Field Excursion IField Excursion II

Field Excursion I

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

Leader: İsmail Ömer Yılmaz (Department of Geological Engineering, METU, 06531, Ankara)
Date: April 11th 2020

Upper Miocene lacustrine-continental sediments widely cropping out around Nallıhan-Beypazarı- Çayırhan town of Ankara display very colorful successions. These successions even form background for the Nallıhan-Çayırhan Bird Sanctuary.

Successions are generally composed of well developed cyclic facies alternations. Overlying Akpinar Limestone, lower part of the Cayirhan Formation presents alternation of thick, dark grey-grey mudstones with thin gypsum, limestone, chert or sandstones. Tuffs take place randomly and encounter occasionally with these alternations.

Mudstones take place at the bottom of the cycles and gypsum, limestone, chert or sandstone take place at the top. Cycles are capped by mudcracks and indicate presence of shallowing-upward and occasionally exposed cycles. In the middle part of the section, dark grey-grey or greenish mudstones alternate with ooidal limestones with fossil fragments or gypsums. Mudstones take place at the bottom and limestones and gypsums towards the top of the cycles. At the top of the cycles, iron nodules, mud cracks or rain drop imprints are observed. In the upper part of the section, greenish mudstones alternate with reddish-brownish mudstones. Paleosoil structures are observed within reddish-brownish mudstones and indicate exposure conditions developed over the greenish mudstones towards the top of the cycles. At the top part of the section, light grey marls alternate with reddish-brownish mudstones and display lensoidal stromatolite developments. This type of cycles is also capped by paleosoil structures.

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

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

When all data combined and analyzed, it is seen that climatic changes took important role in the formation of Upper Miocene lacustrine-continental sediments and small- and large-scale cycles even affected the chemistry of lake water in long term.

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

Field Excursion II

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

Leader: Erhan Altunel (Eskişehir Osmangazi University, Geological Engineering Department)
Date: April 11th 2020

The Gerede segment of the North Anatolian Fault Zone (NAFZ) was reactivated in 1944 with a M 7.3 earthquake. In early 1970s, it was realized that a wall across the fault in Ismetpasa was broken and this deformation was attributed to aseismic creep on this part of the NAF. Previous studies have been mainly concerned with the creep rate and a few researchers recently comment about the length of creeping fault.  Despite the abundance of investigation, field evidence for 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 be indication of aseismic creep. However, there are other signs of aseismic creep on morphology and man-made structures  along the Gerede segment.

During this field trip, the most prominent traces of the fault zone on the morphology and 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 km between Gerede in the west and Çaylı Village in the east. On the basis of field data, it will be discussed whether the present movement on this segment is the post-seismic activity of the 1944 earthquake or aseismic creep.