Mark Leckie's research centers on questions of Earth system history and paleoceanography, with a particular emphasis on biosphere response to changes in the ocean-climate system through time. He studies planktic and benthic foraminifera of Cretaceous and Cenozoic age. His research has included modern and ancient marginal marine depositional environments, late Paleogene-early Neogene neritic glacial marine deposits of the Ross Sea region of Antarctica, Late Cretaceous epicontinental sea depositional systems of the U.S. Western Interior Sea, and a variety of low latitude deep sea settings of Jurassic, Cretaceous and Cenozoic age. Professor Leckie has sailed with 6 legs of scientific ocean drilling (Deep Sea Drilling Project Leg 79, and Ocean Drilling Program Legs 101, 130, 165, 198, 210), as well as 2 Integrated Ocean Drilling Program expeditions associated with the "School of Rock" education and outreach (IODP 312T) and the readiness assessment cruise of the rebuilt and refurbished JOIDES Resolution drill ship (IODP 320T). He has also spent numerous summers conducting fieldwork in the western United States with students and colleagues. Micropaleontological studies by his students include taxonomy, biostratigraphy, lithostratigraphy, and population analyses. In addition, isotope paleoecology of ancient planktic foraminifera and time-series isotopic analyses of multi-species planktic and benthic foraminifera are important components of their deep-sea research as independent and complementary proxies of upper water column hydrography and productivity.

Current research projects focus on the following: 1) mid-Cretaceous Oceanic Anoxic Events and plankton community evolution, 2) Late Cretaceous paleoceanography and sequence stratigraphy of the Western Interior Sea, 3) Campanian-Maastrichtian paleoceanography of the tropical Pacific, and 4) Miocene sea level, constriction of the Indonesian Seaway, and paleoceanography of the western tropical Pacific.

Professor Leckie and his students have also been actively involved with projects to standardize planktic foram taxonomy and create online taxonomic atlases and databases as part of the Mesozoic Planktic Foram Working Group and the Oligocene Planktic Foram Working Group. These and other planktic foram atlases are hosted on the CHRONOS website. Utility of Foraminifera in Paleoenvironmental and Paleoceanographic Research