Geology Reference
In-Depth Information
The Giant wall of Hattusa (Turkey).
Hattusa, the
capital of the Hittite reign (situated near Bogazkale in
central Anatolia), is surrounded by a giant 6 km long
wall built in the middle of the second millenium BC
(Neve 1996; Fig. 19.1). The blocks of the wall are be-
tween 40 and 80 cm high. Most blocks are gray and
red limestones. The latter exhibit conspicuous coral
structures and correspond to coral framestones (Flügel
and Flügel-Kahler 1997). Thin sections show dendroid
corals affected by strong diagenetic alterations charac-
terized by cementation, dissolution and internal sedi-
mentation (Pl. 36/4; Fig. 7.15). The corals exhibit thick
biogenic encrustations. The sediment between the cor-
als is a bioclastic peloidal packstone (Pl. 151/8). Mi-
crofossils indicate an Early Cretaceous age of the lime-
stones. Outcrops of reddish and gray limestones occur
within the boundaries of Hattusa. The material used
for the wall is of domestic origin.
e.g. that most mosaic material came from sources near
or very near to the site of the mosaic. Microfacies pro-
vides a mean of distinguishing between local, regional
and imported material, or recycled material, e.g.
tesserae made from off-cuts of building stones. Local
or domestic material is defined as material derived from
rocks existing at the mosaic site. Regional material
comes from sources within a distance of few to several
tens of kilometers. The term 'imported' refers to mate-
rial imported from far distances.
19.3.1 Mosaic Material: Methods
Microfacies-based provenance analysis of tesserae
(stone or other hard material cut in a cubical or some
other regular shape (Pl. 151/1-5) used for floor and wall
mosaics, comprises eight stages:
Roman building stones on the Magdalensberg,
Carinthia (Austria)
. Starting in the first century BC
and terminating in the middle of the first century AD, a
Roman city developed on the slopes of the Magdalens-
berg near St.Veit in Carinthia (Piccottini 1989). The
building stones used for houses and the public build-
ings were investigated by F. Thiedig and his team with
regard to lithology and source (Thiedig 1998; Thiedig
and Wappis 2003). A detailed survey of more than
47,000 building stones, including mapping and petro-
graphical studies showed that more than 95% of the
excavated walls consist of volcanic rocks outcropping
directly next to or within a distance of a few kilome-
ters to the Roman city. 5% of the building stones are
marbles, travertines and Pleistocene pebbles, includ-
ing crystalline rocks, limestones and sandstones. Mar-
bles used in public building and for grave materials,
came from marble quarries located within a distance
of a few to some tens of kilometers. Travertine quar-
ries were located at a distance of about 30 kilometers.
•
Color.
Macroscopic assessment and definition of
rock color groups. The principal colors of mosaic stones
are white and yellow, black and gray, pink and red as
well as orange and brown. Blue and also some green
tesserae are usually glasses. Many red tesserae were
made of fragments or ceramic tiles. Rock colors can
be altered by burning, an effect probably also known
to Roman mosaicists. The assessment of colors of car-
bonate tesserae must take into account that broken, cut,
ground, smoothened or polished tesserae can exhibit
considerable differences in color gradations and shades.
•
Sampling
based on rock-color categories. Because
color effects are essential for the beauty of polychrome
mosaics, samples must consider the principal rock color
categories. The composition of non-lithic tesserae (ce-
ramics, bricks and tiles, glass) is studied by microscopi-
cal, chemical and isotopical criteria. Sampling has to
consider the relative abundance of differently colored
tesserae within the mosaic. Abundant tesserae may be
of local origin. Rare rock types may indicate the use of
specifically selected and possibly imported material.
For statistical reasons at least five to ten tesserae of
each color group should be taken. Tesserae identical in
color are not a priori identical in microfacies and age
of the limestone!
•
Microfacies analysis.
Texture (Dunham- or Folk
classification), matrix and grain types, and fabrics
(lamination and fine bedding, burrows, nodular struc-
tures, calcite-filled open-space structures, calcite veins,
microbreccias) allow a preliminary grouping of lime-
stone samples within the categories defined by rock
color. Dolomite samples should be differentiated ac-
cording to the size, shape and boundaries of crystals
and the type of crystal fabrics. Microfossils are impor-
19.3 Mosaic Material
Mosaics consist of tailored stones and other material
(e.g. glass or ceramics) juxtaposed to produce specific
patterns and designs. The individually tailored stone
ranging in size less than one centimeter and a few cen-
timeters is called tessera.
Most mosaic studies concentrate on stylistic group-
ings, design development and art history. Provenance
analyses of mosaic stones are rare (see review in Flügel
and Ch. Flügel 1997), although thin-section based stud-
ies can be used for testing some common assumptions,
