Overview: The thin veneer of sedimentary and volcanic materials that comprise the earth's stratigraphic record not only contain our entire fossil fuel resource reserve, they chronicle a 3.8 billion year history that is vital to understanding the geological and biological processes that helped form those reserves in the first place.  Despite the obvious centrality of the rock record in the earth and life sciences, surprisingly little is known about its large-scale temporal and spatial structure.  This research project aims to overcome this limitation by quantifying the spatial and temporal structure of the rock record with unprecedented analytical detail.

Methodology:  The rock record is heterogeneous in both its spatial distribution and temporal resolution.  This heterogeneity is the result of three primary factors:  tectonics, sea level, and climate.  The role of tectonics in determining where and how the rock record forms is evident in a geologic map of the USA, as is sea level, which has left a literal bathtub ring of sediments along the eastern margin of the continent.  Climate also plays an important role in structuring the distribution of rock in time and space, but its direct influence is less evident at the scale of a geologic map.  All three of these factors, tectonics, sea level, and climate, interact with one another and leave distinct, quantitative signals in the rock record.  However, the rock record does not simply passively chronicle these processes, it can also interact with and influence them in very important ways.  Testing the extent to which the formation of the rock record itself has influenced earth systems is among the main goals of this research project.

What is the fundamental structure of the rock record?  At a particular location at the earth's surface, the geologic record consists of packages of rock that were deposited or emplaced more or less continuously at a given scale of temporal resolution.  These packages are bound by temporal gaps in the record that are recognizable at the same scale of temporal resolution.  In the sedimentary record, such gaps are the result of non-deposition and/or erosion and form fundamental divisions known as sequence boundaries.  Gaps form in response to tectonic, climatic, and sea level forcing mechanisms operating at the chosen scale of temporal resolution and are therefore intricately related to the processes that structure the rock record over those time scales.  Gap-bound rock packages constitute the fundamental units that are here used to quantify the rock record. 

The main objective of this research is to compile gap-bound rock packages from a variety of literature and field sources for all of the United States and Canada.  This task is nearly completed for the known rock record at 744 locations using a minimum temporal resolution of stratigraphic stages in the Phanerozoic (approximately 4 million years).  New parameters that summarize the temporal persistence and turnover of sedimentary basins have been derived from these data, quantifying for the first time the spatio-temporal dynamics of sedimentation on the North American continent.  These results have implications for, among other things, understanding the drivers of organic evolution, the rates and consequences of carbon sequestration, and the evolution of the climate system.

Career Impact:  This PRF grant has provided invaluable flexibility in developing an entirely new branch of stratigraphy called "macrostratigraphy," which the PI is attempting to develop as a new analytical tool for sedimentary geology and paleobiology.  Macrostratigraphy is being done through the work described here and through collaboration with colleagues working with analytical basin-fill models.  Without the support of this starter grant, it would be impossible to adequately explore the potential of macrostratigraphy as a viable analytical tool.

Because the data that are being collected for this project will be used to tackle a broad range of questions in the earth and life sciences, this research will have a lasting impact on the PI's career and will serve as the nucleus for a diverse range of collaborations. 

Impact for Students:  Understanding how the rock record is put together should be a critical component of every students' geological education.  Students who have participated in this project have enjoyed hands-on experience in assimilating the rock records of particular regions.  They now know what time intervals are represented and by what rock types.  The students have responded positively to the task and have accomplished a great deal.  Specifically, over the course of the last 12 months, my students have entered the age of first and last occurrence, rock type, thickness, and other information for 21,806 stratigraphic units in North America.  With my remaining grant dollars, I will support additional students in refining these data.  I will also hire a web developer to add functionality to the web-based database, which will allow it to be opened up to the community at large.