A COMPARISON OF TWO COMMON CONTINUOUS FLOW IRMS APPROACHES ON THE ISOPRIME MULTIFLOW AND THE ISOPRIME PYROCUBE FOR δ 13C USING LATE ORDOVICIAN CARBONATES FROM SWEDEN

Nine samples were collected from the Late Ordovician in the Siljan District of Sweden. These samples were collected from rocks (Boda Limestone – Glistjärn Formation) that are known to be from the Hirnantian δ ¹³C Isotope Excursion (HICE) interval. Carbon isotopic composition will be determined for these samples using two common continuous flow IRMS approaches: 1) head space gas analysis with an IsoPrime MultiFlow automatic injection system and 2) elemental analysis by combustion on an IsoPrime PyroCube. Using the MutiFlow system direct measurement of δ ¹³C from inorganic carbon can be obtained, however combustion on the PyroCube results in a δ¹³C value that represents both organic and inorganic carbon in the rock. As a result we will process samples for δ ¹³C _total and for δ ¹³C _org, and then calculate the δ ¹³C _carb (δ ¹³C _total = δ ¹³C _org + δ ¹³C _carb). We will test to see if we get similar values for δ ¹³C _carb using these two methods to determine if it is possible to run samples using only the PyroCube, thus eliminating the need to have two different sample preparations on two different instruments to obtain the same results. The results of the measurements are important, as we will use them to place the samples within Hirnantian Positive Isotope Excursion (HICE). Then, conodonts from these samples will be used to determine the age of the samples and water temperature will be determined using δ¹⁸O from the conodont phosphate.