Schematic illustrations of two styles of graded bedding: left: normal grading; right: inverse grading.Schematic illustrations of two styles of graded bedding: left: normal grading; right: coarse tail grading.
In geology, a graded bed is a bed characterized by a systematic change in grain or clast size from bottom to top of the bed. Most commonly this takes the form of normal grading, with coarser sediments at the base, which grade upward into progressively finer ones. Such a bed is also described as fining upward.[1] Normally graded beds generally represent depositional environments which decrease in transport energy (rate of flow) as time passes, but these beds can also form during rapid depositional events. They are perhaps best represented in turbidite strata, where they indicate a sudden strong current that deposits heavy, coarse sediments first, with finer ones following as the current weakens. They can also form in terrestrial stream deposits.
In reverse grading or inverse grading the bed coarsens upwards. This type of grading is relatively uncommon but is characteristic of sediments deposited by grain flow and debris flow.[2] A favored explanation for reverse grading in these processes is kinetic sieving.[3] It is also observed in aeolian processes, such as in pyroclastic fall deposits.[4] These deposition processes are examples of granular convection.
^Allaby, Michael, ed. (2013). "fining-upward succession". A Dictionary of Geology and Earth Sciences (Fourth ed.). Oxford: Oxford University Press. p. 219. ISBN 9780199653065.
^Tucker, M. (2003). Sedimentary Rocks in the Field. Wiley. p. 115. ISBN 978-0-470-85123-4.
^Gray, J.M.N.T.; Shearer, M.; Thornton, A.R. (2006). "Time-dependent solutions for particle-size segregation in shallow granular avalanches". Proceedings of the Royal Society A. 462 (2067): 947–972. Bibcode:2006RSPSA.462..947G. doi:10.1098/rspa.2005.1580.
^Duffield, W.A.; Bacon, C.R.; Roquemore, G.R. (1979). "Origin of reverse-graded bedding in air-fall pumice, Coso Range, California". Journal of Volcanology and Geothermal Research. 5 (1–2): 35–48. Bibcode:1979JVGR....5...35D. doi:10.1016/0377-0273(79)90031-3.
deposits. These deposition processes are examples of granular convection. Gradedbedding is a sorting of particles according to clast size and shape on a lithified...
or multiple meters thick. Sedimentary structures such as cross-bedding, gradedbedding, and ripple marks are utilized in stratigraphic studies to indicate...
Bedding, also called bedclothes or bed linen, is the materials laid above the mattress of a bed for hygiene, warmth, protection of the mattress, and decorative...
lamination at all, their structural character is called massive bedding. Gradedbedding is a structure where beds with a smaller grain size occur on top...
Development and Evaluation (GRADE) approach Evolutionary grade, a paraphyletic group of organisms Gradedbedding, a description of the variation in grain size through...
currents By structure Sedimentary structures Bedforms cross-bedding duness gradedbedding ripple marks Alluvial fan Alluvial river Fault Fold Paleocurrent...
types of structures form in shallow marine environments. For example, Graded-bedding, which occurs when beds have vertical gradation in grain size, with...
grains of quartz with hematite coating providing an orange colour Cross-bedding and scour in sandstone of the Logan Formation (Lower Carboniferous) of...
currents By structure Sedimentary structures Bedforms cross-bedding duness gradedbedding ripple marks Alluvial fan Alluvial river Fault Fold Paleocurrent...
deposited by the flow Beach cusps – Shoreline formations made up of various grades of sediment in an arc pattern Biorhexistasy – Theory explaining the formation...
leaving the fine grains still in suspension. This results in coarse-tail gradedbedding, which means that there is a bimodal distribution of grain sizes with...
often intensely folded or deformed, recognising younging indicators or gradedbedding is critical to interpretation of the sedimentary section and often the...
lesser brannerite and thucholite. These occur in thin beds exhibiting gradedbedding reminiscent of placer sorting. Alteration is nonexistent to very weak...
transitioning to finer suspended sediment as energy decreases, resulting a gradedbedding pattern when viewed in cross-section. Crevasse channels are ephemeral...
quilt in American English, and a doona in Australian English, is a type of bedding consisting of a soft flat bag filled with either down, feathers, wool,...
bottom-current flow. They are characterised by a near-complete lack of parallel bedding. Mounded drifts are often bounded on one or both sides by non-depositional...
Ph. H.; Migliorini, C. I. (1950). "Turbidity Currents as a Cause of GradedBedding". The Journal of Geology. 58 (2). University of Chicago Press: 91–127...
deposits lack sedimentary structure, other than occasional reverse-gradedbedding towards the base, and they are poorly sorted. The proximal fan may also...
metamorphosed into various schists. The Vishnu Schist exhibits relict gradedbedding and structures indicative of turbidite deposits that accumulated in...
the tops of hills generally have a parabolic concave-up profile, which grades into a convex-up profile around valleys. As hillslopes steepen, however...
Many cross beds are stacked, and truncation always happens up section. Gradedbedding - In certain types of clastic sedimentary rock, the grain or clast size...
The Late Devonian is represented by phyllite and quartzite beds with gradedbedding. Volcanic rocks from Tournaisian and Lower Visean contain manganese...
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