Palaeothermal and compaction studies in the Mochras borehole (NW Wales) reveal Early Cretaceous and Neogene exhumation and argue against regional Palaeogene uplift in the southern Irish Sea

• Published in: Journal of the Geological Society Vol. 162; no. 5; pp. 829 - 840
• Main Authors: Holford, Simon P, Green, Paul F, Turner, Jonathan P
• Format: Journal Article
• Language: English
• Published: London Geological Society of London 01.09.2005; The Geological Society of London; Geological Society; Geological Society Publishing House
• Subjects: Atlantic Ocean; Boreholes; Cenozoic; Compaction; Continental margins; Cretaceous; Earth sciences; Earth, ocean, space; Europe; Exact sciences and technology; Exhumation; fission-track dating; geochronology; Geological time; Geology; Great Britain; Irish Sea; Jurassic; lithostratigraphy; Lower Cretaceous; Marine geology; Mesozoic; Miocene; Mochras Wales; Neogene; North Atlantic; Paleontology; Plate tectonics; reconstruction; relative age; Sediments; stratigraphic units; Stratigraphy; Structural geology; tectonics; Tectonics. Structural geology. Plate tectonics; Tertiary; thermal history; United Kingdom; uplifts; vitrinite reflectance; Wales; Western Europe; Great Britain; Wales; United Kingdom; North Atlantic; Irish Sea; Northeast Atlantic; Western Europe; AN, North Atlantic; ANE, Irish Sea; ANE, British Isles, Wales; compaction; Irish Sea; vitrinite reflectance; exhumation; apatite fission-track analysis; thermal history; Mesozoic; Neogene; Paleogene; Atlantic Ocean; underplating; upper Tertiary; apatite; boreholes; burial; Cenozoic; continental margin; tectonic controls; fission tracks; paleotemperature; reflectance; Europe; Tertiary; Cretaceous; Lower Jurassic; Jurassic; phosphates; Lower Cretaceous; uplifts; cooling; vitrinite; Miocene; Phanerozoic
• ISSN: 0016-7649; 2041-479X
• DOI: 10.1144/0016-764904-118

The North Atlantic continental margins have been subject to widespread exhumation, although the timing, magnitude and causes of this uplift and erosion are debated. Exhumation is thought to be most severe across the Irish Sea basin system (Western UK), and recent years have seen an increasing emphasis on the role of Palaeogene underplating as the primary mechanism of uplift. We present a study of palaeothermal and compaction data from the Mochras borehole (NW Wales). Located near the presumed locus of exhumation, Mochras penetrated thick successions of Lower Jurassic and Oligo-Miocene sediments. Our results indicate that both these successions experienced considerably deeper burial prior to early Cretaceous and Neogene exhumation, respectively. Apatite fission-track analysis (AFTA) and vitrinite reflectance data from the borehole reveal evidence for exhumation-related cooling episodes beginning during the Cretaceous (150-80 Ma) and Cenozoic (50-0 Ma). Regional AFTA results and stratigraphic constraints refine the timing estimates to the early Cretaceous (120-115 Ma) and Neogene (20-0 Ma). Estimates of exhumation magnitudes during these episodes based on palaeothermal and compaction data are c. 2.5 km and c. 1.5 km, respectively. Palaeothermal data provide no evidence for elevated Palaeogene palaeotemperatures indicative of deeper burial, and thus question the basis of Palaeogene exhumation.