First results on determination of cosmogenic 36Cl in limestone from the Yenicekale Complex in the Hittite capital of Hattusha (Turkey)

We have measured ³⁶Cl in three rock surfaces of the Yenicekale building complex in Hattusha (Bo?azköy, Turkey). Hattusha was the capital of Hittite Empire which lasted from about 1650/1600 to 1200 BC. At Yenicekale, Hittite masons flattened the summit of an outcropping limestone knoll to form an artificial platform as the foundation for a building. Next they built a circuit wall along the lateral precipices of the flattened bedrock platform. We took one sample from the limestone bedrock platform and two samples from limestone building blocks of the circuit wall for cosmogenic ³⁶Cl analysis. Calculated exposure ages are 20 ± 1 ka for the sample from the bedrock platform and 24 ± 1 ka and 52 ± 2 ka for the circuit wall blocks. These exposure ages are significantly older than the age expected based on the estimated time of construction between 3.2 ka and 3.7 ka. We conclude that the sampled surfaces contain significant inherited cosmogenic ³⁶Cl. We cannot directly determine exposure ages for the building complex based on these three samples. On the other hand we may use the measured concentrations to determine how much of the rock was removed from the platform during flattening. To this end we modeled the variation of ³⁶Cl production with depth at Yenicekale using the results from the bedrock sample. We conclude that the Hittite masons removed only around 3 m from top of the limestone block. This means that the volume of rock removed from the bedrock platform is significantly less than the volume in the circuit wall atop the platform. They did not gain enough rock from this flattening to make the building. In agreement with this, the first results of our detailed microfacies analysis indicate that many of the building blocks are not of the same facies as the underlying limestone and must have been quarried elsewhere. Although we were not able to exposure date the Yenicekale complex due to the presence of inherited ³⁶Cl, our data suggest that Hittite masons excavated (most of) the building stones not at Yenicekale, but in quarries outside of Hattusha and then transported them to the construction site. These quarries have not yet been identified.     

New approaches in assessment of tsunami deposits in Dalaman (SW Turkey)

Some earthquakes in the Eastern Mediterranean are tsunamigenic and some of their tsunamis affected the coastal area of the Gulf of Fethiye, SW Turkey. Recent trenching surveys on the low-lying coastal areas of Dalaman delta beach across the Rhodes Pass revealed three probable tsunami impacts as a result of the historical earthquakes of 1303, 1481 and 1741. Yet, there have been relatively few studies of the processes associated with tsunami sediment transport, their deposition and nature in geological record. In addition to the interpretation of sedimentary features, accurate paleoenvironmental assessments might be possible by distinctive biogeochemical researches on marine-sourced organic matters, geochemical properties, quantitative amounts of marine-sourced biomarkers and deterministic ratios. The identification of major lipid biomarkers (fatty acids and sterols) in the samples recovered from the sidewalls of the studied trench, for example, indicated biogenic contributions due to the presence of phytoplankton, zooplankton, dinoflagellates and bacteria. Quantitative estimation of biomarkers and deterministic ratios also indicated some evidences for marine-sourced organic matters, implying that biomarkers can be used to answer the open questions in tsunami and paleotsunami researches.     

The earthquakes and related tsunamis of October 6, 1944 and March 7, 1867; NE Aegean Sea

During two distinct earthquakes occurred on March 7, 1867 and October 6, 1944, tsunami waves were also observed at some localities around the Gulf of Edremit, NE Aegean Sea. The first event (M _w = 6.8) mostly affected the city of Mitilini of Lesvos Island while the Gulf of Edremit-Ayvacık earthquake (M _S = 6.8) largely affected the northern and eastern coastal areas of the Gulf of Edremit. In 1944 earthquake, numerous surface cracks and water gushes were reported. The coastal neighborhoods of the town of Ayvalık in the east were flooded by tsunami waves. At the WSW extend of the main fault observed on land, which is parallel to the present-day slip vectors, some normal-oblique faults were observed close and subparallel to the northern coast. On the basis of historical documents, reports, interviews, geological setting, field observations and marine seismic reflection data, the 1944 earthquake was not triggered by one of the main fault segments but by a secondary fault or fault group which was described in this study. Depending on the distribution of tensional and compressional forces in the region, which rotates clockwise under the control of the middle strand of the North Anatolian fault, secondary fault groups become important. The moment tensor parameters of such small-size events have been determined and have obtained consistent results with the faults proposed in this study.     

Geomorphic Signatures of Active Tectonic in Drainage Basins in the Southern Bolkar Mountain,Turkey

Bolkar Mountain forms the northeast extent of the Central Taurus Mountains, which are located north of the eastern Mediterranean Sea and consist of 3000 m or higher summits. The study area southern part of Bolkar Mt, has been investigated for geomorphic signatures of active tectonics using Geographical information system (GIS). The lower valley floor-to-width to height and elongation ratios, higher convexity, stream length-gradient (SL) indices, hypsometric integral and convex nature of the hypsometric curves and topographic asymmetry show that relative tectonic activity is greater in the eastern sector affected by Ecemiş fault. Spatial variations of tectonic activity along rivers studied point to a general trend of decreasing activity towards the west as well as tectonic activity again increase in the west. Westward migration of basin and range extension is consistent with the place of uplift in the southern Bolkar Mt. Topography of the southern sector is the result of Late Miocene-Early Pliocene extension related uplift. Drainage systems in the upper part of the central and western sectors are under the lithological control and karstic denudation; whereas the development of the drainage systems in the middle and outlet parts of all sectors depend on sea level changes and Late Quaternary tectonism. The development of drainage systems of the eastern sector depends mostly on fault tectonism and climatic changes in the Late Quaternary.     

Analysis of recent crustal movement in the central and northern Sierra Nevada, California, using repeated geodetic leveling data

A comparative analysis of repeated geodetic leveling data was made along nine subparallel, E—NE-trending leveling lines located in the central to northern Sierra Nevada and the eastern Central Valley. The analysis was made to identify relative changes of elevation and evaluate these changes with respect to the regional geology and tectonics. The analysis used National Geodetic Survey first- and second-order, unadjusted, observed elevations.The relative changes in elevation indicate that crustal deformation is continuing to occur in the Sierra Nevada along pre-existing zones of crustal weakness and that this deformation is localized along some strands of Late Cenozoic faulting within the Mesozoic Foothills fault system. This deformation is characterized by variable and nonunifor westward tilt of the Sierran block west of the Melones fault zone, and relatively consistent eastward tilt of the Sierran block east of the Melones fault zone. Variable elevation changes occur within the Foothills fault system and are often associated with prominent geological or structural contacts. In addition, subsidence in the Central Valley appears to be of small magnitude and localized in extent, indicating nontectonic changes in elevation problably due to compaction of unconsolidated sediments.     

Alteration of the upper oceanic crust,DSDP site 417: mineralogy and chemistry

Basalts from DSDP Site 417 (109 Ma) exhibit the effects of several stages of alteration reflecting the evolution of seawater-derived solution compositions and control by the structure and permeability of the crust. Characteristic secondary mineral assemblages occur in often superimposed alteration zones within individual basalt fragments. By combining bulk rock and single phase chemical analyses with detailed mineralogic and petrographic studies, chemical changes have been determined for most of the alteration stages identified in the basalts.

1. Minor amounts of saponite, chlorite, and pyrite formed locally in coarse grained portions of massive units, possibly at high temperatures during initial cooling of the basalts. No chemical changes could be determined for this stage.
2. Possible mixing of cooled hydrothermal fluids with seawater resulted in the formation of celadonite-nontronite and Fe-hydroxide-rich black halos around cracks and pillow rims. Gains of K, Rb, H₂O, increase of Fe³⁺/Fe^T, and possibly some losses of Ca and Mg occurred during this stage.
3. Extensive circulation of oxygenated seawater resulted in the formation of various smectites, K-feldspar, and Fe-hydroxides in brown and light grey alteration zones around formerly exposed surfaces. K, Rb, H₂O, and occasionally P were added to the rocks, Fe³⁺/Fe^T increased, and Ca, Mg, Si and occasionally Al and Na were lost.
4. Anoxic alteration occurred during reaction of basalt with seawater at low water-rock ratios, or with seawater that had previously reacted with basalt. Saponite-rich dark grey alteration zones formed which exhibit very little chemical change: generally only slight increases in Fe³⁺/Fe^T and H₂O occurred.
5. Zeolites and calcite formed from seawater-derived fluids modified by previous reactions with basalt. Chemical changes involved increases of Ca, Na, H₂O, and CO₂ in the rocks.
6. A late stage of anoxic conditions resulted in the formation of minor amounts of Mn-calcites and secondary sulfides in previously oxidized rocks. No chemical changes were determined for this stage.

Recognition of such alteration sequences is important in understanding the evolution of submarine hydrothermal systems and in interpreting chemical exchange due to seawater-basalt reactions.     

An oxygen isotopic profile through the upper kilometer of the oceanic crust, DSDP Hole 504B

DSDP Hole 504B is the deepest basement hole in the oceanic crust, penetrating through a 571.5 m pillow section, a 209 m lithologic transition zone, and 295 m into a sheeted dike complex. An oxygen isotopic profile through the upper crust at Site 504 is similar to that in many ophiolite complexes, where the extrusive section is enriched in¹⁸O relative to unaltered basalts, and the dike section is variably depleted and enriched. Basalts in the pillow section at Site 504 haveδ¹⁸O values generally ranging from +6.1 to +8.5‰ SMOW(mean= +7.0‰), although minor zeolite-rich samples range up to 12.7‰. Rocks depleted in¹⁸O appear abruptly at 624 m sub-basement in the lithologic transition from 100% pillows to 100% dikes, coinciding with the appearance of greenschist facies minerals in the rocks. Whole-rock values range to as low as +3.6‰, but the mean values for the lithologic transition zone and dike section are +5.8 and +5.4‰, respectively.

Oxygen and carbon isotopic data for secondary vein minerals combined with the whole rock data provide evidence for the former presence of two distinct circulation systems separated by a relatively sharp boundary at the top of the lithologic transition zone. The pillow section reacted with seawater at low temperatures (near 0°C up to a maximum of around 150°C) and relatively high water/rock mass ratios (10–100); water/rock ratios were greater and conditions were more oxidizing during submarine weathering of the uppermost 320 m than deeper in the pillow section. The transition zone and dikes were altered at much higher temperatures (up to about 350°C) and generally low water/rock mass ratios ( 1), and hydrothermal fluids probably contained mantle-derived CO₂. Mixing of axial hydrothermal fluids upwelling through the dike section with cooler seawater circulating in the overlying pillow section resulted in a steep temperature gradient ( 2.5°C/m) across a 70 m interval at the top of the lithologic transition zone. Progressive reaction during axial hydrothermal metamorphism and later off-axis alteration led to the formation of albite- and Ca-zeolite-rich alteration halos around fractures. This enhanced the effects of cooling and¹⁸O enrichment of fluids, resulting in local increases inδ¹⁸O of rocks which had been previously depleted in¹⁸O during prior axial metamorphism.     

Seismotectonic database of Turkey

Turkey is located in one of the most seismically active regions in the world. Characterizing seismic source zones in this region requires evaluation and integration of geological, geophysical, seismological and geodetical data. This first seismotectonic database for Turkey presented herein was prepared, under the framework of the National Earthquake Strategy and Action Plan—2023. The geographic information system (GIS)-based database includes maps of active faults, catalogues of instrumental and historical earthquakes, moment tensor solutions and data on crustal thickness. On the basis of these data, 18 major seismotectonic zones were delineated for Turkey and the surrounding region. The compilation and storage of the seismotectonic data sets in a digital GIS will allow analyses and systematic updates as new data accrete over time.     

Investigation of summer synoptic climate controls on the mass balance of Meighen Ice Cap

Abstract

The Meighen Ice Cap synoptic climate classification system, developed from the study of six years of summer meteorological and glaciological observations, appears to account for significant variations in the energy‐ and mass‐balance climates of the ice cap. In relating the summer frequency of the three synoptic types to fourteen years of mass‐balance measurements, it was found that variations in surface conditions, solar angle and type of precipitation could be accounted for by the relative sequence of synoptic types. Further it was shown that the types could be represented by the position of the dominant 500‐mb cold Low influencing Meighen Island, thus providing a link between the mass balance and the general circulation.

Dominance of the winter pattern of a 500‐mb Low in the Hudson Bay –Baffin Island region throughout the summer season is capable of maintaining Meighen Ice Cap at its present size. A shift of the 500‐mb Low from the winter position directly to the Beaufort Sea or adjoining Polar Ocean area is capable of increasing the size of the ice cap. On the other hand, a shift of the 500‐mb vortex to the Asiatic side of the Polar Ocean before taking up position in the Beaufort Sea – Polar Ocean area produces negative mass‐balance conditions. When the 500‐mb Low remains on the Asiatic side of the Polar Ocean during most of the summer season the slow accumulation of two decades of Polar Ocean years is destroyed.