미국 유타주 천연기념물 ‘자연교’의 지질과 지형발달 (The Evolution and Geology of ‘Natural Bridge’ in National Monument Utah)

서지정보

· 발행기관 : 한국사진지리학회
· 수록지 정보 : 경관과 지리 / 18권 / 3호 / 1 ~ 10페이지
· 저자명 : 박희두

초록

쎄다메사사암이지표에노출된것은와이트케년과암스트롱케년에흐르던물이그들을자르고침식을시작하였기때문이다. 자연교는쎄다메사사암에있는미앤더경(頸) 부분을물이자르면서사행천이포기되며형성되었다. 주요자연교로는씨파푸, 카치나, 오와코모가있고이들자연교가두케년안에위치한다. 자연교는페름기쎄다메사사암에만들어졌다. 쎄다메사사암은약2억7천만년전페름기에퇴적되었고퇴적된후에쎄다메사사암은점점매몰되어그깊이가1천5백에서3천m에이른다. 삼첩기묀코피와치늘층군및주라기윈게이트사암과같은쎄다메사사암을덮고있는층군들이자연교지역을둘러싸고있는메사에나타난다.이를덮고있는암석은7천4백만년에서6천5백만년사이백악기후기에서제3기라라마이드조산운동동안에자연교로부터침식되기시작하였다. 침식의대부분은지난6백만년동안에콜로라도강과그지류가융기한콜로라도고원을하각하면서일어났다. 자연교의연대는결정하기힘들지만아마도1백64만년에서1만년전제4기플라이스토신세동안에형성되기시작하였다. 그때유타주남동부의기후는현재보다훨씬습윤하였다.자연교는페름기기반암에대한제4기침식의결과이다.

영어초록

Streams flowing in White Canyon and Amstrong Canyon began to cut down into them. The naturalbridges formed as the canyons cut through necks in the Cedar Mesa Sandstone and channel meanders wereabandoned. They call three natural bridges Sipapu, Kachina, Owachomo. These bridges were formed in twocanyons and on the Permian Cedar Mesa Sandstone. The Cedar Mesa Sandstone was deposited about 270millionyears ago. After it was deposited, the Cedar Mesa Sandstone was gradually buried to a depth of 1,500 to 3,000m.The overlying rocks began to be eroded from the natural bridgesarea sometime between 74 and 65 million yearsago, during the Late Cretaceous to Tertiary Laramide orogeny. Most of the erosion occurred during the last 6million years, as the Colorado River and its tributaries cut down through the rising Colorado Plateau. Although theages of the bridges are difficult to determine, they probably began to form during the Pleistocene Epoch of theQuaternary Period (1.64 million -10,000 B.P). At that time the climate in southeastern Utah was considerablywetter than it is today. The natural bridges in this area are the result of Quaternary erosion of Permian bedrock.

참고자료

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