KT Boundary, Haiti Beloc Formation

Millimeters-size clay spherules are found at the base of the KT clastic bed, in arc of over 2500 km in length from Alabama to Haiti. The spherules are usually rounded but many display elongated dumbbell or tear drop shapes very similar to splash form tektites or microtektites [ Izett, 1991; Kring et al., 1991; Sigurdsson et al., 1991a; Smit et al., 1992; Claeys et al., 1993].

Glass fragments have been found preserved within the cores of the clay spherules at Beloc in Haiti [ Izett, 1991; Sigurdsson et al., 1991a; Sigurdsson et al., 1991b] and at two sites in Northeastern Mexico: Mimbral and La Lajilla [ Smit et al., 1992; Bohor and Betterson, 1993; Claeys et al., 1993]. A few pieces of glass < 50 microns in size have also been found at the KT boundary in Deep Sea Drilling Project Sites 536 and 540 between Yucatan and Florida [ Alvarez et al., 1992]. The glass particles range in size from 0.1 to 5 mm and can be classified based on their color into black and yellow types. The black type is roughly andesitic in composition with around 63 wt% SiO, the yellow glass has a more unusual composition and contains of up to 28 wt% CaO.

A broad range of evidence supports the impact origin of the KT boundary glass from the Gulf of Mexico region. This evidence far outweights the proposed volcanic and/or in situ diagenetic origin of the glass suggested by Lyons and Officer [1992] and Stinnesbeck et al., [1993]. Some of the most striking lines of evidence are 1) the similarity of the clay spherule shapes, and morphologies and relict glass surface features to those observed on tektites and microtektites; 2) the lack of high temperature microliths in the glass; 3) the presence of schlieren of yellow glass in the black glass indicative of rapid mixing of two parent composition; 4) a range of major and trace elements unlike volcanic glasses; 5) the high CaO content (28 wt%) of the yellow glass which compatible with impact melting of carbonate sediments but extremely uncommon for igneous processes; 6) the low water content (<0.05 wt%) of the glass, at least an order of magnitude lower than that of volcanic glasses but in the range of impact glasses, 7) large variability in oxygen isotope ratios of the Haiti glasses (4.6 per mil) which is too great to be achieved by igneous processes; and 8) the detection (using Re/Os isotopic system) of a small meteoritic component in the Beloc glass [ Izett, 1991; Sigurdsson et al., 1991a; Sigurdsson et al., 1991b; Blum and Chamberlain, 1992; Smit et al., 1992; Blum et al., 1993; Claeys et al., 1993; Koerberl et al., 1994].

In contrast to the 2 to 3 cm thick clay layer found worldwide, the KT boundary in the Gulf of Mexico region and in Haiti is composed of much thicker coarse clastic deposits. Sand beds indicative of high energy deposition at the KT boundary at Brazos River, Texas, have been interpreted to be the result of a major disturbance of the depositional environment, such as a tsunami approximately 50 to 100 meters high [ Bourgeois et al., 1988]. At Beloc, in Haiti, the KT boundary is interpreted as an ejecta layer probably deposited and reworked on a submarine slope [ Carey et al., 1993]. In Northeastern Mexico the KT boundary is formed by as much as three meters of coarse clastic layers in stark contrast with the deep water fine marls deposited above and below it [ Smit et al., 1992; Alvarez et al., 1994]. The KT layers consist of a basal unit containing impact ejecta (shocked quartz and spherules), overlained by a coarse laminated sandstone derived from coastal areas, and topped by ripples of fine sand and Ir-rich silts [ Smit et al., 1992; Claeys et al., 1993]. This succession containing impact markers at its base and at its top is interpreted as being rapidly deposited (within a few days) by a series of tsunami waves caused by the nearby Chicxulub impact [ Alvarez et al., 1992; Smit et al., 1992; Smit et al., 1994].

Sample weight: 0.2 grams (other weights available) Comes in display perky with authenticity and info.