The Katakturuk Dolomite records an unsurpassed history of Neoproterozoic passive-margin cyclic sedimentation in Arctic Alaska and offers new insights into the evolution of Precambrian carbonate platforms in response to interpreted eustatic sea-level changes. The Katakturuk depicts a south-dipping, low-angle, distally steepened carbonate ramp complex with a complete spectrum of facies types, from proximal, updip tidal-flat complexes to distal, downdip, sub-wave-base allodapic turbidites, debates, and rhythmites. The ramp margin is marked by thick stacks of amalgamated grainstone shoal complexes separating distally steepened downdip facies from ramp-interior facies. Using analysis of cycle stacking patterns, the 2500-m-thick Katakturuk can be subdivided into four second-order supersequences (of roughly equal thickness), each of which is made up of two to four third-order sequences (average a few hundred meters thick).
The high-frequency cyclic architecture of a single third-order depositional sequence (lower gray craggy dolomite member) provides an example of systems-tract development in the Katakturuk Dolomite. On the basis of physical bounding surfaces, two types of cycles are recognized: cycles bounded by marine flooding surfaces across which subfacies deepen, termed “subtidal cycles”, and “peritidal cycles”, that are bounded by subaerial exposure surfaces (e.g., peritidal lamjnites). The systematic vertical variation in cycle type (peritidal vs. subtidal) and cycle thickness, combined with vertical subfacies trends and the recognition of significant subaerial exposure surfaces (karsts, stacked tepees or peritidal breccias) define the transgressive and highstand systems tracts of thirteen third-order depositional sequences. The third-order sequences in tum stack to build larger second-order accommodation cycles. Coinciding second-order and third-order rises in relative sea level resulted in two major backstepping events, which were recorded in the deposition of outer-ramp slope facies directly on peritidal facies. The top of the Katakturuk is marked by a complete spectrum of karst facies, representing a supersequence lowstand superimposed on a third-order late highstand.
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Carbonate Sedimentation and Diagenesis in the Evolving Precambrian World
Carbonate Sedimentation and Diagenesis in the Evolving Precambrian World - Precambrian carbonates are usually regarded at the simple cousins of the sedimentary realm, composed of stromatolites and dolostones, texturally not challenging and commonly altered beyond recognition by the vagaries of time, diagenesis and metamorphism. However, these carbonates that formed deep in time are commonly exquisitely preserved and contain within them a record of the evolving young earth. SEPM Special Publication 67 explores these aspects. Resulting from a 1997 SEPM/CSPG symposium entitled? Precambrian Carbonates,? these 18 papers demonstrate the importance of understanding these rocks, since within them is contained a record of the early ocean, atmosphere, and biosphere.