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.

Abstract U.S. military installations increasingly have become de facto bioreserves as the result of legacy and current land uses, urbanization, and historical siting of installations. The relative value of military lands as bioreserves compared to land holdings of other federal agencies is not proportional to total land area. Ironically, a significant reason that U.S. military installations have become important bioreserves is that they were not established with the purpose of conserving or extracting natural resources. This historical factor has resulted in a broad representation of U.S. ecoregions on military lands and largely has shielded those lands from the habitat loss and degradation that has occurred in surrounding regions due to urbanization, agricultural development, and other non-military land uses. Fort Hood, Texas, is used as a case study to illustrate the characteristics of military installations that fit the model for bioreserves as areas for conservation of biological resources and processes in the context of human use of the environment. A major current challenge for management of natural resources on military lands is that the value of U.S. military lands as bioreserves is increasing as surrounding habitats and natural communities continue to be degraded.

Impact stratigraphy is an extremely useful correlation tool that makes use of unique events in Earth's history and places them within spatial and temporal contexts. The K-T boundary is a particularly apt example to test the limits of this method to resolve ongoing controversies over the age of the Chicxulub impact and whether this impact is indeed responsible for the K-T boundary mass extinction. Two impact markers, the Ir anomaly and the Chicxulub impact spherule deposits, are ideal because of their widespread presence. Evaluation of their stratigraphic occurrences reveals the potential and the complexities inherent in using these impact signals. For example, in the most expanded sedimentary sequences: (1) The K-T Ir anomaly never contains Chicxulub impact spherules, whereas the Chicxulub impact spherule layer never contains an Ir anomaly. (2) The separation of up to 9 m between the Ir anomaly and spherule layer cannot be explained by differential settling, tsunamis, or slumps. (3) The presence of multiple spherule layers with the same glass geochemistry as melt rock in the impact breccia of the Chicxulub crater indicates erosion and redeposition of the original spherule ejecta layer. (4) The stratigraphically oldest spherule layer is in undisturbed upper Maastrichtian sediments (zone CF1) in NE Mexico and Texas. (5) From central Mexico to Guatemala, Belize, Haiti, and Cuba, a major K-T hiatus is present and spherule deposits are reworked and redeposited in early Danian (zone P1a) sediments. (6) A second Ir anomaly of cosmic origin is present in the early Danian. This shows that although impact markers represent an instant in time, they are subject to the same geological forces as any other marker horizons—erosion, reworking, and redeposition—and must be used with caution and applied on a regional scale to avoid artifacts of redeposition. For the K-T transition, impact stratigraphy unequivocally indicates that the Chicxulub impact predates the K-T boundary, that the Ir anomaly at the K-T boundary is not related to the Chicxulub impact, and that environmental upheaval continued during the early Danian with possibly another smaller impact and volcanism.

Planktonic foraminifera show 30 to 45 percent of the species disappearing during the 300,000 to 400,000 years prior to the Cretaceous/Tertiary (K/T) boundary in continental shelf (El Kef, Tunisia) and epicontinental sea (Brazos River, Texas) sections. Their disappearance appears to be linked to a sea-level regression and global cooling. At the K/T boundary a 26 percent species reduction coincides with the geochemical anomalies at El Kef; their disappearance appears to be a direct consequence of the K/T boundary event. No change is observed at Brazos River. At both El Kef and Brazos River, many species (11 and 33 percent, respectively) disappear shortly after the K/T boundary, and all but one of the Cretaceous survivors terminally decline in relative abundance beginning at the K/T boundary. This pattern of species extinctions clearly shows a significant decline in species diversity during the latest Maastrichtian, followed by a sudden decline in diversity at the K/T boundary, which drastically and permanently altered planktonic foraminiferal communities. The K/T boundary event, however, did not cause instantaneous extinctions of nearly all species, as commonly claimed. Initial recovery of the ecosystem appears to have occurred about 230,000 years after the K/T boundary event, as implied by an increase in carbonate sedimentation, carbon isotope values, and diversification of planktonic foraminifera. Carbon and oxygen isotope records of benthic and planktonic foraminifera at Brazos River reveal remarkable new data with far-reaching implications. For instance, the δ 13 C shift, which characterizes the K/T boundary globally, coincides with the micropaleontologically defined boundary and not with the tsunami deposit of Bourgeois and others (1988), indicating that the latter deposit is independent of the boundary event. Moreover, the δ 13 C shift occurs gradually over thousands of years, and not instantaneously as recorded in deep-sea sections, implying a more gradual and long-term effect than commonly assumed. Furthermore, stable isotopic data unequivocally show the survivorship of many Cretaceous species well into the early Tertiary.