NAME DATE BIOSTRATIGRAPHY EXERCISES 1. These three stratigraphic sections all re
ID: 287608 • Letter: N
Question
NAME DATE BIOSTRATIGRAPHY EXERCISES 1. These three stratigraphic sections all represent rocks that accumulated during the transition from the Mis sissippian to the Pennsylvanian (Early to Late Carboniferous). The geographically westernmost (American) section is exposed in Arrow Canyon, Nevada. A central (European) section is exposed in Stonehead Beck North Yorkshire, England. The geographically easternmost section is exposed in Asku, South Tlenshan, Uzbekistan (a former Soviet Republic). Arrow Canyon, Nevada-The basal part of the illustrated section is composed of limestone with chert beds and nodules. The remainder of the section is generally carbonate-rich, but there are some interbedded sand- stones and shales or mudrocks. Stonchead Beck, UK-The section is composed almost exclusively of mudrocks with small beds of iron- bearing limestone. The mudrocks are either gray, dark gray or black, and there may be some silt. The mudrocks are generally fissile and ironstone nodules may be present. Asku, Tlenshan, Uzbekistan The basal rocks in the section are micritic limestones. These are overlain by interbedded shales, cherts, and limestones. There appears to be a depositional cyclicity in the section (the same is characterized by fossiliferous limestone alternating with mudrocks and types of rocks are repeated). Which siliceous concretions. TIEN SHAN-UZBEKISTAN ARROW CANYON-BIRO SPRING FORMATION CONODONT QUIDE FOGSILS A.gigantus l.sultatus -..-. 10 m on.gityl SAMPLE SITE 5-3 BIOSTRATIGRAPHYExplanation / Answer
A- NO
B- Since the lithology varies from Arrow Canyon to Stonehead Beck to Tienshan. The lithology of Arrow Canyon includes mostly of carbonate-rich rocks somewhere intruded by sandstones and mudrocks whereas the lithology of Stonehead Beck excessively comprises of mudrocks. The lithology of Tienshan comprises of cyclic beds. Thus it is difficult to correlate these stratigraphic sections using lithologic principles since no similar rock formations occur.
C- YES
D- We can correlate these lithological sequences using biostratigraphic methods due to the presence of conodonts fossil assemblages. Conodonts are regarded as excellent guide fossils and their global presence makes them an excellent index fossil for the Carboniferous period. Their rapid evolution and easy transportation make them available at far-off continents. Thus the assemblage of D. noduliferous appears in all three lithological sequences and we can easily analyse and correlate the lithologic sequences since its first appearance marks the boundary between Mississippian and Pennsylvanian rocks. Similarly, the respective fossils and their presence help us to correlate the lithologic sequences since they thrived at a certain time zone. THus calculating the respective age of the fossils would help us get to know about the absolute age of the rock sequences in the lithostratigraphic sections.
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