Shanan Peters on Quantifying the Global Sedimentary Record
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Shanan Peters believes we need to assemble a global record of sedimentary rock coverage over geological time. As he explains in the podcast, such a record enables us to disentangle real changes in the long-term evolution of the Earth-life system from biases introduced by the unevenness and incompleteness of the sedimentary record. To this end, he and his team have established Macrostrat, a platform for the aggregation and distribution of our knowledge about the spatial and temporal distribution of sedimentary rocks. In the podcast, he describes some important findings made possible by Macrostrat. One of them is that gaps in the record are often as revealing about the underlying processes involved as the rocks preserved above and below the gaps.
Peters is a Professor in the Department of Geoscience at the University of Wisconsin-Madison.
Podcast Illustrations
Images courtesy of Shanan Peters unless otherwise indicated.
Macrostrat
Peters and his team have created Macrostrat., a platform for the aggregation and distribution of geological data relevant to the spatial and temporal distribution of sedimentary, igneous, and metamorphic rocks, as well as data extracted from them. As of June 2024, it contains 35,481 stratigraphic rock units from 1,534 regions, which are delineated on the map on land as the shaded regions and as green dots on the sea floor.
At https://macrostrat.org/map, clicking on a location brings up a window with information about the lithostratigraphic unit of that location.
Macrostrat enables users to link a column to a geological or topographical map.
Column view by Daven Quinn
Coverage of Sedimentary Rock in North America Over Time
As discussed in the podcast, Macrostrat enabled Peters to compile a record of the proportion of the globe covered by sedimentary rocks. The record shows a dramatic increase at the start of the Phanerozoic. Parc: Paleoarchean; Marc: Mesoarchean; Narc: Neoarchean; Pptz: Paleoproterozoic; Mptz: Mesoproterozoic; Nptz: Neoproterozoic; Pz: Paleozoic; Mz: Mesozoic; Cz: Cenozoic.
Animation of space-time coverage of sedimentary rock in North America over the past billion years, i.e., since the start of the Neoproterozoic. The dramatic increase at the start of the Phanerozoic shows up clearly.
Animation by Jon Husson
Sedimentary Rock Cover and Continental Flooding
This diagram compares the proportion of Macrostrat columns covered by marine sediment in North America (black line with grey error bars) with the global proportion of continental shelves that are flooded (blue line). The disposition of the continents during the Cambrian (C), Permian (P), end-Jurassic (J), and Paleogene (Pg) are shown. The covariation of the sedimentary rock cover and continental shelf flooding is apparent. Both decline significantly between the Permian and Triassic (Tr) during the assembly of the supercontinent Pangea. Cm: Cambrian; O: Ordovician; S: Silurian; D: Devonian; C: Carboniferous; K: Cretaceous; Ng: Neogene; Q: Quaternary.
Reconstruction of sea level during the late Cambrian (right) shows extensive flooding of the North American continental shelf, which corresponds to peaks in the plot of the global proportion of continental shelves that are flooded shown in the previous figure.
The Great Unconformity
Outcrops of the Great Unconformity in Colorado (top) and Wisconsin (bottom) superposed on the Macrostratigraphy time series of proportional coverage of North America by sedimentary rocks with the period when the Great Unconformity was buried highlighted in green.
The Great Unconformity juxtaposes Cambrian sedimentary rocks on top of very much older Proterozoic metamorphic and igneous rocks. It is very prominent in North America, and famously so in the Grand Canyon, but also in other locations around the world. Peters describes the Great Unconformity as identified by Macrostrat as the most important transition in the entire rock record.
Online Access to the Macrostrat Platform
Further Reading
Peters, S. E., et al. (2012), Nature 484, 363
Peters, S.E. (2008), Nature, 454, 626
Peters, S.E., et al. (2022), Annual Review of Earth and Planetary Sciences 50:419