Jurassic sedimentation in the Cleveland Basin: a review

摘要

This review combines two Presidential Addresses (2005, 2006) and aims to provides an up-to-date overview of the stratigraphy and sedimentation of the Jurassic sequence of the Cleveland Basin (Yorkshire), including poorly known data from the western outcrop. These fascinating rocks have been the focus of geological research since the 18th Century and have had a profound influence an the development of the geological sciences. Throughout the 20th Century, the excellent coastal exposures have acted as a magnet for palaeontologists, stratigraphers, sedimentologists and geochemists, as a natural geological laboratory, and in recent decades. the coastal exposures received increased scientific interest as a result of their analogy with hydrocarbon source and reservoir rocks in the North Sea. Designation of the international Global Stratotype Section and Point (GSSP) for the Sinemurian-Pliensbachian stage boundary in Robin Hood's Bay, the establishment of the Dinosaur Coast, and development of the Rotunda Museum in Scarborough have all given the regional geology additional importance.The Lias Group (Hettangian-Toarcian age; 199.6-175.6 Ma), exposed in the well known coastal sections, is illustrated by the fully cored Felixkirk Borehole, located at the western margin of the outcrop, and is one of the best examples of shallow marine sedimentation in an epeiric shelf-sea setting. It comprises two large-scale, upward coarsening cycles, namely the Redcar Mudstone to Staithes Sandstone cycle, followed by the Cleveland Ironstone to Blea Wyke Sandstone cycle. Within this broad pattern, smaller scale transgressive—regressive cycles are described from stratigraphically expanded and reduced successions. Detailed ammonite biostratigraphy provides a finely calibrated temporal framework to study the variations in sedimentation, which include storm-generated limestones and sandstones (`tempestites') interbedded with mudstone deposited during fair-weather periods. Hemipelagic mud, occasionally organic-rich, reflects deeper-water anoxic events that may indicate a response to global climate change.In cores, the tempestite beds (Hettangian-Sinemurian) are characterized by sharp bases that, at outcrop, are often masked by downward penetrating burrows. Cyclicity on a centimetre scale in the overlying Pliensbachian Banded Shales' may be the result of orbitally induced, climatic cycles. Gradational upward coarsening to the Staithes Sandstone Formation marks a transition to sand-rich tempestite deposits, characterized by low angle and swaley cross-lamination, interbedded with sand-starved units (striped siltstones). The sands were probably deposited from sediment-laden, storm-surge and ebb currents in inner- and mid-shelf settings; the sandy substrate was, at some levels, extensively bioturbated by deposit feeding organisms that produced a spectacular range of trace fossil assemblages characteristic of shoreface, inner-, mid-, and outer-shelf settings. Intrabasinal tectonics was a controlling factor during deposition of both the Staithes Sandstone and the overlying Cleveland Ironstone (Late Pliensbachian).