Synthesis of Nanocrystalline Diamond and 6H Diamond Polytype

Spherules in sediments across the Cretaceous-Tertiary (K/T) transition in Central America and the Caribbean are commonly interpreted as ejecta from the Chicxulub impact on Yucatan. Their stratigraphic ages, however, are variable spanning from the late Maastrichtian to the early Danian. Figure 1. Locations of spherule-bearing K/T boundary sections in Central America, and the Caribbean. In northeastern Mexico, three and sometimes four spherule-rich layers are interbedded with marls of the Mendez Formation that span the last 300 kyr of the Maastrichtian (Plummerita hantkeninoides, CF1 zone). [1]. In Guatemala [2], Belize and Haiti [3], spherule-rich deposits are interbedded with early Danian sediments of the Parvularugoglobigerina eugubina (Pla) zone. ODP Sites 1001 and 1049 are very condensed and incomplete, and therefore provide no evidence of deposition precisely at the K/T boundary [4]. Smec-tites analyzed from spherule-rich deposits are very similar and indicate a common origin, except for those in northeastern Mexico, which are compositionally different mainly due to dilution by terrigenous influx related to tectonic activity in the nearby Sierra Madre Oriental [5]. The presence of almost pure Mg-smectite (Cheto type) in spheroid beds and diamictite at Albion Island and Armenia of northern and central Belize and in microspherule deposits of southern Belize and eastern Guatemala [6] indicate therefore a common glass source for both types of spherule deposits and links these to the Chicxulub impact. In addition to the pre-K/T spherule deposits and the well known K/T boundary Ir anomaly and impact event, there is also a widespread early Danian P. eugubina subzone Pla(l) Ir anomaly of cosmic origin. Multiple impacts (comet shower?) are most consistent with current evidence of spherules, Ir anomalies and climate change during the late Maastrichtian to early Danian and support three impact events. The first impact, marked by the oldest spherule deposit in NE Mexico, is related to the Chicxulub crater as suggested by our recent results from the new core Yaxco-poil-1. This event occurred in the late Maastrichtian at about 65.3 Ma nearly coincident with major Deccan volcanism and rapid global warming between 65.4-65.2 Ma [7, 8]. Subsequent late Maastrichtian and early Danian spherule layers may have been repeatedly reworked and redeposited from this event by currents and tectonic activity, though an additional spherule-producing event cannot be completely ruled out. The second impact is the well-known K/T boundary event marked worldwide by an Ir anomaly and other cosmic signals, though this event is not well represented …