TMMOB
Jeoloji Mühendisleri Odası

Teknik Gezi

Field Excursion I

 Cyclostratigraphyand Paleoclimate Records of Upper Miocene Lacustrine-Continental Sediments(Çayırhan, Ankara)

Leader: İsmailÖmer Yılmaz (Department of Geological Engineering, METU, 06531, Ankara)
Date: April11
th 2020

UpperMiocene lacustrine-continental sediments widely cropping out aroundNallıhan-Beypazarı- Çayırhan town of Ankara display very colorful successions.These successions even form background for the Nallıhan-Çayırhan BirdSanctuary.

Successionsare generally composed of well developed cyclic facies alternations. OverlyingAkpinar Limestone, lower part of the Cayirhan Formation presents alternation ofthick, dark grey-grey mudstones with thin gypsum, limestone, chert orsandstones. Tuffs take place randomly and encounter occasionally with thesealternations.

Mudstonestake place at the bottom of the cycles and gypsum, limestone, chert orsandstone take place at the top. Cycles are capped by mudcracks and indicatepresence of shallowing-upward and occasionally exposed cycles. In the middlepart of the section, dark grey-grey or greenish mudstones alternate with ooidallimestones with fossil fragments or gypsums. Mudstones take place at the bottomand limestones and gypsums towards the top of the cycles. At the top of thecycles, iron nodules, mud cracks or rain drop imprints are observed. In theupper part of the section, greenish mudstones alternate with reddish-brownishmudstones. Paleosoil structures are observed within reddish-brownish mudstonesand indicate exposure conditions developed over the greenish mudstones towardsthe top of the cycles. At the top part of the section, light grey marlsalternate with reddish-brownish mudstones and display lensoidal stromatolitedevelopments. This type of cycles is also capped by paleosoil structures.

Thicknessand sedimentary structures of small-scale cycles changes towards the top oflarger-scale cycles in an order. Evolution of facies and thickness changes ofsmall-scale cycles form the characteristic feature of a large-scale cycle.

Independently,when geochemical changes are analyzed, large scale changes are noticed. Thesechanges can be larger or in the same level with cyclicity. Change sin elementalabundances indicate chemistry of lake water changes and sediment influx andweathering effecting the sediment composition during exposure conditions.

Whenall data combined and analyzed, it is seen that climatic changes took importantrole in the formation of Upper Miocene lacustrine-continental sediments andsmall- and large-scale cycles even affected the chemistry of lake water in longterm.

Cyclicalternations of lacustrine-continental facies help to understand to readclimatic and tectonic records and can be used to differentiate their effects inthe same succession. In this field trip, we will discuss how to use cyclicfacies alternation of lacustrine-continental facies to differentiate tectonicand climatic records from each other in the same basin.

 

Field Excursion II

Gerede Segment of the North Anatolian Fault Zone: Symptoms ofAseismic Creep on Morphology and Man-made Structures

Leader: ErhanAltunel (Eskişehir Osmangazi University, Geological Engineering Department)
Date: April11
th 2020

TheGerede segment of the North Anatolian Fault Zone (NAFZ) was reactivated in 1944with a M 7.3 earthquake. In early 1970s, it was realized that a wall across thefault in Ismetpasa was broken and this deformation was attributed to aseismiccreep on this part of the NAF. Previous studies have been mainly concerned withthe creep rate and a few researchers recently comment about the length ofcreeping fault.  Despite the abundance of investigation, field evidencefor the aseismic creep is limited with the well-known broken wall in Ismetpasa.However, there are other field evidences along the Gerede segment that could beindication of aseismic creep. However, there are other signs of aseismic creepon morphology and man-made structures  along the Gerede segment.

Duringthis field trip, the most prominent traces of the fault zone on the morphologyand evidence of aseismic creep on man-made structures (such as telephone poles,walls, field boundaries, graves) will be visited for a distance of about 65 kmbetween Gerede in the west and Çaylı Village in the east. On the basis of fielddata, it will be discussed whether the present movement on this segment is thepost-seismic activity of the 1944 earthquake or aseismic creep.

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