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. Successive stack of erosive-based channels creates wedge-shaped bedding cross-sections. Trough cross bedding is produced by the downflow migration of lunate dunes in both subaqueous and subaerial environments. Planar Laminae are parallel to bedding, e.g. planar. Watch the USGS bedform movies described at: USGS Bedforms page Bedforms and Flow Velocity- The size and shape of subaqueous bedforms depends on flow strength and grain size and can be used to interpret ancient flow characteristics in a depositional environment from looking at sedimentary rocks.
Sedimentary rocks are normally deposited as horizonal layers. These tilted layers contained within larger layers are termed cross bedding. If you go dig trenches into modern sediments, you will find that cross-beds form a part of ripples and dunes. To gain the depositional environment, we need to do environmental analysis. Many sediment structures like planar and trough cross-bedding, upper-flow-regime planar bedding, and ripple-marked surface occur in fluvial deposits. Cross-Bedding. Cross beds can therefore form in any environment with moving water, such as braided or meandering rivers, shorelines of lakes or oceans, or in submarine settings which are affected by deep sea currents. Back to depositional environments.
Bedding forms as a direct consequence of Steno’s law of lateral continuity, that holds that a unit of sediment will extend laterally to the physical margins of the basin it is filing:. At the largest scale, successions of undisturbed formations may appear as superposed beds, however at finer scales, these resolve into other sedimentary structures that may not be strictly planar. In what depositional environment would one most likely expect to find plane bed laminations? One possibility Another. There are four primary ways to estimate depositional environment from well logs: 1. Planar or tabular bedding, as the words suggest, involve flat layers of rock (maybe lying at an angle) laid down in streams, lakes, or in deltas.