Baki Varol

Sea-level changes and related depositional environments on the southern Marmara shelf

Abstract Petrographic data obtained from 182 surface sediment samples together with the available bathymetric data are used to investigate the effects of the last major sea-level changes on shelf evolution in the southern Sea of Marmara. Grain-size analysis reveals the presence of at least three belts or zones which are rich in coarse-grained (sand and gravel) sediments. These coarse-grained belts which are up to 45 km long, 15 km wide, show up to 20 m of relief and are presently found at 40–80 m (average 60 m) water depths. Based on microscopic examination and residual analysis, the sediments from these belts are interpreted as indicators of high-energy shallow waters where detrital siliciclastics, with some benthic contribution, accumulated. The presence of a 62–65 m deep sill in the Canakkale Strait and the consideration of sea-level curves would suggest that the Marmara shelves must have been subaerially exposed down to −65 m water depths for about 10,000 yrs (22,000–12,000 yrs B.P.), sufficient time to modify former shelf topographies and form such bottom relief. While difficult to date, we believe that coarse-grained belts found on the southern Marmara shelf must be relict (i.e., former shorelines, beaches) and their formation is largely related to low stands of sea-level during the Late Pleistocene regression and early Holocene transgression. However, the available high-resolution seismic profiling data suggest that the neotectonism in this seismically active Sea of Marmara plays an important role to explain the raise of these older shorelines to their present levels on the sea-floor.

Turkish earthquakes reveal dynamics of fracturing along a major strike‐slip fault zone

During the last 5 months of 1999, northwestern Turkey experienced two major earthquakes along the North Anatolian Fault Zone (NAFZ). The first earthquake struck the country at 3:01 A.M. local time on August 17, and caused extensive damage in the towns of Yalova, Golcuk, Izmit, Adapazari, and Duzce (Figure 1). The second earthquake occurred at 6:57 P.M. local time on November 12 and caused damage mostly in Duzce and Kaynasli. The 7.4-Mw main shock of the August 17 Izmit earthquake was centered at 40.702°N, 29.987°E and originated at a depth of 17 km. The center was about 11 km southeast of Izmit, a major industrial town (Figure 1). The earthquake was a devastating natural disaster that claimed close to 20,000 lives and left more than 100,000 people homeless.

Development of a mass flow-dominated fan-delta complex and associated carbonate reefs within a transgressive Paleocene succession, central Anatolia, Turkey

Abstract A Paleocene basin-fill succession (Dizilita¢ler Formation) has been studied in an area north of Ankara, Turkey. This basin-margin elastic succession comprises basal alluvial deposits (250 m thick), few vertically stacked marine fan-delta sequences (450 m), and sandy turbiditic deposits (650 m) at the top. The overall stratigraphic facies pattern is transgressive, but the fan-delta sequences represent major regressive (shoreline progradation) pulses. Fringing and patchy carbonate reefs separate these sequences, marking the favourable climate and a reduction in clastic influx during the episodes of fan-delta drowning due to relative rises of sea level. The fan-delta system was persistently dominated by gravelly mass flows, with subordinate braided-stream distributaries. The morphology, particularly slope inclination, of the successive fan-delta wedges was each determined largely by the magnitude of the preceding sea-level rise (actual water depth) which itself controlled the type of reefs. The basin was subsiding, and the five pulses of coarse-clastic influx separated by abrupt sea-level rises are attributed to active faulting at the basin margin. Broader down-faulting and basin expansion promoted deeper-marine turbiditic sedimentation.

Sedimentology of the Miocene evaporitic succession in the north of Çankiri-Çorum basin, central Anatolia, Turkey

The upper Miocene non-marine sediments of the Çankiri-Çorum basin in central Anatolia, have both evaporitic and non-evaporitic successions. These sediments were deposited in an evaporitic lake which had temporary episodes of palustrine conditions in response to seasonal or climatic changes. The successions show different facies such as sulfates, carbonates and siliciclastics. The sulfates comprise primary, reworked and diagenetic gypsum. The primary deposits are predominantly laminated gypsum, bedded gypsum and selenite. The reworked (detrital) gypsum comprises gypsite, gypsarenite, gypsrudite and breccias. The diagenetic type comprises micro- and macrogypsum nodules. The carbonates mainly include clayey limestone, oolitic limestone and dolomite. The siliciclastics comprise red beds and both channel and non-channel, conglomerates and mudstones.Laminated gypsum, composed of alternating gypsum and dolomite, was a result of environmental schizohalinity. Bedded gypsum was precipitated in the deeper part of the lake during high evaporation periods. Chevron-type selenite crystals formed on saline mud flats during the times of aridity, whereas the discoidal-type seen in the organic-rich mudstones occurred in the gypsiferous marshes during the times of humidity. Reworked (detrital) gypsum dominates the lake margin. These formed during periodic wet episodes that caused reworking of primary gypsum. Gypsum nodules occurred as both early and late diagenetic products. Carbonates and siliciclastics were deposited during the freshening periods of the lake.Climatic or seasonal changes were the main causes of the depositional styles of the upper Miocene evaporitic and non-evaporitic lacustrine deposits in Çankiri-Çorum basin. Additionally, the transition upward from alluvial to lake environment implies an important change in drainage patterns that likely occurred as a result of marginal fault activity.

Giant rhinoceros Paraceratherium and other vertebrates from Oligocene and middle Miocene deposits of the Kağızman-Tuzluca Basin, Eastern Turkey

A recent fieldwork in the Kağızman-Tuzluca Basin in northeastern Turkey led us to the discovery of three vertebrate localities which yielded some limb bones of the giant rhino Paraceratherium, a crocodile tooth, and some small mammals, respectively. These discoveries allowed, for the first time to date some parts of the sedimentary units of this basin. This study also shows that the dispersal area of Paraceratherium is wider than it was known before. Eastern Turkey has several Cenozoic sedimentary basins formed during the collision of the Arabian and Eurasian plates. They are poorly documented for vertebrate paleontology. Consequently, the timing of tectonic activities, which led to the formation of the East Anatolian accretionary complex, is not constrained enough with a solid chronological framework. This study provides the first biostratigraphic evidences for the infill under the control of the compressive tectonic regime, which built the East Anatolian Plateau.

The stratigraphical position of Kemiklitepe fossil locality (Eşme, Uşsak) revised: Implications for the Late Cenozoic sedimentary basin development and extensional tectonics in western Turkey

Unlike earlier studies attributing the Kemiklitepe fossil locality to the İnay Group, the present study indicates that it is to be assigned to the Asartepe Formation that unconformably overlying the İnay Group. This seems to verify the early Middle Miocene age of the İnay Group, previously determined by isotopic dating and palynological analyses. However, the early Middle Miocene age and the overall undeformed nature of the İnay Group do not concur with the regional two-stage extension model proposing a compressional phase during the Miocene/Pliocene interval. The correlation of the Asartepe Formation bearing the Kemiklitepe fossil locality further to the north indicates that a NE-SW trending fault was active during the Late Miocene. Recent studies modelling the uplift history of the region are unconvincing because they ignore Late Miocene activity on the NE-SW trending faults and assume a timing of incision of the İnay Group after the Late Pliocene (~3Ma) in their calculations.

A prelimennary study: Celestite-bearing gypsum in the Tertiary Sivas basin, central-eastern Turkey

Celestite-bearing evaporite mineralization is common in the Tertiary evaporitic units of Ulas-Sivas basin, East-Central Turkey.The first occurrence of gypsum which is “laminated in character” (Balatino gypsum) took place in the shallow inner-lagoon or depressions during regression in the upper Eocene. Thick gypsum and overlying beds composed of the bedded, nodular gypsum and sandstone alternations were formed in a coastal sabkha and abandoned channels within the meandered rivers through the Oligocene time. The last occurrence of evaporitic units, represented by massive and bedded gypsum alternating with sandstones and fossiliferous limestones resulted from limited marine transgression in the early Miocene along the southern margin of the Sivas Tertiary basin.The celestite mineralization preferentially took place within the Miocene evaporites and subordinate amount in the shallow marine limestones and terrestrial siliciclastics ranging from late Eocene to Oligocene in age. Celestite shows different depositional characters such as stratabound, massive, fracture and cave filling. According to microscopic studies, three petrographic types have been determined in these different beds of celestite. They are prismatic and bar-like; sub-idiotopic and tabular; fibrous-radial.The source of the celestite in the Sivas Tertiary basin has been debated. There is little evidence for suggesting sedimentary-syngenetic origin. Many geologists believe that it formed during late diagenesis or epigenetic stages, but this interpretation reflects a lack of a comprehensive study and only depends on field observations. This paper includes both field and laboratory studies (light, ore and electron microscopes, microprobe,87/86Sr isotopes) and obtained initial results which have inclined to the diagenetic-epigenetic origin.

Facies changes and high calorific peat formation in a quaternary maar lake, central Anatolia, Turkey: the possible role of geothermal processes in a closed lacustrine basin

Abstract The sedimentary infill of the Acigol maar lake, one of the volcanic centres in the Cappadocia district of Anatolia, contains unusual, high-calorific sub-Recent peat deposits, of which the origin is attributed to geothermal processes. The sedimentary facies record is analyzed to reconstruct the lakes depositional history and to disentangle the combined signal of climatic and geothermal factors. The facies succession comprises: a lake-fringe clastic apron shed from the maar walls; early-stage, coarse-grained tuffaceous deposits of the lake proper, intercalated with brecciated mudstones and limestones; and final-stage, fine-grained tuffaceous deposits of the lake proper, intercalated with peats and plant-bearing clastics and with some terminal travertines. The closed lake was highly dependent on climate, particularly precipitation, and the depositional conditions were further controlled by a connective hydrothermal system which itself was driven by the input of meteoric water. The associated heat flow played an important role by creating a microclimatic niche, where even the impoverished late-Quaternary (cold regional climate) vegetation could flourish and form substantial peats. The varying hydrological budget of the lake was the main “switching” mechanism for the peat-forming conditions, with two water-depth thresholds involved. If the lake level rose too high, the low vegetation was drowned and hemipelagic clastic sedimentation prevailed. If the lake level fell too low, the vegetation was killed and formation of travertine took place. The heat flow through the pore water and clastic sediments was crucial to the high maturation of the peat deposits.

Modern ooids of Cleopatra Beach, Gokova (South Aegean Sea) Turkey: Results from petrographyand scanning electron microscopy

AbstractModern ooids from the Cleopatra Beach on Island in the Gökova Bay, South Aegean Sea, resemble ooids formed on the Bahamian platform. The concentric coatings of the ooids consist of two or more laminae around a carbonate- or non-carbonate nucleus. The oolite cortex is transparent, whereas the non-transparent portions seem to be the dark fields on the oolitic surfaces. The ooids are mixed with molluscan skeletal debris displaying micritic envelopes. Weakly consolidated ooids have been cemented by calcite in the form of meniscus cement.According to electron-microscope studies, three kinds of crystal shapes have been distinguished, as follows:1-Micronodules attributed to microboring organisms such as cyanobacteria or coccoids;2-Tablet-shaped crusts of hemispheres; likely produced by bacterial activity,3-Acicular- or elongate crystals precipitated directly from sea water in vacated holes of the microborings or as of the tangentially orientated parts of the ooids. Algal- and bacterial processes are thought to have been main sources of the carbonate that was precipitated to form the ooids.

Dolomitization, time boundaries and unconformities: examples from the dolostone of the Taurus mesozoic sequence, south-central Turkey

Abstract A Mesozoic carbonate unit in the Taurus platform consists of thick dolostone sequences with both massive, thick beds and thinner beds intercalated with limestone. Dolomite preferentially replaced micrite in the original carbonate. In an initial phase of dolomitization, dolomicrite formed, which later as through dissolution and recrystallization resulted in clear dolomite crystals and dolosparites. An additional type of dolomite is dolosparite filling voids. These dolomite crystals represent either replacement of precursor calcite cement or growth into void space. Dissolution of late, coarsely crystalline dolosparite, precipitation of saddle crystals, local dedolomitization, and some late calcite cement in the voids, all indicate short-term atmospheric exposure of the sequence during or after the main dolomitization event. Dolomitization does not appear to be restricted to a specific environment. There is no evidence that the dolomite formation occurred in an evaporite, supratidal, or high intertidal setting. Our present state of knowledge does not allow an unequivocal explanation of the dolomitization event of massive platform dolomites. However, the association of dolomitization with sea-level fluctuations such as repetitive and minor transgressive and regressive periods might be a clue to the mechanism for the formation of thick dolomite beds in the Taurus Mesozoic platform, as noted by the increasing of the dolostone/limestone ratio near the time boundaries (Triassic/Jurassic and Jurassic/Cretaceous). Stable isotope data support mostly marine-derived solutions as the dolomitizing fluid. Marine solutions can be the only source of the large quantities of Mg 2+ ions needed for dolomitization of massive platform dolomite as was suggested by Land (1985) and Given and Wilkinson (1987).