Origin and Classification of Sedimentary Basins

ABSTRACT A sedimentary basin is a domain of regional subsidence that can be characterized in space, time, and sedimentary fill. Tectonic subsidence of basins is caused by rifting, flexure, or cooling of the lithosphere. It is important to understand basin subsidence mechanisms and to explicitly incorporate them into basin classification and exploration thinking. Previous classifications tend to overemphasize the plate-tectonic setting or other geologic characteristics of basins. A classification of basins based upon both the mechanism of subsidence and the plate-tectonic setting is proposed. INTRODUCTION The origin and the classification of sedimentary basins are closely connected. Both are important for understanding petroleum occurrence in the context of basin history. Over the past decade, substantial progress has been made on understanding the physics of the processes of subsidence. In addition, a wealth of information has accumulated on the nature of plate tectonics as expressed by the deformation of the earth's lithosphere. These developments make it timely to formulate a new classification of sedimentary basins which incorporates both the plate-tectonic setting and the mechanism of subsidence of a basin throughout its history. CLASSIFICATION OF BASINS What is a sedimentary basin? It is a physical depression at the earth's surface which accumulates and preserves sediments. The scale of basins varies greatly, from ocean basins to small ponds. Earth scientists genera11y restrict the term "side minatory basin" to sediment-filled depressions of a regional (100 + kilometers) scale that have subsided deeply, requiring significant crystal deformation for their origin. Basins are further restricted to include depressions that have definable margins, as opposed to broad platforms that accumulate 1–3 kilometers of sediment over a breadth of hundreds of kilometers. What is the proper basis for classification of sedimentary basins? Initially, basins were recognized and defined simply as thick sedimentary accumulate at ions compared to surrounding _ regions. Classifications subsequently were formulated largely on the basis of the "form and origin of the contained rocks" (Kay, 1951), and elaborated in the theory of geosynclines. Classification became complex, based on additional parameters thought to be of genetic significance: the position of the basin with respect to the stable continental croton; the position and timing related to organics belts; the presence of volcanic rocks; and the sources of sediments (Table 1). It is clear that the form of a basin is its essential characteristic, but that the ideal basis of classification would relate to the causes of that form, as well as to the origin of the contained rocks - in short, a tectonic classification including both basin-forming processes and tectonic setting.