Lecture23_depositional systemsII

Lecture23_deposition - Mississippi bird’s foot delta The Delta Cycle • a river in the delta offers a shorter and steeper route to sea • So

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Unformatted text preview: Mississippi bird’s foot delta The Delta Cycle • a river in the delta offers a shorter and steeper route to sea • So, water changes course • an older delta lobe is abandoned-cut off from the primary supply of fresh water and sediment • older lobe undergoes compaction, subsidence, and erosion A typical delta cycle. A new delta lobe forms a “bud” ( a ) that enlarges ( b ). It is eventually abandoned ( c ) as the focus of deposition goes somewhere else, and the lobe “decays” ( d ) by subsidence. The coastline of the northern Gulf of Mexico has moved over geologic time. The following map show how it has changed over millions of years. About 300 million years ago (late Paleozoic) the Appalachian Mountains extended through Arkansas, Oklahoma, and Texas as the Ouachita Mountains. What is West Texas today was occupied by a sea. Streams drained westward from the mountains, a direction opposite to stream flow today. Streams deposited fluvial sediments, and deltas that prograded westward, filling the sea basin with clastic sediment. In places, very deep water prevailed in the seaway until near the end of basin-filling. A block diagram illustrates several components of the delta environment. Coarse bedload (yellow) is confined to distributary channels where it is deposited as elongate “barfinger” sand. Natural levees (orange) comprise the banks of streams. Vast backswamps (blue) are filled with vegetation. Parts of a delta 1. Natural levee 2. Delta plain 3. Channel sand (hydrocarbon reservoir) 4. Prodelta mud (Hydrocarbon source) 5. Delta lobe 6. Marsh, backswamps (Fig. 23-17) 1. Natural levee- embankment of sediments on one or both sides of a river channel 2. Delta plain- nearly flat tract of land at the mouth of a river, crossed by many streams and sediment is supplied by the river 2. Delta plain- nearly flat tract of land at the mouth of a river, crossed by many streams and sediment is supplied by the river 2. Delta plain- nearly flat tract of land at the mouth of a river, crossed by many streams and sediment is supplied by the river 3. Channel sand (hydrocarbon reservoir) 4. Prodelta mud (hydrocarbon source) Source rock 5. Delta lobe- a projection of the delta into the sea 5. Marsh and backswamps In this diagram of a sequence of...
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This note was uploaded on 07/07/2010 for the course GEO geo taught by Professor Long during the Spring '10 term at University of Texas at Austin.

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Lecture23_deposition - Mississippi bird’s foot delta The Delta Cycle • a river in the delta offers a shorter and steeper route to sea • So

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