Asteroids - Extreme Events: A Physical Reconstruction and Risk Assessment - page 237

Figure 9.5. Tektites. Photograph courtesy of Professor D. A. Kring, University of
Arizona.

(2) ubiquitous in the muddy strata, some with extreme lateral continuity;

this indicates that they were deposited in quiet water and not influenced
by shallow-water processes; or

(3) found close to rare, coarse-grained strata also indicating deep-water

deposition.

The spherules consist mainly of K-feldspar crystals that are organised into
radial-fibrous sprays that diverge inward from the grain edges. These textures
are similar to devitrification textures from both lunar impact spherules and
spherules in the K--T boundary layer. Spherules with random textures were also
found. These random textures are interpreted to be a product of primary crys-
tallisation during the cooling of droplets that were originally basaltic in compo-
sition. Replacement of K-feldspar, such as occurred in some of the central spots
of the radial textures, suggests a basaltic composition. The spherule layers are
distinguishable from volcanic deposits, as the volcanic ash at these locations is
fine grained and massive or displays a crude concentric zoning. The spherules
are also distinguishable from carbonate ooids. Iridium and other platinum-group
element anomalies are also present in the layers as well as other particles exhibit-
ing shapes associated with ejecta and irregularly shaped melt-ejecta particles.
Planar deformation features are not evident in the stratigraphy of these sites sug-
gesting that the target area was the ocean floor (Hassler and Simonson, 2001).
All four spherule layers in the Hammersley Basin sequence appear to have
been affected by substrate erosion, wave activity, offshore-directed bottom flows