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Neocomian-Cenomanian Fluvial, Estuarine, and Shoreface Siliciclastic and Carbonate Facies of Western Kazakhstan – Insights from Integrated Seismic Stratigraphic and Geomorphologic Analyses


The Neocomian-Cenomanian succession of western Kazakhstan forms part of the regional seal and overburden above the deeper carbonate reservoirs of Tengiz field as well as provides reservoir facies serving as a source and receiver for water and waste water. Depositional settings range from open to nearshore marine, backbarrier lagoon to estuarine, fluvial to floodplain, and carbonate platform. These deposits have been characterized using 3D seismic data integrated with well logs and core. The base of this succession comprises open marine grading into nearshore marine and shoreface deposits. Seismically the nearshore marine and shoreface deposits are expressed as a belt of parallel lineaments 3-5km wide that extend from north to south. Locally, recurved spits indicating the presence of backbarrier lagoons are observed. Well logs through the shoreface deposits are characterized by a coarsening up-ward trend up to 40m thick. The continuity of these shoreface trends is broken up in a few places by orthogonally-oriented estuaries. Seismically, the estuaries are characterized by a funnel-shaped map pattern. Towards the apex of the estuaries, the funnel shape narrows into a moderate sinuosity channel. The estuarine deposits comprise up to 65m of clean blocky sands. Behind the shoreface, moderate to high-sinuosity channels and channel belts are observed. The section overlying the shoreface (∼350m) is predominantly non-marine with extensive fluvial and floodplain deposits. Little internal detail can be observed within the narrow channel elements. We infer these deposits to be associated with narrow side-attached bars, commonly less than 100m wide. Broader channel belts can be observed as well. A distinctive characteristic of these channel belts is that they commonly have variable widths. The channel belts “pinch” and “swell” ranging from a few kilometers in width to as narrow as 75-100m. This pattern allows for measurements of channel wavelength and subsequently, quantitative predictions of channel belt thickness, ranging from 8-24m thick. Platform carbonates overlie the clastic succession. These carbonate deposits are characterized by progradation towards the northwest and karsting in the form of circular collapse structures (i.e. dissolution features) up to 600m wide. Progradational clinoform architecture can be observed in section dipping at 4-6 degrees. In map view these clinoforms are expressed as a broad belt of curvilinear seismic lineaments.