摘要:

SUMMARYEleven facies of the (Lower Westphalian) Abbotsham Formation and upper portion of the Northam Formation of north Devon are described: black mudstone, silty mudstone, “turbidite”, silty streak, sandy streak, three kinds of oscillatory beds, cross‐stratified sandstones and mudstones, fining‐upwards units and major sandstones. Their relationships to each other are determined and they are shown to recur in a cyclic pattern.Six cycles are distinguished in the 1,200 ft. of the Abbotsham Formation. Each passes upwards gradually from black mudstone into coarser beds, the top of which is sharply separated from the black mudstone of the succeeding cycle.We suggest that the environment of deposition of these cycles ranges from a moderately deep basin, in which mudstones and occasional turbidites were deposited, through the sediments of an advancing coastline, fronted by deltas, to coastal plains in which fluviatile sediments were la

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1965.tb01282.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

SUMMARYVertical walls in quarries of Famennian sandstones near Aywaille (Belgian Ardennes) show in abundance varied sedimentary structures. The most interesting are undoubtedly erosional effects on a few islets (or promontories) of a former sandstone layer that are bordered in several places by microcliffs. Rounded and sub‐circular “wash‐loaves” accompanied by smaller and less regular masses occur near and outside of these cliffs; these are so numerous at one place that they appear as a swarm. Both types are remnants of the islets; they sometimes stand as micro‐stacks, but are also sometimes dragged away some distance, as revealed by the inclined or even vertical laminae that some show in cross‐section. We think that the carving of the microcliffs does not denote an important contemporaneous consolidation of the bed, although its limestone content may have favored firmness. We assume that it is mostly a question of the amount of water in the wet sand. Other examples of microcliffs in ancient formations are known in the vicinity; the swarm of stacks and wash‐debris, on the other hand, seems an exception

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1965.tb01283.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

SUMMARYAn approximately 50 ft. stratigraphic section of the Lower Cretaceous Glen Rose Limestone was sampled at 24 separate localities in central Texas from the standpoint of reconstructing the depositional environment. Among these samples 199 representative specimens were selected and subjected to point‐count analyses, X‐ray analyses, and insoluble residue determinations. Statistical analysis of the accumulated data with an IBM 7090 computer yielded the following facies:Corbulafacies—characterized by a relative abundance of thick‐shelled ostracods, thin‐walled miliolid foraminifers, and the small pelecypodCorbula martinae;steinkern facies—characterized by large mollusc steinkerns, cellular mollusc shells and the foraminiferOrbitolina;mudstone facies—typified by less than 10% sand‐sized grains; and mixed particle facies—characterized by worn skeletal and nonskeletal carbonate grains. The mud‐stone facies subsequently was divided into two subfacies: (1) lime mudstones—characterized by delicate skeletal constituents and lime mud, and (2) marly mud‐stones—consisting of a mixture of lime mud and terrigenous clay‐sized material. Similarly the mixed particle facies was divided into four subfacies: skeletal calcarenites—characterized by sand‐sized skeletal debris; skeletal wackestones—consisting of sand‐sized skeletal particles floating in a mud matrix; nonskeletal calcarenites—characterized by nonskeletal carbonate grains; and nonskeletal wackestones—consisting of nonskeletal carbonate grains floating in a mud matrix. In addition limey sandstone, dolomite, and stromatolite facies were distinguished on the basis of relatively obvious textures and compositions.The attributes of these facies as evidenced by the 199 statistically analyzed specimens were then used to assign each of the additional samples (350) to a particular facies and to identify the distribution of these facies in the field. A reconstruction of the depositional environment was made for each facies, and the following depositional history was interpreted from the resulting facies pattern.The lowermost beds of the unit, consisting largely of stromatolites and nonskeletal calcarenites, are interpreted as representing deposition in very shallow, probably intertidal, waters, Following the deposition of

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1965.tb01284.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

SUMMARYA Lower Devonian algal reef complex, with a basinal algal turbidite facies, offers excellently preserved autochthonous and allochthonous algal textures and structures of the following types: algal calcilutite biolithites of dense, grumous, cellular, tubular, “pelletoid” and “granuloid” textures, algal calcilutite crusts and algal‐bound detritus (e.g., stromatolites), algal pisolites, oolites and circumcrusts, algal pellets and grains (in contrast to faecal and bahamite types), colonial and stem fragments, algal filaments and cells, stromatactis and birdseyes. Encrusting Foraminifera and stromatoporoid colonies were of very subordinate importance in forming the turbulent‐water reefs. Protected pools, crevices, and local lagoons offered a favourable niche for calm‐water Codiaceae, crinoids, polyzoans,Amphiporaand some molluscs. Corals occur rarely.The wave‐resistant calcilutite reefs as well as the high percentage of subsequently introduced fine “internal sediments” within the limestone‐frameworks, indicate that grain‐matrix‐cement ratios do not necessarily reflect degree of turbulence and winnowing.The algal reefs have no effective primary porosity. Channels and cavities, predominantly horizontally oriented, were filled with internal sediments and early‐formed sparite cement.Fibrous calcite cement is confined to limestones that seem to have formed in a littoral environment whereas granular sparite appears to be an intra‐str

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1965.tb01285.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1965.tb01286.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY