Review THIRD EXAM-GEOLOGY OF TEXAS Fall 2017 As in the previous exams, I will se

Question

Review THIRD EXAM-GEOLOGY OF TEXAS Fall 2017 As in the previous exams, I will select questions from the following, with roughly equal from each topic. Tertiary Coastal Plain What are the important economic resources of the Gulf Coastal Plain? Why are they common there? What are salt domes? Where and how did they form in Texas? Why are they important to us How and when did the lignite deposits of the Gulf Coastal Plain form? Why are there so many growth fault zones under the coastal plain? How was uplift of the Edwards Plateau along the Balcones Fault Zone related to development of today? the Tertiary Gulf Coastal Plain? Modern Texas Coast What are the main environments between the ocean and the mainland along the southern Texas coast? How did drowned estuaries such as Galveston Bay form along the Texas coast? Why are there no deltas along the Texas Coast? How does the geomorphology of the Texas Coast increase the destructiveness of hurricanes? It what ways is the modern Texas coast important to our economy? Texas Rivers Along the Trinity River, what are the typical downstream (longitudinal) changes in: gradient, load, discharge, flow velocity and sinuosity? What are the main sedimentary-geomorphic features of a meandering, suspended load river such as the lower Colorado? Why are the Upper Colorado and Upper Brazos rivers entrenched? What has bee Compare, n done in Texas to reduce the frequency and magnitude of flood effects? and give examples of the stream loads of a braided river and a meandering river in Texas

Explanation / Answer

Tertiary Coastal Plain

2) A dome-type structure which is formed when a thick bed of evaporite minerals that is found at the depth intrudes vertically into the surrounding strata of rock which forms a diapir. Salt domes can be formed in a sedimentary basin of salt overlained by younger sediments. In favourable conditions, salt domes can rise upto thousands of feet above salt layer from where they began to grow. Salt domes are important because they are the reservoirs of oil and natural gas, source of salt and sulfur and underground storage of oil and natural gas.

3) Lignite, also called brown coal, deposits are formed from the naturally compressed peat, which contains 60-70% carbon. Majority of the lignite deposits are formed during the tertiary period.

4) There are so many growth fault zones because the plain of growth fault extends parallely to the passive margins which have the high supply of sediment. Their fault plain dips toward the basin and also has the continuous displacement for long term.

Modern Texas Coast

1) Drowned estuaries are formed at the places where the sea level rises as compared to the land, sea water penetrates progressively into the river valleys and the topography of the estuary which remains similar to that of a river valley.

Groundwater

1) Confined aquifer are with the impermeable rock or dirt layer which prevents water from seeping into aquifer from the ground surface. Texas has 9 major and 21 minor aquifers that are the critical source of water for Texas. The Geologic Atlas of Texas exhibits the surface extent of geologic formations and aquifers across the Texas.

4) The Edward aquifer is divided into 3 zones, i.e. the contributing zone, the recharge zone, and the artesian zone. Recharge zon is 1,250 square mile area, faulted and fractured. To recharge the aquifer, 75-80% comes when streams and rivers cross the permeable formation and go underground which is called allogenic recharge. Remaining % of recharge comes when precipitation falls directly on the outcrop called autogenic recharge.

5) When the water reaches ground surface under natural pressure of an aquifer such well is known as flowing Artesian well.

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