RESPONSE OF LATE CRETACEOUS-PALEOCENE RIVERS TO LARAMIDE INTRAFORELAND DEFORMATION AND CONCURRENT CLIMATIC CHANGE: AN EXAMPLE FROM THE RATON BASIN, COLORADO-NEW MEXICO, USA

The Raton Basin of Colorado-New Mexico, USA, hosts a thick succession (4.5 km or 15,000 ft) of marine and continental strata that were deposited during regression of the Western Interior Seaway and the onset of intraforeland deformation in the southeastern Laramide province. We use observations of fluvial channel architecture and trends in sediment provenance from deposits of the Upper Cretaceous-Paleocene Raton and Poison Canyon Formations to investigate the effects of Laramide uplift and concurrent climatic patterns on fluvial style and regional paleodispersal patterns. Fluvial deposits in both formations record the presence of sinuous channel systems. However, fluvial channels of the Raton Formation formed in ever-wet environments and were affected by steady discharge, whereas fluvial channels of the overlying Poison Canyon Formation formed in drier environments and were affected by variable discharge. We interpret this transition to accompany the progradation of fluvial fans across the Raton Basin, which occurred in the wake of increasing climatic variability during Paleocene time. Detrital zircon data from the studied interval demonstrate a transition from distant to local sediment sources, further reflecting the progradation of locally sourced fluvial fans across the basin. While prior work has suggested the influence of Laramide uplift on deposition in the Raton Basin as early as the Campanian (ca. 75 Ma), we argue that Laramide deformation did not exert significant control on subsidence patterns until deposition of the Raton Formation (ca. 65 Ma), and that prominent basin-bounding topography did not develop until deposition of the Paleocene Poison Canyon Formation (ca. 60 Ma).