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Lower Eocene Crustacean Burrows (Israel)
Reflect a Change from K- to r-Type
Mode of Breeding Across the K-T Boundary
Clarifying the Process of the
End-Cretaceous Biological Crisis
Zeev Lewy, Michael Dvorachek,
Lydia Perelis-Grossowicz and Shimon Ilani
Geological Survey of Israel,
Israel
1. Introduction
Crustacean burrows filled with chalk were found at the lowermost part of the Lower Eocene
sequence in southwestern Israel. They are exposed on both sides of a road-cut about 40 m
long (Fig. 1) on the way leading from the city of Be'er Sheva to the Israeli-Egyptian border
(Fig. 2A; site A; N 30 0 57' 36”, E 34 0 39' 20”). The road-cut exposes grey-greenish clay of the
upper part of the Paleocene Taqiya Formation, overlain by white chalk with chert nodules of
the Lower Eocene Mor Formation (Fig. 2B). The burrow system consists of horizontal
galleries leading to heart-shaped flattened casts of chambers embedded in 12-cm-thick
argillaceous chalk (Fig. 2B). This single type of chamber cast preserves on its surface ovoid
blister-like elevations with transversal fine scratches. These peripheral structures are
identical to those on the phosphatic casts of Campanian crustacean burrow-system
chambers described from another exposure along the same road, some 18 km to the east
where two types of chamber fillings were found (Lewy & Goldring, 2006). One is circular
(D=45 mm) and replicates the arched ceiling with finely scratched elevated ovoid structures,
whereas the cast of the floor comprises rings of about eight tubercles replicating pits 4 mm
in diameter and 3.0-3.5 mm in depth. The pits were interpreted to host and protect large
eggs in a brood chamber. The second kind of chamber changes shape and dimensions from
circular (D=45 mm) to arrowhead-shaped up to 100 mm in length with one end rounded
and tapering towards the opposite end. This gradually enlarged chamber was suggested to
host the young (nursery chamber) and perhaps store food or provide gardening sites. The
Lower Eocene burrow system lacks the brood chamber, whereas the heart-like chamber
looks as a shortened modification of the Campanian arrowhead chamber, preserving the
wall structure of the Campanian chambers. The diameter of the galleries of the Campanian
burrows is about 14-17 mm compared to 10-15 mm of the Lower Eocene ones, and the
greatest width of the Campanian chambers (about 7 cm) is similar to that of the Lower
Eocene ones. Accordingly, the Campanian and Lower Eocene crustacean burrows into
pelagic chalk have a similar structure of horizontal galleries connecting between chambers
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