ca. 12.5 Ma, but a substantial orographic barrier was not fully established until ca. 6–3 Ma, when >1 km/m.y. of material was exhumed. Thermal history modeling of the AFT data suggests diminished exhumation thereafter (3–0 Ma), during latest Cenozoic oblique Nazca–South America convergence. This exhumation history is consistent with paleontological data suggesting late Miocene divergence of the three river systems, with associated transcontinental drainage of the Amazon River.

Corrigendum: Loess Plateau storage of Northeastern Tibetan Plateau-derived Yellow River sediment.

The original version of this Article contained errors in the Supplementary Information files: Zircon U-Pb age results for sample 23, shown in Supplementary Fig. 3, are incorrect, and missing from Supplementary Data 1, while several identification labels relating to Yellow River Lanzhou terraces samples are missing from Supplementary Data 2. Supplementary Data 1 and 2 have now been updated to provide the missing information, while the corrected version of Supplementary Fig. 3 appears below.