Interplay of oceanographic and paleoclimate events with tectonism during middle to late Miocene sedimentation across the southwestern USA Charles E. Chapin New Mexico Bureau of Geology and Mineral Resources, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801, USA ABSTRACT INTRODUCTION Miocene (ca. 27–16 Ma) and is refl ected in the unconformities and missing time- stratigraphic Continental sedimentation refl ects a com- The southwestern United States hosts exten- intervals (lacunas) beneath the Ogallala For- plex interplay of tectonics and climate. A sive continental sedimentary deposits of middle mation on the east fl ank of the Southern Rocky 2000-km transect from coastal California to and late Miocene age between the western Great Mountains and the Fence Lake and Bidahochi the western Great Plains documents a major Plains and the coast of California (Fig. 1). The formations on the west fl ank. Cather et al. increase in sedimentation (ca. 16–6 Ma) deposits occur within several physiographic (2007) document ~1230 m of exhumation of the coeval with deposition of the hemipelagic provinces and at variable elevations and tectonic southeastern Colorado Plateau between eolian Monterey Formation along the California settings. Deposition occurred mainly between accumulation of the Chuska erg (ca. 33.5– coast. Basin and Range-style regional exten- 16 and 6 Ma (Fig. 2), coeval with deposition 27 Ma) and deposition of the Bidahochi Forma- sion following elongation of the Pacifi c– of the hemipelagic Monterey Formation (Ingle, tion (16–6 Ma). Similar exhumation (~1500 m) North American transform boundary at 1981; Behl, 1999) along the California coast and timing (ca. 28–16 Ma) were obtained by ca. 17.5 Ma provided fault-bounded basins (Figs. 1 and 2). In several areas, the deposits Flowers et al. (2008) from (U-Th)/He thermo- for accommodation space, but sedimenta- accumulated following long intervals of erosion chronometry. This exhumation began during tion also occurred on unextended erosional and/or nondeposition (Fig. 2). The middle to late the peak of middle Tertiary ignimbrite volca- surfaces of the Great Plains and Colorado Miocene interval of continental sedimentation nism and supports the interpretations of Roy Plateau. Two global climate transitions ended between ca. 6 and 5 Ma, as integration et al. (2004) and Eaton (2008) of magmati- bracket this sedimentary interval. The of drainages brought about widespread incision, cally driven middle Tertiary uplift. The second middle Miocene transition (ca. 17–12 Ma) exhumation, and deposition of contrasting fl u- period of exhumation began in late Miocene records the global change from equatorial to vial deposits of exterior drainages (Eberly and (ca. 7–6 Ma) and is interpreted herein as result- meridional circulation caused by: (1) closing Stanley, 1978; Scarborough, 1989; Spencer et ing from intensifi cation of the North American of the eastern Tethys Seaway (ca. 18 Ma); al., 2001a; Connell, 2004; Mack, 2004; Smith, monsoon and integration of drainage systems (2) opening of the Arctic–North Atlantic 2004, Polyak et al., 2008). that largely ended accumulation of closed-basin connection (ca. 17.5 Ma); (3) growth of Tectonic events affecting middle and late continental deposits. Thus, the two periods of the East Antarctic Ice Sheet (ca. 14 Ma); Miocene sedimentation and erosion across the exhumation illustrated in Figure 2 document and (4) closing of the Indonesian Seaway Southwest were mainly of two types: (1) those both middle Tertiary tectono-magmatic–driven (ca. 12 Ma). Upwelling of cold waters along that resulted in accommodation space for aggra- uplift and late Miocene–Pliocene climatically the California coast, abetted by domina- dation of sedimentary deposits, and (2) those driven exhumation. tion of La Niña phases of El Niño–Southern that changed oceanic and atmospheric circula- The Miocene record of continental sedimen- Oscillation (ENSO), progressively aridifi ed tion, which affected both climate and sedimen- tation and erosion has traditionally been inter- the Southwest as refl ected in sedimentary tation. A correlation chart that summarizes tec- preted in terms of tectonic or epeirogenic uplift and biologic records. The second climate tonic events, oceanic and atmospheric changes, (for example, Trimble, 1980; Steven et al., 1997; transition occurred as opening of the Gulf of and various sedimentation and climatic effects Eaton, 1987, 2008) with little regard to possible California (ca. 6 Ma) intensifi ed the North in a temporal framework is presented as Fig- climatic effects (Molnar and England, 1990; American monsoon, resulting in integration ure 3. The timing of events is based on compila- Molnar, 2004). Since climate is determined of drainages, incision of uplifts, and exhu- tion of published dates of various types from the mainly by coupling of oceanic and atmospheric mation of basin fi lls. The Miocene ended literature. Ages and descriptions of stratigraphic circulation, I burrowed into the oceanographic with the driest climate of the Tertiary (both units are summarized in Appendix 1, with the literature seeking tectonic, oceanographic, and regional and global) accompanied by con- key references. paleoclimate events that had the appropriate version of savanna to steppe or scrub desert, Figures 2 and 3 show two periods of exhu- timing, scale, and location to have infl uenced the spread of C4 grasses, and the greatest mam- mation that affected the Southern Rocky Moun- Miocene sedimentation and erosion history of mal extinction of the Neogene. tains. The fi rst occurred in Oligocene to middle the southwestern USA. Two climate transitions Geosphere; December 2008; v. 4; no. 6; p. 976–991; doi: 10.1130/GES00171.1; 4 fi gures. 976 For permission to copy, contact [email protected] © 2008 Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/4/6/976/3337163/i1553-040X-4-6-976.pdf by guest on 27 September 2021 Miocene sedimentation and climate 125°W 120° 115° 110° 105° 100° W GM NE ID 40° N CB SV OG WY 35 BP NP MP 30 25 GB GS D HP SF M 20 35 CR NV CA UT SL 40 OG M CO KS AZ NM 35° N VR GC R OK B DS LV RGR 45 CP ES O SV RL 30 SB BS SF M V B A LA HP F 50 L S P R Pl W OG ME RG SP T HR BA EP 25 SC ° TX 30 N GOC ME 55 RG 0 500 KM Figure 1. Shaded relief map of the southwestern United States from the western Great Plains on the right (east) to the Pacifi c Coast of California at far left. Northern Gulf of California and Baja Peninsula at lower left. The Southern Rocky Mountains, Rio Grande rift, and Colorado Plateau make up the high topography at center. Selected middle and upper Miocene terrestrial sedimentary deposits (red) were compiled from numerous sources cited in text and Appendix 1. Miocene basins in the Basin and Range province of Arizona and southwest- ern New Mexico are partly obscured by widespread gravel-covered pediments and Pliocene-Quaternary alluvial deposits. Only basins with published Miocene surface or subsurface stratigraphic data are shown. Exposures in Arizona are from Scarborough (1989) and those in southwestern New Mexico modifi ed from Wilks (2005). Monterey Formation and equivalent Miocene deposits of onshore California are shown in blue (from Graham and Williams, 1985, and Williams, 1988). Blue contour lines show the percentage of annual precipitation pro- vided by the North American Monsoon in July, August, and September for the 26-yr period 1963–1988 (from Higgins et al., 1999). Names of states are abbreviated inside their boundaries. A—Albuquerque, B—Bakersfi eld, B—Bidahochi Formation, BA—Baja California, BP—Browns Park Formation, BS—Barstow (Town and Formation), CB—Circle Bar basin, CP—Colorado Plateau, CR—Colorado River, D—Denver, DS—Dove Spring Formation, EP—El Paso, F—Fence Lake Formation, GB—Great Basin, GC—Grand Canyon, GOC—Gulf of California, GM—Granite Mountains basin, GS—Glenwood Springs, HP—High Plains, HR—Hatch–Rincon basin, LA—Los Angeles, LV—Las Vegas, M—Monterey Formation, ME—Mexico, MP—Middle Park, N—North Park, O—Ocate volcanic fi eld, OG—Ogallala Formation, P—Phoenix, PI—Picacho basin, R—Raton, R—Reserve graben, RG—Rio Grande, RGR—Rio Grande rift, S—Socorro, SB— Santa Barbara, SC—Sonoita Creek basin, SF—San Francisco, SF—Santa Fe, SL—San Luis Basin, SP—San Pedro trough, SV—Saratoga Valley, SV—Shadow Valley basin, T—Tucson, V—Verde Basin, VR—Virgin River depression, W—Winston graben. Base from U.S. Geo- logical Survey Shaded Relief Map, R.E. Harrison, 1969, scale 1:7,500,000. Underlined abbreviations used only to distinguish between localities with similar spelling. Geosphere, December 2008 977 Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/4/6/976/3337163/i1553-040X-4-6-976.pdf by guest on 27 September 2021 on 27 September 2021 by guest Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/4/6/976/3337163/i1553-040X-4-6-976.pdf 978 Geosphere, December2008 W ~2000 km E Ma MONTEREY MOJAVE LAKE SOUTHERN FENCE BIDAHOCHI SOUTHERN N. & C. RIO OGALLALA OGALLALA Ma 0 FM DESERT MEAD ARIZONA LAKE FM FM NEW MEXICOGRANDE RIFT S. PLAINS N. PLAINS 0 INTEGRATION OF DRAINAGE ca. 6–3 Ma 5 5 10 S. 10 OGALLALA FM FM FM SHADOW V. DOVE SPG. N. MULTI FMS MULTI MONTEREY MULTI FMS MULTI BIDAHOCHI FENCE LAKE MULTI FMS MULTI OGALLALA 15 15 Chapin BARSTOW MULTI FMS MULTI LACUNA PLATE 20 BOUNDARY LACUNA EARLY 20 BASINS RAINBOW LACUNA GARDENS RIFT MEMBER LACUNA DETACHMENT TERRANES BASINS EARLY DETACHMENT TERRANES RIFT AND MESOZOIC MESOZOIC 25 BASINS VOLCANIC 25 and to MESOZOIC AND and ROCKS PERMIAN OLIGOCENE VOLCANIC ARIKAREE GROUP ROCKS ROCKS PERMIAN ROCKS ROCKS MESOZOIC and WHITE 30 R.