This thesis examines the changes in the microstructure of clays and mudrocks due to the influence of the environment of deposition and subsequent compaction. A sedimentary model is proposed in which the development of fissility in shales and the formation of hydrocarbon source rocks are attributed to the chemical conditions at the time of deposition. The geotechnical properties of fresh sediments are considered and the ability of the depositional environment to affect these properties is assessed. From a SEM analysis of mudrocks it is shown that there is a correlation between microstructure and the conditions at the time of deposition. organic-rich shales formed in anoxic environments are characterized by a preferred orientation of microstructure. Mudrocks formed under oxic conditions show a random orientation. This characteristic fabric of shales results from the peptizing capability of certain organic compounds in the environment of deposition and is considered to be a contributing factor to the development of fissility. A laboratory simulation of the depositional environment is described. Test results show that pure clays sedimented with organic compounds in a marine environment exhibit an increased parallelism of particles compared with those without organic compounds. A mechanism is described whereby the organic compounds are adsorbed onto the clay particle surfaces and promote peptization. The fabric of sediments obtained under laboratory conditions is found to control the rate of consolidation. Clays with a preferred particle orientation have slower rates of water loss and this is suggested to be an important factor with respect to the formation of under-compacted mud rocks. Statistical methods applied to the analysis of directional data obtained from SEM micrographs are reviewed and a measure for the anisotropy index of mudrock microstructure is proposed.

One-dimensional swelling tests were conducted on seven undisturbed and remoulded heavily-overconsolidated clays and indurated mudstones. The samples cover a wide range of properties in terms of geological age, mineralogy, plasticity and diagenetic bonds. It is found that swelling proceeds faster than is predicted by Terzaghi's theory of swelling at low overconsolidation ratios (OCR), but it is slower at high OCR values, probably due to the prominence of secondary swelling. The results show that swelling is of a progressive nature, regardless of plasticity and diagenetic bonds. The coefficient of swelling decreases and the ratio of secondary to primary swelling increases with increasing OCR. At high OCR's, the former drops by more than an order of magnitude below the coefficient of consolidation; the latter can be as high as 0.6 within a log-cycle of time. Progressive softening and failure phenomena in mudrocks are considered to be due to the combined effects of progressive swelling and breakdown of diagenetic bonds. Swelling pressure is found to be indicative of in situ stress conditions. The average swelling index generally increases with pre-consolidation pressure in remoulded samples. Three types of diagenetic bonds are postulated: carbonate cements, viscous-adsorbed-water-type, and mechanical adhesion. Bonds tend to decrease the swelling index and so increase the coefficient of swelling. The fabric of the samples is far different from that assumed in the double-layer theory, which can qualitatively predict the physico-chemical forces involved in swelling. Dead volume, in which the double-layer force cannot operate, is shown to be large. The results of tests using n-decane as pore fluid to suppress osmotic swelling indicates that mechanical swelling is more than 50 to 60 per cent of total swelling in the samples. Both mechanical and total swelling indices are linearly correlated with liquid limit among remoulded samples, except for the Fuller's Earth clay which contains at least 65 per cent smectite (expandable clay).

Carbon and oxygen stable isotope analyses have been performed on well preserved calcareous fossils from Callovian, Oxfordian and Kimmeridgian (Jurassic) mudrock facies of Britain. Assemblages of ammonites, bivalves and belemnites have been sampled from the Lower Oxford Clay of the English Midlands, the Kimmeridge Clay of Wiltshire and the Dorset coast, and the Staffin Shale Formation of Skye. In this way it was hoped to cover a wide stratigraphic and geographic range. Carbon isotope stratigraphy reveals a positive excursion in the Callovian, which is interpreted as an oceanic anoxic event. On the basis of palaeontological and sedimentological evidence, the Callovian has long been viewed as a time of oxygen deficiency. These views are supported by this, the first detailed isotopic study of the stage. A comparison of the 613 C values of the ammonites and infaunal bivalves reveals a major anomaly, in that the latter show very positive values. Tentative suggestions are put forward to account for this. Oxygen isotope (and hence palaeotemperature) stratigraphy reveals a cooling through the Upper Callovian and Oxfordian, consistant with the "Boreal spread" of Arkell (1956), with a warming into the Lower Kimmeridgian. Palaeotemperature variations within individual assemblages raise important questions about palaeoecology. On the basis of this data, it appears that bivalves previously considered to be nekto - or pseudoplanktonic did not occupy the upper reaches of the water column. Suggestions have been made that ammonites were benthic rather than nektonic, but the evidence presented here implies that this was not the case. Relative to the rest of the assemblage, belemnite temperatures tend to be low, highlighting their migratory nature. Boreal ammonites are found to precipitate their shells in cooler waters than those from the Tethyan Realm. The significance of this, and other factors, in terms of controls on provinciality are discussed.

The Giles Creek and upper Chandler formations crop out in the northeastern Amadeus Basin from the north flank of Ross River syncline south to the Pillar Range, and from the nose of Ooraminna anticline east to the Simpson Desert. 'Twenty-four sections of the Giles Creek and nineteen sections of the upper Chandler were measured by the author in this area. The Giles Creek lies disconformably above the upper Chandler Formation and conformably below the Shannon Formation. The upper Chandler is conformably underlain by the lower Chandler throughout the area except at Ross River Gorge and Wallaby No. 1 well. There the upper Chandler overlies the Todd River Dolomite. The Giles Creek and upper Chandler consist of interbedded carbonates, terrigenous-rich carbonates, and mudrocks. Terrigenous-rich carbonates and mudrocks comprise over half of the volume of the Giles Creek at most locations in the area. Lime mudstones and cryptalgalaminated boundstones with dorral stromatolites are common in the Giles Creek. The Phillipson and Northern Facies of the Giles Creek are locally fossiliferous at the base. Ooids are present at the top of the Southern and Phillipson Facies of the Giles Creek at most locations. Anhydrite is present in the carbonates and mudrocks of the Giles Creek at Dingo No. 1 and Wallaby No. 1 wells. Gypsum is present in dolostones of the Giles Creek at Wallaby No. 1 well. Oncolite grainstones and boundstones, crystalgalaminated boundstones, and birdseye-rich lime mudstones are common in the upper Chandler. The mudrocks of the Giles Creek and upper Chandler are composed of quartz, K-feldspar, illite, muscovite, biotite, kaolinite, smectite, plagioclase, and anhydrite, with minor amounts of limonite, hematite, vermiculite, chlorite, and zircon. Calcite and dolamite cement the mudrocks. Acid-insoluble residues of the carbonates are comprised of the above noncarbonate minerals, organic matter, pyrophyllite, and witherite. The size and amount of terrigenous material in the Giles Creek increases to the west-southwest, which indicates that the terrigenous sediments were derived from a source area in that direction. Sediments of the Giles Creek and upper Chandler were dolomitized by seepage-reflux of a hypersaline brine. Lateral and vertical variations in the amount of dolanite are inversely related to the amount of terrigenous material, and indicate that permeability of the sediments was a controlling factor in the distribution of dolomite in the Giles Creek. Sediments of the Giles Creek and upper Chandler accumulated on shoals, in shoal-margin lagoons, on tidal flats, and in intracoastal lagoons. Shallow, open-shelf deposits are also present at the base of the Giles Creek at Ross River Gorge. Cyclicity in the sediments of the Giles Creek was caused by lateral shifts in the position of the tidal flats and intracoastal lagoons during continual subsidence of the basin. Both the Giles Creek and upper Chandler -were deposited during major regressions of the sea. Lateral relations of lithofacies in the Giles Creek indicate that the area was bounded by deeper water to the north and south during the Middle Cambrian. Differential subsidence of the basin resulted in deposition of greater thicknesses of Giles Creek sediments in the Phillipson Pound and Ross River-Fergusson syncline areas. Differential subsidence in the Phillipson Pound area was partially offset by salt-induced growth of Ooraminna, Tood River-Windmill, Brumby, and Teresa anticlines. Facies relations and lateral variations in thickness of the Giles Creek suggest that the amount of offset on the Rodinga and Carrel Flat faults is minor, perhaps on the order of 1 to 2 kilometers at most. Initial carbonate sediments of the Giles Creek and upper Chandler were altered by syngenetic inversion of aragonite to calcite, recrystallization of calcite, precipitation of pyrite, and replacer-rent of calcite by dolomite; anagenetic silicification, compaction, and fracturing; and epigenetic oxidation, precipitation of calcite, dedolomitization, and silicification. Post-depositional changes in the terrigenous sediments include syngenetic oxidation, alteration of clay minerals, precipitation of silica, and dolomitization.

The Arumbera Sandstone consists of mappable informal units which are repeated in a vertical, cyclic succession. Sandstones of fluvial origin form resistant strike ridges separated by strike valleys, which consist of recessive sandstones and mudrocks of marine origin. Lithofacies 1a, 2b, and 3a are probably of marine origin in intertidal environments. Trace fossil assemblages in lithofacies 3a suggest Skolithos and Cruziana inchnofacies were present. Lithofacies 1e, 2a, 2c, 3b, and 4a are probably of fluvial origin, as the result of coalescing braided stream deposits. The Arumbera Sandstone probably was deposited in a deltaic environment characterized by low wave energy, a micro tidal range, and high input of sand-sized sediment br braided streams. In the western MacDonnell Ranges, the Arumbera overlies the Julie or Pertatataka formations along a sharp but conformable contact. The present upper contact is a low-angle regional unconformity which contains paleotopographic elements that resemble pediments, stripped structural plains, and steep erosional scarps. These paleotopographic surfaces are overlain from east to west by the Chandler, hugh River, and Cleland formations in an onlap relationship. The Arumbera Sandstone is considered part of a molasse sequence associated with the Late Proterozoic and Early Cambrian Petermann Ranges orogeny, which occurred along the present southern and southwestern margin of the Amadeus Basin. The uplifted Petermann Ranges shed detritus from metamorphic, sedimentary, and minor amounts of plutonic rocks. Paleocurrents suggest most terrigenous material was derived from the southwestern margin of the basin. The composition of detrital grains and lack of weathering features in labile detrital grains suggest a hot, semiarid to arid climate in the source area and in the basin of deposition. Sandstone samples examined petrographically primarily are subphyllarenites, subarkoses, arkoses, feldspathic litharenites, and lithic arkoses. The inferred paragenetic sequence is: Eogenetic: (1) mechanical compaction, (2) "dust rims" of hematite, illite, and chlorite, and (3) hematite cement; Mesogenetic: (4) syntaxial feldspar overgrowths, (5) syntaxial quartz overgrowths, (6) hematite cement, (7) carbonate cement, (8) kaolinite replacement, (9) formation of secondary porosity; Telogenetic: (10) chert cement and (11) gibbsite or hematite cement.

Heightened industry focus on the Upper Cretaceous (Cenomanian-Turonian) Eagle Ford has resulted from recent discoveries of producible unconventional petroleum resource in this emerging play. However, little has been published on the facies and facies variabilities within this mixed carbonate-clastic mudrock system. This rock-based study is fundamental to understanding the controls, types, and scales of inherent facies variabilities, which have implications for enhanced comprehension of the Eagle Ford and other mixed carbonate-clastic mudrock systems worldwide. This study utilizes 8 cores and 2 outcrops with a total interval equaling 480 feet and is enhanced by synthesis of thin section, XRD, XRF, isotope, rock eval/TOC, and wireline log data. Central Texas Eagle Ford facies include 1) massive argillaceous mudrock, 2) massive argillaceous foraminiferal mudrock, 3) laminated argillaceous foraminiferal mudrock, 4) laminated foraminiferal wackestone, 5) cross-laminated foraminiferal packstone/grainstone, 6) massive bentonitic claystone, and 7) nodular foraminiferal packstone/grainstone. High degrees of facies variability are observed even at small scales (50 ft) within the Eagle Ford system and are characterized by pinching and swelling of units, lateral facies changes, truncations, and locally restricted units. Facies variability is attributed to erosional scouring, productivity blooms, bottom current reworking, and bioturbation. At the 10-mile well spacing scale and greater, the data significantly overestimates intra-formational facies continuity but is successful in defining the following four-fold stratigraphy: The basal Pepper Shale is an argillaceous, moderate TOC, high CGR and GR mudrock. The Waller Member is a newly designated name used in this study for an argillaceous and foraminiferal, high TOC, massive mudrock with a generally moderate CGR and GR profile. The Bouldin Member is a high energy, carbonate-rich (foraminiferal), low TOC, low and variable CGR but high GR zone. Finally, the South Bosque Formation is an argillaceous and foraminiferal, moderate TOC, massive and laminated mudrock with a moderate CGR and GR signature. GR logs alone are inadequate for determination of facies, TOC content, depositional environment, and sequence stratigraphic implications. Using integrated lithologic, isotopic, and wireline log data, cored wells in the study area are correlated across the San Marcos Arch. Geochemical proxies (enrichment in Mo, Mn, U, and V/Cr) indicate that maximum basin restriction occurred during deposition of the Bouldin Member. Bottom current activity influenced depositional processes and carbonate sediment input was driven by water column productivity. These primary controls on Eagle Ford stratigraphy and character are independent from eustatic fluctuation, rendering classical sequence stratigraphy unreliable. / text

Pre-vegetation alluvium is unique; at the present day, plants affect multiple aspects of river functioning and deposition and so those rivers that operated before the evolution of land plants largely lack modern sedimentological analogue. However, such rivers were the norm for the first 90% of Earth history and so a better understanding of their sedimentary product enables insight into both the fundamental underlying mechanisms of river behaviour and the ways in which fluvial processes operated on ancient Earth and other rocky planets. This study presents five original fieldwork based case studies and an analysis of a holistic database of all of Earth’s pre-vegetation alluvium. Together these research strands offer perspectives on the sedimentological characteristics and stratigraphic trends of pre-vegetation alluvium and the behaviour and functioning of pre-vegetation rivers. Results show that, in pre-vegetation alluvial settings: 1) a variety of fluvial styles are represented, but diminished in comparison with syn-vegetation alluvium; 2) ‘sheet-braided’ architectures are common but may record a variety of fluvial planforms; 3) meandering planforms were less frequent, particularly in small- to moderate-sized river systems; 4) mudrock is on average 1.4 orders of magnitude less common than it is in syn-vegetation alluvium; and 5) microbial matgrounds were present, but had negligible effect on preserved architecture and facies. This thesis demonstrates that whilst the physical laws governing fluvial fluid-sediment interaction have not changed, the theatre in which they operated irrevocably evolved with the greening of the continents.

The Yazoo Clay is a calcareous fossiliferous mudrock that outcrops in a northwest-southeast belt across much of Mississippi and in adjacent states. Based on over 240 X-ray diffraction analyses, the average composition of the Yazoo Clay is 28% smectite, 24% kaolinite, 22% quartz, 15% calcite, 8% illite, 2% feldspar, and 1% gypsum. Exposed Yazoo clay is weathered to a depth of 30-40 ft. and has a distinctive yellow/brown color; unweathered Yazoo is blue/gray. In most wells, smectite is more abundant in weathered clay than in unweathered clay. Mineralogic changes correlate well with engineering properties of the samples, which in general show a decrease in plasticity indices with depth. Weathered Yazoo clay exhibits greater mineralogic variability than unweathered clay. Mineralogical content also varies laterally. Lateral variation, along with correlative smectite content and engineering properties, is the reason for ?roller coaster? roadways and structural damage caused by the swelling Yazoo Clay.

No description available.