Crucial Links Among Evolution, Extensional Tectonics, Ammonoid Provincialism and Sequence Surfaces

Abstract

The first- and second-order sequence surfaces are considered to mark the origin, extinction, drastic reduction, and sudden expansion of ammonoid subfamilies on GTM in general, and in IEAP in particular, even farther to other regions, as held consistently over the last three decades in context of ammonoid faunal cuts and expansion events in the Jurassic (Figs. 6.3, 6.4, 6.5 and 6.6). During the second-order TSTs (particularly near the MFSs) of the first-order TSTs, the faunal similarity within IEAP, as also with ETM, SE Pacific, and SW Pacific is found distinctly greater than in the second-order RSTs and TSTs of the first-order RST. The spatial distribution within the basin, in IEAP, and even outside is wider during the second-order TSTs and MFSs than during any other interval. The temporal punctuation of the infraspecifc, intra-generic, intra-lineage evolution (Figs. 6.7, 6.8, 6.9 and 6.10) occurred at second-order sequence surfaces, and is well attested by the heterochronic ammonoid evolutionary processes of unidirectional paedomorphism in the Macrocephalitinae chrysoolithicus lineage (Fig. 6.8), and unidirectional peramorphism in Katroliceratinae lineage (Figs. 6.8, 6.9 and 6.10). The temporal replacement of one lineage by another, also, occurred near exclusively at the sequence surfaces. The explicit control above the subfamilial ammonoid evolution in IEAP by extensional tectonics encouraged further investigation at higher (superfamily/suborder/superorder/subclass/class) level, and the same provided strong links of the entire evolution of the subclass Ammonoidea, and also of the class Cephalopoda, seemingly controlled by extensional tectonics (Fig. 6.2). The origin of Cephalopoda appears linked to the first-order intra-Cambrian MFS, and also of Ammonoidea at the first-order intra-Devonian sequence surface. The origin of Ceratitina, and extinction of Goniantitina may have occurred at the Carboniferous/Permian second-order SB. The origin of Ammonitina is held at the first-order intra-Triassic MFS, and extinction of Stephanoceratina at the first-order intra-Jurassic MFS. The graded decline of the subclass Ammonoidea began at the major intra-Turonian MFS, with the follow up final extinction at the K/Tboundary second-order MFS. The interpretations require confirmation through further investigation. On similar lines are also speculatively related the major evolutionary landmarks, and transformations of marine and non-marine animals and plants to first-order sequence surfaces (Fig. 6.1). The fossil fuel/energy resources of the GTM in general and India in particular are also age-constrained to sequence framework.