South Chukchi–Hope Composite Tectono-Sedimentary Element, Chukchi Sea

Abstract

Abstract The South Chukchi–Hope Composite Tectono-Sedimentary Element (CTSE) rests on the Neocomian folded basement formed as a result of the South Anyui palaeo-ocean closure. The interpretation of 2D seismic data, as well as results of onshore structural field studies and dating of post-kinematic granite plutons, suggest post-collisional extensional/transtensional regimes potentially driving development of the South Chukchi–Hope Basin. The orogenic collapse occurred during the Aptian–Albian, and was followed by continued polyphase extensional/transtensional regime during the Late Cretaceous and Cenozoic. Depositional environments in the basin were most likely to have been non-marine in the Cretaceous and Early Tertiary, and marine from the Late Oligocene (?)–Miocene onwards. Three onshore wells in the adjacent depocentres penetrated Tertiary sediments and have had gas shows from two sites. Geochemical surveys registered anomalies of thermogenic and biogenic methane, and in some instances higher molecular ethane–penthane gases in sea-bottom sediments above gas chimneys observed on seismic lines. The CTSE is characterized by a very high present-day thermal gradient of up to 48°C km −1 recorded in the Alaskan wells and was previously considered to be gas prone.