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Discovery of a New Type of Megalith in Sredna Gora Mountain, Bulgaria
Abstract
This publication aims to present a newly discovered megalithic structure near the village of Rozovets, Brezovo municipality in Southern Bulgaria possessing a set of characteristics not described previously in the scientific literature. To account for them, a new classification type of megalithic constructions is proposed – 'a pair of balanced monoliths' with a subtype of 'a pair of balanced parallel orthostats'. The paper also offers arguments in favour of classing the 'Sredna Gora proto-dolmen' as a separate group of megalithic monuments on the grounds of differing typology and chronology. DESCRIPTION OF THE STRUCTURE The megalith is located in the vicinity of the village of Rozovets in the Brezovo municipality, Sarnena Sredna Gora Mountain (Sredna Gora Mountain is divided into three distinct geographic areas – Sarnena, Sashtinska and Ihtimanska from East to West). It was photographed and published in the Internet for the first time by a group of researchers from the city of Plovdiv on 01.11.2015. Аn artificially levelled rock platform measuring approximately 5x4 meters is situated among a rock cluster, consisting of several dozens of stone blocks. On top of the platform, a pair of parallel vertical stone slabs (orthostats) rise at a distance of 80-90 cm apart. The site is known as "Bratiata" (The Brothers), "Popova turla" (Priest's pit) or "Izpravenite kamani" (Standing stones) among the few locals who are familiar with it. Neither of the two monoliths is connected to the base. They appear to be of the same type of rock as the base; however a geological study would be needed to confirm this. The passage formed between the two orthostats is oriented to the east-southeast and is about four metres long. One orthostat is located north of the passage (hence we denote it as the North Brother) while the other one is to the south (South Brother). The North Brother is about six meters tall, 4.20 m wide and 0.9 m thick at the base. The base has a very small area and the stone is wider mid-height in a distinctive spindle shape. The stone is visibly 'placed' on the leveled rock platform. It does not rest on its entire basis but instead rests on just three
In the present study, an attempt is being made to date samples from three archaeological sites in the Mediterranean using surface luminescence dating techniques. The methods are well established and this study is an effort to apply it to monuments that have not being dated with these methods before. Megalithic structures are eligible for absolute dating using OSL approaches in routine-based procedures. The structures that were chosen for dating are Osirion and Seti A' Temples in Abydos, Egypt, and a precipitate from a Saudi Arabian rock art site. OSL ages obtained for the Saudi Arabia monument refer to geological episodes that ascribe at the Middle Bronze Age (middle 2 nd mill. BC) while for the two Egyptian monuments, the results report for ages during the Middle Kingdom Age and of a younger date, spanning from the begin-ning till the end of 2 nd mill. BC indicating original or later architectural phases.
Precariously balanced rocks in seismically active regions may be used to provide constraints on probabilistic estimates of strong ground motion. A computer program is developed to study the rocking response of models of precariously bal-anced rocks when subjected to various levels of ground accelerations. The computer code, validated by comparing the numerical and experimental results for simple-shaped rigid blocks, is used to study the rocking response of rectangular blocks with various aspect ratios to the E1 Centro strong ground motion recording of the 18 May 1940 Imperial Valley earthquake. Results show that during earthquakes, the hori-zontal components of ground motion play a dominant role in overturning rocking objects. The rederived and corrected Housner's equation (1963) could be used to estimate the minimum overturning acceleration of precarious rocks at different fre-quencies by measuring the quasi-static toppling acceleration in the field.
The Optical Stimulated Luminescence (OSL) surface dating employing the
singlealiquot regenerative (SAR) technique on quartz was applied to some
small enigmatic buildings made of large marble schist slabs in a
skillful corbelling technique, and a fortified megalithic gate, at
Styra, Kapsala, Laka Palli and Kastro Armena in southern Euboea. The
function and origins of the structures have created a puzzle that has
fed the imagination and lead to various interpretations by many
scholars. No archaeological excavations or methods of dating have been
available for the megalithic-like structures. The dates reported suggest
the earliest construction to have taken place during the Classical
period. Re-use of these structures has occurred during Hellenistic and
Roman times (the latter associated with the large scale quarrying of
marbles), as well as, in Medieval times (found in agreement with the
historical literature) and the contemporary period (as reported by
shepherds). In all cases the datable slabs were rather reset as repairs.
Groups of precariously balanced rocks are effectively low-resolution strong-motion seismoscopes that have been operating on solid rock outcrops for thousands of years and, once the methodology has been developed, can provide important information about seismic risk. In one zone, near Victorville, only 30 km from the nearest point on the San Andreas fault, more than 50 precarious rocks have been documented. Widespread rock varnish suggests that many of these rocks have been in their current unstable positions for thousands of years. We have established the mechanical basis for rough estimates of the horizontal accelerations necessary to topple these rocks, using field observations and numerical and physical modeling. To verify that zones of precarious rocks do not occur near historic earthquakes, searches using binoculars were made along roads, with occasional foot surveys, near large earthquakes. Based on these reconnaissance searches, we conclude that no precarious rock zones are found within 15 km of zones of high-energy release of historic large earthquakes. To document the occurrence of precarious rocks in southern California, road surveys were carried out along major roads. Four zones of precarious rocks and seven other zones of somewhat less precarious rocks have been documented. Published probabilistic ground-motion maps for southern California are compared with the occurrence of zones of precarious and semi-precarious rocks. The results are encouraging and suggest that eventually, studies of precarious rocks will provide important constraints on the assumptions on which the maps are based. Results from studies of precarious rocks may eventually provide important information for siting and design of sensitive structures such as hospitals and power plants. Precarious rocks give a direct indication of past ground shaking, in contrast to the indirect inference provided by fault-trenching studies, which may be subject to uncertainties in the actual time history of slip due to the fault (e.g., fault creep, "slow" earthquakes, or unknown dynamic stress drop). It is concluded that precarious rocks warrant further study and quantitative analysis.
Precariously balanced boulders that could be knocked down by strong
earthquake ground motion are found in some seismically active areas of
southern California and Nevada. In this study we used two independent
surface-exposure dating techniques—rock-varnish microlamination
and cosmogenic 36Cl dating methodologies—to estimate
minimum- and maximum-limiting ages, respectively, of the precarious
boulders and by inference the elapsed time since the sites were shaken
down. The results of the exposure dating indicate that all of the
precarious rocks are >10.5 ka and that some may be significantly
older. At Victorville and Jacumba, California, these results show that
the precarious rocks have not been knocked down for at least 10.5 k.y.,
a conclusion in apparent conflict with some commonly used probabilistic
seismic hazard maps. At Yucca Mountain, Nevada, the ages of the
precarious rocks are >10.5 to >27.0 ka, providing an independent
measure of the minimum time elapsed since faulting occurred on the
Solitario Canyon fault.
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- L Tsonev
Tsonev, L. 2012. Megaliths in Bulgaria: availability, specifics, dating, tourist potential (in Bulgarian),
paper presented at the Third national conference in history, archaeology and cultural tourism "Bulgaria
in world cultural heritage", Shumen, May 17-19, 2012.