ABSTRACT The northern segment of the Edwards (Balcones Fault Zone) Aquifer is an important source of water for municipalities, industry, and landowners in central Texas. Rapid population growth in this part of Texas has increased interest in the north segment of the aquifer and heightened concerns about groundwater availability. The aquifer consists of Cretaceous limestone stratigraphic units that crop out along its western margin and dip toward the east. Groundwater primarily flows from the aquifer outcrop recharge zones toward discharge zones along perennial rivers and streams in the outcrop area and to a lesser extent toward deeper parts of the aquifer, eventually discharging by cross-formational flow to overlying stratigraphic units, such as the Del Rio Clay, Buda Limestone, and Austin Chalk. Groundwater isotope compositions in the aquifer indicate that groundwater flow is most active in the unconfined parts of the aquifer and that most recharge occurs during late fall and winter months, even though highest monthly precipitation occurs during the spring. Pumping from the northern segment of the Edwards (Balcones Fault Zone) Aquifer is ~6.8 × 10 7 L/d, having peaked at ~1.0 × 10 8 L/d in 2004, but still up from ~3.4 × 10 7 L/d in the 1980s. Most of this pumping (~90%) is for municipal uses. However, in the rural northern and heavily urbanized southern parts of the aquifer, domestic and manufacturing uses, respectively, account for a significant portion of total pumping.

ABSTRACT The Barton Springs segment of the Edwards (Balcones Fault Zone) Aquifer is a prolific karst aquifer system containing the fourth largest spring in Texas, Barton Springs. The Barton Springs segment of the Edwards Aquifer supplies drinking water for ~60,000 people, provides habitat for federally listed endangered salamanders, and sustains the iconic recreational Barton Springs pool. The aquifer is composed of Lower Cretaceous carbonate strata with porosity and permeability controlled by depositional facies, diagenesis, structure, and karstification creating a triple permeability system (matrix, fractures, and conduits). Groundwater flow is rapid within an integrated network of conduits discharging at the springs. Upgradient watersheds provide runoff to the recharge zone, and the majority of recharge occurs in the streams crossing the recharge zone. The remainder is direct recharge from precipitation and other minor sources (inflows from Trinity Group aquifers, the San Antonio segment, the bad-water zone, and anthropogenic sources). The long-term estimated mean water budget is 68 ft 3 /s (1.93 m 3 /s). The Barton Springs/Edwards Aquifer Conservation District developed rules to preserve groundwater supplies and maximize spring flow rates by preserving at least 6.5 ft 3 /s (0.18 m 3 /s) of spring flow during extreme drought. A paradox of the Barton Springs segment of the Edwards Aquifer is that rapid recharge allows the Barton Springs segment of the aquifer to be sustainable long term, but the aquifer is vulnerable and limited in droughts. The karstic nature of the aquifer makes the Barton Springs segment vulnerable to a variety of natural and anthropogenic contaminants. Future challenges will include maintaining the sustainability of the aquifer, considering climate change, population growth, and related land-use changes.

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.

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.

A chronostratigraphic framework was developed for the subsurface Eagle Ford of South Texas in conjunction with a log-based regional study that was extended across the San Marcos Arch and into East Texas using biostratigraphic and geochemical data to constrain log correlations of 12 horizons from 1729 wells in South and East Texas. Seven regional depositional episodes were identified by the study. The clayrich Maness Shale was deposited during the Early Cenomanian in East Texas and northern South Texas where it correlates to the base of the Lower Eagle Ford. After a fall in sea-level, East Texas was dominated by the thick siliciclastics of the Woodbine Group, whereas in South Texas deposition of the organic-rich EGFD100 marls of the Lower Eagle Ford began during the subsequent Lewisville transgression. A shift in depositional style to the limestones and organic-rich shales of the Eagle Ford Group occurred in East Texas during the Middle-Late Cenomanian EGFD200 and EGFD300 episodes produced by the continued rise in sea-level. Erosion along the Sabine Uplift shifted the focus of deposition in East Texas southward to the Harris delta and deposited the “clay wedge” of northern South Texas during the EGFD400 episode. The introduction of an oxygenated bottom-water mass onto the Texas shelf produced the considerable decrease in TOC preservation that marks the Lower/Upper Eagle Ford contact. This event coincided with the onset of Oceanic Anoxic Event 2 (OAE2) and the Cenomanian-Turonian Boundary sea-level high, which starved much of the Texas shelf of sediment. The only significant source of sediment was from the south; within the study area, the EGFD500 interval is essentially absent north of the San Marcos Arch. Deposition recommenced on much of the Texas shelf during the Late Turonian EGFD600 episode with the Sub-Clarksville delta of East Texas and the carbonate-rich Langtry Member of South Texas and eastern West Texas. Bottom-waters became oxygenated at approximately 90 Ma, initiating the transition from the Eagle Ford Group to the Austin Chalk.