Stratigraphy and Primary Sedimentary Structures of Fine-grained, Well-bedded Strata, Inferred Lake Deposits, Upper Triassic, Central and Southern Connecticut

1968 ◽  
pp. 265-306 ◽  
Author(s):  
John E. Sanders
Keyword(s):  
Upper Triassic ◽  
Fine Grained ◽  
Sedimentary Structures ◽  
Lake Deposits

scholarly journals Ice-rafting in lakes in the early Neoproterozoic: dropstones in the Diabaig Formation, Torridon Group, NW Scotland

2019 ◽  
Vol 56 (1) ◽  
pp. 47-53
Author(s):  
Adrian Hartley ◽  
Bartosz Kurjanski ◽  
Jessica Pugsley ◽  
Joseph Armstrong
Keyword(s):  
Lake Levels ◽  
Fine Grained ◽  
Lateral Distance ◽  
Ice Rafting ◽  
Lake Deposits ◽  
Early Neoproterozoic

A dropstone horizon is described from lake deposits in a palaeo-valley from the c. 1000 Ma Diabaig Formation, Torridon Group, NW Scotland. Dropstones occur in wave-rippled, fine-grained sandstones and siltstones that contain desiccation and syneresis cracks indicative of fluctuating lake levels. Five locally derived dropstones occur at the same horizon over lateral distance of 250 m and display clear evidence of deflection and penetration of laminae at the base, with thinning, onlap and draping of laminae on to clast margins and tops. Mechanisms of dropstone formation are discussed, with ice-rafting considered the most likely explanation. It is suggested that rafting was promoted by cold winters at 35° S in the early Neoproterozoic, possibly in an upland setting. Interpretation of the dropstones as ice-rafted debris provides the first physical record of evidence for ice at the Earth's surface during the late Mesoproterozoic to early Neoproterozoic.

Rise of the Erg—Paleontology and paleoenvironments of the Triassic-Jurassic transition in Northeastern Utah

2016 ◽  
Vol 3 ◽  
pp. 1-32
Author(s):  
Brooks Britt ◽  
Daniel Chure
Keyword(s):  
Biological Activity ◽  
Large Scale ◽  
Three Dimensional ◽  
Late Triassic ◽  
Theropod Dinosaur ◽  
Fine Grained ◽  
Chinle Formation ◽  
History Of ◽  
Lake Deposits ◽  
Lacustrine Deposit

This field trip focuses on the Late Triassic-Early Jurassic transition in northeastern Utah. This transition records one of the most striking terrestrial environmental transformations in the history of North America, wherein the fluvio-lacustrine Chinle Formation is transgressed by the vast erg system of the Nugget (Wingate+Navajo)/Navajo/Aztec Sandstones. Exposures in northeastern Utah are ideal for studying this transition as they are closely spaced and accessible. The uppermost Chinle Formation beds are lacustrine/fluvial fine-grained sediments which are overlain by increasingly drier, sandy, transitional beds. The non-eolian basal beds of the Nugget Sandstone preserve a Late Triassic ichnofauna, with some sites including Brachychirotherium tracks. Large-scale dune deposits comprise most of the Nugget Sandstone and contain vertebrate (Brasilichnium) tracks and a diverse invertebrate ichnofauna. Interdunal, carbonate, spring mounds, as much as 3 m tall, fed carbonate freshwater lake deposits containing gastropod body fossils and invertebrate ichnofossils. Another lacustrine deposit, located at the Saints & Sinners Quarry, is on the shoreline of a non-carbonate interdunal lake/oasis. Over 11,500 bones have been collected from the site and represent two theropod dinosaur taxa, sphenodonts, sphenosuchians, a pterosaur, and drepanosaurs (with many complete, three-dimensional, articulated skeletons). In addition to bones, dinosaur trackways are also preserved in shoreline and other interdunal beds. The fauna shows that this interdunal area of the Nugget Sandstone was the site of intense biological activity. The drepanosaurs are chronologically significant in that they are restricted globally to the Late Triassic, indicating that at least the lower one-fourth to one-third of the formation is Late Triassic in age.

Geochemical Archives in Lake Deposits

2003 ◽  
Author(s):  
Andrew S. Cohen
Keyword(s):  
Careful Consideration ◽  
Geochemical Data ◽  
Time Data ◽  
Fine Grained ◽  
Basin Morphometry ◽  
Information Filters ◽  
Chemical Inputs ◽  
Geochemical Profiles ◽  
Short Time ◽  
Lake Deposits

As we saw in chapter 4, the isotopic, elemental, or molecular constituents of a lake and its sediments reflect both external chemical inputs and the lake’s internal biogeochemical cycles. Lake sediment geochemistry is the product of interactions between these external inputs from watershed geology, groundwater, vegetation, and the airshed, and internal lake processes. Both external and internal inputs are heavily influenced by climate, and for the past few thousand years, human activities. With careful consideration of the various information filters affecting their records, geochemists can greatly broaden the scope of questions that can be addressed using paleolimnology. It is of critical importance when interpreting chemical data, that it be placed in the context of other sedimentological or paleontological archives. With modern, automated techniques, it is possible to amass large amounts of geochemical data in a relatively short time, data that can be compiled into deceptively ‘‘simple’’ geochemical profiles. Perhaps more than any other types of indicator, geochemical profiles are often interpreted as standalone records, without reference to petrographical, or even gross lithofacies information. Although it is tempting to read chemical stratigraphies as a direct record of inputs from a watershed or airshed, the signals are blurred by the whole host of messy, internal processes that we have already encountered in the hydroclimate filter: lag and residence time effects, reworking, particle and redox focusing, organismal uptake, and bioturbation. Lake deposits integrate local changes in source conditions, background sedimentation rates, and geochemical focusing processes (Engstrom and Swain, 1986). As a result, different locations within a lake may provide different geochemical histories, and interpretations of an integrated lake history must take into account these internal variations and their probable causes. This is always harder to do with paleolake deposits, where the original basin morphometry and hydrology is obscure. In this chapter we will also consider postdepositional information filters that affect geochemical archives, in particular bioturbation and diagenesis. Because many geochemical components of interest to paleolimnologists are bound to fine-grained particles, they can be readily mixed by bioturbation.

scholarly journals Controls of Depositional Environments on Reservoir Quality in Terms of Porosity and Permeability Gabo Field Niger Delta

2019 ◽  
Author(s):  
Richmond Ideozu ◽  
Tochukwu Nduaguibe
Keyword(s):  
Niger Delta ◽  
High Energy ◽  
Depositional Environments ◽  
Grain Size Analysis ◽  
Reservoir Quality ◽  
Fine Grained ◽  
Sedimentary Structures ◽  
Facies Associations ◽  
Porosity And Permeability ◽  
Distributary Channel

The controls of depositional environments on reservoir quality have been evaluated in terms of porosity and permeability of the Gabo Field, Niger Delta, Nigeria. Data used in this research include Well logs, Core data and photos, and grain size analysis for Wells 51 and 52 in the study area. Standard methods as applicable in petrophysical and sedimentological analysis has been adopted. Thirteen reservoir units have been identified in wells 51 and 52 which had 5 reservoirs cored each. The lithofacies units of the identified reservoirs across the study area, comprise pebbly sands, coarse -, medium -, fine- and very fine-grained sands, sandy mud, silty sands and heteroliths. The heteroliths – very fine-grained silty muds are highly bioturbated. Ophiomorpha and skolithos are the major trace fossils with sedimentary structures (ripple lamination, wavy lenticular and planar beds, cross bedded sands, coarsening and fining upward). The facies associations interpreted for the study area are Channel and Coastal barrier systems and the environment of deposition as distributary channel, upper and lower shoreface. The sedimentary processes that deposited facies ranged from high energy regimes, reworking by waves to low energy with periodic influx of silts and muds. The average porosity and permeability for reservoirs in Well 51 is 16.7% and 1317 Md, reservoirs in Well 52 is 28.2% and 2330Md whereas porosity range for the study area is 2% - 32% and permeability is 1.2 – 10600 Md. The reservoir quality reservoir of the sand units in Well 51 (7, 9 and 13) and Well 52 (5, 7, 9, 11 and 13) is excellent - good, this is because of the dynamics environments of deposition (upper shoreface and distributary channel) as well as the mechanisms that play out during deposition such as bioturbation, sorting, sedimentary structures formed. Whereas the poor quality across the reservoirs especially the lower shoreface and prodelta facies is as result of lack bioturbation, connectivity, multiplicity of burrows that may have been plugged by clay and intercalation of shale and sand (heteroliths). This research has shown that environments of deposition have direct influence the reservoir quality in terms of porosity and permeability.

Giant Upper Triassic bivalves of Wrangellia, Vancouver Island, Canada

2013 ◽  
Vol 50 (2) ◽  
pp. 142-147
Author(s):  
George D. Stanley ◽  
Thomas E. Yancey ◽  
Hannah M.E. Shepherd
Keyword(s):  
North America ◽  
Vancouver Island ◽  
Upper Triassic ◽  
Warm Water ◽  
Late Triassic ◽  
Fine Grained ◽  
Large Size ◽  
Wallowa Terrane ◽  
Volcanic Islands ◽  
First Time

One of the most distinctive components of the Late Triassic warm-water biota are alatoform, reclining bivalves of the genus Wallowaconcha. Wallowaconcha raylenea was first described from shallow-water, fine-grained Upper Triassic carbonate rocks of the Wallowa terrane, northeastern Oregon, and later found in coeval limestone in the Yukon. Fossils of the family Wallowaconchidae are easily recognized and readily distinguished from other fossil groups by their large size (over a metre in length), alatoform morphology, and especially the chambered wing-like extensions likely associated with photosymbiosis. Several different taxa of Norian age inhabited lagoon and reef-related settings on four separate terranes of western North America (Antimonio terrane, Sonora, Mexico; Wallowa terrane, northeastern Oregon; Stikine terrane in the Yukon; Chulitna terrane of Alaska), which during Triassic time existed as volcanic islands in the eastern Panthalassa Ocean. Outside eastern Panthalassa in the eastern Tethys, two other species of Wallowaconcha come from distant localities in Asia and Arabia. We here report for the first time, in presumed Rhaetian limestone of the upper part of the Parson Bay Formation, Vancouver Island, newly discovered examples of Wallowaconcha. They are from Wrangellia and, based on size and shape of the chambers, are assignable to W. raylenea but unlike other examples they appear to be Rhaetian in age. This species of giant bivalve inhabited warm-water locales outboard of North America during the Late Triassic, and its presence provides possible paleobiogeographic links of Wrangellia with both Stikinia and the Wallowa terrane.

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