Visualization of deformed strata syncline_ppt

Visualization of Folds Jaime Marso Geology 110
Parts of a Fold Fold Axis Limb of
fold Axial Plane
Folded Strata • A fold results from compression as stress is applied slowly, over a long period of time. • Anticline: up­folded structure in which the limbs dip away from the center (axial plane). • Syncline: down­folded structure in which the limbs dip toward the center (axial plane). – Anticlines and synclines may be symmetrical or asymmetrical. • Dome: results from uplift; limbs dip away from the center in all directions. • Basin: subsidence in which limbs dip toward the center in all directions.
Principle of Superposition Anticline Wills Creek Formation (Silurian) North of Hancock, Maryland, Rt. 70­522 exit ramp
Syncline, eastern Tennessee by David K. Brezinski 1989 (revised 1994) • Sideling Hill Syncline (photo by N. Heywood) Sideling Hill may appear to be a somewhat unusual feature, inasmuch as the downfold, or syncline, exposed in the road cut would seem to be more likely to form a valley, rather than a ridge. However, the youngest rocks, or those highest in the stratigraphic section, are the resistant sandstones and conglomerates of the Purslane Formation, which occur in the center of the fold and cap the ridge.
Syncline Syncline in Lockhart Basin, Utah Photo credit: USGS Digital Data Series DDS­21
Plunging Syncline • Limestone beds of Torcer Formation in syncline of Malone Mountains, south of Torcer station. Hudspeth County, Texas. Syncline plunging away from observer. USGS photo.
Anticline • Landsat TM image of northwest trending Mariscal Mountain Anticline, Big Bend National Park, Texas
Anticline Teton Anticline, Utah Photo credit: USGS Digital Data Series DDS­21
Map Symbols • Inclined Beds • Vertical • Horizontal • Syncline • Anticline 30°
FOLDS IN 2­DIMENSIONS:
Anticlines­­ are folds where the originally horizontal strata has been folded upward, and the two limbs of the fold dip away from the hinge of the fold. Synclines­­ are folds where the originally horizontal strata have been folded downward, and the two limbs of the fold dip inward toward the hinge of the fold. Synclines and anticlines usually occur together such that the limb of a syncline is also the limb of an anticline.
• Non­Plunging Symmetrical Anticline and Syncline
• Plunging Symmetrical Anticline and Syncline Folds can be classified based on their appearance Overturned folds in the Baltimore Gneiss Baltimore County, Maryland Ensor Mill Road, along stream, off I­83.
A series of anticlines and synclines
Non­plunging symmetrical Anticline •Strike is always parallel to the fold axis. •Outcrop patterns parallel the fold axis. •Dip directions are away from the vertical axial plane. •Older layers are in core. •A cross section that is parallel to the axis (profile) shows a series of horizontal layers. •The fold axis is horizontal. •Dip directions are towards the vertical axial plane. •Younger layers (higher numbers) are in core.
Non­plunging symmetrical Syncline Non­plunging asymmetrical anticline •Dip directions are away from the non­vertical axial plane. •Older layers are in core. •Strike is always parallel to the fold axis. •Outcrop patterns parallel the fold axis. •A cross section that is parallel to the axis (profile) shows a series of horizontal layers. •Both the dip direction and dip amount change on either side of the fold axis. •The apparent thickness of a layer’s outcrop varies on either side of the fold axis. Non­plunging asymmetrical anticline Plunging symmetrical anticline
•Older layers are in core. •The fold axis is not horizontal. •Dip directions are away from the vertical axial plane and strike varies. •Outcrop patterns form a U­shape. •The plunge direction is towards the closed end of the U. •A cross section that is parallel to the axis shows a series of layers that dip in the plunge direction. Plunging symmetrical anticline A geologic map illustrates the geologic structures of an area