Ooid Cortical Stratigraphy Reveals Common Histories of Individual Co-occurring Sedimentary Grains

Ooids are a common type of carbonate sand grain that form through a combination of constructive and destructive mechanisms: growth via precipitation and diminution via physical abrasion. Because growth and abrasion obey distinct morphometric rules, we developed an approach to quantitatively constrain the history of growth and abrasion of individual ooid grains using the record of evolving particle shape preserved by their cortical layers. We designed a model to simulate >10⁶ possible growth‐abrasion histories for each pair of cortical layer bounding surfaces in an individual ooid. Estimates for the durations of growth and abrasion of each cortical layer were obtained by identifying the simulated history that best fit the observed particle shape. We applied this approach to thin sections of “modern” lacustrine ooids collected from several locations in the Great Salt Lake (GSL), UT, to assess the spatial and temporal variability of environmental conditions from the perspective of individual grains within a single deposit. We found that GSL ooids do not all share the same histories: Clustering ooid histories by a Fréchet distance metric revealed commonalities between grains found together locally within a deposit but distinct differences between subpopulations shared among localities across the GSL. These results support the tacit view that carbonate sedimentary grains found together in the environment do reflect a common history of sediment transport. This general approach to invert ooid cortical stratigraphy can be applied to characterize environmental variability over <1,000 year timescales in both marine and lacustrine ooid grainstones of any geologic age

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

Ooid Cortical Stratigraphy Reveals Common Histories of Individual Co-occurring Sedimentary Grains

Ooids are a common type of carbonate sand grain that form through a combination of constructive and destructive mechanisms: growth via precipitation and diminution via physical abrasion. Because growth and abrasion obey distinct morphometric rules, we developed an approach to quantitatively constrain the history of growth and abrasion of individual ooid grains using the record of evolving particle shape preserved by their cortical layers. We designed a model to simulate >10⁶ possible growth‐abrasion histories for each pair of cortical layer bounding surfaces in an individual ooid. Estimates for the durations of growth and abrasion of each cortical layer were obtained by identifying the simulated history that best fit the observed particle shape. We applied this approach to thin sections of “modern” lacustrine ooids collected from several locations in the Great Salt Lake (GSL), UT, to assess the spatial and temporal variability of environmental conditions from the perspective of individual grains within a single deposit. We found that GSL ooids do not all share the same histories: Clustering ooid histories by a Fréchet distance metric revealed commonalities between grains found together locally within a deposit but distinct differences between subpopulations shared among localities across the GSL. These results support the tacit view that carbonate sedimentary grains found together in the environment do reflect a common history of sediment transport. This general approach to invert ooid cortical stratigraphy can be applied to characterize environmental variability over <1,000 year timescales in both marine and lacustrine ooid grainstones of any geologic age