A Preliminary Evaluation of the Global and Temporal Changes in Accommodation Throughout the Palaeozoic

Abstract

A preliminary evaluation of un-decompacted, time-averaged rates of accumulation can be facilitated by the application of a biostratigraphically calibrated, 3rd-order sequence stratigraphic model to Palaeozoic successions. This comparison was made globally, across a wide range of sedimentary environments and tectonic settings, and resulted in the creation of a unique database that provides the ability to compare sediment accommodation and characterise both the typical rates of accumulation and the generalised lithological composition. The initial results illuminate major temporal changes in the global creation of accommodation and sediment composition throughout the Palaeozoic. For example, a globally pronounced thinning of systems tracts occurs over the Late Cambrian to Early Ordovician that is coupled with a decline in the proportion of carbonate deposition. The application of this, and similar knowledge, can be used in frontier basins to provide insight into the modelling of basin architecture. At the outset, it must be recognised that the absolute generation of accommodation in any one location is affected by the amount of eustatic change. However, at a global scale it is suggested that these systematic trends in the averaged amount of accommodation must be influenced by additional longer term processes at the scale of several millions of years. Due to the biostratigraphically calibrated nature of the sequence stratigraphic model, the database provides an interpretation of a minimum estimate for the range in magnitudes of sedimentation rates throughout the Palaeozoic. These interpretations are preliminary and are based on an interpretation of un-decompacted data. However, it is suggested that the interpreted range in magnitudes is well within that predicted for rock units deposited within a timeframe of 105–106 Ma. However, what is also evident from these data, is that the shorter-duration systems tracts (<2Ma) are deposited at higher, and more variable, sedimentation rates when compared to their longer duration counter parts (>2Ma). These observations are tentatively interpreted to support the notion that globally averaged systems-tract thicknesses are not sediment-limited and that system tracts can accumulate rapidly until they reach the state of balance. This also supports the commonly held view that the stratigraphic record is dominated more by gaps that by rock.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015