The Influence of Geological Process on Interpreting Ediacaran Fossils in the Catalina Formation, Bonavista Peninsula, Newfoundland

Understanding the nature of the earliest complex fossils has presented many challenges over the past century since Billings first described Ediacaran fossils from Newfoundland in 1872. Previous studies have documented abundant Ediacaran fossils in the Bonavista Peninsula of Newfoundland. This thesis focuses on the H14 surface north of Catalina, which contains a nearly monospecific assemblage that includes hundreds of specimens of the rangeomorph, Fractofusus andersoni. Three factors need to be considered when trying to interpret these organisms. The first of these three factors is structural deformation. The area has undergone deformation during the formation of the Appalachian orogenic belt. This has distorted both fossil shape and orientation, requiring retrodeformation to restore the shapes and relationships of fossils to their original form. Two additional taphonomic factors influencing fossil visibility are: partly or completely ash covered fossils and the removal of fossil impressions from the bedding plane by modern weathering. These processes hinder acceptance of some previously published interpretations.

Proton Formation in 2+1 Resonance Enhanced Multiphoton Excitation of HCl and HBr via „=0… Rydberg and Ion-Pair States

Molecular beam cooled HCl was state selected by two-photon excitation of the V (1) summation operator(0(+)) [v=9,11-13,15], E (1) summation operator(0(+)) [v=0], and g (3) summation operator(-)(0(+)) [v=0] states through either the Q(0) or Q(1) lines of the respective (1,3) summation operator(0(+))<--<--X (1) summation operator(0(+)) transition. Similarly, HBr was excited to the V (1) summation operator(0(+)) [v=m+3, m+5-m+8], E (1) summation operator(0(+)) [v=0], and H (1) summation operator(0(+)) [v=0] states through the Q(0) or Q(1) lines. Following absorption of a third photon, protons were formed by three different mechanisms and detected using velocity map imaging. (1) H(*)(n=2) was formed in coincidence with (2)P(i) halogen atoms and subsequently ionized. For HCl, photodissociation into H(*)(n=2)+Cl((2)P(12)) was dominant over the formation of Cl((2)P(32)) and was attributed to parallel excitation of the repulsive [(2) (2)Pi4llambda] superexcited (Omega=0) states. For HBr, the Br((2)P(32))Br((2)P(12)) ratio decreases with increasing excitation energy. This indicates that both the [(3) (2)Pi(12)5llambda] and the [B (2) summation operator5llambda] superexcited (Omega=0) states contribute to the formation of H(*)(n=2). (2) For selected intermediate states HCl was found to dissociate into the H(+)+Cl(-) ion pair with over 20% relative yield. A mechanism is proposed by which a bound [A (2) summation operatornlsigma] (1) summation operator(0(+)) superexcited state acts as a gateway state to dissociation into the ion pair. (3) For all intermediate states, protons were formed by dissociation of HX(+)[v(+)] following a parallel, DeltaOmega=0, excitation. The quantum yield for the dissociation process was obtained using previously reported photoionization efficiency data and was found to peak at v(+)=6-7 for HCl and v(+)=12 for HBr. This is consistent with excitation of the repulsive A(2) summation operator(12) and (2) (2)Pi states of HCl(+), and the (3) (2)Pi state of HBr(+). Rotational alignment of the Omega=0(+) intermediate states is evident from the angular distribution of the excited H(*)(n=2) photofragments. This effect has been observed previously and was used here to verify the reliability of the measured spatial anisotropy parameters.