Questions Regarding the Regional Depositional Environment and Structural Features of The Texas West - Term Paper Example

Introduction This report addresses questions regarding the regional depositional environment, tectonic movements and structural features of the west of Texas, in the region of the Big Bend National Park specifically at Dagger Mountain, inside the National Park. The field trip focused on structural and depositional features of the rock units, such as orientation of the beds, composition of rocks, texture, grain size, fossils, weather resistance, faults and folds. Pre-existing features like faults, folds and fractures are important for the understanding of evolving structural features that have been through various episodes of tectonic deformation, which is exactly the situation that is being dealt with in this case study since there is evidence of influence of Ouachita Orogeny, Laramide Orogeny and Basin and Range deformations in the overall regional structures (Bobbitt, 1994). The rocks available at big bend are Boquillas (Kbo), Buda(Kbu), Del Rio (Kdr), Old alluvium (Qoal), Regular alluvium (Qal) on the stream, and Santa Elena (Kse) (museum). The images obtained are as follows. Photo 1 rock at Big Bend Depositional nature of the rocks and their lithologic compositions and sedimentary tructures record Dagger Mountain is mainly composed of sedimentary rocks, with presence of intrusive sills. The sedimentary units are mainly carbonaceous and rich in fossils. It involves three major limestone formations, Boquillas, Buda and Sta. Elena formations and the fossils present are gastropods, echinoids, corals, bivalves, inoceramus and molusca. Boquilles formation: Photo 2 Inoceramus sp. Inoceramus is a genus of bivalve often used as an index fossil due to being not only common but having a wide distribution but also having a very well defined range in the fossil record. Buda limestone: Photo 3 Scleractinian coral Also known as, Stony Coral are known to mostly live in the photic zone.Photo 4 Budaiceras hyatti (Budaiceras mexicanum, Barroisiceras hyatti) ammonite Found only in Texas and Mexico, this Ammonite lived from 112-94 million years ago. (paleob.org) Photo 5 Nautilus sp. Fossil version of modern Nautilus, though most likely a different species due to gap in time. Photo 6 Turrilites sp. (Ammonite) This genus of Ammonite is found during the Cretaceous period throughout the world from 109-66 million years ago (paleob.org) Photo 7 Macraster sp. (heart Urchin) Heart Urchins are still around today but this genus is found only during the cretaceous period of Texas and Mexico and some parts of Europe. The age range is 125-100 million years ago (paleob.org). Photo 8 Calcareous worm fossils (Serpula sp.) Photo 9 Assorted bivalve and gastropod fossils including Neithea sp. The picture on the right shows cross sections of gastropods. Neithea is a genus of scallop shell shown in the picture on the right (the right Neithea is actually from the Santa Elena). Del Rio clay: Photo 10 Haplostiche texana (foraminifera) (Nodosaria texana) Foraminifera are single celled protists that sometimes construct calcareous shell. In fact, a lot of the Calcium carbonate in limestone and similar rocks comes from the shells of Foraminifera. This species is that found almost exclusively in the Del Rio Clay(Carsey 1926). Santa Elena: Photo 11 Texigryphaea sp. Texigryphaea is a common genus of oyster found in Texas and New Mexico that lived during the Cretaceous period 105-99 million years ago. Those pictured above are from the Austin Chalk but those in The Santa Elena are practically identical. Photo 12 Assorted bivalves and gastropods including Neithea sp. Photo 13 the one on the right was found in this formation. The gastropods are steinkerns that were found in the Austin chalk. Similar such fossils can be found in the area in between the Santa Elena and Buda formations and could come from either formation. The size of such fossils can vary greatly. Fossils present in the formations mapped in Dagger Mountain and how do they reflect changing water depths and environments of deposition? Dagger Mountain is loaded with fossil allover. The most well-known fossils might be gastropods, bivalves and pacton-scalope. Other not so bounteous fossils like echinoid, coral, molusca, plant stems, inoceramus, ammonites and spatangoids. As notice, the range is exceptionally rich in marine creature skeletons, which straightforwardly suggests a marine the earth. For a large portion of the developments, aside from Del Rio, the fossils speak to profound water situations. On account of the Del Rio development, the vicinity of distinctive fossils uncover that the water was not as profound as in alternate establishments. "This translation is backed by a foraminiferal P:b bend made by Mauldin and Cornell (1986). Their information indicate an introductory expand in planktonics throughout transgression from something like 10-20% to in excess of 60%, then a reduction to 0% throughout relapse. Dagger Mountain is found in Sierra del Carmen. At Persimmon Gap is found Laramide thrust faults and Basin and Range high-angle faults crosscut a map-scale overturned anticline in Paleozoic and Cretaceous rocks. Photo 14 Dagger Mountain. Analysis of the western and southern flanks of the Dagger Mountain, depict the excellent display of the polyphase regional structures and the Tertiary sills. Features in the mountain include: Dagger Mountain anticline This is a large NNW-trending anticline, which is interpreted as being a fault-propagation fold on top of a blind reverse fault within the southwest flank from the Marathon-El Burro-Peyotes uplift; a Laramide basement is predominantly uplifted. Feldspathoid-rich Tertiary sills Phaneritic mafic sills display the well-exposed margins, which show evidence of forceful intrusion. Sills that is from moderate to steep and one sill, can be found when both limbs and hinge considering a map scale Laramide anticline. Basin and Range faults They are well exposed and of high-angle faults that cu across Laramide folds and the two Tertiary sills. Folds orientation in Dagger mountain and its comparisons with the regional folding pattern Dagger Mountain is part of the Laramide Orogeny mountain occasions, and, as a result of along these lines, the locale has significant folds all around. The Laramide Orogeny is characterised by the crash of the Farallon plate (maritime plate) with the North American plate (mainland plate) and the subduction of the Farallon plate underneath a wide mantle crest and problem area, making pressure drives that might misshape the general locale (Conner, 2003). In the particular study region of the Dagger Mountain, a succession of folds, syncline and anticline, is available with a topple of cots (Fig 7). (Fig 7- En Echelon anticline) The structure above illustrates the general collapsing example of the region, seeing that throughout the Laramide, the rocks were elevated and the worlds outside was abbreviated because of squeezing of a percentage of the establishments into a tight topple (Conner, 2003). The syncline in the study territory was plunging SE and the anticline was in the inverse course, NW, making an en echelon anticline (Fig 7). That appears to concur with the collapsing example of the general district as stated by Cobb, 1980. By these folds, there was a little chain of ordinary flaws, and that suggests the presence of stretching compels that might be from the Basin and Range distortion. This discoveries lead to the hypothesis that the collapsed range is the consequence of layering constrains in the NE-SW bearing from the Laramide Orogeny. With respect to the provincial collapsing, the field perceptions help that the folds are plunging in a general N-S bearing with compressional constrains in the E-W course. From synthetic weathering by water-borne carbonic corrosive and oxygen to mechanical evacuation of delicate and broken rocks, to scouring ever deeper and more extensively the gullies of Big Bend, water is today, as it has been previously, the significant device in the forming of the area. Each one time you come back to Big Bend National Park it will be diverse, for with each passing day the area is undoubtedly evolving. Reference Blenkinsop, T. G., 2008. Relationships between faults, extension fractures and veins, and stress. Journal of Structural Geology 30, 622-632. Conner and Harrison - Laramide Orogeny. The Traprock, Vol. 2, December 2003, pp. 10 – 14 dAlessio, M. A., and Martel, S. J., 2004. Fault terminations and barriers to fault growth. Journal of Structural Geology 26, 1885-1896. McClay, K. R., Dooley, T., Whitehouse, P., and Mills, M., 2002. 4-D Evolution of Rift Systems: Insights from Scaled Physical Models. AAPG Bulletin 86, 935-959. Museum, Big Bend. Geology of Big Bend. 3 October 2006. 10 April 2014 . Read More