Macrostratigraphy Overview

For the past several years I have been collaborating with Shanan Peters at UW-Madison on research centered around and integration of the Paleobiology Database (PaleoDB) and the Macrostrat database. In combination, these two independently developed databases provide rich data on the spatial and temporal distributions of marine and terrestrial biotas and the environments in which they lived. The map on the right qualitatively illustrates the type of data I work with. The gray areas indicate the areas of North America that have preserved sedimentary rocks, marine and non-marine, deposited during the Maastrichtian (latest Cretaceous), and the red dots show the locations of fossil collections from the PaleoDB. The main thrust of my research at present is attempting to answer two broad questions:
  1. Are macroevolutionary patterns and sedimentary dynamics driven by a common process?
  2. How does large-scale environmental heterogeneity shape the spatial and temporal distributions of marine genera?
Because Macrostrat is limited in scope to Canada, the U.S.A. and the circum-Caribbean region, we are answering these questions within the context of North America.
  • Peters, S.E. and N.A. Heim. 2010. The geological completeness of paleontological sampling in North America. Paleobiology, 36: 61-79. [PDF]

Testing the “common cause” hypothesis

A longstanding concern about macroevolutionary and macroecological conclusions drawn from paleobiological data is that biological patterns in the fossil record are severely biased by spatial and temporal variability in the quantity of preserved sedimentary rocks. Certainly, the correlation between diversity and rock quantity through the past 600 million years is real. However, an alternative to interpretation of correlations as bias is that the processes that drive changes in sediment preservation also drive real changes in biodiversity, the “common cause” hypothesis.
The recent development of macrostratigraphy by Shanan Peters is important for testing the common cause and bias hypotheses because it allows the quantity of preserved sedimentary rocks through time to be quantified with metrics that are quantitatively identical to the macroevolutioanry parameters of diversity (richness), origination rate and extinction rate. In a forthcoming paper in Geological Society of America Bulletin we demonstrate support for the common cause hypothesis. We find that extinction rates are well predicted by reductions in sediment preservation, but origination rates are not predicted by rates of sediment expansion. The graph at the left shows this mismatch between origination and extinction. The histograms show the expected correlation between the fossil and rock records if genera were randomly distributed in time. The vertical lines show the observed correlations. The light line is for origination (ρp) falls within the expected distribution indicating a non-significant correlation between origination and initiation. The dark line is for extinction (ρq) and falls well outside the expected distribution indicating a highly significant correlation between extinction and truncation. This mismatch between origination and extinction dynamics is not consistent with the bias hypothesis, and our working hypothesis for the driver of the observed pattern is systematic spatio-temporal variation environmental heterogeneity.
  • Heim, N.A. and S.E. Peters. 2011. Covariation in macrostratigraphic and macroevolutionary patterns in the marine record of North America. GSA Bulletin, 123: 620-630. [PDF]
  • Peters, S.E. and N.A. Heim. 2011. Stratigraphic distribution of marine fossils in North America. Geology, 39: 259-262. [PDF]

Age, area and environmental heterogeneity of marine genera

A useful attribute of the Macrostrat database is that it allow us quantify the geographic range of taxa in a novel and useful way. From most paleontological databases, geographic range is typically calculated as the minimum area occupied by the observed occurrences. Macrostrat allows us to calculate the geographic range of a taxon as the proportion of available habitat. An example is shown on the map to the right with the brachiopod genus Echinoconchus. Using a combination of data on temporal durations from the PaleoDB, environmental/sedimentary environment data from Macrostrat and geographic range data from the intersection of the two databases, I am testing several hypotheses regarding the role of environmental heterogeneity in driving Phanerozoic-scale biogeographic patterns.
  1. Marine genera endemic to a region (geologic province, North America, etc.) have narrower environmental tolerances and longer stratigraphic durations than cosmopolitan genera within the same region.
  2. On Phanerozoic time scales, the strength of the diversity-area relationship for marine genera is driven not simply by the area of preserved marine sediments, but also by the spatial variation in marine environments (i.e., β diversity).
  • Heim, N.A. and S.E. Peters. 2011. Regional Environmental Breadth Predicts Geographic Range and Longevity in Fossil Marine Genera. PLoS One, 6(5):e18946. [Online Open Access]

Non-marine macrostratigraphy

I have been working with Deb Rook, a Ph.D. student at UW-Madison, on understanding the dynamics of sedimentation and biological evolution in non-marine settings. The common cause hypothesis is somewhat intuitive in marine settings where the mosaic of environments and biogeographic connections are controlled by sea level dynamics. It is less clear, however, how a common cause of terrestrial sedimentation and biological evolution are linked. The main driver of terrestrial sedimentation is a combination of tectonics and climate. More importantly, the non-marine record is apparently much less complete that the sedimentary record of marine sedimentation. This is most easily seen on the plot to the left which shows the number of marine and non-marine sedimentary packages through the Phanerozoic. The non-marine packages show an approximately exponential decrease going back in time suggesting a strong degradation signal that is not seen in the marine record. Deb has been working to ensure that the Late Cretaceous through Pleistocene units are Macrostrat are properly identified, and we indeed find a differences in the strength in the coupling between sedimentation and diversification in the marine and non-marine realms. Going forward, we need to more completely identify all the non-marine units older than Late Cretaceous in North America.
  • §Rook, D.L., N.A. Heim and J. Marcot. 2013. Contrasting patterns and connections of rock and biotic diversity in the marine and terrestrial fossil records of North America. Palaeogeography, Palaeoclimatology, Palaeoecology, 372:123-129. [PDF]

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