Analyses of New High Resolution MCS Data from Guaymas Basin, Gulf of California
This research aims to understand the amount of carbon released from sediments, as CO2 and methane, when those sediments are intruded by magmatic sills with injection temperatures of ~1000°C. This understanding has relevance for modern day climate and also for global-scale carbon budgets. The relevance to modern day climate is related to the Paleocence/Eocene thermal maximum, a period of rapid atmospheric warming, thought to be the best ancient analogue to rapid present-day warming. The Paleocence/Eocene event is hypothesized to have been driven by the rapid and voluminous release of carbon from sediments intruded by igneous sills during a regionally large magmatic event around the time of the opening of the North Atlantic between Greenland and Europe. Defining relationships between igneous sill intrusion into sediments and carbon release from those sediments into the ocean and potentially the atmosphere will help place bounds on the volume of carbon available to create the rapid warming under the sill hypothesis and can be compared to modern atmospheric carbon inputs. In addition, many active magmatic systems exist in the present day that involve sill intrusion into organic-rich sediments, units that have generally been thought of as stable carbon sinks. Broader impacts of the work include understanding the reintroduction of carbon into the ocean and potentially into the atmosphere from sediments in these magmatic systems, something that is presently missing from global carbon cycle models. An additional impact is the support of a drilling leg of the International Ocean Discovery Program, a major NSF and international investment in understanding how the Earth system behaves by drilling into the seafloor and examining the rocks and sediments and their stratigraphy and lithologic relationships. The research will analyze a new high-resolution multi-channel seismic dataset from Guaymas Basin in the Gulf of California in order to advance our understanding of the processes of sediment alteration in response to igneous sill intrusion. The work has two main goals: (1) integration of the new high-resolution data into analyses based on lower-frequency 6-kilometer streamer seismic data aimed at quantifying relationships between igneous sill thickness and alteration of overlying sediments. The new data will enable us to confidently identify sills as thin as 12m and evaluate potential drilling sites for the proposed International Ocean Discovery Program in the Guaymas Basin. These new data are the first that look at the second dimension of the crust in the area of the proposed main drill sites and potential alternate sites. Processes driven by the intrusion of igneous sills into sediments during regionally extensive magmatic episodes are increasingly being invoked as triggers for extinction events and global-scale changes in oceanic and atmospheric chemistry. These hypotheses are largely founded on changes in the carbon content of sediments within metamorphic aureoles of igneous sills observed in ancient outcrops and the assumption that carbon and other elements lost from the aureoles are also lost from the entire subsurface system and efficiently released into the ocean or atmosphere. A key objective of the Guaymas drilling proposal, which this research project supports, is to understand the subsurface and seafloor bio/geochemical cycling of carbon released due to sill intrusion. A key objective of the present proposal is to further the work of developing seismic proxies for alteration intensity that can extend knowledge, based on drill cores, to regional scales. Relationships between sill thickness and changes in seismic velocity within overlying sediments may prove to be a useful proxy, and this project will make co-located measurements along existing long-streamer lines in Guaymas Basin with the aid of the new hi-resolution seismic data. The long-streamer data provide the means to estimate changes in sediment properties (seismic velocity) due to contact metamorphism, while the high-resolution data provide a means to estimate sill thickness, which scales with the available thermal energy of the intrusion.