Peter Holterhoff

Delocrinus subhemisphericus (Ds) is among the most ecologically wide-ranging and abundant Late Pennsylvanian crinoid species in the midcontinent. Multivariate analyses and coenocline reconstructions indicate that Ds was typically the dominant component of low-diversity, moderate depth assemblages. Morphometric analyses of populations of Ds from different systems-tracts of Upper Missourian sequences show that offshore individuals are small and that size increases to a maximum in nearshore facies. These differences can be attributed to developmental flexibility, accomplished by either rapid maturation in offshore populations for equal rates of size increase (growth rate) or slower growth in offshore populations for equal intervals of development (maturation rate). The offshore phenotype of this species is not adaptive in that it does not impart a unique functional advantage over the nearshore phenotype; small size offshore appears to be the outcome of slowed growth in a stressed environment having reduced current flow where larger body sizes could not be maintained. Although the small adult phenotype is not the optimally adapted offshore morphology compared to the dominant open fan crinoids, developmental and life-history flexibility can be considered adaptive for the species as a whole. This flexibility allowed it to occupy a wider range of environments than would have beenmore » habitable had size at maturity been constrained. This pattern reflects either transgressive-regressive tracking by ecophenotype populations or modification of successive generations of established populations with changing sea-level.« less

Crinoids were a common component of Paleozoic benthic paleocommunities, yet they have been under-utilized in paleoecological analyses. Recent efforts to incorporate disarticulated ossicles into these analyses have greatly increased the robustness of paleoecological patterns noted for the Crinoidea. Analyses of crinoid functional morphology, particularly filtration dynamics, have provided testable hypotheses concerning the distribution of crinoids among benthic environments. These models predict that crinoids with dense-mesh filtration fans should be most common in high energy, shoreward paleoenvironments, whereas open-fan crinoids should be most common in low-energy, offshore paleoenvironments. Review of the Paleozoic fossil record appears to support these general predictions—from the Late Ordovician to the end of the Paleozoic, dense-fan crinoids are most abundant in nearshore paleoenvironments, whereas open-fan crinoids are most abundant offshore.The partitioning of crinoid diversity through the Paleozoic shifted through time. Beta diversity was highest in the Ordovician, implying that the early diversification of crinoids was focused on partitioning the benthic landscape among taxa. Beta diversity was quite low by the late Paleozoic, however, local and within-habitat alpha diversity was much greater than during the Ordovician. This resulted in generally higher levels of eurytopy in the late Paleozoic compared to the Ordovician. Patterns of faunal disassembly associated with regional extinctions in North America during the Ordovician and Permian underscore the differences in the paleoecology of these crinoid faunas.

Delocrinus subhemisphericus (Ds) is among the most ecologically wide-ranging and abundant Late Pennsylvanian crinoid species in the midcontinent. Multivariate analyses and coenocline reconstructions indicate that Ds was typically the dominant component of low-diversity, moderate depth assemblages. Morphometric analyses of populations of Ds from different systems-tracts of Upper Missourian sequences show that offshore individuals are small and that size increases to a maximum in nearshore facies. These differences can be attributed to developmental flexibility, accomplished by either rapid maturation in offshore populations for equal rates of size increase (growth rate) or slower growth in offshore populations for equal intervals of development (maturation rate). The offshore phenotype of this species is not adaptive in that it does not impart a unique functional advantage over the nearshore phenotype; small size offshore appears to be the outcome of slowed growth in a stressed environment having reduced current flow where larger body sizes could not be maintained. Although the small adult phenotype is not the optimally adapted offshore morphology compared to the dominant open fan crinoids, developmental and life-history flexibility can be considered adaptive for the species as a whole. This flexibility allowed it to occupy a wider range of environments than would have beenmore » habitable had size at maturity been constrained. This pattern reflects either transgressive-regressive tracking by ecophenotype populations or modification of successive generations of established populations with changing sea-level.« less

High-effort 3D seismic data collected by ADCO in onshore Abu Dhabi are some of the highest quality data ever collected over a carbonate reservoir. These data provide the opportunity to test the limits of high-end seismic technologies in carbonates and to demonstrate the value of seismic for integrated carbonate reservoir characterization. Seismic data were integrated with other subsurface data to develop a new, sequence stratigraphic based reservoir framework. The Lower Cretaceous (Aptian) reservoir records a large-scale transgressive-regressive depositional cycle that, in turn, is divided into six (6) depositional sequences. Reservoir architecture and quality vary predictably within the sequence framework and correspond closely to variations in seismic properties. Sequence-stratigraphic surfaces define the 3D distribution of flow barriers and flow units within the reservoir and are used to guide framework and rock property distributions in 3D reservoir models. Quantitative seismic information on reservoir architecture and porosity variations provides a new understanding of reservoir heterogeneity and the underlying geologic controls. Multi-attribute volume interpretation and co-rendering techniques help to visualize geologic and reservoir variations and provide a volume-based framework for reservoir evaluation. In the southern field area, 3D seismic data reveal a complex mosaic of tidal channels, high-energy rudist shoals, and inter-shoal ponds in detail comparable to Landsat images of modern carbonate environments. These geologic features have different geometries and reservoir properties that impact reservoir sweep and conformance. Seismic imaging of these features provides a 3D framework to integrate production and geoscience data, evaluate reservoir performance and constrain reservoir models. In the northern field area, seismic images of prograding slope clinoforms reveal systematic variations in architecture and reservoir quality that are tied closely to the sequence stratigraphic framework. A pattern gas flood has been implemented in the clinoforms to add pressure support and improve recovery. Seismic detection of clinoforms and their internal porosity variations allows for 3D visualization of reservoir and well-pair connectivity that will assist in gas flood management. Together, the sequence-based reservoir framework and 3D seismic provide an integrated platform for addressing a range of production and performance issues. Applications of these results include:3D seismic visualization as a tool for optimizing well placement, identifying by-passed reservoirs and evaluating reservoir connectivity,integration of quantitative, volume-based seismic information into reservoir models,maximizing recovery through full integration of all subsurface data, andenhanced communication among geoscientists and engineers leading to improved reservoir management practices. Introduction The stratigraphic and diagenetic complexities inherent in carbonate reservoirs require the most accurate reservoir descriptions and models possible to optimize recovery. 3D seismic data provide the only continuous source of information on reservoir properties in the subsurface, and acquisition of 3D seismic has become a standard best practice for carbonate reservoir evaluation. With increasingly more 3D seismic available over carbonate fields, the challenge is to maximize the value of the seismic for characterization of carbonate reservoir architecture and rock properties1–2.

Crinoids were a common component of Paleozoic benthic paleocommunities, yet they have been under-utilized in paleoecological analyses. Recent efforts to incorporate disarticulated ossicles into these analyses have greatly increased the robustness of paleoecological patterns noted for the Crinoidea. Analyses of crinoid functional morphology, particularly filtration dynamics, have provided testable hypotheses concerning the distribution of crinoids among benthic environments. These models predict that crinoids with dense-mesh filtration fans should be most common in high energy, shoreward paleoenvironments, whereas open-fan crinoids should be most common in low-energy, offshore paleoenvironments. Review of the Paleozoic fossil record appears to support these general predictions—from the Late Ordovician to the end of the Paleozoic, dense-fan crinoids are most abundant in nearshore paleoenvironments, whereas open-fan crinoids are most abundant offshore.The partitioning of crinoid divers...

The Upper Pennsylvanian Barnsdall Formation as exposed near Copan, northeastern Oklahoma, represents a low energy, prodeltaic distal shelf environment and constitutes part of the highstand phase (core shale) of the Missourian (=Kasimovian) Stanton cyclothem. Directly overlying a dark grey, phosphatic shale representing maximum highstand, an interval of green mudstone records initial regression and breakdown of water column stratification. Within this upper core shale is a diverse and abundant benthic fossil assemblage, including the highest levels of crinoid diversity recognized in the global Pennsylvanian System. Detailed microstratigraphic and comparative taphonomic analysis reveals that this lithologically monotonous succession records three cycles, each approximately 15 cm (6 in) thick. Each cycle consists of a distal portion (a thin, very time-averaged unit bearing large siderite concretions and a diverse, abundant, and well-preserved crinoid assemblage) overlain by a more prox...

Cyclothems (fifth - order depositional sequences) are the fundamental stratigraphic motif of the Upper Pennsylvanian and Lower Permian of the North American mid - continent. Through this interval, sequences display an overall second order regression modulated by intermediate frequency sea-level fluctuations. Thus, shelfward incursions of offshore (basinal) facies are more extensive in the lower Upper Pennsylvanian, while merely shoaling facies characterize marine units of many higher sequences.Within basal Upper Pennsylvanian (Missourian) sequences, species of the Erisocrinacea are ubiquitous members of nearshore and offshore crinoid assemblages. However, the species Erisocrinus typus and Delocrinus subhemisphericus display significant ecophenotypic variation between facies: smaller mean and maximum size characterizes offshore/transgressive populations while larger size characterizes nearshore/regressive populations. It is proposed that these are hydrographically - controlled phenot...

Crinoids were a common component of Paleozoic benthic paleocommunities, yet they have been under-utilized in paleoecological analyses. Recent efforts to incorporate disarticulated ossicles into these analyses have greatly increased the robustness of paleoecological patterns noted for the Crinoidea. Analyses of crinoid functional morphology, particularly filtration dynamics, have provided testable hypotheses concerning the distribution of crinoids among benthic environments. These models predict that crinoids with dense-mesh filtration fans should be most common in high energy, shoreward paleoenvironments, whereas open-fan crinoids should be most common in low-energy, offshore paleoenvironments. Review of the Paleozoic fossil record appears to support these general predictions-from the Late Ordovician to the end of the Paleozoic, dense-fan crinoids are most abundant in nearshore paleoenvironments, whereas open-fan crinoids are most abundant offshore.

The partitioning of crinoid diversity through the Paleozoic shifted through time. Beta diversity was highest in the Ordovician, implying that the early diversification of crinoids was focused on partitioning the benthic landscape among taxa. Beta diversity was quite low by the late Paleozoic, however, local and within-habitat alpha diversity was much greater than during the Ordovician. This resulted in generally higher levels of eurytopy in the late Paleozoic compared to the Ordovician. Patterns of faunal disassembly associated with regional extinctions in North America during the Ordovician and Permian underscore the differences in the paleoecology of these crinoid faunas.

The Eastern Shelf of the Midland Basin provides a relatively continuous record of Late Paleozoic (Pennsylvanian and Permian) tropical climate evolution and sea-level dynamics. Recent work on the Gondwanan sub-continents shows that the Early Permian was a particularly critical interval of Earth’s climate history (Fielding et al., 2008a). Specifically, the Early Permian marks the transition from the acme of the Late Paleozoic global icehouse in the earliest Permian to an essentially ice – free middle Early Permian world. This transition had a significant impact on terrestrial (Tabor and Montanez, 2004; DiMichele et al., 2006) and marine (Holterhoff, 2006) depositional systems and sequence stratigraphic architecture of the strata filling the Midland Basin along the Eastern Shelf (Holterhoff, 2006, 2009).
The goal of this field trip is to examine the Lower Permian Wolfcampian and Leonardian units exposed on the Eastern Shelf of the Midland Basin to compare and contrast the evolving tropical depositional systems and sequence stratigraphic motifs through this critical interval of Earth history. The Lower Permian outcrop belt on the Eastern Shelf is in an inner platform position over 100km east of the coeval shelf margins of these units. As such, sequence stratigraphic interpretations presented here are based upon lithofacies stacking patterns that should provide a framework for correlation into the subsurface shelf margin and basin equivalents sometime in the future.
Focus intervals/stops on this trip include: 1) the lower Wolfcampian upper Cisco Group between Coleman and Breckenridge to examine the high – amplitude/ high – frequency sequences characteristic of the lower Permian icehouse. These sequences are characterized by abrupt vertical facies transitions, thin but well – developed open marine carbonates during maximum transgression, and well – developed lowstand incised valley fills, 2) the upper Wolfcampian lower Albany Group (Admiral Formation) between Coleman and Albany to examine the transition interval between the Cisco icehouse type sequences and the overlying “greenhouse” sequences architectures of the middle and upper Albany Group, 3) the upper Wolfcampian – lower Leonardian Belle Plains, Clyde, and Lueders formations of the Albany Group between Coleman and Albany to examine the thick carbonate – dominated sequences characteristic of ice – free global climates. These sequences are characterized by stepped vertical facies transitions, thick packages of marginal to open marine carbonate – clastic facies couplets/rhythmites, and poorly developed lowstand lithofacies packages, 4) if time permits, examination of the late Leonardian upper Clear Fork and San Angelo interval around Bronte, representing the late highstand and lowstand transition from the Early to Middle Permian supersequence.