Terrigenous marine sediment records the landscape response to climate and tectonic perturbations. Here, we determined the source of Miocene–Pleistocene debris in the western Gulf of Mexico (WGOM) to understand changes in sediment supply during a greenhouse-glacial transition. Sediment composition at Deep Sea Drilling Project (DSDP) Sites 3, 87, and 89–91 shows a reversal in provenance following the onset of Pleistocene glaciation. During Miocene time, sediment was supplied to the deep WGOM from tectonically active, tropical highlands of southern Mexico, accumulating as sediment-gravity-flow deposits across broad deep-water fan systems. Then, following the mid-Pleistocene transition (ca. 0.7 Ma), the WGOM saw sustained (10 5 yr) influx of sediment from the north due to glacial erosion, high discharge, and expanded drainages across the Mississippi catchment. This major provenance shift points to the importance of glacial controls on marine sediment supply during late Cenozoic cooling.

The western Gulf of Mexico (WGOM) basin is well positioned to study large-scale sediment supply under varying conditions, because it straddles the Tropic of Cancer and is bordered to the south and west by active tectonic regions of Mexico, and to the north by the wide coastal plain of the southern United States (Fig. 1A). Deep-water sediment of the WGOM was the first target of R/V Glomar Challenger on Leg 1 of the Deep Sea Drilling Project (DSDP) (Ewing et al., 1969), and again in 1970 on Leg 10 (Worzel et al., 1973).

The Sigsbee Abyssal Plain extends hundreds of kilometers across the WGOM (Fig. 1A) and is underlain by ∼4 km of Jurassic to Neogene stratigraphy (Ladd et al., 1976). The continental shelf is wide along the Northern Gulf Salt Province and Campeche Bank, but it narrows along its western margin. The continental slope here is cut by two major canyon-like features: the Campeche Trough, comparable in scale to the Mississippi Canyon, and the Veracruz Tongue.

Proximal highlands to the west and south (Fig. 1A) are the result of mostly continuous late Cenozoic tectonic activity, including subduction of the Rivera-Cocos plates beneath North America and passage of the Caribbean plate to the south. The Trans-Mexican Volcanic Belt and Eastern Alkaline Province consist of arc-related intermediate-mafic rocks erupted at ca. 15–0 Ma (Ferrari et al., 2005). To the south, the Chiapas Massif contains middle–late Miocene plutonic and older basement rocks (Schaaf et al., 2002) rapidly exhumed in the late Miocene due to North American–Caribbean transpression (Witt et a., 2012; Molina-Garza et al., 2015).

The Mexican highlands contrast with the more muted landscapes north of the Rio Grande. Rivers reaching the northern WGOM margin are sizable and largely drain low-relief terrain, although some headwaters tap the Rocky Mountains. Also, a wide (∼150 km) coastal plain has formed a depositional buffer between the Laramide–Rocky Mountains and other highlands and the continental margin since late Paleocene time (Galloway et al., 2011; Xu et al., 2017).