Changes

'''Major clastic depositional environments'''

'''Major clastic depositional environments'''

* Alluvial sediments

* [[Alluvial]] sediments

** Alluvial fans

** Alluvial fans

** Fan deltas

** Fan deltas

===Alluvial fan deposits===

===Alluvial fan deposits===

An ''alluvial fan'' is a wedge of clastic detritus that forms at the base of a mountain front as sediments eroding from the mountains are transported downslope by streams or debris flows and deposited at the base ([[:file:lithofacies-and-environmental-analysis-of-clastic-depositional-systems_fig3.png|Figure 3e]]). The fan-shaped body is generally characterized by a gradation from coarser sediments at the apex to finer sediments at the toe. Alluvial fans are commonly divided into [[Proximal alluvial fan|proximal]], [[Middle alluvial fan|mid-fan]], and [[Distal alluvial fan|distal]] fan subenvironments.

An ''[[alluvial]] fan'' is a wedge of clastic detritus that forms at the base of a mountain front as sediments eroding from the mountains are transported downslope by streams or debris flows and deposited at the base ([[:file:lithofacies-and-environmental-analysis-of-clastic-depositional-systems_fig3.png|Figure 3e]]). The fan-shaped body is generally characterized by a gradation from coarser sediments at the apex to finer sediments at the toe. Alluvial fans are commonly divided into [[Proximal alluvial fan|proximal]], [[Middle alluvial fan|mid-fan]], and [[Distal alluvial fan|distal]] fan subenvironments.

Vertical sequences through the proximal fan are generally dominated by gravelly deposits with subordinate sandy deposits. Sequences through the mid- and distal fan are increasingly sand dominated. [[Basic open hole tools#Gamma ray|Gamma ray]], [[Basic open hole tools#Spontaneous potential|SP]], and [[Basic open hole tools#Resistivity|resistivity]] log responses throughout a fan can generally be expected to be blocky to irregular, depending on the amount of clay.

Vertical sequences through the proximal fan are generally dominated by gravelly deposits with subordinate sandy deposits. Sequences through the mid- and distal fan are increasingly sand dominated. [[Basic open hole tools#Gamma ray|Gamma ray]], [[Basic open hole tools#Spontaneous potential|SP]], and [[Basic open hole tools#Resistivity|resistivity]] log responses throughout a fan can generally be expected to be blocky to irregular, depending on the amount of clay.

===Braided and meandering fluvial deposits===

===Braided and meandering fluvial deposits===

[[Dip|Downdip]] from alluvial fans, rivers typically grade first into braided channels then, farther down the alluvial valley toward the coastal plain, into meandering channels. These different channel types can occur in the same river system and produce distinctly different kinds of sandstone bodies.

[[Dip|Downdip]] from [[alluvial]] fans, rivers typically grade first into braided channels then, farther down the alluvial valley toward the coastal plain, into meandering channels. These different channel types can occur in the same river system and produce distinctly different kinds of sandstone bodies.

''[[Braided rivers]]'' and ''braidplains'' form elongate, tabular, sandy and gravelly deposits composed of braided, sand-filled channels and sand and gravel [http://geonames.usgs.gov/apex/f?p=136:8:0::::: bars] (Figure 3c). They typically consist of coarse sand and gravel with relatively minor amounts of clay. Vertical sequences are composed of stacked, upward-fining channel sands and sand and gravel bars. Lateral trends in these deposits are dominated by an overall tabular geometry bounded by [[floodplain]] muds with an internally complex geometry of cross-cutting sands and gravels with subordinate mud-rich beds of varying thickness and dimension. Bar and channel deposits are typically elongate in the paleocurrent direction.

''[[Braided rivers]]'' and ''braidplains'' form elongate, tabular, sandy and gravelly deposits composed of braided, sand-filled channels and sand and gravel [http://geonames.usgs.gov/apex/f?p=136:8:0::::: bars] (Figure 3c). They typically consist of coarse sand and gravel with relatively minor amounts of clay. Vertical sequences are composed of stacked, upward-fining channel sands and sand and gravel bars. Lateral trends in these deposits are dominated by an overall tabular geometry bounded by [[floodplain]] muds with an internally complex geometry of cross-cutting sands and gravels with subordinate mud-rich beds of varying thickness and dimension. Bar and channel deposits are typically elongate in the paleocurrent direction.

Lakes occur in a wide variety of geological settings. They are often very important during the early [[rift]]ing phase of basin formation on [[continental crust]]. Major hydrocarbon-bearing lake deposits are associated with very large and long-lived [[Tertiary]] lakes such as those of the western United States, Indonesia, and China. These deposits are characterized by siliciclastic, carbonate, and organic-rich sediments deposited under generally low energy conditions, often by [[suspension]] deposition. Other processes include [[turbidity flow]]s in the lake interior and wave and current reworking along the lake margin.

Lakes occur in a wide variety of geological settings. They are often very important during the early [[rift]]ing phase of basin formation on [[continental crust]]. Major hydrocarbon-bearing lake deposits are associated with very large and long-lived [[Tertiary]] lakes such as those of the western United States, Indonesia, and China. These deposits are characterized by siliciclastic, carbonate, and organic-rich sediments deposited under generally low energy conditions, often by [[suspension]] deposition. Other processes include [[turbidity flow]]s in the lake interior and wave and current reworking along the lake margin.

Lacustrine rocks are generally the source rocks for hydrocarbons found in alluvial fan, fluvial, eolian, and deltaic rocks rather than the reservoirs. However, sandstone [http://geonames.usgs.gov/apex/f?p=136:8:0::::: bars], [[beaches]], [[turbidites]], and [[fan deltas]] associated with lake margins can be reservoirs sourced by open lake deposits. The core and log response characteristics of these deposits are similar to those described from analogous marine environments.

Lacustrine rocks are generally the source rocks for hydrocarbons found in [[alluvial]] fan, fluvial, eolian, and deltaic rocks rather than the reservoirs. However, sandstone [http://geonames.usgs.gov/apex/f?p=136:8:0::::: bars], [[beaches]], [[turbidites]], and [[fan deltas]] associated with lake margins can be reservoirs sourced by open lake deposits. The core and log response characteristics of these deposits are similar to those described from analogous marine environments.

===Shoreline deposits===

===Shoreline deposits===