On a geologic map,if the contacts between sedimentary rock units form a series of parallel lines,with the youngest unit in the center,the underlying structure is a ________.
A)horizontal anticline
B)plunging anticline
C)horizontal syncline
D)plunging syncline

Question

On a geologic map,if the contacts between sedimentary rock units form a series of parallel lines,with the youngest unit in the center,the underlying structure is a ________. 
A)horizontal anticline 
B)plunging anticline 
C)horizontal syncline 
D)plunging syncline

Quizplus · Accepted Answer

Parallel lines on a geologic map with the youngest unit in the center indicates a horizontal syncline, in which the rock layers have curved downwards into a trough shape. This is different from a plunging syncline, in which the rock layers have tilted downwards in the same direction, causing the contacts to be oblique rather than parallel. Horizontal and plunging anticlines are characterized by upward-arching rock layers, with parallel and oblique contacts, respectively.

On a Geologic Map,if the Contacts Between Sedimentary Rock Units