Although the biota, facies, stacking patterns, sequence stratigraphy, and diagenesis of numerous isolated carbonate platforms have been described and interpreted, trends in the genesis, evolution, and sizes among Phanerozoic examples remain poorly quantified. To provide broad perspectives on Miocene isolated platforms of Central Luconia and Southeast Asia (the focus of this volume), this study summarizes the results of qualitative review of the literature and a quantitative analysis of a relational database of attributes in initiation, growth, character, and demise of more than 850 Phanerozoic isolated platforms. The data and comparisons among parameters reveal numerous trends, including observations that (1) syndepositional tectonics has been interpreted to play an important role in initiation, growth, or demise of more than 44% of isolated platforms; (2) tectonically active platforms are more likely to have higher aspect ratios (more elongate in plan-view and more squat in cross section); (3) stratal geometries are not distributed randomly in time (by era, p = 0.00, and by system, p = 0.04), although aggradational isolated platforms are most common within and among all eras (63% of all platforms); (4) sizes (area, long axis length), thicknesses, and aspect ratios (long axis:short axis; long axis:thickness) of isolated platforms are distinct among Phanerozoic platforms of different eras and systems; (5) although individual platforms steepen as they grow taller, syndepositional relief is not correlated (R 2 = 0.04) with depositional gradient among isolated platforms across the Phanerozoic; (6) causes of isolated platform termination vary nonrandomly through the Phanerozoic (by era, p = 0.00, and by system, p = 0.00). Of all eras, Cenozoic platforms are most likely to drown (68%), in some instances through an association with clastic influx (19%). Subaerial exposure more commonly contributed to the demise of Mesozoic (45%) and Paleozoic (37%) platforms than to that of Cenozoic (13%) platforms. These results, supplemented by more granular comparison of numerous individual platforms, compliment earlier syntheses that focus on the nature of secular changes. The insights suggest that although each platform is unique in many ways, Phanerozoic isolated carbonate platforms include numerous themes that are persistent across ages, sizes, settings, and component biota.

Abstract Hydraulic testing has revealed dramatic underpressures in Paleozoic shales and carbonates at the Bruce nuclear site in Ontario. Although evidence from both laboratory and field studies suggests that a small amount of gas-phase methane could be present in the shale, previous studies examining causal linkages between the gas phase and the underpressure have been inconclusive. To better elucidate processes in such a system, we used a highly simplified 1D representation of the site to test, by using iTOUGH2-EOS7C, the effects of various factors on the evolution of gas-phase methane and pressures within the system. Heterogeneity was represented by three stratigraphic regions with slightly different capillary pressure characteristics and, in one case, three thin distinct zones with very different characteristics. Underpressure occurred only when gas pressures set as an initial condition required it, and even in this case it was geologically short-lived. We conclude that the presence of multiple fluid phases is unlikely to explain the underpressure at the site; we suggest that the influence of gas-phase methane on porewater flow is minimal. This is consistent with prior conceptualizations of the underpressured section as a thick aquiclude, in which solute transport occurs extremely slowly, bounded by aquifers of significantly higher permeability.

ABSTRACT The A-1 Carbonate is the primary hydrocarbon source rock and an important reservoir component of the Silurian (Niagaran) pinnacle reef complexes in the Michigan Basin. The geology of the A-1 Carbonate, however, is not widely known because the majority of published research about this hydrocarbon system focuses on the pinnacle reefs. To gain a better understanding of the sedimentology and stratigraphy of the A-1 Carbonate, we integrated data from slabbed core, thin section petrography, gamma-ray logs, and energy-dispersive X-ray fluorescence spectrometry (ED-XRF). Thirteen distinct lithofacies within the A-1 Carbonate are recognized, with inferred depositional environments ranging from intertidal-sabkha to deep basin. The recognition of deep-water lithofacies contrasts significantly with previous interpretations of the A-1 Carbonate as a shallow, peritidal deposit. Lithofacies stacking patterns and ED-XRF elemental trends within the A-1 Carbonate are consistent with basinwide sea-level fluctuations that resulted in deposition of three major stratigraphic units, called the Lower A-1 Carbonate, Rabbit Ear Anhydrite, and Upper A-1 Carbonate. The basal part of the Lower A-1 Carbonate was deposited during a basinwide transgression, as evidenced by deep-water pelagic carbonate accumulation in the basin center, lithofacies that become progressively muddier from bottom to top, and higher concentrations of Si, Al, and K upward, which are interpreted to reflect the influx of continental sediments. The subsequent highstand deposits of the upper part of the Lower A-1 Carbonate are characterized by a decrease in Si, Al, and K, coupled with a shallowing-upward facies succession consistent with increased carbonate production rates. The Rabbit Ear Anhydrite, which bifurcates the Upper and Lower A-1 Carbonate units, exhibits a variety of anhydrite fabrics across a wide range of paleotopographic settings within the basin. The Rabbit Ear Anhydrite is interpreted to reflect a time-correlative sea-level drawdown, which caused basin restriction, gypsum deposition, and elevated concentrations of redox-sensitive elements, such as Mo and Ni. The Upper A-1 Carbonate represents sedimentation during another major basinwide transgression that culminated in the deposition of shallow-water microbialites on the crests of previously exposed Niagara reef complexes. Similar to the Lower A-1 Carbonate, the base of the Upper A-1 Carbonate exhibits elemental signatures indicative of continental influence, whereas the overlying highstand deposits are characterized by more normal marine conditions and lower concentrations of Si, Al, and K.

ABSTRACT Pennsylvanian red beds are the youngest known rocks in the Michigan Basin. Two new formation-level units, the Pewamo Formation and the Haybridge strata, have recently been described. The Pewamo Formation, composed of Pennsylvanian red sandstones and minor laminated mudstones, is known from outcrops, abandoned quarries, and one core in Ionia County. The Haybridge unit is located in the shallow subsurface and in coal mine tailing piles in Shiawassee County. It consists of red sandstone, red mudstone, coal, and gray mudstone, all hosting Pennsylvanian macroscopic plant fossils. Neither the Pewamo nor the Haybridge rocks have any demonstrated relationship to red core cuttings reported as Jurassic from the central Lower Peninsula of Michigan. No firm evidence exists for Jurassic, or any other post-Pennsylvanian rocks in the Michigan Basin. The red core cuttings may be glacial sediments with reworked palynomorphs from rocks transported from elsewhere. A shallow coring project, followed by detailed sedimentologic, petrographic, mineralogic, and paleontologic studies, is necessary to: (1) refine the vertical and lateral stratigraphy of the Pennsylvanian rocks in Michigan; (2) solve the “Jurassic red bed problem”; and (3) understand the late Pennsylvanian–Pleistocene history of the Michigan Basin.

ABSTRACT The objective of this study was to investigate the geological controls on stratigraphic and lithologic variability in the Ordovician Utica Shale and related Collingwood Member in the Michigan Basin in order to assess CO 2 sequestration cap rock (seal) potential, including petrophysical properties and mechanical fracture responses. Twelve conventional cores and hundreds of modern well logs from the Michigan Basin were analyzed to correlate and calibrate wireline log signatures with whole-rock mineral composition (from X-ray diffraction analysis) and mechanical properties (from core analysis) to identify brittle, fracture-prone zones, and to validate the Utica Shale as a regional geologic seal. Analysis using scanning electron microscopy with Quantitative Evaluation of Minerals by Scanning Electron Microscope (QEMSCAN ®) software was employed to image pores and for quantitative analysis of mineralogy, texture, and porosity. Mercury injection capillary pressure and triaxial strength testing was conducted to assess petrophysical properties and mechanical responses. The results suggest the Utica Shale could reliably contain upwards of 1500 m of buoyant, supercritical CO 2 stored in underlying Cambrian and Ordovician reservoirs.

ABSTRACT Previous work shows that the Burnt Bluff Group was deposited as a series of shallow- to moderate-water-depth facies in a tropical marine setting in the Michigan Basin during the Llandoverian. New interest in the unit for both hydrocarbon resources (subsurface) and aggregate resources (outcrop) is driving research in this poorly understood unit. New cores, as well as investigation of the outcrop belt in the Upper Peninsula of Michigan, allow further elaboration of the depositional model. The traditional interpretation of the Burnt Bluff Group consists, in stratigraphic order, of the open-marine deposits of the Lime Island Formation, the restricted lagoonal–tidal flat Byron Formation, and the open-marine deposits of the Hendricks Formation. The contacts with the underlying Cataract Group and overlying Manistique Group are gradational. Identification and description of facies in both cores and outcrop sections provide new constraints on the stratigraphic nomenclature of the Burnt Bluff Group. New outcrop and core data require the revision of the depositional model for portions of the group because typical Byron-like facies are found interbedded with Hendricks-like facies in both the Byron and Hendricks Formations. Limited age data from published research combined with the new facies model for the Burnt Bluff Group suggest that the unit was deposited as a time-transgressive package on a carbonate ramp during the Llandoverian.