Abstract The development of the Frasnian (Upper Devonian) reef complexes of the southern Timan and Pechora region of northern European Russia is described. Barrier reef complexes progressively prograded eastwards during the Frasnian but the carbonate complexes were interrupted many times by regressive events. Using new conodont and ammonoid bio-stratigraphical dating, the timing of reef building episodes has been established which enables international correlation with other similar Devonian areas. Basinal anoxic and hypoxic deposits associated with the reef complexes of the Domanik facies provide the major hydrocarbon source rocks of the region and the palaeoenvironmental interpretation of these is discussed. Initial transgressions appear to have been associated with the global Taghanic Onlap of the late Givetian. The new level for the base of the Frasnian and Upper Devonian lies in the Timan Formation, after the deposition of which marine conditions mostly prevailed in the area examined until the late Frasnian when a sharp regression occurred with no evidence of the typical Kellwasser facies of Western Europe and other areas. Transgressive pulses initiated ammonoid biofacies in the Regional Sargaev Stage and the widespread Timan Event was marked by the spread of Timanites faunas. A significant deepening event which initiated the Domanik facies correlates approximately with the Middlesex black shale of New York and the main development of the Domanik facies with the Rhinestreet black shale of New York. There are faunal and floral peculiarities of the area, shown by endemic genera and rather different ranges of cosmopolitan species than elsewhere, which complicates precise international correlation. Nevertheless, several of the main sea-level deepening pulses of the Frasnian, documented in North America, Western Europe, North Africa and Australia, are recognizable and these are thought to represent eustatic events.

ABSTRACT More than 100 air-fall volcanic tephra beds are currently documented from Devonian strata in the eastern United States. These beds act as key sources of various geological data. These include within-basin to basin-to-basin correlation, globally useful geochronologic age dates, and a relatively detailed, if incomplete, record of Acadian–Neoacadian silicic volcanism. The tephras occur irregularly through the vertical Devonian succession, in clusters of several beds, or scattered as a few to single beds. In this contribution, their vertical and lateral distribution and recent radiometric dates are reviewed. Current unresolved issues include correlation of the classic Eifelian-age (lower Middle Devonian) Tioga tephras and dates related to the age of the Onondaga-Marcellus contact in the Appalachian Basin. Here, we used two approaches to examine the paleovolcanic record of Acadian–Neoacadian silicic magmatism and volcanism. Reexamination of volcanic phenocryst distribution maps from the Tioga tephras indicates not one but four or more volcanic sources along the orogen, between southeastern Pennsylvania and northern North Carolina. Finally, radiometric and relative ages of the sedimentary basin tephras are compared and contrasted with current radiometric ages of igneous rocks from New England. Despite data gaps and biases in both records, their comparisons provide insights into Devonian silicic igneous activity in the eastern United States, and into various issues of recognition, deposition, and preservation of tephras in the sedimentary rock record.

Abstract The Catskil! Delta Complex of western New York State contains fractured Upper Devonian black shales throughout a 300 km-transect from the more distal, somewhat shallower, deposits of the western region of the state eastward to more proximal and more deeply buried deposits. Each black shale unit grades upward into organically lean grey shale and abruptly overlies another grey shale unit. Within each black shale-grey shale sequence, ENE-trending vertical joints, interpreted to be hydraulic fractures, are best developed (i.e. more closely and uniformly spaced) in the organic-rich shale. Moreover, the density of ENE joints diminishes up-section through each black shale unit, as does the total organic carbon (TOC) content. While ENE joints are less well developed outside the black shale intervals, joints that formed during the Alleghanian orogeny (NW-trending) are found throughout the Upper Devonian shale sequence. Both sets are best developed in black shales in the distal delta sequence, whereas in more proximal deposits the Alleghanian joint sets are best developed in grey shales. Moreover, the density of ENE joints within each stratigraphie level of the black shale exceeds that of Alleghanian joints at the same level, except in the deepest black shale where Alleghanian joints are locally best developed at the top of the black shale interval. The preferential jointing of black shale units in the Appalachian Plateau reflects an extended hydrocarbon generation history. In the distal delta, hydrocarbon generation began when black shale was close to or at maximum burial depth (c. 2.3 km) during the Alleghanian orogeny with the propagation of a NW joint set and continued through post-Alleghanian uplift of the Appalachian Plateau when the ENE joints propagated. In the proximal delta deposits ENE joints propagated before the onset of Alleghanian deformation suggesting that the base of the Upper Devonian section was buried to thermal maturity by progradation of the Catskill Delta Complex before the advent of Alleghanian sedimentation.

Abstract Observations by transmission and scanning electron microscopy (TEM and SEM) of surficial sediment microfabric along with quantitative geochemical tests of organic matter from continental margin deposits reveal important fundamental interrelationships of material properties and processes during diagenesis of mud to shale. Fine-grained surficial muds possessing ≥2% total organic carbon (TOC) and ≥5% smectite commonly have very high porosities (≥90%), low wet bulk densities, and very low effective stresses that are consistent with minimal dewatering and consolidation in the upper few meters subbottom. These muds are characterized by random orientation of clay domains and marine organic material in the form of mucopolysaccharides and living microbiota that bridge between clay particles and aggregates and commonly appear to fill pore space in 2-D EM views. These fine-grained, organic-smectite-rich, clayey muds consolidate to very low porosities (≤30%) under relatively low overburden stress (∼1000 kPa or ∼120 m below the seafloor). In contrast, similar smectite-rich clayey muds possessing ∼0.5% TOC consolidate to approximately the same porosities but at loads of at least six times the overburden stress. In both cases, the microfabric observed by TEM and SEM following consolidation reveals a strong preferred clay particle orientation normal to the direction of the effective stress indicative of significant anisotropy in the permeability. Sandy clayey silts (62%-75% silt) that possess TOC contents of 1.3% to 4.2% consolidate remarkably different from the organic-rich clayey muds. The sandy clayey silts display porosities well above 38% at high consolidation stresses and show significant resistance to consolidation at high stresses probably due to grain-to-grain contact of the sand and large silt particles. Despite the exceptionally high depositional porosities of the sandy clayey silts, these muds, even those having high TOC, dewater significantly less under large consolidation stress compared to the organic-smectite-rich clayey sediments. A general correlation is found in the fine-grained sediment between the amount of smectite and the amount of organic material in the sediment. Studies have shown that smectite has a strong affinity for organic material and correlates well with water content, high porosities, and low wet bulk densities. Thus, the presence of organic material (≥2% TOC) largely controls the microfabric during early sediment diagenesis and has a significant impact on post depositional consolidation. The microfabric, mineralogy, and organic content of muds largely control the porosity and permeability of not only the sedimentary analogs of mudstone and shale but also largely determines the ultimate properties of the rocks in the geologic column. Noteworthy is that many highly fissile shales are rich in organic material. It is postulated that the presence of large amounts of organic material ( i.e ., ≥2% TOC) in sediments during consolidation and early diagenesis may ultimately affect the mechanical properties and response of the mudstones and shales during deep burial and tectonic stresses at passive and active margins and in epicontinental seas. The insoluble organic component of sedimentary rocks, kerogen, can be differentiated on the basis of the amount of hydrogen and carbon present in the material. The different types of kerogen influence not only the consolidation behavior but also may affect the development of fractures and migration pathways during continental margin evolution. Upon thermal maturation, some geochemical types of kerogen produce oil (types I and II), while type III produces natural gas. Kerogen of mainly terrestrial origin (type III) consists largely of negatively-charged polymers that inhibit adsorption of the organic matter onto negatively-charged clay mineral surfaces. Type I and II kerogen, which are of marine origin, are more readily adsorbed onto clay particles and can be expected to influence the development of geotechnical properties differently than kerogen of terrestrial origin. The kerogen types would be expected to behave differently in different stratigraphic sequences and perhaps even enhance fracture healing, retard stress fracturing, or conversely, promote fracturing during deformation. Thus, the clay microfabric, organic content, and isotropy/anisotropy of a mudrock or shale largely determines the stratigraphic formation functionally in terms of its role as either a petroleum source rock, reservoir seal, or migration pathway. Continental margin tectonic patterns result from regional stress fields imposed on stratigraphic sequences developed with different properties characteristic of the environments of deposition. The rock types developed and the productivity of the source rocks at depth appear to primarily depend upon the mineralogy, grain size distribution, organic material, microfabric, stress regime/depth of burial, and probably the differences in the material properties (porosity, permeability, strength, etc. ) of the sand, mudstone, and shale in the stratigraphic sequences.