Table of Contents
How does herringbone cross stratification form?
Tidal Sedimentary Structures Often the onshore and offshore flows are not in the same location, but they shift around. This gives rise to current ripples showing transport in two directions and dune migration in two directions producing herringbone cross stratification.
What are cross laminations?
An arrangement of laminations, transverse to the planes of stratification of the strata concerned. They generally end abruptly at the top, but in general tend to become more or less parallel to the bedding planes below. Ref: AGI.
What does cross-bedding indicate?
Cross-bedding forms during deposition on the inclined surfaces of bedforms such as ripples and dunes; it indicates that the depositional environment contained a flowing medium (typically water or wind). Examples of these bedforms are ripples, dunes, anti-dunes, sand waves, hummocks, bars, and delta slopes.
What does hummocky cross stratification indicate about environment?
31.3A). Ripple bedding, hummocky cross stratification, parallel (horizontal) to low-angle lamination and erosion structures (e.g., gutter and pot casts) indicate a deposition as proximal tempestites above the fair-weather wave base with frequent influence of storms (Knaust and Langbein, 1995).
How is cross-stratification produced?
This structure is developed by the migration of small ripples, sand waves, tidal-channel large-scale ripples, or dunes and consists of sets of beds that are inclined to the main horizontal bedding planes.
What is ripple cross lamination?
Wave-ripple cross-lamination is characterized by a variety of distinctive features, including: unidirectional cross-laminae, sometimes with drapes (sand laminae) oriented in the opposite direction; lensoid and complexly interwoven cross-sets; irregular, undulatory bases to cross-sets; and laminae which are discordant …
What is ripple cross-lamination?
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 takes the form of a series of “smile”-like shapes, crosscutting each other.
How do you tell the direction of cross-bedding?
The cross-beds reflect the steep faces of ripples and dunes. These steep faces tilt down-current and thus indicate current flow direction. Cross-beds are commonly curved at the base; this gives a handy way of determining right-side up in complexly deformed rocks.
Why is hummocky cross-stratification important?
It is typically interbedded with bioturbated mudstone. It commonly contains concretions of abundant mica and plant detritus in the tops of many laminae. This helps indicate a shape sorting.
What causes Swaley cross-stratification?
Swaley cross-stratification is also hypothesized to be deposited by an aggrading hummocky bed between fair-weather and storm wave base, but in shallower water where aggradation rates are low enough to cause preferential preservation of swales.
What is tabular cross-stratification?
Cross-bedding (or cross-stratification) is a primary sedimentary feature characterized by layers that intersect at an angle with each other through planar erosional surfaces that truncate inclined beds and laminae.