Miocene to recent evolution of the Cilicia Basin with emphasis on the Pliocene-Quaternary sedimentary relationship between the Goksu river and the Cilicia Basin: a quantitative study of volumetrics, subsidence in the Cilicia Basin and concomitant uplif

Kennedy, Susan Carmel (2012) Miocene to recent evolution of the Cilicia Basin with emphasis on the Pliocene-Quaternary sedimentary relationship between the Goksu river and the Cilicia Basin: a quantitative study of volumetrics, subsidence in the Cilicia Basin and concomitant uplif. Masters thesis, Memorial University of Newfoundland.

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Abstract

Mountain building occurs at convergent plate margins once oceanic lithosphere has been subducted and continental lithosphere from one plate collides with continental lithosphere from the other. Intermontane plateaux develop during orogenesis and their uplift is accompanied by erosion and the transport of sediments within the plateau and out beyond their margins into adjacent seas. The histories of uplift, erosion and deposition shed light on the geodynamic processes involved. The Central Anatolian Plateau results from the active collision of the African and Eurasian plates, with the Aegean-Anatolian microplate caught in between. An international research program is currently studying the uplift and erosion history of the plateau and surrounding mountains. The research in this thesis complements the terrestrial research with estimates of the sediment deposited from the plateau and adjacent Taurus Mountains into the ‘sink’ of the Cilicia Basin in the eastern Mediterranean. The research is based on the interpretation of seismic reflection profiles run across marine sediments that are contributed by the Goksu River - the main distributary at the southern side of the Taurus Mountains. -- On the western shelf-edge of the Inner Cilicia Basin, immediately seaward of the Goksu River, the Pliocene-Quaternary sedimentary successions arc composed of a number of stacked, prograded delta successions which overlie Messinian evaporites and pre-Miocene basement. The architecture of these deltas shows clear east- and south-east prograded clinoform reflections and this strongly suggests that they were sourced from the Goksu River. Further examination of seismic reflection profiles from the Cilicia Basin confirms the presence of additional vertically stacked and prograded delta packages with southwest-directed clinoform reflections a long the northeastern edge of the basin, immediately seaward of the larger Scyhan. Ceyhan and Tarsus Rivers. The particular architecture of these packages strongly suggests a northern source. The main focus of this study has been to examine the nature of the sedimentary by-products of the Goksu River and the rates and modes of deposition through time, particularly during the Pliocene and Quaternary. Two chronostratigraphic boundaries arc defined corresponding to dated horizons observed in exploration wells: (i) the M-reflector (defining the top of the Messinian i.e. 5.3 Ma) and (ii) the A-reflector (Early-Late Pliocene boundary i.e. 3.6 Ma). A third boundary, the P-reflector, occurs within the Quaternary successions and was also used in the analysis. The age of this boundary is tentatively assigned to be 1.9 Ma. The volumetrics of these three intervals (i.e. M- to A-reflector, A- to P-reflector and P-reflector to seabed) were calculated to determine the differential rates of sedimentation into the Cilicia Basin throughout the Pliocene-Quaternary. To conduct the analysis, the sedimentary volumes were separated in to contributions from the Goksu River in the west versus the Seyhan, Ceyhan and Tarsus Rivers to the north. The total resultant volume of sediment assumed to arrive into the Cilicia Basin during the Pliocene and Quaternary from the Goksu River was found to be ~6305 km³, somewhat in excess of the volume of sediments eroded from the Goksu gorge of ~5789 km³, i.e. 92% of the sediments are accounted for. The remainder must come from the Taurus Mountains and the Central Anatolian Plateau to the north. The volume of sediments contained in each interval was converted in to an average sedimentation on rate and compared with the present-day sedimentation rate of the Goksu River. The sedimentation rates of the three intervals we re found to be: (i) 6.45 x 10⁶ tonnes/y r for the interval bound by the M- and A-reflectors, (ii) 2.67 x 10⁶ tonnes/yr for the interval bound by the A- and P-reflectors and (iii) 8.33 x 105 tonnes/y r for the interval bound by the P-reflector and the seabed. The present-day rate of sedimentation by the Goksu River is reported to be 2.16 x 10⁶ tonnes/yr. These results show that sedimentation in the Early Pliocene interval l was significantly greater than it is today, suggesting a more rapid period of uplift along the adjacent landmass, with sedimentation rates likely slowing in the Late-Pliocene-Quaternary as uplift rates fell. -- The analysis of the sedimentary volumes arriving into the Cilicia Basin contained in each interval brought out two additional conclusions. Firstly, the temporal offset toward the southwest of the locus of progressively younger delta lobes known to be sourced by the Goksu River allowed for a conservative estimate of sinistral slip along the offshore component of the Kazan Fault Zone between 0.6- 1.0 cm/yr. This fault is a splay of the sinistral East Anntolian Transform Fault that forms the eastern boundary of the Aegean-Anatolian Pl ate. There are no slip rate estimates available for the Kazan Fault on land; however, the slip rate estimated is compatible with estimates for the adjacent Ecemis Fault Zone. Secondly, the buried topset-to-foreset transitions of the dated deltas allowed for some estimates of subsidence a long the western shelf-edge of the Inner Cilicia Basin. Subsidence rates in this region were found to decrease from ~0.6-0.8 mm yr⁻¹ in the Early Pliocene interval to ~0.10-0.20 mm yr⁻¹ in the Late Pliocene-Quaternary interval. The subsidence is concomitant with the uplift of the plateau and Taurus Mountains and it is suggested that the subsidence results from the thrust load of the adjacent and thickened Taurus Mountains. The suggestion of others that the plateau uplift is caused by the collision of seamounts with the subduction zone south of Cyprus is incompatible with the observed subsidence of the Cilicia Basin in the Pliocene and Quaternary.

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