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 oxygen isotopic composition of turtle phosphate from Early (Aptian–Albian) Cretaceous turtles from several North American palaeolatitudes was measured to estimate the isotopic compositions of groundwater δ 18 O w . In Earth's history, under greenhouse conditions, researchers have recorded an intensification of the hydrological cycle as global heat was distributed from the equator to the poles via latent heat transport. Previous studies, using pedogenic carbonate nodules, show an increased rainout effect, causing intense depletion in δ 18 O w at high latitudes due to this phenomenon. This study shows the utility of another palaeo- δ 18 O w proxy, turtle phosphate oxygen from turtle carapace and plastron. Turtle δ 18 O p was sampled from several Early Cretaceous sites. We find that turtle-derived δ 18 O w values range from −3.1 ± 0.9‰ at a palaeolatitude of 29.5° N to −7.2‰ at 40° N. Turtles at the lowest latitude (Arkansas) plot off the carbonate-derived δ 18 O w gradient; however, turtles at 34° N and 40° N plot within the range of carbonate-derived δ 18 O w . Turtles from Arkansas (29.5° N) were likely to have been influenced by marine water and/or enriched Gulf of Mexico water vapour resulting in a deviation from the expected δ 18 O w gradient. These data are encouraging steps towards using turtles to estimate palaeohydrological dynamics; however, additional analysis of lower- and higher-latitude specimens is necessary to confirm this trend.

ABSTRACT The four largest spring systems in the mid-continent receive recharge through large interconnected voids in fractured and solution-weathered dolostones of the Ordovician and Cambrian systems. Cumulative thickness of the carbonate bedrock aquifer ranges up to 700 m in the Ozark region. Recharge from the surface occurs through weathered overburden, sinkholes, and losing streams and has been traced up to 60 km (straight-line horizontal distance) using fluorescent dyes. Mean discharge of the combined flow of these four spring systems is ~1400 cubic feet/second (ft 3 /s) or 40 m 3 /second (m 3 /s). All four spring systems will be visited while discussing the karst terrane that recharges them. Environmental and engineering challenges in the region will be discussed, such as wastewater treatment systems, solid waste disposal, and failed reservoirs. Hodgson Mill Spring represents a branch of the Rainbow/North Fork/Hodgson Mill System. While it receives base flow from the main system, it also receives local recharge that Rainbow and North Fork springs do not. A portion of the Mammoth Spring recharge system will be viewed at Grand Gulf State Park in Missouri, where a cave collapse has created cliffs and a natural bridge and exposed a small losing tributary that flows into a cave that has been traced to the spring. Mammoth Spring State Park in Arkansas offers a historical perspective of the development and use of large springs. Greer Spring in Missouri was used as a power source for grist, flour, and lumber mills, but has now largely returned to its predevelopment state and is managed by the U.S. Forest Service. Big Spring, featured in a former state park in Missouri, is now part of the Ozark National Scenic Riverways.