Architectural-Element Analysis: A New Method of Facies Analysis Applied to Fluvial Deposits

A review of the braided-river depositional environment

https://ro.uow.edu.au/cgi/viewcontent.cgi?article=1989&context=smhpapers

A genetic classification of floodplains

Inclined heterolithic stratification—Terminology, description, interpretation and significance

Studies in fluviatile sedimentation: Bars, bar-complexes and sandstone sheets (low-sinuosity braided streams) in the brownstones (L. devonian), welsh borders

SUMMARY

Primary sedimentary structures in modern point bar deposits of the Amite River in Louisiana and the Colorado River in Texas are analogous to features observed in Eocene Simsboro and Pleistocene Colorado River deposits of the Texas Gulf Coastal Plain.



Short-duration peak flow, channel pattern, average stream gradient of about 2–3 ft./mile, and bank stabilization by dense vegetation are major parameters controlling the depositional pattern of coarse sand and pebble gravel of the Amite and Colorado rivers. Stratification is directly related to specific depositional features and consists of: large-scale trough-fill cross-stratification in the scour pool; trough-fill cross-stratification and foreset cross-stratification in the lower point bar; parallel laminae, large foreset cross-stratification, and trough-fill cross-stratification in the chute bar; parallel inclined laminae, climbing ripple laminae, and mud drapes in the chute fill; and parallel inclined laminae, mud drape, and foreset cross-stratification in overbank, flood-plain deposits.



Fundamental differences between point bars of bed-load streams (low suspended load/bed load ratio) and mixed-load streams (high suspended load/bed load ratio) are that upper point bar sediments with small trough sets and parallel inclined laminae occur only in fine-grained (mixed load) fluvial deposits, and large scale foresets of chute bars are common to coarse-grained (bed load) fluvial deposits but are not found in fine-grained fluvial deposits. Upward fining sequences, characteristic of fine-grained fluvial deposits, are uncommon in sediments deposited by bed-load streams such as the Amite and Colorado rivers.



The Simsboro Sandstone consists mainly of scour pool, lower point bar, and chute bar sediments. Chute fill and flood-plain deposits are preserved only in the highest stratigraphic sequence. Pleistocene Colorado River deposits display the same sequence of stratification types as the Simsboro but are composed of coarser material.

Physiographic features and stratification types of coarse‐grained pointbars: modern and ancient examples1

The Gulf shoreline of Texas: processes, characteristics, and factors in use.

The open Texas coast is characterized by 3 distinct types of shoreline: (1) barrier islands consisting of sand beaches, fore-island dunes, and a vegetated or barren back-island area; (2) peninsulas where beaches are dominated by shell (shell ramps with or without incipient dunes form the crest of the peninsula), and storm channels and washover deposits dominate the back-island area; and (3) strand plain a few to several hundred feet across, where shell material and rock fragments are dominant over terrigenous sand. Physiographic features of strand plains are a steep forebeach and a wide shell ramp that terminates as a steep avalanche face. Only the barrier islands and peninsulas are associated with bays and lagoons. When viewed separately, these shoreline features appear to have a random distribution. However, when their occurrence is considered in the context of Pleistocene and Holocene depositional history of the Texas coastal zone, there is order in their distribution. Barrier islands develop in the same areas as do sand-rich Pleistocene deltas with broad strand plains. Peninsulas are positioned along Pleistocene interdeltaic areas. Strand plains are situated along the distal parts of mud-rich Pleistocene and Holocene deltas. Distribution of these 3 shoreline types along the Texas coast cannot be explained adequately by a sand source from modern rivers being transported by longshore drift. Occurrence of the 3 shoreline types can be explained best by local Pleistocene and early Holocene sediment sources. Broad, sand-rich barrier islands are presently moving toward an equilibrium state where sediment input is about equaled by intensity of physical processes. End_Page 1900------------------------------ Narrow, shell-rich peninsulas are moving toward the mainland at rates of 2-14 ft/year. Narrow, shell-rich strand plains are in a state of rapid erosion--up to 30 ft/year. End_of_Article - Last_Page 1901------------

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Lee Edwin Garner

Papers

Physiographic features and stratification types of coarse‐grained pointbars: modern and ancient examples1

The Gulf shoreline of Texas: processes, characteristics, and factors in use.

Significance of Changes in Shoreline Features along Texas Gulf Coast: ABSTRACT