Stratigraphy and sedimentology of the Hamill Group in the northern Selkirk Mountains, British Columbia: evidence for latest Proterozoic – Early Cambrian extensional tectonism

1989 ◽  
Vol 26 (3) ◽  
pp. 515-533 ◽  
Author(s):  
William J. Devlin
Keyword(s):  
British Columbia ◽  
Fault Scarp ◽  
Gravity Flow ◽  
Tectonic Activity ◽  
Turbidity Currents ◽  
Early Cambrian ◽  
Shallow Marine ◽  
Sedimentary Characteristics ◽  
Sediment Gravity Flow ◽  
Selkirk Mountains

Three informal stratigraphic divisions are recognized in the uppermost Proterozoic – Lower Cambrian Hamill Group in the northern Selkirk Mountains of British Columbia. These informal divisions include a lower sandstone unit, a greenstone–graded-sandstone unit, and an upper sandstone unit. Both the lower and upper sandstone units display sedimentary characteristics that are uniform along strike and indicate a shallow-marine environment of deposition. As is typical of other exposures of the Hamil Group in southeastern British Columbia, the lower sandstone unit is coarser grained and more poorly sorted than the mature quartz arenites of the upper sandstone unit.The greenstone–graded-sandstone unit is a complex assemblage of mafic metavolcanic rocks and associated sandstone facies. This unit is highly variable along strike but essentially consists of a thick succession of subaqueous extrusive rocks overlain by a variety of sediment gravity-flow deposits. These latter deposits include resedimented conglomerates, debris-flow deposits, and trubidites (deposited from both high- and low-density turbidity currents). Stratigraphic sections of this unit are described in detail from three different localities and are examined in terms of their transport and depositional mechanisms.The stratigraphic succession of the Hamill Group indicates that deposition of the shallow-marine sands of the lower sandstone unit was abruptly interrupted by a period of volcanism, the creation of a paleoslope, and the deposition of a large volume of sediment gravity-flow deposits of the greenstone–graded-sandstone unit. These relations are attributed to an episode of syndepositional normal faulting. The inferred fault(s) could have served as the conduit for the extrusion of the volcanics. Offset along the fault(s), the tilting of fault blocks, and the consequent formation of an unstable slope adjacent to a fault scarp created an environment favorable for deposition of the sediment gravity flows. In general, deposition of proximal, base-of-slope deposits was followed by an aggradational basin-fill phase of sedimentation. With the waning of tectonic activity and the filling of the fault-bounded basin, depositon of shallow-marine sands resumed (the upper sandstone unit). The stratigraphic relations of the Hamill Group in the northern Selkirk Mountains are considered direct evidence for an episode of latest Proterozoic – Early Cambrian extensional tectonism. The evidence for an episode of rift-related tectonism in the northern Selkirk Mountains supports inferences concerning the timing of this event as derived from tectonic subsidence analyses of post-rift strata of the Cordilleran miogeocline.

Gravity flows: Types, definitions, origins, identification markers, and problems

2020 ◽  
Vol 37 (2) ◽  
pp. 61-90
Author(s):  
Shanmugam G
Keyword(s):  
Debris Flow ◽  
Deep Water ◽  
Sediment Concentration ◽  
Gravity Flow ◽  
Turbidity Currents ◽  
Hyperpycnal Flows ◽  
Gravity Flows ◽  
Sediment Gravity Flow ◽  
Aeolian Dunes ◽  
C 50

Abstract This review covers 135 years of research on gravity flows since the first reporting of density plumes in the Lake Geneva, Switzerland, by Forel (1885). Six basic types of gravity flows have been identified in subaerial and suaqueous environments. They are: (1) hyperpycnal flows, (2) turbidity currents, (3) debris flows, (4) liquefied/fluidized flows, (5) grain flows, and (6) thermohaline contour currents. The first five types are flows in which the density is caused by sediment in the flow, whereas in the sixth type, the density is caused by variations in temperature and salinity. Although all six types originate initially as downslope gravity flows, only the first five types are truly downslope processes, whereas the sixth type eventually becomes an alongslope process. (1) Hyperpycnal flows are triggered by river floods in which density of incoming river water is greater than the basin water. These flows  are confined to proximity of the shoreline. They transport mud, and they do not transport sand into the deep sea. There are no sedimentological criteria yet to identify hyperpycnites in the ancient sedimentary record.  (2) A turbidity current is a sediment-gravity flow with Newtonian rheology  and turbulent state in which sediment is supported by flow turbulence and from which deposition occurs through suspension settling. Typical turbidity currents can function as truly turbulent suspensions only when their sediment concentration by volume is below 9% or C < 9%. This requirement firmly excludes the existence of 'high-density turbidity currents'. Turbidites are recognized by their distinct normal grading in deep-water deposits.  (3) A debris flow (C: 25-100%) is a sediment-gravity flow with plastic rheology and laminar state from which deposition occurs through freezing en masse. The terms debris flow and mass flow are used interchangeably. General characteristics of muddy and sandy debrites are floating clasts, planar clast fabric, inverse grading, etc.  Most sandy deep-water deposits are sandy debrites and they comprise important petroleum reservoirs worldwide. (4) A liquefied/fluidized low (>25%) is a sediment-gravity flow in which sediment is supported by upward-moving intergranular fluid. They are commonly triggered by seismicity. Water-escape structures, dish and pillar structures, and SSDS are common. (5) A grain flow (C: 50-100%) is a sediment-gravity flow in which grains are supported by dispersive pressure caused by grain collision. These flows are common on the slip face of aeolian dunes. Massive sand and inverse grading are potential identification markers.  (6) Thermohaline contour currents originate in the Antarctic region due to shelf freezing and  the related increase in the density of cold saline (i.e., thermohaline) water. Although they begin their journey as downslope gravity flows, they eventually flow alongslope as contour currents. Hybridites are deposits that result from intersection of downslope gravity flows and alongslope contour currents. Hybridites mimic the "Bouma Sequence" with traction structures (Tb and Tc). Facies models of hyperpycnites, turbidites, and contourites  are obsolete. Of the six types of density flows, hyperpycnal flows and their deposits are the least understood.

Early Cambrian and Older Trace Fossils from the Southern Cordillera of Canada

1972 ◽  
Vol 9 (1) ◽  
pp. 1-17 ◽  
Author(s):  
F. G. Young
Keyword(s):  
British Columbia ◽  
Marine Environment ◽  
Carbonate Rocks ◽  
Trace Fossils ◽  
Trace Fossil ◽  
Older Age ◽  
Early Cambrian ◽  
Shallow Marine ◽  
Sedimentary Environments ◽  
Organic Life

Metazoan trace fossils of Early Cambrian and older age have been found in parts of the Gog, Cariboo, and Miette Groups of eastern British Columbia and western Alberta. Most of them occur in beds immediately below the zones containing the earliest Cambrian trilobites and archaeocyathids. These beds represent a variety of sedimentary environments, including the beach and littoral (Skolithos – facies), and shallow marine (Cruziana – facies) environments in the upper McNaughton Formation of the Gog Group: and a moderately deep marine environment in the Midas Formation of the Cariboo Group. Below these zones evidence of organic life is mainly restricted to stromatolites in carbonate rocks, and simple feeding-burrows in argillaceous silt-stones. A rare, but important trace fossil in this zone is a doubly furrowed trail, which is herein named Didymaulichnus miettensis (gen. et sp. nov.). This fossil indicates that metazoans existed before the Cambrian Period by a span of time represented by the net deposition of up to 2000 m of detrital sediments.

Causes of varied sediment gravity flow types on the Alsek Prodelta, northeast Gulf of Alaska

1988 ◽  
Vol 7 (4) ◽  
pp. 317-342 ◽  
Author(s):  
William C. Schwab ◽  
Homa J. Lee ◽  
Bruce F. Molnia
Keyword(s):  
Gulf Of Alaska ◽  
Gravity Flow ◽  
Sediment Gravity Flow

Slumping and a sandbar deposit at the Cretaceous-Tertiary boundary in the El Tecolote section (northeastern Mexico): An impact-induced sediment gravity flow

Geology ◽  
2001 ◽  
Vol 29 (3) ◽  
pp. 231 ◽  
Author(s):  
Ana R. Soria ◽  
Carlos L. Liesa ◽  
Maria Pilar Mata ◽  
José A. Arz ◽  
Laia Alegret ◽  
...  
Keyword(s):  
Gravity Flow ◽  
Sediment Gravity Flow ◽  
Northeastern Mexico

scholarly journals Age and paleoenvironment of the Nukhul Formation, Gulf of Suez, Egypt: Insights from palynology, palynofacies and organic geochemistry

GeoArabia ◽  
2013 ◽  
Vol 18 (4) ◽  
pp. 137-174
Author(s):  
Haytham El Atfy ◽  
Rainer Brocke ◽  
Dieter Uhl
Keyword(s):  
Nile Delta ◽  
Organic Geochemistry ◽  
Regional Scale ◽  
Tectonic Activity ◽  
Gulf Of Suez ◽  
Spores And Pollen ◽  
Shallow Marine ◽  
History Of ◽  
Geochemical Analyses ◽  
Rock Eval

ABSTRACT Palynological results of a detailed study carried out on 56 samples retrieved from two selected wells (GH 404-2A and SA-E6A) of the Hilal and Shoab Ali fields within the southern part of the Gulf of Suez, Egypt, are presented. This study is mainly focused on the poorly dated Nukhul Formation, for which very little information from palynology is available despite its importance from a petroleum viewpoint. The assemblages discovered in our study are moderately preserved and reveal a sparse but significant record of spores and pollen and dinoflagellates together with highly diverse fungi and algal taxa, e.g. Botryococcus and Pediastrum. A latest Oligocene–Early Miocene (Chattian–Aquitanian) age has been suggested for the Nukhul Formation, based on compiling palynostratigraphic and ecologic data obtained from palynomorphs that have previously been assumed to be representatives for this period on a regional scale. In addition, the Oligocene/Miocene Boundary (OMB) could be lithostratigraphically defined within the studied formation, most likely at the boundary between the lower Shoab Ali Member and upper Ghara Member. A fungal/algal ‘event’ within the interval from 11,370–11,430 ft in the GH 404-2A Well may be associated with a strong regressive phase. Such a regression was previously observed in the Nile Delta and other locations around the Red Sea province, and may be assigned to the global Mi-1 glaciation event at the OMB. However, not only glacial-driven eustacy but also tectonic activity related to the Gulf of Suez rifting may have contributed in forming such an event. Palynofacies investigations were carried out under both transmitted and fluorescence microscopy and the results were partly supplemented by existing organic geochemical analyses (GH 404-2A Well) involving Rock-Eval pyrolysis and total organic carbon (TOC) measurements. The analysis was used to interpret the depositional regime, paleoenvironment and thermal maturation history of the studied succession. These results support the temporary existence of shallow, pond- or lake-like aquatic habitats during deposition of the lower Shoab Ali Member that evolved into a shallow-marine environment with the onset of the deposition of upper Ghara Member of the Nukhul Formation.

Multi-scale influence of topography on shallow-marine successions associated with long-term transgressions

2021 ◽  
Author(s):  
Miquel Poyatos-Moré ◽  
Ernesto Schwarz ◽  
Salvador Boya ◽  
Luz Elena Gomis-Cartesio ◽  
Ivar Midtkandal
Keyword(s):  
Regional Scale ◽  
Coarse Grained ◽  
Continuous Exposure ◽  
Entire Study ◽  
Shallow Marine ◽  
Sedimentary Characteristics ◽  
Multi Scale ◽  
Depositional Processes ◽  
Mouth Bars

&lt;p&gt;Thick shallow-marine successions associated with long-term transgressions are less well known than their thin, well-sorted counterparts, widely studied due to their potential to form good reservoirs. In these successions, particularly in storm-dominated examples, bioturbation can obliterate primary sedimentary characteristics, making stacking patterns and sequences difficult to define, and challenging our understanding of the main controls in their resulting depositional architecture. This study presents an example from the Jurassic of the Neuqu&amp;#233;n Basin (Argentina), with the aim to: a) refine the depositional model of a thick, shallow-marine succession associated with a long-term, early post-rift transgression, b) constrain multi-scale controls on stratigraphic architecture and lateral facies variability, and c) discuss their preservation and response to post-depositional processes. To do this, a &lt;300 m-thick succession has been studied along a &gt;10 km continuous exposure, with mapping, sedimentary logging and correlation of stratigraphic units, integrated with subsurface, biostratigraphic and ichnological data. The succession shows an overall retrogradational-aggradational-retrogradational stacking pattern, with several higher frequency regressive units (parasequences and parasequence sets, PSS). The lower part (PSS I) comprises laterally-discontinuous (10's of m) mouth-bars and distributary channel fills, dominated by several m-thick coarsening- and fining-up sandstone packages and m-scale erosive conglomeratic lenses. Above these, the succession (PSS II-IV) is composed by laterally-continuous (&gt;100's of m) storm-dominated lower-shoreface to upper-offshore deposits, dominated by &lt;1m-thick fine-grained and highly bioturbated tabular muddy sandstones and sandy mudstones, with rarely-preserved HCS and bioclastic-rich limestones; their internal characteristics and bed boundaries are diffuse due to pervasive bioturbation, suggesting overall low sedimentation rates and recurrent periods of colonization. The coarse-grained nature and lithology of the mouth bars and channel fills in the lower succession (PSS I) are consistent with a proximal sediment source, associated with erosion of intra-basinal highs. Its variable thickness, lateral distribution and onlap against underlying syn-rift deposits demonstrates partial infill of localized higher-accommodation areas. The well-sorted and finer-grained nature of the shoreface-offshore strata the middle and upper succession (PSS II-IV) indicates a more mature, distal source, with sediment redistributed by longshore currents, and then intensely bioturbated. These deposits display well-defined parasequences internally composed of laterally-continuous bedsets (&lt;5 m-thick). They extend along the entire study area, but show a significant vertical thickness variability. The integration of outcrop and subsurface data mapping (well and seismic) reveals this variability records the stratigraphic response of transgression over a complex, regional-scale ramp-step and underfilled rift topography, which controlled the location of main thickness and facies changes, and promoted areas of favored biogenic reworking. This study offers new insights in how to interpret thick transgressive successions based on primary depositional mechanisms and postdepositional processes, and provides useful tools to understand and predict the nature and potential preservation of these deposits in limited subsurface datasets.&lt;/p&gt;

Sign in / Sign up

Export Citation Format

Share Document