Steven Bergman

Decoupling of the carbon cycle during Ocean Anoxic Event 2

The Cenomanian to Turonian boundary transition (ca. 95–93 Ma) represents one of the most profound global perturbations in the carbon cycle of the past 140 m.y. This interval is characterized by widespread deposition of organic-rich fine-grained sediment marked by a globally recognized positive carbon isotope excursion (CIE) reflecting the widespread removal of 12 C-enriched organic matter in marine sediments under global anoxic greenhouse conditions. However, the exact timing and trigger of this inferred global phenomenon, termed Oceanic Anoxic Event 2 (OAE-2), is still debated, with recent studies showing diachroneity between the deposition of the organic-rich sediment and the CIE, and conflicting interpretations on detailed redox analyses in several of these inferred anoxic settings. Here we present the first evidence for widespread and persistent oxygenation during OAE-2 based primarily on the distribution of redox-sensitive trace metals and biota preserved in sedimentary rocks from the Western Interior Seaway of North America. Our data indicate anoxic-euxinic conditions in the mid- to late Cenomanian, but improved bottom-water oxygenation prior to and during the CIE. Trace metal enrichments support large volumes of mafic volcanism possibly from the High Arctic large igneous province (HALIP), which occur within the middle of the CIE indicating that the emplacement of LIPs was not the primary trigger of the Cenomanian-Turonian CIE. The apparent paradox of an oxygenated phase within OAE-2 suggests a much more complex carbon cycle during these global perturbations than previously thought. These findings have important implications for greenhouse carbon cycle changes over time scales of 0.1–10 m.y.

Geological data extraction from lidar 3-D photorealistic models: A case study in an organic-rich mudstone, Eagle Ford Formation, Texas

The use of lidar (light detection and ranging) 3-D photorealistic outcrop models, combined with traditional sedimentological and structural field data, improves the accuracy and efficiency of qualitative and quantitative characterization of outcrops, which in turn can be used as analogs for reservoir modeling and other geologic purposes. This paper illustrates how geological data extraction from 3-D photorealistic outcrop models can be exploited, and presents some novel workflows that reduce the time needed for postprocessing. The extracted data are calibrated with conventional outcrop studies and allow extensive quantitative analyses and detailed statistical examinations of the distribution, dimension, and shape of geological features that can be used to define and build geological models. We present the first statistical characterization based on lidar of a set of geological outcrops at centimeter resolution (bed scale) over a distance of 45 km (basin scale). These innovative methods of outcrop visualization and characterization are applied to the Eagle Ford Formation, an important unconventional hydrocarbon play in Texas. The Eagle Ford Formation consists of alternating organic-rich mudstone, limestone, and bentonites; mudstones represent the source and reservoir of the hydrocarbons, limestones control the rock’s brittleness, and bentonites provide time lines for dating and correlating sections. The presented analyses provide empirical relationships that can be applied to better understand geologic processess, to build geologic models, and to reduce uncertainties in exploration and development of hydrocarbon systems.

Cenozoic deformation and exhumation of the Kampot Fold Belt and implications for south Indochina tectonics

Latest Mesozoic to earliest Cenozoic deformation affected SE Asias Sundaland core. The deformation event bridges the Mesozoic SE Asian fusion with the Cenozoic era of rifting, translation, basin formation, and the creation of modern SE Asian oceans. Southern Cambodia and Vietnam are central to this shift, but geological investigations of the region are in their infancy. Based on apatite and zircon fission track analyses (AFTA and ZFTA), stratigraphic and structural observations, seismic data, thermal maturity, and igneous rock dating, the geological evolution of southern Cambodia and Vietnam is investigated. Diverse depositional styles, igneous activity, structural deformation and subsurface unconformities testify to a highly variable Phanerozoic tectonic setting. Major latest Cretaceous to Paleocene thrusting and uplift affected the Kampot Fold Belt and surrounding regions and the associated up to ~11 km exhumation probably exceeds earlier denudation events since at least Permian time. The present relief of the Bokor Mountains rising high above the Kampot Fold Belt represents an artifact after differential erosion and only 2.5–4.5 km of erosion affected this area. The latest Cretaceous to Paleocene orogenesis affected much of greater Indochina probably owing to plate collision along eastern Sundaland or a combination of collisions along both east and west Sundaland. AFTA and ZFTA data document protracted cooling of Cretaceous granites and locally elevated thermal gradients persisting a few tens of million years after their emplacement. The thermal gradient had stabilized by early Miocene time, and Miocene cooling probably reflects a renewed denudation pulse driven by either regional tectonism or climate-enhanced erosion.