Wayne A. Pryor

Biogenic Sedimentation and Alteration of Argillaceous Sediments in Shallow Marine Environments

The feeding activities and excretory products of the marine decapod Callianassa major Say and the marine annelid Onuphis microcephala Hartman have been studied in shallow marine environments of the southern Atlantic and eastern Gulf of Mexico coasts of the United States. These filter-feeding organisms produce depositionally significant quantities of argillaceous fecal pellets that are transported and deposited as granular clay with hydraulically equivalent quartz sand grains. At average population densities observed in shallow marine environments, these organisms are calculated to be capable of removing and pelletizing approximately 12 metric tons of suspended materials per square kilometre per year and of depositing fecal pellet mud as thick as 4.5 mm yearly. Recent deposits of Onuphis pellets up to 30 cm thick and Callianassa pellets as thick as 60 cm have been observed. The complex, species-specific, sand-sized fecal pellets are composed of 80 to 90 percent clay-mineral particles and 5 to 10 percent undigested organic particles and small amounts of quartz sand and silt grains. The digestive systems of the organisms significantly alter the clay mineralogy of the sediments extracted from suspension, and Callianassa major produces fecal pellets of different clay-mineral compositions from fecal pellets produced by Onuphis microcephala . The digestive processes wholly or partly destroy chlorite. Mixed-layer clay minerals are partly destroyed, and kaolinite and illite are in part disordered. Fecal pellets, rich in organic matter, enter the coprophagic cycle where further clay-mineral alteration takes place. Decay of the organic matter creates microreducing conditions within the pellets, thus promoting the processes of glauconitization. Whereas flocculation is the important process in the deposition of argillaceous sediments in deltaic environments, biogenic pelletization may be the most important process in depositing argillaceous sediments in shallow marine interdeltaic environments.

Permeability-Porosity Patterns and Variations in Some Holocene Sand Bodies

Sandstone reservoirs are the results of long and commonly complex histories of geologic evolution. The combined processes of deposition, burial, compaction, diagenesis, and structural deformation yield final reservoir bodies of widely varied geometries, permeability-porosity characteristics, and structural configurations that are difficult to predict. In unraveling the evolution of sandstone reservoirs it is necessary to have detailed knowledge of their initial depositional characteristics and of the postdepositional modifications impressed upon them. This knowledge can provide a rational basis in predicting the characteristics of reservoir bodies away from areas of data control. Little information pertaining to the reservoir characteristics of freshly deposited sand bodi s has been available. In an API sponsored study, permeability, porosity, and textural parameters were derived from 992 oriented and undisturbed sand samples of river bars, beaches, and dunes undergoing active sedimentation. River point-bar samples have permeabilities ranging from 4 md to more than 500 darcys and average 93 darcys. Porosities in the river point-bars range from 17 to 52 percent and average 41 percent. Beach sand samples have a permeability range of 3.6 to 166 darcys and average 68 darcys. Porosities in beach sands range from 39 to 56 percent and average 49 percent. Permeability values in dune sands range from 5 to 104 darcys and average 54 darcys. Dune sand porosities range from 42 to 55 percent and average 49 percent. Permeability values in river-bar sands are extremely varied in comparison to those of beaches and dunes. In river bars, permeability decreases systematically downstream and bankward. Although of low variability, permeabilities on beaches are low on the beach faces, high on t e beach crests, and variable on the beach-berm areas. Both river-bar and beach sands have well organized directional permeabilities, parallel with the length of the bodies in river bars and perpendicular to the length of the bodies in beaches. Dunes are characterized by low variability in permeability and porosity and show no significant patterns or trends. There is greater variability within bedding and lamination packets than between them. In addition the boundary conditions between bedding and lamination packets are important factors in determining the effective reservoir characteristics of sand bodies, to the extent that a bedding unit of higher permeability completely surrounded by units of lower permeabilities will not demonstrate its ultimate through-flow capabilities, but will have an effective permeability influenced by and largely determined by the lower permeabilities of the bounding units. River-bar sand bodies have significantly different arrangement and variability between bedding units from those of beaches or dunes. The ideal relations between permeability-porosity and textural parameters that have been set forth by various authors for artificially packed particles are demonstrated only slightly by these natural sands from different depositional environments. In all three depositional environments permeability increases with increase in grain size and porosity increases with increase in grain sorting. However, in river-bar sands permeability increases as grain sorting increases and porosity increases as grain size increases, just the opposite of the relations in beach-dune sands and in the artificially packed grain experiments. The underlying cause of these deviations is the different style of grain packing in the river-bar sands.

Cyclic alteration of proximal and distal storm facies; Kope and Fairview formations (Upper Ordovician), Ohio and Kentucky

The Upper Ordovician Kope and Fairview Formations and the Bellevue Tongue of the Grant Lake Limestone exposed in the Cincinnati, Ohio region, represent storm-dominated sedimentation on a prograding, intracratonic ramp. The upper Kopelower Fairview transition zone (25 m thick) is an outer to intermediate ramp lithofacies and is composed of numerous (1-3 m thick) shallowing-upward subtidal cycles. Bedding cycles are composed of two depth-controlled facies: 1) a shale-dominated distal facies and 2) a fossiliferous proximal facies . The distal facies records low-energy, largely single-storm events and consists of thin graded shale beds, nearly in situ fragile-fossil accumulations, thin parautochthonous packstones, and quartzose siltstone beds. Siltstones contain abundant storm-depositional indicators: tool-marked soles, gutter casts, mud-filled scours, hummocky lamination, and hummocky bedforms. The proximal facies represents deposition in an energetic, storm-wave-swept environment and consists of amalgamated sets of thick-bedded, fine- to coarse-grained skeletal grainstones and packstones with low-angle cross-lamination, megaripples, and shale lithoclasts. Sedimentary structures and paleocurrent patterns from both facies record deposition under a combined flow regime with the unidirectional current vector oriented in the offshore direction. Cycles are laterally continuous across the 35 km by 32 km study area. Cycle boundaries (flooding surfaces) are parallel to a unique storm-generated marker bed, implying that these surfaces are effective time lines. Their widespread character and relatively deep subtidal-facies assemblage argues against autocyclic processes in cycle formation. We propose that the alternation of proximal and distal facies was tied to fluctuations in storm-wave base driven by short-term glacio-eustasy. Three scales or orders of sedimentary cyclicity are recognized in the study area. Meter-scale bedding cycles are considered fifth-order parasequences (20-100 Ka duration) and stack into genetically related parasequence sets. These fourth-order units have been previously described as member-scale lithostratigraphic tongues. Analysis of Fischer plots suggest that cycle thickness and subfacies composition was controlled by both accommodation and siliciclastic sediment supply. These higher-order stratal units are super-imposed onto the highstand portion of the Kope to Bellevue depositional sequence and give insight into the high-frequency controls on the progradation of the ramp complex.

Dispersal Centers of Paleozoic and Later Clastics of the Upper Mississippi Valley and Adjacent Areas

Three major dispersal centers of the Paleozoic, Cretaceous, and Tertiary elastics of the upper Mississippi Valley and adjacent areas were located through integrated study of petrography, directional structures, facies maps, and regional stratigraphic relations. In pre-Mississippian time, nearly all the elastics originally were derived from the Precambrian rocks centered around the Lake Superior region of the Canadian Shield. Relatively modest streams supplied sands and muds and recycling on a stable craton produced mature and supermature sandstones. The second and third major dispersal centers resulted from Appalachian orogenic activity. Although some contributions from the Lake Superior region and Canadian Shield continued, the tectonic borderlands of the northern Appalachian mountains were the chief dispersal center of Mississippian and Pennsylvanian elastics. In post-Pennsylvanian time, this center shifted to the east of the southern Appalachian mountains. The post-Devonian clastic sediments were transported to the shallow marine shelves, coastal plains, and small deltas of the craton by a series of large, recurring drainage systems. Despite major shifts in dispersal centers, the slope of the craton in the upper Mississippi Valley and adjacent areas has persisted to the south and southwest throughout Paleozoic, Mesozoic, and Tertiary time. Inherent in the foregoing regional results are some problems of general interest. These include sedimentary differentiation, intrastratal solution, and the relationships between paleoslope, regional unconformities, and cross-bedding directions.

Hierarchical Levels of Heterogeneity in a Mississippi River Meander Belt and Application to Reservoir Systems: Geologic Note (1)

Six hierarchical levels of sand heterogeneity that would be present in analogous reservoirs are recognized in a Mississippi River meander-belt system in southeastern Missouri: (1) meander belt, (2) meander scroll, (3) channel, point bar, and splay, (4) lobe sheet, (5) bedding unit, and (6) laminae. Heterogeneity level 1 is similar in size to an oil field and consists of (1) 9 million ac-ft (11.1 billion m{3}) of high-permeability channel sands in numerous meander scrolls and (2) 4 million ac-ft (4.9 billion m{3}) of low-permeability clay plugs (in numerous abandoned channels) that separate a field into isolated pools and reservoirs. Overbank flood-plain muds capping the meander-belt system are barriers to vertical migration of fluids. Heterogeneity level 2 is the size of pools within a field and has 1.2 million ac-ft (1.5 billion m{3}) of highly permeable, laterally accreted channel and point-bar sands, partly or wholly isolated from other sand bodies by low-permeability, abandoned-channel clay plugs. Abandoned mud-filled chutes impede lateral migration of fluids in the upper pa ts of the meander scroll. The third level of heterogeneity is composed of about 70,000 ac-ft (86.3 million m{3}) of individual, permeable channel, point-bar, and crevasse-splay sand bodies, with numerous thin sheets and lenses of low-permeability muds and silts (derived from chute fill and mud drapes) that impede vertical migration of fluids. Heterogeneity level 4 is the lobe sheet unit (reservoir pay zone about 450 ac-ft or 555,000 m{3} in volume) comprising channel, point-bar, and splay sand bodies. The fifth level of heterogeneity is the single bedding unit (about 10 ac-ft or 12,000 m{3}) at the scale of a reservoir flow unit or perforated interval. Permeable, cross-bedded sand bundles are separated by low-permeability, inclined and horizontal mud-silt layers and lenses present along bed-set boundaries. Heterogeneity level 6 is individual sand laminae (grain-flow lenses or grain-fall sheets) separated by textural variations (and hence permeability-porosity variations) and isolated mud-silt laminae. Permeabilities range from 90-160 d in sand; several millidarcys to 50 d in muddy sand, silt, and sandy silt beds from the levee, crevasse, and abandoned-channel fill; and less than 10 md in muddy silts and muds from abandoned-channel and chute-fill mud sheets and laminae. At all levels within a fluvial meander-belt system, these permeability heterogeneities are the principal controls on productivity throughout the life of a reservoir.

Blade-Shaped Crustacean Burrows of Eocene Age: A Composite Form of Ophiomorpha

The trace fossil, Ophiomorpha nodosa Lundgren, reported in rocks from Pleistocene to Cretaceous in age, is considered by a number of workers to be a burrow analogous to that constructed by the decapod crustaceans (callianassids) found in Holocene marine sands of the littoral zone. In a road outcrop 48.1 mi south of Starkville, Mississippi, well-preserved, cemented, typical Ophiomorpha nodosa and Ophiomorpha-like burrows were found in fine-to coarse-grained, cross-bedded, nonlithified sand of Eocene age. The burrows consist of (1) individual nodose cylindrical forms, 15 to 25 mm in diameter and as much as 1 m in length, oriented normal to and parallel with bedding and (2) morphologically similar vertically oriented compound blade-shaped forms with the long axes horizontal. X-radiographs of serial sections show that the blade forms consist of distinct burrow tubes stacked in a vertical array. Burrow remnants appear as Spreiten in vertical section and suggest that the organism worked upward through the sediment, constructing “permanent” domiciles. Petrographic studies of thin sections and bulk mineral analyses by x-ray diffraction show that the burrow cement, the dwelling burrow lining, and the burrow filling consist of opaline silica. As the enclosing sediment contains no opaline silica matrix and only the burrows are cemented, the burrow-building organisms could have extracted silica from the silica-rich waters of the littoral environment and concentrated it in their burrows Blade-like burrow composites of this general type have been described as Teichichnus. However, the tubular and nodose character of the outer wall, the presence of burrow linings, the abnormal abundance of opaline silica matrix, the occurrence of sand-grain aggregates (pellets) throughout the burrow walls, the presence of burrows that range in form from simple tube to multiple-stacked blade forms, and the morphological similarity to and connection with individual cylindrical Ophiomorpha burrows, all strongly suggest that the two types of burrows were constructed by the same organism. The informal name Ophiomorpha nodosa var. spatha is suggested for this blade-shaped burrow.

Petrology of the Permian Yellow Sands of northeastern England and their North Sea Basin equivalents

Abstract The Permian Yellow Sands of northeastern England and the Permian Weissliegendes of the English North Sea Basin are petrologically defined as multicycle, moderately sorted, subrounded graywackes, subgraywackes and subarkoses with post-depositionally etched and overgrown grains. These sandstones were derived by the marine reworking of the Permian Rotliegendes and transported from the east to the southwest. Petrologic data show that these Upper Permian sandstones were deposited in a shallow marine environment and that the commonly held aeolian dune interpretation for them should be rejected. Their formation during the transgression of the Zechstein Sea places them within the Zechstein sequence and therefore they are Thuringian in age rather than Saxonian.

Biogenic directional features on several recent point-bars

Abstract Fresh-water pelecypods and gastropods are distributed on Recent point-bars of the Wabash River in western Indiana and the Whitewater River in western Ohio with the larger species and individuals at the upper, coarse sediment ends of the bars and the smaller species and individuals at the lower, fine sediment ends of the bars. Molluscs trapped in the back-bar slough areas during and after floods make random patterned trails and burrows; and the molluscs on the bar-foreshore migrate down-slope with the shore line, leaving straight, long trails oriented at right angles to the shore line. On the foreshore, burrows and articulated shells are oriented downslope toward the Thalweg. These products of biogenic origin have a potential use as paleogeographic indicators of point-bar orientation and meander migration direction in ancient river sediments.

Cretaceous-Tertiary Clay Mineralogy of the Upper Mississippi Embayment

ABSTRACT An integrated stratigraphic, paleontologic, and petrologic study shows the presence of three general environments of deposition for the Cretaceous and Tertiary sediments of the Upper Mississippi Embayment: (1) fluviatile, (2) inner neritic, and (3) outer neritic. Prior petrologic studies have shown similar provenance features for all stratigraphic units involved. X-ray diffraction analyses of 199 clay samples from the three environments and from all the stratigraphic units studied show kaolinite, illite, and montmorillonite as the dominant clay minerals, with small amounts of mixed-lattice and chloritic materials in a few samples. There are three clay mineral assemblages--one dominantly kaolinite, a second dominantly montmorillonite, and a third having nearly equal amounts of kaolinite, illite, and montmorillonite. The clays of the Eocene (undifferentiated) formations and of the Cretaceous McNairy and Tuscaloosa Formations and the northern part of the Coffee Formation are dominantly kaolinite; those of the Porters Creek, Clayton, and Owl Creek Formations and the Southern part of the Selma Formation are dominantly montmorillonite; and those of the Coon Creek Formation, the northern part of the Selma Formation, and the southern part of the Coffee Formation are kaolinite, illite, and montmorillonite in nearly equal amounts. Clays deposited in the fluviatile environment are dominantly kaolinite, those in the outer neritic environment are dominantly montmorillonite, and those in the inner neritic environments are composed of nearly equal amounts of kaolinite, illite, and montmorillonite. Segregation of clay minerals in the depositional environments is believed responsible for these variations in clay mineralogy. Diagenesis and variations in contributions from the source area are believed to be insignificant factors.

Large-Scale Cross-Stratification in the St. Peter Sandstone

Large-scale cross-stratification is present in the St. Peter Sandstone of southern Wisconsin. Sets of cross-bedding are as much as 35 ft thick and are made up of thick master fore-set units which contain sets of smaller scale, internal cross-stratification. The master fore-set units occur as two types of cross-stratification: convex upward, planar and convex downward, tangential. Both the large-scale master fore-set bedding and the small-scale internal fore-set bedding dip toward the southwest, parallel to the regional paleocurrent pattern. The large-scale cross-stratification in the St. Peter Sandstone is the result of internal structures developed in large migrating sand waves, dunes, banks, or ridges.