ABSTRACT Paleocene Lower Wilcox Group sedimentation rates are three times the Cenozoic average for the Gulf of Mexico region and are attributed to Laramide tectonism within the Laramide–Rocky Mountains region. These increased rates likely represent the erosion of easily weathered Phanerozoic strata that blanketed the Laramide-age basement-cored uplifts. Geologic observations and U-Pb geochronology are not sufficient to fully address this hypothesis alone, so we conducted 439 Lu-Hf isotopic analyses on detrital zircons from eight samples from the San Juan Basin and five samples from the Gulf of Mexico Basin. Focusing on the zircons younger than 300 Ma allowed us to make direct comparisons to the eight principal components that comprise the North American Cordilleran magmatic arc: (1) Coast Mountains batholith; (2) North Cascades Range; (3) Idaho batholith; (4) Sierra Nevada batholith; (5) Laramide porphyry copper province; (6) Transverse Ranges; (7) Peninsular Ranges; and (8) Sierra Madre Occidental. The εHf ( t ) results range from +8.9 to –27.0 for the San Juan Basin samples and from +13.0 to –26.6 for the Gulf of Mexico samples. Using the San Juan Basin samples as a proxy for the eroded Mesozoic cover that was shed from the Laramide uplifts, we show that much of the sediment entering the Gulf of Mexico through the Houston and Mississippi embayments during the late Paleocene was derived from reworked cover from the greater Laramide–Rocky Mountains region. However, the Gulf of Mexico samples also include a distinct juvenile suite (εHf [ t ] ranging from +13 to +5) of zircons ranging in age from ca. 220 to 55 Ma that we traced to the Coast Mountains batholith in British Columbia, Canada. This transcontinental connection indicates an extension to the headwaters of the previously defined paleo-Mississippi drainage basin from ca. 58 to 56 Ma. Therefore, we propose a through-going fluvial system (referred to here as the “Coast Mountains River”) that was routed from the Coast Mountains batholith to the Gulf of Mexico. This expands the previously defined paleo-Mississippi drainage basin area by an estimated 280,000 km 2 . Our comprehensive Hf isotopic compilation of the North American Cordilleran magmatic arc also provides a benchmark εHf ( t ) versus U-Pb age plot, which can be used to determine provenance of detrital zircons (85–50 Ma) at the scale of specific region(s) within the Cordillera based on their εHf ( t ) values.

Abstract The Arguello submarine canyon/channel system extends over 300 km from the continental shelf off Point Arguello and Point Conception in southern California westward onto the oceanic crust of the Pacific plate. In the northernmost reaches where the canyon system originates, all stages in the evolution of seafloor morphologic fluid flow features—from pockmarks to gullies to converging rills—are observed, similar to what has been described for the Ascension slope, north of Monterey Bay. These features appear to be active today and are linked to fluid leakage from the underlying hydrocarbon basin. The channel dissects a continental slope that exhibits features consistent with large-scale mass wasting. Upslope scarps may be the source of the morphological feature at the base of the slope previously referred to as the “Arguello submarine fan,” with topographic expressions (e.g., large channel meanders, ridges) that are more consistent with mass transport deposits than with deep-sea fan depositional lobes. The modern canyon crosscuts these deposits and parallels an older, meandering channel/canyon to the west. Modern seismicity along the shelf and slope may have, and potentially still can, trigger landslides on the slope. Seismicity associated with seamount volcanism, past subduction, and Borderland transrotational and extensional processes most likely played a role in stimulating mass wasting. The presence of abundant nearby petroleum suggests that gas venting and hydrate dissociation cannot be ruled out as a triggering mechanism for the slope destabilization occurring today. The canyon/channel continues due south on a path possibly determined by the structural grain of north–south-aligned abyssal hills underlying oceanic basement. At latitude 33°18′N, the channel makes a 90° turn (bend) to the west at the E–W-striking Arguello transform fault wall and develops into a meandering channel system that crosses over abyssal hill crustal fabric. The system ultimately straightens as it continues west before veering north, curving around a thickened crustal bulge at a corner offset in the Arguello fracture zone in complex basement structure, and then finally empties into an 800-m-deep basin depocenter.

Abstract: An integrated palynological and sedimentological study of Wilcox/Carrizo outcrops in and near Tahitian Village, Bastrop County, Texas, has led to a reevaluation of their chronostratigraphic significance and depositional environments. Strata at the well-known Pine Forest Golf Course and nearby Red Bluff outcrops, together with lesser-known outcrops in the vicinity, are important for source-to-sink linkages with coeval downdip Wilcox Group strata in the deep-water Gulf of Mexico (GOM). This updip succession is fragmentary, with erosional breaks between lithologic units. It represents nearshore shallow-marine to coastal environments throughout, with widespread evidence of tidal influence. Shallow-marine trace fossils are present, and although these are generally sporadic in sandstones, the Calvert Bluff Formation includes extensive Ophiomorpha galleries. Sabinetown Formation parasequences are mostly mud-dominated tidalites with locally common marine trace fossils in more arenaceous intervals. A bioturbated siltstone immediately above the Sabinetown Formation yielded the first Texas record of common to abundant Apectodinium, an acme potentially indicating the Paleocene–Eocene Thermal Maximum (PETM), and thereby providing a correlation with PETM intervals in GOM wells. At all locations, the base of the Carrizo Formation is a marine Glossifungites surface. Siltstone rip-up clasts draped on sigmoidal cross-beds and robust Ophiomorpha indicate the Carrizo Formation probably represents a tidal delta, not fluvial channels.