scholarly journals Measured stratigraphic section in the upper Schrader Bluff Formation (Late Campanian-Maastrichtian?), Ivishak River, Alaska

2021 ◽  
Author(s):  
D.L. LePain ◽  
M.A. Wartes ◽  
R.A. Kirkham ◽  
J.R. Mongrain
Keyword(s):  
Stratigraphic Section

The Antimonio Formation in Sonora, Mexico, and the Triassic – Jurassic boundary

1996 ◽  
Vol 33 (3) ◽  
pp. 418-428 ◽  
Author(s):  
Carlos M. González-León ◽  
David G. Taylor ◽  
George D. Stanley Jr
Keyword(s):  
System Boundary ◽  
Stratigraphic Section ◽  
Jurassic System ◽  
Bounded Below ◽  
Stratigraphic Succession ◽  
Regressive Events

The Antimonio Formation furnishes a record of sedimentation across the Triassic–Jurassic system boundary and is one of a few stratigraphic sections globally that preserves latest Triassic to Hettangian ammonoids in stratigraphic succession. The boundary falls near the middle of the formation, within a 155 m thick stratigraphic section, which is divided into five distinct sedimentary packages. The laminated shales and siltstones in the middle of package 4 represent deposition in an anoxic or disaerobic setting. Although shales of package 4 themselves are poorly fossiliferous, they are bounded below and above by Triassic and Jurassic biotas, respectively. The Triassic–Jurassic system boundary should fall within or stratigraphically close to the laminated beds. The transgressive–regressive signature from the Antimonio Formation corresponds closely to that of the Gabbs and Sunrise formations in Nevada and jointly shows eustatic regressive events at or near the beginning of the latest Triassic Crickmayi Zone and another near the top of the Hettangian. The beds from package 4 indicate a transgression closely associated with the Triassic–Jurassic system boundary.

Generation of a Synthetic Vertical Profile of a Fluvial Sandstone Body

1967 ◽  
Vol 7 (03) ◽  
pp. 243-251 ◽  
Author(s):  
Paul Edwin Potter ◽  
Robert F. Blakely
Keyword(s):  
Random Processes ◽  
Sand Wave ◽  
Ripple Mark ◽  
Stratigraphic Section ◽  
Depositional Processes ◽  
Sandstone Body ◽  
Depositional Process ◽  
Fluvial Sandstone ◽  
Synthetic Generation ◽  
Transition Procedure

Abstract Any stratigraphic section or bedding sequence can be synthesized if there is a transition procedure from one lithology or bedding type to another, and if thickness distributions of the different lithologies are known. Stratigraphic sections of a fluvial sandstone body were synthesized with five bedding types: cross-bedding, massive beds, parting lineation, ripple mark and mudstone. The transition procedure from one bedding type to another used dependent, Markovian random processes which have a memory that extends one step backward in the depositional process. As observed in nature, median grain size and sand wave thickness (cross-bedding and ripple mark) decline upward in the synthesized sections as proportions of the different bedding types change. Grain size and permeability were also incorporated into the sections. By changing the transition procedures, bed thickness distributions, rate of upward decline or sand wave height and length, different types of sections can be synthesized, thus making it possible to model many different sedimentation problems. Introduction This paper describes a general method for synthesizing stratigraphic sections and bedding sequences of sedimentary, metamorphic or igneous origin. Synthetic generation is of interest for several reasons. Close correspondence between real and synthetic sections suggest that the factors used in the synthesizing model may indeed be the correct ones, thus giving the investigator a check on his assumptions. Rapid, inexpensive simulation of many stratigraphic sections permits one to synthesize a rock body (sandstone or carbonate reservoir) or, on a larger scale, the fill of a sedimentary basin. Harbaugh gives an example of mathematical simulation of a carbonate basin. He simulated the basin in the hope that improved prediction would follow better understanding of the depositional processes. From the petroleum engineer's viewpoint it seems reasonable to believe that the synthetic generation of rock properties and their distribution in a reservoir should be relevant in the study of reservoirs. Any stratigraphic section or bedding sequence can be generated provided there is a transition procedure from one lithology or bedding type to another and provided the thickness distributions of the different units are known. The transition procedure involves random processes that are either independent or dependent. If the depositional process is independent, previous deposition will have no influence on present deposition. However, if it is dependent, past deposition will influence either present or future deposition. Such a dependent depositional process can be thought of as having a memory that extends backward in time through one or more pulses of deposition. A process with a memory can be described by a Markov process. Because the concept of memory or dependence appears to be in accord with our understanding of many depositional processes, Markov processes were used to synthesize the bedding sequences of this study (see Appendix). The above methods are perfectly general and are appropriate for any stratigraphic section or bedding sequence: bedding types in a beach deposit, an evolving carbonate bank or the changing lithologic fill of a thick geosyncline sequence. We chose to synthesize a vertical profile of a fluvial sandstone body because its characteristics were well documented, much was known about fluvial processes and fluvial-deltaic sandstone bodies constitute an important class of petroleum reservoirs. CHARACTERISTICS AND ORIGIN OF FLUVIAL CYCLE The fluvial cycle has been well documented in recent years by Bersier, Allen and Visher. Deposits from fluvial cycles range from 10 to 150 ft or more in thickness and are characterized by a "fining upwards": coarse sandstones with occasional conglomerates grade upward into medium- to fine-grained sandstone, and hence into siltstone and mudstone. SPEJ P. 243ˆ

scholarly journals Lithology and geochemistry of the Guadalupe Group base around Tunja, Boyacá, Colombia

2020 ◽  
pp. 35-65
Author(s):  
German Martínez Aparicio ◽  
Pedro Patarroyo ◽  
Roberto Terraza Melo
Keyword(s):  
Type Locality ◽  
Geochemical Analysis ◽  
Rock Samples ◽  
Stratigraphic Section ◽  
Intermediate Units ◽  
Lower Campanian

The base of the Guadalupe Group, in the Tunja area of Colombia, contains cherts, porcellanites, mudstones, and siltstones with subordinate quartz arenites. The lithostratigraphic description of two stratigraphic sections showed that the dominant facies have fine granular textures and siliceous compositions, which considerably differ from those of the prevailing sandy terrigenous facies described in the type locality in the Eastern Hills of Bogotá, in the Arenisca Dura Formation, the basal unit of the  Guadalupe Group in this sector. The units that form the Guadalupe Group (base of the Guadalupe Group, Plaeners, and Arenisca Tierna) markedly differ from each other morphologically, which facilitates their mapping because the base and top units generate a steep morphology, and the intermediate units form surface depressions or valleys, similar to the morphology of the Guadalupe Group in its type locality in the Eastern Hills of Bogotá. The base of the Guadalupe Group consists of cherts and porcellanites toward the NW of the study area (Alto del Gavilán section), with mudstones, siltstones, quartz arenites, and to a lesser extent porcellanites and cherts prevailing toward the SE (Vereda Salitre section). Geochemical analysis of total rock samples by XRD and XRF confirmed the primarily siliceous nature of the base of the Guadalupe Group, with SiO2 ranging from 62 to 98%, CaO less than 3.0%, and P2O5 peaking at 15.0%. Etayo-Serna (2015) conducted paleontological determinations of ammonites found in the stratigraphic section of Alto del Gavilán and assigned the base of the Guadalupe Group mainly to the Lower Campanian.

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