What indicates a paleocurrent?
What indicates a paleocurrent?
A paleocurrent or paleocurrent indicator is a geological feature (typically a sedimentary structure) that helps one determine the direction of flowing water in the geologic past. This is an invaluable tool in the reconstruction of ancient depositional environments.
What is paleocurrent analysis?
Paleocurrent analysis is involved using sedimentary structures to determine the direction of flow like that of a river, a group of streams within a basin, the wind direction within a region, or the direction of oceanic currents (Potter and Pettijohn, 1978). Ten sites were measured for paleocurrent analysis.
What can be used to determine paleocurrent direction?
The paleocurrent direction can be determined by analyzing the direction of permeability. The permeability direction can be determined by using imaging logging data. Permeability direction of fluvial sand bodies and channel sand bodies is consistent with paleocurrent direction.
Which three sedimentary structures can tell you paleocurrent direction?
Sedimentary structures that may contain useful paleocurrent information include: Ripple marks (q.v.) and crossbedding (see Cross-lamination). Dune and ripple crests are typically oriented transverse to flow, while the foresets of crossbed structures normally dip in a downstream direction.
What are flute marks?
Typically, flute marks are bilaterally symmetrical heel-shaped hollows eroded into mud beds by debris-laden currents, acting either on prior defects on or within the bed, or on self-created defects, if the mud is insufficiently strong. Mud ripples closely resemble two-dimensional forms of current ripple.
Where does cross-bedding occur?
Cross-bedding can form in any environment in which a fluid flows over a bed with mobile material. It is most common in stream deposits (consisting of sand and gravel), tidal areas, and in aeolian dunes.
How does cross lamination tell you the Paleocurrent direction?
Cross-beds can tell geologists much about what an area was like in ancient times. The direction the beds are dipping indicates paleocurrent, the rough direction of sediment transport. The type and condition of sediments can tell geologists the type of environment (rounding, sorting, composition…).
Which force of erosion tends to only move sand sized or smaller particles?
The four forces of erosion are water, wind, glaciers, and gravity. Water is responsible for most erosion. Water can move most sizes of sediments, depending on the strength of the force. Wind moves sand-sized and smaller pieces of rock through the air.
How does hummocky cross stratification form?
Hummocky cross-stratification is a type of sedimentary structure found in sandstones. It is a form of cross-bedding usually formed by the action of large storms, such as hurricanes. It is only formed at a depth of water below fair-weather wave base and above storm-weather wave base.
Why is cross-bedding important?
Cross bedding forms on a sloping surface such as ripple marks and dunes, and allows us to interpret that the depositional environment was water or wind. Examples of these are ripples, dunes, sand waves, hummocks, bars, and deltas.
How is cross stratification produced?
Cross-bedding is formed by the downstream migration of bedforms such as ripples or dunes in a flowing fluid. The sediment that goes on to form cross-stratification is generally sorted before and during deposition on the “lee” side of the dune, allowing cross-strata to be recognized in rocks and sediment deposits.
Which is the best text for Paleocurrent analysis?
Potter and Pettijohn (1977) is the definitive text. The methodology, interpretation, and applications of paleocurrent analysis are now described in turn. A wide range of sedimentary structures can be used in paleocurrent analysis. Some structures yield only the sense of current flow, others yield both sense and direction.
How is Paleocurrent analysis used in Subsurface Studies?
Paleocurrent analysis, as this discipline is called, forms an integral part of facies analysis both at outcrop and, using the dipmeter, in subsurface studies. There is an extensive literature on this topic.
How is paleocurrent data entered in a field notebook?
Paleocurrent data may be entered in a field notebook and subsequently published in tabular form. The azimuths are, however, generally manipulated in some way to make their interpretation easier. The first step involves the removal of tectonic dip on a stereographic net where applicable.
How are variations in the paleocurrent trend represented?
If data from multiple localities or stratigraphic intervals is aggregated, will important variations in paleocurrent trend be represented. For example, if there are local bimodal trends representing tidal ebb and flood currents, will these be ‘lost’ if all coastal data is analysed as a single block of data?